Eleven-vertex nido-[(qS-C5Me5)RhBloH11CI(PMe2Ph)], when dissolved in CH2C12 solution in the presence of H20, yields the open twelve-vertex oxametalladodecaborane [(~5-CSMe5)RhOBloH9Cl( PMe2Ph)],t which is the first non-carbon-containing open twelve-vertex polyhedral boron cluster compound, and the first boron cluster compound that contains an oxygen atom bound solely to boron in a contiguous cluster position.

The dimeric pentamethylcyclopentadienylrhodium complex [{ Rh(qS-C,Me,)CI,},] is potentially a high-yield rhodaborane synthon, and reacts quantitatively with arachno- [ B, H, , ] to give [6-(q5-C, Me, ) -nido-6-RhB9H,,] as an orange-red air-stable solid, which has been examined by X-ray crystallography. Crystals are orthorhombic, space group Pbca, with a = 1 977.2(3), b = 1 440.1 (2), c = 2 450.1 (4) pm, and Z = 16; the final R factor is 0.0429 for 3 678 observed reflections. N.m.r. data are also presented and briefly discussed; these together with the molecular structure confirm the complex to be a nido-decaborane analogue in which the HB(6) unit is replaced by an isolobal and isoelectronic R h(qS-C,Me,) centre.* nido-6-(q 5-Pentamethylcyclopentadienyl)-6-rhodadecaborane. Supplementary data available (No. SUP 56414, 9 pp.

No abstract

Chromatography in air on silica of the nido eleven-vertex metallaborane [(q5-C5Me5)RhBloH13CI] 2, yields the p-9,9'-oxo-bridged bis(nido-5rhodadecaboranyl) species [ {(q5-C5Me5)RhB9H12}20] 3, whereas treatment with NEt, before exposure to air and chromatography on silica results in the novel contiguous nido twelve-vertex oxarhodadecaborane [7-(q5-C5Me5)l 0-(NEt,)-nido-7,l 2-RhOBloHl0] 4.

as a bright yellow air-stable compound in low yield. Crystals are triclinic, space group P i with a = 948.8(4), b = 1 675.5(6), c = 1 855.0(6) pm, a = 101.48(3), reaction is the yellow compound [1,1-( PMe,Ph),-1 ,2-p-H-2-CI-5-OMe-isoc/oso-l -RhB,,H,], crystals of which are orthorhombic, space group P2,2,2,, with a = 1 267.5(3), b = 1 269.9(3), c = 1 683.4(3) pm, and Z = 4. In each compound the RhB,, cluster is a closed eleven-vertex deltahedron, the hexahapto borane-metal linkage being effected via one Rh-H-B and five Rh-B connectivities. The metal centre is an 18-electron ds rhodium(iti) atom which can be thought to contribute four orbitals to the metallaborane cluster bonding scheme, thus inducing 'isocloso' cluster character. The presence of a bridged metal-hydrogen-boron linkage on the closed polyhedral cluster is also notable. = 99.55(3), y = 99.82(3)", and Z = 4. An occasional by-product of the