Uncovering diverse reactivity of NHCs with diazoalkane: C-H activation, C&z.dbd;C bond formation, and access to N-heterocyclic methylenehydrazine

• Published in: Chemical science (Cambridge) 2024-11, Vol.15 (44), p.18387-18394
• Main Authors: Balayan, Kajal, Sharma, Himanshu, Vanka, Kumar, Gonnade, Rajesh G, Sen, Sakya S
• Format: Article
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d4sc05740f

N-heterocyclic carbenes (NHCs) have attracted significant attention due to their strong σ-donating capabilities, as well as their transition-metal-like reactivity towards small molecules. However, their interaction with diazoalkanes remains understudied. In this manuscript, we explore the reactivity of a series of stable carbenes, encompassing a wide range of electronic properties, with Me 3 SiCHN 2 . 5-SIPr activates the C-H bond of Me 3 SiCHN 2 , resulting in the formation of a novel diazo derivative ( 1 ), while carbenes such as 5-IPr, 6-SIPr, and diamido carbene yield N-heterocyclic methylenehydrazine derivatives ( 3 , 4 , and 8 ). The reaction of Me 3 SiCHN 2 with 5-I t Bu unexpectedly leads to the formation of a triazole ring linked with the imidazole moiety via a C&z.dbd;C double bond ( 6 ) alongside the azine product ( 7 ). Substituting the diazoalkane with diazoester consistently yields azine derivatives ( 9-12 and 14 ). Only in the case of 5-I t Bu, an imidazolium salt with tetrazenide anion ( 13 ) was obtained as a side product. The reaction of 4 with HCl resulted in the desilylprotonation to form a salt, 5a , which undergoes deprotonation upon using bases such as Et 3 N and KHMDS to form N-heterocyclic methylene hydrazine, 5 . Theoretical calculations have been conducted to elucidate the diverse mechanisms underlying product formation. Systematic investigation of Me 3 SiCHN 2 with various types of nucleophilic and electrophilic NHCs resulted in diverse reactivities.