AB-INITIO NMR-STUDIES ON PER-B-F AND PER-B-CL DERIVATIVES OF C4B2H6 AND C2B4H6 - CLASSICAL VS CARBORANE-CAGE STRUCTURES - CORRELATION OF B-11, F-19, AND CL-35 NMR DATA AMONG RELATED FLUOROBORON AND CHLOROBORONCOMPOUNDS

Ab initio IGLO/B-11-NMR and IGLO/Cl-35-NMR calculations as well as GIA O/NMR studies on two plausible B-Cl-4-C2B4H2 structures lead to the co nclusion that the only known compound of that formula most probably pr efers a ''classical'' structure rather than a close configuration of c arbon and boron atoms. IGLO and GIAO calculations on a [2.1.1] bicycli c system, perhaps fluxional in nature, with the two carbon atoms at th e bridgehead positions are reasonably consistent with available NMR da ta. The proposed static planar structure for the known B,B'-difluoro d erivative of C4B2H6 is supported by IGLO/B-11-NMR and IGLO/F-19-NMR, a s well as corresponding GIAO/NMR results. Calibration of the B-11, F-1 9, and Cl-35 NMR correlative approaches involved the comparison of cal culated and experimental NMR shifts for the simple haloboron compounds , XB(CH=CH2)(2), X(2)BCH=CH2, XBMe(2), X(2)BMe, BX(3), BX(4)(-) ion, ( X=F, Cl), ClBF2, and Cl2BF.