Synthesis and Characterization of Tricarbastannatranes and Their Reactivity in B(C₆F₅)₃‐Promoted Conjugate Additions

Abstract

The synthesis and characterization of as eries of tricarbastannatranes,i nt he solid state and in solution, are described.The structures of the complexes [N(CH 2

Changes in Tricarbastannatrane Transannular N–Sn Bonding upon Complexation Reveal Lewis Base Donicities

“…23 These expectations are borne out in, for example, the X-ray structure of the hydroxide bound 1 + dimer where the N•••Sn distance is measured to be 2.37 Å and C−Sn−C = 117.35°. 9,24 Similar elongation of the N−Sn bond length and reduction of the N−Sn−C bond angles are calculated for each of the 1 + •Lewis base complexes described below (see Table 1).…”

“… and 1 + •BF 4  , respectively. 9 In comparison, analogous calculations for the neutral derivatives 1-Cl and 1-CH 3 yield transannular N•••Sn distances of 2.55 and 2.74 Å, respectively. 20 This is consistent with the expected elongation of the transannular N•••Sn distance upon complexation at the apical site of the tin center.…”

“…It is immediately apparent from Figure 4 where Lewis base = DABCO, THF, acetonitrile, and diphenylacetylene (DPA) were investigated in the solution phase using 1 H, 13 C, and 119 Sn NMR spectroscopy. 9 In their study, Kavoosi and Fillion added 1 equiv of the Lewis bases to a dichloroethane solution containing 1 + and recorded the 119 Sn chemical shifts. To compare with the solution phase work, 1 + complexes (as characterized by IRMPD) were embedded in a dichloroethane PCM, geometries of the Lewis acid/base complexes were reoptimized, and 119 Sn NMR chemical shifts were calculated using the GIAO method.…”

“…Tricarbastannatrane cation [N(CH 2 CH 2 CH 2 ) 3 Sn] + (1 + ) was synthesized in acetonitrile as [N(CH 2 CH 2 CH 2 ) 3 Sn(acetonitrile)](BF 4 ) and [N(CH 2 CH 2 CH 2 ) 3 Sn(acetonitrile)](SbF 6 ) as described by Kavoosi and Fillion. 9 Following filtration or centrifugation, the solution or supernatant was mixed with various Lewis bases, namely, DABCO, pyridine, acetamide, and DMSO to form electrospray ionization (ESI) solutions of ca. 100 μmol L −1 concentration, which were injected at 100 μL/h.…”

“…15 Dichloroethane was chosen for these calculations because it was the solvent that was employed in NMR experiments reported by Kavoosi and Fillion. 9 NMR chemical shifts for 119 Sn were then calculated using the gauge independent atomic orbital (GIAO) method. 16 These calculations were undertaken at the B3LYP/6-311++G(d,p) level of theory using an all electron DZVP basis set 17 for Sn.…”