Effect of the Substitution on the Protonation of Allyl Cyclopentadienyl Molybdenum(II) Compounds

Synthesis, characterization, and reactivity of new allyl cyclopentadienyl molybdenum­(II) compounds [(η3-C3H4R1)­(η5-C5H3(R2)2)­Mo­(CO)2] (R1 = H, COOMe; R2 = COOMe, CONHtBu) are reported. Although these compounds are structural analogues of [(η3-C3H5)­(η5-Cp)­Mo­(CO)2], their reactivity is very different. While protonation of [(η3-C3H5)­(η5-Cp)­Mo­(CO)2] gives a cationic cyclopentadienyl complex, the presented compounds give cationic allyl complexes [(η3-C3H4R)­Mo­(CO)2(NCMe)3]­[BF4] (R = H, COOMe) or stable cationic allyl cyclopentadienyl complexes. The theoretical calculations have shown that this behavior is a result of high affinity of the functional groups in the cyclopentadienyl ligand toward protonation.