Structural diversity in monomeric cadmium phenoxides

Three monomeric Cd(II) phenoxide complexes have been prepared by reacting Cd[N(SiMe3)(2)](2) with 2 equiv of 2,6-disubstituted phenols bearing sterically bulky tert-butyl or phenyl groups. The strongly coordinating solvents THF, tetrahydrothiophene (TWT), and pyridine used for these reactions were incorporated into the metal's coordination sphere, leading to complexes with a general formulation of Cd(O-2,6-R2C6H3)(2)(solv)(2-3). The Cd complexes obtained have been characterized crystallographically and have been found to adopt differing solid-state geometries. The X-ray crystal structure of Cd(O-2,6-(BuC6H3)-Bu-t)(2)(THF)(2), 1, previously reported by Buhro, displayed unusual square-planar coordination of the metal center. Complex 2, Cd((OBuC6H3)-Bu-t)(2)(THT)(2), has been found to take on the same square-planar geometry, even with the more strongly donating thioether ligand. Alternatively, complex 3, Cd(O-2,6-Ph2C6H3)(2)(THF)(2), has been found to adopt distorted-tetrahedral geometry, guile similar to its zinc congener. The O(1)-Cd-O(2) angle between the phenoxide ligands in 3 is 150.1(2)degrees, and the angle between the ether ligands is 83.1(3)degrees. When the strongly basic solvent pyridine was used, a five-coordinate complex 4, Cd(O-2,6-(BuC6H3)-Bu-t)(2)(py)(3), was isolated. This complex 4 is best described as having trigonal bipyramidal geometry with the phenoxide ligands and one pyridine defining the equatorial plane and two axial pyridine ligands having an angle of 169.7(2)degrees. The angle between the phenoxide ligands in 4 is 156.1(2)degrees. These complexes 1-4 have also been characterized in noncoordinating solvent solutions by H-1, C-13, and Cd-113 NMR spectroscopy and have been found to contain labile donor ligands. Preliminary studies indicate that in a noncoordinating solvent, a rapid equilibrium exists between species with and without coordinated donor solvent ligands.