Synthesis and Characterization of (n3-CPh₃)Re(CO)₄, a Thermal Precursor for Generation of the Re(CO)₅ Radical

Reaction of NaRe(CO)₅ with Ph₃CPF₆ affords Re(CO)₄(η³-CPh₃) (1). Complex 1 reacts readily with CO at room temperature to give the ^•Re(CO)₅ radical, which forms Re₂(CO)₁₀ in the absence of trapping agents. The radical reacts with CCl₄ to give Re(CO)₅Cl and with Fe(CO)₅ to give Re₂Fe(CO)₁₄ (2). Compounds 1 and 2 have been structurally characterized. Compound 1 crystallizes in the triclinic space group P1 with lattice parameters a = 11.062 (2) Å, b = 11.383 (1) Å, c = 17.961 (3) Å, α = 104.62 (1)°, γ = 94.77 (2)°, and γ = 98.52 (1)°. The final R value was 3.7%. The structure shows a Re(CO)₄ moiety coordinated to the central carbon of the triphenylmethyl unit and two carbons of one phenyl ring. Complex 2 crystallizes in the monoclinic space group C2/m with lattice parameters a = 12.083 (3) Å, b = 14.705 (4) Å, c = 11.822 (3) Å, and β = 97.43 (2)°. The final R value was 3.4%. The structure shows a linear Re-Fe-Re array.