Probing for a Leaving Group Effect on the Generation and Reactivity of Phenyl Cations

Abstract

Phenyl cations are smoothly generated by the photoheterolytic cleavage of an Ar-LG bond (LG = leaving group). With the aim of evaluating the scope of the method, a series of 4-methoxy-2-(trimethylsilyl)phenyl derivatives (sulfonic, LG = MeSO(3) and CF(3)SO(3), phosphate, LG = (EtO)(2)(O)PO esters and the corresponding chloride) have been compared as probes for evaluating the leaving group ability. The photocleavage was a general reaction, with the somewhat surprising order (EtO)(2)(O)PO ∼ Cl > CF(3)SO(3) > MeSO(3) (Φ = 0.50 to 0.16 in CF(3)CH(2)OH and lower values in MeCN-H(2)O). The ensuing reactions did not depend on the LGs but only on the structure of the phenyl cation (the silyl group tuned the triplet to singlet intersystem crossing and the electrophilicity) and on the medium (formation of a complex with water slowed the electrophilic reactions).

Aryl tosylates as non-ionic photoacid generators (PAGs): photochemistry and applications in cationic photopolymerizations

“…A peculiar case is represented by 1g. As previously observed in related sulfonate esters (mesylates, triates), 16 the presence of a silicon-based substituent ortho to the sulfonate moiety signicantly increased the overall photoreactivity. 16 The same behaviour was found here, although the cleavage shied from heterolysis of an Ar-OS bond (in the cases of mesylate and triate) 16 to ArO-S homolysis (in the case of tosylate).…”

“…As previously observed in related sulfonate esters (mesylates, triates), 16 the presence of a silicon-based substituent ortho to the sulfonate moiety signicantly increased the overall photoreactivity. 16 The same behaviour was found here, although the cleavage shied from heterolysis of an Ar-OS bond (in the cases of mesylate and triate) 16 to ArO-S homolysis (in the case of tosylate). The presence of oxygen promoted efficient trapping of the ArSO 2 c radical II (Scheme 2, path e), prior to recombination with the phenoxy radical, and PTSA was obtained via the corresponding arylperoxysulfonyl radical IV.…”

“…The silylated derivative 1g was also tested because we previously demonstrated that the presence of silicon-based substituents was able to inuence the photoreactivity of aryl sulfonates. 16,17 These were synthesized from the corresponding phenols. 18 The photophysical and photochemical properties of tosylates 1a-g are presented in Table S1 and Fig.…”

Acetonitrile as a Building Block and Reactant

“…The reaction of 4-methoxy-2-(trimethylsilyl)benzene derivatives with acetonitrile/acetone/water was found to be dependent upon the leaving group (Scheme 52). 271 The electrochemical acetamidation of benzene, benzoic acid, ethyl benzoate, and acetophenone was carried out using acetonitrile and a platinum electrode; no yields were reported. 272 The proposed mechanism involves the formation of a radical cation, which is attacked by the acetonitrile nitrogen.…”

The 3,5‐dinitroanilide anion: a singlet anilide anion with evidence for a thermally accessible triplet state

“…[1][2][3][4][5][6][7][8][9][10] Although the long-term aspiration of designing commercially interesting organic magnetic materials remains elusive, fundamental studies have identified several families of organic species that are either ground state triplets or have low-energy triplet states. [11][12][13][14][15][16][17][18] These include carbenes, [19][20][21] nitrenes, [22][23][24][25] diradicals, [1,[26][27][28][29][30][31][32] nitrenium ions, [33,34] certain aryl cations, [35][36][37][38][39] , and antiaromatic cations such as cyclopentadiene. [40,41] Recent computational and experimental studies in our laboratory have characterized several new types of ion-diradicals that also have low energy triplet states.…”