STUDIES ON TETRABORANE(8) CARBONYL, B4H8.CO - ITS ISOMERIC COMPOSITION IN THE GAS-PHASE AND IN SOLUTION, AND ITS REACTIONS WITH ALKENES

B-11 NMR spectra of tetraborane(8) carbonyl, B4H8 . CO I, reveal a cha ngeover in the distribution of isomers in going from toluene solution to the gas phase. Fortuitously the distribution is 60:40 in each case, but comparison with published electron diffraction data and ab initio /IGLO computations indicates that the CO group is disposed endo with r espect to the B-4 'butterfly' framework in the predominant isomer in t he gas phase, and exo in solution. The results also allow conclusions to be drawn about the geometries of other B4H8 . L isomers on the basi s of their reported proton NMR chemical shifts. Reactions of B4H8 . CO with ethene and propene at ca. 30 bar yield products, R4B4H4 . CO (R = Et 2 or Pr-3 3), in which all four wingtip hydrogen atoms of the tet raborane carbonyl have been replaced by alkyl groups. Variable-tempera ture B-11 and H-1 NMR spectra of 2 and 3 reveal interesting fluxional behaviour. (C) 1998 Elsevier Science S.A.