Thermolysis of (C5Me5)Rh(C2H4)2 in the presence of thiophene leads to the formation of the new product, [(C5Me5)Rh]2[1,2,3,4-eta4-5,6,7,10-eta4-S(CH)8S]. The related reaction with dibenzothiophene leads first to the sulfur-bridged C-S-inserted cis dimer [(C5Me5)Rh(mu2-eta2-SC12H8)]2 and then to the trans dimer of the same formula. These complexes have been structurally characterized, with the cis complex crystallizing in monoclinic space group C2/c with a = 16.323 (6) angstrom, b = 15.355 (5) angstrom, c = 14.646 (5) angstrom, beta = 92.61 (3)-degrees, Z = 4, and V = 3666.8 (4.1) angstrom3. The trans isomer crystallizes in triclinic space group P1BAR, with a = 9.995 (3) angstrom, b = 10.290 (2) angstrom, c = 11.230 (2) angstrom, alpha = 112.02 (1)-degrees, beta = 97.99 (2)-degrees, gamma = 114.66 (2)-degrees, Z = 1, and V = 911.2 (1.1) angstrom3. The reaction of (C5Me5)Rh(C2H4)2 with 2-methoxythiophene is found to lead to the monomer (C5Me5)Rh[C(OMe)=CHCH=CHS], which is in equilibrium with the corresponding cis and trans sulfur-bridged dimers. The rate of cleavage of the cis dimer to give the monomer at 22-degrees-C is 3.12 (12) x 10(-3) s-1. The rate of cleavage of the trans dimer to give the monomer at 22-degrees-C is 1.25 (4) x 10(-5) s-1. Equilibrium parameters for the cis half arrow right over half arrow left monomer equilibrium are DELTAH-degrees = 7.0 (0.7)kcal/mol and DELTAS-degrees = 19 (2) eu. Equilibrium parameters for the trans half arrow right over half arrow left monomer equilibrium are DELTAH-degrees = 10.4 (0.7 kcal/mol and DELTAS-degrees = 28 (2) eu. An X-ray structural determination of the cis dimer shows the complex to crystallize in triclinic space group P1BAR, with a = 8.335 (4) angstrom, b = 10.096 (3) angstrom, c = 19.832 (5) angstrom, alpha = 89.54 (2)-degrees, beta = 78.49 (3)-degrees, gamma = 67.97 (3)-degrees, Z = 2, and V = 1511.9 (2.1) angstrom3. The trans dimer crystallizes in triclinic space group P1BAR, with a = 10.814 (3) angstrom, b = 10.816 (5) angstrom, c = 16.301 (4) angstrom, alpha = 84.79 (3)-degrees, beta = 88.15 (2)-degrees, gamma = 68.79 (3)-degrees, Z = 2, and V = 1770.1 (2.2) angstrom3. These structures are discussed with regard to the mechanism of the C-C bond forming reaction.
