Synthesis and Cyclic Voltammetric Studies of the Diiron Complexes ER2[(η5-C5H4)Fe(L2)Me]2 (E = C, Si, Ge, Sn; R = H, alkyl; L2 = diphosphine) and (η5-C5H5)Fe(L2)ER2Fc (Fc = (η5-C5H4)Fe(η5-C5H5))
journal contributionposted on 22.09.2008, 00:00 by Mukesh Kumar, Francisco Cervantes-Lee, Keith H. Pannell, Jianguo Shao
Cyclic voltammetric studies on ER2[(η5-C5H4)Fe(L2)Me]2 (L2 = dppe; ER2 = CH2 (1a), SiMe2 (2a), GeMe2 (3a), SnMe2 (4a)) revealed two well-resolved reversible waves (1E1/2 = −0.33 V, 2E1/2 = −0.20 V (for 1a); 1E1/2 = −0.35 V, 2E1/2 = −0.21 V (for 2a); 1E1/2 = −0.36 V, 2E1/2 = −0.23 V (for 3a); 1E1/2 = −0.36 V, 2E1/2 = −0.22 V (for 4a)) in CH2Cl2, suggesting electronic communication between two iron centers, which is seen for the first time in this family of organometallic complexes. The resolution between two reversible waves increases in the order 1a < 2a < 3a < 4a; however, coordinating solvents such as pyridine, PhCN, DMSO, and DMF decreased these interactions, attributable to the stabilization of cationic species formed after the first oxidation. UV/vis spectroelectrochemistry of 1a−4a revealed two distinct absorbance patterns for both redox processes and reflected the stepwise oxidation. Homobimetallic complexes containing ferrocenyl groups, (η5-C5H5)Fe(L2)ER2Fc (ER2 = none, L2 = cis-dppen (5a); ER2 = SiMe2, L2 = cis-dppen (6a), dppm (6b); ER2 = GeMe2, L2 = cis-dppen (7a), dppm (7b); ER2 = SntBu2, L2 = dmpe (8a); Fc = (η5-C5H4)Fe(η5-C5H5)), were prepared and studied in terms of electrochemistry. The cyclic voltammogram of 5a exhibited two well-resolved one-electron reversible waves at 1E1/2 = −0.21 V and 2E1/2 = 0.58 V corresponding to oxidation of the Fe(P−P) and Fc iron atoms, respectively. Other complexes in this series (6a/6b, 7a/7b, 8a) containing direct Fe−E−Fc (E = Si, Ge, Sn) bridging units were not stable under electrochemical conditions, and rupture of the Fe−E bonds was observed.