Donor Strength Determination of Benzoxazolin-2-ylidene, Benzobisoxazolin-2-ylidene, and Their Isocyanide Precursors by C-13 NMR Spectroscopy of Their Pd-II and Au-I Complexes

作者：Meier Martin; Tan Tristan Tsai Yuan; Hahn F Ekkehardt^*; Han Vinh Huynh^*

来源：Organometallics, 2017, 36(2): 275-284.

DOI：10.1021/acs.organomet.6b00736

A series of mono- and dinuclear palladium(II), and gold(I) complexes containing the Pr-i(2)-biroy reporter ligand and monodentate or Janus-type beta-functionalized aryl (di)isocyanides have been prepared. Cyclization of the isocyanide ligands afforded complexes of monodentate or Janus-type N,O-heterocyclic carbenes (NOHCs) via a template-directed process. Using the Pr-i(2)-bimy C-13(carbene) signals in these complexes, the electron-donating ability of NOHCs and their isocyanide precursors could be evaluated and compared for the first time. Overall, NOHCs were found to be rather weakly donating carbenes. Spectroscopic comparison of mono- with dinuclear complexes indicated that electronic communication between two metal centers occurs only across the Janus-type diNOHC, but not for the diisocyanide ligand. Support for this claim was, also found in the solid-state molecular structures, which revealed coplanarity of all ligands only in the diNOHC complex as a prerequisite for pi-electron delocalization.

• 出版日期2017-1-23