Functionalization of Cp₄Fe₄(CO)₄: Contrasts and comparisons with ferrocene

Thermolysis of a xylene solution of Cp₂Fe₂(CO)₄ and PPh₃ yields primarily Cp₄Fe₄(CO)₄ (1) together with smaller amounts of (C₅H₄Ph)Cp₃Fe₄(CO)₄ and Cp₃Fe₃(CO)₃(PPh₂). Cluster 1 can be alkylated and arylated by using organolithium reagents to give the derivatives (C₅H₄R)Cp₃Fe₄(CO)₄. This reaction is competitive with reduction of 1 by the organolithium reagent. A more versatile method for functionalizing 1 involves its deprotonation with lithium diisopropylamide (LDA) followed by treatment with electrophiles to give (C₅H₄X)Cp₃Fe₄ (X = C(OH)HCH₃, CO₂H, CHO, SPh, PPh₂). An excess of LDA gave increased amounts of the di- and even trifunctionalized derivatives (C₅H₄X)(x)Cp(4-x)Fe₄(CO)₄ (x = 2, 3). Treatment of (C₅H₄- CHO)Cp₃Fe₄(CO)₄ with the lithiated cluster gave the double cluster [(C₅H₄)Cp₃Fe₄(CO)₄]₂CHOH. The use of the cluster as a ligand was demonstrated by the synthesis of the adducts (C₅H₄PPh₂ML(n))Cp₃Fe₄(CO)₄, where ML(n) = RuCl₂(cymene), IrCl(1,5-C₈H₁₂). Single-crystal X-ray diffraction was employed to characterize [(C₅H₄)Cp₃Fe₄(CO)₄]₂CHOH and (C₃H₄PPh₂)Cp₃Fe₄(CO)₄RuCl₂(cymene).