Calcium-stabilised transition metal bis(formyl) complexes: structure and bonding.

Reaction of a molecular calcium hydride with a series of group 9 dicarbonyl complexes [M(η 5 -C 5 Me 5 )(CO) 2 ] (M = Co, Rh, Ir) led to the formation of both mono(formyl) and bis(formyl) complexes. The bis(formyl) complexes are unique. They have been characterised by multinuclear NMR spectroscopy and examples have been crystallographically characterised for the first time.