A Reversible NO-Triggered Multiple Metallaborane Cluster Fusion by Ligand Expulsion/Addition from (PMe 2 Ph) 4 Pt 2 B 10 H 10 to Afford (PMe 2 Ph) 8 Pt 8 B 40 H 40 and (PMe 2 Ph) 5 Pt 4 B 20 H 20

The dimetallic boron hydride cluster, (PMe2 Ph)4 Pt2 B10 H10 ( 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 {(PMe2 Ph) x Pt2 B10 H10 } units to afford the metallaborane conglomerates (PMe2 Ph)8 Pt8 B40 H40 ( 2 -Pt8 , 38%) and (PMe2 Ph)5 Pt4 B20 H20 ( 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 (PMe2 Ph)2 Pt2 B10 H10 4 in quantitative yield. The compounds were characterized by mass spectrometry, multielement NMR spectroscopy, and single-crystal X-ray diffraction studies.