The copper nanocluster [Cu₃(μ₃-H)(μ₃-BH₄)L^Ph₃](BF₄), 1a·BF₄ (L^Ph = (PPh₂)₂NH = dppa), can potentially react with substrates at either the coordinated hydride or borohydride sites. Reaction of 1a·BF₄ with CS₂ has given rise to [Cu₃(μ₃-H)(μ₂,μ₁-S₂CH)L^Ph₃](BF₄), (2a·BF₄), which was structurally characterised using electrospray ionisation (ESI) with high-resolution mass spectrometry (HRMS), X-ray crystallography, NMR, IR and UV-Vis spectroscopy. The copper(I) atoms adopt a planar trinuclear Cu₃ geometry coordinated on the bottom face by a μ₃-hydride, on the top face by a μ₂,μ₁-dithioformate and surrounded by three bridging L^Ph ligands. Reaction of 1a·BF₄ with elemental sulfur gives the known cluster [Cu₄(L^Ph-H + 2S)₃](BF₄), (3·BF₄), which was structurally characterised via X-ray crystallography. ESI-MS of 2a·BF₄ produces [Cu₃(H)(S₂CH)L^Ph₃]⁺ and its gas-phase ion chemistry was examined under multistage mass spectrometry conditions using collision-induced dissociation (CID). The primary product, [Cu₃(H)(S₂CH)L^Ph₂]⁺, formed via ligand loss, undergoes further fragmentation via loss of thioformaldehyde to give [Cu₃(S)L^Ph₂]⁺. DFT calculations exploring rearrangement and fragmentation of the model system [Cu₃(H)(S₂CH)L^Me₂]⁺ (L^Me = (PMe₂)₂NH = dmpa) provide a feasible mechanism. Thus, coupling of the coordinated hydride with the dithioformate ligands gives [Cu₃(S₂CH₂)L^Me₂]⁺, which then undergoes CH₂S extrusion via C–S bond cleavage to give [Cu₃(S)L^Me₂]⁺.