Electrospray Ionization Tandem Mass Spectrometry and DFT Survey of Copper(I) Ate Complexes Containing Coordinated Borohydride Anions.

Copper(I) borohydride ate complexes of the type Cat[XCu(BH)] have been previously postulated as intermediates in the reactions of copper salts with borohydride. Negative ion electrospray ionization of an acetonitrile solution of copper(I) phenylacetylide with a 10-fold excess of sodium borohydride (NaBH) revealed the formation of a diverse range of mononuclear, dinuclear and trinuclear cuprates with different numbers of BH, H and CN ligands, the latter likely being formed by abstraction of CN from the acetonitrile solvent. Collision-induced dissociation was used to examine the fragmentation reactions of the following borohydride containing cuprates: [Cu(H)(BH)], [Cu(BH)], [Cu(BH)(CN)], [Cu(H)(BH)], [Cu(H)(BH)], [Cu(BH)(CN)], [Cu(H)(BH)(CN)], [Cu(H)(BH)], [Cu(H)(BH)], [Cu(H)(BH)], [Cu(BH)(CN)], and [Cu(H)(BH)(CN)]. In all cases, BH loss is observed. For many of the dinuclear and trinuclear complexes cluster fragmentation by loss of CuH was also observed. In the case of [Cu(H)(BH)] and [Cu(H)(BH)], loss of H was also observed. DFT calculations were used to explore potential structures of the various borohydride-containing cuprates and to predict the overall reaction energetics for the various fragmentation channels.