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(CO)4 (X = C(OH)HCH3, CO2H, CHO, SPh, PPh2). An excess of LDA gave increased amounts of the di- and even trifunctionalized derivatives (C5H4X)xCp4-xFe4(CO)4 (x = 2, 3). Treatment of (C5H4CHO)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 (C5H4PPh2MLn)Cp3Fe4(CO)4, where MLn = 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).