Reactions of isocyanide complexes of palladium(II) and platinum(II) with azetidine: synthesis of acyclic diaminocarbene derivatives and X-ray structure of [PdCl(PMe2Ph)(CH2CH2CH2NH){C(NCH2CH2CH2)NHC6H4OMe-p}]Cl·CH2Cl2

Abstract

Azetidine reacts in tetrahydrofuran (thf) at room temperature or below with the co-ordinated RNC ligand in each of the neutral cis-[MCl2(PPh3)(CNR)][M = Pd or Pt; R = C6H4OMe-p or But) and cationic trans-[MCl(PPh3)2(CNC6H4OMe-p)]BF4(M = Pd or Pt) complexes to form the corresponding derivatives containing the acyclic diaminocarbene moiety M–C([graphic omitted]H2)NHR. Azetidine reacts also with the bis(isocyanide) complexes cis-[PdCl2(CNR)2](R = But or C6H4OMe-p) converting one (R = But) or two (R = C6H4OMe-p) isocyanide ligands into acyclic carbenes. The isocyanide complexes cis-[MCl2(PMe2Ph)(CNC6H4OMe-p)](M = Pd or Pt) react in thf with 2 equivalents of azetidine to afford the cationic acyclic diaminocarbene complexes [MCl(PMe2Ph)([graphic omitted]H){C([graphic omitted]H2)NHC6H4OMe-p}]Cl containing a metal-co-ordinated azetidine ligand. In contrast to the reactions of the three-membered heterocycle aziridine with isocyanide ligands which lead to five-membered cyclic carbenes, the corresponding reactions of azetidine give no evidence of six-membered diaminocarbenes. The carbene complexes have been characterized by their elemental analyses, i.r., 1H, and 31P n.m.r. spectra and in a few cases by their 13C n.m.r. and mass spectra. The structure of [PdCl(PMe2Ph)([graphic omitted]H){C([graphic omitted]H2)NHC6H4OMe-p}]Cl·CH2Cl2 was determined by X-ray diffraction: space group P21/n, a= 24.849(4), b= 10.174(2), c= 11.895(2)A, β= 91.85(3)°, R= 0.054 (R′= 0.059) for 3 734 observed reflections. The geometry around Pd is a distorted square with the diaminocarbene ligand trans to chloride. The Pd–C(sp2) distance is 1.990(6)A and the bond lengths within the carbenoid system indicate extensive electronic delocalization.