Coordination properties of novel hemilabile acetamide-derived P,O phosphine ligands. Crystal structures of Ph2PNHC(O)Me and [PdMe{PPh2NHC(O)Me}{PPh2NHC(O)Me}][O3SCF3]

Abstract

Cationic methyl Pd(II) complexes are described in which the new heterofunctional phosphine ligands Ph₂PNHC(O)Me 1 or Ph₂PN(Me)C(O)Me 3 behave as rigid and/or hemilabile P,O chelates. The chelating ability of 3 is higher than that of 1 and both are compared to that of other P,O ligands, such as the keto- and amido-phosphines Ph₂PCH₂C(O)Ph and Ph₂PCH₂C(O)NPh₂, respectively. The crystal structure of 1 reveals the presence in the solid-state of an intermolecular hydrogen-bonded network N–H⋯O and that of [PdMe{PPh₂NHC(O)Me}{PPh₂NHC(O)Me}][O₃SCF₃] 12b establishes the presence of both a chelating and a monodentate ligand 1 in the same complex. Carbonylation of the cationic methyl complexes 8a, 17, 18a and 20a afforded the corresponding acetyl complexes in which this ligand occupies a position cis to phosphorus, irrespective of that of the alkyl ligand in the precursor complex.