Platinum(II)- and palladium(II)-amide complexes [formula omitted] derived from 2-azetidinone (β-propiolactam); a synthetic, electrospray mass spectrometric and X-ray crystallographic study

Abstract

A number of platinum(II) and palladium(II) complexes 3 and 4 containing amido ligands derived from β-propiolactam (2-azetidinone, Haz) have been synthesised in high yield by the silver(I) oxide-mediated reactions of the complexes cis-[MCl 2L 2] [M = Pt, L = cycloocta-1, 5-diene (COD) or PPh 3; M = Pd, L= 2, 2′-bipyridine (BIPY) or 1, 10-phenanthroline (PHEN)] with 2-azetidinone. Displacement of the COD ligand allowed the synthesis of a number of other derivatives containing phosphine, phosphite and isocyanide ligands. Electrospray mass spectrometry has also been used to further characterize these complexes, to probe the strength of binding of the amide ligands and to investigate the ability of the complexes to act as metallo-ligands towards other mono-, di- and trivalent cations. A detailed study on the bis(triphenylphosphine) platinum complex 3b shows that fragmentation, induced by higher cone voltages, proceeds initially via loss of a deprotonated azetidinone monoanion (az −) ligand, yielding [Pt(az)(PPh 3) 2] +. Upon further increasing the cone voltage, cyclometallation of one of the triphenylphosphine ligands occurs. Complex 3b readily forms adducts with a range of alkali-metal cations, Ag +, divalent cations (Ba 2+, Cu 2+, Zn 2+ and Pb 2+) and a trivalent cation (Pr 3+). Complex 3b shows selectivity for Na 2+ ions over other alkali-metal cations in forming a dipositively charged aggregate of the type [2M + 2Na] 2+ at low cone voltages. The X-ray structure of complex 3b is also reported.