Molybdenum-alkynyl complexes

CaldweU LM, HUl AF, Hulkes AG, McQueen CMA, White AJP, WUliams DJ. Alkynyl selenolate complexes of iron, nickel, and molybdenum. Organometallics. 2010 29 6350-6358. 

However, yields in the intermolecular cycloaddition reactions of vinylcarbene complexes, formed by intramolecular insertion of an alkynyl tethered metal carbene complex, are higher when molybdenum rather than chromium or tungsten carbene complexes are employed. Mild thermolysis (THF, 65 °C, 1 h) in the presence of ten equivalents of an electronically undemanding alkene directly leads to the 2-alkyl-2-(2-methoxycyclopentenyl)cyclopropanes 31. ... 

Based on these studies and choosing to focus on Ru for practical considerations such as cost, we envisioned a possible catalytic cycle shown in Scheme 1.1, wherein an oa-alkynyl alcohol 1 would cycloisomerize to the dihydropyran. Although McDonald s group has pioneered the use of molybdenum- and tungsten-mediated processes, several issues related to chemoselectivity and the common need for stoichiometric amounts make the development of other catalysts for such processes desirable [8]. Using CpRu(PAr3)2Cl-based complexes, less electron-rich arylpho-sphine ligands such as m- or p-fluorophenylphosphines promote such processes (Equation 1.2) [9]. 

While examining the strategies for the preparation of molybdenum dithiolene complexes as models for oxidoreductase enzymes, a series of potentially bioactive pentathiepino-pyrrolo[l,2-a]-pyrazine derivatives, 258, was discovered and reported (13CC4343). These pentathiepins fused with bis-heterocychc rings are the result of the reaction between alkynyl-substituted heterocycles 257 with elemental sulfur in the presence of molybdenum 0x0 bis-tetrasulfide. 

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