from 1,2 H, additions to adjoining 6-5 bonds. The formation of this isomer is, however, unlikely because isolated X, addition to 6-5 bonds of C,, has never been observed and is calculated to be at least 20 kcalmol-' less stable than addition to 6-6 bonds at all levels of theory.
The coupling constants observed in the 'H NMR spectra of the isomers A-E are all consistent with 1,2 addition to 6-6 bonds. The assignment of product F with a resonance signal at 6 = 6.33 to 8 is tentative, but is consistent with the exceptionally low-field resonance signal of C,,H, at 6 = 5.93. All other resonance signals observed for C,,H, products are upfield from that observed for C,,H, . The structure of B can be unambiguously assigned to 4, but the structures of the products A, D, and E are consistent with any of the remaining five isomers. We plan to assign structures to these isomers through crystallographic analysis.
Experimental Procedure
To a solution of C,,H, [I) (10 mg. 14 pmol) in toluene (15 mL) was added BH, (14pL. 1 . 0 ~ solutioninTHF) a t 0 " C under argon. Themixture wasstirred at O'C for 45 min. warmed to room temperature for 45 min. and quenched by addition of water (1 .0 mL). The organic layer was separated, dried over MgSO,, and the C,,H, fraction isolated by preparative chromatography on a Buckyclutcher I column (10 mm x 25.0 cm) with a tolueneihexane (1 :1) mobile phase. The total yield of C,,,H, products is 10%. less than the 20-30% yields of C,,H, that are obtained from C,, under similar conditions (C,,H, isomers were first obtained as side products in < I "h yields in this reaction). Positive-ion FAB MS (for the mixture): observed, 724.0309. calculated 724.03 13 (no evidence for C,,H,). From this mixture three C,,H, isomers were separated (Table ). The UV;VIS spectrum o f C ( = 1) in toluene!hexane ( 1 ; l ) tails from 290 nm with a shoulder at 342 nm and a distinct absorption at 442 nm, both of which may be diagnostic for this substitution pattern. Positive-ion FAB MS: observed. 724.0309: calculated. 724.031 3. Similar for A. distinct maximum at 325 nm and weak absorption maxima at 410 and 430 nm. For B, distinct maxima are absent. shoulders at 330, 380, 425, and a broad feature at 475 nm are observed. Isolation of the materials is limited to concentrated solutions (1 mgmL-') which are handled routinely in light and air. Such solutions may be stored indefinitely at -20 "C, but removal of the solvent leads to solids which do not completely redissolve. Products A and B that were previously separated from C (1) were eluted on a Buckyclutcher I column that contained an unusually high amount of residual platinum from the preparation of the Buckyclutcher Iigand. Repeated elutions resulted in conversion of A and B to C.