Reactivity of Ir(I)-aminophosphane platforms towards oxidants

Abstract

The iridium(I)-aminophosphane complex [Ir{κ³C,P,P′-(SiNP-H)}(cod)] has been prepared by reaction of [IrCl(cod)(SiNP)] with KCH₃COO. DFT calculations show that this reaction takes place through an unexpected outer sphere mechanism (SiNP = SiMe₂{N(4-C₆H₄Me)PPh₂}₂; SiNP-H = CH₂SiMe{N(4-C₆H₄Me)PPh₂}₂). The reaction of [IrCl(cod)(SiNP)] or [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with diverse oxidants has been explored, yielding a range of iridium(III) derivatives. On one hand, [IrCl(cod)(SiNP)] reacts with allyl chloride rendering the octahedral iridium(III) derivative [IrCl₂(η³-C₃H₅)(SiNP)], which, in turn, reacts with tert-butyl isocyanide yielding the substitution product [IrCl(η³-C₃H₅)(CN^tBu)(SiNP)]Cl via the observed intermediate [IrCl₂(η¹-C₃H₅)(CN^tBu)(SiNP)]. On the other hand, the reaction of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with [FeCp₂]X (X = PF₆, CF₃SO₃), I₂ or CF₃SO₃CH₃ results in the metal-centered two-electron oxidation rendering a varied assortment of iridium(III) compounds. [Ir{κ³C,P,P′-(SiNP-H)}(cod)] reacts with [FeCp₂]⁺ (1 : 2) in acetonitrile affording [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃]²⁺ isolated as both the triflato and the hexafluorophosphato derivatives. Also, the reaction of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with I₂ (1 : 1) yields a mixture of iridium(III) derivatives, namely the mononuclear compound [IrI(κ²P,P′-SiNP)(η²,η³-C₈H₁₁)]I, containing the η²,η³-cycloocta-2,6-dien-1-yl ligand, and two isomers of the dinuclear derivative [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃]I, the first species being isolated in low yield. DFT calculations indicate that [IrI(κ²P,P′-SiNP)(η²,η³-C₈H₁₁)]I forms as the result of a bielectronic oxidation of iridium(I) followed by the deprotonation of the cod ligand by iodide and the protonation of the methylene moiety of the [Ir{κ³C,P,P′-(SiNP-H)}] platform by the newly formed HI. Finally, the oxidation of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] by methyl triflate proceeds via a hydride abstraction from the cod ligand, with the elimination of methane and the formation of the η²,η³-cycloocta-2,6-dien-1-yl ligand with the concomitant two-electron oxidation of the iridium centre. The crystal structures of selected compounds have been determined.

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Introduction

In the last decade, aminophosphanes have attracted increasing attention due to their modular synthesis¹ and their consequent suitability to tailor the steric and electronic properties of the resulting metal complex. Actually, a variety of mono and bidentate aminophosphano ligands have been reported, giving rise to a range of metal–ligand architectures^2–5 with applications including catalysis,² bond activation,^2a,3 redox-active multimetallic systems⁴ and metaloenzyme mimics.⁵ On this background, our group has focussed on the preparation of rhodium⁶ and iridium⁷ derivatives with the aminophosphano ligands RNP (R = H, SiMe₃) and SiNP (SiMe₂{N(4-tolyl)PPh₂}₂, Fig. 1) showing that besides the foreseeable coordination through phosphorus atom(s) of either monodentate RNP (A, Fig. 1) or bidentante SiNP ligands (B), intramolecular C–H oxidative addition processes give rise to unexpected κ²C,P (C) and κ³C,P,P′ platforms (D).

Fig. 1 Ligands RNP (R = H, SiMe₃) and SiNP and their coordination modes to rhodium⁶ and iridium.⁷

Relevant to this paper, it is worth a mention that, so far, the κ³C,P,P′ coordination of SiNP has been found to be promoted by π-acceptor ligands like carbon monoxide,^7atert-butyl isocyanide^7d and trimethyl phosphite,^7b with the concomitant formation of an iridium(III)-hydride moiety (Scheme 1). Also, in our hands, the reactivity of the resulting iridium(III) complexes with substrates like alkynes or alkenes was observed to be absent plausibly due to the substitutional inertness of the ancillary ligands.^7a,b,d Thus, we decided to explore alternative routes leading to the Ir{κ³C,P,P′-(SiNP-H)} platform. More specifically, on one hand, we envisioned that the introduction of an allyl group at the Ir(κ²P,P′-SiNP) moiety might trigger the deprotonation of one SiCH₃ group along with the elimination of propene, rendering the desired Ir{κ³C,P,P′-(SiNP-H)} platform (SiNP-H = CH₂SiMe{N(4-C₆H₄Me)PPh₂}₂). On the other hand, we decided to explore the use of acetate as a Brønsted base in order to access the Ir{κ³C,P,P′-(SiNP-H)} platform. Thus, we report herein the reaction of [IrCl(cod)(SiNP)] with either allyl chloride or potassium acetate and the study of the reactivity of the resulting metal complexes.

Scheme 1 Formation of the [Ir{κ³C,P,P′-(SiNP-H)}] platform upon oxidative addition of the SiCH₂-H bond to iridium(I).^7a,b,d

Results and discussion

Reaction of [IrCl(cod)(SiNP)] with allyl chloride

The iridium(I) complex [IrCl(cod)(SiNP)] reacts with allyl chloride affording almost quantitatively the iridium(III) derivative [IrCl₂(η³-C₃H₅)(SiNP)] (1) as a result of the formal oxidative addition of the carbon–chlorine bond to iridium(I) and the release of the cod ligand (Scheme 2).

Scheme 2 Preparation of [IrCl₂(η³-C₃H₅)(SiNP)] (1).

As shown in Fig. 2, the crystal structure of 1 reveals a distorted octahedral coordination polyhedron at the metal centre, similar to that already reported for [RhCl₂(η³-C₃H₅)(SiNP)].⁶ Indeed, the SiNP exhibits a κ²P,P′ coordination [P1–Ir–P2 92.08(3)°] and the chlorido ligands adopt a mutually cis disposition [Cl1–Ir–Cl2 88.10(3)°] rendering a see–saw IrP₂Cl₂ fragments, with the η³-allyl completing the coordination sphere of the metal. The resulting complex is chiral (Δ configuration is shown in Fig. 2), however it is worth noting that both enantiomers Δ and Λ are present in the crystal as a consequence of the centrosymmetric space group, namely, P2₁/c. Reasonably, as a consequence of the different trans influence of phosphorus (P2) and chlorine (Cl1), a non-symmetric coordination of the η³-allyl ligand is observed. As a matter of fact, different metal–carbon bond lengths [Ir–C41 2.138(4), Ir–C42 2.188(4), Ir–C43 2.277(4) Å] are observed along with different carbon–carbon bonds [C41–C42 1.440(5), C42–C43 1.388(6) Å], similar to that observed in iridium-η³-allyl systems reported in the literature.⁸ Finally, as previously observed in related Ir-SiNP complexes,^7d,e N1 and N2 exhibits an almost planar geometry (, ) with nitrogen–phosphorus (1.689 Å, av.), nitrogen–silicon (1.762 Å, av.) and nitrogen–carbon (1.438 Å, av.) bond lengths which suggest that nitrogen–phosphorus backdonation is operative to some extent and is responsible for the planar geometry of both N1 and N2.

Fig. 2 ORTEP plot of 1. For clarity, most hydrogen atoms are omitted, and tolyl and phenyl groups are shown in a wireframe style. Thermal ellipsoids are at 50% probability. Selected bond lengths (Å) and angles are (°): C41–Ir 2.138(4), C42–Ir 2.188(4), C43–Ir 2.277(4), P1–Ir 2.2676(9), P2–Ir 2.2959(9), Cl1–Ir 2.4469(9), Cl2–Ir 2.4566(9), C42–C41 1.440(5), C43–C42 1.388(6), N1–P1 1.681(3), N1–Si 1.758(3), N2–P2 1.697(3), N2–Si 1.765(3), C15–N1 1.455(4), C34–N2 1.461(4), P1–Ir–P2 92.08(3), Cl1–Ir–Cl2 88.10(3), P1–Ir–Cl2 176.63(3), C41–Ir–Cl1 160.35(10), C43–Ir–P2 160.13(11), N1–Si–N2 107.12(14), C1–Si–C2 108.27(18), C34–N2–P2 118.1(2), C15–N1–P1 120.6(2), C15–N1–Si 112.5(2), P1–N1–Si 126.94(18), C34–N2–Si 110.7(2), P2–N2–Si 125.34(17).

As for the solution structure of 1, at 298 K sharp well-shaped ³¹P{¹H} doublets at 30.6 and 24.3 ppm (²J_PP = 25.2 Hz) are observed suggesting the presence of two non-equivalent phosphorus atoms occupying mutually cis coordination sites. On the other hand, broad ¹H signals between 6 and 8 ppm suggests that at room temperature the rotation of the tolyl and the phenyl groups around the N–C and P–C bonds, respectively, may be hindered. On this ground, the spectroscopic characterization of 1 was carried out at 233 K. At that temperature, two ¹H and two ¹³C{¹H} resonances for the SiCH₃ groups are observed (δ_H, δ_C: 0.83, 2.4; −0.35, 2.7 ppm) confirming the presence of two different ligands at the axial positions (taking the IrP₂ plane as the equatorial plane). As for the η³-allyl moiety, three ¹³C resonances are observed at 102.9 (C²), 72.1 (C¹) and 43.2 ppm (C³) along with five ¹H signals (δ_H 4.84, C²H; 4.03 and 3.94, C¹H₂; 2.06 and 1.43 ppm, C³H₂).

Contrary to our expectation, compound 1 is thermally stable in toluene, neither elimination of propene nor decomposition being observed (¹H NMR) even after 18 h heating at reflux. In view of this thermal stability, the reaction of 1 with tert-butyl isocyanide was carried out in order to explore its reactivity. As a matter of fact, 1 reacts with tert-butyl isocyanide smoothly yielding [IrCl(η³-C₃H₅)(CN^tBu)(κ²P,P′-SiNP)]Cl (2Cl) as isocyanide ex/isocyanide exchange (Scheme 3).

Scheme 3 Reaction of 1 with tert-butyl isocyanide.

