Tin(II)–Nitrene Radical Complexes Formed by Electron Transfer from Redox-Active Ligand to Organic Azides and Their Reactivity in C(sp³)–H Activation

Abstract

A tin(II) complex coordinated by a sterically demanding o-phenylenediamido ligand is synthesized. The ligand is redox-active to reach a tin(II) complex with the diiminobenzosemiquinone radial anion in the oxidation by AgPF 6 . The tin(II) complex reacts with a series of nosylazides (x-NO 2 C 6 H 4 −SO 2 −N 3 ; x = o, m, or p) at −30 °C to yield the corresponding nitrene radical bound tin(II) complexes. The nitrene radical complexes exhibit C(sp 3 )−H activation and amination reactivity.

A rhodium(ii)/rhodium(iii) redox couple for C–H bond amination with alkylazides: a rhodium(iii)–nitrenoid intermediate with a tetradentate [14]-macrocyclic ligand

“…Since a monomer rhodium(II) complex, 1, that was generated by the dissociation of [Rh(TMAA)] 2 has been proposed to react with CO/H 2 in the formation of a rhodium(III) formyl complex from [Rh(TMAA)] 2 under a CO/H 2 atmosphere, a reaction of 1 with N 3 -Trs was taken into account for the calculations. 17 3, a kinetic isotope effect (KIE) of 6.5 was obtained, which is close to those observed in the amination reactions of xanthene with other metal-nitrene radical complexes of rhodium(III) and tin(II) (KIE 5.7 at 375 K and 5.6 at 375 K, respectively), 24,36 being consistent with the involvement of hydrogen atom abstraction in the present case.…”

“…Then, a subsequent radical rebound process takes place via the transition state TS2 with a low barrier of 3.3 kcal mol −1 to yield the product complex 1 sultam . When a 1 : 1 mixture of xanthene (17.5 μmol) and dideuterated-xanthene (xanthene- d 2 , 17.5 μmol) was aminated with 4-nitrophenylazide under the same conditions shown in entry 3 of Table 3, a kinetic isotope effect (KIE) of 6.5 was obtained, which is close to those observed in the amination reactions of xanthene with other metal–nitrene radical complexes of rhodium( iii ) and tin( ii ) (KIE 5.7 at 375 K and 5.6 at 375 K, respectively), 24,36 being consistent with the involvement of hydrogen atom abstraction in the present case.…”

Reactions of main group compounds with azides forming organic nitrogen-containing species

“…In 2021, Sugimoto, Sato, Yoshizawa, Itoh et al investigated the reactions of bulky N-heterocyclic stannylene Sn9 with the nosylazides (NO 2 C 6 H 4 –SO 2 –N 3 ). 172 Sn9 reacts with NsN 3 leading to nitrene radical bound Sn( ii ) complex Sn9-P1 (Scheme 103b). The X-band EPR analysis of Sn9-P1 disclosed that the spin-triplet state exists in a thermally excited state.…”

Ligand-Based Redox: Catalytic Applications and Mechanistic Aspects

“…Itoh in collaboration with other groups has very recently established that such nitrene generation is possible in a complex comprising a main group metal, as long as the ligand-based electron can reduce the nitrogen center. 74 As a straightforward demonstration of this concept, a tin nitrene was prepared where the redox-active ophenylenediamino backbone supplied the electron for the said reduction. Such a nitrene was utilized for the C−H amination reaction of xanthene, giving 15% yield of the aminated product N-xanthyl-p-nitrobenzenesulfonamide.…”

“…Moreover, the formation of a ligand–radical complex was also supported by multiple EPR experiments performed at both room temperature and 50 K. In this case, the nature of the porphyrin rings helps to manifest the behavior of the nitrene radical and enable radical reactions in a controlled manner, leading to selective products. Itoh in collaboration with other groups has very recently established that such nitrene generation is possible in a complex comprising a main group metal, as long as the ligand-based electron can reduce the nitrogen center . As a straightforward demonstration of this concept, a tin nitrene was prepared where the redox-active o -phenylenediamino backbone supplied the electron for the said reduction.…”