Iridium complexes featuring a tridentate SiPSi ligand: from dimeric to monomeric 14, 16 or 18-electron species†‡

Cynthia A. Cuevas-Chávez ^ab, Laure Vendier ^b, Sylviane Sabo-Etienne *^b and Virginia Montiel-Palma *^ac
aCentro de Investigaciones Químicas, IICBA, Universidad Autónoma del Estado de Morelos, Avenida Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos C. P. 62209, Mexico
^bLCC-CNRS, Université de Toulouse, CNRS, UPS, 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France. E-mail: sylviane.sabo@lcc-toulouse.fr
^cDepartment of Chemistry, Mississippi State University, Box 9573, Mississippi State, Mississippi 39762, USA. E-mail: vmontiel@chemistry.msstate.edu

First published on 4th September 2019

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Introduction

Versatile ligands able to stabilize metal centres in specific coordination geometries, oxidation states and nuclearities are treasured resources for chemists seeking to achieve selective transformations including catalytic developments and new synthetic routes. Likewise, from a fundamental perspective, incorporating Si atoms as binding sites into phosphine or nitrogen based frameworks, has led to remarkable advances illustrating the rich chemistry and applicability of these species.^1–4 Recent fascinating examples include the tripodal tris(phosphinophenyl)silylide Rh and Ir complexes featuring two-centre, three-electron σ-half M–Si bonds;⁵ the catalytic deuteration of trialkylsilanes by C₆D₆ with Ir complexes bearing a hemilabile silyl-pyridine-amine ligand;⁶ the selective C–H functionalization promoted by an N-heterocyclic silylene-silyl Rh containing a chelate Si(II)–Si(IV) ligation;⁷ the fixation of N₂ by Fe and Co complexes with PSiP type ligands,⁸ as well as a stable η²-(H–Si)Fe dihydride complex;⁹ and the activation of H₂ and O₂ by Co(II) complexes among others.¹⁰ This remarkable reactivity has been linked to the nature of Si atoms which generates electron rich metal centres concomitantly labilizing trans substituents. Indeed, the strong trans influence¹¹ of the silyl donor in a Rh(P₂Si) complex is deemed responsible for alkene hydrogenation through competitive bi- and unimolecular processes, energetically similar.¹²

Throughout the literature, the number of metal derivatives with polydentate P or N ligands featuring two Si atoms is limited as is the study of their reactivity.^3,13–15 This, despite numerous authors demonstrating that the presence of two Si atoms induces specific properties^16–19 even enhancing catalytic activity as in disilametallacycles.^20,21 In the frame of our programme aimed at developing the coordination chemistry of phosphinosilane compounds, we have recently reported our results on the coordination ability of SiPSi dibenzylsilylphosphine compounds featuring methyl or isopropyl substituents on Si towards group 9 metal centres.^22,23 We now focus on reactivity studies on the dinuclear iridium complex [μ-Cl-Ir(SiMe₂CH₂-o-C₆H₄)₂PPh]₂ (1) featuring a SiPSi ligand on each metal centre. We show that the dimeric structure gives rise to mononuclear 14-, 16- or 18-electron complexes upon reactivity with two electron donors whereas the dinuclear core is retained upon reaction with hydride sources.

Results and discussion

Access to a 14-electron species from the dinuclear complex [μ-Cl-Ir(SiMe₂CH₂-o-C₆H₄)₂PPh]₂ (1)

The dinuclear complex 1 had been previously synthesized and characterized on the basis of solid state NMR spectroscopic data and by comparison to its rhodium analogue whose structure was determined by X-ray diffraction.²² In brief, the yellow crystalline solid was characterized by a broad signal at δ 11.8 in the ³¹P CP MAS NMR spectrum, two broad signals at δ 22.7 and 13.8 in the ²⁹Si CP MAS NMR spectrum as well as four methyl and two methylene signals in the ¹³C CP MAS NMR spectrum, in line with two chemically inequivalent Si groups (one apical and one equatorial). The complex was found to be slightly soluble in benzene, toluene, THF and dichloromethane. We have now been able to obtain crystals suitable for an X-ray determination from a concentrated C₆D₆ solution confirming the proposed structure in the solid state (Fig. 1). As for the rhodium analogue,²² the geometry around each iridium centre can be described as a distorted square pyramid (χ Kono value²⁴ = 0.3) with one apical Si trans to a vacant site. The two Ir–Si distances (2.2980(8) Å and 2.3031(8) Å) are very similar and in the mid-range of distances reported for multidentate ligands incorporating Si atoms (2.219–2.454 Å).^1,16,25 In contrast, the Ir–P distance of 2.2056(8) Å is somewhat shorter than those reported for Ir(III) complexes featuring monosilylphosphines SiP_n (n = 1, 2, 3) commonly in the range 2.264–2.396 (Å). We attribute this behaviour to the presence of two Si atoms, excellent σ-donors, which boost the electron density at the metal by comparison to complexes bearing only one Si moiety. The high trans influence of Si is manifested in the difference of the Ir–Cl bond distances (2.5534(7) trans to Si and 2.4120(7) Å trans to P).

