Synthesis, structure, and condensed-phase reactivity of [Ag3(μ3-H)(μ3-BH4)LPh3](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)₂NH = L^Ph) and NaBH₄ in acetonitrile and thereby direct the synthesis of the silver nanocluster [Ag₃(μ₃-H)(μ₃-BH₄)L^Ph₃](BF₄), 3b·BF₄, formed via reaction of AgBF₄, bis(diphenylphosphino)amine (dppa = (Ph₂P)₂NH = L^Ph) and NaBH₄ in acetonitrile. The X-ray structure of 3b·BF₄ highlights that the cation adopts a planar trinuclear Ag₃ geometry surrounded by three dppa ligands and coordinated on the bottom face by a μ₃-hydride and on the top face by a μ₃-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 [Ag₃(μ₃-H)(μ₃-BH₄)L^Ph₃]⁺ cluster cation in solution. ESI-MS and in situ¹H and HSQC NMR spectroscopy reveals that 3b·BF₄ reacts with CS₂ in solution at the BH₄ site to yield [Ag₃(H)(S₂CH)L^Ph₃]⁺, 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 [Ag₃(H)(S₂CH)L^Ph₃]⁺ was examined under multistage mass spectrometry conditions using collision-induced dissociation (CID) and compared to that of the previously examined copper analogue, [Cu₃(H)(S₂CH)L^Ph₃]⁺. While both cluster cations fragment via ligand loss, the CID spectra of the resultant [M₃(H)(S₂CH)L^Ph₂]⁺ are different. Unlike [Cu₃(H)(S₂CH)L^Ph₂]⁺, which solely undergoes loss of thioformaldehyde to give [Cu₃(S)L^Ph₂]⁺, [Ag₃(H)(S₂CH)L^Ph₂]⁺ 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 [M₃(H)(S₂CH)L^Me₂]⁺ ((Me₂P)₂NH = 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.