Rigid bidentate nitrogen ligands in organometallic chemistry and homogeneous catalysis, 14 - Monodentate and bridging coordination of 3,3 '-annelated 2,2 '-bipyridines in zero-valent palladium- and platinum-p-quinone complexes

Compounds of the type M(N boolean AND N-kappa N)(nq)(2) and M-2(mu(2)-N boolean AND N)-(mu(2)-pbq)(2), in which nq = 1,4-naphthoquinone, pbq = 1,4-benzoquinone, and N boolean AND N is a monodentate or bridging Ligand of the alpha-diimine type, were obtained from reactions of Pd(dba)(2) in toluene with the 3,3'-annelated-2,2'-bipyridines: 4,5-diazafluoren-9-one (dafo) and 4,5-diazafluorene (dafe) in the presence of the appropriate p-quinone. In the corresponding reactions with 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2'-bipyrimidine (bpym), N, N'-dicyclohexyl-1,4-diaza-1,3-butadiene (chex-dab), bis[N-(o,o'-diisopropyl)phenylimino]acenaphthene (o,o'-iPr(2)-bian) and 5,6-dihydro1,10-phenanthroline (dh-phen) only complexes of the type M(N boolean AND N-kappa(2)N)(Q) were formed (Q = nq, pbq). The structures of the complexes have been established by NMR in solution and by X-ray diffraction in the solid state; crystal structures of Pd(bpy-kappa(2)N)(eta(2)-pbq) (1) Pd(dafo-kappa N)(eta(2)-nq)(2) (14) and Pd-2(mu(2)-dafo) (mu(2),eta(2):eta(2)-pbq)(2) (16) have been determined. Of the Ligands, dafo and dafe are the only ones apt to form complexes containing a monodentate or bridging N boolean AND N ligand. This behaviour is ascribed to the geometrical constraints of dafo and dafe; the annelation by one carbon atom at the 3,3'-positions in these Ligands causes an increase in bite angle from approximately 77 degrees to 82 degrees.