Synthesis and Protonation of N-Heterocyclic-Carbene-Supported Dinitrogen Complexes of Molybdenum(0)

Abstract

The N-heterocyclic-carbene-supported dinitrogen (N2) complexes of molybdenum(0) trans-Mo(N2)2(LR)4 (LR = 1,3-R2-4,5-dimethylimidazol-2-ylidene; 2a: R = Me, 2b: R = Et) and mer-Mo(N2)3(LR)3 (3: R = iPr) were synthesized from MoCl4(THF)2 and KC8 in the presence of LR under an atmosphere of N2. In agreement with the characteristically strong σ-donation from the N-heterocyclic carbenes to molybdenum, complexes 2a, 2b, and 3 exhibited lower N–N stretching frequencies in their IR spectra and displayed longer N–N as well as shorter Mo–N bond lengths in their molecular structures relative to corresponding phosphine analogues. Although protonation of the molybdenum-bound N2 ligands in these phosphine complexes with H2O is unprecedented, it was accomplished for 2a, 2b, and 3 under concomitant release of ammonia.