PC(sp³)P pincer carbonyl complexes of iridium(i), and iridium(iii)

Abstract

The previously reported complex trans-[IrHCl{cis-1,3-bis-(di-tert-butylphosphino)methyl}cyclohexane] (2) forms the 18-electron carbonyl compound anti-[Ir(CO)HCl{cis-1,3-bis-((di-tert-butylphosphino)methyl)} cyclohexane] (5a) upon reaction with 1 atm CO. The structural isomer syn-[IrH(CO)Cl{cis-1,3-bis-((ditert-butylphosphino)methyl)}cyclohexane] (5b) is obtained directly upon complexation of the ligand (1) with IrCl 3 $H 2 O in refluxing DMF. syn-5b is the first iridium aliphatic pincer complex with this orientation of the hydrogens and is the thermodynamically more stable isomer. Both compounds 5a and 5b afford the Ir(I) complex trans-[Ir(CO){cis-1,3-bis-((di-tert-butylphosphino)methyl)}cyclohexane] (4) upon treatment with KO t Bu. Complex 4 was also synthesised in a more straightforward fashion from the previously known terminal nitrogen complex trans-[Ir(N 2 ){cis-1,3-bis-((di-tert-butylphosphino)-methyl)} cyclohexane] (3) under atmospheric CO. The complexes 4, 5a and 5b were characterised spectroscopically and in the solid state. IR data point to a more electron rich metal centre as compared to the corresponding aromatic complexes.

The underappreciated influence of ancillary halide on metal–ligand proton tautomerism

“…For the 6 complexes with H and CO trans to each other, d Ir-H (t) is reported between À5 and À10, and 2 J H-P between 14-18 Hz. [45][46][47][48][49][50][51] With d Ir-H (t) À17.22 and 2 J H-P ¼ 12 Hz for the neutral [H-L Ir-Cl], the data are most consistent with H and Cl trans to each other (as depicted in Scheme 1).…”

“…31 To conrm that the major set of 1 H NMR spectral signals are correctly attributed to the ionic species [ LH Ir][Cl] that was observed in the solid state, the related ionic compound [ LH Ir] [PF 6 ] was synthesized. As hexauorophosphate is a weakly coordinating anion, 32 34 In the 15 examples where H and X are trans to each other, [35][36][37][38][39][40][41][42][43][44][45] the d Ir-H (t) is observed between À15 to À20 with 2 J H-P < 15 Hz. For the 6 complexes with H and CO trans to each other, d Ir-H (t) is reported between À5 and À10, and 2 J H-P between 14-18 Hz.…”

Cyclohexane-Based Phosphinite Iridium Pincer Complexes: Synthesis, Characterization, Carbene Formation, and Catalytic Activity in Dehydrogenation Reactions

“…An AMX system in the 31 P­{ 1 H} NMR spectrum of 11b points to a desymmetrized structure (high-field hydride is not decoupled); the presence of 13 C NMR signals in the olefin region (154.5 and 127.5 ppm) which reveal a resolvable C–H coupling with the hydride unambiguously point to migration of one of the β-hydrogens to Ir with formation of a C–C double bond. A hydride resonance at −17.96 appears as a doublet of doublets; such chemical shifts are typical for a hydride trans to a weak-field ligands like Cl (for instance, −18.7 ppm for phosphine complex (PCyP)­IrH­(CO)­Cl) . In agreement, a 2 J CH of 4 Hz between Ir–H and CO indicates a mutual cis arrangement of these ligands .…”

Poison or Promoter? Investigating the Dual-Role of Carbon Monoxide in Pincer-Iridium-Based Alkane Dehydrogenation Systems via Operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy

“…The characteristic differences between the present work and previously explored analogous solution-phase chemistry 25,27 are higher temperatures and the presence of a carbonylbound catalytic resting state. While the chemistry of pincer-iridium carbonyl complexes has been explored in some detail, [71][72][73][74][75] these complexes have generally been treated as quintessentially inactive toward alkane dehydrogenation, at least at the temperatures accessible by these catalysts.…”