¹H, ¹³C and ³¹P studies of cyclopentadienylruthenium complexes with cyclooctatetraene or cyclooctadiene ligands. X-ray structure of [(η⁵-C₅H₅)Ru(η⁴-C₈H₈)(P(OCH₃)₃)]PF₆

The X-ray crystal structure of [(η⁵-C₅H₅)Ru(η⁴-COT)(P(OCH₃)₃)]PF₆ (COT = cyclooctatetraene) (formula C₁₆H₂₂F₆O₃P₂Ru) was determined. The compound crystallizes in the monoclinic space group no. 4 P2₁ (a 11.007(3), b 11.066(3), c 8.660(3) Å, β 105.56(20)°, Z = 2). The structure consists of discrete disordered PF₆^- anions and [(η⁵-C₅H₅)Ru(η⁴-COT)(P(OCH₃)₃)]⁺ cations. The cation exhibits a planar, C₅H₅^- unit. (RuC distances of 2.221(7) Å), a P(OCH₃)₃ ligand (RuP distance of 2.306(2) Å) and an η⁴-COT ligand in the tub conformation. The η⁴-COT ligand is bound to the Ru atom through two different Ru bond distances 2.298(5) and 2.223(6) Å, the longer distance appropriate to the RuC bonds nearest the RuP bond. The ¹H, ¹³C and ³¹P NMR spectra of [(η⁵-C₅H₅)Ru(η⁴-COT) (P(OCH₃)₃)]PF₆,[(η⁵-C₅H₅)Ru(η⁴-COT)(CO)PF₆,[(η⁵-C₅H₅)Ru(η⁶-COT)PF₆ and [(η⁵-C₅H₅)Ru(η⁴-COD)(P(OCH₃)₃]PF₆ (COD = 1,5-cyclooctadiene) were obtained. Comparison of the ¹H NMR and ¹³C spectra of [(η⁵-C₅H₅)Ru(η⁴-COT)(P(OCH₃)₃]PF₆ and [(η⁵-C₅H₅)Ru(η⁴-COD)(P(OCH₃)₃)]PF₆ confirm that the COT complex retains the solid state structure in solution. Through comparison and simulation of the ¹H and ¹H{³¹P} NMR spectra of [(η⁵-C₅H₅)Ru(η⁴-COT)(P(OCH₃)₃)]PF₆ all eight COT protons are found to exhibit ¹H-³¹P coupling. The allylic coupling constants that involve hydrogens bound to a coordinated carbon have small positive values, rather than the small negative values usually found in 'pure' organic systems.