1-Boraadamantane: Reactivity Towards Di(1-alkynyl)silicon and -tin Compounds: First Access to 7-Metalla-2,5-diboranorbornane Derivatives

Abstract

1-Boraadamantane (1) reacts with di(1-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 intramolecular 1,1-vinylboration, to give siloles 5a-c and the stannole 5e, respectively, in which the tricyclic 1-boraadamantane system is enlarged by two carbon atoms. Owing to the high reactivity of 1, a second fast intermolecular 1,1-alkylboration competes with the intramolecular 1,1-vinylboration as the second major step in the reaction if the substituent R at the C...C bond is small (2a) and/or if the M-C... bond is also highly reactive, as in 2d (M=Sn, R= Me) and 2e (M=Sn, R=SiMe3). This leads finally to the novel octacyclic 7-metalla-2,5-diboranorbornane derivatives 8a, 8d, and 8e, of which 8e was characterized by X-ray analysis in the solid state. 1,1,2,2-Tetramethyldi(1-propynyl)disilane, MeC...C-SiMe2SiMe2-C...CMe (3), reacts with 1 to give mainly a 1,2-dihydro-1,2,5-disilaborepine derivative 9 and the octacyclic compound 11, which is analogous to 8a but with an Me4Si2 bridge. All new products were characterized in solution by 1H, 11B, 13C, 29Si, and 119Sn NMR spectroscopy. For 8 and 11, highly resolved 29Si and 119Sn NMR spectra revealed the first two-bond isotope-induced chemical shifts, 2delta10/11B(29Si) and 2delta10/11B(119Sn) respectively, to be reported.

Isotope‐induced chemical shifts 2Δ10/11B(29Si) in alkenylsilanes containing three‐ and four‐coordinate boron. A new tool for studying weak intramolecular boron–element bonds

“…Interestingly, the known 2  10/11 B( 29 Si) values (across an aliphatic carbon atom) are also positive and of the same order of magnitude as for 10. 3 Theory predicts 16,19 a negative sign for 2  10/11 B( 29 Si), the same as for 1  values. A change in this sign cannot be explained by the dynamic factor which always leads to a negative sign considering the shortening of bonds in the heavier isotopomer.…”

“…In contrast, NMR signals of spin-1 2 nuclei, non-adjacent to boron, are in general sharp or only slightly broadened, and if there are n  10/11 B(X) (n ½ 2) effects these parameters can be measured. We have observed for the first time 2  10/11 B( 29 Si) and 2  10/11 B( 119 Sn) isotope effects for threecoordinate boron, 3 and also 2  10/11 B( 31 P) for four-coordinate boron, 4 all across an intervening aliphatic carbon atom. More surprisingly, it has been found that there are significant…”

Design of Neutral Lewis Superacids of Group 13 Elements

“…Several heteroatom derivatives of adamantane featuring nitrogen, boron, and silicon atoms have been prepared in the laboratory. − The compound 1-boraadamantane, reported by Mikhailov, shows exceptionally high reactivity toward donor molecules. A broad chemistry involving boraadamantanes has been developed . The complex of 1-boraadamantane with 1-azaadamantane, which is stable in air and insensitive to moisture, has been reported by Bubnov et al Another structural pattern considered in the present work features trisaryl ligands tied together by a CH unit.…”

A novel 4‐methylene‐3‐borahomoadamantane: 1,1‐organoboration of an alkyn‐1‐ylsilane using 1‐boraadamantane

“…The molecule 3 is chiral both in the solid state and in solution. Restricted rotation of the alkenyl groups bearing the organometallic substituents is indicated by the diastereotopic nature of the carbon atoms C(9,10), C (6,8) and C(5,11) ( Fig. 2).…”