A Reversible NO-Triggered Multiple Metallaborane Cluster Fusion by Ligand Expulsion/Addition from (PMe₂Ph)₄Pt₂B₁₀H₁₀ to Afford (PMe₂Ph)₈Pt₈B₄₀H₄₀ and (PMe₂Ph)₅Pt₄B₂₀H₂₀

The dimetallic boron hydride cluster, (PMe₂Ph)₄Pt₂B₁₀H₁₀ (1-Pt₂), is known to reversibly sequester small molecules (e.g., O₂, CO, and SO₂) across its Pt–Pt cluster vector. Here, we report the very different effect of the addition of nitric oxide (NO) to solutions of (1-Pt₂) that prompts the elimination of some of its phosphine ligands and the autofusion of the resultant {(PMe₂Ph)_xPt₂B₁₀H₁₀} units to afford the metallaborane conglomerates (PMe₂Ph)₈Pt₈B₄₀H₄₀ (2-Pt₈, 38%) and (PMe₂Ph)₅Pt₄B₂₀H₂₀ (3-Pt₄, 34%). Single-crystal X-ray studies of these multicluster assemblies reveal the links between the clusters to be a combination of both Pt–Pt bonds and Pt-μH-B 2-electron, 3-center bonds in (2-Pt₈) and Pt-μH-B 2-electron, 3-center bonds in (3-Pt₄). For compound (2-Pt₈), the cluster assemblage can be effectively reversed by the addition of ethyl isonitrile (EtNC) to afford (EtNC)₃(PMe₂Ph)₂Pt₂B₁₀H₁₀ 4 in quantitative yield. The compounds were characterized by mass spectrometry, multielement NMR spectroscopy, and single-crystal X-ray diffraction studies.