Expanding the allyl analogy: accessing η³-P,B,P diphosphinoborane complexes of group 10

Abstract

Using the diphosphinoborane, (PPh₂)₂BMes (Mes = 2,4,6-Me₃C₆H₃), we report the first examples of η³-P,B,P-ligated complexes using Ni(0) and Pt(ii). Reaction of (PPh₂)₂BMes with Ni(COD)₂ or Pt(COD)Me₂ (COD = 1,5-cyclooctadiene) results in gradual COD displacement to give [η³-P,B,P-(PPh₂)₂BMes]Ni(COD) (3) or [η³-P,B,P-(PPh₂)₂BMes]Pt(CH₃)₂ (6). Complex 3 serves as a versatile Ni-containing synthon for the preparation of square planar or tetrahedral Ni(0) complexes. Notably, the M–B interaction in these systems is non-negligible – with coordination resulting in an upfield shift of ca. 80 ppm in the ¹¹B NMR spectrum. We also show that treatment of the Pt^IV halide precursor, [PtMe₃I]₄ with this ligand framework results in migration of X-type ligands (CH₃⁻ and I⁻) to boron and reductive elimination of ethane (C₂H₆) to give a distorted square planar zwitterionic Pt^II complex, Pt[κ²-P,P-(PPh₂)₂B(Mes)(CH₃)][κ²-P,P-(PPh₂)₂B (Mes)(I)] (10). This reactivity suggests the feasibility of (PPh₂)₂BMes-ligand-induced labilization of M–X ligands.

Introduction

Allyl ligands [C₃H₅]⁻ represent a cornerstone of organometallic chemistry, stabilizing transition and main group elements in a η¹- or η³-bonding fashion. Drawing inspiration from the ‘all-carbon’-based allyl fragment, related ligands have emerged incorporating a Z-type¹ accepting boron atom in lieu of carbon. Shapiro and co-workers, for example, reported that the zwitter-ionic bis(triphenylphosphinemethylenido)borane ligand coordinates in an η³-C,B,C fashion to both Zr(iv) and Pd(ii) (Chart 1A).² By analogy, Emslie and co-workers found that vinylboranes (R₂C=CR–BR₂) serve as precursors to η³-B,C,C coordinated complexes of Ni(0) and Pt(0) adopting borataallyl coordination modes (Chart 1A).³ In a similar vein, our group and others have characterized related η³-B,C,C complexes using (phosphine)borane-based ligand platforms, where the metal centre engages in bonding with both boron and a π-acidic aryl ring.^4–6 Building on our group’s previous efforts in P,B-containing coordination complexes of late transition metals, we wished to explore direct P–B linkages as isolobal fragments to C=C bonds e.g., [R₂C=CR–CR₂]⁻ vs. R₂P=B(R)–PR₂. This approach has been highlighted by isolation of the η⁶-P₃,B₃-containing arene complex [{η⁶-[(P^tBu)(BMes)]₃}Cr(CO)₃]7 and the η²-P,B phosphinoborane complexes, Pt(PPh₃)₂(η²-R₂P=B(C₆F₅)₂) (R = Cy or tBu), providing evidence for alkene-type coordination of P=B multiple bonds (Chart 1B).⁸ We now disclose that the diphosphinoborane, (PPh₂)₂BMes (1: Mes = 2,4,6-Me₃C₆H₃) first prepared by Power and co-workers,⁹ serves as a practical starting point from which η³-P,B,P bonded complexes of group 10 transition metals can be accessed.

Chart 1.

Overview of boron-based ligand platforms.

