Amido-pincer complexes of Cu(II): Synthesis, coordination chemistry and applications in catalysis

作者：Taghvaee Mahroo; Rodriguez Alvarez Maria J; Garcia Alvarez Joaquin; del Rio Ignacio; Lough Alan J; Gossage Robert A^*

来源：Journal of Organometallic Chemistry, 2017, 845: 107-114.

DOI：10.1016/j.jorganchem.2017.03.021

• Pincer
• Copper
• Amido
• Oxazoline
• Heteroannulation catalyst

The synthesis and characterisation of five novel copper (II) complexes incorporating an amido pincer ligand derived from the deprotonation of N-(2-{4,4-dimethyl-4,5-Dihydrooxazol-2-yl} phenyl) picolinamide (i.e., L1H) or a chiral indanol-based congener (L2H) are described. These Cu materials are obtained from the treatment of EtOH solutions of L1H or L2H with CuX2(OH2)(n) species (X = Cl, Br, NO3, BF4). All of these compounds have been characterised by single crystal X-ray diffraction methods, which confirms a k(3)-N, N', N"-binding mode of the formally anionic L1 or L2 displaying an amido N-Cu bond following H+ loss. Complexes of stoichiometry Cu(L1) X (X = Cl [1], Br [2]) are shown to be slightly distorted square planar compounds with an N3X ligand binding set. For X = BF4, the Cu compound retains a coordinated H2O molecule and a non-coordinated BF4 counteranion to form [Cu(L1)(OH2)] BF4 center dot H2O (3). This species demonstrates extended solid-state structure which is likewise detailed. In the case of X = NO3, the isolated species (4) is six-coordinate in nature with a k(2)-O, O'-NO3 ligand and a non-coordinated solvent of crystallisation (H2O). This latter species displays a bridged dimeric structure in the solid-state and can alternatively be produced, albeit in reduced yields, from 1 and AgNO3 in wet THF mixtures. A chiral derivative, Cu(L2) Cl (i.e., 5), has also be produced by similar synthetic protocols and structurally elucidated; it displays a solid-state structure somewhat different to that of 1. The catalytic activity of both 1 and 3 was investigated towards C-C bond forming chemistry, notably the Henry (i.e., nitroaldol) reaction and methyl methacrylate polymerisation. Electrochemical investigations of these complexes display irreversible one-electron reduction potentials; a facet which helps to explain their negligible catalytic activity in (presumed) ATRP. However, both 1 and 3 are marginally active in promoting the nitroaldol reaction but the product profile is hampered by both low conversions and the formation of by-product alkenes. In contrast, 1-4 are very effective catalytic promoters of the heteroannulation reaction of 2-iodophenol and phenylacetylene to yield the corresponding 2-phenylbenzofuran in the presence of base.

• 出版日期2017-9-15