Anionic coordination complexes of C60 and C70 with cyclopentadienyl and pentamethylcyclopentadienyl molybdenum dicarbonyl

Abstract

Crystalline anionic coordination complexes (PPN⁺){CpMo(CO)₂(η²-C₆₀)}⁻ (1), (PPN⁺){CpMo(CO)₂(η²-C₇₀)}⁻·0.5C₆H₁₄ (2) and (PPN⁺){Cp*Mo(CO)₂(η²-C₆₀)}⁻·C₆H₅CN·C₆H₄Cl₂ (3) containing cyclopentadienyl (1, 2) and pentamethylcyclopentadienyl (3) molybdenum dicarbonyl η²-coordinated to fullerenes have been obtained by the reaction of the (PPN⁺)(fullerene˙⁻) salt with the {Cp(*)Mo(CO)₃₍₂₎}₂ dimers (PPN⁺ is bis(triphenylphosphoranylidene)ammonium cation). The {CpMo(CO)₂(η²-C₆₀₍₇₀₎)}⁻ anions contain neutral C₆₀ and C₇₀. The optical properties and geometry of the CpMo(CO)₂ moieties in 1 and 2 are similar to those in (PPN⁺){CpMo⁰(CO)₃}⁻. The analysis of optical data for 3 shows that η²-coordinated C₆₀ molecules are more negatively charged in 3 than in 1 and 2. Complexes 1–3 show weak EPR signals indicating that the major part of the samples is EPR silent and diamagnetic. Diamagnetism of the anions in 1–3 is explained by the chemical bond formation between the initially paramagnetic CpMo^I(CO)₂ and (fullerene)˙⁻ units. The DFT calculations for 1 and 3 support the diamagnetic singlet ground state for both complexes, in which the singlet–triplet energy gaps calculated at the M11/cc-pVTZ-PP/cc-pVDZ level of theory are about 1.27 and 0.95 eV, respectively. According to the calculations, C₆₀ molecules are more negatively charged in 3 than in 1 and that can be explained by stronger back donation from the molybdenum moieties to fullerenes.