Generation of [η³-P,B,P-(PPh₂)₂BMes]Ni(COD) (2; COD = 1,5-cyclooctadiene) was achieved by combination of (PPh₂)₂BMes with Ni(COD)₂ in benzene at ambient temperature, which provides a dark brown solution (Scheme 1). Monitoring the reaction by ¹H NMR spectroscopy evidences loss of cyclooctadiene (C₆D₆: δ_H = 5.58 and 2.21 ppm) and formation of a new C_s-symmetric Ni(0) complex. Notably, three unique mesityl –CH₃ signals are observed (each of integration 3H) at δ = 2.58, 2.13, and 1.30 ppm, indicative of both (1) hindered B–C bond rotation and (2) the absence of a B–Ni decoordination/recoordination process (where the boron atom transiently dissociates only to reassociate on the opposite face of the molecule). Further, by ¹H NMR spectroscopy, coalescence of the ortho-CH₃(mesityl) groups is not observed at elevated temperature (95 °C, tol-d₈). It is noteworthy that this phenomenon is observed for all η³-P,B,P-(PPh₂)₂BMes complexes discussed herein. A strong Ni–B interaction is corroborated by ¹¹B NMR spectroscopy [δ_B = +4.0; Δδ = −81.0 cf. 1] (Fig. 1), while ³¹P NMR spectroscopy provides a new signal at δ_P = −16.6 (Δδ = −16.5 cf. 1) – coupling between ¹¹B and ³¹P is not observed. High-resolution FAB-MS also provides a [M]⁺ signal consistent with the molecular formula of 2 at m/z = 666.229 (calcd 666.229).

Scheme 1.

Generation of η³-P,B,P-(PPh₂)₂BMes Ni complexes.

Fig. 1.

¹¹B{¹H} NMR spectra of ligand 1 and complexes 2 and 3 (128 MHz, C₆D₆, 298 K).

Orange/brown crystals of 2 can be obtained from a saturated Et₂O solution at −35 °C allowing for unambiguous structural determination using single crystal X-ray diffraction (Fig. 2). Complex 2 crystallizes in the triclinic space group, P$\stackrel{‒}{1}$ and features a tetrahedral Ni(0) complex bonded to PBP and COD co-ligands having Ni(1)–P(1) and Ni(1)–P(2) bond lengths of 2.183(1) and 2.190(1) Å and a Ni(1)–B(1) bond distance of 2.329(4) Å. This distance is considerably shorter than that noted for a related compound, [(Ph₃P)₂Ni(η³-B,C,C-VB^Ph)] (VB^Ph = (E)-PhHC=CH–B(C₆F₅)₂ (d_Ni–B = 2.660(3) Å)).³ The boron centre also retains sp²-hybridization [∑(X–B–X) = 360°] and upon coordination, little perturbation in P–B bond length is noted [1.888(4)/1.907(4) Å cf. 1.879(2)/1.901(2) Å for 1]. Consistent with increased planarization, the sum of angles at phosphorus, [∑(X–P–X) = 340.2° and 342.7°] also increase by ca. 20° [318.8° and 324.5° for 1]. These data indicate that coordination of 1 involves some degree of P–B–P communication/π-orbital overlap, signifying that the ligand is electronically distinct from its relative, bis(diphenylphosphino) methane (dppm). Highlighting the electrophilic nature of boron in this family of compounds, treatment of 1 with NiCl₂ or NiBr₂(dme) (dme = 1,2-dimethoxyethane) in THF or Et₂O leads to rapid B–P bond rupture, forming the known tetrahedral Ni(0)-species, Ni(PPh₂H)₄¹⁰ and MesBX₂ (X = Cl, Br). We posit that the H-atoms in Ni(PPh₂H)₄¹⁰ arise from radical H-atom transfer (HAT), presumably from solvent.

Fig. 2.

ORTEP depiction of the solid-state molecular structure of 2 (displacement ellipsoids are shown at the 50% probability, hydrogens omitted for clarity). Selected bond lengths [Å] and angles (°). Ni(1)–P(1) 2.183(1), Ni(1)–P(2) 2.190(1), Ni(1)–B(1) 2.329(4), P(1)–Ni(1)–P(2) 85.46(4), P(1)–B(1)–P(2) 102.8(2).

