Closo and semipseudocloso forms of the same carbametallaborane: synthesis and spectroscopic and crystallographic characterisation of 1-CCPh-2-Ph-3-(η-L)-3,1,2-RhC2B9H9 (L=C5H5 and C5Me5): Part 25. Steric effects in heteroboranes

The compounds of 1-CCPh-2-Ph-3-(η-L)-3,1,2-RhC2B9H9 (L=C5H5, 1, and C5Me5, 2) have been prepared. The weighted average 11B-NMR chemical shift (〈δ11B〉) for 1 is +2.53 ppm, suggesting that the cage is distorted into a semipseudocloso structure. For 2 in CDCl3 〈δ11B〉 is −0.7 ppm, between that anticipated for semipseudocloso and closo forms. Compound 2 crystallises in two different forms. Orange 2a is semipseudocloso, with C(1)–C(2) 2.052(5) Å, whilst yellow 2b is essentially closo, with C(1)–C(2) 1.828(7) Å. Dissolution of both 2a and 2b in CDCl3 affords an identical solution.