Stereoelectronic Profiling of Expanded-Ring N-Heterocyclic Carbenes

Anuj Kumar; Dan Yuan; Han Vinh Huynh

doi:10.1021/acs.inorgchem.9b00786

Stereoelectronic Profiling of Expanded-Ring N-Heterocyclic Carbenes

Inorg Chem. 2019 Jun 3;58(11):7545-7553. doi: 10.1021/acs.inorgchem.9b00786. Epub 2019 May 10.

Authors

Anuj Kumar¹, Dan Yuan², Han Vinh Huynh¹

Affiliations

¹ Department of Chemistry , National University of Singapore , 3 Science Drive 3 , Singapore 117543.
² Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Dushu Lake Campus , Soochow University , Suzhou 215123 , People's Republic of China.

PMID: 31074971
DOI: 10.1021/acs.inorgchem.9b00786

Abstract

Heterobis(carbene) complexes of palladium(II) and gold(I) containing expanded-ring N-heterocyclic carbenes (erNHCs) have been prepared in order to study their electronic properties. erNHCs with mesityl substituents were found to exhibit anisotropic interferences, which hampered ranking of their donicities by ¹³C NMR spectroscopy. The anisotropy effects were found to be stronger in the linear gold complexes, where a smaller coordination number allows the wingtips to spread out more. erNHCs with flexible N-benzyl groups are more suitable, and their donor strengths were found to gradually increase from five- to seven-membered heterocycles. The same trend can also be obtained by comparing the ¹ J(C-H) coupling constants of the respective salts, although significant differences between seven- and eight-membered erNHCs could not be detected. The % V_bur values of erNHCs obtained from structures of their palladium and gold complexes revealed that the anisotropic interferences increase with overall steric bulk.