Cp-runthenium chemistry of donor-substituted indene and indenide ligands

Pentamethylcyclopentadienyl-ruthenium (Cp*Ru) compounds constitute an important class of reactive organometallic complexes. The established utility of coordinatively unsaturated Cp*Ru species in a range of challenging stoichiometric and catalytic E-H bond activation processes (where E = any main group element) has led to a search for new Cp*Ru complexes that exhibit novel or improved reactivity properties. Described herein is the application of P,N-substituted indene and indenide ligands to provide structurally related cationic and zwitterionic Cp*Ru species. A pursuit of the first coordinatively unsaturated Cp*Ru(kappa2-P,N)+ complex resulted in reversible metalation of one of the methyl substituents of the amine donor. In combination with this dynamic process, the lability of the {NMe2} fragment of the supporting ligand of this cation permits facile double geminal Si-H bond activation in silane substrates; these findings provide experimental support for a key step in a recently proposed alkene hydrosilylation mechanism. Also reported is the facile isomerization of a structurally related, unsaturated zwitterion to a Cp*Ru(H)(kappa 2-P,Carbene) complex by way of an apparent double geminal C-H bond activation process that is enabled by the proton-accepting ability of the indenide unit in the backbone of the ancillary ligand. Spectroscopic investigations provided evidence for the reversibility of the second C-H activation step, which represents an unusual example of reversible alpha-elimination at Ru. As well, reactivity studies involving the Cp*Ru(H)(kappa2 -P,Carbene) complex have revealed Si-H and B-H bond activations. Utilizing the Cp*Ru hydridocarbene complex as a precursor, an unsaturated Cp*Ru(kappa2-P,Carbene) zwitterion was targeted, which instead led to preparation of a Cp*Ru(kappa3 -P,C,Carbene) complex. Reactivity and spectroscopic investigations demonstrated that this complex provides access to the intended zwitterionic Cp*Ru(kappa2-P,Carbene) by way of facile and reversible Ru-C(sp3) cleavage. Also discussed are attempts to synthesize a related neutral, coordinatively unsaturated Cp*Ru(kappa 2-P,O) complex; in the course of these studies, the isolation of a functional precursor to the target complex was achieved, as well as E-H bond activation involving the {Ru-O} linkage.