Synthesis and Coordination Chemistry of a New Chiral Tridentate PCP N-Heterocyclic Carbene Ligand Based on a Ferrocene Backbone

The new chiral imidazolium salt 1,3-bis[( R )-1-(( S )-2-diphenylphosphinoferrocenyl)ethyl]imidazolium iodide ( 4, (PCPH)I) was prepared in three steps from commercially available N,N -dimethyl-1-ferrocenylethylamine ( 1 ) in 55% overall yield. Salt 4 is the precursor for the in situ generation of a novel tridentate carbene ligand that could not be isolated upon deprotonation of 4 with NaO t Bu. Reaction of 4 with [Pd(OAc) 2 ] 3 afforded (SP-4)-1,3-bis[( R )-1-(( S )-2-diphenylphosphino-κ P -ferrocenyl)ethyl]imidazol-2-ylideneiodopalladium(II) acetate, [PdI(PCP)]OAc ( 6 ). Treatment of 4 with NaO t Bu and [RuCl 2 (PPh 3 ) 3 ] gave the mixed halide complex (SP-5)-1,3-bis[( R )-1-(( S )-2-diphenylphosphino-κ P -ferrocenyl)ethyl]imidazol-2-ylidenechloroiodoruthenium(II) [RuClI(PCP)] ( 7a ), as a mixture of two isomers in 60% yield. Additional complexes that could be obtained from 4 are [PdCl(PCP)]PF 6 ( 5 ), [RuCl 2 (PCP)] ( 7b ), and [RuI(PCP)(NCCH 3 ) 2 ]PF 6 ( 8 ). The crystal and molecular structures of 5 and 7a were determined by X-ray diffraction. The Ru(II) center undergoes a weak agostic interaction with one of the two stereogenic methine units.