Coordination behavior of (ferrocenylethynyl)diphenylphosphane towards binuclear iron and cobalt carbonyls

Abstract

The reaction of PPh2(C≡CFc) (Fc = Fe(η5-C5H4)(η5-C5H5)) (1) with Fe2(CO)9 (2) and Co2(CO)8 (3) afforded Fe(CO)4(PPh2(C≡CFc)) (4), Fe(CO)3(PPh2(C≡CFc))2 (5), Fe2(CO)6(μ,η2-C≡CFc)(μ-PPh2) (6) (reaction of 1 with 2), PPh2((η2-C≡CFc)Co2(CO)6) (7) and Co2(CO)7(PPh2((η2-C≡CFc)Co2(CO)6)) (8) (reaction of 1 with 3). Treatment of 4 with one equiv of 3 produced Fe(CO)4(PPh2((η2-C≡CFc)Co2(CO)6)) (9). This compound was also obtained when 7 was reacted with 2. All compounds were characterized by NMR, UV–Vis and IR spectroscopy, high resolution ESI-TOF mass-spectrometry and elemental analysis. The structures of 4 and 6–8 in the solid state were determined by single crystal X-ray structure analysis. These studies verified that 1 acts as a κP-ligand to a Fe(CO)4 fragment in 4. In 7 and 8 the C≡C unit is μ-κC:κC′ coordinated to a Co2(CO)6 fragment, and additionally for 8 the PPh2 unit is datively-bonded to a Co2(CO)7 moiety. By the reaction of 1 with 2 at elevated temperature, the PC bond in 1 is cleaved and hence 6 is formed in which the Ph2P unit is μ-1:2κ2P coordinated and the FcC≡C moiety is bonded in a μ-1:2κ2C1,κC2 fashion to a Fe2(CO)6 (FeFe) entity. The electronic properties of 4–6 and 9 were studied by cyclic and square-wave voltammetry. The replacement of a CO ligand in 4 with a 2nd PPh2(C≡CFc) ligand induces electrochemical reversibility of the Fe(CO)3 moiety in 5. As compared to non-coordinated 1, a cathodic shift of the Fc redox potentials is characteristic for 6 and 9, respectively, whereas an anodic shift is observed for 4 and 5.