To evaluate the effect of co-ligand on η³-P,B,P bonding and to further study the nature of the Ni–B interaction, we next ventured to treat complex 2 with L-type ligands. Dissolution of complex 2 in coordinating solvents: MeCN-d₃, pyridine-d₅, or THF-d₈ did not result in Ni–B dissociation as judged by ¹¹B and ³¹P NMR spectroscopy. Conversely, treatment of a benzene solution of complex 2 with 2,2′-bipyridine (2,2′-bpy) slowly (4 days) produces a dark purple solution, identified as the tetrahedral Ni(0) complex, [η³-P,B,P-(PPh₂)₂BMes]Ni(2,2′-bpy) (3) along with free COD (Scheme 1). This complex displays two deshielded resonances in the ¹H NMR spectrum at δ = 9.92 and 8.92 ppm for each of its two ortho-CH pyridyl groups, indicating C_s-symmetry. Further, ¹¹B NMR spectroscopy supports a maintained interaction between Ni and B [δ_B = −7.7], while ³¹P NMR spectroscopy provides a new signal at δ_P = −20.9. Purple blocks, suitable for X-ray analysis were obtained from a concentrated THF/pentane solution at −35 °C (Fig. 3). Complex 3 possesses similar Ni(1)–P(1) and Ni(1)–P(2) bond lengths to complex 2 of 2.1625(6) and 2.1751(9) Å, albeit a shorter Ni(1)–B(1) bond length of 2.201(3) Å. For the 2,2′-bpy ligand, all bond lengths are consistent with redox innocence.¹¹

Fig. 3.

ORTEP depiction of the solid-state molecular structure of 3 and 5 (displacement ellipsoids are shown at the 50% probability, hydrogens omitted for clarity).

By analogy, the COD ligand of complex 2 is readily displaced by the π-accepting ligands 2,6-dimethylphenylisonitrile (CNXyl) or diphenylacetylene to give complexes 4 and 5, respectively (Scheme 1). For the bis(CNXyl) analogue 4 a single ¹¹B and ³¹P NMR resonance at δ_B = +4.8 ppm and δ_P = −8.5 ppm is observed. Three broad signals are observed by IR spectroscopy at ν(CN) = 2078, 2039, and 1993 cm⁻¹ (cf. 2123 cm⁻¹ for free CNXyl), again indicating moderate π-back donation. Over a period of hours complex 4 decomposes in solution to as yet unidentified species, obviating analysis by X-ray crystallography. For the square planar complex 5, NMR spectroscopy supports the formation of a C_s-symmetric complex (δ_B = +6.7 ppm and δ_P = −8.1 ppm) and the IR spectrum exhibits a feature at 1823 cm⁻¹ (consistent with π-back donation by η³-P,B,P-Ni⁰). The solid-state structure of complex 5 was also obtained (Fig. 3). By contrast to complexes 2 and 3, for complex 5, Ni(1)–P(1) and Ni(1)–P(2) bonds of 2.2040(7) and 2.1905(9) Å represent a slight elongation at the cost of the Ni(1)–B(1) bond [2.254(3) Å], which is slightly shortened. Complex 5 is structurally similar to the η²-alkyne complex, reported by Hillhouse et al. [dtbpe]Ni(η²-PhCuCPh) (dtbpe = 1,2-bis(di-tert-butyl)phosphinoethane) for which ν(CC) = 1790 cm⁻¹.¹²

Expansion of the ligand platform to Pt^II was also established. Combination of 1 and Pt(Me)₂(COD) in benzene at ambient temperature provides a light yellow solution over a period of four days (Scheme 2). NMR spectroscopic analysis of a C₆D₆ solution of this mixture provides evidence for two Pt-containing species in a 9: 1 ratio: [η³-P,B,P-(PPh₂)₂BMes] Pt(Me)₂ (6) and the known complex, Pt(PHPh₂)₂(Me)₂.¹³ Complex 6 could be purified and separated by recrystallization from Et₂O at −35 °C in 88% yield. By analogy to complex 2, the ¹H NMR spectrum of 6 features three diagnostic signals, each of integration of 3H at δ = 2.81, 2.78, and 2.06 ppm for the mesityl group, while for the platinum-methyl groups, an apparent triplet is observed at δ = 2.18 ppm [³J_Pt,H = 80 Hz] that corresponds to δ_c = 4.52 ppm (t, ²J_C,P = 27.8 Hz) with ¹⁹⁵Pt satellites (¹J_C,Pt = 688 Hz) in the ¹³C NMR spectrum. Coordination of Pt^II to the PBP unit is also evidenced by ³¹P and ¹¹B NMR spectroscopy, which provides a signal at δ_P = −21.6 [¹J_Pt,P = 839 Hz] and δ_B = +7.9 ppm [Δδ_B= −77.1 cf. 1].