The ³¹P{¹H} NMR spectrum of 2Cl contains two doublet at 28.3 and 25.9 ppm (²J_PP = 20.9 Hz) confirming the κ²P,P′ coordination of SiNP. The ¹H and ¹³C{¹H} NMR spectra are also indicative of the presence of the η³-allyl moiety (δ_H 4.89, C²H; 3.86, 3.72, C¹H; 2.31, 2.00 ppm, C³H; δ_C 108.3, C²; 63.6, C¹; 60.1 ppm, C³) and of the tert-butyl isocyanide ligand (δ_H = 2.04, δ_C = 31.0 ppm). Interestingly, when the formation of 2Cl was monitored by NMR spectroscopy, [IrCl₂(η¹-C₃H₅)(CN^tBu)(κ²P,P′-SiNP)] (3) was observed as an intermediate (Scheme 3). In our hands, 3 could eventually be isolated along with around 20% of 1 (Fig. 3). Nonetheless, it was fully characterised in solution at 233 K, even in the presence of 1. The ³¹P{¹H} singlet at 31.9 ppm is indicative of two equivalent phosphorus atoms and, as a consequence, of a symmetric environment at the metal centre. Accordingly, two equivalent tolyl moieties are observed (δ_H 2.09, δ_C 20.9 ppm, CH₃^tol). Also, two ¹H signals at 0.47 (δ_C 4.5 ppm) and −0.05 ppm (δ_C 3.4 ppm) point at two non-equivalent SiCH₃ groups, confirming the presence of two different axial ligands (taking the IrP₂ plane as the equatorial plane). As for the allyl group, the ¹H and ¹³C{¹H} NMR spectra show a pattern different from those observed for 1 and 2Cl, which indicates an η¹ coordination. Indeed, two ¹³C signals at 148.2 and 108.3 ppm are indicative of an uncoordinated olefinic CH=CH₂ group, whereas the signals at 3.34 (¹H) and 5.3 ppm (¹³C) have been assigned to the IrCH₂ moiety. The tert-butyl isocyanide ligand (δ_H 1.06; δ_C 29.5 ppm, CH₃) completes the coordination sphere of the metal centre.

Fig. 3 ³¹P{¹H} NMR spectrum of 3 in the presence 20 mol% of 1 (CD₂Cl₂, 233 K).

On this ground, the Cl⁻/CN^tBu exchange reaction between 1 and tert-butyl isocyanide should follow an associative pathway taking advantage of the η³ → η¹ → η³ haptotropic shift of the allyl ligand (Scheme 4). In this regard, DFT calculations were performed in order to shed light on the reaction sequence leading to 2Cl. Firstly, the η³ → η¹ shift of the allyl ligand in 1 renders the coordinatively unsaturated intermediate I. In turn, I isomerises to II, which ultimately reacts with tert-butyl isocyanide yielding the observed intermediate 3. Afterwards, 3 should release one chlorido ligand (3 → IIICl) and finally the η¹ → η³ shift should give rise to 2Cl. As for the calculated relative Gibbs free energy of the proposed intermediates, the formation of both 3 and 2Cl from 1 is calculated to be exergonic in agreement with the observed course of the reaction of 1 with tert-butyl isocyanide. As far as the calculated relative stability of 2Cl vs. 3 is concerned, unaccounted solvation effects and/or underestimated ion pair stabilization for 2Cl may be responsible for the calculated higher stability of 3 with respect to 2Cl.

Scheme 4 Reaction sequence for the reaction of 1 with tert-butyl isocyanide along with the calculated values of relative Gibbs free energy (kcal mol⁻¹, B97D3/def2svp).

Depending on the topology of the η³ → η¹ shift in 1, IV may also form (Scheme 4). Nonetheless, its formation is calculated to be significantly more endergonic than the formation of I and II, thus ruling out IV as a possible intermediate.

Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(cod)]

The reaction of [IrCl(cod)(SiNP)] with potassium acetate in dichloromethane smoothly affords the metallated iridium(I) derivative [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4) as a result of the deprotonation of one SiCH₃ moiety (Scheme 5). Remarkably, as mentioned before, previously reported Ir{κ³C,P,P′-(SiNP-H)} platforms^7a,b,d were obtained via SiCH₂-H oxidative addition to iridium(I) and, as a result, contained the iridium(III)-hydride moiety (Scheme 1), whereas in this case, for the first time, the reaction implies the base-assisted metal–carbon bond formation (vide infra), with no change of the metal oxidation state. The crystal structure of 4 reveals a distorted bipyramidal geometry at the metal centre (TBPY-5-23) with the ligand SiNP-H occupying three mutually cis positions [C1–Ir–P1 85.89(11)°, C1–Ir–P2 81.96(11)°, P1–Ir–P2 98.82(4)°] and the cod ligand completing the coordination sphere [CT1–Ir–CT2 84.910(15)°] (Fig. 4). Similar to what previously observed in the related iridium(I) complex [Ir{κ³C,P,P′-(SiNP-H)}(CO)₂],^7a the distance Ir–CT2 is longer than Ir–CT1 [Ir–CT1 2.0153(3), Ir–CT2 2.1007(3) Å] due to the high trans influence of the methylene group. Accordingly, the bond C41–C42 [1.447(6) Å] is longer than C45–C46 [1.409(6) Å] indicating a higher degree of backdonation to the coordinated olefinic bond lying in the equatorial plane. As for the κ³C,P,P′-(SiNP-H) backbone, when compared with the uncomplexed SiNP ligand,^7d the wider angle C1–Si–C2 [123.3(2)°] and the smaller angles P1–N1–Si [111.41(18)°] and P2–N2–Si [111.47(19)°] are reasonably the consequence of the metallation and the subsequent formation of two fused five-member cycles [SiNP: C1–Si–C2 111.48(10)°, P1–N1–Si 121.40(9)°, P2–N2–Si 120.94(9)°].^7d

Scheme 5 Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4).

Fig. 4 ORTEP plot of 4. For clarity, most hydrogen atoms are omitted, and tolyl and phenyl groups are shown in a wireframe style. Thermal ellipsoids are at 50% probability. Selected bond lengths (Å) and angles are (°): C1–Ir 2.167(4), P1–Ir 2.2976(10), P2–Ir 2.3451(10), Ir–CT1 2.0153(3), Ir–CT2 2.1007(3), C41–C42 1.447(6), C45–C46 1.409(6), N1–P1 1.701(3), N1–Si 1.759(3), N2–P2 1.704(3), N2–Si 1.770(4), C1–Ir–P1 85.89(11), C1–Ir–P2 81.96(11), P1–Ir–P2 98.82(4), CT1–Ir–CT2 84.910(15), CT1–Ir–C1 86.76(11), CT2–Ir–C1 171.59(11), CT1–Ir–P1 125.65(3), CT1–Ir–P2 133.11(3), C1–Si–C2 123.3(2), N1–Si–N2 113.45(16), C15–N1–P1 123.5(3), C15–N1–Si 124.4(3), P1–N1–Si 111.41(18), C34–N2–P2 124.5(3), C34–N2–Si 119.0(3), P2–N2–Si 111.47(19). CT1 and CT2 are the centroids of C41 and C42, and of C45 and C46, respectively.

The solution structure of 4 is similar to that observed in the solid state. The ³¹P{¹H} singlet at 47.1 ppm along with the ¹H/¹H{³¹P} triplet/singlet at 0.14 ppm and the ¹H singlet at −0.83 ppm, assigned to the SiCH₂Ir and SiCH₃ moieties, respectively, confirm that the κ³C,P,P′ coordination is preserved in a symmetrical metal environment. Accordingly, two ¹H signals are observed at 3.60 and 2.60 ppm for the cod ligand. Notably, no cross peaks are observed between them in either the ¹H–¹H COSY or the ¹H–¹H NOESY spectra, thus ruling out the square pyramidal geometry SPY-5-32 for 4 in solution. Accordingly, the SPY-5-32 isomer was calculated to be less stable than 4 (TBPY-5-23) by 11.2 kcal mol⁻¹ (vide infra).

The course of the formation of 4 was explored by means of DFT calculations (Fig. 5). Two mechanisms were considered,⁹ one based on the well-established acetate-assisted C–H activation, and the other on the outer sphere deprotonation of the SiCH₃ moiety of [IrCl(cod)(SiNP)] by acetate. Fig. 5 shows the Gibbs free energy profiles for the two explored routes along with the structures of calculated transition states.

Fig. 5 Gibbs free energy profiles for the formation of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4) (black, outer sphere deprotonation; gray, acetate-assisted CH activation; kcal mol⁻¹, B97D3/def2svp), along with the calculated structures of TS_VI-VII and TS_VIII-4 and selected interatomic distances (Å). Gray, carbon; white, hydrogen; violet, nitrogen; red, oxygen; yellow, silicon; orange, phosphorus, blue, iridium.

Considering the outer sphere mechanism, the first step should be the chloride abstraction/substitution to yield the pentacoordinate acetato derivative V or the square planar intermediate VI, or an equilibrium mixture of the two. In turn, VI should undergo metallation via an outer sphere interaction of the SiCH₃ moiety with free acetate ion. Indeed, acetate deprotonates the SiCH₃ group as long as the metal–carbon bond forms (TS_VI-VII). As a result, the square pyramidal derivative VII (SPY-5-32) forms which ultimately isomerises to the observed more stable trigonal bypiramidal product 4 (TBPY-5-23). The overall transformation [IrCl(cod)(SiNP)] + CH₃COO⁻ → 4 + CH₃COOH + Cl⁻ is calculated to be slightly endergonic (ΔG_r = +0.9 kcal mol⁻¹), thus the formation of solid potassium chloride should be decisive for the outcome of the reaction. Regarding the base-assisted C–H bond cleavage mechanism, starting from pentacoordinate acetato derivative V, the preliminary η², η² → η² haptotropic shift of the cod ligand should take place (V → VIII) in order to allow the required arrangement of the C–H bond, the metal centre and the acetato ligand. Once the square planar intermediate VIII forms, the acetate assisted deprotonation/metalation of the SiCH₃ moiety takes place via the transition state TS_VIII-4. A thorough examination of interatomic distances in TS_VIII-4 (Fig. 5) indicates that no metal–hydrogen interaction should exist thus ruling out any oxidative character of the SiCH₂-H bond cleavage.⁹ From an energy standpoint, the acetate-assisted C–H activation mechanism is not a competitive route and should be ruled out, since the TS_VIII-4 (+30.7 kcal mol⁻¹) is not accessible under the experimental conditions. On the other hand, the calculated activation barrier (TS_VI-VII, +19.7 kcal mol⁻¹) for the outer sphere mechanism nicely fits in with the observed outcome under the experimental conditions.

The endergonic character of the formation of 4 prompted us to carry out the reaction of 4 with triflic acid, as a strong Brønsted acid, in order to establish if the metalation of SiNP could be reverted, i.e. the Ir-CH₂Si could be protonated. As a matter of fact, when CF₃SO₃H was added to a CD₂Cl₂ solution of 4 (1 : 1 molar ratio) in an NMR tube, the instantaneous complete conversion of 4 to [Ir(cod)(SiNP)]⁺ was observed, as established by comparison with the ³¹P{¹H} and ¹H NMR data previously reported for [Ir(cod)(SiNP)]⁺.^7a Accordingly, on top of that, the reaction 4 + CF₃SO₃H → [Ir(cod)(SiNP)]⁺ + CF₃SO₃⁻ was calculated to be highly exergonic (−22.7 kcal mol⁻¹) likely as a consequence of the strong acidic character of CF₃SO₃H. In this respect, it is worth mentioning that in a previous study^7d the reactivity of the iridium(III) derivative [IrH{κ³C,P,P′-(SiNP-H)}(CN^tBu)₂][PF₆] towards Brønsted acids, such as HBF₄, HPF₆ and CF₃COOH, was explored, showing that the Ir-CH₂Si bond is not reactive, rather the Si–N bonds break as a result of the formal addition of HF (formed in situ by reaction of PF₆⁻ with either CF₃COOH or HBF₄). On these grounds, the stability of the Ir{κ³C,P,P′-(SiNP-H)} platform towards Brønsted acids seems to be subtly determined by the oxidation state of the metal centre, the metal–carbon bond being reactive towards H⁺ only in the case of iridium(I).

