Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2024 Apr 23;63(18):8302–8311. doi: 10.1021/acs.inorgchem.4c00612

Diverse Reactivity of Amidinate-Supported Boron Centers with the Hypersilyl Anion and Access to a Monomeric Secondary Boron Hydride

Sanjukta Pahar †, Yara van Ingen †, Rasool Babaahmadi †, Benson M Kariuki ‡, Thomas Wirth ‡, Emma Richards †,‡,*, Rebecca L Melen †,*
PMCID: PMC11080068  PMID: 38652816

Abstract

graphic file with name ic4c00612_0016.jpg

Diverse reactivity of the bulky tris(trimethylsilyl)silyl substituent [Si(SiMe3)3], also known as the hypersilyl group, was observed for amidinate-supported dichloro- and phenylchloroborane complexes. Treatment of the dichloroborane with potassium tris(trimethylsilyl)silyl led to the activation of the backbone β-carbon center and formation of saturated four-membered heterocyclic chloroboranes R′{Si(SiMe3)3}C(NR)2BCl [R′ = Ph, R = Cy (3); R′ = Ph, R = iPr (6); R′ = tBu, R = Cy (8)], whereas the four-membered amidinate hypersilyl-substituted phenyl borane 4 {PhC(NCy)2B(Ph)[Si(SiMe3)3]} was observed for the case of an amidinate-supported phenylchloroborane. The highly deshielded 11B NMR spectroscopic resonance and the distinct difference in the 29Si NMR spectrum confirmed the presence of a σ-donating hypersilyl effect on compounds 3, 6, and 8. Reaction of 3 with the Lewis acid AlCl3 led to the formation of complex 11 in which an unusual cleavage of one of the C–N bonds of the amidinate backbone is observed. Nucleophilic substitution at the boron center of saturated chloroborane 3 with phenyllithium generated the phenylborane derivative 12, whereas the secondary monomeric boron hydride 13 was observed after treatment with alane (AlH3). All compounds (2–13) have been fully characterized by NMR spectroscopy and single-crystal X-ray structure determination studies.

Short abstract

Diverse reactivity of strong σ-donating hypersilyl group on CN2B heterocycles of amidinate-supported dichloroboranes and phenylchloroborane afforded the unprecedented β-carbon activation of the amidinate ligand backbone with the hypersilyl group for dichloro-substituted amidinate–borane complexes, whereas the boron-substituted product has been observed for phenylchloroborane. A rare and thermally stable monomeric secondary borohydride was accomplished from the hypersilyl backbone-substituted saturated choloroborane, without adding any significant steric or electronic support to the compound.

Introduction

The early 21st century witnessed enormous interest in the development of bidentate monoanionic nitrogen–donor amidinate ligands of the general formula [R′C(NR)2]−, as a popular replacement for the cyclopentadienyl ligand, as well as a close association with guanidinates as the ligand architecture.1 Among a plethora of ligands, amidinates have been designed in such a way that the steric and electronic effects can be readily modified by tailoring the C- and N-centered substituents to stabilize and tune the reactivity of various transition metals, lanthanides, and more recently, main group compounds. Following the first use with rare-earth metals in 1992 by Edelmann et al.,2 the application of amidinates rapidly expanded and fulfilled the quest for the preparation and stabilization of low-valent main group compounds3−10 together with applications in homogeneous catalysis11−15 and materials chemistry.12 Within the domain of p-block chemistry, group 13 and group 14 metal halide and metal–alkyl fragments have been well established using the amidinate ligand scaffold. For example, amidinate-supported silylenes have been reported for various small molecule activation and hydroboration reactions,11,16−19 and amidinate-supported alkyl aluminum cations have been shown as active catalysts for olefin polymerization.20,21 In addition, amidinate-based tetra-coordinated boron compounds have also been proven to act as photoluminescent materials22 and have been shown to activate gaseous CO and CO2, as well as carbonyl and nitrile functional groups.18 Surprisingly, a survey of known amidinate boron compounds reveals that the majority of amidinate boranes contain either halogen,22,24,25 Ph,27,28 or Me29 groups at the boron center (Scheme 1A). We hypothesize that alternative reactivity or catalytic activity of amidinate-supported boranes could be achieved by adding strong σ-donor ligands and effectively reducing the HOMO–LUMO gap.26 However, this would be more synthetically challenging. In 1981, Brook discovered the first well-defined organometallic compound containing a Si=C double bond by the photolysis of an acylsilane, using the hypersilyl group, [tris(trimethylsilyl)silyl], with main group compounds.30 More recently, substantial research has been reported on the use of the tris(trimethylsilyl)silyl group as a stabilizing group for novel main-group elements by the groups of Stalke,31 Aldridge,32 Inoue,33,34 Castel,35,36 Rivard,37 Leszczyńska,38 Sen,3,17,39−41 Marschner, Müller, Baumgartner, and others.42−44 The rapid growth of the use of the hypersilyl group in the synthesis and stabilization of several organometallic and main group compounds is a result of its pronounced steric effect, along with the strong σ-donor strength of the silyl ligand. The commercial readiness of the precursors and the easy access of further functionalization of the SiMe3 moieties makes the hypersilyl group advantageous with a delicate balance between strong σ-donation and kinetic protection. Although a few borasilene or silaborene compounds have been reported with other silyl precursors (Scheme 1B), there does not seem to be any literature on boranes containing the hypersilyl group until date.45−47 Herein, we investigate the different reactivities of the hypersilyl group on amidinate-supported dichloroboranes and phenylchloroborane by the treatment of the four-membered CN2B heterocycle with KSi(SiMe3)3 (Scheme 1C). The reactivity of the Si(SiMe3)3-substituted products is also explored.

Scheme 1. (A) Selected Examples of Amidinate-Supported Haloborane, Phenyl-, and Methyl-Chloro Boranes; (B) Reported Structures of Borasilene or Silaborene; (C) Diverse Reactivities of the Hypersilyl Group with Dichloro- and Phenylchloroborane Found in This Work.

Scheme 1

Open in a new tab

Results and Discussion

Initially, the dichloroborane precursor LBCl2 {L = [PhC(NCy)2]} was synthesized following literature procedures.24 We commenced our investigation by preparing amidinate-supported dichloroborane (1) and phenylchloroborane (2) by treating an equimolar amount of BCl3 or PhBCl2, respectively, with lithium N,N′-dicyclohexylamidinate [Ph(NCy)2Li] (Scheme 2). While compound 1 had been previously reported by Cowley and co-workers,482 could be extracted with toluene to afford a thermally stable colorless crystalline solid in 96% yield. Compound 2 crystallizes in monoclinic symmetry with the P21/c space group. The B–Cl bond length 1.867(2) Å for 2 is comparatively longer than the reported bond length for compound 1 [1.832(3) Å] (Figure 1). The 11B NMR spectrum showed a peak at δ = 8.7 ppm for 2, similar to that observed for dichloroborane precursor 1 (δ = 6.7 ppm).

