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

Copper(II) aryl species are proposed key intermediates in Cu-catalyzed cross-coupling reactions. Novel three-coordinate copper(II) aryls [Cu-II]-C6F5 supported by ancillary beta-diketiminate ligands form in reactions between copper(II) alkoxides [Cu-II]-(OBu)-Bu-t and B(C6F5)(3). Crystallographic, spectroscopic, and DFT studies reveal geometric and electronic structures of these Cu(II) organometallic complexes. Reaction of [Cu-II]-C6F5 with the free radical NO(g) results in C-N bond formation to give [Cu](eta(2)-ONC6F5). Remarkably, addition of the phenolate anion PhO- to [Cu-II]-C6F5 directly affords diaryl ether PhO-C6F5 with concomitant generation of the copper(I) species [Cu-I] (solvent) and {[Cu-I]-C6F5}(-). Experimental and computational analysis supports redox disproportionation between [Cu-II]-C6F5 and {[Cu-II](C6F5)(OPh)}(-) to give {[Cu-I]-C6F5}(-) and [Cu-III] (C6F5) (OPh) unstable toward reductive elimination to [Cu-I] (solvent) and PhO-C6F5.