FORMATION, STRUCTURE, SPECTRA, AND REACTIVITY OF THE ADDUCT BETWEEN (ETA(5)-CYCLOPENTADIENYL)(1,2-DIMETHOXYCARBONYL-1,2-ETHYLENEDITHIOLATO)RHODIUM(III) AND DIMETHYL ACETYLENEDICARBOXYLATE

A dithiolatorhodium complex [Rh(Cp)(S(2)C(2)Z(2))] (2, Z=COOMe) reacts with dimethyl acetylenedicarboxylate (DMAD) to give a 1:1 adduct (3) in 85% yield. The same adduct is obtained in a prolonged reaction of [Rh(Cp)(cod)] (1) with S-8 and DMAD in 39% yield. In the adduct, DMAD adds between Rh and S. The adduct has been characterized by spectroscopic and by X-ray diffraction techniques. Red-brown crystals of the adduct are triclinic P (1) over bar, with a = 11.789(4), b = 10.789(3), c = 7.960(1) Angstrom, alpha = 92.33(2), beta = 94.07(2), gamma = 101.51(2)degrees, and D-c = 1.736(calcd) g cm(-1) for Z = 2. Least-squares refinement gives a final conventional R value of 0.028 for 4091 independent observed reflections. The adduct has a piano-stool structure consisting of a four-membered ring of Rh-S-C=C and a five-membered ring of rhodiadithiolene. The adduct is pyrolyzed to afford the decomposition product, tetramethyl 2,3,4,5-thiophenetetracarboxylate (TTME), together with a dissociation product, [Rh(Cp)(S(2)C(2)Z(2))] (2). Adduct 3 is also photochemically dissociated to regenerate [Rh(Cp)(S(2)C(2)Z(2))] 2.