Synthesis and characterization of novel Pd(II) and Pt(II) complexes with 5-ring chelating iminoylcarbene ligands

Abstract

A novel N-iminoylimidazolium salt serves as a precursor to an iminoyl-substituted N-heterocyclic carbene ligand system with the potential to form 5-ring chelates. Reaction of 3 - Me - 1 - [ C ( C 6 H 5 ) N ( 2 , 6 - i Pr 2 C 6 H 3 ) ] C 3 H 3 N 2 + Cl - ( 3; (C–N)H +Cl −) with Ag 2O leads to the silver carbene complex (C–N)AgCl 4. A crystallographic analysis of 4 reveals a monomeric (carbene)AgCl moiety with a κ 1-(C) bonded iminoylcarbene ligand, in accord with NMR and IR spectroscopic data. Carbene transfer from Ag to Pd occurs upon reaction of 4 with (COD)PdCl 2, resulting in the κ 2-(C,N) iminoylcarbene complex (C–N)PdCl 2 ( 5). Carbene transfer from 4 to Pt takes place with Pt 2Me 4(μ-SMe 2) 2 yielding (C–N)PtMe 2 ( 6), which was characterized by X-ray crystallography. The monomeric Pt complex contains a 5-ring chelate with a κ 2-(C,N)-bonded iminoylcarbene ligand. The Pt–Me bond distances in 6 are nearly identical (2.071(5) Å trans to carbene-C; 2.051(4) Å cis) but the 2 J( 195Pt–H) coupling constants are significantly different (63.1 Hz trans; 92.0 Hz cis), as are the 1 J( 195Pt–C) coupling constants (618 Hz trans; 799 Hz cis).