Synthesis of inequivalently bridged cyclopentadienyl dimers of molybdenum and a comparison of their reactivities with unsaturated molecules and with hydrogen

A series of dimeric cyclopentadienyl complexes of molybdenum which are bridged by two inequivalent dithiolate ligands have been synthesized. The new complexes include (CpMo)/sub 2/(S/sub 2/CH/sub 2/)(SC/sub 2/H/sub 4/S), IVa, (CpMo)/sub 2/(S/sub 2/C(CH/sub 3/)/sub 2/)(SC/sub 2/H/sub 4/S),IVb, (Cp'Mo)/sub 2/(S/sub 2/CS)(SC/sub 2/H/sub 4/S), V, and (CpMo)/sub 2/(SCHCPhS)(SC/sub 2/H/sub 4/S), VI (Cp = C/sub 5/H/sub 5/, Cp' = CH/sub 3/C/sub 5/H/sub 4/). The relative tendencies of the ethanedithiolate ligands to eliminate ethylene have been compared for the above series. The studies establish that the ligand lability is influenced by the nature of the other dithiolate bridge as well as by substituents on the cyclopentadienyl ligands. Alkynes and cumulenes react with the ethanedithiolate ligands in IV-VI to displace ethylene and form derivatives with unsaturated dithiolate bridges. Some of these unsaturated complexes can be hydrogenated under the mild conditions of 1-2 atm of H/sub 2/ at 60/sup 0/C. The reactions result in the stoichiometric reduction of alkynes to cis-alkenes, allenes to alkenes, and ketenes to aldehydes. The relationship between hydrocarbon lability in the dithiolate ligands and hydrogenation activity is discussed. Two X-ray diffraction studies of complexes which contain a ..nu../sup 2/-..mu..-1,1-alkanedithiolate ligand have been completed. The acetylene adduct (Cp'Mo)/sub 2/(S/sub 2/CH/sub 2/)(SC/sub 2/H/sub 2/S)more » crystallizes in space group P2/sub 1//c with a = 7.855 (2) A, b = 8.433 (2) A, C = 13.428 (3) A, and ..beta.. = 104.61 (2)/sup 0/. The methylated derivative (Cp'Mo)/sub 2/(S/sub 2/CH/sub 2/)(SCH/sub 3/)/sub 2/ crystallizes in space group Pbcn with a = 17.143 (4) A, b = 12.023 (2) A, and c = 8.931 (2) A. Structural parameters for these dimers are compared with those of other cyclopentadienylmolybdenum dimers with bridging thiolate ligands.« less