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(BH4)]- 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 (NaBH4) revealed the formation of a diverse range of mononuclear, dinuclear and trinuclear cuprates with different numbers of BH4 -, 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)(BH4)]-, [Cu(BH4)2]-, [Cu(BH4)(CN)]-, [Cu2(H)(BH4)2]-, [Cu2(H)2(BH4)]-, [Cu2(BH4)2(CN)]-, [Cu2(H)(BH4)(CN)]-, [Cu3(H)(BH4)3]-, [Cu3(H)2(BH4)2]-, [Cu3(H)3(BH4)]-, [Cu3(BH4)2(CN)2]-, and [Cu3(H)(BH4)2(CN)]-. In all cases, BH3 loss is observed. For many of the dinuclear and trinuclear complexes cluster fragmentation by loss of CuH was also observed. In the case of [Cu2(H)2(BH4)]- and [Cu3(H)3(BH4)]-, loss of H2 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.

Automated summary

This study investigates the fragmentation reactions of borohydride-containing cuprates using negative ion electrospray ionization. The experiment reveals the formation of different types and numbers of copper acid salts in the reaction between copper(I) phenylacetylide and sodium borohydride. The loss of different ligands is observed in the fragmentation reactions, and the overall reaction energetics are predicted using DFT calculations.