Reaction of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with oxidants

In order to expand the family of iridium complexes with the κ³C,P,P′-(SiNP-H) ligand, the reactivity of 4 towards oxidants, namely [FeCp₂]X (X = PF₆, CF₃SO₃), I₂ or CF₃SO₃Me, was explored.

4 undergoes a two-electron oxidation when treated with [FeCp₂]⁺ (Ir : Fe 1 : 2 molar ratio) in acetonitrile affording the octahedral cation [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃]²⁺ (5²⁺) isolated as either the trifluromethanesulfonate or the hexafluorophosphate salt (Scheme 6).

Scheme 6 Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃][X]₂ (5[X]₂).

Crystal structure of 5[CF₃SO₃]₂ shows an octahedral coordination polyhedron at the metal centre with a facial coordination of the κ³C,P,P′-(SiNP-H) ligand [C1–Ir–P1 85.81(9)°, C1–Ir–P2 83.12(8)°, P1–Ir–P2 96.27(3) Å] (Fig. 6). The three remaining coordination sites are occupied by acetonitrile ligands. Noticeably, as a consequence of the higher trans influence of the metallated SiCH₂ moiety, the iridium–nitrogen N42–Ir [2.117(3) Å] is longer than N45–Ir [2.071(3) Å] and N48–Ir [2.091(3) Å]. When comparing the κ³C,P,P′-(SiNP-H) ligand in 5²⁺ and 4, regardless of the oxidation state of the metal centre, the IrCH₂SiCH₃(NP)₂ backbones are virtually superimposable, minor differences being observed exclusively in the orientation of the phenyl and tolyl groups, probably as a consequence of the steric hindrance of ancillary ligands and/or the coordination polyhedron. The NMR spectra of 5²⁺ confirm that the solid state structure is preserved in solution. Actually, two sets of signals are observed in both the ¹H and the ¹³C{¹H} NMR spectra for the acetonitrile ligand, namely at δ_H 2.24 ppm and δ_C 3.2 ppm for the acetonitrile ligands trans to phosphorus and at δ_H 2.44 and δ_C 3.9 ppm for the acetonitrile ligand trans to carbon. As for the SiNP-H ligand, in agreement with the proposed structure, one ³¹P{¹H} NMR signal at 18.2 ppm indicates the equivalence of the two phosphorus atoms. Also, the ¹H and ¹³C{¹H} signals at 1.46 and at −19.6 ppm, respectively, are assigned to the metallated methylene group, whereas the ¹H and ¹³C{¹H} signals at 0.36 and −1.3 ppm, respectively, are assigned to the SiCH₃ group.

Fig. 6 ORTEP plot of 5²⁺ in 5[CF₃SO₃]₂. For clarity, most hydrogen atoms are omitted, and tolyl and phenyl groups are shown in a wireframe style. Thermal ellipsoids are at 50% probability. Selected bond lengths (Å) and angles are (°): N42–Ir 2.117(3), N45–Ir 2.071(3), N48–Ir 2.091(3), P1–Ir 2.2994(8), P2–Ir 2.3012(8), C1–Ir 2.105(3), N1–P1 1.687(2), N1–Si 1.757(3), N2–P2 1.678(2), N2–Si 1.780(2), C1–Ir–P1 85.81(9), C1–Ir–P2 83.12(8), P1–Ir–P2 96.27(3), C1–Ir–N42 175.88(10), N45–Ir–P1 171.92(7), N48–Ir–P2 168.94(7).

The treatment of 4 with I₂ (1 : 1) affords a mixture of three products, namely the iridium(III) derivatives [IrI(κ²P,P′-SiNP)(η²,η³-C₈H₁₁)]I (6I) and two isomers of the dinuclear species [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃]I (7aI and 7bI), in a molar ratio 6⁺ : 7a⁺ : 7b⁺ 54 : 33 : 13 (Scheme 7, top). The mixture of 7aPF₆ and 7bPF₆ was independently prepared either by reaction of 4 with [FeCp₂][PF₆] in acetone and subsequent addition of NaI, or by direct reaction of 5[PF₆]₂ with NaI (Ir : I = 2 : 3) (Scheme 7 and Fig. 7). On the other hand, 6I was isolated in low yields from the mixture 6I + 7aI + 7bI upon recrystallization from CH₃CN/Et₂O (Fig. 7).

Scheme 7 (Top) Synthesis of 6I, 7aX and 7bX (X = I, PF₆). (Bottom) Selected NMR data for 6⁺ [δ_C, along with J_CP, italics, and δ_H (CD₂Cl₂)].

Fig. 7 ³¹P{¹H} NMR spectra (CD₂Cl₂, 298 K) of (A) the solid mixture resulting from the reaction of 4 with I₂; (B) 7a⁺ + 7b⁺ obtained from the reaction of 5[PF₆]₂ with NaI; (C) 6I after recrystallization of a mixture of 6I + 7aI + 7bI from CH₃CN/Et₂O.

The crystal structure of 6I shows a virtually octahedral geometry at the metal centre with a bidentate κ²P,P′ coordination of SiNP [P1–Ir 2.3215(13) Å, P2–Ir 2.3442(13) Å, P1–Ir–P2 91.53(4)°] (Fig. 8). The iodido ligand lies cis to both phosphorus atoms [I1–Ir 2.7247(4) Å, P1–Ir–I1 90.94(3)°, P2–Ir–I1 93.04(3)°] with the cycloocta-2,6-dien-1-yl ligand formally occupying the three remaining coordination sites. Notably, the olefinic moiety lies trans to one phosphorus atom [Ir–CT 2.2494(2) Å, CT–Ir–P1 171.79(3)°], and the allyl moiety spans the remaining coordination sites trans to P2 and I1 [C43–Ir 2.294(5) Å, C42–Ir 2.200(5) Å, C41–Ir 2.278(6) Å, C41–Ir–I1 155.72(14)°, C43–Ir–P2 169.58(15)°]. To the best of our knowledge, only few examples of cod activation leading to the formation of the cycloocta-2,6-dien-1-yl ligand have been reported for iridium complexes.¹⁰ NMR spectra indicate that the solution structure of 6⁺ is similar to that observed in the solid state. As a matter of fact, two ³¹P{¹H} NMR doublets (δ_P 32.1, 23.2 ppm, ²J_PP = 25.3 Hz) are observed for the two non-equivalent phosphorus atoms. In addition, the ¹H and ¹³C{¹H} NMR signals assigned to the C₈H₁₁ ligand (Scheme 7, bottom) confirm the presence of the cycloocta-2,6-dien-1-yl ligand.

Fig. 8 ORTEP plot of 6⁺ in 6I. For clarity, most hydrogen atoms are omitted, and tolyl and phenyl groups are shown in a wireframe style. Thermal ellipsoids are at 50% probability. Selected bond lengths (Å) and angles are (°): P1–Ir 2.3215(13), P2–Ir 2.3442(13), I1–Ir 2.7247(4), C41–Ir 2.278(6), C42–Ir 2.200(5), C43–Ir 2.294(5), Ir–CT 2.2494(2), C41–C42 1.422(8), C42–C43 1.404(8), C46–C47 1.377(8), C41–Ir–I1 155.72(14), C42–Ir–I1 123.76(16), C43–Ir–I1 90.23(16), P1–Ir–P2 91.53(4), P1–Ir–I1 90.94(3), P2–Ir–I1 93.04(3), CT–Ir–I1 97.262(10), CT–Ir–P1 171.79(3), CT–Ir–P2 88.27(3), C41–Ir–P2 108.65(14), C42–Ir–P2 142.90(17), C43–Ir–P2 169.58(15), C15–N1–P1 118.2(3), C15–N1–Si 112.2(3), P1–N1–Si 129.3(3), C34–N2–P2 116.5(3), C34–N2–Si 111.6(3), P2–N2–Si 131.6(3). CT, centroid of C46 and C47.

Regardless of the synthetic route, a mixture of 7a⁺ and 7b⁺ (70 : 30, aprox.) was always obtained and, in our hands, it could not be separated. In addition, heating a solution containing a mixture of 7a⁺ and 7b⁺ resulted in the coalescence of their ³¹P signals, suggesting that an equilibrium between the two isomers could be operative in solution. Finally, the MALDI-TOF mass spectra uniquely revealed one molecular peak at m/z 2040.8 (calcd. 2041.1, [M]⁺) which suggests that 7a⁺ and 7b⁺ might be isomers. The crystal structure of 7a⁺ (in 7aPF₆) shows a dinuclear [Ir(μ-I)₃Ir] core [see Fig. 9 for Ir–I bond lengths and Ia–Ir–Ib angles] featuring a non-interaction intermetallic distance [Ir1⋯Ir2 3.7116(16) Å], with one κ³C,P,P′-(SiNP-H) ligand completing the coordination sphere of each metal centre. The methylene moieties lie trans to the same iodido ligand (I2) rendering a virtual C_2v symmetry with two equivalent phosphorus atoms. As a consequence of the higher trans influence of the SiCH₂ group when compared to the PPh₂N moiety, the Ir1–I2 [2.7909(9) Å] and Ir2–I2 [2.8105(9) Å] bond lengths are longer than the remaining iridium–iodine bond lengths [Ir1–I1 2.7308(8), Ir1–I3 2.7386(9), Ir2–I1 2.7342(8), Ir2–I3 2.7316(8) Å]. The NMR spectra of 7a⁺ suggest that its structure in solution is similar to that in the solid state. Actually, one ³¹P{¹H} singlet was observed at 20.7 ppm along with one ¹H and one ¹³C{¹H} signal for the methyl group of the tolyl fragment [δ_H 2.05; δ_C 21.5 ppm] confirming the equivalence of the two SiNP arms. On the other hand, the resonances at δ_H 2.05 and 0.00 ppm as well as at δ_C −11.7 and −0.6 ppm are assigned to the IrCH₂Si and SiCH₃ moieties, respectively.

Fig. 9 ORTEP plot of 7a⁺ in 7aPF₆. For clarity, most hydrogen atoms are omitted, and tolyl and phenyl groups are shown in a wireframe style. Thermal ellipsoids are at 50% probability. Selected bond lengths (Å) and angles are (°): I1–Ir1 2.7308(8), I1–Ir2 2.7342(8), I2–Ir1 2.7909(9), I2–Ir2 2.8105(9), I3–Ir2 2.7316(8), I3–Ir1 2.7386(9), P1–Ir1 2.3037(15), P2–Ir1 2.2902(15), P3–Ir2 2.2886(15), P4–Ir2 2.3096(15), C1–Ir1 2.132(5), C41–Ir2 2.149(5), C1–Ir1–P2 83.36(13), C1–Ir1–P1 84.84(14), P2–Ir1–P1 97.36(6), C41–Ir2–P3 84.65(13), C41–Ir2–P4 84.44(14), P3–Ir2–P4 98.25(6), I1–Ir1–I3 77.36(3), I1–Ir1–I2 80.95(3), I3–Ir1–I2 80.80(3), I3–Ir2–I1 77.42(3), I3–Ir2–I2 80.57(3), I1–Ir2–I2 80.54(3).

