A New Class of Modular Oxazoline-NHC Ligands and Their Coordination Chemistry with Platinum Metals

A novel family of enantiomerically pure imidazolium salts [(NHC-Ox)H]X-+(-) (2a-g) has been generated hearing an oxazoline unit and in which both heterocycles are connected by a (dimethyl)m ethylene bridge. Deprotonation of the imidazolium salt 2f and subsequent reaction of the resulting free carbene with [Rh(nbd)Cl](2) (nbd = norbornadiene) afforded the neutral rhodium(I) complex [(NHC-Ox)Rh(nbd)Br] (3) in which the ligand was found to be monodentate. Bromide abstraction lead to the air-stable cationic complex [(NHC-Ox)Rh(nbd)]PF6 (4) with the expected bidentate coordination mode of the ligand. Reaction of the imidazolium salt 2d with Karstedt's catalyst and one equivalent of KOtBu gave the trigonal planar platinum(0) complex [(NHC-Ox)Pt(dvtms)] (5) (dvtms = divinyltetramethylsiloxane), which was oxidized by CsBr3 to give the square planar platinum(II) complex [(NHC-Ox)PtBr2] (6). Complex [(NHC-Ox)PtCl2] (7) was directly prepared by reaction of the imidazolium salt with Ag2O followed by the addition of [PtCl2(1,5-cod)]. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)