Dissolution of 1 in C₆D₆ led, according to NMR data, to the formation of the monomeric species [IrCl(SiMe₂CH₂-o-C₆H₄)₂PPh] (1′) featuring an unsaturated 14-electron Ir(III) centre (Scheme 1). Its HMQC ¹H–²⁹Si NMR spectrum shows only one ²⁹Si signal at δ 15.45 correlating with the only two ¹H methyl signals (ESI Fig. S1†). We have recently reported the synthesis and characterization, including X-ray diffraction, of 14-electron rhodium and iridium complexes [M(SiPSi)Cl] (M = Rh, Ir) featuring analogous benzylphosphinosilane ligands with isopropyl substituents at silicon.²³ Bulkier isopropyl substituents on Si allowed the isolation of highly unsaturated species displaying a seesaw geometry devoid of agostic interactions with each silicon atom trans to a vacant site. Surprisingly, these complexes were found to be air stable and isolable pointing to the stabilization presumably conferred by the presence of two strong σ-donors Si. Several authors have postulated a dimer/monomer equilibrium taking place in chloro bisphosphine Rh(I) species of the type [Rh(diphos)(μ-Cl)]₂,^26–28 and in the more closely related Ir(III) systems [Ir(POCOP)H(μ-Cl]₂.^29,30 In these examples, a rapid dimer/monomer equilibrium resulting in identical NMR chemical shifts was proposed and even suggested to strongly determine the reactivity.²⁶

The presence of two Si atoms in the ligand is herein shown to play a fundamental role in the stabilization of the unsaturated monomeric species in solution as does the ability of the ligand to adopt facial and meridional coordination modes as previously reported.^15,22

Since 1 dissociates in solution into the 14-electron species 1′, we first examined its reactivity towards 2-electron donors such as P- and N-donors, and CO. As we will see, depending on sterics and electronics, the corresponding 16- or 18-electron species [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(L)_x] (x = 1, 2) were obtained (Scheme 1).

[IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(P(OEt)₃)₂] (2)

Addition of 4 equiv. of P(OEt)₃ to a suspension of complex 1 in toluene at 298 K leads to immediate formation of a colourless solution. After workup, a white solid is isolated in an excellent yield (88%) and fully characterized as the 18-electron complex [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(P(OEt)₃)₂] (2). The X-ray structure shows a distorted octahedral geometry around the metal centre with the SiPSi ligand in facial geometry disposing one Si atom trans to Cl and a second Si trans to P(OEt)₃ (Fig. 2). The differences amongst the three Ir–P, and the two Ir–Si distances correlate with the respective σ-donor/π-acceptor properties of the trans ligands (see ESI†). In solution, multinuclear NMR data including selective decoupling experiments are in agreement with preservation of the solid state structure. Three ³¹P{¹H} NMR signals are observed, two of them displaying identical large J_PP coupling constants of 493 Hz indicating one P(OEt)₃trans to SiPSi. It is worth noting that a ²⁹Si {¹H} DEPT experiment only showed the Si signal trans to Cl at δ −8.9 as a doublet of triplets. It was necessary to acquire a ¹H–²⁹Si HMQC spectrum to identify the second Si signal at δ 3.5, which appeared as a doublet with a large J_SiP value of 196 Hz in agreement with trans disposition (Fig. 3).

[IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(PPh₃)] (3)

In contrast, when reacting a suspension of 1 with excess PPh₃, immediate dissolution occurred with a change of colour from yellow to orange, and the unsaturated 16-electron complex [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(PPh₃)] (3) was isolated in good yield (67%) and fully characterized. The X-ray structure displays a square-based pyramidal geometry with one Si in the apical position (Fig. 4). The calculated Konno value²⁴ of 0.17 is closer to the ideal geometry than the starting dimer 1 (0.3).

In solution, the ¹H–²⁹Si HMQC spectrum shows at room temperature one broad ²⁹Si signal at δ 10 correlating with the two ¹H methyl signals at δ −0.03 and δ 0.44. However, at 193 K decoalescence is observed with two ²⁹Si signals at δ 22.7 and δ −0.3, each one correlating with two methyl signals at δ −0.29 and δ 0.73, and δ 0.12 and δ 0.44, respectively. We propose that fast exchange is established at room temperature with the chloride jumping between two positions, trans to each silicon nuclei. Such a process has been invoked in related pentacoordinated Ir(III) complexes featuring a PSiP ligand.³¹

[IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(PCy₃)] (4)

Employment of the more basic and sterically demanding phosphine,³² PCy₃, leads to the observation of an equilibrium between 1′ and the pentacoordinate complex [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(PCy₃)] (4) as evidenced by multinuclear NMR spectroscopic data. We were able to isolate crystals suitable for X-ray diffraction and the structure confirmed a geometry analogous to that found for complex 3 with PCy₃ in place of PPh₃ (Fig. 4). The calculated Konno value²⁴ of 0.14 is also closer to the one determined for complex 3 (0.17).

Variable temperature NMR experiments in toluene-d₈ solution demonstrate the reversible dissociation of 4 into 1′ and free PCy₃ (Fig. 5). At 358 K, only complex 1′ and free PCy₃ were detected whereas at 193 K, only complex 4 was present. At intermediate temperatures such as 298 K, an AX spin system in the ³¹P{¹H} NMR spectrum was observed with doublet signals at δ 16.91 and δ 0.36 corresponding to complex 4 together with the two singlet resonances for 1′ and PCy₃. Additionally, as in the case of 3, a similar dynamic phenomenon was observed rendering the two silyl groups equivalent at room temperature.

Thus, a combination of the sigma donor/π acceptor abilities of the P-ligands, P(OEt)₃, PPh₃ or PCy₃ and crucially their bulkiness strongly determine their coordination to unsaturated 1′. The smaller cone angle phosphite is prone to coordinate two units, in turn making the Ir centre achieves an 18 electron configuration. With PPh₃, only one ligand is coordinated to the resulting 16-electron iridium complex whereas an equilibrium is established between 1′ and the complex bearing the bulkiest PCy₃. The equilibrium is strongly shifted at the lowest studied temperature towards the formation of complex 4.

[IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(CD₃CN)₂] (5a)

Upon dissolution of complex 1 in CD₃CN, a pale yellow solution was obtained from which colourless crystals were grown at 235 K. The X-ray structure indicates the formation of the saturated complex [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(CD₃CN)₂] (5a) with one CD₃CN trans to Si and a second CD₃CN trans to P, adopting a geometry very similar to that of complex 2 (Fig. 2). Here again, one corroborates the high trans influence of Si evidenced in the significant difference of the two Ir–N distances, (2.215(3) versus 2.067(3) Å) the longer one trans to the Si ligand.

2D multinuclear NMR experiments at variable temperatures, as well as EXSY spectroscopy allowed us to propose the structures depicted in Scheme 2. In addition to 5a, isomerization occurred to a species in which each CD₃CN arranges trans to Si (5b). The 16-electron species [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(CD₃CN)] (5c) incorporating only one CD₃CN in its coordination sphere could also be detected by this technique. The presence of adventitious water resulted in the formation of [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(H₂O)₂] (5d) with aquo ligands replacing acetonitrile. Its formation was independently ascertained by addition of H₂O into the NMR tube leading to the increase of the most shielded signal in the ³¹P{¹H} NMR spectrum attributed to 5d. We found that at 358 K, all the species are in fast exchange as only one broad signal was observed in the ³¹P{¹H} NMR spectrum.

In order to gauge the impact of the identity of N-donors in the coordination number, we replaced CD₃CN by pyridine-d₅. In that case, we detected complex 6b as the major isomer with two pyridine ligands in cis disposition each trans to a Si atom (Scheme 1). Isomer 6a (analogous to 5a, Scheme 2) was only detected in a ratio 1:10 with respect to 6b, significantly different from the ratio obtained for 5a:5b in the same conditions (1:2.5). We thus propose that the isomer ratio depends on the basicity of the N-donor ligand.

[IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(CO)₂] (7b)

Exposure of a CD₃CN solution of 1 to 3 bar CO led to the isolation of crystals characterized as the dicarbonyl complex [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(CO)₂] (7b) (Scheme 1). In contrast to complexes 2 and 5a, the X-ray diffraction structure indicates that each CO disposes trans to a Si atom (Fig. 2). The solid-state structure is retained in CD₃CN solution, as shown by the ²⁹Si singlet observed in the ¹H–²⁹Si HMQC NMR spectrum at δ 4.5 as well as the singlet at δ 170.2 in the ¹³C{¹H} NMR spectrum for the two equivalent carbonyl ligands. However, isomerisation of 7b occurs in toluene-d₈ solution to form 7a with one CO trans to Si and the other one trans to P. This is evidenced by NMR studies which show, at room temperature, the two isomers in fast exchange as corroborated by the broad ³¹P{¹H} NMR signal at δ −20 which splits at 193 K into two sharp signals at δ −18.13 and δ −23.03 in a ratio 2:1 for 7b:7a. ¹³C{¹H} and ¹³C{¹H}{³¹P} NMR spectra confirmed the trans disposition of CO and P in 7a with the signal at δ 174.1 displaying a large J_CP value of 107 Hz.

In addition, exposure of a toluene-d₈ solution of 1 to only 1 bar CO allowed the detection by NMR spectroscopy of a new species that we tentatively formulate as the monocarbonyl complex [IrCl{(SiMe₂CH₂-o-C₆H₄)₂PPh}(CO)] (7c), characterized by a sharp singlet at δ −16.26 in the ³¹P{¹H} NMR spectrum, downfield to the dicarbonyl species 7a/7b. Complex 7c was only detected at short reaction times as upon prolonged CO exposure, 7c disappeared to the benefit of 7a/7b. All our attempts to isolate 7c failed.

Reactivity of complexes 1 and 3 with hydride sources

We first examined the reactivity of 1 under 1 to 3 bar H₂ gas and observed by ¹H NMR spectroscopy the initial formation of several hydride species. Fast decomposition took place preventing further characterization and/or isolation. On the other hand, upon reaction of 1 with LiBHEt₃, HBpin or Et₃SiH, several species were formed but a common hydride complex was predominantly generated. The reaction of 1 with Et₃SiH under toluene refluxing conditions led to the isolation in 80% yield of the dinuclear complex [Ir₂{P(o-C₆H₄CH₂SiMe₂)₂Ph}₂(μ-H)(μ-Cl)], (8). Yellow crystals were obtained by slow evaporation from a C₆D₆ solution, and the X-ray structure is depicted in Fig. 6. The unit cell contains two independent molecules with four molecules of C₆D₆ though only one is reported here for clarity. Apart from the replacement of one Cl by H (the hydride was located, Ir–H 1.76 (3) Å), the major difference by comparison to complex 1 is the disposition of the P atoms which are now cis to Cl and trans to H whereas in 1, each P is trans to a chloride.

H/Cl metathesis can be inferred from the detection of Et₃SiCl when monitoring by NMR the in situ reaction of 1 with Et₃SiH in toluene-d₈ solution. Solution NMR data for 8 are in agreement with the retention of the dinuclear structure in solution showing a ¹H NMR integration ratio between the hydride, the methyl and methylene signals of 1:24:8. The hydride resonates at δ −3.63 as a triplet with a large J_HP coupling constant of 50.3 Hz. The ¹H–²⁹Si HMQC spectrum shows at room temperature two ²⁹Si signals at δ 3.51 and δ 11.80 each correlating with their respective methyl and methylene signals. These findings are in accordance with chemically inequivalent Si atoms in solution, one arranging trans to chloride while the other trans to a vacant site.