As for 7b⁺, full characterization could not be achieved. Nonetheless, in view of the two resonances at δ_P 22.0 and 21.0 ppm (Δν_1/2 = 50 Hz), the SiCH₂ moieties are proposed to lie trans to different bridging iodine atoms at the [Ir(μ-I)₃Ir] core, thus rendering a virtual C₂ symmetry with two non-equivalent phosphorus atoms slowly exchanging on the NMR timescale at 298 K. As a confirmation, the relative Gibbs free energy for 7a⁺ (0.0) and 7b⁺ (+1.3 kcal mol⁻¹) nicely confirms that 7b⁺ should be observed in solution along with 7a⁺ (vide infra).

The course of the reaction of 4 with I₂ has been investigated by DFT calculations (Scheme 8). As a result of the two-electron oxidation of 4, the iridium(III) species IX²⁺ is assumed to be the starting point of two independent pathways, leading to either 6⁺ or 7a/b⁺, respectively. As for the formation of 7a/b⁺, the cod ligand of IX⁺ should be displaced by incoming iodide rendering the dinuclear species 7a⁺ or 7b⁺. On the other hand, when dealing with the formation of 6⁺, the iodido ligand should dissociate (IX⁺ → X²⁺I⁻) and eventually act as a base, abstracting H⁺ from the cod ligand of X²⁺ (X²⁺I⁻ → XI⁺ + HI). Thereafter, the intermediate XI⁺, that contains the η²,η³-cycloocta-2,6-dien-1-yl ligand, should react with the newly formed HI undergoing the protonation of the methylene group IrCH₂Si, finally yielding 6⁺ (the structures of the transition state TS_X²⁺I⁻-XI⁺ and TS_XI⁺-6⁺ are shown in Scheme 8). For the sake of comparison, the isomer XII⁺ of [IrI(κ²P,P′-SiNP)(η²,η³-C₈H₁₁)]⁺ was calculated to be 9.1 kcal mol⁻¹ less stable than 6⁺, which rules out its presence in solution in agreement with the observed NMR spectra.

Scheme 8 (Top) Reaction sequences for the formation of 7a + 7b⁺ (left) and 6⁺ (right) with relative Gibbs free energy of intermediates (kcal mol⁻¹, B97D3/def2svp). (Bottom) Calculated structures of the transition states TS_X²⁺I⁻-XI⁺ and TS_XI⁺-6⁺ along with selected interatomic distances (Å). Gray, carbon; white, hydrogen; violet, nitrogen; yellow, silicon; orange, phosphorus; blue, iridium; purple, iodine.

The reaction of 4 with methyl triflate also resulted in the formal two-electron oxidation of iridium. As a matter of fact, upon reaction of 4 with methyl triflate (1 : 1) for 4 days at room temperature, [Ir{κ³C,P,P′-(SiNP-H)}(η²,η³-C₈H₁₁)][CF₃SO₃] (8CF₃SO₃) forms along with methane (observed via both GC and ¹H NMR spectroscopy) as a consequence of the unusual hydride abstraction from the cod ligand (Scheme 9). 8⁺ contains the iridium(III)-κ³C,P,P′-(SiNP-H) platform and the cycloocta-2,6-dien-1-yl ligand (C₈H₁₁) exhibiting a η²,η³ coordination. The ¹H and ³¹P{¹H} NMR spectra indicate that the κ³C,P,P′ coordination of the ligand SiNP-H is preserved and experiments a non-symmetric environment. Actually, two ³¹P{¹H} signals (35.4, 31.5 ppm; ²J_PP = 9.2 Hz) are observed along with two ¹H multiplets for the non-equivalent hydrogen atoms of the methylene group IrCH₂Si (0.55, 0.46 ppm, δ_C −13.8 ppm). Fig. 10 (top) shows a selection of ¹H and ¹³C{¹H} NMR data for the ligand C₈H₁₁ of 8⁺. It is worth a mention that the putative isomer XIII⁺ exhibiting the olefinic group at one of the coordination sites trans to phosphorus and the allyl moiety formally spanning the remaining sites trans to phosphorus and trans to CH₂ was not observed (Scheme 9). Actually, confirming the proposed structure for 8⁺, XIII⁺ was calculated to be 5 kcal mol⁻¹ less stable than 8⁺ (Scheme 9).

Scheme 9 (Top) Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(η²,η³-C₈H₁₁)][CF₃SO₃] (8CF₃SO₃). (Bottom) Calculated structures for 8⁺ and XIII⁺ along with relative Gibbs free energy (kcal mol⁻¹, B97D3/def2svp). For clarity, only ipso atoms of phenyl and tolyl groups are shown. Gray, carbon; white, hydrogen; violet, nitrogen; yellow, silicon; orange, phosphorus, blue, iridium.

Fig. 10 (Top) Selected NMR data for 8⁺ [δ_C, along with J_CP, italics, and δ_H]. (Bottom) Gibbs free energy profile for the reaction of 4 with methyl triflate (kcal mol⁻¹, B97D3/def2svp) along with the calculated structure of TS_4-8⁺ and selected interatomic distances (Å). Gray, carbon; white, hydrogen; violet, nitrogen; red, oxygen; pale green, fluorine; yellow, silicon; orange, phosphorus; dark yellow, sulphur; blue, iridium.

The mechanism of the formation of 6⁺ was explored by means of DFT calculations showing that it consists of a straightforward hydride abstraction from the coordinated cod promoted by methyl triflate, ultimately acting as an electrophile (Fig. 10), and goes through the transition state TS_4-8⁺ (+28.9 kcal mol⁻¹).

Conclusions

The iridium(I)-aminophoshane derivative [IrCl(cod)(SiNP)] is a versatile precursor for the preparation of a range of iridium(III) complexes with the SiNP ligand coordinated either κ²P,P′ or κ³C,P,P′. The oxidative addition of allyl chloride to [IrCl(cod)(SiNP)] affords the thermally stable [IrCl₂(η³-C₃H₅)(SiNP)] (1) which, in turn, reacts with tert-butyl isocyanide rendering the substitution product [IrCl(η³-C₃H₅)(CN^tBu)(SiNP)]Cl (2Cl). The observed intermediate [IrCl₂(η¹-C₃H₅)(CN^tBu)(SiNP)] (3) as well as DFT calculations point out that the mechanism is associative. In this connection, the η³ ⇄ η¹ haptotropic shift of the allyl ligand is key for the outcome of the reaction.

The iridium(I) pentacoordinate [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4) is smoothly obtained treating [IrCl(cod)(SiNP)] with potassium acetate via an outer sphere mechanism in which the acetate ion deprotonate the SiCH₃ group while the carbon–iridium bond forms. The two-electron oxidation of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4) gives rise to a variety of iridium(III) derivatives. The reaction of 4 with ferrocenium in acetonitrile leads to the oxidation of iridium(I) to iridium(III) rendering the octahedral cation [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃]²⁺ (5²⁺) as a result of the substitution of the cod ligand by three acetonitrile ligands. Alternatively, I₂ readily oxidises 4 yielding a mixture of iridium(III) complexes as a consequence of either cod activation or cod substitution, namely [IrI(κ²P,P′-SiNP)(η²,η³-C₈H₁₁)]⁺ (6⁺) and [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃]⁺ (7a⁺/7b⁺), respectively. As a matter of fact, once [Ir{κ³C,P,P′-(SiNP-H)}(cod)] is oxidised, I⁻ is able to either displace cod affording dinuclear species 7a⁺/7b⁺ or shuttle one H⁺ ion from cod to the κ³C,P,P′-(SiNP-H) ligand in a step-wise fashion, eventually affording the iridium(III) complex 6⁺. Finally, methyl triflate is also able to oxidise 4 affording 8⁺ as a result of the hydride abstraction from the cod ligand.

Experimental

General section

All the operations were carried out using standard Schlenk tube techniques under an atmosphere of pre-purified argon or in a Braun glove-box under argon. Solvents were dried and purified according to standard procedures and distilled under argon, or obtained oxygen-and water-free from a solvent purification system (Innovative Technologies). The compounds SiMe₂{N(4-C₆H₄CH₃)(PPh₂)}₂ (SiNP)⁶ and [IrCl(cod)(SiNP)]^7a were prepared according to the literature. NMR spectra were recorded with Bruker spectrometers (AV300, AV400, or AV500) and are referred to SiMe₄ (¹H, ¹³C), and H₃PO₄ (³¹P). The proposed ¹H, ¹³C, and ³¹P assignment relies on the combined analysis of 1D [¹H, ¹H{³¹P}, ¹³C{¹H}-apt, ³¹P{¹H}] and 2D NMR spectra (¹H–¹H COSY, ¹H–¹H NOESY, ¹H–¹³C HSQC, ¹H–¹³C HMBC, ¹H–³¹P HMBC). Fig. 11 shows the numbering scheme used for the assignment of NMR signals in 1, 2Cl, 6I, and 8CF₃SO₃. Whenever labels P¹ and P², are used for non-equivalent phosphorus atoms, superscript labels “tol-P1/2” and “PhP1/2” are used for hydrogen and carbon atoms belonging to the tolyl and phenyl groups attached/linked to the phosphorus atom P¹/P², respectively.

Fig. 11 Numbering scheme for the assignment of NMR signals for 1, 2⁺, 6⁺, and 8⁺.

MALDI-TOF mass spectra were recorded using a Bruker AutoFLEX III-TOF/TOF using trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) as a matrix.

