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Carbonyl groups exchange between metals

It is well over 40 years since Pfeiffer discovered that certain reactions of a-amino acid esters, in particular, ester exchange, racemization and oxygenation, are effected very readily when their Schiff bases with salicylaldehyde are complexed to a transition metal ion (most notably Cu11). The Schiff bases result from a condensation reaction between a reactive carbonyl group and the amino group of the amino acids. Snell and his co-workers43 were also one of the first to point out that similar reactions also occurred if pyridoxal was used instead of salicylaldehyde, and that there is a close analogy with pyridoxal phosphate-promoted enzymic reactions of a-amino acid metabolism. Since then much work has been due on these and other similar systems and their reactivities. [Pg.751]

Fluoride ion first becomes coordinated with the silicon atom of tin reagent 33. Further coordination with the carbonyl oxygen atom of substrate 34 leads to an especially activated hypervalent silicon species 35.21 from which a stannyl anion is eliminated. I Ialogen-metal exchange between the tin anion and inyhc iodide 36 produces vinylic anion 37, which attacks in an intramolecular way the carbonyl group that has been activated through silicon coordination. Aqueous workup leads to alcohol 38. [Pg.153]

Similarly to the analogous reaction with furo[2,3-Z>]pyridines, metallation of compound (20) with n-butyllithium in TMEDA followed by the addition of DMF afforded the 2-formyl derivative in 66% yield. Likewise, metallation of the isomer (22) under the same conditions afforded the 2-formyl derivative in comparable yield <84JHC785>. Introduction of a carbonyl group at C-3 of compound (20) was accomplished by halogen-metal exchange between 3-bromothieno[2,3-6]pyridine and n-butyllithium. Table 45 lists some of the thieno[2,3-Z>]pyridine derivatives formed by this method <74JHC355>. [Pg.198]

Substitution reactions are well documented for the three Group 6 metal hexacarbonyls. Since they are low-spin d systems, reactivity is normally lower than that of other metal carbonyls. To promote substitution reactions, it is necessary to use elevated temperatures or uv irradiation. The hexacarbonyls usually undergo substitution via a dissociative mechanism, unless direct attack of a nucleophile at coordinated carbonyl groups occurs. Usually MoCCO) is more reactive than its two congeners. This is shown, inter alia, by kinetic studies on the isotopic exchange reaction between M( CO)6 and The higher kinetic lability of Mo(CO)6 may effect some of the reductions and oxidations, when the electron transfer process is accompanied by loss of carbonyl groups, e.g., equations (a), (e)-(g), and (1). [Pg.482]

The first indication that metal phosphine complexes were active for catalytic reactions of alkanes came from Shilov s group finding that CoH3(PPh3)3 catalyzes H/D exchange between and CH4. These systems probably involve oxidative addition (equation 1), but they were not followed up at the time because of the greater interest in the Pt system discussed above. Since 1980, a variety of Rh, Ir, Re and Ru complexes have shown activity for alkane dehydrogenation and carbonylation. The intermediate alkyl... [Pg.659]

Allylation of carbonyl and imino groups is one of the most convenient methods for the introduction of allylic functions.107-110 Allylic tin compounds have high interaction between C=C and C-Sn bonds which makes them more reactive than the corresponding silicon derivatives.111,112 In spite of their high reactivity, tin compounds are stable enough to be isolated and to react at ambient temperature under aerobic conditions. These factors allow them to be applicable to various types of reactions, for example, thermal,113 high-pressure,116 transition metal-catalyzed,117,118 radical,119,120 photochemical,121,122 tin-lithium exchange reactions,108,113 and so on. A broad... [Pg.351]


See other pages where Carbonyl groups exchange between metals is mentioned: [Pg.373]    [Pg.413]    [Pg.169]    [Pg.143]    [Pg.256]    [Pg.813]    [Pg.127]    [Pg.168]    [Pg.172]    [Pg.327]    [Pg.20]    [Pg.413]    [Pg.431]    [Pg.314]    [Pg.189]    [Pg.476]    [Pg.6]    [Pg.502]    [Pg.6]    [Pg.145]    [Pg.1274]    [Pg.229]    [Pg.158]    [Pg.417]    [Pg.431]    [Pg.688]    [Pg.296]    [Pg.448]    [Pg.196]    [Pg.219]    [Pg.186]    [Pg.354]    [Pg.74]    [Pg.13]    [Pg.161]    [Pg.41]    [Pg.90]    [Pg.58]    [Pg.28]    [Pg.496]    [Pg.1424]    [Pg.321]    [Pg.123]    [Pg.1007]   
See also in sourсe #XX -- [ Pg.121 ]




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Metal groups carbonylation

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