Scheme 2.

Generation of η³-P,B,P-(PPh₂)₂BMes Pt^II complex 6.

The solid-state structure of complex 6 is depicted in Fig. 4. The four-coordinate geometry is best described as square planar, having Pt(1)–P(1) and Pt(1)–P(2) contacts of 2.305(3) and 2.318(2) Å and a Pt(1)–B(1) distance of 2.403(11) Å. The Pt(1)–C(1) and Pt(1)–C(2) bond lengths are non-exceptional.

Fig. 4.

ORTEP depiction of the solid-state molecular structure of 6 (displacement ellipsoids are shown at the 50% probability, hydrogens omitted for clarity). Selected bond lengths [Å] and angles (°). Pt(1)–P(1) 2.305(3), Pt(1)–P(2) 2.318(2), Pt(1)–B(1) 2.403(11), Pt(1)–C(1) 2.093(9), Pt(1)–C(2) 2.103(12), P(1)–Pt(1)–P(2) 81.08(9), P(1)–B(1)–P(2) 106.9(5).

Given the halophilic nature of 1, we wondered if capture of an X-type ligand by B could be performed in a controlled manner – in effect promoting metal–ligand cooperativity.^14–19 As a result, 1 was treated with 0.25 equiv. of the Pt^IV precursor, [PtMe₃I]₄ resulting in slow effervescence of C₂H₆ [δ_H = 0.80 ppm] as judged by ¹H NMR spectroscopy. By ³¹P NMR spectroscopy, consumption of the ligand and the appearance of a broad multiplet centred at δ_P = −35.7 was observed (see ESI, Fig. S28†) over a period of four days. Removal of volatiles in vacuo and recrystallization of the resulting solid from Et₂O at −35 °C, provided colourless prisms suitable for single crystal analysis. Analysis of the resulting crystal data provides evidence for Pt[κ²-P,P-(PPh₂)₂B(Mes)(I)][κ²-P,P-(PPh₂)₂B(Mes) (CH₃)] (10) (Fig. 5). Notably, the B–CH₃ resonance for complex 10 appears as a phosphorus-coupled triplet at δ_H = 1.45 [³J_P,H = 19.4 Hz]. We posit that coordination of ‘PtMe₃I’ to 1 provides the octahedral Pt^IV complex 7, which is susceptible to halide abstraction by 1, providing the coordinatively unsaturated five-coordinate complex 8. Reductive elimination of ethane (C₂H₆) from 8 thus provides complex 9, which upon methyl abstraction by another equivalent of 1 gives complex 10. Abstraction of X-type halide and methyl groups by group 13 Lewis acids is well documented.^20–24 The crystal structure of 10 features a distorted square planar Pt(ii) centre (τ₄ = 0.23)²⁵ bonded by four phosphorus atoms. By contrast to complex 6, each boron atom in the ligand is sp³-hybridized in nature, owing to association of the X-type iodide or methyl anion causing the P–B bond lengths elongate: [2.036(4) and 2.064(4) Å cf. 1.85(1) and 1.89(1) Å for 6].

Fig. 5.

Generation of complex 10 and ORTEP depiction of the solid-state molecular structure of 10 (displacement ellipsoids are shown at the 50% probability, hydrogens omitted for clarity).

