Influence of the bridging ligand on the substitution chemistry of neutral and cationic triruthenium carbonyl cluster complexes derived from 1,1-dimethylhydrazine

The reactivity of the neutral triruthenium carbonyl cluster [Ru3(μ-H)(μ3-HNNMe2)(CO)9] (1) and its protonated derivative [Ru3(μ-H)2(μ3-HNNMe2)(CO)9][BF4] (2), both containing a face-capping 5-electron donor 1,1-dimethylhydrazido ligand, with triphenylphosphane has been studied. Compound 1 gives a mixture of two non-interconvertible isomeric carbonyl substitution products [Ru3(μ-H)(μ3-HNNMe2)(CO)8(PPh3)] which bear the phosphane ligand attached to the same Ru atom as either the NMe2 (3a) or the NH fragments (3b). Protonation of the 3a and 3b mixture with [HOEt2][BF4] gives a mixture of two non-interconvertible isomeric cationic dihydrido derivatives [Ru3(μ-H)2(μ3-HNNMe2)(CO)8(PPh3)][BF4] (4a and 4b) which maintain the phosphane ligand in the same position as their neutral precursors. Compound 4a can be selectively prepared from complex 2 and triphenylphosphane. Deprotonation of complex 4a with triethylamine gives compound 3a, selectively. These results contrast with those previously known for carbonyl substitution reactions on triruthenium clusters isostructural with compounds 1 and 2 but containing other face-capping five-electron donor ligands. The hardness of the bridging ligand is presented as an important factor in relation to the observed regioselectivity. The X-ray structures of compounds 2 and 4a are reported.