Synthesis and Structures of Triple-Decker Complexes with a Bridging Tetramethylcyclopentadienyl Ligand

Abstract

New triple-decker complexes with bridging tetramethylcyclopentadienyl ligands were synthesized by the reaction of electrophilic metal fragments with octamethylferrocene, Cp′2Fe (Cp′ = C5Me4H). The reaction of coordinatively unsaturated ruthenium cations [(C5R5)Ru]+ (R = H, CH3) with Cp′2Fe afforded purple-colored heterometallic triple-decker complexes [(C5R5)Ru(μ-Cp′)FeCp′]+ by direct electrophilic addition. Surprisingly, the analogous reaction with the coordinatively unsaturated manganese cation [Mn(CO)3]+ and Cp′2Fe produced a blue homometallic triple-decker complex, [Cp′Fe(μ-Cp′)FeCp′]+, by ring abstraction and subsequent addition of the newly generated cation [Cp′Fe]+ to an equivalent of Cp′2Fe. Three air-stable triple-decker complexes, [Cp′Fe(μ-Cp′)FeCp′]+ (2), [CpRu(μ-Cp′)FeCp′]+ (3), and [Cp*Ru(μ-Cp′)FeCp′]+ (4), have been characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

Syntheses and Structures of Triple-Decker Complexes Incorporating Octamethylruthenocene and Nonamethylruthenocene

“…17 Table 1 presents results from 1 H NMR and 13 C NMR experiments for the three diamagnetic monocations 1−3 plus Cp′RuCp′. Table 2 presents 1 H NMR and 13 C NMR data for the two diamagnetic monocations 4 and 5 plus Cp′RuCp*, 6. Assignments were made based on comparisons between related compounds and by carbon−hydrogen correlation NMR experiments.…”

“…In like manner, the proton and carbon signals for the Cp* rings in 4 and 5 exhibit resonances close to those of Cp* in nonamethylruthenocene. For all five bridging Cp′ ligands, the 13 C NMR resonances for the unsubstituted ring carbons are 9.3−12.3 ppm upfield of the resonances for the methylated ring carbons. This significant difference in frequency correlates with the fact that Ru−C(H) bond lengths are typically shorter than Ru−C(Me) bonds (Figures 1−5).…”

“…Assignments were made based on comparisons between related compounds and by carbon−hydrogen correlation NMR experiments. For 1−3, 1 H and 13 C NMR data for terminal Cp′ rings of the triple-decker complexes are close to those for Cp′ in octamethylruthenocene. In like manner, the proton and carbon signals for the Cp* rings in 4 and 5 exhibit resonances close to those of Cp* in nonamethylruthenocene.…”

“…Moreover, insofar as bond length can be correlated with bond strength, these data suggest weaker Ru−C and C−C interactions for the doubly coordinated central ring compared with the singly coordinated outer rings. 17 Table 1 presents results from 1 H NMR and 13 C NMR experiments for the three diamagnetic monocations 1−3 plus Cp′RuCp′. Table 2 presents 1 H NMR and 13 C NMR data for the two diamagnetic monocations 4 and 5 plus Cp′RuCp*, 6.…”

“…While incorporation of octamethylruthenocene or nonamethylruthenocene into a triple-decker complex ion does not significantly affect the NMR data for its terminal ring protons and carbons, this is not the case for the bridging Cp′ ligand. Instead Tables 1 and 2 reveal that π-coordination to two ruthenium atoms shifts the 1 H and 13 C signals significantly from those in the free metallocene. For complexes 1−3, the 1 H signals for the 13 protons on the central ligand are shifted downfield of those in Cp′RuCp′ by 0.36−0.91 ppm.…”