I t Oct (I t Octyl) - pushing the limits of I t Bu: highly hindered electron-rich N-aliphatic N-heterocyclic carbenes

Md Mahbubur Rahman; Guangrong Meng; Elwira Bisz; Błażej Dziuk; Roger Lalancette; Roman Szostak; Michal Szostak

doi:10.1039/d3sc01006f

I t Oct (I t Octyl) - pushing the limits of I t Bu: highly hindered electron-rich N-aliphatic N-heterocyclic carbenes

Chem Sci. 2023 Apr 18;14(19):5141-5147. doi: 10.1039/d3sc01006f. eCollection 2023 May 17.

Authors

Md Mahbubur Rahman¹, Guangrong Meng¹, Elwira Bisz², Błażej Dziuk³, Roger Lalancette¹, Roman Szostak⁴, Michal Szostak¹

Affiliations

¹ Department of Chemistry, Rutgers University 73 Warren Street Newark NJ 07102 USA michal.szostak@rutgers.edu.
² Department of Chemistry, Opole University 48 Oleska Street Opole 45-052 Poland.
³ Department of Chemistry, Wroclaw University of Science and Technology Norwida 4/6 14 Wroclaw 50-373 Poland.
⁴ Department of Chemistry, Wroclaw University F. Joliot-Curie 14 Wroclaw 50-383 Poland.

Abstract

ItBu (ItBu = 1,3-di-tert-butylimidazol-2-ylidene) represents the most important and most versatile N-alkyl N-heterocyclic carbene available in organic synthesis and catalysis. Herein, we report the synthesis, structural characterization and catalytic activity of ItOct (ItOctyl), C₂-symmetric, higher homologues of ItBu. The new ligand class, including saturated imidazolin-2-ylidene analogues has been commercialized in collaboration with MilliporeSigma: ItOct, 929 298; SItOct, 929 492 to enable broad access of the academic and industrial researchers within the field of organic and inorganic synthesis. We demonstrate that replacement of the t-Bu side chain with t-Oct results in the highest steric volume of N-alkyl N-heterocyclic carbenes reported to date, while retaining the electronic properties inherent to N-aliphatic ligands, such as extremely strong σ-donation crucial to the reactivity of N-alkyl N-heterocyclic carbenes. An efficient large-scale synthesis of imidazolium ItOct and imidazolinium SItOct carbene precursors is presented. Coordination chemistry to Au(i), Cu(i), Ag(i) and Pd(ii) as well as beneficial effects on catalysis using Au(i), Cu(i), Ag(i) and Pd(ii) complexes are described. Considering the tremendous importance of ItBu in catalysis, synthesis and metal stabilization, we anticipate that the new class of ItOct ligands will find wide application in pushing the boundaries of new and existing approaches in organic and inorganic synthesis.