Scheme 2. Synthesis of Dichloroborane (1) and Phenylchloroborane (2).

Scheme 2

Open in a new tab

Figure 1.

Figure 1

Open in a new tab

Solid-state structure of 2. Anisotropic displacement parameters are drawn at 50% probability. B is shown in pink, C in gray, N in blue, and Cl in green. Cy groups have been drawn as wireframes, and H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: B1–Cl1 1.867(2), N1–B1 1.572(2), N2–B1 1.594(2), C7–N1 1.329(2), C7–N2 1.334(2), B1–C20 1.594(2), C7–C8 1.471(2); N1–C7–N2 101.4(1), N1–B1–N2 81.3(1), N2–B1–Cl1 111.7(1), N1–B1–C20 116.0(1), Cl1–B1–C20 113.0(1).

In line with the significant growth of the use of the electropositive tris(trimethylsilyl)silyl group for the synthesis of numerous organometallic compounds,49 we treated compounds 1 and 2 with equimolar amounts of KSi(SiMe3)3 in toluene at room temperature. While 2 smoothly afforded the hypersilyl-substituted phenylborane derivative (4) in high yields (94%) from substitution at the boron atom via traditional salt metathesis; under similar reaction conditions, 1 led to the formation of compound 3 instead of the analogous hypersilyl-substituted chloroborane 3′ (Scheme 3). Here, substitution at the backbone β-carbon of the amidinate moiety occurred giving the product 3 in 90% yield. Concentrated toluene solutions of both 3 and 4 at low temperature (−20 °C) produced high quality colorless crystals within 3–4 days. Single-crystal X-ray diffraction studies confirmed the structures of both compounds. The single crystal of compound 3 undergoes a solid-state phase transition at 200 K from the high temperature form (290 K) to the low temperature form (120 K), and the transformation occurs in a single-crystal-to-single-crystal manner (discussed in Supporting Information). The molecular structure of 3 contains a B–Cl bond length of 1.772(3) Å (Figure 2), which is shorter than that of the previously reported dichloroborane precursor 1 [1.832(3) Å]. A slightly longer Si–C bond than their covalent radii was observed for 3 at 1.977(2) Å, and an elongated B–Si bond of 2.102(2) Å was observed for 4 (Figure 2). 3 and 4 were further characterized by multinuclear NMR spectroscopy. Although the 1H NMR spectroscopic resonance for the three SiMe3 groups for 3 and 4 were observed in the same range, at δ = 0.40 and 0.53 ppm, respectively, the distinguishable 11B resonances at δ = 21.8 and 9.1 ppm validated the different reactivity and coordination around the boron center of 3 and 4, respectively. The 29Si NMR spectroscopic signals were detected at δ = −70.28 [Si(SiMe3)] and −13.58 [Si(SiMe3)] ppm with a large resonance gap between two Si centers for 3, whereas for 4, these were observed at δ = −10.77 [Si(SiMe3)] and −11.30 [Si(SiMe3)] ppm. The molecular ion peaks were detected with the highest relative intensity at m/z 577.3232 and 619.3937 for 3 and 4, respectively. Interestingly, when we tried similar reactions with difluoro and dibromo boranes, we had no success in observing either the backbone-substituted or the hypersilyl-substituted borane products by either NMR spectroscopic studies or single-crystal X-ray diffraction.

Scheme 3. Diverse Reactivity of the Hypersilyl [tris(trimethylsilyl)silyl] Group with Compounds 1 and 2 and the Synthesis of Compounds 3 and 4.

Scheme 3

Open in a new tab

Figure 2.

Figure 2

Open in a new tab

Solid-state structures of compounds 3 and 4. Anisotropic displacement parameters are depicted at the 50% probability level. B is shown in pink, C in gray, N in blue, Cl in green, and Si in beige. Cy and SiMe3 groups have been drawn as wireframes, and H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: for 3: B1–Cl1 1.772(3), C1–Si1 1.977(2), Si1–Si2 2.3763(9), B1–N1 1.403(3), B1–N2 1.408(3), C1–N1 1.497(3), C1–N2 1.509(3); N1–B1–N2 95.6(2), N1–C1–N2 87.7(2), N2–B1–Cl1 130.9(2), N1–B1–Cl1 133.5(2), N1–C1–Si1 112.6(1), C1–C1–Si1 117.8(2); for 4: B1–C14 1.612(3), B1–Si1 2.102(2), Si1–Si2 2.3530(7), B1–N1 2.593(2), B1–N2 1.607(3), C1–C7 1.482(3); N1–B1–N2 80.3(1), N1–C7–N2 101.2(2), N2– B1–Si1 116.3(1), C14–B1–Si1 116.3(1).

Encouraged by the clean and high-yielding formation of 3 over 3′, we conducted density functional theory (DFT) studies to understand the thermodynamic and kinetic accessibility of the reaction at the SMD (toluene)/M06-2X-D3/def2-TZVP//BP86/6-31g(d) level of theory considering a less bulky silyl anion (–SiMe3) as 3-SiMe3 and 3′-SiMe3 (Figure 3). The DFT calculations reveal that the formation of 3-SiMe3 is favorable (−42.7 kcal/mol) with an activation barrier of 8.0 kcal/mol (TS_3A), whereas the reaction energy is much higher for the formation of 3′-SiMe3 (−38.1 kcal/mol), as well as its respective transition state TS_3′A (30.3 kcal/mol), which determines the formation of backbone β-carbon-substituted product 3.

Figure 3.

Figure 3

Open in a new tab

Energy profile for the formation of 3-SiMe3 versus 3′-SiMe3. Relative energies are given in kcal/mol. B is shown in pink, C in gray, N in blue, Cl in green, K in purple, and Si in beige. Hydrogen atoms are omitted for clarity.