Finally, we also tested the reactivity of the triphenyl complex 3 with LiBHEt₃ (Scheme 3). The reaction was conducted at 333 K in C₆D₆ for 4 h and led to the formation of one major product 9 that we were not able to isolate. However, multinuclear and 2D NMR data allowed us to propose the formulation [IrH{η²-H-SiMe₂CH(o-C₆H₄)P(o-C₆H₄CH₂SiMe₂)Ph}(PPh₃)] depicted in Scheme 3. The complex is characterized by two doublets in the ³¹P{¹H} NMR spectrum with a small coupling constant of 10.2 Hz indicative of two P in a cis arrangement. Two hydride signals are seen in the ¹H NMR spectrum: a doublet of doublets at δ −10.36 with a large J_HP coupling constant of 116 Hz and a broad signal at δ −5.92 with ²⁹Si satellites from which a J_SiH value of 78 Hz, indicative of a rather strong agostic interaction, was measured. The ¹H–²⁹Si HMQC data confirmed our assignment with two ²⁹Si signals at δ 2.20 and δ −44.42, the latter one for the carbometallated agostic group. It is worth noting that precedents exist at ruthenium centres for the activation of benzyl spacers in related phosphinosilanes. We previously isolated Ru{η²-H-SiMe₂CH(o-C₆H₄)PPh₂}₂ displaying two carbometallated and two agostic Si–H groups as a result of the activation of the starting PSi ligand Ph₂P(o-C₆H₄)CH₂SiMe₂H.³³ Here, we propose that H/Cl metathesis is first occurring producing the corresponding disilyl hydrido iridium(III) complex followed by Si–H interaction by the metal center which could favour the activation of the acidic methylene to produce the final compound.

Conclusion

The dimeric complex [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(μ-Cl)]₂ featuring tricoordinate phosphinodisilyl ligands dissociates in benzene solution to yield the 14 electron monomeric species [Ir(SiPSi)Cl] which readily reacts with two electron donors. 16- and 18-electron configurations are obtained depending mainly on sterics in the case of P-derivatives. For the diacetonitrile and the dicarbonyl complexes, different dispositions of the L ligands were characterized by X-ray diffraction (fac-mer and mer-mer, respectively) and isomerisation processes were evidenced by multinuclear NMR studies. Even if iridium is prone to perform oxidative additions, we also showed that, as in a related ruthenium complex, Si–H agostic bonding can favour C–H activation of an adjacent acidic methylene group leading to a tetradentate ligation. The next step will be to explore the catalytic properties of this new class of complexes featuring a SiPSi ligand as they have been shown to be rather robust and to allow access to highly unsaturated species.

Experimental section

General considerations

All experiments were performed under argon atmosphere using standard Schlenk methods or in MBraun glove boxes. THF, Et₂O, toluene, CH₂Cl₂, and pentane were purified over a MBraun column system and degassed prior to use. Benzene-d₆, toluene-d₈, CD₃CN were degassed via three freeze–pump–thaw cycles and stored over molecular sieves in an ampoule fitted with a J. Young's valve. [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(μ-Cl)]₂ (1) was synthesized according to our previous report.²² The other reagents were purchased from Sigma Aldrich and used as received. Nuclear magnetic resonance spectra in solution were recorded on Bruker Avance 400, 500, 600. All chemical shifts for ¹H, ²⁹Si and ¹³C are relative to TMS. ³¹P chemical shifts were referenced to an external 85% H₃PO₄ sample. Infrared spectra were recorded on a Bruker Alpha FT-IR spectrophotometers in ATR modes. Microanalyses were performed at the Laboratoire de Chimie de Coordination on a PerkinElmer 2400 Series II Analyzer.

[Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(P(OEt)₃)₂], (2)

To a Schlenk flask containing compound 1 (50.2 mg, 0.039 mmol) in 5 mL of toluene, P(OEt)₃ (26.7 μL, 0.156 mmol) was added. After the reaction mixture was left stirring overnight, the volatiles were removed by reduced pressure in a warm oil bath leading to a white solid, which was dissolved in 0.5 mL of THF and stored at 235 K. Colourless crystals were obtained by slow evaporation of the solvent, filtered, washed with cold pentane and dried under vacuum. Yield 88%. Anal. calcd for C₃₆H₅₉ClIrO₆P₃Si₂: C, 44.83; H, 6.17. Found: C, 44.92; H, 6.21. ¹H NMR (400 MHz, C₆D₆, 298 K): δ 8.9 (br s, 1H, CH_arom), 7.4 (br s, 1H, CH_arom), 7.14–7.05 (m, 6H, CH_arom), 6.95 (ψt, ³J_H–P = 8.8 Hz, 2H, CH_arom), 6.79 (m, 2H, CH_arom), 6.68 (ψt, ³J_H–P = 8.8 Hz, 1H, CH_arom), 4.21 (m, ²J_H–H = 10 Hz, ³J_H–H = 7 Hz, 3H, H_b), 3.99 (m, 6H: 3H_b′ and 3H_c′), 3.75 (m, ²J_H–H = 10 Hz, ³J_H–H = 7 Hz, 3H, H_c), 3.27 (br d, ²J_Ha′–Ha = 12.5 Hz, 1H, H_a′), 2.56 (d, ²J_Hd′–Hd = 12.9 Hz, 1H, H_d′), 2.42 (m, ²J_Ha–Ha′ = 12.6 Hz, ⁴J_Ha–Pc = 9.0 Hz, ⁴J_Ha–Pa = 7.0 Hz, 1H, H_a), 2.48–2.31 (br s, 1H, H_d), 1.14 (t, ³J_H–H = 7.0 Hz, 9H, P_bOCH₂CH₃), 1.01 (t, ³J_H–H = 7.0 Hz, 9H, P_cOCH₂CH₃), 1.06–1.00 (br s, 3H, Si_dMe₂), 0.64 (s, 3H, Si_aMe₂), 0.46 (s, 3H, Si_aMe₂), 0.43 (d, ⁴J_H–Pc = 3.6 Hz, 3H, Si_dMe₂). ³¹P{¹H} NMR (161.9 MHz, C₆D₆, 298 K): δ 87.3 (t, ²J_P–P = 34.1 Hz, P_c), 83.1 (br dd, ²J_P–P = 494 Hz, ²J_P–P = 32 Hz, P_b), −18.5 (br d, ²J_P–P = 492 Hz, P_a). ¹³C{¹H} NMR (100.6 MHz, C₆D₆, 298 K): δ 151.87 (br s, C_arom), 148.78 (d, J_C–P = 11.2 Hz, C_arom), 132.1 (s, C_arom), 130.56 (dd, J_C–P = 22.1 Hz, J_C–P = 7.0 Hz, C_arom), 130.25 (dd, J_C–P = 56.3 Hz, J_C–P = 2.0 Hz, C_arom), 123.69 (dd, J_C–P = 21.2 Hz, J_C–P = 8.1 Hz, C_arom), 62.90 (d, J_C–P = 10.1 Hz, P_bOCH₂CH₃), 61.39 (d, J_C–P = 10.1 Hz, P_cOCH₂CH₃), 32.05 (dd, J_C–P = 16.1 Hz, J_C–P = 4.0 Hz, Si_aCH₂), 31.88 (d, J_C–P = 15.4 Hz, Si_dCH₂), 16.10 (d, J_C–P = 6.0 Hz, P_bOCH₂CH₃), 16.04 (d, J_C–P = 6.0 Hz, P_cOCH₂CH₃), 7.72 (s, SiMe₂), 7.16 (dd, J_C–P = 5.0 Hz, J_C–P = 2.0 Hz, SiMe₂). ¹H–²⁹Si HMQC NMR (C₆D₆, 298 K): δ 3.52 (d, ²J_Sia–Pc = 195.5 Hz, Si_a), −8.91 (Si_d). See Fig. S1–5.†

[Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(PPh₃)], (3)

To a Schlenk flask containing compound 1 (57.1 mg, 0.045 mmol) in 5 mL of THF, PPh₃ (23.8 mg, 0.09 mmol) was added. After the reaction mixture was left stirring for 4 h, the volatiles were removed by reduced pressure leading to an orange solid which was washed with cold pentane and dried under vacuum. Yield 67%. Anal. calcd for C₄₂H₄₄ClIrP₂Si₂: C, 56.39; H, 4.96. Found: C, 56.45; H, 5.30. ¹H NMR (400 MHz, C₆D₆, 298 K): δ 8.3 (br s, 1H, CH_arom), 7.91 (m, 6H, CH_arom), 7.29 (ddd, 2H, J = 10.3 Hz, J = 7.7 Hz, J = 1.3 Hz, CH_arom), 7.07 (m, 15H, CH_arom), 6.98 (m, 2H, CH_arom), 6.89 (tt, 2H, J = 7.6 Hz, J = 1.6 Hz, CH_arom), 2.34 (dd, 2H, ²J_H–H = 13.1 Hz, ⁴J_H–P = 3.0 Hz, SiCH₂), 2.12 (dd, 2H, ²J_H–H = 13.7 Hz, ⁴J_H–P = 3.3 Hz, SiCH₂), 0.44 (s, 6H, SiMe₂), −0.03 (s, 6H, SiMe₂). ³¹P{¹H} NMR (161.9 MHz, C₆D₆, 298 K): δ 21.63 (d, ²J_P–P = 326 Hz), 12.34 (d, ²J_P–P = 326 Hz). ¹³C{¹H} NMR (100.6 MHz, C₆D₆, 298 K): δ 147.11 (d, J_C–P = 12.7 Hz, C_arom), 137.54 (s, C_arom), 135.95 (d, J_C–P = 10.1 Hz, C_arom), 134.58 (d, J_C–P = 47.6 Hz, C_arom), 132.91 (s, C_arom), 130.85 (d, J_C–P = 2.1 Hz, C_arom), 130.61 (d, J_C–P = 2.4 Hz, C_arom), 130.32 (d, J_C–P = 8.1 Hz, C_arom), 129.01 (dd, J_C–P = 53.3 Hz, J_C–P = 1.0 Hz, C_arom), 128.6 (d, J_C–P = 10.0 Hz, C_arom), 128.15 (d, J_C–P = 8.1 Hz, C_arom), 126.28 (d, J_C–P = 58.2 Hz, C_arom), 124.45 (d, J_C–P = 8.4 Hz, C_arom), 33.05 (d, J_C–P = 17.6 Hz, SiCH₂), 8.10 (d, J_C–P = 4.0 Hz, ¹J_C–Si = 44.3 Hz, SiMe₂), 6.83 (s, SiMe₂). ¹H–²⁹Si HMQC NMR (C₆D₆, 298 K): δ 10.12. See Fig. S6–10.†

Formation of an equilibrium mixture containing [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)], (1′) and [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(PCy₃)], (4)

