Synthesis, structure, and condensed-phase reactivity of [Ag3(μ3-H)(μ3-BH4)L3Ph](BF4) (LPh = bis(diphenylphosphino) amine) with CS2

Electrospray ionisation mass spectrometry (ESI-MS) was used to monitor the reaction of AgBF4, bis(diphenylphosphino) amine (dppa = (Ph2P)(2)NH = L-Ph) and NaBH4 in acetonitrile and thereby direct the synthesis of the silver nanocluster [Ag-3(mu(3)-H)(mu(3)-BH4)L-3(Ph)](BF4), 3b.BF4, formed via reaction of AgBF4, bis(diphenylphosphino) amine (dppa = (Ph2P)(2)NH = L-Ph) and NaBH4 in acetonitrile. The X-ray structure of 3b.BF4 highlights that the cation adopts a planar trinuclear Ag-3 geometry surrounded by three dppa ligands and coordinated on the bottom face by a mu(3)-hydride and on the top face by a mu(3)-BH4. The solution phase structure of 3b.BF4 was characterised by multinuclear NMR and DOSY NMR, which showed that the borohydride anion remains bound in the [Ag-3(mu(3)-H)(mu(3)-BH4) L-3(Ph)](+) cluster cation in solution. ESI-MS and in situ H-1 and HSQC NMR spectroscopy reveals that 3b.BF4 reacts with CS2 in solution at the BH4 site to yield [Ag-3(H)(S2CH)L-3(Ph)](+), 4b, which has to date eluded structural characterisation via X-ray crystallography due to lack of formation of suitable crystals. The gas-phase ion chemistry of [Ag-3(H)(S2CH)L-3(Ph)](+) was examined under multistage mass spectrometry conditions using collision-induced dissociation (CID) and compared to that of the previously examined copper analogue, [Cu-3(H)(S2CH)L-3(Ph)](+). While both cluster cations fragment via ligand loss, the CID spectra of the resultant [M3(H)(S2CH) LPh 2]+ are different. Unlike [Cu-3(H)(S2CH) L-2(Ph)](+), which solely undergoes loss of thioformaldehyde to give [Cu-3(S)L-2(Ph)](+), [Ag-3(H)(S2CH)L-2(Ph)](+) gives a richer CID spectrum with fragmentation channels that include ligand loss, CH2S loss and reductive elimination of dithioformic acid. DFT calculations exploring rearrangement and fragmentation of the model systems [M-3(H)(S2CH)L-2(Me)]+ ((Me2P)(2)NH = dmpa = L-Me) were used to suggest plausible mechanisms and examine the energetics of the three competing channels: ligand loss, CH2S loss and reductive elimination of dithioformic acid.