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Migration metal carbonyl

Double-bond isomerization can also take place in other ways. Nucleophilic allylic rearrangements were discussed in Chapter 10 (p. 421). Electrocyclic and sigmatropic rearrangements are treated at 18-27-18-35. Double-bond migrations have also been accomplished photochemically, and by means of metallic ion (most often complex ions containing Pt, Rh, or Ru) or metal carbonyl catalysts. In the latter case there are at least two possible mechanisms. One of these, which requires external hydrogen, is called the nwtal hydride addition-elimination mechanism ... [Pg.772]

Although decarbonylation of supported metal carbonyl clusters sometimes occurs almost without changes in the metal frames, the chemistry is complex and only partially understood. When decarbonylation takes place at elevated temperatures (depending on the support), migration and aggregation of the metal inevitably occur, and these processes are less well understood than the decarbonylation with near retention of the metal frame. [Pg.216]

Shriver et al. ( ) have shown that the presence of a Lewis acid strongly enhances the rate of methyl migration in metal carbonyls. Recently, theoretical calculations by Blyholder displayed a stabilization of formyl species by interaction of Li (40) with the 4 electrons of CO (mainly on the oxygen). This interaction also results in an increase in the positive charge on the carbon atom. [Pg.240]

The conversion of a metal hydride into a metal formyl by hydride migration, as in (16), has been regarded for some time as a very difficult or improbable reaction. Certainly, there is evidence to suggest that for a number of metal carbonyl complexes alkyl migration to a carbonyl ligand, as follows ... [Pg.344]

Very few such compounds are known. Three general procedures can be used for their preparation (a) addition of the olefin to a transition metal compound (b) replacement of carbon monoxide in metal carbonyls and (c) migration of organosilicon groups from metal to ligand in some reactions of silylmetal compounds with acetylenes. [Pg.120]

A chiral metal center, as is found in a pseudotetrahedral iron complex with cyclopentudienyl. carbonyl, triphenylphosphine, and ethyl ligands, hus also beer used to address the question of alkyl migration versus carbonyl insertion. Inversion of... [Pg.884]

Pichler and Schulz were the first to suggest that the initial step in metal-catalyzed CO/H2 reactions might be the migration of catalyst-bound hydride to CO to yield a formyl intermediate [Eq. (1)] (3). The alkyl ligand in many isolable metal carbonyl alkyls can similarly be induced to migrate to coordinated CO (4. ). Thus, Eq. (1) has some precedent in homogeneous chemistry. Other suggestions for the involvement of formyl intermediates have come from Wender (6) and Henrici-Olive and Olive (7). [Pg.2]

A special case of substitution reaction is the migratory insertion (see Migratory Insertion) reaction of alkyl or aryl metal carbonyls (see equation 58), by which an alkyl or aryl metal carbonyl is converted into an acyl or aroyl metal carbonyl by the action of a Lewis base. This reaction has been studied extensively, and in the case of Mn(Me)(CO)5 is found to proceed through a coordinatively unsaturated tetracarbonyl resulting from methyl migration on to one of the terminal CO groups in a cis position, (see equation 59). ... [Pg.654]

The dominant isomerization pathway for the trimeric allenyl clusters [M3H(CO)9(/Li3-i7, V> 7 I C =C=CHR)] is via a thermal 1,2-hydrogen migration to afford the 1,3-dimetalloallyl clusters [M3H(CO)9(/H3-i7, t7, t7 -RCCHCR)] (53c). Reaction of alkynes and dienes with metal carbonyls M3(C0)2 (M = Ru, Os) often occurs with C-H activation adjacent to the unsaturated carbon-carbon bond (54) however, the final products isolated are often of the 1,3-dimetalloallyl type, the intermediate allenyl complex formed being thermodynamically unstable under the reaction conditions necessary to initiate C-H activation. [Pg.114]

Transition metal carbonyls such as Co2(CO)8 and CoH(CO)4, formed in the reaction of R3SiH with dimer (but also Fe(CO)5 and M3(CO)i2 (M = Fe, Ru, Os)) have been found to be active catalysts for the hydrosilylation of olefins, dienes, unsaturated nitriles, and esters as well as for hydrosilylation C=0 and C=N bonds [56]. Hydrosilylation of phenylthioacetylenes in the presence of this catalyst is extremely regioselective [57]. Cobalt(I) complexes, e. g., CoH(X)2L3 (X = H, N), could be prospective candidates for investigation of the effectiveness of alkene hydrosilylation by trialkoxysilanes as well as dehydro-genative silylation [58]. Direct evidence for the silyl migration mechanism operative in a catalytic hydrosilylation pathway was presented by Brookhart and Grant [59] using the electrophilic Co cationic complex. [Pg.497]

The silylene migration may be involved in some stoichiometric reactions of hydrodisilanes with transition-metal complexes, forming disilanyl complexes through activation of Si-H bonds. Binuclear Ru and Os complexes 39 having terminal silyl groups and silylene bridges are isolated in the reactions of pentame-thyldisilane with Ru3(CO)12 and Os3(CO)12, respectively, albeit in low yields (Eq. 16) [33]. Similar silylene migration may be involved in the reactions of hydrodisilane with other transition-metal carbonyls such as Fe2(CO)9 and Co2(CO)8 [34]. [Pg.139]

Metal atom clusters in the 26-hedra could (as with water molecules) contain many metal atoms. An example is the fourteen atom Agg+8Ag+ cluster in Y-irradiated zeolite Ag-A[25]. Saturation is achieved for mercury sorbed into silver-exchanged faujasites and other zeolites [26]. The Ag+ is reduced to Ag atoms and then at an approximate critical pressure of mercury vapour there is nucleation of mercury clusters which fill all the pore volume as the pressure of Hg vapour increases further. Mercury-zeolite systems are the oily ones in which sorption isotherms have been investigated quantitatively. Hcwever other metal atoms introduced into zeolites (by ion exchange and reduction, or as metal carbonyls and their decomposition) all show, on heating, a strong tendency to form clusters by migration of atoms, which can aggregate both within and outside the crystals. [Pg.551]

Both UV and visible light have sufficient energy to initiate many processes in coordination complexes. Decarbonylation is one of the most typical photoreactions, because the dissociation energy of a common metal carbonyl oxide bond is as low as 200kJ mol 1.1048 Scheme 6.154 presents two examples the fission of (a) metal—CO1049 and (b) metal—CO—alkyl1050 bonds in some carbonyl complexes. In the latter case, irradiation of an enantiomerically pure iron complex 348 leads to decarbonylation, which is followed by alkyl migration. [Pg.337]


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See also in sourсe #XX -- [ Pg.99 , Pg.596 ]




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