150499-82-4Relevant academic research and scientific papers
Balancing Steric and Electronic Effects in Carbonyl–Phosphine Molybdacarboranes
Robertson, Alasdair P. M.,Reckziegel, Alexander,Jones, John J.,Rosair, Georgina M.,Welch, Alan J.
, p. 4581 - 4588 (2017)
Analysis of the literature structures [(CO)(PPh3)2MC2B9H11] and [(CO)2(PPh3)MC2B9H11] suggests that in [L3MC2B9H11] metallacarboranes the trans influence of CO is greater than that of PPh3. Extending this study to the [L4MC2B9H11] system the new molybdacarboranes [3,3,3-(CO)3-3-PPh3-3,1,2-closo-MoC2B9H11] (2), [1,2-Me2-3,3,3-(CO)3-3-PPh3-3,1,2-closo-MoC2B9H9] (3) and trans-[3,3-(CO)2-3,3-(PPh3)2-3,1,2-closo-MoC2B9H11] (4) were prepared and fully characterised. Consideration of the exopolyhedral ligand orientations (ELO) in 2 confirms that, in terms of trans influence, CO > PPh3 in [L4MC2B9H11] also. The ELO is effectively reversed in 3 through intramolecular steric crowding between the cage CH3 groups and the PPh3 ligand. The dicarbonylbis(triphenylphosphine) compound 4 has effective Cs symmetry with one CO ligand trans and the other CO ligand cis to the cage C–C connectivity. Unexpectedly the Mo–CO bond lengths are equal. DFT calculations on 4 reproduce this unusual result, but suggest that in the less-crowded PH3 analogue, the Mo–CO bond length trans to cage C would be about 0.2 ? shorter than that trans to cage B. To test this prediction, the analogous PEt3 complex was prepared as cis and trans structural isomers 5 and 6. The cis isomer 5 is quantitatively converted into the trans isomer 6 when heated to reflux in THF. In 6 the Mo–CO bond more trans to cage C is about 0.2 ? shorter than that which is more trans to cage B, in line with the DFT prediction.
Alkyne-Carbaborane Coupling at a Molybdenum Centre: Crystal Structure of 2-C(H)=C(H)SiMe3>-3,1,2-MoC2B9H10>
Dossett, Stephen J.,Li, Sihai,Mullica, Donald F.,Sappenfield, Eric L.,Stone, F. Gordon A.
, p. 3551 - 3558 (2007/10/02)
In CH2Cl2 the complex decomposed to yield a mixture of and 2-C(Ph)=C(H)Ph>-3,1,2-MoC2B9H8>.Protonation (HBF4*Et2O) of , in CH2Cl2 at -78 deg C, in the presence of an excess of Me3SiCCSiMe3, afforded a chromatographically seperable mixture of and 2-C(H)=C(H)SiMe3>-3,1,2-MoC2B9H10>.The latter complex forms via the intermediacy of Me3SiCCH, generated by HF cleavage of Me3SiCCSiMe3, and its structure was established by X-ray diffraction.The molibdenum atom is ligated on one side by three CO groups, and on the other by the open pentagonal face of the nido-1,2-C2B9 cage framework.The boron atom located in the β site with respect to the two carbons carries a vinyl substituent C(H)=C(H)SiMe3, and this exopolyhedral group is η2 co-ordinated to the molybdenum atom .Treatment of and Me3SiCCH with HBF4*Et2O gives initially the complex , which subsequently rearranges to 2-C(H)=C(H)SiMe3>-3,1,2-MoC2B9H8>.Use of Me3SiCCD in the synthesis, combined with NMR studies, suggests that insertion of the alkyne into the cage B-H bond proceedds via the intermediacy of a molybdenum vinylidene species.The NMR data (1H, 13C-, 11B-, and 31P-) for the new compounds are reported and discussed in relation to the structures proposed.
