A general method of generating agostic interaction between RuII and C–H bonds of tert-butyl, methyl, aryl, heterocyclic or alkenyl groups using azine phosphines

Abstract

Treatment of [RuCl₂(PPh₃)₃]2 with the azine phosphine Z,E-PPh₂CH₂C(Bu^t)N–NC(Me)Bu^t3a, derived from MeC(O)Bu^t, gave the δ-agostic tert-butyl complex mer,trans-[RuCl₂(PPh₃){PPh₂CH₂C(Bu^t)N–NC(Me)Bu^t}]4a, in which all nine hydrogens of the tert-butyl group are agostically interacting with ruthenium on the NMR time-scale at 20°C. The analogous δ-agostic tert-butyl complex mer,trans-[RuCl₂(PPh₃){PPh₂CH₂C(Bu^t)N–NC(H)Bu^t}]4b was also prepared. Treatment of 2 with the symmetrical azine diphosphine Z,Z-PPh₂CH₂C(Bu^t)N–NC(Bu^t)CH₂PPh₂5 gave the δ-agostic tert-butyl complex mer,trans-[RuCl₂(PPh₃){PPh₂CH₂C(Bu^t)N–NC(Bu^t)CH₂PPh₂}]6, in which one of the PPh₂ groups is unco-ordinated. Treatment of 2 with the azine phosphine Z,E-PPh₂CH₂C(Bu^t)N–NC₁₀H₁₆7, derived from pinacolone–fenchone mixed azine, gave the δ-agostic methyl complex mer,trans-[RuCl₂(PPh₃){PPh₂CH₂C(Bu^t)N–NC₁₀H₁₆}]8, in which the methyl group (C¹⁰H₃) in the 1-position of the fenchone residue interacts with ruthenium (fenchone = 1,3,3-trimethylbicyclo[2.2.1]heptan-2-one). The unsymmetrical camphor azine monophosphine Z,Z-PPh₂C₁₀H₁₅N–NC₁₀H₁₆9 also gave a similar δ-agostic methyl complex mer,trans-[RuCl₂(PPh₃){PPh₂-C₁₀H₁₅N–NC₁₀H₁₆}]10(camphor = 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one). Treatment of 2 with the azine Z,E-PPh₂CH₂C(Bu^t)N–NCH(C₆H₄NMe₂-4)11a, derived from 4-dimethylaminobenzaldehyde, gave the δ-agostic complex mer,trans-[RuCl₂(PPh₃){PPh₂CH₂C(Bu^t)N–NCH(C₆H₄NMe₂-4)}]12a, in which the hydrogens in the 2 and 6 positions of the aryl group are agostically interacting with ruthenium. Similarly, the azines 11b and 11c, derived from 4-methoxybenzaldehyde or 4-nitrobenzaldehyde, gave the δ-agostic complexes 12b and 12c, respectively. Treatment of 2 with the azine 13, derived from 1-methylpyrrole-2-carbaldehyde, gave the δ-agostic complex 14, in which the hydrogen in the 3-position of the heterocyclic group is agostically interacting with ruthenium. Treatment of 2 with the azine 15, derived from benzylideneacetone, gave the δ-agostic alkenyl complex 16. Proton, ³¹P-{¹H} and some ¹³C-{¹H} NMR data are given.