Chelating Phosphane–Boranes as Hemilabile Ligands – Synthesis of[Mn(CO) 3 (η 2 ‐H 3 B·dppm)][BAr F 4 ] and [Mn(CO) 4 (η 1 ‐H 3 B·dppm)][BAr F 4 ]

Manganese complexes bearing the chelating phosphane–borane ligand H 3 B · dppm [dppm = bis(diphenylphosphanyl)methane] have been prepared. Addition of H 3 B · dppm to Mn(CO) 5 Br using Na[BAr F 4 ] as a halide‐abstracting reagent affords [Mn(CO) 3 (η 2 ‐H 3 B · dppm)][BAr F 4 ] ( 1 ). This reacts with CO to open the bidentate borane to afford [Mn(CO) 4 (η 1 ‐H 3 B · dppm)][BAr F 4 ] ( 2 ) in which the borane is now bound in a monodentate manner. The CO addition is reversible, and placing 2 under vacuum (hours) regenerates 1 quantitatively, demonstrating that the chelating phosphane–boranes can act as hemilabile ligands. The complexes 1 and 2 have been fully characterised by NMR spectroscopy and X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)