Synthesis of [IrCl₂(η³-C₃H₅)(κ²P,P′-SiNP)] (1). A dichloromethane suspension (10 mL) of [IrCl(cod)(SiNP)] (242 mg, 0.248 mmol, 974.64 g mol⁻¹) was added with allyl chloride (20.2 μL, 0.248 mmol, 76.52 g mol⁻¹, 0.939 g mL⁻¹). The light yellow resulting suspension was stirred at 313 K for 6 h, evaporated up to 5 mL and added with hexane (5 mL), affording a light yellow solid which was filtered off, washed with hexane, dried in vacuo and finally identified as [IrCl₂(η³-C₃H₅)(κ²P,P′-SiNP)] (1, 227 mg, 97% yield). Found: C 54.69, H 4.78, N 3.01. Calcd for C₄₃H₄₅Cl₂IrN₂P₂Si (942.99 g mol⁻¹): C 54.77, H 4.81, N 2.97. ¹H NMR (CD₂Cl₂, 298 K): δ_H 8.26–7.71 (7H tot; 4H, o-PPh; 2H, m-PPh; 1H, p-PPh), 7.53 (br, 2H, m-PPh), 7.43–7.26 (4H tot; 2H, o-PPh; 1H, p-PPh; 1H, C²H^tol-P2), 7.24–6.94 (10H tot; 2H, o-PPh; 4H, m-PPh; 2H, p-PPh; 1H, C²H^tol-P1; 1H, C³H^tol-P1), 6.80 (d, 1H, ³J_HH = 8.2 Hz, C³H^tol-P2), 6.67–6.51 (3H tot; 1H, C²H^tol-P2; 1H, C³H^tol-P1; 1H, C³H^tol-P2), 5.48 (d, 1H, ³J_HH = 8.2 Hz, C²H^tol-P1), 4.86 (m, 1H, C²H^all), 4.16–4.03 (2H tot; 1H, C¹H_a^all; 1H, C¹H_b^all), 2.21 (s, 3H, CH₃^tol-P1), 2.14 (m, 1H, C³H_b^all), 2.08 (s, 3H, CH₃^tol-P2), 1.49 (br, 1H, C³H_a^all), 0.88 (s, 3H, SiCH₃^b), −0.28 (s, 3H, SiCH₃^a). ³¹P{¹H} NMR (CD₂Cl₂, 298 K): δ_P 30.6 (d, 1P, ²J_PP = 25.2 Hz, SiNP¹), 24.3 (d, 1P, ²J_PP = 25.2 Hz, SiNP²). ¹H NMR (CD₂Cl₂, 233 K): δ_H 9.59 (br, 1H, o-PPh), 8.75 (dd, 1H, ³J_HP = 11.5 Hz, ³J_HH = 7.4 Hz, o-PPh), 8.04–7.59 (5H tot; 2H, o-PPh; 2H, m-PPh; 1H, p-PPh), 7.53 (t, 2H, ³J_HH = 7.1 Hz, m-PPh), 7.36–7.25 (2H tot; 1H, p-PPh; 1H, C²H^tol-P2), 7.18 (t, 2H, ³J_HH = 7.4 Hz, o-PPh), 7.15–7.08 (3H tot; 2H, m-PPh; 1H, C²H^tol-P1), 7.07–6.98 (3H tot, 2H, p-PPh; 1H, C³H^tol-P1), 6.88 (m, 2H, m-PPh), 6.79 (d, 1H, ³J_HH = 7.9 Hz, C³H^tol-P2), 6.67–6.51 (5H tot; 2H, o-PPh; 1H, C²H^tol-P2; 1H, C³H^tol-P1; 1H, C³H^tol-P2), 5.32 (d, 1H, ³J_HH = 7.9 Hz, C²H^tol-P1), 4.84 (m, 1H, C²H^all), 4.03 (m, 1H, C¹H_a^all), 3.94 (dd, ³J_HH = 12.6 Hz, ³J_HP = 7.4 Hz 1H, C¹H_b^all), 2.17 (s, 3H, CH₃^tol-P1), 2.06 (br, 1H, C³H_b^all), 2.03 (s, 3H, CH₃^tol-P2), 1.43 (br, 1H, C³H_a^all), 0.83 (s, 3H, SiCH₃^b), −0.35 (s, 3H, SiCH₃^a). ¹³C{¹H} NMR (CD₂Cl₂, 233 K): δ_C 138.6 (d, ²J_CP = 10.2 Hz, C^{1, tol-P1}), 138.0 (d, ²J_CP = 7.3 Hz, C^{1, tol-P2}), 137.1 (C^{2, PhP}), 136.9 (d, ⁵J_CP = 1.1 Hz,C^{4, tol-P1}), 135.9 (d, ⁵J_CP = 2.2 Hz, C^{4, tol-P2}), 135.4 (d, ¹J_CP = 68.3 Hz, C^{1, PhP}), 134.8 (d, ¹J_CP = 59.4 Hz, C^{1, PhP}), 134.77 (d, ¹J_CP = 60.1, Hz, C^{1, PhP}), 134.75 (d, ¹J_CP = 60.7, Hz, C^{1, PhP}), 133.9 (C^{2, tol-P2}), 132.8 (C^{2, PhP}), 132.3 (d, ⁴J_CP = 1.6 Hz, C^{4, PhP}), 132.1 (d, ⁴J_CP = 1.1 Hz, C^{4, PhP}), 131.9 (C^{3, PhP}), 131.3 (C^{2, PhP}), 131.0 (C^{3, PhP}), 130.7 (C^{3, tol-P1}), 129.3 (C^{3, tol-P2}, C^{3, tol-P1}, C^{2, tol-P1}, C^{3, PhP}), 128.8 (C^{2, tol2}), 128.1 (C^{4, PhP}), 127.0 (C^{3, PhP}), 125.7 (C^{4, PhP}), 102.9 (C^{2, all}), 72.1 (d, ²J_CP = 30.5 Hz, C^{1, all}), 43.2 (C^{3, all}), 21.0 (CH₃^tol-P1), 20.9 (CH₃^tol-P2), 2.7 (d, ³J_CP = 2.3 Hz, SiCH₃^a), 2.4 (SiCH₃^b). ³¹P{¹H} NMR (CD₂Cl₂, 233 K): δ_P 30.2 (d, 1P, ²J_PP = 25.8 Hz, SiNP¹), 23.8 (d, 1P, ²J_PP = 25.8 Hz, SiNP²).

Synthesis of [IrCl(η³-C₃H₅)(CN^tBu)(κ²P,P′-SiNP)]Cl (2Cl). A toluene suspension (15 mL) of [IrCl₂(η³-C₃H₅)(κ²P,P′-SiNP)] (1, 114 mg, 0.121 mmol, 942.99 g mol⁻¹) was added with CN^tBu (13.7 μL, 0.121 mmol, 83.13 g mol⁻¹, 0.735 g mL⁻¹). The resulting light yellow suspension was stirred for 24 h, evaporated up to 5 mL and added with hexane (5 mL). The resulting colourless solid was filtered off, washed with hexane, dried in vacuo and finally identified as [IrCl(η³-C₃H₅)(CN^tBu)(κ²P,P′-SiNP)]Cl (2Cl, 85.4 mg, 69% yield). Found: C 56.25, H 5.25, N 4.18. Calcd for C₄₈H₅₄Cl₂IrN₃P₂Si (1026.12 g mol⁻¹): C 56.18; H, 5.30; N, 4.10. ¹H NMR (CDCl₃, 298 K): δ_H 8.03 (m, 1H, p-P¹Ph), 7.92 (dt, 2H, ³J_HH = 7.5, ³J_HP = 3.3 m-P¹Ph), 7.85 (m, 2H, o-P¹Ph), 7.67 (m, 2H, o-P²Ph), 7.57 (t, 1H, ³J_HH = 7.3 p-P²Ph), 7.47–6.99 (15H tot; 2H, o-P¹Ph; 2H, o-P²Ph; 2H, m-P¹Ph, 4H, m-P²Ph; 1H, p-P¹Ph; 1H, p-P²Ph; 1H, C²H^tol-P1; 1H, C²H^tol-P2; 1H, C³H^tol-P2), 6.78 (d, 1H, ³J_HH = 8.3 Hz C³H^tol-P1), 6.66 (d, 1H, ³J_HH = 8.3 Hz, C³H^tol-P1), 6.62 (d, 1H, ³J_HH = 8.2 Hz, C³H^tol-P2), 6.47 (d, 1H, ³J_HH = 8.2 Hz, C²H^tol-P2), 5.43 (d, 1H, ³J_HH = 8.3 Hz, C²H^tol-P1), 4.89 (m, 1H, C²H^all), 3.86 (dd, 1H, ³J_HH = 7.7 Hz, ³J_HP = 4.6 Hz, C¹H_b^all), 3.72 (dd, 1H, ³J_HH = 12.6 Hz, ³J_HP = 7.1 Hz, C¹H_a^all), 2.31 (d, 1H, ³J_HH = 20.3 Hz, C³H_b^all), 2.19 (s, 3H, CH₃^tol-P2), 2.13–1.97 (12H tot; 9H, CN^tBu; 3H, CH₃^tol-P2) 2.00 (br, 1H, C³H_a^all), 0.58 (s, 3H, SiCH₃), −0.33 (s, 3H, SiCH₃). ¹³C{¹H} NMR (CDCl₃, 298 K): δ_C 138.1 (d, ⁵J_CP = 2.2 Hz, C^{4, tol-P2}), 137.7 (d, ⁵J_CP = 2.5 Hz, C^{4, tol-P1}), 137.43 (d, ²J_CP = 9.4 Hz, C^{1, tol-P2}), 137.41 (d, ²J_CP = 7.8 Hz, C^{1, tol-P1}), 135.9 (d, ²J_CP = 10.1 Hz, C^{2, PhP-P2}), 135.0 (d, ¹J_CP = 68.6 Hz, C^{1, PhP-P1}), 133.6 (C^{4, PhP1}) 133.5 (d, ²J_CP = 8.4 Hz, C^{2, PhP1}), 133.2 (d, ²J_CP = 9.3 Hz, C^{2, PhP2}), 133.1 (d, ⁴J_CP = 2.4 Hz, C^{4, PhP2}), 132.4 (C^{4, PhP1}), 132.2 (C^{4, PhP2}), 131.8 (d, ³J_CP = 2.3 Hz, C^{2, tol-P1}), 131.5 (d, ³J_CP = 2.5 Hz, C^{2, tol-P1}), 131.1 (d, ¹J_CP = 64.8 Hz, C^{1, PhP2}), 131.0 (C^{3, tol-P2}), 130.9 (d, ²J_CP = 8.3 Hz, C^{2, PhP-P1}), 130.43 (d, ⁴J_CP = 3.5 Hz, C^{3, tol-P1}), 130.39 (d, ⁴J_CP = 5.4 Hz, C^{3, tol-P2}), 130.0 (d, ³J_CP = 3.0 Hz, C^{2, tol-P2}), 129.9 (d, ³J_CP = 1.9 Hz, C^{2, tol-P2}), 129.9 (d, ³J_CP = 10.7 Hz, C^{3, PhP1}), 129.2 (C^{3, tol-P1}), 128.63 (d, ³J_CP = 11.3 Hz, C^{3, PhP2}), 127.6 (d, ³J_CP = 11.6 Hz, C^{3, PhP1}), 127.4 (d, ³J_CP = 11.5 Hz, C^{3, PhP2}), 108.3 (C^{2, all}), 63.6 (d, ²J_CP = 28.6 Hz, C^{1, all}), 60.1 (C^{3, all}), 31.0 (CH₃CN^tBu), 21.1 (CH₃^tol-P2), 21.0 (CH₃^tol-P1), 3.3 (CH₃Si^down), 2.9 (d, ³J_CP = 2.7 Hz, CH₃Si^up). ³¹P{¹H} NMR (CDCl₃, 298 K): δ_P 28.3 (d, 1P, ²J_PP = 20.9 Hz, SiNP¹), 25.9 (d, 1P, ²J_PP = 20.9 Hz, SiNP²).

