Metallaheteroborane chemistry. Part 10. Synthesis and characterisation of closo-structured rhodathiaborane complexes [1-(CO)-1-L-3-L′-1,2-RhSB9H8](L = L′= PPh3; L = PMe2Ph, L′= PMe2Ph or PPh3)

Abstract

The reaction of CO with [8,8-(PPh₃)₂-8,7-RhSB₉H₁₀]1 in benzene yields [8-(CO)-8,8-(PPh₃)₂-nido-8,7-RhSB₉H₁₀]3 in 98% yield. Refluxing a benzene solution of 3 produces [1-(CO)-1,3-(PPh₃)₂-closo-1,2-RhSB₉H₈]4 in 46% yield. The reaction between 4 and excess of PMe₂Ph in refluxing benzene affords [1-(CO)-1-(PMe₂Ph)-3-L-closo-1,2-RhSB₉H₈][L = PMe₂Ph 5(25%) or PPh₃6(46%)]. NMR data (¹H, ¹¹B and ³¹P) confirm the nido nature of 3 and the closo structures of compounds 4–6. X-Ray diffraction studies of 4, 4′(=4·1.5C₆H₅Me), and 5 showed that there was conformational disorder in all three cases. The structure of 5 was solved in space group P2₁/n with unit cell dimensions of a= 9.626(2), b= 23.714(5), c= 11.595(2)Å, β= 109.00(2)°, and Z= 4. The final R factor was 0.027 for 4472 observed reflections. Principal interatomic distances are Rh(1)–S(2) 2.3736(7), Rh(1)–P(1) 2.3090(7), Rh(1)–C(1) 1.855(3), Rh(1)–B(3) 2.101(3), Rh(1)–B (4, 5, 6, 7) 2.380(3)–2.444(3), S(2)–B 1.923(3)–1.989(4), B–B 1.719(4)–1.897(4) and B(3)–P(2) 1.895(3)Å. The geometry of the RhSB₉ cage in 5 was used as a template in the final refinement of the structures of 4 and 4′ which were more disordered: 4, space group C2/c, a= 37.529(11), b= 10.749(5), c= 19.536(5)Å, β= 101.96(2)°, Z= 8, R 0.051 for 3970 observed reflections; 4′, space group P, a= 11.933(2), b= 14.157(2), c= 14.190(2)Å, α= 79.25(1), β= 83.27(1), γ= 87.32(1)°, Z= 2, R 0.041 for 6959 observed reflections.