Synthesis and reactivity of (pyrazol-1-yl)acyl iron complexes

Abstract

Treatment of 1-methyl-3,5-dialkylpyrazoles with n-BuLi, and subsequently with iron carbonyl and iodine yielded (pyrazol-1-yl)acyl iron complexes CH2(CO) (3,5-R2Pz)Fe(CO)3I (R = Me or Pri, Pz = pyrazol-1-yl). Reaction of CH2(CO) (3,5-Me2Pz)Fe(CO)3I with PhSNa gave a dimeric complex [CH2(CO) (3,5-Me2Pz)Fe(CO)2(SPh)]2, while similar reactions of CH2(CO) (3,5-R2Pz)Fe(CO)3I with PySNa (Py = 2-pyridyl) gave mononuclear complexes CH2(CO) (3,5-R2Pz)Fe(CO)2(SPy), which exhibited an isomerization in solution. Treatment of the dimeric complex with PPh3 at room temperature resulted in the decomposition of the starting material. Furthermore, this dimeric complex readily underwent reductive elimination to generate CH2(COSPh) (3,5-Me2Pz) when heated at relatively low temperature, and thermal decomposition reaction to give PhSSPh in refluxing toluene solution. Reaction of mononuclear complexes with PPh3 caused one carbonyl to be replaced by phosphine ligand to give complexes CH2(CO) (3,5-R2Pz)Fe(CO) (PPh3) (SPy). All these acyl iron complexes were fully characterized by IR and NMR spectroscopy, and their structures were unambiguously determined by X-ray crystallography.