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

Ligand design and construction is an important aspect of controlling s tructure and reactivity in coordination chemistry, and here we describ e the synthesis and effects conferred upon the structure, spectroscopy and electrochemistry of [LCu(II)Cl](+) (1-4), where L is a tripodal t etradentate donor, TMPA (=tris[((2-pyridyl)methyl)-methyl]amine), or c orresponding, ligands with one (BPQA), two (BQPA), or three (TMQA) 2-q uinolyl groups substituted for 2-pyridyl donors. Previous investigatio ns (Karlin, K.; et al. J. Am. Chem. Sec. 1993, 115, 9506, Wei, N.; et al. Inorg. Chem.: 1994, 33, 1953) have indicated dramatic influences u pon stoichiometry, structure and kinetic/thermodynamics in the O-2-rea ctivity with corresponding reduced copper(I) species [LCu(I)](+). Reac tions of the quinolyl-containing ligands with copper(II) chloride, fol lowed 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; [(TMQ A>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(I I) ion in 2 and 4 are best described as distorted square-based pyramid al, with the latter being nearly perfectly so; the Cl- donor is one of the equitorial ligands. These findings contrast with that observed fo r [(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 struct ures observed are maintained in solution, e.g., 2-4 manifest typical t etragonal EPR spectra, while that for 1 is ''reversed'' with g(perpend icular to) > g(parallel to). Cyclic voltammetric measurements carried out on 1-4 in dimethylformamide reveal dramatic effects of the quinoly l for pyridyl replacement in the ligands along the series of complexes . Steric, environmental and/or electronic influences of the quinolyl g roups cause an overall increase of similar to 0.45 V for E(1/2) on goi ng from 1 to 4. Discussions include comparisons of properties with oth er Cu(I) or Cu(II) complexes with tripodal tetradentate ligands, and t he possible relevance to [LCu(I)](+)/O-2 reaction product structure: