Abstract
A dinucleating 1,8-naphthyridine ligand featuring fluorene-9,9-diyl-linked phosphino side arms (PNNP(Flu)) was synthesized and used to obtain the cationic dicopper complexes 2, [(PNNP(Flu))Cu(2)(μ-Ph)][NTf(2)]; [NTf(2)] = bis(trifluoromethane)sulfonimide, 6, [(PNNP(Flu))Cu(2)(μ-CCPh)][NTf(2)], and 3, [(PNNP(Flu))Cu(2)(μ-O(t)Bu)][NTf(2)]. Complex 3 reacted with diboranes to afford dicopper μ-boryl species (4, with μ-Bcat; cat = catecholate and 5, with μ-Bpin; pin = pinacolate) that are more reactive in C(sp)-H bond activations and toward activations of CO(2) and CS(2), compared to dicopper μ-boryl complexes supported by a 1,8-naphthyridine-based ligand with di(pyridyl) side arms. The solid-state structures and DFT analysis indicate that the higher reactivities of 4 and 5 relate to changes in the coordination sphere of copper, rather than to perturbations on the Cu-B bonding interactions. Addition of xylyl isocyanide (CNXyl) to 4 gave 7, [(PNNP(Flu))Cu(2)(μ-Bcat)(CNXyl)][NTf(2)], demonstrating that the lower coordination number at copper is chemically significant. Reactions of 4 and 5 with CO(2) yielded the corresponding dicopper borate complexes (8, [(PNNP(Flu))Cu(2)(μ-OBcat)][NTf(2)]; 9, [(PNNP(Flu))Cu(2)(μ-OBpin)][NTf(2)]), with 4 demonstrating catalytic reduction in the presence of excess diborane. Related reactions of 4 and 5 with CS(2) provided insertion products 10, {[(PNNP(Flu))Cu(2)](2)[μ-S(2)C(Bcat)(2)]}[NTf(2)](2), and 11, [(PNNP(Flu))Cu(2)(μ,κ(2)-S(2)CBpin)][NTf(2)], respectively. These products feature Cu-S-C-B linkages analogous to those of proposed CO(2) insertion intermediate.