Piano-stool acylcyclopentadienyl iron complexes: photolytic syntheses and X-ray crystal structure of [Fe(η5-C5H4COMe)(dppe)(NCMe)]PF6

Abstract

Photolysis of monoacyl iron(II) metallocenes, [Fe(η⁵-C₅H₄COR)(η⁶-arene)] PF₆(R = Me or Ph), in solvents of low electron donicity, at 273 K, and in the presence of two-electron ligands L [L = P(OMe)₃, NCCH₃, CO, or dppe (Ph₂PCH₂CH₂PPh₂)], leads to exchange of the arene by three L ligands. Thermal ligand exchange of the derived piano-stool cations [Fe(η⁵-C₅H₄COR)L¹(L²)L³]PF₆, [L¹= L²= P(OMe)₃, or L¹–L²= dppe; L³= NCMe] in the dark and at low CO pressure (5 atm) leads to the corresponding carbonyl derivatives [Fe(η⁵-C₅H₄COR) L¹(L²)(CO)]PF₆. In acetonitrile and under irradiation with visible light, the latter yield the corresponding acetonitrile complexes [Fe(η⁵-C₅H₄COR)L¹(L²)(NCMe)]PF₆. A new series of acyl substituted piano-stool cations [graphic omitted] is obtained showing chirality at the acetylcyclopentadienyl ring. Diastereotopic phenomena in the racemic series of these asymmetric compounds have been observed by ¹H and ³¹P n.m.r. spectroscopy. The X-ray structure of the acyl derivative [Fe(η⁵-C₅H₄COMe)(dppe)(NCMe)]PF₆ has been determined and compared with the unsubstituted cyclopentadienyl piano-stool acetonitrile and carbonyl cationic complexes.