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

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.