Synthesis, Reactivity and Coordination Chemistry of Group 9 PBP Boryl Pincer Complexes: [(PBP)M(PMe3)(n)] (M = Co, Rh, Ir; n=1, 2)

The unsymmetrical diborane(4) derivative [(d(CH2P(iPr)(2))abB)-Bpin] (1) proved to be a versatile PBP boryl pincer ligand precursor for Co(I) (2a, 4a), Rh(I) (2-3b) and Ir(I/III) (2-3c, 5-6c) com-plexes, in particular of the types [(d(CH2P(iPr)(2))abB)M(PMe3)(2)] (2a-c) and [(d(CH2P(iPr)(2))abB)M- PMe3] (2b-c). Whilst similar complexes have been obtained before, for the first time, the coordination chemistry of a homologous series of PBP pincer complexes, in particular the interconversion of the five-and four-coordinate complexes 2a-c/3a-c, was studied in detail. For Co, instead of the mono phosphine complex 2a, the dinitrogen complex [(d(CH2P(iPr)(2))abB)Co(N-2)(PMe3)] (4a) is formed spontaneously upon PMe3 abstraction from 2a in the presence of N-2. All complexes were compre-hensively characterised spectroscopically in solution via multinuclear (VT-)NMR spectroscopy and structurally in the solid state through single-crystal X-ray diffraction. The unique properties of the PBP ligand with respect to its coordination chemical properties are addressed.