Synthesis and Crystal Structure of N-Heterocyclic Carbene Complexes of Bis((eta)^5-cyclopentadienyl)molybdenum

The one-pot reaction of [Mo((eta)^5-C5H5)2(H)(OTs)] (1) with 1,3-diisopropylimidazolium chloride (IiPr·HCl, 2a) in the presence of two equivalents of KOtBu in THF gave a bis((eta)^5-cyclopentadienyl)molybdenum derivative bearing the 1,3-diisopropylimidazol-2-ylidene ligand, [Mo((eta)^5-C5H5)2(IiPr)] (3a). 1,3-Dimethyl- and 1,3-bis (2,4,6-trimethylphenyl)imidazol-2-ylidene coordinated molybdenocene complexes (3b, 3c) were prepared in a similar fashion (Method A). The treatment of [Mo((eta)^5C5H5)2(H)Li]4 (6-Mo) with the corresponding imidazolium salt in THF under photo-conditions also gave carbene complexes 3a-3c (Method B). X-ray crystal structure analyses of 3a and 3b revealed that the N-heterocyclic carbene ligand is bonded to a bent molybdenocene skeleton. The Mo-C(carbene) bond distances are 2.219(7) A for 3a and 2.212(6) A for 3b. The five-membered carbene ligand in both complexes is located on the bisecting plane between two cyclopentadienyl rings.