Photochemical decomposition of triphenylboron and its complexes

Photochemical Intramolecular C−H Addition of Dimesityl(hetero)arylboranes through a [1,6]‐Sigmatropic Rearrangement

“…Zuschriften lowest excited singlet states (S 2 )w ere conducted at the B3LYP/6-31G(d) level of theory.T he geometry optimization on S 0 at the UB3LYP/6-31G(d) level of theory afforded two electronic structures for the transition state (TS) of the [1,6]H-shift, that is,a no pen-shell TS(OS)a nd ac losed-shell singlet state TS(CS), which lead to the H-shifted biradical (5aCC)a nd zwitterionic (5a +À )i ntermediates,r espectively, prior to the formation of the spirocyclic product 4a (Figure 4; see Figure S3). Thee nergies of the geometries of these intermediates relative to the optimized geometry of 3a in S 0 are + 56.1 kcal mol À1 [TS(OS)], + 68.0 kcal mol À1 [TS-(CS)], + 44.3 kcal mol À1 (5aCC), + 53.8 kcal mol À1 (5a +À ), and + 12.5 kcal mol À1 (4a).…”

“…These findings suggest the spontaneous formation of 4a even in the ground state,once 5a is produced. Moreover,S 1 and S 0 seem to form an unavoidable crossing in the vicinity of TS(CS)o wing to the nonadiabatic coupling between the two states.O verall, the photoinduced cyclization likely proceeds through a [ 1,6]Hshift in S 1 ,followed by anonadiabatic transition from S 1 to S 0 to produce 5a +À ,and aspontaneous CÀCbond formation via either 5a +À or 5aCC in S 0 to afford 4a (Scheme 1). In the early reaction stage,near the Franck-Condon state for 3a,S 1 and S 2 are energetically comparable.Incontrast, the S 2 potential energy surface for the H-shift from 3a to TS is significantly less favorable (ca.…”

“…Thes imilar photochemical behavior for anionic tetracoordinate boron compounds and neutral tetracoordinate carbon compounds has long been recognized. [6][7][8] We have recently reported isosteric reactivity for at riorganoborane and its cationic carbon congener.S pecifically,t he 9-dimesitylboryl-substituted dibenzoborepin 1 underwent an isomerization to the borata-allyl product 2 upon photoirradiation, [9] ar eaction which can be regarded as ab ora-Nazarov cyclization (Figure 1c). [2][3][4] Wang and co-workers have recently applied this type of reaction to develop ap hotochromic system.…”

“…[2][3][4] Wang and co-workers have recently applied this type of reaction to develop ap hotochromic system. This reaction likely involves a [ 1,6]-sigmatropic hydrogen rearrangement, which should result from as ignificant contribution of the vacant p orbital of the boron atom. [6][7][8] We have recently reported isosteric reactivity for at riorganoborane and its cationic carbon congener.S pecifically,t he 9-dimesitylboryl-substituted dibenzoborepin 1 underwent an isomerization to the borata-allyl product 2 upon photoirradiation, [9] ar eaction which can be regarded as ab ora-Nazarov cyclization (Figure 1c).…”

A laser desorption ionization mass spectrometry investigation of triarylboranes and tri-9-anthrylborane photolysis products

“…An early study of the photolysis of triphenylborane in cyclohexane by Williams et al [3] found no hydrocarbon products; photolysis in methanol did yield small amounts of biphenyl, attributed to photochemistry of the triphenylborane methanol complex. This photochemistry is analogous to the extensively studied [4] photolysis of the tetraphenylborate anion to form biphenyl and products from another carbene analog, Ph 2 B:.…”