Terminal and Internal Alkyne Complexes and Azide-Alkyne Cycloaddition Chemistry of Copper(I) Supported by a Fluorinated Bis(pyrazolyl)borate

Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HC equivalent to CSiMe3 are also reported. They are three-coordinate copper complexes featuring eta(2)-bound alkynes. Raman data show significant red-shifts in C equivalent to C stretch of [H2B(3,5-(CF3)(2)Pz)(2)]Cu(HC equivalent to CH) and [H2B(3,5-(CF3)(2)Pz)(2)]Cu(HC equivalent to CSiMe3) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The pi-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu-2(mu-[3,5-(CF3)(2)Pz])(2)(HC equivalent to CH)(2) display similar Cu-alkyne bonding features. The mononuclear [H2B(3,5-(CF3)(2)Pz)(2)]Cu(NCMe) complex catalyzes [3 + 2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {mu-[3,5-(CF3)(2)Pz]Cu}(3) involving bridging pyrazolates.