To understand the preferred formation of 3 instead of 3′ and to investigate the effect of the substituents on the nitrogen center of the amidinate ligand, we prepared the previously reported dichloroborane 5,23 containing an isopropyl group attached to the nitrogen center of the amidinate ligand, and performed the reaction with KSi(SiMe3)3 under similar reaction conditions (Scheme 4). As for dichloroborane 3, an attack at the backbone of the amidinate occurred, and the formation of 6 was observed in 94% yield. The downfield shift in the 11B and 29Si NMR spectrum at δ = 22.1 ppm and δ = −69.73 [Si(SiMe3)] and −13.52 [Si(SiMe3)] ppm, respectively, further confirmed the formation of 6, along with 1H NMR spectroscopic resonances at δ = 1.42 and 0.67 ppm for the 6H atoms of the isopropyl groups and at δ = 0.36 ppm for the 27H of the three SiMe3 groups. Single crystals of 6 were grown from a saturated toluene solution in a –20 °C freezer, and it crystallized in the triclinic space group P1̅ with B–Cl and C–Si bond lengths of 1.768(2) and 1.974(2) Å, respectively (Figure 4).

Scheme 4. Synthesis of Dichloroboranes 5 (Reported) and 7 and Backbone-Substituted Hypersilyl Group Containing Choloroboranes 6 and 8.

Scheme 4

Open in a new tab

Figure 4.

Figure 4

Open in a new tab

Solid-state structure of 6. Anisotropic displacement parameters are depicted at the 50% probability level. B is shown in pink, C in gray, N in blue, Cl in green, and Si in beige. iPr and SiMe3 groups have been drawn as wireframes, and H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: B1–Cl1 1.768(2), C1–Si1 1.974(2), C1–N1 1.502(2), C1–N2 2.511(2), B1–N1 1.409(2), B1–N2 1.412(3), C1–C9 1.522(2); N1–B1–N2 95.1(1), N1–C1–N2 87.5(1), N1–C1–Si1 112.6(1), C9–C1–Si1 117.4(1), N2–B1–Cl1 132.2(2), N1–B1–Cl1 132.7(2).

In an attempt to prevent attack at the backbone β-carbon center of the amidinate ligand and to encourage substitution at the boron center, we introduced further steric hindrance into the ligand by changing the phenyl group attached to the carbon atom of the amidinate ligand with a more bulky tert-butyl group. Compound 7 was prepared following the same literature procedure23 for 5 using tert-butyl lithium instead of phenyllithium in the first step. 7 was then reacted with KSi(SiMe3)3 under similar reaction conditions to those described for the synthesis of 6. Again, an attack occurred at carbon, yielding the analogous saturated chloroborane compound 8 in high yields (94%) (Scheme 4). Colorless single crystals of 7 and 8 suitable for X-ray diffraction studies were grown from saturated toluene solutions at −20 °C. The notable downfield 11B NMR spectroscopic shift of 8 at δ = 20.8 ppm compared to δ = 5.1 ppm of 7 again confirms the formation of 8 from the attack of the hypersilyl group at the backbone carbon of the amidinate scaffold. The 1H and 29Si NMR spectroscopic shifts for the three Si(SiMe3) groups show peaks at δ = 0.42 ppm (27H), δ = −71.62 [Si(SiMe3)], and −12.05 [Si(SiMe3)] ppm, respectively, and the molecular ion peak was detected at m/z 557.3547 for 8. Compound 7 crystallized in the triclinic space group P1̅, whereas 8 crystallized in the monoclinic space group P21/c (Figure 5). The B–Cl bond length [1.767(2) Å] is significantly shorter for compound 8 than for 7 [1.844(2) and 1.834(2) Å] similar to the amidinate-supported saturated chloroboranes discussed earlier (3 and 6).

Figure 5.

Figure 5

Open in a new tab

Solid-state structures of compounds 7 and 8. Anisotropic displacement parameters are depicted at the 50% probability level. B is shown in pink, C in gray, N in blue, Cl in green, and Si in beige. Cy and SiMe3 groups have been drawn as wireframes, and H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: For 7: B1–Cl1 1.834(2), B1–Cl2 1.844(2), N1–B1 1.551(2), N2–B1 1.558(3), C1–N1 1.342(2), C1–N2 1.342(2), C1–C2 1.510(3); N1–C1–N2 100.0(1), N1–B1–N2 82.7(1), N2–B1–Cl2 114.6(1), N1–B1–Cl1 115.9(1), Cl1–B1–Cl2 110.8(1); For 8: B1–Cl1 1.767(2), C1–Si1 2.002(2), C1–N1 2.514(3), C1–N2 2.513(3), B1–N1 1.414(3), B1–N2 1.407(3), C1–C14 1.563(3); N1–B1–N2 95.6(2), N1–C1–N2 87.3(1), N1–C1–Si1 110.5(1), C14–C1–Si1 116.8(1).

To introduce further steric hindrance at the backbone carbon, we synthesized the Dipp (Dipp = 2,6-diisopropylphenyl) amidinate-substituted dichloroborane [DippC(NCy)2BCl2] (9, 86% yield) and treated it with KSi(SiMe3)3 following the same reaction procedure. Despite a distinct color change in the reaction from pale yellow to red, neither the backbone-substituted nor the hypersilyl-substituted boron product was observed (Scheme 5). A saturated toluene solution of 9 formed suitable single crystals for X-ray diffraction studies and proved the desired steric protection with proximal alignment of the hydrogens from the isopropyl groups of the Dipp substituents and cyclohexyl groups of the amidinate ligand framework in compound 9 (molecular structure with H atoms shown in Figure S48 in the Supporting Information) to prevent the backbone attack by the hypersilyl group (Figure 6).

Scheme 5. Synthesis of Dipp-Amidinate-Substituted Dichloroborane 9.

Scheme 5

Open in a new tab

Figure 6.

Figure 6

Open in a new tab

Solid-state structure of compound 9. Anisotropic displacement parameters are depicted at the 50% probability level. B is shown in pink, C in gray, N in blue, Cl in green, and Si in beige. Cy and iPr groups have been drawn as wireframes, and H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: B1–Cl1 1.814(9), B1–Cl2 1.822(9), N1–B1 1.571(9), N2–B1 1.571(9), C1–N1 1.334(7), C1–N2 1.328(8), C1–C2 1.484(6); N1–C1–N2 101.5(5), N1–B1–N2 82.0(5), N2–B1–Cl2 114.7(5), N1–B1–Cl1 113.9(5), Cl1–B1–Cl2 112.4(5).

