Synthesis, crystal structures and reactivity of rhodium(III) complexes containing β-ketophosphine and phosphino enolate ligands

Abstract

The reaction of 3 equivalents of the ketophosphine Ph₂PCH₂C(O)Ph (L) with RhCl₃·3H₂O in ethanol yielded [[graphic omitted])Ph}{Ph₂PCH₂C(O)Ph}] in the form of the mer,trans-(1) and mer,cis-(2) isomers. Complex 2 exhibits fluxional behaviour on the ¹H NMR time-scale as a result of dynamic exchange between the pendant and the co-ordinated keto functions, the activation energy for this process being 75 ± 2 kJ mol^–1. Treatment of 2 with TIPF₆ in CH₂Cl₂ afforded the cationic complex trans,cis,cis-[[graphic omitted])Ph}₂]PF₆3, which reacts with excess L to give mer,cis-[[graphic omitted])Ph}{Ph₂PCH₂C(O)Ph}]PF₆5. Complex 5 has an unprecedented ligand set: two ligands L, Bound in two different co-ordination modes (terminal through P and chelating), and the corresponding phosphino enolate as the other chelate. In solution, fluxional behaviour is observed by ³¹P NMR spectroscopy with an activation energy of 56 ± 1 kJ mol^–1. The reaction of 3 with NaH afforded [{[graphic omitted])Ph]₂}₂]6. The chloride bridges are readily cleaved by PMePh₂, affording [[graphic omitted])Ph}₂(PMePh₂)]7. Treatment of [RhCl(PPh₃)₃] with 3 equivalents of L in toluene afforded the Rh^III complex mer,cis-[[graphic omitted])Ph₂{Ph₂PCH₂C(O)Ph}]8. Complex 2 and L reacted with NaOMe to afford the tris(enolato) Rh^III complex fac-[[graphic omitted])Ph}₃]9, which could be also obtained from [RhCl(PPh₃)₃]. The solid-state structures of 3·CH₂Cl₂, 5 and 8·CH₂Cl₂ have been determined by single crystal X-ray analysis.