Conclusion

In close, we have provided here the first examples of Ni⁰ and Pt^II compounds containing a P–B–P diphosphinoborane ligand. This work expands the scope of P–B bond coordination complexes beyond that of the known η⁶-PvB and η²-PvB coordination modes and illustrates the use of diphosphinoboranes as modular η³-P,B,P chelates.

Experimental section

General considerations

All experiments were carried out employing standard Schlenk techniques under an atmosphere of dry nitrogen or argon employing degassed, dried solvents in a solvent purification system supplied by SG Water, LLC. Combustion analyses were carried out by Midwest Microlabs (Indianapolis). N.B. The results provided represent the best analysis values obtained. Multinuclear NMR spectroscopy has been provided (see ESI†) to illustrate sample homogeneity. Non-halogenated solvents were tested with a standard purple solution of sodium benzophenone ketyl in tetrahydrofuran in order to confirm effective moisture removal. (PPh₂)₂BMes⁹ was prepared according to a literature procedure. All other reagents were purchased from commercial vendors and used without further purification unless otherwise stated.

Physical methods

Fourier transform infrared ATR (FT-IR ATR) spectra were collected on a Thermo Scientific Nicolet iS5 Spectrometer with diamond ATR crystal. NMR data were collected on a Varian 400 MHz instrument with chemical shifts reported in ppm relative to C₆D₆ or THF-d₈, using residual solvent resonances as internal standards. N.B. In some instances, not all aromatic carbon atoms are viewed due to overlap with residual C₆D₆. ³¹P chemical shifts are reported in ppm relative to 85% aqueous H₃PO₄. ¹¹B{¹H} NMR spectra were acquired using quartz NMR tubes.

(PPh₂)₂BMes (1)

This compound was prepared as previously, however the ¹H and ¹³C NMR data were not provided.⁹ Also, in our hands a ¹¹B{¹H} NMR chemical shift of 85.0 ppm was recorded in C₆D₆ or 1: 1 C₆D₆:THF, which is different from that reported (30.0 ppm). ¹H NMR (400 MHz, C₆D₆, 298 K): δ = 7.29 (m, 8H; o-PPh₂), 6.90 (m, 8H; m-PPh₂), 6.89 (m, 4H; p-PPh₂), 6.69 (s, 2H; Mes), 2.20 (s, 3H; Mes), 2.18 (s, 6H; Mes). ¹³C{¹H} NMR (100 MHz, C₆D₆, 298 K): δ = 137.61 (t, J_C,P = 2.1 Hz), 137.28 (t, J_C,P = 5.9 Hz), 134.61 (t, J_C,P = 7.9 Hz), 134.19 (t, J_C,P = 6.4 Hz), 128.42 (t, J_C,P = 4.2 Hz), 128.00 (under C₆D₆), 127.92 (t, J_C,P = 4.2 Hz), 22.51 (t, J_C,P = 2.5 Hz), 21.38. ³¹P{¹H} NMR (161.9 MHz, C₆D₆, 298 K): δ = −0.01. ¹¹B{¹H} NMR (128 MHz, C₆D₆, 298 K): δ = 85.0.

[η³-P,B,P-(PPh₂)₂BMes]Ni(COD) (2)

