1-boraadamantane: Reactivity towards di(1-alkynyl)silicon and -tin compounds: First access to 7-metalla-2,5-diboranorbornane derivatives

1-Boraadamantane (1) reacts with di(l-alkynyl)silicon and -tin compounds 2 (Me2M(C=CR)(2): M = Si. R = Me (a), tBu (b), SiMe3 (c): M = Sn, R = SiMe3 ( e)) in a 1:1 ratio by intermolecular 1,1-alkylboration, followed by intramo lecular 1,1-vinylboration, to give siloles 5a-c and the stannole 5e, respec tively, in which the tricyclic 1-boraadamantane system is enlarged by two c arbon atoms. Owing to the high reactivity of 1, a second fast intermolecula r 1,1-alkylboration competes with the intramolecular 1,1-vinylboration as t he second major step in the reaction if the substituent R at the C=C bond i s small (2a) and/or if the M-Cr bond is also highly reactive, as in 2d (M = Sn, R = Me) and 2e (M = Sn, R = SiMe3). This leads finally to the novel oc tacyclic 7-metalla-2,5-diboranorbornane derivatives 8a, 8d, and 8e, of whic h 8e was characterized by X-ray analysis in the solid state, 1. 1,2,2-Tetra methyldi(1-propynyl)disilane, MeC=C-SiMe2SiMe2-C=CMe (3), re acts with 1 to give mainly a 1,2-dihydro-1,2.5-disilaborepine derivative 9 and the octacy clic compound 11, which is analogous to 8a but with an Me4Si2 bridge. All n ew products were characterized in solution by H-1, B-11, C-13,Si-29, and Sn -119 NMR spectroscopy. For 8 and 11, highly resolved Si-29 and Sn-119 NMR s pectra revealed the first two-bond isotope-induced chemical shifts, (2)Delt a B-10/11(Si-29) and (2)Delta B-10/11(Sn-119) respectively, to be reported.