Evidence of disruption of conjugation involving delta bonds in intramolecular electronic coupling.

A dimer of dimers containing two quadruply bonded [Mo 2 (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 [Mo 2 (DAniF) 3 ] 2 (C 2 S 2 N 2 Me 2 ), 1, termed by tne Mo 2 NSC 2 SNMo 2 atoms shows two fused but non planar six-membered rings, which differs from that of the βform of dimethyloxamidate analogue that has a heteronaphthalene-type structure (Cotton, F. A.; Liu, C. Y.; Murillo, C. A.; Villagran, D.; Wang, X. J. Am. Chem. Soc. 2004, 126,14822). For these two analogous compounds electronic coupling between the two [Mo 2 ] units, as determined by electrochemical measurements, diminishes considerably upon replacement of 0-donor by S-donor atoms (ΔE 1/2 = 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 0-donor analogue, which is consistent with the electrochemical data.