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

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)(κ2-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. Dissociation of the distal OAc arm, however, leads to a higher energy four-membered (σ-bond metathesis) transition state, while oxidative addition is even higher in energy. For this Ir3+ system, these three mechanisms appear to lie within a continuum in which the participation of the metal center and an H-accepting ancillary ligand are inversely related. The ability of the ancillary ligand to act as a proton acceptor is the key factor in determining which mechanism pertains

N−H versus C−H Activation of a Pyrrole Imine at {Cp*Ir}: A Computational and Experimental Study

Reaction of a pyrrole imine with [IrCl2Cp*]2/NaOAc leads to N−H activation in preference to C−H activation at the pyrrole; however, with the N-methylated ligand C−H activation occurs. Density functional calculations show that N−H bond activation is both kinetically and thermodynamically preferred to C−H activation. Both reactions occur with relatively low energy barriers by an electrophilic agostic interaction with the metal with simultaneous intramolecular hydrogen bonding with acetate leading to deprotonation via a six-membered transition state

N−H versus C−H Activation of a Pyrrole Imine at {Cp*Ir}: A Computational and Experimental Study

Reaction of a pyrrole imine with [IrCl2Cp*]2/NaOAc leads to N−H activation in preference to C−H activation at the pyrrole; however, with the N-methylated ligand C−H activation occurs. Density functional calculations show that N−H bond activation is both kinetically and thermodynamically preferred to C−H activation. Both reactions occur with relatively low energy barriers by an electrophilic agostic interaction with the metal with simultaneous intramolecular hydrogen bonding with acetate leading to deprotonation via a six-membered transition state

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