Cleavage of phosphorus–phenyl and phosphorus-2-pyridyl bonds in the reactions of mixed phenyl-(2-pyridyl) phosphines with [Ru3(CO)12]

The compound [Ru3(CO)12] reacts at room temperature in tetrahydrofuran with tri(2-pyridyl)phosphine, P(2-C5H4N)3′ when catalysed by [N(PPh3)2]Cl, to give a product derived by cleavage of a phosphorus-2-pyridyl bond, [Ru3(µ-2-C5H4N){µ3-P(2-C5H4N)2}(CO)9]1. No simple substitution compounds could be isolated. The likely intermediates [Ru3(CO)n{P(2-C5H4N)3}](n= 10 and/or 11) spontaneously decarbonylate while a 2-pyridyl group migrates from phosphorus to ruthenium atoms. A similar reaction using phenyldi(2-pyridyl) phosphine, PPh(2-C5H4N)2′ leads to the competitive transfer of 2-pyridyl and pheyl groups to give almost equal quantities of two products, [Ru3(µ-2-C5H4N){µ3-PPh(2-C5H4N)}-(CO)9] and [Ru3(µ-PhCO){µ3-P(2-C5H4N)2}(CO)9]. The crystal structure of 1 shows that the 2-pyridyl group that has migrated bridges two ruthenium atoms with no Ru-Ru bond between them and that the di(2-pyridyl) phosphido ligand is triply bridging with one nitrogen co-ordinated and one free. As in the reported reaction of [Ru3(CO)12] with PPh2(2-C5H4N) to give [Ru3(µ-PhCO){µ3-PPh(2-C5H4N)}(CO)9], the reason why P-C bond cleavage occurs under remarkably mild conditions and the mechanism of the processes have still to be determined.