Indenyl Hemilability: Unveiling a Masked (η⁵-C₅Me₅)Ru(κ²-<i>P</i>,<i>C</i>arbene) Zwitterion Via Facile and Reversible Ru−C(sp³) Bond Cleavage

Data obtained from dynamic NMR investigations and reactivity studies revealed that the isolable, 18-electron Cp*Ru(κ3-P,C,C′) complex 3 provides access to the reactive, coordinatively unsaturated Cp*Ru(κ2-P,C) zwitterionic intermediate 4 by way of an unprecedented and reversible Ru−C(sp3) bond cleavage process that can be described as ‘indenyl hemilability’. Indirect support for the reversible generation of 4 from 3 was obtained through the isolation of adducts of the type 4·L upon treatment of 3 with various L-donor substrates (L = CO, PPh3, PHPh2, 4-dimethylaminopyridine, NH3, piperidine, and 2,6-dimethylaniline). The reactivity observed upon treatment of 3 with E−H containing substrates (H2, iPrOH, Ph3SiH, Ph2SiH2, PhNH2, and pyrrole) can be rationalized in terms of net cooperative substrate activation involving the Lewis acidic metal fragment and the Lewis basic indenide unit in the reactive intermediate 4. In the apparent reaction of 4 with PHPh2 and PH2Ph, an unusual ancillary ligand rearrangement involving the net metathesis of P−H and C−N bonds was observed, resulting in the formation of zwitterionic Cp*Ru(=CH(NHMe))(κ2-P,P) complexes that feature the first examples of κ2-P,P-indenide ligation.