Preparation of η2 : η2-o-xylylene complexes of ruthenium(0)via facile δ-hydrogen abstraction reactions. The crystal and molecular structure of [Ru(CH2C6H4CH2)(PMe2Ph)3]

Abstract

Reactions of cis- or trans-[RuCl₂L₄](L = PMe₂Ph, PMePh₂, or PEt₃) with o-MeC₆H₄CH₂MgBr produce [R[graphic omitted]H₂)L₃] as the only isolable product at temperatures down to –30 °C, presumably by δ-hydrogen-abstraction reactions. For L = PMe₃ no reaction is observed but [R[graphic omitted]H₂)(PMe₃)₃] may be synthesised from [RuCl₂(PMe₃)₄] and o-MeC₆H₄CH₂Li·tmen (tmen = Me₂NCH₂CH₂NMe₂) in toluene. The yellow colour of the complexes, as well as their ¹H and ³¹P n.m.r. spectra and their reaction with CO to give substitution products rather than adducts, suggest a diene like (η²:η²) binding of the xylylene ligand. This is fully confirmed by an X-ray study of [R[graphic omitted]H₂)(PMe₂Ph)₃] which is monoclinic, space group P2₁/c, with a= 15.919(2), b= 11.643(2), c= 16.674(3)Å, β= 104.60(30)°, and Z= 4. The structure was determined with 3 098 observed intensities measured on an automatic diffractometer and refined to an R value of 0.029. The co-ordination geometry can be considered as distorted square pyramidal with the diene molecule occupying two basal sites and bound through its exocyclic double bonds. The C–C distances suggest localisation of bonding in the xylylene ring and the angle between the plane containing Ru,C(1),C(4) and the extension of that of C(1),C(2),C(3),C(4) is 93°, confirming the η²:η² binding of the xylylene ligand.