The desire to form a stable boron compound with unusual structure, bonding, and reactivity has led to the synthesis of several low-valent and low coordinated boron compounds50 and has challenged the predominance of transition metals in catalysis,51 small molecule and bond activation,52,53 and has furthered the development of functional materials.54 Low-coordinate cationic boron centers are attractive and reactive Lewis acidic entities. Nöth and co-workers introduced the nomenclature of boronium, borenium, and borinium cations for the four-, three-, and two-coordinate boron-centered complexes, respectively.55 These highly Lewis acidic boron complexes are important in the field of bond activation and catalysis.56 Subsequently, we attempted to prepare the corresponding boron cations from complexes 2 and 3 by abstracting the chloride ligand. The treatment of 2 and 3 with chloride abstracting agents such as AgBF4, AgSbF6, AgNOx (X = 2 or 3), AgOTf, GaCl3, and K[B(C6F5)4] failed to abstract the chloride, even in the presence of carbenes, phosphines, DMAP (4-dimethylaminopyridine), and other Lewis bases that can stabilize the resulting boron cations.57−59 However, the addition of 1 equiv of AlCl3 to a benzene solution of 3 in the absence of a Lewis base led to the cleavage of the C–N bond of the amidinate backbone and binding of Namidinate to AlCl3, leading to zwitterionic 11 in 73% yield (Scheme 6). The reaction is expected to be driven by the formation of a tetra-coordinated anionic aluminum fragment through N → Al bond formation. A possible reaction mechanism is proposed in the Supporting Information (Scheme S1) for the formation of 11. Colorless single crystals of 11 suitable for X-ray diffraction studies were grown from the saturated benzene solution at −4 °C in a freezer; the molecular structure of 11 validates our spectroscopic evidence. Compound 11 crystallizes in the triclinic space group, P1̅. The B–Cl bond length of 11 is 1.785(2) Å, slightly longer than the saturated chloroborane 3 [1.772(3) Å], and the new Namidinate–Al bond is observed at a distance of 1.868(1) Å (Figure 7). The aluminum center adopts a tetrahedral geometry with bond angles of 109.04(6), 108.99(5), 107.3(1), and 114.76(6)°. The only partial solubility of adduct 11 in most organic solvents did not allow us to record 13C, 29Si, or 27Al NMR spectra even after several attempts, as with time some decomposed solid compounds precipitated out. Gradual decomposition of 11 was also observed in 1H NMR spectroscopy with the appearance of undesired peaks (Figure S26 in the Supporting Information), whereas the 11B NMR spectrum showed a downfield resonance at δ = 28.7 ppm due to the cationic charge distribution over the fragment.

Scheme 6. Reactivity of Chloroborane 3 and Synthesis of 11–13.

Scheme 6

Open in a new tab

Figure 7.

Figure 7

Open in a new tab

Solid-state structure of compound 11. Anisotropic displacement parameters are depicted at the 50% probability level. B is shown in pink, C in gray, N in blue, Cl in green, Si in beige, and Al in rosy brown. Cy and SiMe3 groups have been drawn as wireframes, and H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: B1–Cl1 1.785(2), C1–Si1 1.962(2), N1–Al1 1.868(1), B1–N1 1.361(3), B1–N2 1.546(2), C1–N2 1.296(3), Al1–Cl2 2.1364(9); N1–B1–N2 122.7(2), N2–C1–Si1 130.2(1), B1–N1–Al1 130.4(1).

Cleavage of the stable B–Cl bond of saturated chloroborane 3 was unsuccessful under harsh reaction conditions, such as using Li-naphthalide or KC8 as a reducing agent, except in the presence of phenyllithium. The toluene solution of 3 produced nucleophilic-substituted product 12 when treated with phenyllithium, exhibiting a B–CPh bond, with removal of LiCl over a prolonged reaction time more than 36 h (Scheme 6). Compound 12 crystallizes in triclinic symmetry with a P1̅ space group. The boron center adopts a trigonal-planar geometry (Figure 8) with a B–CPh bond length of 1.570(3) Å, which is slightly shorter than the phenyl-substituted tetra-coordinated B–CPh bond [1.612(3) Å] of compound 4. The 1H NMR spectrum displays a singlet at δ = 0.46 ppm for the three Si(SiMe3) groups, and the 29Si NMR spectrum exhibits resonances at δ = −73.29 [Si(SiMe3)] and −13.42 [Si(SiMe3)] ppm for both the Si centers, while the 11B NMR spectroscopic signal is observed at δ = 32.8 ppm.

Figure 8.

Figure 8

Open in a new tab

Solid-state structure of 12. Anisotropic displacement parameters are depicted at the 50% probability level. B is shown in pink, C in gray, N in blue, and Si in beige. Cy and SiMe3 groups have been drawn as wireframes, and H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: B1–C8 1.570(3), B1–N1 1.430(3), B1–N21 1.423(3), N1–C1 1.504(3), N2–C1 1.491(2), C1–Si1 1.974(2), C1–C2 1.530(2); N1–B1–N2 92.7(2), N1–C1–N2 87.2(1), C2–C1–Si1 116.5(1), N1–B1–C8 134.6(2), N2–B1–C8 132.5(2).

Boranes containing at least one B–H bond have appeared as powerful synthetic tools for hydroboration reactions. Among the many hydroborating borane catalysts, secondary boranes are very effective for the transformation, moreover, Piers’ borane [HB(C6F5)2] has emerged as a highly effective catalyst for hydroboration and acts as an efficient reagent in various other organic transformations due to its high Lewis acidity.60 Electrophilic secondary boranes are typically preferred and stable as monomer–dimer equilibria in solution,61,62 and isolable monomeric secondary boranes are extremely rare without sufficient steric provision.63 Recently, the research group of Martin reported a significantly high Lewis acidic monomeric secondary borane [tris(ortho-carboranyl)borane] containing two electron-withdrawing ortho carborane substituents and further utilized it as a potent hydroborating reagent.64 Inspired by Martin’s work, the addition of alane (AlH3·NMe2Et) to a toluene solution of 3 smoothly afforded the stable boron hydride 13 in 90% yield (Scheme 6). Surprisingly, compound 13 is monomeric in both solid and solution state with the absence of any steric protection, which was confirmed by NMR spectroscopy, mass spectrometry, and infrared spectroscopy. Variable temperature 1H NMR spectroscopic studies of a toluene-d8 solution of 13 displayed a resonance of the B–H at δ = 4.62 ppm (Figures S33 and S34 in the Supporting Information) along with a singlet for the Si(SiMe3)3 group, even at −60 °C. The 11B NMR spectroscopic resonance was observed at δ = 26.61 ppm for the tricoordinated boron center. The distinguishable IR stretching frequency with one sharp band at 2557 cm–1 confirmed the monomeric nature of B–H bond (Figure S38 in the Supporting Information), which is in good agreement with the monomeric secondary boron hydride reported by Martin and co-workers.64 Thermal characterization by differential scanning calorimetry (DSC) shows an endothermic melting event at 150.4 °C (Figure S40 in the Supporting Information), corroborating the analogous melting point measurement (∼162–164 °C). In addition, 13 shows thermal stability up to 250 °C, and no exothermic crystallization point could be observed in the cooling curve, suggesting that the crystallization of the sample takes place at temperatures below 30 °C (Figure S39 in the Supporting Information). Colorless crystals of 13 were grown from cooling a concentrated toluene solution. 13 crystallizes in the triclinic space group P1̅ adopting a distorted trigonal planar geometry (Figure 9). The hydride was detected in the difference Fourier map and refined isotropically. Due to the stability of the hydride compound, the traditional hydroboration reaction using 13 as an effective catalyst did not provide any significant results compared to the reported Piers’ borane [HB(C6F5)2] and/or tris(ortho-carboranyl)borane. Thus, we are currently exploring other organic transformations using monomeric boron hydride as well as catalytic studies with compounds 4 and 13, which will be published in the future.