Synthesis of [IrCl₂(η¹-C₃H₅)(CN^tBu)(κ²P,P′-SiNP)] (3). A toluene suspension (10 mL) of [IrCl₂(η³-C₃H₅)(κ²P,P′-SiNP)] (1, 83.6 mg, 88.7 μmol, 942.99 g mol⁻¹) was added with CN^tBu (10.0 μL, 88.4 μmol, 83.13 g mol⁻¹, 0.735 g mL⁻¹). After 1 h stirring, the resulting light yellow suspension was evaporated up to 5 mL and added with hexane (5 mL). The resulting colourless solid was filtered off, washed with hexane, dried in vacuo and finally identified as a mixture of 1 and [IrCl₂(η¹-C₃H₅)(CN^tBu)(κ²P,P′-SiNP)] (3) (3 : 1 = 4 : 1, 60.1 mg). NMR data for 3: ¹H NMR (CD₂Cl₂, 233 K): δ_H 7.62 (m, 4H, o-PPh), 7.49–7.33 (10H tot: 4H, o-PPh; 4H, m-PPh, 2H, p-PPh), 7.25 (t, 2H, ³J_HH = 7.2 Hz, p-PPh), 7.10 (t, 4H, ³J_HH = 7.2 Hz, m-PPh), 6.74–6.68 (5H tot: 1H, C²H^all, 2H, C²H^tol; 2H, C³H^tol), 6.59 (d, 2H, ³J_HH = 8.2 Hz, C³H^tol), 6.34 (d, 2H, ³J_HH = 8.2 Hz, C²H^tol), 5.18 (d, 1H, ³J_{HH trans} = 17.1 Hz, C³H^{all trans}), 5.03 (d, 1H, ³J_{HH cis} = 9.7 Hz, C³H^{all cis}), 3.34 (br, 2H, C¹H^all), 2.09 (s, 6H, CH₃^tol), 1.06 (s, 9H, CN^tBu), 0.47 (s, 3H, CH₃Si), −0.05 (s, 3H, CH₃Si); ¹³C{¹H} NMR (CD₂Cl₂, 233 K): δ_C 148.2 (C^{2, all}), 138.6 (t, ³J_CP = 4.3 Hz, C^{1, tol}), 136.7 (t, ²J_CP = 4.4 Hz, C^{2, PhP}), 136.5 (C^{4, tol}), 133.4 (C^{2, tol}), 133.1 (t, ²J_CP = 4.1 Hz, C^{2, PhP}), 132.3 (C^{2, tol}), 130.7 (C^{2, PhP}), 130.5 (C^{2, PhP}), 129.1 (C^{3, tol}), 127.4 (t, ³J_CP = 5.4 Hz, C^{3, PhP}), 126.0 (t, ³J_CP = 5.4 Hz, C^{3, PhP}), 108.3 (C^{3, all}), 56.9 (C̲N^tBu), 29.5 (CH₃^CNtBu), 20.9 (CH₃^tol), 5.28 (C^{1, all}), 4.5 (CH₃Si), 3.4 (CH₃Si); ³¹P{¹H} NMR (CD₂Cl₂, 233 K): δ_P 31.9 (2P, SiNP).

Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4). A dichloromethane suspension (8 mL) of [IrCl(cod)(SiNP)] (180 mg, 0.185 mmol, 974.64 g mol⁻¹) was added with potassium acetate (21.7 mg, 0.221 mmol, 98.14 g mol⁻¹). After 20 h stirring, the resulting suspension was filtered, evaporated up to 2 mL and added with hexane (5 mL) affording a light yellow solid which was filtered off, washed with hexane, dried in vacuo and finally identified as [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4, 138 mg, 80% yield). Found: C 61.69, H 5.31, N 3.15. Calcd for C₄₈H₅₁IrN₂P₂Si (938.18 g mol⁻¹): C 61.45, H 5.48, N 2.99. ¹H NMR (CD₂Cl₂, 298 K): δ_H 7.59 (m, 4H, o-PPh), 7.42–7.27 (8H tot; 4H, m-PPh, 4H, p-PPh), 7.08 (t, 4H, ³J_HH = 7.3 Hz, m-PPh), 7.95 (m, 4H, o-PPh), 6.82 (d, 4H, ³J_HH = 8.1 Hz, C³H^tol), 6.57 (d, 4H, ³J_HH = 8.1 Hz, C²H^tol), 3.60 (br, 2H, C^sp2H^cod), 2.60 (br, 2H, C^sp2H^cod), 2.21 (s, 6H, CH₃^tol), 2.03–1.62 (m, 8H, C^sp3H^cod), 0.14 (t, 2H, ³J_HP = 9.3 Hz, SiCH₂Ir), −0.83 (s, 3H, SiCH₃). ¹³C{¹H} NMR (CD₂Cl₂, 298 K): δ_C 143.4 (t, ²J_CP = 5.8 Hz, C^{1, tol}), 136.4 (dd, ¹J_CP = 47.8 Hz, ³J_CP = 7.8 Hz, C^{1, PhP1}), 135.2 (t, ²J_CP = 6.3, C^{2, PhP}), 134.8 (C^{4, tol}), 133.4 (dd, ²J_CP = 6.8 Hz, C^{2, PhP}), 130.7 (C^{2, tol}), 129.9 (C^{4, PhP}), 129.5 (C^{4, PhP}), 127.9 (C^{3, PhP}), 76.0 (C^{sp2 cod}), 56.8 (dd, ³J_CP = 42.7 Hz, ³J_CP = 16.7 Hz, C^{sp2 cod}), 34.7 (C^{sp3 cod}), 33.8 (C^{sp3 cod}), 21.3 (CH₃^tol), −0.06 (t, ³J_CP = 7.5 Hz, CH₃Si), −14.7 (t, ²J_CP = 4.2 Hz, CH₂Si). ³¹P{¹H} NMR (CD₂Cl₂, 298 K): δ_P 47.1 (s, SiNP).

Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃][PF₆]₂ (5[PF₆]₂). An acetonitrile suspension (10 mL) of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4, 112 mg, 0.119 mmol, 938.18 g mol⁻¹) was added with ferrocenium hexafluorophosphate (79.1 mg, 0.239 mmol, 331.00 g mol⁻¹). After 2 h stirring, the resulting orange solution was evaporated up to 4 mL and added with hexane (5 mL) affording a colorless solid which was filtered off, washed with diethyl ether (3 × 5 mL), dried in vacuo and finally identified as [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃][PF₆]₂ (5[PF₆]₂, 105 mg, 71% yield). Found: C 44.62, H 3.92, N 5.59. Calcd for C₄₆H₄₈F₁₂IrN₅P₄Si (1243.09 g mol⁻¹): C 44.45, H 3.89, N 5.63. ¹H NMR (CD₂Cl₂, 298 K): δ_H 7.62 (12H tot, 4H, o-PPh; 4H, m-PPh; 4H, p-PPh), 7.24 (t, 4H, ³J_HH = 7.8 Hz, m-PPh), 7.10 (dd, 4H, ³J_HP = 11.8 Hz, ³J_HH = 7.8 Hz, o-PPh), 6.92 (d, 4H, ³J_HH = 8.2 Hz, C³H^tol), 6.52 (d, 4H, ³J_HH = 8.2 Hz, C²H^tol), 2.44 (s, 3H, CH₃CN^ax), 2.24 (s, 6H, CH₃^tol), 1.98 (s, 6H, CH₃CN^eq), 1.46 (t, ³J_HP = 1.6 Hz, 2H, SiCH₂Ir), 0.36 (s, 3H, SiCH₃). ¹³C{¹H} NMR (CD₂Cl₂, 298 K): δ_C 137.3 (C^{4, tol}), 137.2 (t, ²J_CP = 4.3 Hz, C^{1, tol}), 134.5 (t, ²J_CP = 5.3, C^{2, PhP}), 133.6 (C^{4, PhP}), 133.2 (C^{4, PhP}), 133.04 (t, ²J_CP = 4.9 Hz, C^{2, PhP}), 131.6 (d, ¹J_CP = 65.5, C^{2, PhP}), 130.8 (C^3,tol), 129.8 (t, ³J_CP = 5.8, C^{3, PhP}), 129.3 (t, ³J_CP = 5.9, C^{3, PhP}), 129.01 (t, ³J_CP = 2.0, C^{2, tol}), 126.6 (d, ¹J_CP = 70.2 Hz, C^{1, PhP}), 122.8 (CH₃C̲N^ax), 121.7 (t, ³J_CP = 9.7, CH₃C̲N^eq), 21.2 (CH₃^tol), 3.9 (C̲H₃CN^ax), 3.2 (C̲H₃CN^eq), −1.32 (t, ³J_CP = 6.8 Hz, CH₃Si), −19.6 (t, ²J_CP = 4.0 Hz, CH₂Si). ³¹P{¹H} NMR (CD₂Cl₂, 298 K): δ_P 18.2 (2P, SiNP), −145.5 (hept, 2P, ¹J_PF = 710.8 Hz, PF₆⁻).

Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃][CF₃SO₃]₂ (5[CF₃SO₃]₂). An acetonitrile suspension (10 mL) of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4, 304 mg, 0.324 mmol, 938.18 g mol⁻¹) was added with ferrocenium triflate (217 mg, 0.648 mmol, 335.10 g mol⁻¹). The work up was similar to that described for 5[PF₆]₂, yielding [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃][CF₃SO₃]₂ as a colourless solid (5[CF₃SO₃]₂, 303 mg, 75% yield). Found: C 45.99, H 3.92, N 5.55. Calcd for C₄₈H₄₈F₆IrN₅O₆P₂S₂Si (1251.30 g mol⁻¹): C 46.07, H 3.87, N 5.60. ¹H, ¹H{³¹P} and ³¹P{¹H} NMR of 5[CF₃SO₃]₂ are similar to those given for 5[PF₆]₂.

