Unsupported Bonds between Copper(I) and Heavier Pnictogens

This study highlights the use of fluorinated poly(pyrazolyl)borate ligands to stabilize copper(I) complexes with heavy pnictogen donors such as SbPh 3 and BiPh 3 . It presents two series of valence isoelectronic molecules, enabling a direct and meaningful comparison between the lighter and heavier analogues. Specifically, [HB(3,5-(CF 3 ) 2 Pz) 3 ] − and [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ] − have been utilized in the stabilization of a series of copper(I) complexes with EPh 3 (E = As, Sb, Bi), along with full characterization including their molecular structures and a detailed analysis of group 15 trends. The isolation of a copper–bismuthine complex, [HB(3,5-(CF 3 ) 2 Pz) 3 ]Cu(BiPh 3 ), is especially notable as an example of a direct, unsupported Cu–Bi bond. DFT calculations show that the stabilization energy of Cu–E interactions decreases from P to Bi, illustrating the difficulty in stabilizing bismuthine ligands and the role of relativistic effects in reducing the bonding and Lewis basicity characteristics of the E coordinating center. The Cu-EPh 3 bond mainly relies on electrostatic interactions, but orbital interactions are also significant, with the Ph 3 E→Cu σ-donation being much stronger than Ph 3 E←Cu π-backdonation. Reactivity studies of [HB(3,5-(CF 3 ) 2 Pz) 3 ]Cu(BiPh 3 ) and computational investigations on how fluorinated supporting ligands on Cu(I) affect the formation of the Cu–E adduct are also included.