Figure 9.

Figure 9

Open in a new tab

Solid-state structure of 13. Anisotropic displacement parameters are depicted at the 50% probability level. Hydrogen atoms (except B–H) are omitted for clarity. B is shown in pink, C in gray, N in blue, Si in beige, H in white. Cy and SiMe3 groups have been drawn as wireframes for clarity. Selected bond lengths [Å] and angles [deg]: B1–N1 1.432(6), B1–N21 1.422(7), N1–C7 1.501(6), N2–C7 1.498(5), C7–Si1 1.967(3), C7–C8 1.527(6); N1–B1–N2 92.9(4), N1–C7–N2 87.2(3), C8–C7–Si1 118.5(3).

Conclusions

The chemistry of the amidinate ligand in main-group chemistry is in its infancy compared to other ligand scaffolds. In this work, we have shown a unique β-carbon activation of the amidinate ligand with a hypersilyl group for dichloro-substituted amidinate–borane complexes with various electronic and steric C- and N-substituents (3, 6, and 8). The treatment with amidinate-supported phenylborane finally produced the expected hypersilyl-substituted phenylborane derivative (4) in high yields. Further attempts to cleave the exceptionally stable B–Cl bond of 3 led to the formation of ionic compound 11 upon cleavage of the ligand backbone and nucleophilic-substituted phenylborane 12 in the presence of AlCl3 and PhLi, respectively. Moreover, the formation of a rare and thermally stable monomeric secondary borohydride 13 was achieved from compound 3 from the reaction with alane, without significant steric or electronic support to compound 13.

Acknowledgments

S.P., E.R., and R.L.M. would like to thank the Leverhulme Trust (RPG-2020-016) for funding. R.B., T.W., and R.L.M. would like to thank the Royal Society for an International Newton Fellowship (NIF/R1/21130).

Data Availability Statement

Information about the data that underpins the results presented in this article can be found in the Cardiff University data catalogue at 10.17035/d.2024.0315834338.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.4c00612.

  • General experimental information, structural description of 2–13, details of synthesis, representative NMR spectra, thermal characterization data for compound 13, tentative mechanism for the formation of compound 11, crystallographic data for the structural analysis of compounds 2–13, crystal structure of compounds 2–13 with thermal ellipsoids, solid-state phase transformation details of compound 3, and computational details (PDF)

Author Contributions

S.P. designed the project and conducted all the synthetic experimental work. Y.v.I. and B.M.K. performed the crystal structure analysis. S.P. drafted the manuscript and the ESI. R.L.M., E.R., and T.W. directed the project. All authors proofread and edited the manuscript.

The authors declare no competing financial interest.

Supplementary Material

ic4c00612_si_001.pdf (3.9MB, pdf)

