Novel bonding modes of .alpha.-diimines. Synthesis and characterization of [MCl2L(.alpha.-diimine)] and [MCl2(.alpha.-diimine)n] (M = palladium, platinum; L = phosphine, arsine; n = 1, 2) containing .sigma.,.sigma.-N,N', .sigma.-N, or .sigma.-N .tautm. .sigma.-N' bonded .alpha.-diimines

Abstract

Compounds of the type [PdX2(RN=CHCH=NR),] (n = 1,2; X = C1, Br, I) and [MCl,L(RN=CHCH=NR)] (L = monodentate phosphine or arsine; M = Pd, Pt; R = alkyl) have been synthesized starting from the a-diimine (R-dim) and [PdCI,(PhCN),] or [(MCl,L),], respectively. Three types of metal-a-diimine interactions have been established: (i) up-N,N' chelate bonded R-dim in [PdXz(R-dim)]; (ii) u-N monodentate bonded Rdim in monomeric tr~ns-[PdX~(R-dim)~] ('H and C NMR spectroscopy reveals that the R-dim ligand has the anti conformation with the C-C and Pd-N bonds of the coordinated part of the ligand in the cis configuration. This brings the @-imine proton (S(CH) 9.70) in the proximity of the palladium atom.); (iii) u-N - u-N' bonded R-dim in the monomeric complexes, tr~ns-[M~~Cl,L(R-dim)], which contain monodentate (u-N) bonded R-dim in the slow-exchange limit (-55 C). At 120 OC (fast-exchange limit) the complexes are fluxional by an intramolecular process which involves a pentacoordinate intermediate containing up-N,N' bonded R-dim. These novel bonding modes for the R-dim ligand in these palladium and platinum complexes are a clear indication of the versatile coordination properties of the R-dim ligand compared with ligands such as bpy and phen, which also contain the N=CC=N skeleton.