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 4 )] - 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 4 ) revealed the formation of a diverse range of mononuclear, dinuclear and trinuclear cuprates with different numbers of BH 4 - , 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 4 )] - , [Cu(BH 4 ) 2 ] - , [Cu(BH 4 )(CN)] - , [Cu 2 (H)(BH 4 ) 2 ] - , [Cu 2 (H) 2 (BH 4 )] - , [Cu 2 (BH 4 ) 2 (CN)] - , [Cu 2 (H)(BH 4 )(CN)] - , [Cu 3 (H)(BH 4 ) 3 ] - , [Cu 3 (H) 2 (BH 4 ) 2 ] - , [Cu 3 (H) 3 (BH 4 )] - , [Cu 3 (BH 4 ) 2 (CN) 2 ] - , and [Cu 3 (H)(BH 4 ) 2 (CN)] - . In all cases, BH 3 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 2 (H) 2 (BH 4 )] - and [Cu 3 (H) 3 (BH 4 )] - , loss of H 2 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.