Reversibility in Reactions of Linker-Bridged Distannenes with Terminal Alkynes at Ambient Temperature

Abstract

The linker-bridged distannene [(2,6-Mes2)C6H3Sn]2C12H8 (1) featuring an acenaphthene linker and the sterically demanding terphenyl substituent Ar(Me) (= C6H3-2,6-Mes2; Mes = C6H2-2,4,6-Me3) was prepared and characterized by single-crystal analysis, NMR spectroscopy, as well as elemental analysis. Furthermore, the reactivity of distannene 1 and previously reported distannenes 2 and 3, bearing either a naphthalene or a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar(Me), as well as bis(stannylene) 4, featuring a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar(iPr) (= C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3), toward terminal alkynes at ambient temperature was investigated, leading to the formal [2 + 2] cycloaddition products 5-9. The reactions of distannene 1 with trimethylsilylacetylene and phenylacetylene, the reaction of distannene 2 with trimethylsilyl-acetylene, as well as the reaction of bis(stannylene) 4 with phenylacetylene show reversibility, while distannenes 2 and 3 react irreversibly with phenylacetylene at room temperature. A van't Hoff analysis of variable-temperature (1)H NMR spectra of the cycloadduct of the reaction of distannene 1 with trimethylsilylacetylene afforded a dissociation enthalpy (ΔHdiss) of 71.6 kJ·mol(-1), which is in surprisingly good agreement with the results of accompanying DFT calculations (ΔHdiss = 70.9 kJ·mol(-1)).

Neutral Diboron Analogues of Archetypal Aromatic Species by Spontaneous Cycloaddition

“…[25] Unlike diborene VI, VII did not display any reactivity towards 2-butyne under these reaction conditions. Although the analogous reaction with acetylene ( Figure 4) also yielded ad eep-blue solution, the resulting product, 3,p roved to be diamagnetic and presented as ingle 11 BNMR resonance at 24.8 ppm (Figure 4). Examination of the 1 HNMR spectrum also provided acharacteristic singlet at 7.31 ppm, integrating at 4H relative to the CAAC-derived resonances,a nd correlating with a 13 Cr esonance at 150.5 ppm, hinting at the formation of as ix-membered 6 paromatic B 2 C 4 ring.T his was later confirmed by X-ray diffraction analysis of 3,w hich revealed the expected 1,4diborabenzene ring supported by two boron-coordinated CAAC ligands (Figure 4).…”

“…[19] It was thus of interest to compare the reactivity of VII towards alkynes with that of VI.Aviolet solution of VII in benzene,l eft unstirred under an atmosphere of propyne, turned deep blue over the course of one day at room temperature ( Figure 3). NMR spectroscopic analysis of the reaction mixture showed no 11 BNMR resonance and only very broad and weak 1 HNMR signals,s uggesting the formation of ap aramagnetic species.T his was further confirmed by an EPR measurement of af rozen-solution sample of 2 in 2-methyltetrahydrofuran which yielded aweak half-field signal and af our-line spectrum in the g = 2r egion attributable to the triplet state of biradical 2 ( Figure S3).…”

“…[10] In some cases of bridged distannenes, this reaction was shown to be reversible. [11] Recently the isolation of the first heavier group 14 alkyne analogues has also enabled the synthesis of the first 6π-aromatic 1,2-disilabenzene derivatives, IIa and IIb, and 4π-antiaromatic 1,2-digermacyclobutadiene, III, by alkyne cycloaddition (Fig. 1).…”

“…2). Removal of the solvent and washing of the residue with pentane yielded a colorless solid presenting a broad 11 B NMR singlet at 25.6 ppm, characteristic of a three-coordinate boron center, and a new broad 31 P NMR resonance at 23.1 ppm, both significantly downfield of the diborene NMR resonances at δ11B 16.7 and δ31P -24.4 ppm, respectively. [20] [ Single-crystal X-ray analysis revealed an asymmetric unit comprised of two molecules of compound 1, a monophosphine-stabilized homoaromatic 1,3-dihydro-1,3-diborete in which phosphine coordination has shifted from boron to one of the carbon atoms of the central BCBC ring (Fig.…”

“…[10] Fors ome bridged distannenes,t his reaction was shown to be reversible. [11] Recently the isolation of the first heavier Group 14 alkyne analogues has also enabled the synthesis of the first 6 paromatic 1,2-disilabenzene derivatives, IIa and IIb,a nd 4 pantiaromatic 1,2-digermacyclobutadiene III by alkyne cycloaddition ( Figure 1). [12] With regards to heavier Group 13 alkene analogues,T okitoh and co-workers described the addition of alkynes to adialumene-benzene adduct leading to the formation of 1,2-dialuminacyclobut-3-enes (IV) ( Figure 1), [13] while Power and co-workers synthesized 1,4digallacyclohexa-2,5-diene V by double cycloaddition of phenylacetylene to adigallene ( Figure 1).…”