To a Schlenk flask containing compound 1 (32.5 mg, 0.025 mmol) in 5 mL of THF, PCy₃ (14.0 mg, 0.050 mmol) was added. After the reaction mixture was left stirring for 4 h, the volatiles were removed by reduced pressure leading to a yellow solid. Yellow crystals were obtained by dissolving the solid in CH₂Cl₂ layered with pentane at 235 K. After washing with cold pentane, the crystals were dried under vacuum to give compound 4. Yield 62%. When analysing a sample of the crystals in C₆D₆ or tol-d₈ solution, a mixture of 4, 1′ and PCy₃ was detected. NMR refers to compound 4, unless otherwise indicated. ¹H NMR (400 MHz, C₆D₆, 298 K): δ 8.3 (br s, 1H, CH_arom), 7.8 (dd, 1H, J = 12.0 Hz, J = 4.0 Hz, CH_arom1′), 7.30–6.85 (overlap of aromatic protons of both compounds 4 and 1′), 6.75 (t, 1H, J = 7.6 Hz, CH_arom), 3.15 (br s, 2H, coordinated PCy₃), 2.42 (dd, 2H, ²J_H–H = 13.3 Hz, ⁴J_H–P = 2.9 Hz, SiCH₂), 2.17 (dd, 2H, ²J_H–H = 13.2 Hz, ⁴J_H–P = 4.2 Hz, SiCH₂), 0.99–2.06 (overlap of protons of free and coordinated PCy₃), 0.55 (s, 6H, SiMe₂), 0.52 (s, 6H, SiMe₂). ³¹P{¹H} NMR (161.9 MHz, tol-d₈, 298 K): δ 16.91 (d, ²J_P–P = 296 Hz), 0.36 (d, ²J_P–P = 296 Hz). ¹³C{¹H} NMR (100.6 MHz, C₆D₆, 298 K): δ 148.17 (d, J_C–P = 12.0 Hz, C_arom), 147.64 (d, J_C–P = 12.9 Hz, C_arom), 136.97 (d, J_C–P = 9.6 Hz, C_arom), 135.10 (d, J_C–P = 10.3 Hz, C_arom), 132.79 (d, J_C–P = 4.4 Hz, C_arom), 132.19 (d, J_C–P = 7.0 Hz, C_arom), 131.23 (d, J_C–P = 8.9 Hz, C_arom), 130.94 (dd, J_C–P = 34.2 Hz, J_C–P = 2.0 Hz, C_arom), 130.57 (d, J_C–P = 2.0 Hz, C_arom), 130.43 (d, J_C–P = 8.1 Hz, C_arom), 130.23 (d, J_C–P = 2.5 Hz, C_arom), 129.92 (d, J_C–P = 50.8 Hz, C_arom), 128.63 (d, J_C–P = 10.5 Hz, C_arom), 125.54 (d, J_C–P = 57.2 Hz, C_arom), 124.57 (d, J_C–P = 8.4 Hz, C_arom), 38.57 (d, J_C–P = 20.4 Hz, SiCH₂), 32.54 (s, Cy₃), 32.31 (d, J_C–P = 18.1 Hz, Cy₃), 31.70 (d, J_C–P = 12.5 Hz, Cy₃), 28.06 (d, J_C–P = 9.3 Hz, Cy₃), 27.86 (d, J_C–P = 10.1 Hz, Cy₃), 27.00 (s, Cy₃), 26.57 (s, Cy₃), 7.77 (s, SiMe₂), 7.71 (s, SiMe₂). ¹H–²⁹Si HMQC NMR (C₆D₆, 298 K): δ 0.40. See Fig. S11–16.†

Formation of an equilibrium mixture containing [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(CD₃CN)₂], (5a,b) [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(CD₃CN)], (5c) and [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(OH₂)₂], (5d)

Compound 1 (10.0 mg, 0.008 mmol) was dissolved in 0.6 mL of CD₃CN in a NMR tube equipped with J. Young valve. When analysing this sample by NMR, a mixture of 5a–d was detected. ¹H NMR (500 MHz, CD₃CN, 298 K): δ 7.77–6.40 (aromatic protons overlap in this region), δ 2.30–2.0 (methylene protons overlap in this region), δ 0.4 to −0.2 (methyl protons overlap in this region). ³¹P{¹H} NMR (161.9 MHz, CD₃CN, 298 K): δ −8.55 (s, 5a or 5b), −9.95 (s, 5c), −12.15 (s, 5b or 5a), −13.20 (s, 5d). See Fig. S17–21.†

NMR characterization of [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(pyr-d₅)₂], (6b)

Compound 1 (10.0 mg, 0.008 mmol) was dissolved in 0.6 mL of pyridine-d₅ in a NMR tube equipped with a J. Young valve. The sample was analysed by multinuclear NMR. ¹H NMR (400 MHz, pyr-d₅, 298 K): δ 7.42 (tt, 4H, J = 7.3 Hz, J = 1.6 Hz, CH_arom), 7.34 (dd, 2H, J = 7.6 Hz, J = 4.53 Hz, CH_arom), 7.25 (one aromatic proton overlaped with the deuterated solvent), 7.09 (t, 4H, J = 7.5 Hz, J = 7.5 Hz, CH_arom), 7.01 (m, 2H, CH_arom), 2.94 (d, 2H, ²J_H–H = 12.8 Hz, SiCH₂), 2.55 (d, 2H, ²J_H–H = 12.8 Hz, SiCH₂), 0.35 (s, 6H, SiMe₂), 0.31 (s, 6H, SiMe₂). ³¹P{¹H} NMR (161.9 MHz, pyr-d₅, 298 K): δ −13.91 (s). ¹³C{¹H} NMR (100.6 MHz, pyr-d₅, 298 K): δ 133.01 (d, J_C–P = 5.9 Hz, C_arom), 131.77 (d, J_C–P = 8.4 Hz, C_arom), 131.33 (d, J_C–P = 2.3 Hz, C_arom), 130.63 (d, J_C–P = 52.3 Hz, C_arom), 130.43 (s, C_arom), 128.15 (d, J_C–P = 10.0 Hz, C_arom), 126.93 (d, J_C–P = 61.5 Hz, C_arom), 124.59 (d, J_C–P = 9.0 Hz, C_arom), 30.20 (d, J_C–P = 11.0 Hz, SiCH₂), 4.99 (s, SiMe₂), 3.87 (s, ¹J_C–Si = 40.2 Hz, SiMe₂). ¹H–²⁹Si HMQC NMR (pyr-d₅, 298 K): δ −5.99. See Fig. S22–24.†

[Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(CO)₂], (7b)

