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.