Synthesis of acyl iron complexes based on bis(heteroaryl)methanes

Abstract

Treatment of the lithium salts, derived from the lithiation of bis(pyrazol-1-yl)methanes, bis(1-methylimidazol-2-yl)methane [CH2(mim)2] and 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine [CH2(3,5-Me2Pz)(Py)] using n-BuLi at low temperature, with iron carbonyl and iodine resulted in significantly different acyl iron derivatives. Reaction of bis(pyrazol-1-yl)methanes with n-BuLi, and subsequently with iron carbonyl and iodine yielded bis(pyrazol-1-yl)acyl iron complexes, while similar reaction of CH2(mim)2 gave valeryl iron complex CH2(mim)2Fe(CO)2(COBu-n)I, which was also obtained by the sequential treatment of iron carbonyl with n-BuLi, CH2(mim)2 and iodine. Additionally, the consecutive reaction of CH2(3,5-Me2Pz)(Py) with n-BuLi, iron carbonyl and iodine yielded (3,5-dimethylpyrazol-1-yl)(2-pyridyl)acyl iron complex. The corresponding valeryl iron complex CH2(3,5-Me2Pz)(Py)Fe(CO)2(COBu-n)I was obtained when iron carbonyl was reacted with n-BuLi, and subsequently with CH2(3,5-Me2Pz)(Py) and iodine. However, analogous valeryl iron complexes supported by bis(pyrazol-1-yl)methanes could not be formed by these methods. The different electron-donating ability of these bis(heteroaryl)methanes and the distinct nucleophilicity of the bis(heteroaryl)methyl carbanions were possibly responsible for the diversification of reactivities. All these acyl iron complexes were fully characterized by IR and NMR spectroscopy, and their structures were unambiguously determined by X-ray crystallography.