New Azoniaboratacyclopropanes from (F3C)2BNMe2 and Diazomethane Derivatives – Structure ofcyclo-(F3C)2B–CPh2–NMe2 and HOB(CF3)2–CHC6F5–NHMe2

1,1-Dimethyl-2,2-bis(trifluoromethyl)azoniaboratacyclopropanes, cyclo-(F3C)2B–CR1R2–NMe2 [R1 = R2 = C6H5 (2a); R1/R2 = C12H8 (2b); R1 = H, R2 = C6H5 (2c), 4-FC6H4 (2d), 3-FC6H4 (2e), 2-FC6H4 (2f), C6F5 (2g), iPr (2h), tBu (2i); R1 = Me, R2 = C(=O)OMe (2j), C(=O)OEt (2k)] have been obtained from (F3C)2BNMe2 (1) and diazomethanes R1R2CN2. In contrast to compound 2a, the B–N bonds of 2b–2k hydrolyze to form the zwitterionic species Me2NH–CR1R2–B(CF3)2OH (3b–3k). The diazoacetic acid esters HC(N2)C(=O)OMe and HC(N2)C(=O)OtBu react with 1 to form three-membered rings, which hydrolyze rapidly to form Me2NH–CR1R2–B(CF3)2OH [R1 = H, R2 = C(=O)OMe (3l), C(=O)OtBu (3m)]. F3CSiF3 reacts under elimination of CF2 with 1 to form the acyclic derivative (F3C)2BF–CF=NMe2 (4). The structures of 2a and 3ghave been investigated crystallographically. A nearly eclipsed conformation is found for the central B–C bond of 3g, which is 0.097(7) Å longer than the B–C bond length in the three-membered ring of 2a.