Uncovering diverse reactivity of NHCs with diazoalkane: C–H activation, C Created by potrace 1.16, written by Peter Selinger 2001-2019 C bond formation, and access to N-heterocyclic methylenehydrazine

• Published in: Chemical science (Cambridge) 2024-10
• Main Authors: Balayan, Kajal, Sharma, Himanshu, Vanka, Kumar, Gonnade, Rajesh G., Sen, Sakya S.
• Format: Article
• Language: English
• Subjects: Chemistry
• 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 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.