Activation of terminal alkynes at the sulfur-rich bimetallic site [(Mo2Cp2)-Cp-III(mu-SMe)(3)](+): Alkyne-vinylidene conversion and C-S and C-C couplings promoted by addition of unsaturated substrates (RC CH, RN C, S=C=S). Crystal structures of mu-e

摘要

Reactions of the bis(nitrile) compound [Mo2Cp2(MeCN)(2)(mu -SMe)(3)] (BFa) (1) with terminal alkynes in a 1:1 ratio in dichloromethane at room temperature led to the alkyne adduct [Mo2Cp2(mu -SMe)(3)(RCCH)] (BF4)(2: R = Tol (2a), Ph (2b), CH3C=CH2 (2c), nPr (2d), CO2Me (2e), CF3 (2f)), Compounds 2a-d were readily deprotonated with Et3N to give neutral acetylide derivatives [Mo2Cp2(mu-eta (1):eta (2)-C drop CR)(mu -SMe)(3)] (3). Protonation of 3 afforded exclusively the vinylidene complexes [Mo2Cp2(mu-eta (1):eta (2)-C=CHR)(mu -SMe)(3)] (BF3) (4), Reaction of 1 with an excess of terminal alkyne RCCH in dichloromethane gave either the six-membered metallacycle compounds [Mo2Cp2(mu-eta (2):eta (4)-CR=CHCR=CHSMe)(mu -SMe)(2)] (BF4) (5) or the S-methylthiophenium derivatives [Mo2Cp2(mu-eta (2):eta (4)-C4H2R2SMe)(mu -SMe)(2)] (BF4) (6), depending on the nature of the R groups. Further reactions of the alkyne adducts 2 with isocyanide and carbon disulfide led to the vinyl-thioether complexes [Mo2Cp2(mu-eta (1):eta (3)-CR=CR'-SMe)-(mu -SMe)(2)(RNC)] (BF4) (7, 8) and to their CS2 adducts [Mo2Cp2(S2C-CR'=CRSMe)(mu -SMe)(2)]-(BF4) (9, 10), which arise from regioselective C-S coupling. A mechanism is proposed for the formation of the cyclic thiometalla compounds 5, 9, and 10 and of the thiophenium species 6 which assigns a key intermediate role to vinyl-thioether species. The molecular structures of 3a, 4b, and 7a have been established by X-ray diffraction studies. [References: 72]