Bis-alkynyl diruthenium compounds with built-in electronic asymmetry: toward an organometallic Aviram-Ratner diode

Conditions to prepare trans-Ru2(dmba)4(Ctriple chemical bond]CAr)2] from Ru2(dmba)4(NO(3))2] (DMBA=N,N'-dimethylbenzamidinate) and HCtriple 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-(ArCtriple chemical bond]C)Ru(2)(dmba)4(Ctriple 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-(ArCtriple chemical bond]C)Ru2(dmba)4(Ctriple chemical bond]CAr')] moiety results in an energetic alignment of frontier orbitals that favors a directional electron flow, a necessary condition for unimolecular rectification.