Reaction of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with I₂. A dichloromethane solution (10 mL) of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4, 121 mg, 0.129 mmol, 938.18 g mol⁻¹) was added with I₂ (32.7 mg, 0.129 mmol, 253.81 g mol⁻¹) at 233 K. The resulting yellow solution was stirred for 30 min, evaporated up to 3 mL and added with hexane (5 mL) affording an orange solid which was filtered off, washed with hexane, dried in vacuo finally identified as a mixture of [IrI(η²,η³-C₈H₁₁)(κ²P,P′-SiNP)]I (6I) and [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃]I (7aI + 7bI) and (110 mg, 6I : 7aI : 7bI = 54 : 33 : 13, ³¹P). A small amount (22 mg) of analytically and spectroscopically pure 6I was recovered by crystallization in acetonitrile/Et₂O. Found: C 48.89, H 4.32, N 2.29. Calcd for C₄₈H₅₁I₂IrN₂P₂Si (1191.99 g mol⁻¹): C 48.37, H 4.31, N 2.35. ¹H NMR (CD₂Cl₂, 298 K): δ_H 8.08–7.83 (br, 4H tot; 2H, o-P¹Ph; 2H, o-P²Ph), 7.69–7.60 (2H tot, 1H, p-P¹Ph; 1H, p-P²Ph), 7.47 (td, 2H, ³J_HH = 7.9 Hz, ⁴J_HP = 2.8 Hz, m-P²Ph), 7.43–7.31 (8H tot; 4H, m-P¹Ph; 2H, m-P²Ph; 1H, p-P¹Ph; 1H, p-P²Ph), 7.27 (m, 2H, o-P¹Ph), 7.19 (dd, 2H, ³J_HP = 11.1 Hz, ³J_HH = 7.9 Hz, o-P²Ph), 7.03 (dt, 1H, ³J_HH = 8.0 Hz, ⁴J_HP = 2.0 Hz, C²H^tol-P1), 6.96 (dt, 1H, ³J_HH = 8.2 Hz, ⁴J_HP = 1.7 Hz, C²H^tol-P2), 6.88 (dd, 1H, ³J_HH = 8.0 Hz, ⁵J_HP = 1.0 Hz, C³H^tol-P1), 6.74 (dd, 1H, ³J_HH = 8.2 Hz, ⁵J_HP = 0.9 Hz, C³H^tol-P2), 6.64 (dd, 1H, ³J_HH = 8.2 Hz, ⁵J_HP = 1.2 Hz, C³H^tol-P1), 6.52 (dd, 1H, ³J_HH = 8.2 Hz, ⁵J_HP = 1.4 Hz, C³H^tol-P2), 6.09 (dt, 1H, ³J_HH = 8.2 Hz, ⁴J_HP = 1.9 Hz, C²H^tol-P1), 6.06 (dt, 1H, ³J_HH = 8.2 Hz, ⁴J_HP = 1.7 Hz, C²H^tol-P2), 5.08 (m, 1H, C¹H^cod), 4.17 (dd, 1H, ³J_HP = 14.1 Hz, ³J_HH = 6.0 Hz, C²H^cod), 3.89 (m, 1H, C³H^cod), 3.67–3.59 (2H tot; 1H, C⁵H^cod; 1H, C⁶H^cod), 3.39 (br, 1H, C⁴H^cod), 3.35–3.19 (2H tot; 1H, C⁴H^cod; 1H, C⁷H^cod), 3.03 (m, 1H, C⁷H^cod), 2.48 (m, 1H, C⁸H^cod), 2.16 (s, 3H, CH₃^tol-P1), 2.06 (s, 3H, CH₃^tol-P2), 1.69 (m, 1H, C⁸H^cod), 1.28 (s, 3H, CH₃Si), −0.35 (s, 3H, CH₃Si). ¹³C NMR (CD₂Cl₂, 298 K): δ_C 138.9 (d, ²J_CP = 9.1 Hz, C^{1, tol-P2}), 138.3 (d, ²J_CP = 8.3 Hz, C^{1, tol-P1}), 138.0 (d, ⁵J_CP = 1.5 Hz, C^{4, tol-P1}), 137.8 (d, ⁵J_CP = 1.7 Hz, C^{4, tol-P2}), 135.2 (br, C^{2, PhP1}; C^{2, PhP2}), 134.9 (d, ²J_CP = 12.1 Hz, C^{2, PhP2}), 133.10 (C^{4, PhP1}), 133.03 (C^{4, PhP2}), 132.83 (d, ³J_CP = 2.4 Hz, C^{2, tol-P1}), 132.75 (d, ²J_CP = 9.2 Hz, C^{2, PhP2}), 132.5 (C^{2, tol-P2}), 132.4 (d, ³J_CP = 3.1 Hz, C^{2, tol-P2}), 131.9 (d, ³J_CP = 3.0 Hz, C^{2, tol-P1}), 130.18 (C^{3, tol-P1}), 130.10 (C^{3, tol-P1}), 130.03 (C^{3, tol-P2}), 129.96 (d, ³J_CP = 11.6 Hz, C^{3, PhP2}), 129.88 (C^{3, tol-P2}), 129.4 (d, ³J_CP = 11.1 Hz, C^{3, PhP1}), 128.4 (d, ³J_CP = 11.3 Hz, C^{3, PhP2}), 128.2 (d, ³J_CP = 10.3 Hz, C^{3, PhP2}), 111.7 (d, ²J_CP = 14.3 Hz, C^{6, cod}), 92.2 (C^{2, cod}), 83.6 (d, ²J_CP = 28.1 Hz, C^{1, cod}), 64.0 (dd, ²J_CP = 5.4; 2.9 Hz, C^{5, cod}), 34.5 (d, ²J_CP = 3.4 Hz, C^{3, cod}), 33.3 (d, ³J_CP = 4.5 Hz, C^{7, cod}), 28.2 (C^{8, cod}), 21.32 (CH₃^tol-P1), 21.23 (CH₃^tol-P2), 19.8 (C^{4, cod}), 5.6 (CH₃Si), 5.0 (CH₃Si). ³¹P NMR (CD₂Cl₂, 298 K): δ_P 32.1 (d, ²J_PP = 25.3 Hz, P¹), 23.2 (d, ²J_PP = 25.3 Hz, P²).

Synthesis of [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃][PF₆] (7aPF₆ + 7bPF₆). Method 1. An acetone solution (5 mL) of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (4, 98.5 mg, 0.105 mmol, 938.18 g mol⁻¹) was added with ferrocenium hexaphluorophosphate (69.5 mg, 0.210 mmol, 331.00 g mol⁻¹). After 1 h stirring, sodium iodide (23.6 mg, 0.157 mmol, 149.89 g mol⁻¹) was added and the suspension stirred for 1 h. The resulting suspension was filtered, and the solution evaporated up to 2 mL and added with diethyl ether (5 mL), affording a yellow solid which was filtered off, washed with diethyl ether (2 × 5 mL), dried in vacuo and finally identified as [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃][PF₆] (7aPF₆ + 7bPF₆) (80.9 mg, 71% yield). Method 2. A dichloromethane solution (10 mL) of [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃][PF₆]₂ (5[PF₆]₂, 119 mg, 95.7 μmol, 1243.09 g mol⁻¹) was added with sodium iodide (21.5 mg, 0.143 mmol, 149.89 g mol⁻¹). The resulting yellow suspension was stirred for 1 h, filtered off, evaporated up to 3 mL and added with diethyl ether (5 mL) affording a yellow solid which was filtered, washed with diethyl ether (3 × 5 mL), dried in vacuo and finally identified as [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃][PF₆] (7aPF₆ + 7bPF₆) (90.3 mg, 86% yield). Found: C 43.85, H 3.58, N 2.64. Calcd for C₈₀H₇₈F₆I₃Ir₂N₄P₅Si₂ (2185.68 g mol⁻¹): C 43.96, H 3.60, N 2.56. MS (MALDI+, m/z): calcd for [Ir₂(μ-I)₃{κ³C,P,P′-(SiNP-H)}₂]⁺ 2041.1; found 2040.8 [M]⁺. ¹H NMR (CD₂Cl₂, 298 K): δ_H 7.42–7.14 (12H tot; 4H, o-PPh; 4H, m-PPh; 4H, p-PPh), 7.05–6.90 (8H tot; 4H, o-PPh, 4H, m-PPh), 6.70 (d, 4H, ³J_HH = 7.3 Hz, m-PPh), 7.02–6.90 (m, 4H, o-PPh), 6.82 (d, 4H, ³J_HH = 8.2 Hz, C³H^tol), 6.26 (d, 4H, ³J_HH = 8.2 Hz, C²H^tol), 2.08 (s, 6H, CH₃^tol), 2.05 (s, 2H, SiCH₂Ir), −0.00 (br, 3H, SiCH₃). ¹³C{¹H} NMR (CD₂Cl₂, 298 K): δ_C 140.06 (C^{1, PhP}), 139.4 (C^{1, PhP}), 138.8 (C^{4, tol}), 136.7 (C^{1, tol}), 136.0 (C^{2, PhP}), 133.0 (C^{4, PhP}), 132.5 (d³J_CP = 7.6 Hz, C^{3, PhP}), 130.5 (C^3,tol), 129.6 (C^2,tol), 129.0 (C^{2, PhP}), 128.6 (C^{3, PhP}), 21.5 (CH₃^tol), −0.6 (CH₃Si), −11.7 (CH₂Si). ³¹P{¹H} NMR (CD₂Cl₂, 298 K): δ_P 20.7 (s, SiNP), −144.4 (hept, 1P, ¹J_PF = 710.3 Hz, PF₆⁻).

