Diruthenium Phenylacetylide Complexes Bearing para-/meta-Amino Phenyl Substituents

Abstract

Presented herein is the synthesis and characterization of four diruthenium(II,III) compounds of formulas Ru2(Xap)4(CC-C6H4-4-NH2) (Xap is 2-anilinopyridinate, 1a; and 2-(3,5-dimethoxy)anilinopyridinate, 1b) and Ru2(Xap)4(CC-C6H4-3-NH2) (2a/2b). X-ray structural studies of compounds 1b and 2a revealed minimal changes in the coordination sphere of the Ru2 core. Voltammetric measurements showed that compounds 1 exhibit three one-electron redox processes: a reversible reduction of Ru2, a reversible oxidation of Ru2, and a quasi-reversible oxidation of an amino group. Compounds 2 display the same Ru2-based redox processes but not the −NH2 oxidation. Compounds 1a/1b were successfully converted to the corresponding diazonium salts [Ru2(Xap)4-(CC-C6H4-4-N2)](BF4) (3a/3b) via oxidation by nitrosonium tetrafluoroborate, which was generated in situ from t-BuONO and BF3. However, the attempt to convert compounds 2 to the corresponding diazonium salts was unsuccessful. DFT calculations of model compounds were performed to rationalize some unusual structural and electrochemical characteristics observed for compounds 1/2.

Diruthenium σ-iminophenylacetylide complexes from on-complex Schiff base condensation

“…3 and 4) with peaks at circa 460 and 755 nm, which are similar to those of related Ru 2 (ap) 4 (C^CR)-type compounds from prior studies [2,37,47,49,50,54]. Based on a previous TD-DFT study of the model compounds for 1 and 2 [54], the high energy band arises from the transition of p(C^C) to d * (RueRu), while the low energy band is due to a combination of the p(RueN) and p(RueRu) to d * (RueRu).…”

“…The double peak feature observed in 3 implies that two orthogonal components of p(C^C) are no longer degenerate. This can be rationalized using our prior DFT study [37]: the 4-N center is conjugated to one of the p(C^C) orbitals through a quinoidal resonance structure that stabilizes the p orbital while leaving the other unperturbed. The splitting of the p(C^C) orbitals is evident in the parent compound 1, where a shoulder is present at 570 nm.…”

“…In the precursor compound 1, the oxidation couple is 20 mV more positive than that for 2 due to the increased electron donating ability of an amino in the para-position than the meta-position [37]. In contrast, the oxidation for 3 and 4b/c are centered near 0.44 V while 4a is slightly less positive at 0.42 V. This is a surprising result since the para-imine (Hammett constant s(4-N]CHeC 6 H 4 ) ¼ À0.55) is significantly more electron donating than in the meta-imine (s(3eN]CHeC 6 H 4 ) ¼ À0.08) [55].…”

“…With the [Ru 2 (ap) 4 ]e(C^CeC 6 H 4 e4/3eNH 2 ) type compounds (1/2) already prepared by us [37], it is conceivable to prepare the imine containing derivative via Schiff base condensation with a substituted benzaldehyde. The condensation reaction occurred without a catalyst under reflux conditions (in either THF or toluene), but degradation products were present.…”

“…While the research during the ensuing 40þ years has focused on the structure and bonding [26,27], recent years have witnessed new development in molecular magnetism [28e31], small molecule activation [32,33] and catalysis [34e36]. Described in this contribution, as the first step toward organometallic wires containing an imine moiety, are the preparation of compounds 3 and 4 (Scheme 1) by the condensation reaction between [Ru 2 (ap) 4 ]e(C^CeC 6 H 4 e4/3eNH 2 ) (compounds 1/2) [37] and arylaldehydes and their characterization.…”