17864-15-2Relevant articles and documents
Synthesis and Structures of Bis(indolyl)-Coordinated Titanium Dichlorido Complexes and Their Catalytic Application in the Cyclotrimerization of Alkynes
Itoh, Keigo,Miura, Narumi,Miyamoto, Ryo,Ohta, Shun,Okazaki, Masaaki,Saitoh, Keiichiro,Satoh, Sora
, p. 2826 - 2835 (2021/09/02)
The impact of the terminal ligands on the titanium center on the coordination features of deprotonated 2,2′-bis(indolyl)methanes (henceforth: bis(indolyl)s) was studied via a structural comparison between {bis(indolyl)}Ti(NEt2)2 complexes and the corresponding dichlorido complexes. As a result, several flexible aspects of bis(indolyl) coordination were found. For example, it was revealed that an η1-coordinated indolyl moiety can change its coordination mode to coordination via the five-membered ring of indolyl when the terminal diethylamido ligands are replaced by chlorido ligands. Moreover, we found that the methoxy group in the central aromatic ring of the bis(indolyl) ligand can coordinate to the titanium center. The synthesized dichlorido complexes were applied for catalytic alkyne cyclotrimerization reactions, as Ti-based catalyst systems are less developed than Co-, Ni-, Ru-, Rh-, and Ir-based systems. During this study, the cyclotrimerization of HCCSiMe3 was found to preferentially produce the 1,3,5-form (1,3,5-form:1,2,4-form = 79:21), contrary to the typical trend of transition-metal-mediated alkyne cyclotrimerization, and the isolated yield (72%) is the highest among the known 1,3,5-favoring reactions using Ti-based catalyst systems. Furthermore, the reaction mechanism was experimentally verified to proceed through a typical stepwise mechanism involving monomeric species.
Iron-catalyzed regioselective cyclotrimerization of alkynes to benzenes
Gawali, Suhas Shahaji,Gunanathan, Chidambaram
, p. 139 - 149 (2019/01/03)
We report the synthesis and characterization of simple di(aminomethyl)pyridine ligated iron-pincer complexes, which catalyzed the regioselective [2+2+2] cyclotrimerization of terminal aryl and alkyl alkynes to provide the 1,2,4-trisubstituted benzene molecules. Interestingly, internal alkynes also exhibited similar cyclization and resulted in hexa-substituted benzene compounds. Increased steric bulk on pincer ligands diminished the selectivity for cycloaddition. Cyclotrimerization reactions proceeded at room temperature upon activation of catalyst by a Grignard reagent. EPR studies indicated thermally induced spin crossover effect in catalyst.
Oxidative nitrene transfer from azides to alkynes via Ti(ii)/Ti(iv) redox catalysis: Formal [2+2+1] synthesis of pyrroles
Pearce, Adam J.,See, Xin Yi,Tonks, Ian A.
supporting information, p. 6891 - 6894 (2018/06/26)
Catalytic oxidative nitrene transfer from azides with the early transition metals is rare, and has not been observed without the support of redox noninnocent spectator ligands. Here, we report the formal [2+2+1] coupling of azides and alkynes via TiII/TiIV redox catalysis from simple Ti halide imido precatalysts. These reactions yield polysubstituted N-alkyl pyrroles, including N-benzyl protected pyrroles and rare examples of very electron rich pentaalkyl pyrroles. Mechanistic analysis reveals that [2+2+1] reactions with bulky azides have different mechanistic features from previously-reported reactions using azobenzene as a nitrene source.
