Three-Coordinate Copper(II) Aryls: Key Intermediates in C-O Bond Formation.

Abstract

Copper(II) aryl species are proposed key intermediates in Cu-catalyzed cross-coupling reactions. Novel three-coordinate copper(II) aryls [CuII]-C6F5 supported by ancillary β-diketiminate ligands form in reactions between copper(II) alkoxides [CuII]-OtBu and B(C6F5)3. Crystallographic, spectroscopic, and DFT studies reveal geometric and electronic structures of these Cu(II) organometallic complexes. Reaction of [CuII]-C6F5 with the free radical NO(g) results in C-N bond formation to give [Cu](η2-ONC6F5). Remarkably, addition of the phenolate anion PhO- to [CuII]-C6F5 directly affords diaryl ether PhO-C6F5 with concomitant generation of the copper(I) species [CuI](solvent) and {[CuI]-C6F5}-. Experimental and computational analysis supports redox disproportionation between [CuII]-C6F5 and {[CuII](C6F5)(OPh)}- to give {[CuI]-C6F5}- and [CuIII](C6F5)(OPh) unstable toward reductive elimination to [CuI](solvent) and PhO-C6F5.