In the glovebox, 1 (45 mg, 0.090 mmol) and Ni(COD)₂ (25 mg, 0.091 mmol) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the orange solution was allowed to stir for 4 days at 25 °C. The solvent was removed in vacuo and the resulting orange oil was washed with pentane to afford an orange/brown solid. Recrystallization from saturated Et₂O at −35 °C gave orange crystals (56 mg, 93%). ¹H NMR (400 MHz, THF-d₈, 298 K): δ = 7.40 (m, 4H; PPh₂), 7.08 (m, 12H; PPh₂), 6.89 (t, ³J_H,H = 7.2 Hz, 4H; PPh₂), 6.66 (s, 1H; Mes), 6.44 (s, 1H; Mes), 5.09 (s, 2H; COD), 4.27 (s, 2H; COD), 2.83 (br, 2H; COD), 2.58 (s, 3H; Mes), 2.47 (br m, 4H; COD), 2.27 (br m, 2H; COD), 2.13 (s, 3H; Mes), 1.30 (s, 3H; Mes). ¹³C{¹H} NMR (100 MHz, C₆D₆, 298 K): δ = 141.36, 139.78, 136.70 (t, J_C,P = 33 Hz), 135.46, 134.86 (t, J_C,P = 5.4 Hz), 133.74 (t, J_C,P = 5.1 Hz), 132.05 (t, J_C,P = 23 Hz), 128.40, 93.07, 87.63, 32.13, 31.06, 25.86, 23.26, 21.17. ³¹P{¹H} NMR (161.9 MHz, THF-d₈, 298 K): δ = −16.6 (br). ¹¹B{¹H} NMR (128 MHz, THF-d₈, 298 K): δ = +4.03 (br). FAB-MS (m/z): 666.229 (calcd 666.229). Anal. calcd for C₄₁H₄₃BNiP₂ (666.23): C, 73.80; H, 6.50. Found: C, 72.20; H, 7.11.

[η³-P,B,P-(PPh₂)₂BMes]Ni(2,2′-bipy) (3)

In the glovebox, 2 (30 mg, 0.045 mmol) and 2,2′-bipyridine (7.0 mg, 0.048 mmol) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the orange solution was allowed to stir for 4 days at 25 °C. The solvent was removed in vacuo and the resulting purple oil was recrystallized from pentane at −35 °C to give purple crystals (14 mg, 44%) N.B. Low yields are due to the high solubility of complex 3 in pentane. 1H NMR (400 MHz, C6D6, 298 K): δ = 9.92 (d, ³J_H,H = 5.6 Hz, 1H; bpy), 8.92 (d, ³J_H,H = 5.7 Hz, 1H; bpy), 7.75 (m, 4H; PPh₂), 7.50 (m, 4H; PPh₂), 7.25 (d, ³J_H,H = 8.3 Hz, 1H; bpy), 7.09 (d, ³J_H,H = 8.1 Hz, 1H; bpy), 7.02 (s, 1H; Mes), 7.00–6.76 (m, 15H; Ar), 6.60 (m, 2H; Ar), 3.24 (s, 3H; Mes), 2.47 (s, 3H; Mes), 2.24 (s, 3H; Mes). ¹³C{¹H} NMR (100 MHz, C₆D₆, 298 K): δ = 152.39, 150.10, 142.15 (m), 140.62 (m), 135.89, 134.18, 129.82, 129.20, 128.60, 127.34, 123.47, 122.49, 121.32, 120.69, 26.40, 22.90 (br), 21.44. ³¹P{¹H} NMR (161.9 MHz, C₆D₆, 298 K): δ = −20.9 (br). ¹¹B{¹H} NMR (128 MHz, C₆D₆, 298 K): δ = −7.68 (br). Anal. calcd for C₄₃H₃₉BN₂NiP₂ (714.20): C, 72.21; H, 5.50; N, 3.92. Found: C, 70.19; H, 5.50; N, 3.74.

[η³-P,B,P-(PPh₂)₂BMes]Ni(CNXyl)₂ (4)

In the glovebox, 2 (15 mg, 0.015 mmol) and 2,6-dimethylphenylisocyanide (5.9 mg, 0.030 mmol) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the resulting orange/green solution was allowed to stir for 30 min at 25 °C. The solvent was removed in vacuo and the resulting brown solid was washed with pentane to afford a brown solid (9.2 mg, 50%). This compound is unstable in solution (t_1/2 = 60 min) providing a mixture of as yet unidentified species including a broad resonance at δ_B = 31.2 ppm for the boroxin, (MesBO)₃²⁶ for which ¹H NMR (400 MHz, C₆D₆, 298 K) δ = 6.67 (s, 2H), 2.49 (s, 6H), 2.14 (3H). ¹H NMR (400 MHz, C₆D₆, 298 K): δ = 7.77 (m, 4H; PPh₂), 7.72 (m, 4H; PPh₂), 7.07–6.68 (m, 20H; Ar), 2.98 (s, 3H; Mes), 2.45 (s, 3H; Mes), 2.30 (s, 6H; CNXyl), 2.23 (s, 6H; CNXyl), 2.11 (s, 3H; Mes). ¹³C{¹H} NMR (100 MHz, C₆D₆, 298 K): δ = 141.98, 141.67, 137.81, 137.47, 137.13, 136.70 (t, J_C,P = 6.2 Hz), 135.01, 134.73, 134.26, 134.01 (t, J_C,P = 6.0 Hz), 128.81, 128.76, 128.59, 126.96, 126.88, 125.84, 28.38, 26.62, 25.63, 19.13, 19.10. ³¹P {¹H} NMR (161.9 MHz, C₆D₆, 298 K): δ = −8.5. ¹¹B{¹H} NMR (128 MHz, C₆D₆, 298 K): δ = 4.75 (br). FT-IR ATR (neat solid, cm⁻¹): 2078, 2039, 1993 (br, ν(CN)). Appropriate elemental analysis could not be obtained for complex 4 due to decomposition.

[η³-P,B,P-(PPh₂)₂BMes]Ni(η²-C₂Ph₂) (5)

In the glovebox, 2 (21 mg, 0.031 mmol) and diphenylacetylene (5.5 mg, 0.031 mmol) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the orange solution was allowed to stir for 2 days at 25 °C. The solvent was removed in vacuo and the resulting orange solid was washed with pentane to afford an orange solid. Recrystallization from Et₂O or pentane at −35 °C gave orange crystals (16 mg, 70%). ¹H NMR (400 MHz, C₆D₆, 298 K): δ = 8.17 (d, ³J_H,H = 7.1 Hz, 4H; Ph₂C₂), 7.52 (m, 4H; PPh₂), 7.47 (m, 4H; PPh₂), 7.13 (t, ³J_H,H = 7.5 Hz, 6H; Ar), 7.03 (t, ³J_H,H = 7.4 Hz, 2H; Ar), 6.84 (m, 6H), 6.74 (m, 2H), 6.59 (t, ³J_H,H = 7.6 Hz, 4H; Ar), 2.85 (s, 3H; Mes), 2.60 (s, 3H; Mes), 2.08 (s, 3H; Mes). ¹³C{¹H} NMR (100 MHz, C₆D₆, 298 K): δ = 141.31, 140.49, 136.51, 136.35 (t, J_C,P = 6.2 Hz), 133.07, 133.86 (m), 133.51 (m), 133.36 (t, J_C,P = 6.0 Hz), 131.07, 128.99, 128.82, 128.74, 128.56, 128.42, 128.21, 127.94, 127.39, 25.78, 25.03, 21.26. ³¹P{¹H} NMR (161.9 MHz, C₆D₆, 298 K): δ = −8.1. ¹¹B {¹H} NMR (128 MHz, C₆D₆, 298 K): δ = 6.67 (br). FT-IR ATR (neat solid, cm⁻¹): 1823 (ν(CC)). Anal. calcd for C₄₇H₄₁BNiP₂ (736.21): C, 76.57; H, 5.61. Found: C, 74.29; H, 5.76.

[η³-P,B,P-(PPh₂)₂BMes]Pt(CH₃)₂ (6)

