Comparative ten-vertex metallaborane chemistry: some nido-6-metalladecaboranes of tungsten, rhenium, ruthenium, osmium, and iridium; including the crystal and molecular structures of [6,6,6,6,6-(PMe2Ph)3H2-nido-6-WB9H13] and [6,6,6-(PMe2Ph)3-nido-6-OsB9H13

Abstract

Reaction of [WH6(PMe2Ph)3] with [NEt4][B9H14] yields the first wolfraborane, [6,6,6,6,6(PMe2Ph)3H2-nido-6-WB9H13]; the halcyon-blue air-stable compound has been characterised by a single-crystal X-ray diffraction analysis and by n.m.r. spectroscopy. Crystals are monoclinic, space group P21/n, with a= 1 571.7(5), b= 1 049.1 (5), c= 1 961.5(8) pm, β= 94.30(3)°, and Z= 4. The molecular structure closely resembles that of nido-B10H14 with the BH unit at position 6 being subrogated by a WH2(PMe2Ph)3 metal centre. In solution the compound exhibits fluxionality of the five exo-polyhedral ligands (PMe2Ph)3H2 on the metal centre. Reaction of mer-[OsCl3(PMe2Ph)3] with [NBu4][B9H14] yields the new red air-stable osmaborane [6,6,6-(PMe2Ph)3-nido-6-OsB9H13] which has also been characterized by a single-crystal X-ray diffraction analysis and n.m.r. spectroscopy. Crystals are monoclinic, space group P21/c, with a= 957.8(1), b= 1 990.0(4), c= 1 671.4(3) pm, β= 94.01(1)° and Z= 4. The structure comprises nido-decaborane-like molecules in which the 6-BH unit has been subrogated by the isolobal Os(PMe2Ph)3 unit. The analogous reaction with mer-[RuCl3(PMe2Ph)3] yields the new dark amber ruthenaborane [6,6,6-(PMe2Ph)3-nido-6-RuB9H13], and with [ReH5(PMe2Ph)3] and [NEt4][B9H14] the previously reported rhenaborane [6,6,6,6-(PMe2Ph)3H-nido-6-ReB9H13] is formed in an improved yield of 65%. The new tungsten and osmium species together with the known nido-6-metalladecaboranes [(PMe2Ph)3HReB9H13] and [(PR3)2HIrB9H13](R = Me or Ph) permit the structural and n.m.r. comparison of the metallaboranes across four adjacent groups of the Periodic Table; the systematic variation of the exo-polyhedral metal ligands across the sequence WH2(PMe2Ph)3, ReH(PMe2Ph)3, Os(PMe2Ph)3, IrH (PR3)2 implies that each 18-electron metal centre is a three-orbital two-electron contributor to the cluster bonding, just like 6-BH in the structural parent nido-B10H14. For the compounds studied there is a progressive diminution of ca. 5 pm per elemental step in both the M–B and M–P interatomic distances across the series W, Re, Os, Ir, but the 11B and 1H n.m.r. properties indicate that the cluster bonding retains essentially nido-decaborane-like behaviour throughout.