Synthesis and Reactivity of Molybdenum and Tungsten Alkyne Complexes Containing 6-Methylpyridine-2-thiolate Ligands

A series of M(II) and M(IV) (M=Mo, W) alkyne adducts employing two 6-methylpyridine-2-thiolate (6-MePyS) ligands was synthesized and investigated towards the nucleophilic attack of PMe3 on the coordinated alkynes. For this approach, 2-butyne (C2Me2), phenylacetylene (HC2Ph), and diphenylacetylene (C2Ph2) were used. For the exploration of an intramolecular attack, but-3-yn-1-ol (HCCCH2CH2OH) was coordinated to the metal centers. A nucleophilic attack of PMe3 was observed in [W(CO)(HC2Ph)(6-MePyS)(2)] yielding an eta(2)-vinyl compound. Reaction of [W(CO)(C2Ph2)(6-MePyS)(2)] with excess PMe3 resulted in the selective coordination of one molecule of PMe3 concomitant with decoordination of the nitrogen atom of one 6-MePyS ligand. In contrast, the W(IV) complexes did not react with PMe3. While no selectivity was observed in the reaction of the Mo(II) compounds with PMe3, alkynes in the Mo(IV) compounds were replaced by PMe3. Addition of Et3N to the but-3-yn-1-ol complexes did not lead to the anticipated formation of 2,3-dihydrofuran.