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 SbPh3 and BiPh3. It presents two series of valence isoelectronic molecules, enabling a direct and meaningful comparison between the lighter and heavier analogues. Specifically, HB(3,5-(CF3)2Pz)3- and H2B(3,5-(CF3)2Pz)2- have been utilized in the stabilization of a series of copper(I) complexes with EPh3 (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-(CF3)2Pz)3Cu(BiPh3), 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-EPh3 bond mainly relies on electrostatic interactions, but orbital interactions are also significant, with the Ph3E→Cu σ-donation being much stronger than Ph3E←Cu π-backdonation. Reactivity studies of HB(3,5-(CF3)2Pz)3Cu(BiPh3) and computational investigations on how fluorinated supporting ligands on Cu(I) affect the formation of the Cu-E adduct are also included.