Synthesis, Reactivity and Coordination Chemistry of Group 9 PBP Boryl Pincer Complexes: [(PBP)M(PMe(3))(n)] (M = Co, Rh, Ir; n = 1, 2)

The unsymmetrical diborane(4) derivative [(d(CH(2)P(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) complexes, in particular of the types [(d(CH(2)P(iPr)(2))abB)M(PMe(3))(2)] (2a–c) and [(d(CH(2)P(iPr)(2))abB)M–PMe(3)] (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(CH(2)P(iPr)(2))abB)Co(N(2))(PMe(3))] (4a) is formed spontaneously upon PMe(3) abstraction from 2a in the presence of N(2). All complexes were comprehensively 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.