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

The 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.

Intramolecular Nitrile C–H Bond Activation in Nickel NHC Complexes: A Route to New Nickelacycles

“…In addition, in the (nondisordered) molecule A of 1a , the C–C–C angles in this ligand range from 104.1 to 111.2°; the internal angles of the Cp ligand in complex 1b are much more regular (107.9 ± 0.8°). Similar distortions have been previously observed and studied in other Cp or Cp*Ni systems …”

“…Both complexes display asymmetry in their Ni–C Cp and C Cp –C Cp distances, but the distortions are somewhat more pronounced in complex 3d . Both complexes also exhibit short CN···H intermolecular contacts, and in each case, the nitrile nitrogen atom interacts with two hydrogen atoms; distances of 2.531 Å for an NHC ligand hydrogen atom and of 2.691 Å for a mesityl hydrogen atom are observed in 3b , while values of 2.667 and 2.588 Å, respectively, are seen for an NHC hydrogen atom and for a methylene hydrogen atom that is α to the NHC nitrogen atom in 3d .…”

Synthesis and Structural Characterization of Half-Sandwich Nickel Complexes Bearing Two Different N-Heterocyclic Carbene Ligands

“…The Cp ring of the mixed bis­(carbene) complex 2ab exhibits structural distortions, as there are significant variations in the Ni–C Cp distances, as well as fluctuations in the C Cp –C Cp distances. Similar distortions have been previously observed and studied in other Cp or Cp*Ni systems . Some of the imidazolylidene hydrogen atoms are relatively close and interact weakly with some F atoms of the PF 6 – anion (H···F distances lie in the 2.35–2.55 Å range).…”

Synthesis and Catalytic Activity in Suzuki Coupling of Nickel Complexes Bearing n-Butyl- and Triethoxysilylpropyl-Substituted NHC Ligands: Toward the Heterogenization of Molecular Catalysts

“…In all six structures, the η 5 -C 5 R 5 rings exhibit structural distortions with significant variations in both the C Cp† –C Cp† and Ni–C Cp† distances. Such variations have been occasionally observed in other Ni(η 5 -C 5 R 5 ) systems and arise from “allyl-ene”, “diene”, or intermediate distortions (between “ally-ene” and “diene”) of the η 5 -C 5 R 5 ring. , Thus, “diene” distortions are observed in complexes 1a , 1b , 1e , 2d , and 2e , and intermediate distortions are seen in complex 1d (see Scheme S1 in the Supporting Information).…”