A solution of 1 (28.2 mg, 0.022 mmol) in 0.6 mL of acetonitrile contained in a Fisher-Porter tube was frozen by placing it in a liquid-N₂ bath to remove the argon atmosphere under vacuum. After placing the reaction mixture at 258 K, it was pressurized with 3 atm of dynamic CO for 45 min. Subsequently, colourless crystals were formed. After replacing the CO atmosphere by argon, the crystals were separated from the solution and dried under vacuum. Yield 64%. Anal. calcd for C₂₆H₂₉ClIrO₂PSi₂: C, 45.37; H, 4.25. Found: C, 45.52; H, 4.61. ¹H NMR (400 MHz, CD₃CN, 298 K): δ 7.59 (m, 3H, CH_arom), 7.47 (m, 2H, CH_arom), 7.29 (m, 4H, CH_arom), 7.16 (m, 2H, CH_arom), 6.66 (dd, 2H, J = 12.9 Hz, J = 7.8 Hz, CH_arom), 2.44 (dd, 2H, ²J_H–H = 13.1 Hz, ⁴J_H–P = 2.7 Hz, SiCH₂), 2.31 (dd, 2H, ²J_H–H = 13.0 Hz, ⁴J_H–P = 2.3 Hz, SiCH₂), 0.35 (s, 6H, SiMe₂), 0.15 (s, 6H, SiMe₂). ³¹P{¹H} NMR (161.9 MHz, CD₃CN, 298 K): δ −17.21 (s). ¹³C{¹H} NMR (100.6 MHz, CD₃CN, 298 K): δ 170.2 (s, CO), 148.51 (d, J_C–P = 10.8 Hz, C_arom), 134.63 (d, J_C–P = 10.4 Hz, C_arom), 133.27 (d, J_C–P = 2.5 Hz, C_arom), 133.16 (d, J_C–P = 2.8 Hz, C_arom), 132.5 (d, J_C–P = 8.1 Hz, C_arom), 132.14 (d, J_C–P = 8.1 Hz, C_arom), 130.33 (d, J_C–P = 11.3 Hz, C_arom), 125.90 (d, J_C–P = 10.5 Hz, C_arom), 30.62 (d, J_C–P = 13.1 Hz, SiCH₂), 4.59 (s, SiMe₂), 2.13 (s, SiMe₂). ¹H–²⁹Si HMQC NMR (CD₃CN, 298 K): δ 4.62. IR: 2075 cm⁻¹ (ν_CO), 2035 cm⁻¹ (ν_CO). See Fig. S25–28.†

Isomerization of 7b to 7a

An isomerization process was detected when dissolving 7b (12.0 mg, 0.017 mmol) in 0.6 mL of tol-d₈ in a NMR tube equipped with J. Young valve producing 7a in a relative proportion of 2:1, respectively. 7b: ¹H NMR (500 MHz, tol-d₈, 193 K): δ 8.25 (ψt, 2H, CH_arom), 7.4–6.5 (overlap of aromatic protons of both isomers 7a,b and of the deuterated solvent), 2.26 (m, 2H, SiCH₂), 2.09 (the rest of SiCH₂ protons overlap with the deuterared solvent), 1.16 (s, 3H, SiMe₂), 0.50 (s, 3H, SiMe₂), 0.07 (s, 3H, SiMe₂), −0.01 (s, 3H, SiMe₂). ³¹P{¹H} NMR (202.5 MHz, tol-d₈, 193 K): δ −18.13 (s). ¹³C{¹H} NMR (100.6 MHz, tol-d₈, 193 K): δ 169.33 (s, CO), 148.30 (d, J_C–P = 10.0 Hz, C_arom), 130.0–135.0 (overlap of aromatic carbons of both isomers 7a,b), 30.87 (d, J_C–P = 14.0 Hz, SiCH₂), 4.83 (s, SiMe₂), 2.21 (s, SiMe₂). ²⁹Si{¹H} DEPT NMR (119.2 MHz, tol-d₈, 193 K): δ 1.58 (d, ²J_Si–P = 9 Hz), 13.77 (d, ²J_Si–P = 8 Hz). 7a: ¹H NMR (500 MHz, tol-d₈, 193 K): δ 9.53 (ψt, 2H, CH_arom), 7.4–6.5 (overlap of aromatic protons of both isomers 7a,b and of the deuterated solvent), 3.29 (d, ²J_H–H = 8.2 Hz 2H, SiCH₂), 2.09 (the rest of SiCH₂ protons overlap with the deuterared solvent), 0.64 (s, 3H, SiMe₂), 0.52 (s, 6H, SiMe₂), −0.05 (s, 3H, SiMe₂). ³¹P{¹H} NMR (202.5 MHz, tol-d₈, 193 K): δ −23.03 (s). ¹³C{¹H} NMR (100.6 MHz, tol-d₈, 193 K): δ 174.08 (d, ²J_C–P = 107 Hz, CO), 170.49 (s, CO), 130.0–135.0 (overlap of aromatic carbons of both isomers 7a,b), 28.41 (d, J_C–P = 16 Hz, SiCH₂), 7.64 (s, SiMe₂), 4.23 (s, SiMe₂), 3.91 (s, SiMe₂), 2.97 (s, SiMe₂). ²⁹Si{¹H} DEPT NMR (119.2 MHz, tol-d₈, 193 K): δ 5.27 (d, ²J_Si–P = 9 Hz) 11.20 (d, ²J_Si–P = 8 Hz). See Fig. S29–32.†

NMR characterization of [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(Cl)(CO)], (7c)

