Isonitrile ligand effects on small-molecule-sequestering in bimetalladodecaborane clusters

The bimetalladodecaborane cluster compound [(PMe2Ph)4Pt2B10H10] 1, quantitatively reacts with EtNC at room temperature to afford [{(EtNC)(PMe2Ph)3}(μ-EtNC)Pt2B10H10] 3 in which one molecule of EtNC replaces a terminal PMe2Ph ligand, and a second molecule of EtNC bridges the Pt–Pt vector. The metal-bridging EtNC molecule can be ejected from 3, either by irradiation with UV light, or via displacement with CO to form [{(EtNC)(PMe2Ph)3}(μ-CO)Pt2B10H10] 4. The CO-bridge may then in turn be replaced with SO2 to give [{(EtNC)(PMe2Ph)3}(μ-SO2)Pt2B10H10] 5. If 3 is allowed to react directly with SO2 then the SO2 molecule takes up a bridging position and the bridging EtNC displaces a terminal metal-bound phosphine to afford [{(EtNC)2(PMe2Ph)2}(μ-SO2)Pt2B10H10] 6. The transient absorption spectrum of 3 under UV illumination is investigated and shows that the bridging isonitrile is ejected to produce a transient spectrum very similar to that of [(PMe2Ph)4Pt2B10H10] 1. Reaction of [(PMe2Ph)4Pd2B10H10] 7, viz. the dipalladium analogue of 1, with EtNC results in the displacement of two PMe2Ph phosphine ligands forming [{(EtNC)2(PMe2Ph)2}Pd2B10H10] 8, which has no bridging EtNC unit and which shows only a weak ability to form an adduct with SO2. DFT calculations at the B3LYP/6-31G* level mirror the observed data well.