(Dinitrogen)molybdenum Complexes Supported by Asymmetric Silicon-Centered Tripod Ligands: Steric and Electronic Influences on the Coordination of Mono- and Diphosphine Coligands



A reliable and generally applicable synthetic route for the rational synthesis of silicon-centered tripod ligands with mixed dialkylphosphine/diarylphosphine donors is developed. On the basis of this protocol, two new asymmetric SiPPP′ ligands, SiPMe2PPh and SiPMe2PiPr, were prepared and employed for the synthesis of (dinitrogen)molybdenum complexes of the types [Mo(N2)(SiPPP′)(P2)] [P2 = (diphenylphosphino)methane (dppm), (dimethylphosphino)methane (dmpm), or two PMe2Ph] and [Mo(N2)2(SiPPP′)(PMe2Ph)]. The constitution of the complexes is elucidated by 31P NMR spectroscopy and analyzed on the basis of steric and electronic factors. The activation of N2 in the synthesized dinitrogen complexes is determined by IR spectroscopy and correlated with the donor/acceptor properties of the phosphine coligands.