A series of compounds of formula 1,2-M(2)(sigma-Th)(2)(NMe(2))(4), 1, has been prepared, where M = Mo and/or W and Th = 2-thienyl[2-Th], 3-thienyl[3-Th], 5-methyl-2-thienyl[2,5-MeTh], and 2-benzothienyl[2-BTh]. In hydrocarbon solvents-these compounds exist as a mixture of anti and gauche rotamers having a central CN(2)M=MN(2)C core. Addition of (t)BuOH or CF(3)Me(2)COH to hydrocarbon solutions of 1, where M = W, lead to ring-opened products, 2, when the thienyl ligand is attached via the 2-carbon position. No ring-opening occurs for 3-thienyl derivatives. W-2(OR)(5) (mu-CCH2CHCHS) (sigma-2-Th), 2, where one of the 2-thienyl rings has been opened, has been fully characterized and shown to be derived from a ring-opened mu-vinylidene intermediate W-2(O(t)Bu)(4)(mu-CCHCHCHS)(sigma-2-Tn). Rather interestingly, the compound W-2(sigma-2-Th)(NMe(2))(5) reacts with (t)BuOH to give only W-2(2-Th)(O(t)Bu)(5) and HNMe(2). Reactions between 1 and the less sterically demanding alcohols (PrOH)-Pr-i and (t)BuCH(2)OH lead to W-2(OR)(6) compounds with liberation of HNMe(2) and the sulfur containing hydrocarbon. Compound 1 (M = W, 2-Th) reacts with CO2 to give W-2(NMe(2))(2)(O-2(NMe(2))(2)(sigma 2-Th)(2), 3, while with pivalic anhydride W-2(O(2)C(t)Bu)(4) is formed via reductive elimination of the C-C coupled product 2,2’-bithiophene and (t)BuCONMe(2) (4 equiv). 1 (M = W, 2-Th) and CO yield a product formulated as W-2(NMe(2))(4)(mu-CCHCHCHS)(sigma-2-Th)(CO)(3) wherein one ring has opened to form a mu-vinylidene thiolate Ligand. Attempts to prepare 1,2-W(2)L(2)(NMe(2))(4) compounds are described where L = an eta(1)- nitrogen containing heterocycle but only for L = 2-methylindolyl was a compound successfully characterized, Reactions of these compounds with (t)BuOH gave W-2(O(t)Bu)(6) and LH (2 equiv). The compound W-2(sigma-2-FU)(2)(NMe(2))(4) was prepared and characterized (2-Fu = 2-furyl) and shown to undergo ring-opening in its reaction with (t)BuOH to give W-2(O(t)Bu)(5)(mu u-CCH2CHCHO) (sigma-2-Fu), 4, in an analogous manner to the 2-Th complex. The complexes 1 (M = W, 2-Th), 2, 3, and 4 have been characterized by single crystal X-ray studies. The results described herein are compared to other ring-opening reactions of S, N, and O organic heterocyclic compounds as models for the activation of S, N, and O containing fossil fuels in hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodeoxygenation (HDO) processes. The cleavage of the C-X bonds at the (M=M)(6+) centers (M = Mo, W and X = S, N and O) is also compared with earlier cleavage reactions involving C=O, RC=N, R(2)C=O, and Ar2C=S compounds.