Aldehydes insertions into metal-carbon

Ketones and aldehydes undergo subsequent insertion into metal-carbon bonds generated from ketene insertion into Ti-OR bonds (Eq. 2.297) ... 

Insertions of Aldehydes and Imines into Metal-Carbon Bonds... 

The classical Reformatsky reaction consists of the treatment of an a-halo ester 1 with zinc metal and subsequent reaction with an aldehyde or ketone 3. Nowadays the name is used generally for reactions that involve insertion of a metal into a carbon-halogen bond and subsequent reaction with an electrophile. Formally the Reformatsky reaction is similar to the Grignard reaction. 

The efficiency of transmetalation from boron to palladium in the catalytic 1,4-addition of aryl or 1-alkenylboronic acids to enones encouraged us to extend the protocol to the addition of aryl- and 1-alkenylboronic adds to aldehydes in an aqueous solution (Eq. 4). The insertion of carbonyl groups into transition metal-carbon bonds has not received much attention, but the catalytic use of transition metals may allow such addition of various organometallics which are inert without a catalyst, the asymmetric addition using a chiral phosphine complex, or the reaction in an aqueous phase. 

Transition-metal-catalyzed hetero-[2 + 2 + 2]-cy-cloaddition of alkynes with carbon—heteroatom multiple bonds, such as isocyanides, carbon dioxide, nitriles, aldehydes, and ketones, provides heteroare-nes and unsaturated heterocycles. This reaction can be categorized into two groups one is the reaction of l,a>-diynes 397 with carbon—heteroatom multiple bonds, and the other is reaction of the alkynes 399, having a carbon—heteroatom multiple bond with alkynes as illustrated in Scheme 127. The reaction of 1,6 -diynes 397 proceeds through formation of the metalacyclopentadiene intermediate 398 followed by insertion of a carbon—heteroatom multiple bond, such as heterocumulenes (route a),189 nitriles (route b),190 and carbonyls (route c).191 On the other hand, the... 

Homogeneous catalysis with defined soluble transition metal complexes as catalysts has become one of the most effective means of transforming simple olefins into more valuable materials. The technically important hydroformylation of olefins to aldehydes or alcohols the Wacker process the dimerization of propylene to linear hexenes the oligomerization of ethylene to linear a-olefins are only a few examples. A feature common to all these processes is the insertion of a substrate olefin molecule, which is coordinatively bonded to the transition metal center M, into a metal-carbon or metal-hydrogen bond present at the same center ... 

The electrophile ftat modifies a coordinated ligand can be a proton, a strong Lewis acid, or an unsaturated electrophile. Examples of Lewis acids include tiityl cahon or per-fluoroarylboranes, and examples of unsaturated electrophiles include CO, SO, isocyanates, aldehydes, ketones, and related compoimds. Reactions of these electrophiles can lead to the formation of catioruc metal complexes by abstraction of a hydride or hydrocarbyl group by the Lewis acid, or they can lead to products from insertion of the unsaturated electrophile into the metal-carbon bond. These reactions are sho-wn generically in Equations 12.1-12.3. 

With the exception of direct insertion into CO and isocyanides [51], carbon-carbon bond formation from organozirconocenes requires the use of metal salts for transmetalation or (chloride) ligand abstraction. The former protocol has been successfully applied for many carbonyl additions and crosscouplings, whereas the latter strategy is particularly useful for conversions with electrophiles such as epoxides and aldehydes. 

Carbonylation (the addition of carbon monoxide to organic molecules) is an important industr process as carbon monoxide is a convenient one-carbon feedstock and the resulting metal-acyl cor plexes can be converted into aldehydes, acids, and their derivatives. The 0X0 process is the hydr formylation of alkenes such as propene and uses two migratory insertions to make higher val aldehydes. Though a mixture is formed this is acceptable from very cheap starting materials. 

Several examples of transition metal-catalyzed insertions of carbon monoxide and isocyanide into the C-H bond are known. The carbonylation of a C-H bond to an aldehyde requires photoirradiation conditions. Eisenberg et al. have found iridium-[45,46] or rhodium-catalyzed [47] photocarbonylation of benzene affording benzaldehyde, albeit with low efficiency [45-47]. They have also reported the photochemical carbonylation of benzene catalyzed by ruthenium(O) complexes [48]. 

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