Preparation, structure, and nuclear magnetic resonance properties of the nine-vertex nido-rhenaborane [(PMe2Ph)3H2ReB8H11] and some related chemistry

Abstract

Thermolysis of [6,6,6-(PMe₂Ph)₃-6-H-nido-6-ReB₉H₁₂-9-(OEt)](1) in C₂D₂Cl₄ solution gives the new, pale yellow air-stable compound [2,2,2-(PMe₂Ph)₃-2,2-H₂-nido-2-ReB₈H₁₁](2) in 80% yield. Crystals of the CH₂Cl₂ hemisolvate of (2) are monoclinic, space group P2₁/c, with a= 1 130.0(3), b= 1 292.2(3), c= 2 424.0(5) pm, β= 94.15(2)°, and Z= 4; the molecular structure was refined to R= 0.0399, R′= 0.0454. The detailed n.m.r. behaviour of compound (2) together with data for previously reported rhodium and iridium analogues permits the location of the substituent site on previously unconfirmed [2-(CO)-2,2-(PMe₃)₂-nido-2-IrB₈H₁₀-3-Cl] and thence provides information on mechanistic pathways for the formation of these and related metallaboranes. Detailed n.m.r. data for the non-metalla analogues [B₉H₁₂]^– and previously unassigned [3-ClB₉H₁₁]^– provide information on their mechanism of formation and a comparison with the metallaborane analogues. The n.m.r. work includes extensive use of [¹¹B–¹¹B]-COSY and [¹H–¹H]-COSY experiments and establishes general points.