The novel chelating PNP pincer ligand 2,5-bis((diphenylphosphino)methyl)-1H-pyrrole (1) was prepared and its nickel coordination chemistry explored. The reaction with Ni(COD)(2) led to a diamagnetic dinuclear nickel(I) complex (4) which was also obtained by the reaction of the square planar Ni(II) complexes [(PNP-Ph(2))NiX] (X = Cl (2), X = I (3)) with Li(Et(3)BH).

Two new monoanionic PNP pincer type ligands have been synthesized, the achiral 3,6-di-tert-butyl-1,8-bis((diphenyl-phosphino)methyl)-9H-carbazole CbzdiphosH (5) and the chiral 3,6-di-tert-butyl-1,8-bis(((2R,5R)-2,5-diphenylphospholan-1-yl)methyl)-9H-carbazole CbzdipholH (7), both of which were initially prepared as their borane complexes. The synthesis of CbzdiphosH is based on the reaction between the key intermediate 1,8-bis(bromomethyl)-3,6-di-tert-butyl-9H-carbazole (3) and lithium diphenylphosphide-borane complex. The chiral ligand CbzdipholH was prepared by treating 3 with lithium (2R,5R)-2,5-diphenylphospholanide-borane complex and subsequent deprotection with diethylamine. The complexation of the two ligands with nickel, palladium and rhodium was investigated, for which the conformational behavior of the ligands was found to be different. Although the arrangement of the donor atoms in all crystallographically characterized complexes is approximately square planar, the carbazole plane in Cbzdiphos complexes is inclined relative to the coordination plane. On the other hand, a helical twist is observed in Cbzdiphol complexes.

The coordination chemistry of the monoanionic PNP pincer ligand 3,6-di-tert-butyl-1,8-bis[(diphenylphosphanyl)methyl-]carbazole (Cbzdiphos) was investigated for different iridium(I) and iridium(III) complexes. Reaction of the protio ligand with [Ir(acac)(cod)] (acac = acetylacetonate; cod = 1,5-cyclooctadienyl) gave [(Cbzdiphos)Ir(cod)] (1). Upon hydrogenation the dihydrido complex [(Cbzdiphos)IrH 2 ] (2) was obtained, and its reactivity in different organometallic transformations was examined. Treating 2 with ammonia afforded