Methyl MeCO

Other reactions which apparently involve transfer to nucleophiles include those of [MeCo(salen)] with MeMgl to give ethane as well as methane and H2 64), and of [MeCo(DMG)2X]complexes with CN and PhNMe , apparently to give MeCN and PhNMe2 161). The mechanisms of these processes have not been studied. Nevertheless it is known that the reaction of methyl- and ethylcobalamin with cyanide (products not known) requires oxygen, and shows an induction period [see Chapter 13 of ref. 136)). 

An extensive paper by Burgada et l. reports the reactions of cyclic phosphites (75 ab) and cyclic phosphoramidites (76 ab) with trans-1,2-dibenzoylethene, methyl fumarate, benzalacetone (PhCH=CH COMe), methyl-4-keto-pent-2-enoate (MeCO.CH=CH.COgMe) and benzalacetophenone (PhCH=CHCOPh)95. These reactions lead to... 

Casey et al. have studied the decarbonylation reactions of [cis-(OC)4M(MeCO)(PhCO)], in which M is Mn or Re (16,17). These complexes lose a carbonyl ligand to form five-coordinate intermediates of the type [(OC)3M(MeCO)(PhCO)]. Reversible methyl migration proceeds much more rapidly than does phenyl migration. In the course of these studies, a phosphine substituted rhena-/3-diketonate complex, [fac-(OC)3(Et3P)Re(MeCO) (PhCO)], was prepared. 

Acetyl-2-hydroxy-2-methyl-2,3-dihydrobenzo-l,4-dioxan (42, R = H R = MeCO R = Me) exists as a mixture of two cyclic diastereomers 42B and B, both stabilized by an intramolecular hydrogen bond (42B-Z and 48- ). The proportion of the open-chain tautomer 42A, also containing an intramolecular hydrogen bond in the enolized pentane-l,3-dione moiety, is very small ( 1%) at equilibrium (89ZOR1273). 

A rare example of the formation of an alkoxide ligand in a metal cluster compound is seen in the reaction between methyl fluorosulfonate and the triiron carbonyl clusters anion [Fe3(CO)9(/i3-MeCO)], which gives Fe3(CO)9(/x3-CMe)(/i3-OMe) by C—O bond cleavage.135,136 The C—O bond cleavage provides a possible model for a step in Fischer-Tropsch chemistry.121... 

The generalization of these reactions to other captodative olefins was often successful from a preparative point of view, as demonstrated by the reported results on the addition of fBuO, MeCO [55], RS [54], and MeCONMe—CH2 [54] radicals to various captodative olefins (Table 3). Additions of (iV-methyl-iV-... 

Ir2(ju PPh2)(CO)(PNNP)] reacts in two successive irreversible oxidative addition steps with either acetyl chloride or methyl iodide to give the diacyl [Ir2 (/z-PPh2 )(CO)2 (PNNP)(MeCO)2 (Cl)2] and dimethyl [Ir2(/t-PPh2)(CO)2(PNNP)(Me)2(I)2] complexes, respectively, in which iridium is Ir111.586... 

Among the many reactions of these species is the conversion to chiral species such as 18-D-XIX. This compound can be obtained in enantiomerically pure form and can be converted to the CpRe(NO)PPh3 ion.69 This ion is a chiral Lewis base that binds a variety of prochiral molecules (olefins, ketones, aldehydes, amines). With these adducts one may conduct numerous reactions where enantiomeric excesses >98% are obtained. As an example, a prochiral methyl ketone will bind selectively, as in 18-D-XX and is then subject to attack by R X to produce only one enantiomer of the RR MeCO product. 

Molecular orbital (MO) calculations on MeCo(CO)4 place a negative charge on the methyl carbon atom with polarization of the Co-Me bond. Substitution of CO ligands withdraws electron density from the alkyl carbon atom and delivers electron density to the metal, thus stabilizing the Co-C bond. 

The compositionMeCo(PR3)4 isreahzed, apart from PMes, with various phosphines. The PPhs complex, however, has a lower coordination number, that is, MeCo(PPh3)3 is found in the solid, but it partially dissociates in solution into MeCo(PPh3)2, reminiscent of the behavior of RhCl(PPh3)3 (see Wilkinson s Catalyst). In protic solvents, this compound decomposes by proton abstraction, releasing methane, and this observation may explain its abihty to effect aldol condensation of certain ketones (acetone and methyl ethyl ketone) in an aprotic solvent (equation 36). 

A significant observation for cobaloximes as B12 models was the reduction of MeCo L4(B) by Cr(aq) +, which gave Co L4(B) and Cr(Me)(aq) + (equation 37). These products are indicative of an inner-sphere (see Inner-sphere Reaction) electron transfer with Me as the bridging ligand. This result has promoted further studies, notably methyl transfer between cobaloximes and nickel tetraazacycle complexes, which provides a possible model for the methylcobalamin alkylation of CO hydrogenase. ... 

Diketones 253 and -keto esters 254, with the same procedure, were converted into the corresponding monoprotected vicinal tricarbonyl compounds 255 and 256, respectively (Scheme 40) [120]. Whenever the group linked to ketonic carbonyl was a methyl (R = Me), the diprotected vicinal tetracarbonyl compounds 257 and 258 were produced. The formation of these products represents a further example of the easiness with which the MeCO group is converted into the a-keto acetal under these experimental conditions. 

Cyanomethyltributyltin is a reagent for Pd-catalyzed cyanomethylation of aryl bromides with the Me, MeO or Cl substituent, but not with the MeCO, CN or NOj substituent (equation 111). ° Dicyano-methylation of aryl iodides can be achieved with a sodium salt of malononitrile in the presence of Pd complexes (equation 112). 2i... 

Pr, Bu", MeCO, CH2=CHCH2, aniline). The [Rhpy4Cl2] ion reacts with a variety of Schiff bases in boiling pyridine solution (in the presence of Zn dust and PF ), to generate a family of complexes of the form [Rh(SB)py2]PFt (121)." These all formed methyl adducts with Rh "—Me bonds when reacted with methyl iodide. " A similar reaction path ([Rh(py)4Cl2]Cl + Zn dust + Schiff base) was used to prepare [Rh(N—0)2py2] (122). In the absence of Zn dust, [Rh(py)4Cl2] is unreactive toward Schiff bases, even when refluxed in pyridine for many hours. The best yields are obtained when equivalent amounts of Zn and Rh are reacted." ... 

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