¹H NMR (500 MHz, tol-d₈, 193 K): δ 7.73 (ψt, 1H, CH_arom), 7.3–6.3 (overlap of aromatic protons of 7a,b,c and deuterated solvent), 2.4–1.9 (overlap of methylene protons of 7a,b,c and deuterated solvent), 1.10 (s, 3H, SiMe₂), 0.85 (s, 3H, SiMe₂), 0.68 (s, 3H, SiMe₂), 0.26 (s, 3H, SiMe₂). ³¹P{¹H} NMR (202.5 MHz, tol-d₈, 193 K): δ −16.26 (s). ²⁹Si{¹H} DEPT NMR (119.2 MHz, tol-d₈, 193 K): δ 7.40 (d, ²J_Si–P = 12 Hz), 5.06 (d, ²J_Si–P = 11 Hz). See Fig. S33–36.†

[Ir₂{P(o-C₆H₄CH₂SiMe₂)₂Ph}₂(μ-H)(μ-Cl)], (8)

To a Schlenk flask containing compound 1 (70.6 mg, 0.056 mmol) in 10 mL of toluene, Et₃SiH (19.1 μL, 0.12 mmol) was added. After refluxing the reaction mixture under argon for 45 min a colour change from yellow to reddish was observed. The volatiles were removed by reduced pressure leading to an orange solid which was washed with cold pentane and dried under vacuum. Yield 80%. Anal. calcd for C₄₈H₅₉ClIr₂P₂Si₄: C, 46.87; H, 4.83. Found: C, 47.52; H, 5.02. ¹H NMR (600 MHz, C₆D₆, 298 K): δ 8.1 (br s, 2H, CH_arom), 7.13–6.70 (m, 24H, CH_arom), 2.49 (br, 2H, SiCH₂), 2.32 (d, 2H, ²J_H–H = 13.3 Hz, SiCH₂), 2.20 (d, 2H, ²J_H–H = 13.0 Hz, SiCH₂), 1.86 (d, 2H, ²J_H–H = 13.3 Hz, SiCH₂), 0.89 (s, 6H, SiMe₂), 0.44 (s, 6H, SiMe₂), 0.24 (s, 6H, SiMe₂), 0.15 (s, 6H, SiMe₂), −3.63 (t, ²J_H–P = 50.3 Hz, 1H, IrHIr). ³¹P{¹H} NMR (243.0 MHz, C₆D₆, 298 K): δ −15.17 (s). ¹³C{¹H} NMR (100.6 MHz, C₆D₆, 298 K): δ 149.04 (s, C_arom), 147.26 (s, C_arom), 132.45 (s, C_arom), 131.91 (d, J_C–P = 52.3 Hz, C_arom), 131.52 (s, C_arom), 131.08 (s, C_arom), 131.00 (s, C_arom), 130.66 (s, C_arom), 130.51 (s, C_arom), 125.17 (d, J_C–P = 54.3 Hz, C_arom), 124.94 (s, C_arom), 124.72 (s, C_arom), 31.67 (s, SiCH₂), 28.93 (s, SiCH₂), 10.56 (s, SiMe₂), 7.70 (s, SiMe₂), 7.27 (s, SiMe₂), 5.91 (s, SiMe₂). ¹H–²⁹Si HMQC NMR (C₆D₆, 298 K): δ 11.80 (SiMe₂), 3.51 (SiMe₂). See Fig. S37–40.†

NMR characterization of [IrH{η²-H-SiMe₂CH(o-C₆H₄)P(o-C₆H₄CH₂SiMe₂)Ph}(PPh₃)], (9)

¹H NMR (400 MHz, C₆D₆, 298 K): δ 7.8–6.6 (overlap of aromatic protons of [SiCPSi] skeleton and PPh₃) 3.48 (m, 1H, H_c), 2.13 (dd, ²J_H–H = 12.6 Hz, ⁴J_H–P = 5.1 Hz, 1H, Si_dCH₂), 1.67 (d, ²J_H–H = 12.6 Hz, 1H, Si_dCH₂), 0.94 (s, 3H, Si_dMe₂), 0.59 (d, ³J_H–Ha = 2.3 Hz, 3H, Si_aMe₂), −0.15 (s, 3H, Si_dMe₂), −0.27 (d, ³J_H–Ha = 2.3 Hz, 3H, Si_aMe₂), −5.92 (br s, ¹J_Ha–Sia = 78 Hz, 1H, Si_aH_a), −10.36 (dd, ²J_Hb–P = 116 Hz, ²J_Hb–P = 20 Hz, 1H, H_b). ³¹P{¹H} NMR (161.9 MHz, C₆D₆, 298 K): δ 16.01 (d, ²J_P–P = 11 Hz), 12.94 (d, ²J_P–P = 10 Hz). ¹H–²⁹Si HMQC NMR (C₆D₆, 298 K): δ 2.2 (Si_d), −44.4 (Si_a). See Fig. S41–44.†

Crystal structure determinations of 1–4, 5a, 7b

See ESI.† The structures have been deposited at the Cambridge Crystallographic Data Centre (CCDC 1939175–1939181†).

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by CONACyT (project 242818, PhD studentship and exchange grant for CACC), ANR-CONACyT (ANR-15-CE07-0024 «N2CDFun»/274001) and CNRS. We also acknowledge the French-Mexican International Laboratory (LIA-LCMMC) for support.

Notes and references

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Footnotes

† Electronic supplementary information (ESI) available: Additional spectroscopic (NMR and IR) characterisation of all complexes and X-Ray data of complexes 1–4, 5a, 7b and 8. CCDC 1939175–1939181. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9dt03136g

‡ Both SSE and VMP had the privilege to work with Prof Robin Perutz at different stages of their careers and they are extremely happy to dedicate him this Dalton contribution to celebrate his 70th birthday. Collaborating with Robin has been thoroughly enjoyable and fruitful. Joyeux anniversaire and feliz cumpleaños Robin!

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