Synthesis of new heterotridentate ligands comprising mixed hard-soft donor sets and their complexation with Group 10 metals

The new phosphorus-containing heterotridentate ligands 2-(2-Ph2P)C6H4CH=NCH(Me)CK(OH)Ph-IS,2R (HL1) and 2-(2-Ph2P)C6H4N=CHC6H4OH (HL2) were prepared by the condensation of 2-(diphenylphosphino)benzaldehyde with 1S,2R-norephedrine (HL1) and 2-(diphenylphosphino)aniline with salicylaldehyde (HL2). The co-ordination chemistry of HL1 and HL2 with Group 10 metals was explored, together with that of the previously reported ligand 2-(2-Ph2P)C6H4CH=NC6H4OH (HL3) which is isomeric with (HL2). Compound HL1 affords cationic complexes of general formula [M(HL1)CI]CI, where M = Ni (I), Pd (2) or Pt (3). Spectroscopic, microanalytical and crystallographic data for 1-3 confirm that deprotonation of the hydroxyl group does not occur on complexation. In contrast, both HL2 and HL3 deprotonate on complexation to form neutral species of general formula [MLCl] where L = L-2, M = Ni (4), Pd (5) or Pt (6); L = L-3, M = Ni (7), Pd (8) or Pt (9). The crystal structures of 4, 5, 7 and 9 confirm tridentate PNO co-ordination of the deprotonated ligands to the metal centres, forming 5- and 6-membered rings.