A tricyclic N-pyrrolylborane with an exceptionally stable B-N bond.
Hydroboration of 2,5-diallylpyrrole by using a mixt. diethylborane/triethylborane (Et2BH/Et3B) leads to the 1st tricyclic N-pyrrolylborane 3 (shown as I) which possesses an exceptionally stable B-N bond. In accordance with the pronounced Lewis-acidic character of 3, it is readily converted into adducts or borates. The crystal structure of 3 was detd. by x-ray anal. (triclinic, space group P.hivin.1, Z = 8) showing a fairly long B-N bond (mean value 144 pm), the 1st example of a diorgano N-pyrrolyl borane in which the pyrrole ring is not twisted against the C2BN-plane. Nuclear magnetic shielding (11B, 13C, 14N) was calcd. using the GIAO procedure. BN(pp)p bonding is discussed from MO calcns.
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