Synthesis and electrochemical aspects of group 14 iron complexes of the type (η5-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2;: E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (eta(5)-C5H5)Fe(L)(2)ER3(L-2 = (CO)(2) (a), (Ph2P)(2)CH2 (b); ER3 = CH3 (1a/b); SiMe3 (2a/b), GeMe3 (3a/b), SnMe3 (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E-ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn approximate to Ge > C; those for 1b-4b (involving replacement of the excellent retrodative pi-accepting CO ligands by the superior sigma-donor and poorer pi-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si approximate to Ge > C. This latter oxidation potential pattern relates directly to the solution 31 P NMR chemical shift data illustrating that stronger donation lowers the Eox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems. (C) 2007 Elsevier B.V. All rights reserved.