Bis‐alkynyl Diruthenium Compounds with Built‐in Electronic Asymmetry: Toward an Organometallic Aviram–Ratner Diode

Abstract

Conditions to prepare trans-[Ru2(dmba)4(C[triple chemical bond]CAr)2] from [Ru2(dmba)4(NO(3))2] (DMBA=N,N'-dimethylbenzamidinate) and HC[triple chemical bond]CAr were optimized; Et2NH was found to be the most effective among a number of weak bases in facilitating the product formation. Furthermore, a series of unsymmetric trans-[(ArC[triple chemical bond]C)Ru(2)(dmba)4(C[triple chemical bond]CAr')] compounds were prepared under optimized conditions, in which one or both of Ar and Ar' are donor (NMe2)-/acceptor (NO(2))-substituted phenyls. While the X-ray crystallographic studies revealed a minimal structural effect upon donor/acceptor substitution, voltammetric measurements indicated a significant influence of substituents on the energy level of frontier orbitals. In particular, placing a donor and an acceptor on the opposite ends of trans-[(ArC[triple chemical bond]C)Ru2(dmba)4(C[triple chemical bond]CAr')] moiety results in an energetic alignment of frontier orbitals that favors a directional electron flow, a necessary condition for unimolecular rectification.

Diruthenium compounds of heterocycle-containing acetylides

“…As shown in Scheme 2, the reaction between Ru 2 (Y-DMBA) 4 (NO 3 ) 2 (Y = H(a) and Y = mMeO (b)) and HC"C-2-N 2 C 4 H 3 (2-5 equiv) [17] in the presence of Et 2 NH afforded compounds 1a/b in satisfactory yield. Treating Ru 2 (Y-DMBA) 4 (C"C-4-C 5 H 4 N) 2 [15] with iodomethane in THF resulted in the corresponding N-methylpyridinium derivatives 2a/b in excellent yield. Isolated as the iodide salt, compounds 2a/ b are insoluble in THF but very soluble in acetone.…”

“…The weak base assisted protocol has been proven as an efficient method for the preparation of Ru 2 (DM-BA) 4 (C"CAr) 2 type compounds [14][15][16]. As shown in Scheme 2, the reaction between Ru 2 (Y-DMBA) 4 (NO 3 ) 2 (Y = H(a) and Y = mMeO (b)) and HC"C-2-N 2 C 4 H 3 (2-5 equiv) [17] in the presence of Et 2 NH afforded compounds 1a/b in satisfactory yield.…”

“…We previously reported a series of symmetrical Ru 2 (DMBA) 4 (C"CAr) 2 (DMBA: N,N 0 -dimethylbenzamidinate) compounds where Ar is phenyl bearing electron donor or acceptor substituent, and the effect of the donor/acceptor substitution on the electronic nature of these diruthenium species [14]. More recently, unsymmetric (ArC"C)Ru 2 (DMBA) 4 (C"CAr 0 ) (Ar 6 ¼ Ar 0 ) type compounds were synthesized under the optimized conditions and the electronic asymmetry in compounds of D-Ru 2 -A arrangement was elaborated [15]. Described in this contribution are the synthesis and characterization of symmetric Ru 2 (Y-DMBA) 4 (C"CAr) 2 (Y = H, 1; m-MeO, 2) with Ar as hetercyclic rings (see Scheme 1).…”

A Theoretical Study of Substitution Effects in Unimolecular Rectifiers

“…[19][20][21][22] This effect, however, can have different origins in the nanojunction: [23,24] i) an asymmetry in the coupling of the molecule to the two electrodes. [25,26] This effect can be explained by charging effects that depend on the energetic positions of HOMO and LUMO relative to the Fermi levels of the electrodes.…”

“…Of course, we only draw here conclusions for the molecules studied in this article and do not claim that our results can be readily applied to every possible single molecule junction. It has to be noted that the calculated RR are rather small compared to some experimental measurements, [19][20][21][22][23] for which it is not so easy to determine whether the observed effect comes from unimolecular rectification only. However, there are some characteristic features in the selected molecular structures that are found in the unimolecular rectifiers described so far in the literature.…”