In the glovebox, 1 (60 mg, 0.12 mmol) and Pt(Me)₂(COD) (40 mg, 0.12 mmol) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the orange solution was allowed to stir for 4 days at 25 °C. The solvent was removed in vacuo and the resulting yellow solid was recrystallized from saturated Et₂O at −35 °C to give yellow crystals (77 mg, 88%). N.B. Heating this reaction mixture results in decomposition to Pt(0) and undesired organic by-products. ¹H NMR (400 MHz, C₆D₆, 298 K): δ = 7.47 (m, 4H; PPh₂), 7.42 (m, 4H; PPh₂), 6.81 (m, 8H; PPh₂), 6.72 (s, 1H; Mes), 6.66 (s, 1H; Mes), 6.62 (t, ³J_H,H = 7.6 Hz, 4H; PPh₂), 2.81 (s, 3H; Mes), 2.78 (s, 3H; Mes), 2.17 (s with ¹⁹⁵Pt satellites, ³J_H,Pt = 80 Hz, 6H; Pt–CH₃), 2.06 (s, 3H; Mes). ¹³C{¹H} NMR (100 MHz, C₆D₆, 298 K): δ = 142.64, 140.08, 136.30 (t, J_C,P = 5.1 Hz), 133.60 (t, J_C,P = 4.8 Hz), 129.74, 129.62, 129.41, 128.82, 128.54 (t, J_C,P = 6.1 Hz), 128.24 (t, J_C,P = 6.0 Hz), 124.75 (t, J = 33 Hz), 25.50, 25.45, 21.21, 4.52 (t with ¹⁹⁵Pt satellites, J_C,Pt = 688 Hz, J_C,P = 27.8 Hz; Pt–CH₃). ³¹P{¹H} NMR (161.9 MHz, CD₂Cl₂, 298 K): δ = −21.6 (br t, ¹J_Pt,P = 853 Hz). ¹¹B{¹H} NMR (128 MHz, CD₂Cl₂, 298 K): δ = +7.9 (br). Anal. calcd for C₃₅H₃₇BP₂Pt (725.21): C, 57.94; H, 5.14. Found: C, 59.23; H, 5.08.

Pt[κ²-P,P-(PPh₂)₂B(Mes)(I)][κ²-P,P-(PPh₂)₂B(Mes)(CH₃)] (10)

In the glovebox, 1 (30 mg, 0.12 mmol, 2 equiv.) and [Pt(Me)₃(I)]₄ (11 mg, 0.03 mmol, 0.25 equiv.) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the colorless solution was allowed to stir for 4 days at 25 °C. The solvent was removed in vacuo and the resulting pale yellow solid was recrystallized from saturated Et₂O at −35 °C to give clear colorless crystals (14 mg, 38%). ¹H NMR (400 MHz, C₆D₆, 298 K): δ = 7.92 (br; 4H PPh₂), 7.77 (br, 4H; PPh₂), 7.05 (br, 12H; PPh₂), 6.92 (t, ³J_H,H = 7.6 Hz, 4H; PPh₂), 6.82 (t, ³J_H,H = 7.6 Hz, 4H; PPh₂), 6.77 (s, 2H; Mes), 6.75 (t, ³J_H,H = 7.6 Hz, 4H; PPh₂), 6.69 (s, 2H; Mes), 6.63 (t, ³J_H,H = 7.6 Hz, 4H; PPh₂), 6.56 (t, ³J_H,H = 7.6 Hz, 4H; PPh₂), 2.23 (s, 6H; Mes), 2.15 (s, 9H (6H + 3H); Mes), 2.08 (s, 3H; Mes), 1.45 (t, ³J_H,P = 19.4 Hz, 3H; B–CH)₃. ¹³C{¹H} NMR (100 MHz, THF-d₈, 298 K): δ = 142.08 (m), 140.85 (m), 137.07 (m), 136.44, 136.25 (m), 135.91 (m), 134.90 (m), 134.35, 133.26, 132.07, 130.90, 129.87, 129.68 (m), 129.30 (m), 128.85, 128.61 (m), 128.41, 128.25, 127.99, 127.25, 26.64, 26.26, 20.56, 20.55, 8.66 (br, B–CH₃). ³¹P{¹ H} NMR (161.9 MHz, C₆D₆, 298 K): δ = −35.65 (m). ¹¹B{¹H} NMR (128 MHz, C₆D₆, 298 K): δ = 4.94. Anal. calcd for C₆₇H₆₅B₂IP₄Pt (1337.29): C, 60.16; H, 4.90. Found: C, 58.05; H, 4.96.