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Abstract

Multiple bonding in the terminal phosphido complex [Ru(PCy₂)(η⁵-indenyl)(PPh₃)] (2a) is clearly demonstrated by solution, solid-state, and computational studies. Reactions of this dark blue, half-sandwich complex with CO, MeI, HNEt₃Cl, HCl, NH₄PF₆, H₂, and Et₃SiH demonstrate an unusual range of behavior resulting from combined coordinative unsaturation at Ru, high nucleophilicity/basicity of the phosphido P, and π-character of the Ru−P interaction. The terminal, π-bound phosphido structure is general for a range of PR₂ species (R = Prⁱ (2b), Ph (2c), Tol^p (2d)). The very reactive diarylphosphido analogues 2c,d have been observed spectroscopically at low temperatures and can be trapped quantitatively as their CO adducts, [Ru(PAr₂)(η⁵-indenyl)(CO)(PPh₃)] (3c,d), in which the Ru−P bond order is reduced to 1. Complex 2a and its analogue [Ru(PPrⁱ₂)(η⁵-indenyl)(PPh₃)] (2b) are consistently isolated with ∼15% of their structural isomers, the ruthenium hydrido phosphaalkenes 9a,b, resulting from an apparent 1,2-H shift.