Synthesis of a Library of Iridium-Containing Dinuclear Complexes with Bridging PNNN and PNNP Ligands (BL), [LM(μ-BL)M‘L‘]BF₄. 2. Preparation, Basic Coordination Properties, and Reactivity of the Carbonyl Complexes

A series of dinuclear carbonyl complexes with PNNP and PNNN ligands, [(L)M(PNNX)M‘(L)]BF₄ (X = P, N; M(L), M‘(L‘) = Ir(CO)₂, Rh(CO)₂, Pd(allyl)), have been prepared by carbonylation (1 atm) of the corresponding cod complexes, and the Rh/Ir complexes have been further converted to μ-η¹:η²-acetylide complexes, where effective π-back-donation to the acetylide ligand is essential to stabilize them. On the basis of the stability of the acetylide complexes, the π-donating ability of the metal fragment in the PNNX system is estimated to be (P,N)Rh > (P,N)Ir > (N,N)M. The dinuclear PNNX complexes catalyze alkyne hydrogenation, alkene hydroformylation, and allylation of aniline with allyl alcohol, and, for the allylation, a dinuclear mechanism involving activation of allyl alcohol by interaction with a CO ligand is proposed.