Metallaheteroborane chemistry. Part 4. The synthesis of closo-[2,2-(PPh3)2-2-H-1,2-XMB10H10](X = Se or Te, M = Rh or Ir) compounds, their characterisation by nuclear magnetic resonance techniques, and the crystal and molecular structure of the X = Te, M = Rh complex

Abstract

The reactions between [M(PPh₃)₃Cl](M = Rh or Ir) and the nido-[7-XB₁₀H₁₁]^–(X = Se or Te) anions in ethanol afford air-stable closo-[2,2-(PPh₃)₂-2-H-1,2-XMB₁₀H₁₀] complexes in moderate to high yields. N.m.r. data confirm the presence of the M(PPh₃)₂H units and the closo nature of the metallaheteroboranes. An X-ray diffraction study of closo-[2,2-(PPh₃)₂-2-H-1,2-TeRhB₁₀H₁₀]·0.5-C₆H₁₂ shows the triclinic crystals to belong to the P space group with Z= 2 and cell dimensions a= 12.406(1), b= 17.872(4), c= 10.010(1)Å, α= 94.30(1), β= 107.25(1), and γ= 94.31(1)°. The final R factor was 0.033 for 5 380 observed reflections. Principal interatomic distances include Rh–Te 2.617 2(4), Rh–B 2.238(4)–2.333(5), and Te–B 2.296(4)–2.399(4)Å. The conformation of the Rh(PPh₃)₂H unit above the TeB₄ face to which it is bonded has the Rh–H and Rh–Te vectors trans to each other. The conformational preferences of M(PPh₃)₂H units in the new complexes and in electronically related metallacarbaboranes are discussed. The detailed n.m.r. properties indicate a close electronic relationship with the previously reported [2,2-(PR₃)₂-1,2-XPtB₁₀H₁₀](X = Se or Te) species.