Synthesis of [Ir{κ³C,P,P′-(SiNP-H)}(η²,η³-C₈H₁₁)][OTf] (8CF₃SO₃). A dichloromethane solution (5 mL) of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] (114 mg, 0.122 mmol, 938.18 g mol⁻¹) was added with methyl trifluoromethylsulphonate (13.9 μL, 0.123 mmol, 164.10 g mol⁻¹, 1.45 g mL⁻¹). After 4 d stirring at room temperature, the solution was evaporated and the residue extracted with acetonitrile/diethyl ether (1 : 20 mL). The solution was dried in vacuo affording a colorless solid finally identified as [Ir{κ³C,P,P′-(SiNP-H)}(η²,η³-C₈H₁₁)][OTf] (8OTf) (59.4 mg, 45% yield). Found: C 54.27, H 4.53, N 2.56. Calcd for C₄₉H₅₀F₃IrN₂O₃P₂SSi (1086.24 g mol⁻¹): C 54.18, H 4.64, N 2.58. ¹H NMR (CD₂Cl₂, 298 K): δ_H 7.90 (ddd, 2H. ³J_HP = 10.4 Hz, ³J_HH = 7.6 Hz, ⁵J_HP = 1.2 Hz, o-P²Ph), 7.82 (ddd, 2H. ³J_HP = 11.2 Hz, ³J_HH = 7.6 Hz, ⁵J_HP = 1.9 Hz, o-P²Ph), 7.65–7.56 (6H tot; 2H, o-P¹Ph; 2H, m-P²Ph; 2H, p-P²Ph), 7.55–7.45 (6H tot; 2H, m-P¹Ph; 2H, m-P²Ph; 2H, p-P¹Ph), 7.07 (td, 2H, ³J_HH = 7.6 Hz, ⁴J_HP = 2.5 Hz, o-P¹Ph), 7.02 (d, 2H, ³J_HH = 8.2 Hz, C³H^tol-P2), 6.70 (d, 2H, ³J_HH = 8.2 Hz, C³H^tol-P1), 6.69 (d, 2H, ³J_HH = 8.2 Hz, C²H^tol-P1), 6.49 (ddd, 2H, ³J_HP = 10.9 Hz, ³J_HH = 7.6 Hz, ⁵J_HP = 1.1 Hz, o-P¹Ph), 6.28 (d, 2H, ³J_HH = 8.2 Hz, C²H^tol-P2), 4.37–4.32 (2H tot; 1H, C²H^cod; 1H, C⁶H^cod), 4.08 (m, 1H, C¹H^cod), 3.76 (m, 1H, C⁵H^cod), 3.38 (m, 1H, C⁴H^cod), 2.94–2.83 (2H tot; 1H, C⁷H^cod; 1H, C⁴H^cod), 2.52 (m, 1H, C⁷H^cod), 2.30 (s, 3H, CH₃^tol-P2), 2.26 (m, 1H, C⁸H^cod), 2.15 (m, 1H, C³H^cod), 2.10 (s, 3H, CH₃^tol-P1), 1.68 (m, 1H, C⁸H^cod), 0.55 (ddd, 1H, ²J_HH = 12.4 Hz, ³J_HP = 8.3 Hz, ³J_HP = 3.0 Hz, SiCH̲^aH^bIr), 0.46 (ddd, 1H, ²J_HH = 12.4 Hz, ³J_HP = 7.0 Hz, ³J_HP = 2.4 Hz, SiCH^aH̲^bIr), 0.12 (s, 3H, SiCH₃). ¹³C{¹H} NMR (CD₂Cl₂, 298 K): δ_C 143.1 (dd, ¹J_CP = 51.5 Hz, ³J_CP = 2.6 Hz, C^{1, PhP1}), 139.2 (d, ²J_CP = 8.0 Hz, C^{1, tol-P1}), 138.3 (d, ²J_CP = 10.0 Hz, C^{1, tol-P2}), 137.4 (d, ⁵J_CP = 1.6 Hz, C^{4, tol-P2}), 136.0 (d, ²J_CP = 11.9 Hz, C^{2, PhP1}), 135.5 (C^{4, tol-P1}), 133.7 (d, ²J_CP = 9.4 Hz, C^{2, PhP2}), 133.3 (d, ²J_CP = 10.7 Hz, C^{2, PhP2}), 133.1 (d, ⁴J_CP = 2.1 Hz, C^{4, PhP1}), 132.7 (d, ⁴J_CP = 2.5 Hz, C^{4, PhP2}), 132.6 (d, ⁴J_CP = 2.4 Hz, C^{4, PhP1}), 131.8 (d, ⁴J_CP = 1.8 Hz, C^{4, PhP1}), 130.9 (d, ⁴J_CP = 2.2 Hz, C^{3, tol-P1}), 130.7 (d, ⁴J_CP = 1.2 Hz, C^{3, tol-P2}), 130.2 (d, ²J_CP = 10.2 Hz, C^{2, PhP1}), 129.9 (C^{2, tol-P1}), 129.7 (d, ³J_CP = 9.9 Hz, C^{3, PhP1}), 129.6 (d, ³J_CP = 8.7 Hz, C^{3, PhP2}), 129.4 (d, ³J_CP = 10.7 Hz, C^{3, PhP2}), 128.9 (d, ³J_CP = 10.6 Hz, C^{3, PhP1}), 128.1 (d, ³J_CP = 4.1 Hz, C^{2, tol2}), 106.1 (d, ²J_CP = 2.0 Hz, C^{2 cod}), 98.8 (C^{6 cod}), 71.0 (d, ²J_CP = 35.7 Hz, C^{1 cod}), 53.9 (d, ²J_CP = 3.6 Hz, C^{5 cod}), 49.2 (d, ²J_CP = 17.2 Hz, C^{3 cod}), 34.2 (d, ³J_CP = 5.3 Hz, C^{7 cod}), 29.4 (d, ³J_CP = 3.4 Hz, C^{8 cod}), 21.4 (CH₃^tol-P2), 21.0 (CH₃^tol-P1), 20.5 (d, ³J_CP = 4.5 Hz, C^{4 cod}), −1.6 (t, ³J_CP = 6.9 Hz, CH₃Si), −13.8 (t, ²J_CP = 4.1 Hz, CH₂Si). ³¹P{¹H} NMR (CD₂Cl₂, 298 K): δ_P 35.4 (d, 1P, ²J_PP = 9.1 Hz, SiNP¹), 31.5 (d, 1P, ²J_PP = 9.2 Hz, SiNP²).

DFT calculations. Molecular structure optimizations and frequencies calculations were carried out with the programs Gaussian09 (revision D.01)¹¹ or Gaussian16 (revision C.01)¹² using the method B97D3,¹³ including the D3 dispersion correction scheme by Grimme with Becke–Johnson damping.¹⁴ The def2-SVP¹⁵ basis and pseudo potential were used for all atoms and the “ultrafine” grid was employed in all calculations. Stationary points were characterized by vibrational analysis. The structures were optimized in dichloromethane (298 K, 1 atm) using the CPCM method.¹⁶

Crystal structure determination. X-ray diffraction data were collected at 100(2) K on a Bruker SMART APEX (1, 6I) or APEX DUO (4, 5, and 7aPF₆) CCD diffractometers with graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) using ω rotations. Intensities were integrated and corrected for absorption effects with SAINT-PLUS¹⁷ and SADABS¹⁸ programs, both included in APEX2 package. The structures were solved by the Patterson method with SHELXS-97 ¹⁹ and refined by full matrix least-squares on F² with SHELXL-2014,²⁰ under WinGX.²¹ In the case of 6 and 7 the program SQUEEZE²² was used to treat the residual electron density.

Crystal data and structure refinement for 1. C₄₅H₄₉Cl₆IrN₂P₂Si, 1112.79 g mol⁻¹, monoclinic, P2₁/c, a = 9.7848(5) Å, b = 24.1760(13) Å, c = 19.4510(10) Å, β = 91.1030(10)°, V = 4600.4(4) ų, Z = 4, D_calc = 1.607 g cm⁻³, μ = 3.381 mm⁻¹, F(000) = 2224, yellow prism, 0.300 × 0.300 × 0.180 mm³, θ_min/θ_max 1.344/26.373°, index ranges: −12 ≤ h ≤ 12, −30 ≤ k ≤ 30, −24 ≤ l ≤ 24, reflections collected/independent 98 360/9414 [R(int) = 0.0405], T_max/T_min 0.4045/0.3179, data/restraints/parameters 9414/35/536, GooF(F²) = 1.035, R₁ = 0.0304 [I > 2σ(I)], wR₂ = 0.0762 (all data), largest diff. peak/hole 2.050/−1.461 e Å⁻³. CCDC deposit number 2282657.‡

Crystal data and structure refinement for 4. C₉₉H₁₀₈Cl₆Ir₂N₄P₄Si₂, 2131.05 g mol⁻¹, triclinic, P1̄, a = 13.1665(17) Å, b = 13.8662(18) Å, c = 15.261(3) Å, α = 108.940(2)°, β = 90.289(2)°, γ = 118.034(2)°, V = 2284.3(6) ų, Z = 1, D_calc = 1.549 g cm⁻³, μ = 3.231 mm⁻¹, F(000) = 1074, colourless prism 0.320 × 0.200 × 0.070 mm³, θ_min/θ_max 1.437/26.371°, index ranges: −16 ≤ h ≤ 16, −16 ≤ k ≤ 17, −19 ≤ l ≤ 18, reflections collected/independent 20 795/9338 [R(int) = 0.0354], T_max/T_min 0.5490/0.4262, data/restraints/parameters 9338/1/529, GooF(F²) = 1.038, R₁ = 0.0326 [I > 2σ(I)], wR₂ = 0.0847 (all data), largest diff. peak/hole 2.621/−1.325 e Å⁻³. CCDC deposit number 2282655.‡

Crystal data and structure refinement for 5[CF₃SO₃]₂. C₄₈H₄₈F₆IrN₅O₆P₂S₂Si, 1251.26 g mol⁻¹, monoclinic, P2₁/c, a = 17.3156(16) Å, b = 21.0500(19) Å, c = 14.0982(13) Å, β = 93.2640(10)°, V = 5130.4(8) ų, Z = 4, D_calc = 1.620 g cm⁻³, μ = 2.844 mm⁻¹, F(000) = 2504, colourless prism 0.260 × 0.150 × 0.100 mm³, θ_min/θ_max 1.178/28.282°, index ranges: −23 ≤ h ≤ 23, −26 ≤ k ≤ 27, −18 ≤ l ≤ 18, reflections collected/independent 52 030/12 697 [R(int) = 0.0512], T_max/T_min 0.6205/0.4784, data/restraints/parameters 12 697/0/646, GooF(F²) = 1.014, R₁ = 0.0298 [I > 2σ(I)], wR₂ = 0.0598 (all data), largest diff. peak/hole 1.039/−0.685 e Å⁻³. CCDC deposit number 2282656.‡

Crystal data and structure refinement for 6I. C₅₁H₅₇Cl₆I₂IrN₂P₂Si, 723.36 g mol⁻¹, triclinic, P1̄, a = 10.3680(8) Å, b = 14.1270(11) Å, c = 19.6166(16) Å, α = 100.9810(10)°, β = 98.2830(10)°, γ = 103.0900(10)°, V = 2694.2(4) ų, Z = 2, D_calc = 1.783 g cm⁻³, μ = 4.040 mm⁻¹, F(000) = 1412, orange prism, 0.250 × 0.140 × 0.090 mm³, θ_min/θ_max 2.056/26.372°, index ranges −12 ≤ h ≤ 12, −17 ≤ k ≤ 17, −24 ≤ l ≤ 24, reflections collected/independent 39 544/10 963 [R(int) = 0.0353], T_max/T_min 0.5264/0.3558, data/restraints/parameters 10 963/0/540, GooF(F²) = 1.052, R₁ = 0.0372 [I > 2σ(I)], wR₂ = 0.0949 (all data), largest diff. peak/hole 2.043/−1.903 e Å⁻³. CCDC deposit number 2282659.‡

Crystal data and structure refinement for 7aPF₆. C₈₇H₉₄Cl₂F₆I₃Ir₂N₄P₅Si₂, 2356.69 g mol⁻¹, monoclinic, P2₁/n, a = 21.602(9) Å, b = 18.519(8) Å, c = 22.985(10) Å, β = 104.342(8)°, V = 8908(7) ų, Z = 4, D_calc = 1.757 g cm⁻³, μ = 4.260 mm⁻¹, F(000) = 4592, yellow prism 0.300 × 0.230 × 0.180 mm³, θ_min/θ_max 1.158/25.027°, index ranges −25 ≤ h ≤ 25, −21 ≤ k ≤ 22, −25 ≤ l ≤ 27, reflections collected/independent 60 741/15 721 [R(int) = 0.0406], T_max/T_min 0.3444/0.2500, data/restraints/parameters 15 721/4/913, GooF(F²) = 1.016, R₁ = 0.0303 [I > 2σ(I)], wR₂ = 0.0753 (all data), largest diff. peak/hole 2.080/−1.144 e Å⁻³. CCDC deposit number 2282658.‡

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

Financial support from the Spanish Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033, under the project PID2019-103965GB-I00, and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42_23R) is gratefully acknowledged.

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Footnotes

† Dedicated to Prof. Guido Pampaloni, mentor and friend, on the occasion of his retirement, in recognition of his remarkable contributions to coordination and organometallic chemistry, and his extraordinary commitment to the education of generations of chemists.

‡ Electronic supplementary information (ESI) available: ¹H, ¹³C{¹H}-apt and ³¹P{¹H} NMR spectra. Coordinates of calculated structures (xyz). CCDC 2282655–2282659. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d3dt02361c

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