Toward the Development of Molecular Wires:  Ruthenium(II) Terpyridine Complexes Containing Polyferrocenyl as a Spacer

Abstract

The preparations of multinuclear supramolecules assembled from 1,1‘-bis(terpyridyl)ferrocene, 1,1‘-bis(terpyridyl)biferrocene, and 1,1‘-bis(terpyridyl)triferrocene (tpy-(fc) n -tpy, n = 1−3) redox-active moieties with Ru 2+ metal centers are described. The electrochemical measurements of the Ru 2+ complexes of tpy-(fc) n -tpy ( 1a ( n = 1); 1b ( n = 2); 1c ( n = 3)) are dominated by the Ru 2+ /Ru 3+ redox couple ( E 1/2 from 1.35 to 1.38 V), Fe 2+ /Fe 3+ redox couples ( E 1/2 from ∼0.4 to ∼1.0 V), and tpy/tpy - /tpy 2 - redox couples ( E 1/2 from −1.3 to −1.5 V). The appreciable variations detected in the Fe 2+ /Fe 3+ oxidation potentials indicate that there is an interaction between the spacer and the Ru 2+ metal centers. Coordination of Ru 2+ metal centers to tpy-(fc) n -tpy results in a red-shifted and more intense 1 [(d(π) Fe ) 6 ] → 1 [(d(π) Fe ) 5 (π* tpy Ru ) 1 ] transition in the visible region. The observed red-shifted absorption from 526 nm in the monomeric [Ru(fctpy) 2 ] 2+ complex to ∼560 nm in 1b and 1c reveals that there is a qualitative electronic coupling within the ferrocenyl array. The Fe−Fe interactions result in a red characteristic of the 1 [(d(π) Fe ) 6 ] → 1 [(d(π) Fe ) 5 (π* tpy Ru ) 1 ] MMLCT transition.