An approach to megalo-boranes. Mixed and multiple cluster fusions involving iridaborane and platinaborane cluster compounds. Crystal structure determinations by conventional and synchrotron methods

Abstract

Several new macropolyhedral metallaboranes have been isolated from thermolytic mixed cluster fusion reactions involving metallaboranes and molten B 10H 14 as solvent. Co-thermolysis of B 10H 14 with nine-vertex [(CO)(PMe 3) 2HIrB 8H 12] ( 1) engenders 18-vertex [(CO)(PMe 3) 2IrB 17H 20] ( 3), via double cluster fusion; this has the 18-vertex configuration of syn-B 18H 22, but with a metal atom in the 10-position. From the same reaction, triple cluster fusion engenders 28-vertex [(PMe 3) 2IrB 26H 24Ir(CO)(PMe 3) 2] ( 4), which structurally is based on an intimate interfusion of closed 10-vertex and 12-vertex subclusters, to generate a tetrahedral tetraboron core that also has a more open commo one-boron linkage to a nido nine-vertex {IrB 8} subcluster. Compound 4 exhibits interesting consequences of cluster-crevice formation and introduces the concept of globular megalo-borane structures that have borons-only cores surrounded by boron-hydride sheaths. Examination for incipient megalo-borane globular behaviour in another system, viz. [IrCl(PPh 3) 3] ( 7) with anti-B 18H 22, reveals a four-atom core feature in 19-vertex [(PPh 3)HIrB 18H 18(PPh 3)] ( 6), which has a closo-type {IrB 10} 11-vertex subcluster fused to a nido 10-vertex {B 10} subcluster to generate a four-atom {IrB 3} tetrahedron. Examination for mixed cluster fusion in other systems reveals the generation of [(PMe 2Ph) 2Pt- anti-B 18H 20] ( 8), from the co-thermolysis of [(PMe 2Ph) 2PtB 8H 12] ( 2) and B 10H 14, and examination for multiple cluster fusion reveals the formation of 30-vertex [(PMe 2Ph) 2(PMe 2C 6H 4) 2Pt 2B 28H 32] ( 10), 29-vertex [(PMe 2Ph) 2PtB 28H 32] ( 11) and 27-vertex [(PMe 2Ph) 2PtB 26H 26(PMe 2Ph)] ( 12) from the same reaction. Structurally, compound 10 is based on a 10-vertex arachno-{6,9-Pt 2B 8} unit linked, via one B–B two-electron two-centre bond each, to two 10-vertex nido-{B 10} units; it also exhibits molecular condensation in the form of two P-phenylene ortho-cycloboronations. Compound 11 is based on the 19-vertex [(PMe 2Ph) 2Pt-η 4- anti-B 18H 22] configuration with an additional 10-vertex nido-{B 10H 13} moiety bound to the non-platinated subcluster via one B–B two-electron two-centre bond. Compound 12 is based on two nido 11-vertex {PtB 10} units joined by a single commo Pt vertex, with one of these units conjoined to an arachno eight-boron unit via a two-boron common edge and an open bridging {B–H( exo)–Pt–μ-B 2} link. Thermolysis of [(PMe 2Ph) 2PtB 8H 12] ( 2) with the pre-formed double-cluster compound anti-B 18H 22 generates triple-contiguity 27-vertex [(PMe 2Ph)PtB 26H 26(PMe 2Ph)] ( 13) which, structurally, consists of a nido 11-vertex {PtB 10} unit that is fused to a second 11-vertex nido {PtB 10} unit with a triangular {PtB 2} face in common, and also fused to a 10-vertex nido {B 10} unit with a {B 2} edge in common. The sequence 12→ 11→ 10→ 13→ 4 represents a progression of increasing intimacy of cluster fusion. Small crystals of compounds 3, 11 and 12 necessitated synchrotron X-radiation for sufficient diffraction intensity.