Transition-Metal Carbonyl Complexes of 2,5-Diferrocenyl-1-phenyl‑1H‑phosphole

Pentacarbonyl­(2,5-diferrocenyl-1-phenyl-1H-phosphole)­metal complexes 3a–c (3a, M = Cr; 3b, M = Mo; 3c, M = W) have successfully been synthesized by the reaction of 2,5-diferrocenyl-1-phenyl-1H-phosphole (1) with M­(CO)5(thf) (2a, M = Cr; 2b, M = Mo; 2c, M = W). Further irradiation of 3a–c with 1 equiv of 1 in tetrahydrofuran leads to tetracarbonylbis­(2,5-diferrocenyl-1-phenyl-1H-phosphole)metal complexes 4a–c (4a, M = Cr; 4b, M = Mo; 4c, M = W). In addition, the reaction of 1 with Fe2(CO)9 gave tetracarbonyl­(2,5-diferrocenyl-1-phenyl-1H-phosphole)iron (6) and heptacarbonyl­[μ-(2,3,4,5-η)-1-(2,5-diferrocenyl-1-phenyl-1H-phosphole)]­diiron (7), respectively. Treatment of 2,5-diferrocenyl-1-phenyl-1H-phosphole sulfide (8) with Fe2(CO)9 afforded tricarbonyl­[(2,3,4,5-η)-(2,5-diferrocenyl-1-phenyl-1H-phosphole 1-sulfide)]iron (9). Complexes 3b,c, 4c, 7, and 9 have been characterized by single-crystal X-ray diffraction. Molecules 3b,c and 4c exhibit a distorted-octahedral geometry, whereas in 4c the two phosphole units are cis-oriented. Coordination of the dienic system to Fe­(CO)3 in 7 and 9, respectively, resulted in a deflection of the phosphorus atom from the C4 plane. Electrochemical measurements of 3a–c, 4a–c, and 9 demonstrated that the ferrocenyl units can be oxidized separately. The coordination of the dienic system to the Fe­(CO)3 building block leads to a decrease of the redox splitting (ΔE°′ = 190 mV) in comparison to 8 (ΔE°′ = 240 mV). Mixed-valence [3a–c]+, [4a–c]2+, and [9]+ show IVCT absorptions of weak to moderate strengths. The coordination of the phosphorus atom to M­(CO)5 in 3a–c has no significant influence on the metal–metal interaction in the mixed-valent species. However, the coordination of the dienic system in 9 results in a significantly decreased electronic communication of the Fc/Fc+ termini via the heterocyclic core.