Reduction–oxidation properties of organotransition-metal complexes. Part 10. Formation and reactivity of the paramagnetic cyclobutadiene-iron and -ruthenium derivatives [M(CO)3–nLn(C4Ph4)]+(n= 1–3, L = phosphorus donor)

Abstract

The tetraphenylcyclobutadiene complexes [M(CO)_3–n L_n(η⁴-C₄Ph₄)][1: M = Fe, n= 1, L = PPh₃ or P(OMe)₃; M = Fe, n= 2, L = P(OMe)₃; M = Ru, n= 2 or 3, L = P (OMe)₃] undergo reversible one-electron oxidation, at the platinum electrode in CH₂Cl₂, to give the paramagnetic radical cations [M(CO)_3–nL_n(C₄Ph₄)]⁺(2). Chemical oxidation of (1) with Ag[BF₄] or [N(C₆H₄Br-p)₃][PF₆] in CH₂ Cl₂ affords salts of [2: M = Fe, n= 1, L = PPh₃; M = Fe, n= 2, L = P(OMe)₃]. Complexes (2) are implicated as intermediates in the formation of [Fe(CO)(NO){P(OMe)₃}(η⁴-C₄Ph₄)]⁺ from [Fe (CO){P(OMe)₃}₂(η⁴-C₄Ph₄)] and Ag[NO₃], of [Fe(CO){P(OMe)₃}(η²-tcne)(η⁴-C₄Ph₄)](3) from tetracyanoethylene (tcne) and [Fe(CO){P(OMe)₃}₂(η⁴-C₄Ph₄)], and of [MX(CO)_3–nL_n(η⁴–C₄Ph₄)]⁺[4; X = Cl, Br, or I] from (1) and halogens, X₂. The reaction of polyhalide salts of [RuX(CO){P(OMe)₃}₂(η⁴-C₄Ph₄)]⁺(4; X = Cl or Br) with PPh₃ leads to cleavage of the metal–ring bond and formation of halogenotetraphenylcyclobutenyl radicals, C₄Ph₄X.