[(1,2,5,6-η)-Cyclo­octa-1,5-diene](1-methyl-3-propylimidazol-2-yl­idene-κC)(tri­phenyl­phosphane-κP)iridium(I) tetra­fluorido­borate

Benedikt Kienle; Michael Gau; Daniel R Albert; Edward Rajaseelan

doi:10.1107/S2414314626008527

. 2026 Aug 25;11(Pt 8):x260852. doi: 10.1107/S2414314626008527

[(1,2,5,6-η)-Cycloocta-1,5-diene](1-methyl-3-propylimidazol-2-ylidene-κC)(triphenylphosphane-κP)iridium(I) tetrafluoridoborate

Benedikt Kienle ^a, Michael Gau ^b, Daniel R Albert ^c, Edward Rajaseelan ^c,^*

Editor: M Weil^d

PMCID: PMC13548383 PMID: 42707921

The complex cation in the title compound has a distorted square-planar conformation around the Ir^I atom, formed by a bidentate cycloocta-1,5-diene (COD) ligand, a phosphane ligand, and an N-heterocyclic carbene (NHC) ligand.

Keywords: crystal structure, N-heterocyclic carbene, COD ligand, iridium complex, disorder

Abstract

A new imidazole-based N-heterocyclic carbene iridium(I) cationic complex with a tetrafluoridoborate counter-anion, [Ir(C₈H₁₂)(C₇H₁₂N₂)(C₁₈H₁₅P)]BF₄, has been synthesized and structurally characterized. The complex cation has a distorted square-planar conformation around the Ir^I atom, formed by a bidentate cycloocta-1,5-diene (COD) ligand, a phosphane ligand, and an N-heterocyclic carbene (NHC) ligand. The complex crystallizes in the triclinic space group P1 with one cationic Ir-NHC complex and one disordered [BF₄]⁻ anion in the asymmetric unit. Bond lengths and bond angles are as expected for an Ir-NHC complex. Several non-classical C—H⋯F hydrogen-bonding interactions between the various ligands (triphenylphosphane, NHC, and COD) and the tetrafluoridoborate anion orient the metal cationic complex and the counter-anion in the crystal structure. graphic file with name x-11-x260852-scheme1-3D1.webp

Structure description

N-heterocyclic carbenes (NHCs) have emerged as excellent alternative ligands for phosphines in transition metal complexes in the study of homogeneous catalysis (Cazin, 2013 ▸; de Frémont et al., 2009 ▸; Díez-González et al., 2009 ▸; Rovis & Nolan, 2013 ▸; Ruff et al., 2016 ▸; Zuo et al., 2014 ▸). Their catalytic activity in the transfer hydrogenation of unsaturated double bonds, especially in ketones and imines, has also been studied and reported (Albrecht et al., 2002 ▸; Gnanamgari et al., 2007 ▸). The NHC ligands can be tuned sterically and electronically by having different substituents (wing tips) on the nitrogen atoms (Gusev, 2009 ▸). We continue to synthesize new imidazole- and triazole-based NHC complexes of rhodium and iridium, to study the catalytic effect of different substituents on the NHCs and have reported the syntheses, structures, and intra- and inter-molecular hydrogen-bonding interactions in several complexes with triphenylphosphane as an ancillary ligand (Nichol et al., 2009 ▸, 2011 ▸, 2012 ▸; Idrees et al., 2017 ▸; Rood et al., 2021 ▸; Newman et al., 2021 ▸; Castaldi et al., 2021 ▸; Maynard et al., 2023 ▸; Lerch et al., 2024a ▸,b ▸, 2025 ▸). Here we report the crystal structure of a new Ir^I NHC complex with a [BF₄]⁻ counter-anion, [Ir(C₈H₁₂)(C₇H₁₂N₂)(C₁₈H₁₅P)][BF₄] (2).

The molecular entities of (2) are illustrated in Fig. 1 ▸. No solvent molecules were found in the structure. The coordination sphere around the Ir^I cation, formed by the bidentate cycloocta-1,5-diene (COD), the NHC, and the triphenylphosphane ligands, results in a distorted square-planar conformation, characterized by a C1_NHC—Ir1—P1 bond angle of 91.96 (6)°. The C1 atom of the NHC ligand deviates from the expected sp² hybridization in that the N1—C1—N2 bond angle in the imidazole-based carbene is 104.6 (2)°. Other selected bond lengths in the structure are: Ir1— C1_(NHC) = 2.045 (2) Å and Ir1— P1 = 2.3190 (6) Å. Fig. 2 ▸ shows the packing diagram of the crystal structure with non-classical C—H⋯F interactions displayed as dashed orange lines. The close F⋯H contacts and other numerical data of these interactions are summarized in Table 1 ▸. The short anomalous C—H⋯F interactions are likely artefacts of the positional disorder associated with the [BF₄]⁻ anion. The cationic units pack with triphenyl phosphane ligands oriented towards each other on adjacent metal complexes. However, no substantial C—H⋯π interactions were found between the phenyl moieties.

Molecular entities in the crystal structure of the title compound (2). Displacement ellipsoids are drawn at the 50% probability level.

Packing diagram of the title compound (2) viewed along the a axis. Non-classical hydrogen-bonding interactions between the the cationic metal complex ligands and the tetrafluoridoborate anions are shown as dashed orange lines.

