Evidence of Disruption of Conjugation Involving Delta Bonds in Intramolecular Electronic Coupling

A dimer of dimers containing two quadruply bonded [Mo2(DAniF)3]+ units (DAniF = N,N′-di(p-anisyl)formamidinate) linked by the S-donor linker, dimethyldithiooxamidate was synthesized, structurally characterized, and electronic communication was probed. The core of [Mo2(DAniF)3]2(C2S2N2Me2), 1, formed by the Mo2NSC2SNMo2 atoms shows two fused but non planar six-membered rings, which differs from that of the β form of dimethyloxamidate analogue that has a heteronaphthalene-type structure (Cotton, F. A.; Liu, C. Y.; Murillo, C. A.; Villagrán, D.; Wang, X. J. Am. Chem. Soc. 2004, 126, 14822). For these two analogous compounds electronic coupling between the two [Mo2] units, as determined by electrochemical measurements, diminishes considerably upon replacement of O-donor by S-donor atoms (ΔE1/2 = 531 mV and 440 mV, respectively). This suggests that the non planar conformation of the linker in 1 hampers a pathway leading to π conjugation. Density functional theory (DFT) calculations show that the highest occupied molecular orbitals HOMO−HOMO-1 energy gap of 0.12 eV for 1 is much smaller than that of 0.61 eV for the O-donor analogue, which is consistent with the electrochemical data.