Reactions of 3‐(Diethylboryl)stannoles with Isocyanates

Abstract

Diethynyl(diphenyl)stannane was prepared, fully characterised in solution and in the solid state, and its reaction with triethylborane, BEt3, afforded 3‐(diethylboryl)‐4‐ethyl‐1,1‐diphenyl‐stannole in essentially quantitative yield. Treatment with isocyanates converted this stannole and the known analogous 1,1‐dimethyl derivative into novel bicyclic compounds containing an aminoborane unit. These reactions were found to proceed diastereoselectively, again in essentially quantitative yield. The bicyclic compounds react with methanol through rearrangement and elimination of ethyl(dimethoxy)borane to give novel 1‐stannacyclopent‐3‐ene derivatives, one of which could be structurally characterised by X‐ray analysis. All final products and intermediates were studied in solution by multinuclear NMR spectroscopy (1H, 11B, 13C, 119Sn NMR).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Selective Synthesis of Stannoles by 1,1‐Carboboration of Bis(trimethylsilylethynyl)tin Compounds Using Weakly and Strongly Electrophilic Triorganoboranes: Characterization of a Zwitterionic Intermediate

“…In the case of 3a, the molecular structure was established by X-ray crystallography ( Figure 2). Few structural data are available for dialkynyl(diorgano)-tin compounds, [12,13] and 3a is the first example with trimethylsilylethynyl groups. All the bond lengths are in the usual range, but the bond angles at tin are of interest because in 3a, as a consequence of the six-membered ring, the endocyclic bond angle C5-Sn-C9 is fairly small [100.97 (8) [a] for the bis(trimethylsilylethynyl)diorganotin compounds.…”

“…The δ Si values and the assignments were confirmed by calculation of the 29 Si nuclear magnetic shielding. [25] The characteristic 13 After several days in C 6 D 6 or toluene at room temp., the intermediates 6(C 6 F 5 ) rearrange completely into the stannoles 7(C 6 F 5 ). This process is indicated by the 11 B NMR spectra in which the relatively sharp 11 B NMR signal in the borate region disappears and the typically broad 11 B NMR signal for the trigonal-planar boron atom grows.…”

“…[9] In contrast, 1,1-carboboration using triphenylborane, BPh 3 , has led to mixtures of stannoles and 1,4-stannaboracyclohexa-2,5-diene derivatives. [9] In addition, the use of tris(pentafluorophenyl)borane, B(C 6 F 5 ) 3 , for the 1,1-carboboration of R 1 2 Sn(CϵC-R) 2 (R 1 = alkyl, Ph; R = H, nBu) selectively affords 1,4-B, 13 C, 19 F, 29 Si, 119 Sn NMR) was used to characterize the intermediates and the stannoles as the final products. Some of the NMR parameters ( 11 B, 13 C, 29 Si) of the intermediates were calculated by DFT methods using the optimized gas-phase geometries.…”

“…Previous work on the synthesis of 2 and related stannoles with Me 3 Si groups [6,8] had revealed no evidence for reactive intermediates, and it was hoped that more electrophilic triorganoboranes could be helpful in this respect. All the reactions were studied by multinuclear magnetic resonance methods ( 1 H, 11 B, 13 C, 29 Si, and 119 Sn NMR spectroscopy) to elucidate mechanistic aspects of the 1,1-carboboration reactions.…”

Alkynylsilanes and Alkynyl(vinyl)silanes. Synthesis,Molecular Structures and Multinuclear Magnetic Resonance Study

“…All bond lengths and angles (Tables 3 and 4) are within the expected ranges [23], except for the bond length C23-C24 (106.0(2) pm) in 31. This distance is too short for a C≡C bond, and the value determined here may be affected by C≡C and ≡C-H stretching vibrations, since similar "short" C≡C bonds were found for ethynyltin compounds [24], both at room temperature and 133 K. Other structural parameters of the Si-C≡C-Si unit in 31 are comparable to those of another disilylethyne (Table 4) [25]. The dialkynylsilane 31 is one of few structurally characterized examples of ethynylsilanes [23d, h].…”