Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Unravelling strong temperature-dependence of JHD in transition metal hydrides: solvation and non-covalent interactions versus temperature-elastic H-H bonds

A number of transition metal hydrides reveal intriguing temperature-dependent JHD in their deuterated derivatives and possibly the temperature dependent hydrogen-hydrogen distance (r(H-H)) as well. Previously, theoretical studies rationalized JHD and r(H-H) changes in such compounds through a "temperature-elastic" structure model with a significant population of vibrational states in an anharmonic potential. Based on the first variable temperature neutron diffraction study of a relevant complex, (p-H-POCOP)IrH2, observation of its elusive counterpart with longer r(H-H), crystallized as an adduct with C6F5I, and thorough spectroscopic and computational study, we argue that the model involving isomeric species in solution at least in some cases is more relevant. The existence of such isomers is enabled or enhanced by solvation and weak non-covalent interactions with solvent, such as halogen or dihydrogen bonds. "Non-classical" hydrides with r(H-H) ≈ 1.0-1.6 Å are especially sensitive to the above-mentioned factors.

Iridium(III) bis(thiophosphinite) pincer complexes: synthesis, ligand activation and applications in catalysis

Iridium(III) bis(thiophosphinite) complexes of the type [(^RPSCSP^R)Ir(H)(Cl)(py)] (^RPSCSP^R = κ³-(2,6-SPR₂)C₆H₃) (R = tBu, iPr, Ph) can be prepared from the ligand precursors 1,3-(SPR₂)C₆H₄ by C-H activation at Ir using [Ir(COE)₂Cl]₂ or [Ir(COD)Cl]₂. Optimisation of the protocol for complexation showed that direct cyclometallation in the absence or presence of pyridine, as well as C-H activation in the presence of H₂ are viable options that, depending on the phosphine substituent furnish the five-coordinate Ir(III) hydride chloride complexes 2-R or the base stabilised species 3-R in good yields. In case of the ^PhPSCSP^Ph ligand, P-S activation results in the formation of a thiophosphine stabilised Ir(III) hydride complex [(^PhPSCSP^Ph)Ir(H)(Cl)(PPh₂SH)] (4). Reaction of 2-tBu with H₂ in the presence of base furnishes an Ir(III) dihydride complex (5) via a labile Ir(III) dihydride-dihydrogen complex (6). All complexes are inactive for transfer dehydrogenation of cyclooctane in the presence of NaOtBu and tert-butylethylene, likely due to decomposition of the Ir complex in the presence of base at higher temperature.

2,6-Bis[bis(1,1-dimethylethyl)phosphinito-κP]phenyl-κC]-trans-chlorohydro(phenylphosphine)iridium(III)

The molecular structure of an iridium complex featuring a phenylphosphine ligand is described. The reaction of (POCOP)IrHCl (1, POCOP = 2,6-(tBu2PO)2C6H3–) with phenylphosphine gives (POCOP)IrHCl(PH2Ph) (2) under mild conditions. The structural features are consistent with a classic pseudo-octahedral iridium compound with three neutral phosphine donors. Compound 1 is unreactive at elevated temperatures and is unreactive toward excess phenylphosphine under the sampled conditions.

Rhodium hydride enabled enantioselective intermolecular C–H silylation to access acyclic stereogenic Si–H

The tremendous success of stereogenic carbon compounds has never ceased to inspire researchers to explore the potentials of stereogenic silicon compounds. Intermolecular C–H silylation thus represents the most versatile and straightforward strategy to construct C–Si bonds, however, its enantioselective variant has been scarcely reported to date. Herein we report a protocol that allows for the enantioselective intermolecular C–H bond silylation, leading to the construction of a wide array of acyclic stereogenic Si–H compounds under simple and mild reaction conditions. Key to the success is (1) a substrate design that prevents the self-reaction of prochiral silane and (2) the employment of a more reactive rhodium hydride ([Rh]-H) catalyst as opposed to the commonly used rhodium chloride ([Rh]-Cl) catalyst. This work unveils opportunities in converting simple arenes into value-added stereogenic silicon compounds.

Construction of chiral organosilicon compounds could have implications in photophysical, biological, and chemical fields, as silicon is isoelectronic with carbon, and can mimic carbon atoms while providing slightly different properties. Here the authors present an intermolecular, enantioselective C–H silylation of heterocycles via rhodium catalysis.

Mono- and dinuclear zirconocene(iv) amide complexes for the catalytic dehydropolymerisation of phenylsilane

Mono- and dinuclear zirconocene amide complexes were tested as catalysts for the dehydropolymerisation of phenylsilane. The dinuclear complex is surprisingly stable, producing mixtures of polysilanes and cyclic oligomers.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

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

Dimer [Ir{P(o-C₆H₄CH₂SiMe₂)₂Ph}(μ-Cl)]₂ featuring tricoordinate phosphinodisilyl ligands dissociates in solution to the reactive 14 electron monomer [Ir(SiPSi)Cl].

An electron poor iridium pincer complex for catalytic alkane dehydrogenation

A novel electron deficient 4,6-bis(trifluoromethyl)-1,3-phenylene diphosphinite ligand 4 was developed and synthesized. Reaction of Ir precursors with ligand 4 gave chloro(hydride) pincer complex 5, which demonstrated a higher TON in alkane dehydrogenation reactions compared to similar phosphinite based pre-catalysts. The formation of cyclooctene (COE) and tert-butylethylene adducts of the 14e catalysts was also studied and the COE adduct is implicated as the resting state of the catalyst. All compounds were characterized by NMR spectroscopy and, in addition, the molecular structures of key complexes were confirmed by X-ray analysis.

Iridium(iii) hydrido complexes for the catalytic dehydrogenation of hydrazine borane

A series of POCOP iridium hydride complexes with differently substituted aryl backbones catalyse the selective release of one equivalent of hydrogen from hydrazine borane.