Copper(I) Complexes of Amide Functionalized Bisphosphine: Proximity Enhanced Metal-Ligand Cooperativity and Its Catalytic Advantage in C(sp 3)-H Bond Activation of Unactivated Cycloalkanes in Dehydrogenative Carboxylation Reactions

The reactions of amide functionalized bisphosphine, o-Ph2PC6H4C-(O)N(H)C6H4PPh2-o (1) (BalaHariPhos), with copper salts is described. Treatment of 1 with CuX in a 1:1 molar ratio yielded chelate complexes of the type [CuX{(o-Ph2PC6H4C(O)N(H)C6H4PPh2-o)}-kappa(2)-P,P] (X = Cl, 2; Br, 3; and I, 4), which on subsequent treatment with (KOBu)-Bu-t resulted in a dimeric complex [Cu(o-Ph2PC6H4C(O)(N)C6H4PPh2-o)](2) (5). Interestingly, complexes 2-4 showed weak N-H<middle dot><middle dot><middle dot>Cu interactions. These weak H-bonding interactions are studied in detail both experimentally and computationally. Also, Cu-I complexes 2-5 were employed in the oxidative dehydrogenative carboxylation (ODC) of unactivated cycloalkanes in the presence of carboxylic acids to form the corresponding allylic esters. Among complexes 2-5, halide-free dimeric Cu-I complex 5 showed excellent metal-ligand cooperativity in the oxidative dehydrogenative carboxylation (ODC) in the presence of carboxylic acids to form the corresponding allylic esters through C(sp(3))-H bond activation of unactivated cycloalkanes. Mechanistic details of the catalytic process were established by isolating the precatalyst [Cu{(o-Ph2PC6H4C(O)(NH)C6H4PPh2-o)-kappa(2)-P,P}(OOCPh)] (6) and fully characterized by mass spectrometry, NMR data, and single-crystal X-ray analysis. Density functional theory-based calculations further provided a quantitative understanding of the energetics of a series of H atom transfer steps occurring in the catalytic cycle.