posted on 2008-01-23, 00:00authored byAaron D. Wilson, Kendra Fraze, Brendan Twamley, Susie M. Miller, Daniel L. DuBois, M. Rakowski DuBois
The complex [Ni(PCy2NBz2)2](BF4)2, 1, reacts rapidly and reversibly with carbon monoxide (1 atm)
at 25 °C to form [Ni(CO)(PCy2NBz2)2](BF4)2, 2, which has been characterized by spectroscopic data and by
an X-ray diffraction study. In contrast, analogous Ni(II) carbonyl adducts were not observed in studies of
several other related nickel(II) diphosphine complexes. The unusual reactivity of 1 is attributed to a complex
interplay of electronic and structural factors, with an important contribution being the ability of two positioned
amines in the second coordination sphere to act in concert to stabilize the CO adduct. The proposed
interaction is supported by X-ray diffraction data for 2 which shows that all of the chelate rings of the cyclic
ligands are in boat conformations, placing two pendant amines close (3.30 and 3.38 Å) to the carbonyl
carbon. Similar close C−N interactions are observed in the crystal structure of the more sterically demanding
isocyanide adduct, [Ni(CNCy)(PCy2NBz2)2]2(BF4)2, 4. The data suggest a weak electrostatic interaction between
the lone pairs of the nitrogen atoms and the positively charged carbon atom of the carbonyl or isocyanide
ligand, and illustrate a novel (non-hydrogen bonding) second coordination sphere effect in controlling
reactivity.