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 bearing an oxazoline unit and in which both heterocycles are connected by a (dimethyl)methylene 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)]PF 6 ( 4 ) with the expected bidentate coordination mode of the ligand. Reaction of the imidazolium salt 2d with Karstedt's catalyst and one equivalent of KO t Bu gave the trigonal planar platinum(0) complex [(NHC‐Ox)Pt(dvtms)] ( 5 ) (dvtms = divinyltetramethylsiloxane), which was oxidized by CsBr 3 to give the square planar platinum(II) complex [(NHC‐Ox)PtBr 2 ] ( 6 ). Complex [(NHC‐Ox)PtCl 2 ] ( 7 ) was directly prepared by reaction of the imidazolium salt with Ag 2 O followed by the addition of [PtCl 2 (1,5‐cod)]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)