9-BORABARBARALANES

The reaction of MgCOT(thf)(x) with tBuBF(2) or PhBCl(2) affords the fi rst 9-borabarbaralanes 2 (C(8)H(8)BR, a: R = tBu; b: R = Ph). With the aminoboron dihalides BCl2NiPr2 and BCl2N(SiMe(3))tBu 9-borabicyclo[4. 2.1]-nona-2,4,7-trienes 3 (a: R = NiPr2, b, R = N(SiMe(3))tBu) and the trans-9-borabicyclo[4.3.0]nona-2,4,7-triene 4 are obtained. The bicyc lic compounds 3a and 3b are converted into 9-borabarbaralanes 2c and 2 d, respectively, by irradiation in solution as well as by heating. All 9-borabarbaralanes 2 are fluxional in solution. In the crystalline st ate, the B-phenyl derivative 2b displays a well-ordered van der Waals crystal structure, The theoretical prediction that the degenerate Cope rearrangement in barbaralanes will be retarded by pi-acceptor groups in the 9 position has been verified. Quantum chemical calculations emp loying density functional theory support and help interpret the experi mental findings. The isoelectronic 9-barbaralyl cations, in contrast, have such high Cope barriers that other rearrangement pathways are fol lowed instead.