References

  1. Carrillo-Hermosilla F.; Fernández-Galán R.; Ramos A.; Elorriaga D. Guanidinates as Alternative Ligands for Organometallic Complexes. Molecules 2022, 27 (18), 5962. 10.3390/molecules27185962. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Wedler M.; Knösel F.; Pieper U.; Stalke D.; Edelmann F. T.; Amberger H.-D. Sterische Cyclopentadienyl-Äquivalente in Der Chemie Der f-Elemente: Monomere, Homoleptische Lanthanid(III)-Tris[N,N′-Bis(Trimethylsilyl)-Benzamidinate]. Chem. Ber. 1992, 125 (10), 2171–2181. 10.1002/cber.19921251003. [DOI] [Google Scholar]
  3. Ajithkumar V. S.; Ghanwat P. B.; Raj K. V.; Vanka K.; Gonnade R. G.; Sen S. S. Synthesis of Si(IV)- and Ge(II)-Substituted Amines, Hydrazone, and Hydrazine from Hypersilyl Germylene. Organometallics 2023, 42 (20), 2983–2990. 10.1021/acs.organomet.3c00318. [DOI] [Google Scholar]
  4. Yadav S.; Kumar R.; Vipin Raj K.; Yadav P.; Vanka K.; Sen S. S. Amidinato Germylene-Zinc Complexes: Synthesis, Bonding, and Reactivity. Chem.—Asian J. 2020, 15 (19), 3116–3121. 10.1002/asia.202000807. [DOI] [PubMed] [Google Scholar]
  5. Sen S. S.; Khan S.; Kratzert D.; Roesky H. W.; Stalke D. Reaction of a Base-Stabilized Bis(Silylene) [PhC(NtBu)2Si]2 with Cyclooctatetraene without Cleavage of the Si-Si Bond. Eur. J. Inorg. Chem. 2011, 2011, 1370–1373. 10.1002/ejic.201100063. [DOI] [Google Scholar]
  6. Sen S. S.; Roesky H. W.; Stern D.; Henn J.; Stalke D. High Yield Access to Silylene RSiCl (R = PhC(NtBu)2) and Its Reactivity toward Alkyne: Synthesis of Stable Disilacyclobutene. J. Am. Chem. Soc. 2010, 132 (3), 1123–1126. 10.1021/ja9091374. [DOI] [PubMed] [Google Scholar]
  7. Zhou Y.; Richeson D. S. Bulky Amidinate Complexes of Indium(III). Synthesis and Structure of [CyNC(tBu)NCy]2InCl. Inorg. Chem. 1996, 35 (9), 2448–2451. 10.1021/ic950943a. [DOI] [PubMed] [Google Scholar]
  8. Coles M. P.; Swenson D. C.; Jordan R. F.; Young V. G. Synthesis and Structures of Mono- and Bis(Amidinate) Complexes of Aluminum. Organometallics 1997, 16 (24), 5183–5194. 10.1021/om9706323. [DOI] [Google Scholar]
  9. Kushvaha S. K.; Kallenbach P.; Rohman S. S.; Pandey M. K.; Hendi Z.; Rüttger F.; Herbst-Irmer R.; Stalke D.; Parameswaran P.; Roesky H. W. A Neutral Planar Four-Membered Si2B2 2π-Aromatic Ring. J. Am. Chem. Soc. 2023, 145 (47), 25523–25527. 10.1021/jacs.3c09131. [DOI] [PubMed] [Google Scholar]
  10. Hobson K.; Carmalt C. J.; Bakewell C. Aluminum Amidinates: Insights into Alkyne Hydroboration. Inorg. Chem. 2021, 60 (15), 10958–10969. 10.1021/acs.inorgchem.1c00619. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Bisai M. K.; Pahar S.; Das T.; Vanka K.; Sen S. S. Transition Metal Free Catalytic Hydroboration of Aldehydes and Aldimines by Amidinato Silane. Dalton Trans. 2017, 46 (8), 2420–2424. 10.1039/C6DT04893E. [DOI] [PubMed] [Google Scholar]
  12. Edelmann F. T. Lanthanide Amidinates and Guanidinates: From Laboratory Curiosities to Efficient Homogeneous Catalysts and Precursors for Rare-Earth Oxide Thin Films. Chem. Soc. Rev. 2009, 38 (8), 2253–2268. 10.1039/b800100f. [DOI] [PubMed] [Google Scholar]
  13. Bambirra S.; van Leusen D.; Meetsma A.; Hessen B.; Teuben J. H. Yttrium Alkyl Complexes with a Sterically Demanding Benzamidinate Ligand: Synthesis, Structure and Catalytic Ethene Polymerisation. Chem. Commun. 2003, 522–523. 10.1039/b208502j. [DOI] [PubMed] [Google Scholar]
  14. Basalov I. V.; Yurova O. S.; Cherkasov A. V.; Fukin G. K.; Trifonov A. A. Amido Ln(II) Complexes Coordinated by Bi- and Tridentate Amidinate Ligands: Nonconventional Coordination Modes of Amidinate Ligands and Catalytic Activity in Intermolecular Hydrophosphination of Styrenes and Tolane. Inorg. Chem. 2016, 55 (3), 1236–1244. 10.1021/acs.inorgchem.5b02450. [DOI] [PubMed] [Google Scholar]
  15. Zhang L.; Nishiura M.; Yuki M.; Luo Y.; Hou Z. Isoprene Polymerization with Yttrium Amidinate Catalysts: Switching the Regio- and Stereoselectivity by Addition of AlMe3. Angew. Chem., Int. Ed. 2008, 47, 2642–2645. 10.1002/anie.200705120. [DOI] [PubMed] [Google Scholar]
  16. Swamy V. S. V. S. N.; Raj K. V.; Vanka K.; Sen S. S.; Roesky H. W. Silylene Induced Cooperative B-H Bond Activation and Unprecedented Aldehyde C-H Bond Splitting with Amidinate Ring Expansion. Chem. Commun. 2019, 55 (24), 3536–3539. 10.1039/C9CC00296K. [DOI] [PubMed] [Google Scholar]
  17. Bisai M. K.; Swamy V. S. V. S. N.; Das T.; Vanka K.; Gonnade R. G.; Sen S. S. Synthesis and Reactivity of a Hypersilylsilylene. Inorg. Chem. 2019, 58 (16), 10536–10542. 10.1021/acs.inorgchem.9b00418. [DOI] [PubMed] [Google Scholar]
  18. Swamy V. S. V. S. N.; Bisai M. K.; Das T.; Sen S. S. Metal Free Mild and Selective Aldehyde Cyanosilylation by a Neutral Penta-Coordinate Silicon Compound. Chem. Commun. 2017, 53 (51), 6910–6913. 10.1039/C7CC03948D. [DOI] [PubMed] [Google Scholar]
  19. Swamy V. S. V. S. N.; Parvin N.; Vipin Raj K.; Vanka K.; Sen S. S. C(Sp3)-F, C(Sp2)-F and C(Sp3)-H Bond Activation at Silicon(II) Centers. Chem. Commun. 2017, 53 (71), 9850–9853. 10.1039/c7cc05145j. [DOI] [PubMed] [Google Scholar]
  20. Dagorne S.; Guzei I. A.; Coles M. P.; Jordan R. F. Synthesis and Structures of Cationic Aluminum and Gallium Amidinate Complexes. J. Am. Chem. Soc. 2000, 122 (2), 274–289. 10.1021/ja992104j. [DOI] [Google Scholar]
