Reduction of dichlorotris(triphenylphosphine)ruthenium(II) in the presence of acetonitrile, pyridine, 2,2′-bipyridyl, and styrene

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Abstract
The reduction of dichlorotris(triphenylphosphine)ruthenium(II) in tetrahydrofuran–acetonitrile by sodium or magnesium amalgam produces a compound shown to be a hydrido ortho-metallated phosphine ruthenium(II) complex RuH(C6H4PPh2)(MeCN)(PPh3)2. This compound has all the characteristics of a complex previously reported and alleged to be a ruthenium(0) complex containing a π-bonded acetonitrile ‘Ru(MeCN)(PPh3)4·MeCN’. Detailed study of the system shows that there are labile intermediates, Ru(MeCN)2(PPh3)2 which is paramagnetic, Ru(MeCN)3(PPh3)2, and Ru(MeCN)(PPh3)3. The reduction in pyridine gives two isomers of RuH(C6H4PPh2)(C5H5N)(PPh3)2 while in the presence of 2,2′-bipyridyl the main product is a purple complex RuH(C6H4PPh2)(bipy)(PPh3). In styrene the known complex Ru(styrene)2(PPh3)2 is obtained. Reactions of the ruthenium(II) species RuH(C6H4PPh2)(MeCN)(PPh3)2 with propene and water are reported. The various compounds have been characterised by i.r. and 1H and 31P n.m.r. spectroscopy. It is concluded that reductions of RuCl2(PPh3)3 or 4 lead to the abstraction of hydride from the solvent if no strongly co-ordinating ligand is present. In the presence of co-ordinating ligands, species containing ortho-metallated triphenylphosphine groups are formed via intramolecular oxidative addition of a C–H bond to transient ruthenium(0) intermediates.