One-step assembly of a chiral palladium bis(acyclic diaminocarbene) complex and its unexpected oxidation to a bis(amidine) complex

Abstract

Addition of trans-N,N'-dimethyl-1,2-diaminocyclohexane to a palladium bis(arylisocyanide) complex leads to the one-step formation of the first chiral bis(acyclic diaminocarbene) complex, which is thermally stable under N(2) but undergoes slow oxidation to a bis(amidine) complex under air.

Application of palladium complexes bearing acyclic amino(hydrazido)carbene ligands as catalysts for copper-free Sonogashira cross-coupling

“…In addition, 1 H NMR spectra exhibit two broad peaks from PdAC carbene @N(H)N(H)Y protons in the range of d 8.8-11.0. Addition of 5-21 to 1-4 in all possible combinations is accompanied by a pronounced downfield d 13 C shift of one of the isocyanide quaternary C atom to the range specific for ADC PdAC carbene (d 160-224 ppm) [5,6,[18][19][20][21][22][23][24][25]. The C carbene @NH 13 C signals in 34-35, 40-41, and 46-49 were found to resonate at ca.…”

Palladium complexes of bis(acyclic diaminocarbene) ligands with chiral N-substituents and 8-membered chelate rings

“…A propylene linker was chosen for the initial studies, because the resulting 8-membered bis(ADC) chelate ring should have greater conformational flexibility compared to the 7-membered chelate structures previously reported by us (C and D, Fig. 1) [6,29], thus potentially allowing the chiral groups to approach the metal in some ligand conformations. The chiral N-substituents chosen were 1-phenylethyl and 1-(1-naphthyl)ethyl groups, providing two bis(ADC) precursors with different amounts of steric bulk.…”

“…Subsequently, we extended this synthetic approach to chiral bis(ADC) palladium complexes C and D (Fig. 1) by reaction of arylisocyanide complexes with chiral secondary diamines [6,29]. In addition to providing the first chiral ADC ligands, this one-step synthetic route provides a strategy for systematically varying the chiral structure and chelate ring size.…”

Amidines in Organic Synthesis

“…Bicyclic bisamidines can be prepared from trans-N,N 0 -dimethyl-1,2-diaminocyclohexane and a palladium bis(arylisocyanide) complex [38] (Scheme 3.22). Oxidation of the initially-formed palladium bis(acyclic diaminocarbene) complex with air or idosobenzene (PhI ¼ O) followed by treatment with excess amounts of methylisonitrile (MeNC) yields bicyclic bisamidines.…”