  21. Coles M. P.; Jordan R. F. Cationic Aluminum Alkyl Complexes Incorporating Amidinate Ligands. Transition-Metal-Free Ethylene Polymerization Catalysts. J. Am. Chem. Soc. 1997, 119 (34), 8125–8126. 10.1021/ja971815j. [DOI] [Google Scholar]
  22. Kannan R.; Nayak P.; Arumugam R.; Krishna Rao D.; Mote K. R.; Murali A. C.; Venkatasubbaiah K.; Chandrasekhar V. Blue Emissive Amidinate-Based Tetra-Coordinated Boron Compounds. Dalton Trans. 2023, 52 (45), 16829–16840. 10.1039/D3DT03378C. [DOI] [PubMed] [Google Scholar]
  23. Dureen M. A.; Stephan D. W. Reactions of Boron Amidinates with CO2 and CO and Other Small Molecules. J. Am. Chem. Soc. 2010, 132 (38), 13559–13568. 10.1021/ja1064153. [DOI] [PubMed] [Google Scholar]
  24. Hill N. J.; Findlater M.; Cowley A. H. Synthetic and Structural Chemistry of Amidinate-Substituted Boron Halides. Dalton Trans. 2005, 3229–3234. 10.1039/b509392a. [DOI] [PubMed] [Google Scholar]
  25. Ergezinger C.; Weller F.; Dehnicke K. Amidinatokomplexe von Bor, Aluminium, Gallium, Indium Und Zinn Die Kristallstrukturen von Ph-C(NSiMe3)2AICl2 Und Ph-C(NSiMe3)2SnCl3/Amidinato Complexes of Boron, Aluminium, Gallium, Indium, and Tin The Crystal Structures of Ph-C(NSiMe3)2AlCl2 and Ph-C(NSiMe3)2SnCl3. Z. Naturforsch., B 1988, 43 (12), 1621–1627. 10.1515/znb-1988-1215. [DOI] [Google Scholar]
  26. Brauer D. J.; Buchheim-Spiegel S.; Bürger H.; Gielen R.; Pawelke G.; Rothe J. Novel [2 + 2] Cycloaddition Reactions of (Dimethylamino)Bis(Trifluoromethyl)Borane, (CF3)2BNMe2, with N-Sulfinylsulfonamides, Aminoiminophosphines, Carbodiimides, and a Keteneimine. Organometallics 1997, 16 (24), 5321–5330. 10.1021/om970262i. [DOI] [Google Scholar]
  27. Blais P.; Chivers T.; Downard A.; Parvez M. Synthesis and X-Ray Structures of Amidinate, Oxoamidate, and Thioamidate Complexes of Boron. Can. J. Chem. 2000, 78 (1), 10–15. 10.1139/v99-221. [DOI] [Google Scholar]
  28. Findlater M.; Hill N. J.; Cowley A. H. Amidinate-Substituted Boron Halides: Synthesis and Structure. Polyhedron 2006, 25 (4), 983–988. 10.1016/j.poly.2005.11.012. [DOI] [Google Scholar]
  29. Kundu G.; Pahar S.; Tothadi S.; Sen S. S. Stepwise Nucleophilic Substitution to Access Saturated N-Heterocyclic Carbene Haloboranes with Boron-Methyl Bonds. Organometallics 2020, 39 (24), 4696–4703. 10.1021/acs.organomet.0c00691. [DOI] [Google Scholar]
  30. Brook A. G.; Abdesaken F.; Gutekunst B.; Gutekunst G.; Kallury R. K. A Solid Silaethene: Isolation and Characterization. J. Chem. Soc. Chem. Commun. 1981, 191–192. 10.1039/c39810000191. [DOI] [Google Scholar]
  31. Heine A.; Stalke D. Synthesis and Structure of the Disilagermirane R2Ge(SiR2)2 and the Solvent-Separated Ion Pair [Li([12]Crown-4)2] [GeR3]; (R = SiMe3). Angew. Chem., Int. Ed. 1994, 33 (1), 113–115. 10.1002/anie.199401131. [DOI] [Google Scholar]
  32. Protchenko A. V.; Schwarz A. D.; Blake M. P.; Jones C.; Kaltsoyannis N.; Mountford P.; Aldridge S. A Generic One-Pot Route to Acyclic Two-Coordinate Silylenes from Silicon(IV) Precursors: Synthesis and Structural Characterization of a Silylsilylene. Angew. Chem., Int. Ed. 2013, 52 (2), 568–571. 10.1002/anie.201208554. [DOI] [PubMed] [Google Scholar]
  33. Wendel D.; Porzelt A.; Herz F. A. D.; Sarkar D.; Jandl C.; Inoue S.; Rieger B. From Si(II) to Si(IV) and Back: Reversible Intramolecular Carbon-Carbon Bond Activation by an Acyclic Iminosilylene. J. Am. Chem. Soc. 2017, 139 (24), 8134–8137. 10.1021/jacs.7b05136. [DOI] [PubMed] [Google Scholar]
  34. Wendel D.; Szilvási T.; Jandl C.; Inoue S.; Rieger B. Twist of a Silicon-Silicon Double Bond: Selective Anti-Addition of Hydrogen to an Iminodisilene. J. Am. Chem. Soc. 2017, 139 (27), 9156–9159. 10.1021/jacs.7b05335. [DOI] [PubMed] [Google Scholar]
  35. Matioszek D.; Katir N.; Ladeira S.; Castel A. Novel Stable Silyl, Germyl, and Stannyl Germanium(II) Compounds Containing an Amidinato Ligand. Organometallics 2011, 30 (8), 2230–2235. 10.1021/om200024d. [DOI] [Google Scholar]
  36. Katir N.; Matioszek D.; Ladeira S.; Escudié J.; Castel A. Stable N-Heterocyclic Carbene Complexes of Hypermetallyl Germanium(II) and Tin(II) Compounds. Angew. Chem., Int. Ed. 2011, 50 (23), 5352–5355. 10.1002/anie.201100634. [DOI] [PubMed] [Google Scholar]
  37. Roy M. M. D.; Ferguson M. J.; McDonald R.; Zhou Y.; Rivard E. A Vinyl Silylsilylene and Its Activation of Strong Homo- and Heteroatomic Bonds. Chem. Sci. 2019, 10 (26), 6476–6481. 10.1039/C9SC01192G. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Leszczyńska K. I.; Deglmann P.; Präsang C.; Huch V.; Zimmer M.; Schweinfurth D.; Scheschkewitz D. Pentamethylcyclopentadienyl-Substituted Hypersilylsilylene: Reversible and Irreversible Activation of CC Double Bonds and Dihydrogen. Dalton Trans. 2020, 49 (38), 13218–13225. 10.1039/D0DT02943B. [DOI] [PubMed] [Google Scholar]
  39. Gour K.; Bisai M. K.; Sen S. S. The Hypersilyl Substituent in Heavier Low-Valent Group 14 Chemistry. Eur. J. Inorg. Chem. 2022, 2022, e202200071 10.1002/ejic.202200071. [DOI] [Google Scholar]
  40. Pahar S.; Sharma V.; Tothadi S.; Sen S. S. Pyridylpyrrolido Ligand in Ge(II) and Sn(II) Chemistry: Synthesis, Reactivity and Catalytic Application. Dalton Trans. 2021, 50 (45), 16678–16684. 10.1039/D1DT03136H. [DOI] [PubMed] [Google Scholar]
  41. Bisai M. K.; Ajithkumar V. S.; Gonnade R. G.; Sen S. S. Access to a Variety of Ge(II) and Sn(II) Compounds through Substitution of Hypersilyl Moiety. Organometallics 2021, 40 (15), 2651–2657. 10.1021/acs.organomet.1c00306. [DOI] [Google Scholar]
