Biferrocene NCN pincer metal-d8 complexes: Synthesis, reaction chemistry and cyclovoltammetric studies

The synthesis of biferrocene-bridged NCN pincer palladium and platinum complexes (NCN = [1-C6H2(CH2NMe2)2-3,5]−) is discussed. Sonogashira cross-coupling of [(η5-C5H4)Fe(η5-C5H4Ctriple bond; length of mdashCH)]2 (1) with I-1-NCN-4-X (2a, X = H; 2b, X = Br) produces [(η5-C5H4)Fe(η5-C5H4Ctriple bond; length of mdashC-1-NCN-4-X)]2 (3a, X = H; 3b, X = Br). Homobimetallic 3b further reacts with [Pd2(dba)3 · CHCl3] (4) or [Pt(tol)2(SEt2)]2 (5) (dba = dibenzylidene acetone, tol = 4-tolyl), respectively, to give tetrametallic [(η5-C5H4)Fe(η5-C5H4Ctriple bond; length of mdashC-4-NCN-1-MBr)]2 (6, M = Pd; 7, M = Pt) in which NCN-MBr fragments are connected by a biferrocene unit. Cyclovoltammetric studies show that the ferrocene moieties can independently be oxidized. The difference of the Fe(II)/Fe(III) redox couples amounts to ca. 300 mV and is not affected by the nature of the NCN pincer metal moities.