The action of fluoroboric acid on dihydridotetrakis(triphenylphosphine)ruthenium(II) or on acetatohydridotris(tri-phenylphosphine) ruthenium(II) in methanol produces the salt [RuH(η⁶-C₆H₅PPh₂)(PPh₂)₃][BF₄] in which the phenyl group of one triphenylphosphine molecule is π-bonded to the metal. In the presence of benzene or toluene, similar arene complexes, [RuH(η⁶-Ar)(PPh₃)₂][BF₄] are obtained.

The interaction of RuH₂(PPh₃)₄ with phenol gives a neutral complex, RuH(C₆H₅O)(PPh₃)₂, that may also be obtained with two additional molecules of phenol hydrogen bonded to the oxygen atom of the phenoxo-ligand. The C₆H₅O^– ligand can be considered to be bound as an η⁶-phenoxo or probably more realistically as an η⁵oxacyclohexadienyl ligand. Re-investigation of the compounds obtained by action of phenol on methyl- or phenyl-tris(triphenyIphosphine)rhodium(I) shows that these also are α-phenoxo-complexes.

An η⁶-toluene-p-sulphonate is also described.

I. r., ¹H, and ³¹P n.m.r. spectra of the compounds are given.