CHEMISTRY OF PENTACOORDINATE [LCU(II)-CL](+) COMPLEXES WITH QUINOLYL CONTAINING TRIPODAL TETRADENTATE LIGANDS L

Ligand design and construction is an important aspect of controlling structure and reactivity in coordination chemistry, and here we describe the synthesis and effects conferred upon the structure, spectroscopy and electrochemistry of [LCu(II)Cl](+) (1-4), where L is a tripodal tetradentate donor, TMPA (=tris[((2-pyridyl)methyl)-methyl]amine), or corresponding, ligands with one (BPQA), two (BQPA), or three (TMQA) 2-quinolyl groups substituted for 2-pyridyl donors. Previous investigations (Karlin, K.; et al. J. Am. Chem. Sec. 1993, 115, 9506, Wei, N.; et al. Inorg. Chem.: 1994, 33, 1953) have indicated dramatic influences upon stoichiometry, structure and kinetic/thermodynamics in the O-2-reactivity with corresponding reduced copper(I) species [LCu(I)](+). Reactions of the quinolyl-containing ligands with copper(II) chloride, followed by metathesis with NaPF66 afforded hexafluorophosphate salts of 2-4. New X-ray structures are reported: [(BPQA)CuCl]-PF6.0.5Et(2)O (2-PF(6)0.5Et(2)O), monoclinic C2/c, a = 15.509 (3), b = 22.945 (4), c = 14.745 (5) Angstrom, beta = 110.14 (2)degrees, Z = 8, R = 0.049; [(TMQA>CuCl]PF6.CH3CN.0.5Et(2)O, 4-PF6.CH3CN.0.5Et(2)O, monoclinic C2/c, a = 30.787 (7), b = 13.454(8); c = 19.927 (9) Angstrom, beta = 128.49 (1)degrees, Z = 8, R = 0.054. The coordination geometries about the Cu(II) ion in 2 and 4 are best described as distorted square-based pyramidal, with the latter being nearly perfectly so; the Cl- donor is one of the equitorial ligands. These findings contrast with that observed for [(TMPA)Cu-II](+) (1), which is a near-perfect trigonal pyramid, and steric effects of the quinolyl donors appear to be responsible for the: distortions in 2-4. The solution structures of 2-4 were probed using UV-vis and EPR spectroscopies, suggesting that the solid-state structures observed are maintained in solution, e.g., 2-4 manifest typical tetragonal EPR spectra, while that for 1 is ''reversed'' with g(perpendicular to) > g(parallel to). Cyclic voltammetric measurements carried out on 1-4 in dimethylformamide reveal dramatic effects of the quinolyl for pyridyl replacement in the ligands along the series of complexes. Steric, environmental and/or electronic influences of the quinolyl groups cause an overall increase of similar to 0.45 V for E(1/2) on going from 1 to 4. Discussions include comparisons of properties with other Cu(I) or Cu(II) complexes with tripodal tetradentate ligands, and the possible relevance to [LCu(I)](+)/O-2 reaction product structure: