Homoleptic Cobalt and Copper Phenolate A2[M(OAr)4] Compounds:  The Effect of Phenoxide Fluorination

Two series of homoleptic phenolate complexes with fluorinated aryloxide ligands A2[M(OAr)4] with M = Co2+ or Cu2+, OAr- = (OC6F5)- (OArF) or {3,5-OC6H3(CF3)2}- (OAr‘), A+ = K (18-crown-6)+, Tl+, Ph4P+, Et3HN+, or Me4N+ have been synthesized. Two related complexes with nonfluorinated phenoxide ligands have been synthesized and studied in comparison to the fluorinated aryloxides demonstrating the dramatic structural changes effected by modification of OPh to OArF. The compounds {K(18-crown-6)}2[Cu(OArF)4], 1a; {K(18-crown-6)}2[Cu(OAr‘)4], 1b; [Tl2Cu(OArF)4], 2a; [Tl2Cu(OAr‘)4], 2b; (Ph4P)2[Cu(OArF)4], 3; ( n Bu4N)2[Cu(OArF)4], 4; (HEt3N)2[Cu(OArF)4], 5; {K(18-crown-6)}2[Cu2(μ2-OC6H5)2(OC6H5)4], 6; {K(18-crown-6)}2[Co(OArF)4], 7a; {K(18-crown-6)}2[Co(OAr‘)4], 7b; [Tl2Co(OArF)4], 8a; [Tl2Co(OAr‘)4], 8b; (Me4N)2[Co(OArF)4], 9; [Cp2Co]2[Co(OAr‘)4], 10; and {K(18-crown-6)}2-[Co2(μ2-OC6H5)2(OC6H5)4], 11, have been characterized with UV−vis and multinuclear NMR spectroscopy and solution magnetic moment studies. Cyclic voltammetry was used to study 1a, 1b, 7a, and 7b. X-ray crystallography was used to characterize 1b, 3, 4, 5, 6, 7a, 7b, 10, and 11. The related [MX4]2- compound (Ph4P)2[Co(OArF)2Cl2], 12, has also been synthesized and characterized spectroscopically, as well as with conductivity and single-crystal X-ray diffraction. Use of fluorinated aryloxides permits synthesis and isolation of the mononuclear, homoleptic phenolate anions in good yield without oligomerized side products. The reaction conditions that result in homoleptic 1a and 7a with OArF upon changing the ligand to OPh result in μ2-OPh bridging phenoxides and the dimeric complexes 6 and 11. The [M(OArF)4]2- and [M(OAr‘)4]2- anions in 1a, 1b, 3, 4, 5, 7a, 7b, 9, and 10 demonstrate that stable, isolable homoleptic phenolate anions do not need to be coordinatively or sterically saturated and can be achieved by increasing the electronegativity of the ligand.