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.