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

Synthesis and reactivity of PC(sp3)P-pincer iridium complexes bearing a diborylmethyl anion

Novel PCP-pincer iridium complexes bearing a diborylmethyl anion were synthesized. Strong σ-electron-donation to the metal and significant π-backdonation from the metal to boron atoms at the β-position were observed both experimentally and computationally. H/D exchange of the aromatic C-H bond proceeded smoothly and, in addition, the α-methine-hydrogen between boron atoms was found to be replaced with deuterium in benzene-d₆ solution possibly through diborylcarbene metal complexes as intermediates.

Tuning Ruthenium Carbene Complexes for Selective P-H Activation through Metal-Ligand Cooperation

The use of iminophosphoryl‐tethered ruthenium carbene complexes to activate secondary phosphine P−H bonds is reported. Complexes of type [(p‐cymene)‐RuC(SO₂Ph)(PPh₂NR)] (with R = SiMe₃ or 4‐C₆H₄−NO₂) were found to exhibit different reactivities depending on the electronics of the applied phosphine and the substituent at the iminophosphoryl moiety. Hence, the electron‐rich silyl‐substituted complex undergoes cyclometallation or shift of the imine moiety after cooperative activation of the P−H bond across the M=C linkage, depending on the electronics of the applied phosphine. Deuteration experiments and computational studies proved that cyclometallation is initiated by the activation process at the M=C bond and triggered by the high electron density at the metal in the phosphido intermediates. Consistently, replacement of the trimethylsilyl (TMS) group by the electron‐withdrawing 4‐nitrophenyl substituent allowed the selective cooperative P−H activation to form stable activation products.

Carbocyclic pincer carbene complexes of ruthenium: syntheses and reversible hydrogenation

The ruthenium carbene pincer complex 2 was synthesized treating the benzo annulated cycloheptatriene bisphosphine 1 with RuCl₃. Addition of three equivalents of hydrogen to the carbocyclic carbene complex 2 was achieved in reaction of 2 with hydrogen at elevated temperatures. Hydrogenated complex 4, exhibiting a rigid chair conformation in solution, was dehydrogenated by heating a toluene solution of complex 4 to reflux for 5-7 d. In reaction with ethylene, complex 4 transfers one equivalent of hydrogen, forming ethane and alkyl complex 5.

Access to and Reactivity of Fe0 , Fe-I , FeI , and FeII PCcarbene P Pincer Complexes

Despite their promising metal-ligand cooperative reactivity, PC_carbene P pincer ligands are rarely reported for first-row transition-metal centres. Using a dehydration methodology, we report access to an Fe⁰ PC_carbene P pincer complex (1) that proceeds via an isolated α-hydroxylalkyl hydrido complex (3). Reversible carbonyl migration to the carbene position in 1 is found to allow coordination chemistry and E-H bond addition (E=H, B, Cl) across the iron-carbene linkage, representing a unique mechanism for metal-ligand cooperativity. The PC_carbene P pincer ligand is also found to stabilize formal Fe^II , Fe^I , and Fe^-I oxidation states, as demonstrated with synthesis and characterization of the complexes [11-X][BAr^F ₂₀ ] (X=Br, I), 12, and K[13]. Compound K[13] is found to be highly reactive, and abstracts hydrogen from a range of aliphatic C-H sources. Computational analysis by DFT suggests that the formal Fe^I and Fe^-I complexes contain significant carbene radical character. The ability of the PC_carbene P ligand scaffold to partake in metal-ligand cooperativity and to support a range of iron oxidation states renders it as potentially useful in many catalytic applications.

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy production. In particular, pincer-type ligation shows promising properties in terms of long-term stability and selectivity, as well as allowing for mild reaction conditions and low catalyst loading. Indeed, pincer complexes have been applied to a plethora of sustainable chemical processes, such as hydrogen release, CO2 capture and conversion, N2 fixation, and biomass valorization for the synthesis of high-value chemicals and fuels. In this work, we show the main advances of the last five years in the use of pincer transition metal complexes in key catalytic processes aiming for a more sustainable chemical and energy production.

Catalytic oxidations by dehydrogenation of alkanes, alcohols and amines with defined (non)-noble metal pincer complexes

The present review highlights the latest developments in the field of transition metal-catalysed oxidations, in particular C–C–, C–O– and C–N-bond dehydrogenations.

Transfer-dehydrogenation of secondary alcohols catalyzed by manganese NNN-pincer complexes

Novel catalytic systems based on pentacarbonylmanganese bromide and stable NNN-pincer ligands are presented for the transfer-dehydrogenation of secondary alcohols to give the corresponding ketones in good to excellent isolated yields.

Mesityl(amidinato)tetrylenes as ligands in iridium(i) and iridium(iii) complexes: silicon versus germanium and simple κ1-coordination versus cyclometallation

The reactivity of the germylene Ge(^tBu₂bzam)Mes with [Ir₂(μ-Cl)₂(η⁴-cod)₂] and [Ir₂Cl₂(μ-Cl)₂(η⁵-Cp*)₂] differs considerably from that previously communicated for the isostructural silylene Si(^tBu₂bzam)Mes.

Cooperative bond activation reactions with carbene complexes

This review highlights the recent advances in the application of carbene complexes in bond activation reactions via metal–ligand cooperation.

Cationic PCP iridaepoxide and carbene complexes for facile water elimination and activation processes

Pathways for water activation and elimination at cationic iridium PCP pincer compounds are explored.

Facile generation of iridium PCcarbeneP pincer complexes via water elimination from an alcohol proligand

We report the facile generation of Ir PC_carbeneP pincer systems.