Isolation and structure of [(PPh3)(3)(PPh2)(2)Pd4B20H16]. A possible prognostic for new globular borane-based cluster architectures

A novel metallaborane compound, [(PPh3)(3)(PPh2)(2)Pd4B20H16], prepared fro m [PdCl2(PPh3)(2)] and [B10H10](2-) in EtOH, exhibits a globular cluster ar chitecture consisting of two twelve-vertex closo {PdB11} cluster units fuse d to generate a condensed globular {PdB20) assembly that has a tetrahedral (B-4) borons-only core. There is dynamic bonding between this borane-based assembly and an unusual exopolyhedral palladium-based domain consisting of a {(PPh3)Pd(PPh2)Pd(PPh2)Pd(PPh3)} string. The central tetrahedral borons-o nly core suggests a new type of globular "megaloborane" architectural princ iple for higher condensed boron hydrides, which is assessed by nb initio st udies at the STO-3G level on protonated [B28H18](2-) and related structures : results suggest energetic minimisation at neutral [B27H21].