Reactions of Unsaturated Nickel–Molybdenum and –Tungsten Complexes with Primary Amines: Chemoselective N‐Coordination to Nickel To Give the First Structurally Characterised Primary Amine–Organonickel Complexes

Abstract

AbstractThe reactions of selected primary amines with the unsaturated heterodimetallic complex [(η‐C5Me5)Ni(μ‐CO)Mo(CO)2(η‐C5H5)](Ni[pb2]Mo) (1a) were investigated. Primary aminesreact with this heterodimetallic complex to form unstable adducts, which are in equilibrium with the free amine and complex 1a in solution. Complex 1b, the nickel–tungsten analogue of 1a, reacts similarly with benzylamine. The position of the equilibrium shifts in favour of the adducts at low temperature, and crystals of the allylamine and benzylamine complexes [(η‐C5Me5)(RNH2)Ni–Mo(CO)3(η‐C5H5)], (2a, R = C3H5; 4a, R = PhCH2) could be isolated. Their structures were established by single‐crystal X‐ray diffraction studies. The primary amines in complexes 2a and 4a are each coordinated, by means of their respective nitrogen atoms, to the nickel atom and thus provide the first structurally characterised examples of primary amine organometallic nickel complexes. The bonding of the amine to the heterodimetallic centre is in contrast to what has been observed with phosphorus‐containing 2‐electron donor ligands, in which the phosphane ligand is coordinated to the group 6 metal atom. A measure of the Ni–N bond dissociation enthalpy for the (benzylamine)nickel–tungsten complex 4b was obtained from a VT 1H NMR spectroscopic study and was found to be –149 ± 10 kJ mol–1. N‐Bonded hydrogen atoms in both 2a and 4a exhibit intermolecular hydrogen‐bonding interactions in the solid state with carbonyl oxygen atoms of adjacent molecules. These molecules exist as loosely bound dimers in the solid state. Complex 2a (C21H27MoNNiO3) crystallises in the monoclinic space group P21/n with a = 10.1922(2), b = 11.1538(3), c = 18.8053(4) Å, β = 90.777(2)° and Z = 4. Complex 4a (C25H29MoNNiO3) also crystallises in the monoclinic space group P21/n with a = 12.0840(4), b = 10.9490(4), c = 17.4930(6) Å, β = 90.396(3)° and Z = 4.