Hydrides, Alkyls, and Aryls

The photolysis of manganese pentacarbony 1 hydride results in decarbony lation with formation of MnH(CO)4  

The reverse carbonylation reaction occurs at longer wavelength photolysis. The 16-electron species MnH(CO)4 has been observed in a frozen argon matrix. A similar pathway is followed for ReH(CO)s. Thus, when the photolysis is carried out in the presence of a ligand such as PBus, substitution occurs, resulting in the formation of ReH(CO)4(PBu3) (Ref. 68)  

When alkyl-substituted carbonyl complexes are photolyzed, reactions other than ligand substitution can occur. One such reaction is the migratory insertion reaction that involves carbonylation of an alkyl complex to give an acyl product. Thus when MnCH3(CO)5 is photolyzed in an argon matrix at 17 K, the 5-coordinate acetyl complex Mn(COCH3)(CO)4 formed by migratory insertion is observed  

Such a reaction is an important one since this intermediate has been proposed for the carbonylation of MnCH3(CO)5 to Mn(COCH3)(CO)5 under thermal condi-tions. The pathways followed in these photochemical insertion reactions have been studied both by low-temperature matrix techniques and by time-resolved infrared spectroscopy. At 12 K, photolysis of rraw - / -cpMo(CO)2MeL (L = P(OEt)3, PPh3, PBu3) results in CO loss, followed by the rapid reverse thermal carbonylation of the coordinately unsaturated intermediate  

For the cis complex cf5- / -cpMo(CO)2Me(P(OEt)3), a similar photodissociation of CO occurs, but for cw- / -cpMo(CO)2MeL, where L is PPhs or PBus, the ligand L is photodissociated. Photolysis of the acetyl complex trans-rj -cpMo(CO)2(COMe)L leads to the stereospecific production of trans-rj -cpMo(CO)2MeL, where dissociation of a carbonyl ligand is the primary photoprocess  

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The terms hydrides, alkyls, and aryls classify compounds containing reacting hydrogens, alkyl groups, and aryl groups, respectively for example, RCHj-H - RCHjCOOH (carboxylic acids from hydrides), RMe -> RCOOH (carboxylic acids from alkyls), RPh RCOOH (carboxylic acids from aryls). Note the distinction between R CO — RjCHj (methylenes from ketones) and RCOR RH (hydrides from ketones). 

Alkah metal derivatives, including hydrides, alkyls and aryls, hydroxides, alkoxides, and amides, have been used as initiators for the anionic polymerization of epoxides. Sodium, potas-sirrm, and to a lesser extent cesium are the most often used alkali metals. Lithium derivatives are generally avoided since after the insertion of the first epoxide unit, they yield alkoxide species that are unable to properly propagate the polymerization, due to sUong association. Anionic polymerization of... 

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