  42. Arp H.; Baumgartner J.; Marschner C.; Müller T. A Cyclic Disilylated Stannylene: Synthesis, Dimerization, and Adduct Formation. J. Am. Chem. Soc. 2011, 133 (15), 5632–5635. 10.1021/ja1100883. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Arp H.; Marschner C.; Baumgartner J.; Zark P.; Müller T. Coordination Chemistry of Disilylated Stannylenes with Group 10 D10 Transition Metals: Silastannene vs Stannylene Complexation. J. Am. Chem. Soc. 2013, 135 (21), 7949–7959. 10.1021/ja401548d. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Arp H.; Baumgartner J.; Marschner C.; Zark P.; Müller T. Dispersion Energy Enforced Dimerization of a Cyclic Disilylated Plumbylene. J. Am. Chem. Soc. 2012, 134 (14), 6409–6415. 10.1021/ja300654t. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Franz D.; Szilvási T.; Pöthig A.; Inoue S. Isolation of an N-Heterocyclic Carbene Complex of a Borasilene. Chem.—Eur. J. 2019, 25 (47), 11036–11041. 10.1002/chem.201902877. [DOI] [PubMed] [Google Scholar]
  46. Nakata N.; Sekiguchi A. A Stable Silaborene: Synthesis and Characterization. J. Am. Chem. Soc. 2006, 128 (2), 422–423. 10.1021/ja0570741. [DOI] [PubMed] [Google Scholar]
  47. Suzuki Y.; Ishida S.; Sato S.; Isobe H.; Iwamoto T. An Isolable Potassium Salt of a Borasilene-Chloride Adduct. Angew. Chem., Int. Ed. 2017, 56 (16), 4593–4597. 10.1002/anie.201612545. [DOI] [PubMed] [Google Scholar]
  48. Hill N. J.; Moore J. A.; Findlater M.; Cowley A. H. Isolation of an Intermediate in the Insertion of a Carbodiimide into a Boron-Aryl Bond. Chem. Commun. 2005, 43, 5462–5464. 10.1039/b511080g. [DOI] [PubMed] [Google Scholar]
  49. Roddick D. M.; Tilley T. D.; Rheingold A. L.; Geib S. J. Coordinatively Unsaturated Tris(Trimethylsilyl)Silyl Complexes of Chromium, Manganese, and Iron. J. Am. Chem. Soc. 1987, 109 (3), 945–946. 10.1021/ja00237a076. [DOI] [Google Scholar]
  50. Weetman C.Low Valent Main Group Compounds in Small Molecule Activation. In Encyclopedia of Inorganic and Bioinorganic Chemistry; Scott R. A., Ed.; Wiley, 2021; pp 1–27. [Google Scholar]
  51. Lam J.; Szkop K. M.; Mosaferi E.; Stephan D. W. FLP Catalysis: Main Group Hydrogenations of Organic Unsaturated Substrates. Chem. Soc. Rev. 2019, 48 (13), 3592–3612. 10.1039/c8cs00277k. [DOI] [PubMed] [Google Scholar]
  52. Chu T.; Nikonov G. I. Oxidative Addition and Reductive Elimination at Main-Group Element Centers. Chem. Rev. 2018, 118 (7), 3608–3680. 10.1021/acs.chemrev.7b00572. [DOI] [PubMed] [Google Scholar]
  53. Welch G. C.; Juan R. R. S.; Masuda J. D.; Stephan D. W. Reversible, Metal-Free Hydrogen Activation. Science 2006, 314 (5802), 1124–1126. 10.1126/science.1134230. [DOI] [PubMed] [Google Scholar]
  54. Baumgartner T.; Jaekle F.. Main Group Strategies towards Functional Hybrid Materials; John Wiley & Sons: Hoboken, NJ, 2018. [Google Scholar]
  55. Koelle P.; Noeth H. The chemistry of borinium and borenium ions. Chem. Rev. 1985, 85, 399–418. 10.1021/cr00069a004. [DOI] [Google Scholar]
  56. Franz D.; Inoue S. Cationic Complexes of Boron and Aluminum: An Early 21st Century Viewpoint. Chem.—Eur. J. 2019, 25 (12), 2898–2926. 10.1002/chem.201803370. [DOI] [PubMed] [Google Scholar]
  57. Prokofjevs A.; Kampf J. W.; Solovyev A.; Curran D. P.; Vedejs E. Weakly Stabilized Primary Borenium Cations and Their Dicationic Dimers. J. Am. Chem. Soc. 2013, 135 (42), 15686–15689. 10.1021/ja407458k. [DOI] [PMC free article] [PubMed] [Google Scholar]
  58. Matsumoto T.; Gabbaï F. P. A Borenium Cation Stabilized by an N-Heterocyclic Carbene Ligand. Organometallics 2009, 28 (16), 4898–4898. 10.1021/om900649g. [DOI] [Google Scholar]
  59. Wang Y.; Robinson G. H. Carbene Stabilization of Highly Reactive Main-Group Molecules. Inorg. Chem. 2011, 50 (24), 12326–12337. 10.1021/ic200675u. [DOI] [PubMed] [Google Scholar]
  60. Patrick E. A.; Piers W. E. Twenty-Five Years of Bis-Pentafluorophenyl Borane: A Versatile Reagent for Catalyst and Materials Synthesis. Chem. Commun. 2020, 56 (6), 841–853. 10.1039/C9CC08338C. [DOI] [PubMed] [Google Scholar]
  61. Parks D. J.; Piers W. E.; Yap G. P. A. Synthesis, Properties, and Hydroboration Activity of the Highly Electrophilic Borane Bis(Pentafluorophenyl)Borane, HB(C6F5)21. Organometallics 1998, 17 (25), 5492–5503. 10.1021/om980673e. [DOI] [Google Scholar]
  62. Hübner A.; Qu Z.-W.; Englert U.; Bolte M.; Lerner H.-W.; Holthausen M. C.; Wagner M. Main-Chain Boron-Containing Oligophenylenes via Ring-Opening Polymerization of 9-H-9-Borafluorene. J. Am. Chem. Soc. 2011, 133 (12), 4596–4609. 10.1021/ja110947k. [DOI] [PubMed] [Google Scholar]
  63. Tsao F. A.; Stephan D. W. Synthesis and Reactions of 4H-1,4-Telluraborine. Chem. Commun. 2018, 54 (2), 208–211. 10.1039/C7CC08765A. [DOI] [PubMed] [Google Scholar]
  64. Akram M. O.; Tidwell J. R.; Dutton J. L.; Martin C. D. Bis(1-Methyl-Ortho-Carboranyl)Borane. Angew. Chem., Int. Ed. 2023, 62 (34), e202307040 10.1002/anie.202307040. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ic4c00612_si_001.pdf (3.9MB, pdf)

Data Availability Statement

Information about the data that underpins the results presented in this article can be found in the Cardiff University data catalogue at 10.17035/d.2024.0315834338.

Articles from Inorganic Chemistry are provided here courtesy of American Chemical Society

RESOURCES