ORGANOZINC COMPLEXES WITH MONOANIONIC CHELATING PHENOLATES OR 2-PYRIDYLMETHANOLATES - MOLECULAR-STRUCTURE OF [ZN(CH2SIME3)(OCH2(2-PY))]4

The influence of the chelate ring size and of the presence of sterical ly demanding groups in the chelating ligand on the degree of associati on of organozinc ortho-substituted phenolates and alpha-substituted 2- pyridylmethanolates has been studied. Organozinc derivatives were made of phenols with one or two potentially ortho-chelating (dimethylamino )methyl groups and of the alpha-substituted 2-pyridylmethanols, 2-(2-p yridyl)propan-2-ol, 2,4-dimethyl-3-(2-pyridyl)pentan-3-ol, diphenyl-2- pyridylmethanol, 1-phenyl-1-(2-pyridyl)ethanol, and 2,2-dimethyl-1-(2- pyridyl)-propanol. The CH2NMe2-substituted phenolate compound 1a, cont aining a six-membered chelate ring via Zn-N coordination is dimeric, w hereas compounds 2b and 2b', having two CH2NMe2 substituents in the ph enolate ligand, exist in benzene as a monomer-dimer equilibrium. The a lkylzinc 2-pyridylmethanolate complexes 3c and 3c', in which intramole cular Zn-N coordination leads to a five-membered chelate ring, are tri meric in solution. Surprisingly, 3c is a tetramer in the solid state. Introduction of substituents in the five-membered chelate ring of thes e 2-pyridylmethanolates affects the stability of the aggregates in sol ution. Complexes 3d and 3g, with small substituents on the a-carbon at oms of the pyridylcarbinolate fragment, exist in solution as equilibri a of dimers and trimers, whereas compounds 3e, 3f, and 3h, with more s terically demanding a-substituents, are concentration independent dime rs in solution. The molecular structure of tetrameric 3c in the solid state contains a puckered eight-membered Zn4O4 ring in which the zinc atoms are coordinatively saturated by four intramolecularly coordinati ng pyridyl fragments. Crystals of [Zn(CH2SiMe3){OCH2(2-PY)}]4, 3c, are monoclinic, space group P2(1)/c with unit-cell dimensions a = 12.625( 1) angstrom, b = 17.815(1) angstrom, c = 12.299(1) angstrom, beta = 11 1.23(1)-degrees, and final R = 0.028.