Molybdenum complexes oligomeric

Molybdenum complexes A (Figure 3.46) react efficiently with terminal and internal alkenes in toluene (e.g. 500 eq. Z-2-pentene are metathesized in 2 min at 25 °C 20 eq. of styrene in 2 h at 25 °C). These catalysts also oligomerize 2,4-hexadiene [808] and 1,5-hexadiene [809] and promote RCM of enol ethers. Isomerization of alkenes by catalysts A is a potential catalytic side-reaction [810-812]. 

Oxidations of cyclic ketones to lactones by H2O2 take place in the presence of catalytic amounts of certain molybdenum complexes. The catalysts are peroxo-molybdenum complexes stabilized by picolinato- and pyridine-2,6-dicarboxyl-ato-ligands, e.g. [Mo(0)(02) CsH3N(C02)2 ]- Although the reaction is catalytic, turnover numbers are low (25 or less) and chemical yields are variable. Moreover, competing reactions are the formation of oligomeric peroxides and ring-opened products. 

Reduction of [Mo(CO)(Bu C=CH)2Cp] + BF4 with KBHBu3(s) at — 78°C in an atmosphere of carbon monoxide yields a complex of a vinyl substituted y-lactone linked tj3 t]2 (220). The allylidene ruthenium complex 64, obtained by photochemical addition of one alkyne molecule to a /x-carbene derivative, is transformed into pentadienylidene complexes 65 and 66 on photolysis with more alkyne substrate. These reactions show clearly the stepwise growth of chains in alkyne oligomerizations at dimetal centers [Eq. (31)] (221). Similar reactions are also known for dinuclear iron (222), molybdenum (223), and tungsten (224) complexes. 

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