P- versus P,O- coordination in complexes of N-(diphenylphosphino)arylamide ligands ArC(O)NHPPh₂ (Ar=3-pyridyl, phenyl). X-ray crystal structures of [RhCl₂(η⁵-C₅Me₅)L²] and [NiCl(EtOH)L²₂]•Cl•[NiCl₂L²₂] (L²=C₆H₅CONHPPh₂)

The N-(diphenylphosphino)arylamide ligands 3-NC5H4CONHPPh2 (L-1) and C6H5CONHPPh2 (L-2) function as monodentate p-donors in the complexes [RhCl2(eta (5)-C5Me5)L], [RuCl2(eta (6)-p-cymene)L] and cis-[PtCl2L2], as exemplified by the X-ray crystallographically determined structure of [RhCl2(eta (5)-C5Me5)L-2]. For nickel(II), P,O- chelation by L-1,L-2 is exhibited in the bis(bidentate) complexes [NiCl2L2], as demonstrated by the crystal structure of [NiCl(EtOH)L-2(2)]. Cl . [NiCl2L22]; the five-membered Ni-O-C-N-P chelate rings are approximately planar with the phosphorus atoms in the dichloro complex being trans whereas their arrangement is cis in the cation. Comparison of this structure with [RhCl2(eta (5)-C5Me5)L-2] reveals slight elongation of the C=O and P-N lengths upon P,O-chelation of L-2. Solvatochromism for the Ni(II)-L-2 complex (green in ethanol or acetone, brown in chlorinated solvents) arises from solvent-dependent hemilability of the amide oxygen atom, although the L-1 complex of NI(II) is exempt from this behaviour. (C) 2001 Elsevier Science Ltd. All rights reserved.