Highly modular P-OP ligands for asymmetric hydrogenation: synthesis, catalytic activity, and mechanism.

A library of enantiomerically pure P-OP ligands (phosphine-phosphite), straightforwardly available in two synthetic steps from enantiopure Sharpless epoxy ethers is reported. Both the alkyloxy and phosphite groups can be optimized for maximum enantioselectivity and catalytic activity. Their excellent performance in the Rh-catalyzed asymmetric hydrogenation of a wide variety of functionalized alkenes (26 examples) and modular design makes them attractive for future applications.

A computational study of the methanolysis of palladium-acyl bonds.

Density functional calculations suggest that intermolecular attack of methanol may be important in the methanolysis of simple Pd-acyl systems and that the energetics of this process are strongly dependent on the metal coordination environment.

Photochemical isomerization of N-heterocyclic carbene ruthenium hydride complexes: in situ photolysis, parahydrogen, and computational studies.

Low-temperature UV irradiation of the N-heterocyclic carbene complex Ru(IEt2Me2)(PPh3)2(CO)H2 (IEt2Me2 = 1,3-bis(ethyl)-4,5-dimethylimidazol-2-ylidene) leads to a remarkable photoisomerization reaction. By combining in situ photolysis and parahydrogen experiments to characterize the ultimate photoproducts and DFT calculations to interrogate the structures of the key 16-electron intermediates, the importance of both PPh3 and H2 loss pathways has been established.

Electrophilic C-H activation at Cp*Ir: ancillary-ligand control of the mechanism of C-H activation.

Density functional calculations on the low-temperature cyclometalation of dimethylbenzylamine with [IrCl2Cp*]2/NaOAc have characterized a novel electrophilic activation pathway for C-H bond activation. C-H activation occurs from [Ir(DMBA-H)(kappa2-OAc)Cp*]+, and OAc plays a central role in determining the barrier for reaction. Dissociation of the proximal OAc arm sets up a facile intramolecular deprotonation via a geometrically convenient six-membered transition state.

Computational study of the mechanism of cyclometalation by palladium acetate.

Various mechanisms for the cyclometalation of dimethylbenzylamine by palladium acetate have been studied by DFT calculations. Contrary to previous suggestions, the rate-limiting step is the electrophilic attack of the palladium on an ortho arene C-H bond to form an agostic complex rather than a Wheland intermediate. The cyclometalated product is then formed by intramolecular deprotonation by acetate via a six-membered transition state; this step has almost no activation barrier.