The kinetics of hydride transfer from Re( R bpy)-(CO) 3 H (bpy = 4,4′-R-2,2′-bipyridine; R = OMe, t Bu, Me, H, Br, COOMe, CF 3 ) to CO 2 and seven different cationic N-heterocycles were determined. Additionally, the thermodynamic hydricities of complexes of the type Re( R bpy)(CO) 3 H were established primarily using computational methods. Linear free-energy relationships (LFERs) derived by correlating thermodynamic and kinetic hydricities indicate that, in general, the rate of hydride transfer increases as the thermodynamic driving force for the reaction increases. Kinetic isotope effects range from inverse for hydride transfer reactions with a small driving force to normal for reactions with a large driving force. Hammett analysis indicates that hydride transfer reactions with greater thermodynamic driving force are less sensitive to changes in the electronic properties of the metal hydride, presumably because there is less buildup of charge in the increasingly early transition state. Bronsted α values were obtained for a range of hydride transfer reactions and along with DFT calculations suggest the reactions are concerted, which enables the use of Marcus theory to analyze hydride transfer reactions involving transition metal hydrides. It is notable, however, that even slight perturbations in the steric properties of the Re hydride or the hydride acceptor result in large deviations in the predicted rate of hydride transfer based on thermodynamic driving forces. This indicates that thermodynamic considerations alone cannot be used to predict the rate of hydride transfer, which has implications for catalyst design.

The kinetics of carbon dioxide insertion into a pincer-supported palladium methyl complex are studied. The complex inserts carbon dioxide at room temperature, and we explore both solvent and Lewis acid effects on carbon dioxide insertion.

A square planar platinum­(II) carbene complex [{PC­(sp2)­P}H­Pt­(PMe3)] ([PC­(sp2)­P]H = (bis­[2-(di-iso-propyl­phos­phino)­phenyl]­meth­ylene) was synthesized through the dehydrohalogenation of [{PC­(sp3)­HP}H­PtCl] in a microwave reactor. The tert-butyl substituted analogue, [{PC­(sp2)­P} tBu­Pt­(PMe3)] ([PC­(sp2)­P] tBu = bis­[2-(di-iso-propyl­phos­phino)-4-tert-butyl­phenyl]­meth­ylene), was synthesized via an analogous route. The nucleophilic nature of the carbene carbon was confirmed through DFT calculations and reactivity with HCl. Additionally, [{PC­(sp2)­P}H­Pt­(PMe3)] was treated with 0.5 equiv of I2 to generate a paramagnetic product, [{PC­(sp2)­P}H­PtI]. The Evans method and EPR spectroscopy revealed that a one-electron oxidation occurred at the carbene carbon, thus generating a persistent radical carbene.

The synthesis of a range of PBP supported palladium pincer complexes with different alkyl ligands is described. The rates of CO2 insertion into the alkyl group are quantified and rationalized based on the identity of the alkyl ligand.