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3⋯F4ⁱ	0.95	2.38	3.100 (4)	133
C5—H5A⋯F1ⁱⁱ	0.99	2.46	3.265 (3)	138
C7—H7B⋯F1*ⁱⁱ	0.98	2.53	3.263 (13)	132
C10—H10⋯F2*ⁱⁱ	0.95	2.31	3.073 (16)	136
C19—H19⋯F3	0.95	2.47	3.413 (4)	171
C19—H19⋯F3*	0.95	2.53	3.272 (16)	135
C28—H28B⋯F4*ⁱⁱ	0.99	2.37	3.292 (18)	154

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Symmetry codes: (i) Inline graphic ; (ii) .

Synthesis and crystallization

The synthesis of [(1,2,5,6-η)-cycloocta-1,5-diene] (1-methyl-3-propylimidazol-2-ylidene)chloridoiridium (1) has been published previously (Kienle et al., 2026 ▸). All other compounds used in the syntheses, summarized in Fig. 3 ▸, were obtained from Sigma-Aldrich and used as received. NMR spectra were recorded at room temperature in CDCl₃ on a 400 MHz Varian spectrometer (operating at 100 MHz for ¹³C and 162 MHz for ³¹P) and referenced to the residual solvent peak (δ in p.p.m.).

Reaction scheme for the synthesis of the title compound (2)

[(1,2,5,6-η)-Cycloocta-1,5-diene] (1-methyl-3-propylimidazol-2-ylidene)(triphenylphosphine)iridium(I) tetrafluoridoborate (2): Triphenylphosphane (0.075 g, 0.287 mmol) and AgBF₄ (0.056 g, 0.287 mmol) were added to (1) (0.132 g, 0.287 mmol) in CH₂Cl₂ (15 ml). The solution was stirred in the dark for 1.5 h under a nitrogen atmosphere. The resulting mixture was filtered through Celite, and the solvent was removed under reduced pressure. The bright orange–red solid product (2) was dried under vacuum. Yield: 0.219 g (99.5%). Orange–red crystals suitable for data collection were obtained by slow diffusion of pentane into a CH₂Cl₂ solution. ¹H NMR: δ 7.49–7.21 (m, 15H, H_phenyl), 7.04 (d, 1H, N—C4H), 6.94 (d, 1H, N—C5H), 5.29 (s, 3H, N—CH₃), 4.45–4.29 (m, 4 H, CH of COD), 3.49 (t, 2H, N–CH₂ of propyl), 2.37 (m, 2 H, CH₂ of propyl), 2.28 (m, 2H, CH₂ of COD), 2.03–1.94 (m, 2H, CH₂ of COD), 1.64–1.58 (m, 2H, CH₂ of COD), 1.37–1.33 (m, 2H, CH₂ of COD), 0.88 (t, 3 H, CH₃ of propyl). ¹³C NMR: δ 173.06 (Ir—C), 133.62 (N—C4H), 133.52 (N—C5H), 131.28–128.92 (C_phenyl), 86.69, 86.58, 85.49, 85.37 (CH of COD), 51.91 (N—CH₃), 37.23 (N—CH₂ of propyl), 31.54, 31.04, 31.01, 30.85 (CH₂ of COD), 23.00 (CH₂ of propyl), 11.36 (CH₃ of propyl). ³¹P NMR: δ 18.38.

Refinement

Crystal data, data collection, and structure refinement details are summarized in Table 2 ▸. The F atoms of the [BF₄]⁻ anion are disordered over two sets of sites in a refined 0.893 (3):0.107 (3) ratio (minor component labelled with asterisks). For modelling the disorder, B—F bond lengths and F—B—F angles were restrained to reasonable values, and the anisotropic displacement parameters of the B and F atoms to be similar.

Table 2. Experimental details.

Crystal data
Chemical formula	[Ir(C₈H₁₂)(C₇H₁₂N₂)(C₁₈H₁₅P)]BF₄
M _r	773.64
Crystal system, space group	Triclinic, P
Temperature (K)	100
a, b, c (Å)	9.9795 (2), 10.2191 (2), 17.4844 (4)
α, β, γ (°)	98.173 (2), 98.654 (2), 116.906 (2)
V (Å³)	1526.60 (6)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	4.48
Crystal size (mm)	0.13 × 0.1 × 0.08

Data collection
Diffractometer	Rigaku XtaLAB Synergy-S
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2025 ▸)
T_min, T_max	0.719, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	38499, 7566, 6931
R _int	0.047
(sin θ/λ)_max (Å⁻¹)	0.667

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.023, 0.048, 1.07
No. of reflections	7566
No. of parameters	418
No. of restraints	116
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.89, −0.85

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Computer programs: CrysAlis PRO (Rigaku OD, 2025 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL (Sheldrick, 2015b ▸), OLEX2 (Dolomanov et al., 2009 ▸) and publCIF (Westrip, 2010 ▸).

Supplementary Material

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2414314626008527/wm4257sup1.cif

x-11-x260852-sup1.cif^{(1.1MB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S2414314626008527/wm4257Isup2.hkl

x-11-x260852-Isup2.hkl^{(600.9KB, hkl)}

CCDC reference: 2581838

Additional supporting information: crystallographic information; 3D view; checkCIF report

Acknowledgments

BK was supported by Lancaster Country Day School under the mentorship of Todd Trout.

full crystallographic data