Reaction of lithium alkyls and aryls with 1,1′-diphosphaferrocenes. Synthesis and structure of a stable bis(diene)iron(-I) species

Article abstract of DOI:10.1021/ic50224a023

The reaction of 2 equiv of alkyllithium and 3 equiv of alkyl halide with 1,1′-diphosphaferrocene yields a stable green paramagnetic bis(η⁴-phospholium)iron halide in which iron bears formally 17 electrons. The stability of these species increases with the bulkiness of the alkyl chains. The product with tert-butyl and methyl P substituents was studied by X-ray. The two most striking characteristics of its structure are the absence of a phosphorus-iron bond and the impressive folding of the phospholium nucleus around the Cα-Cα′ axis (?31°). Crystal data for FeP₂IC₂₂H₄₀ are a = 10.640 (1) A?, b = 10.865 (2) A?, c = 24.908 (4) A?, α = 90.14 (1)°, β = 95.06 (1)°, γ = 112.24 (1)°, V = 2653 A?³, Z = 4, d_calcd = 1.37 g cm^-3, and space group P1. The mechanism of formation of these products probably includes the nucleophilic attack of alkyllithium onto one of the phosphorus atoms of 1,1′-diphosphaferrocene followed by the electrophilic attack of the alkyl halide onto the same phosphorus giving a transient (phospholium)(phospholyl)iron species. When phenyllithium was used, this transient species was spontaneously oxidized and gave a stable (η⁴-phospholium)(η ⁵-1-hydroxy-1-oxophospholato)iron diamagnetic zwitterion, the structure of which was also established by X-ray. The existence of such a compound demonstrates that the phosphole P(O)OH acids are able to chelate a metal between their phosphinate function and their dienic system. Crystal data for FeP₂O₃C₁₉H₂₆ are a = 9.822 (1) A?, b = 9.845 (1) A?, c = 10.913 (1) A?, α = 74.64 (1)°, β = 67.02 (1)°, γ = 80.74 (1)°, V = 935 A?³, Z = 2, d_calcd = 1.49 g cm^-3, and space group P1.