Norbomene, insertion into

The study of alkene insertions in complexes containing diphosphine ligands turned out to be more complicated than the study of the CO insertion reactions [13], When one attempts to carry out insertion reactions on acetylpalladium complexes decarbonylation takes place. When the reaction is carried out under a pressure of CO the observed rate of alkene insertion depends on the CO pressure due to the competition between CO and ethene coordination. Also, after insertion of the alkene into the acetyl species (3-elimination occurs, except for norbomene or norbomadiene as the alkene. In this instance, as was already reported by Sen [8,27] a syn addition takes place and in this strained skeleton no (3-elimination can take place. Therefore most studies on the alkene insertion and isolation of the intermediates concern the insertion of norbomenes [21,32], The main product observed for norbomene insertion into an acetyl palladium bond is the exo species (see Figure 12.8). 

If however, a bicyclic alkene is used, yn-jS-hydride elimination from the carbopaUada-tion product is disfavored,and the reaction proceeds further through a sequence of steps until a favorable reductive elimination becomes feasible. A precedent of an insertion equilibrium not leading to /3-hydride elimination can be found in nickel chemistry, where it was shown that norbomene inserted into a methaUylnickel bond in the presence of acetate anion and deinserted in the presence of hydrogen halides (Scheme 4). 

Acrylonitrile or methyl acrylate readily inserts into allylnickel bonds (example 34, Table HI). A trans double bond is formed by loss of a proton. Insertion of acetylene followed by oxidative elimination with allyl halides gives cis double bonds (example 32, Table III). Insertion of methyl propiolate, followed by proton uptake, leads to a trans double bond (example 33, Table III). Norbomene has been shown to insert stereoselectively cis.exo into an allylnickel bond (example 35, Table III). 

Carbene 103 undergoes 1,3-CH insertion to nortricyclene (105), but this reaction is either too rapid for LFP measurement by the pyridine ylide method (r <0.1 ns), or the insertion occurs by RIES of the precursor 2-norbomyldiazirine. Theoretically, a short lifetime is expected for 103 AG for the carbene insertion into the 6-endo-CU bond (103 — 105) is computed at 5.2 kcal/mol, about 6.7 kcal/mol less than the (unobserved) exo- 1,2-H shift to norbomene.16... 

Strained alkenes such as norbomene, norbomadiene and bicyclo[2.2.2]octenes readily insert into ir-allyl complexes with the less substituted allyl terminus linked to the alkene (equation 81).233-261 This reaction has been utilized to prepare interesting prostaglandin analogs.233 234... 

Analogously, it was observed that norbomene could be inserted into an arylpalladium bond and the resulting product was stabilized through the formation of a dimer or by appropriate ligands (Scheme... 

In 2000, Mitsudo and co-workers reported the first example of catalytic C-C bond activation/olefin insertion of cyclobutenediones [82, 83] using Ru3(CO)i2 as the catalyst (Scheme 24). The authors proposed that Ru3(CO)i2 inserts into bond b similar to Pt(PPh3)4 insertion (Scheme 21), after which decarbonylation and insertion into norbomene yields cyclopentenone 107. When CO was used, the... 

Cyclopentene, norbomene, or other cyclic olefins are incorporated exclusively by 1,2-insertion into the growing copolymer chain no ring opening occurs. The insertion of the huge norbomene monomer is very fast by metallocene/MAO catalysts. 

Arndt et al. [58, 59] gathered information about norbomene insertion and dimer and trimer microstmcture by hydrooligomerization with metallocene catalysts known to produce atactic, isotactic, and s3ndiotactic poly(a-olefins) isolation and characterization of model dimers and trimers. Norbomene was shown to undergo cis-exo insertion into the metal-carlxMi bonds, and the different stereochemistry of oligomers (and polymers) was demonstrated [58, 59]. 

NMR experiments and ab initio theoretical chemical shift calculations, combined with rotational isomeric state (RIS) statistics of the P-N chain, gave the first assignment of the NMR spectra of P-N copolymers [95-97]. Cis-2,3-exo norbomene insertion is considered to occur into the metal-carbon bond as in... 

The low activity was demonstrated to result from the difficulty of insetting a propene into the Mt-tertiary carbon bond formed after the norbomene insertion (Mt-N), which is even more sterically crowded than the sites formed after a propene (2,1) r oirregular insertion, less reactive than sites with a primary growing polypropene chain. Despite the relatively lower polymerization activity, at low... 

After elimination of ethoxytrimethylsilane, 7,7-dimethyl-1-norbomene (6) rearranges to 3,3-dimethyl-2-norbomylidene (7), which undergoes a 1,3-CH insertion reaction into the endo-6-H to give tricyclane 8. Nortricyclane formation has been shown to be the fastest intramolecular mode of stabilization of 2-norbomylidene.5,6... 

Insertion of aUcynes into aromatic C-H bonds has been achieved by iridium complexes. Shibata and coworkers found that the cationic complex [Ir(COD)2]BF4 catalyzes the hydroarylation of internal alkynes with aryl ketones in the presence of BINAP (24) [111]. The reaction selectively produces ort/to-substituted alkenated-aryl products. Styrene and norbomene were also found to undergo hydroarylation under similar condition. [Cp IrCl2]2 catalyzes aromatization of benzoic acid with two equivalents of internal alkyne to form naphthalene derivatives via decarboxylation in the presence of Ag2C03 as an oxidant (25) [112]. 

Given the published studies that indicate that the insertion of nonfunction-alized norbomenes into metal-carbon bonds occurs with exo, exo- stereochemistry (e.g., Fig. 9.1) we sought to determine whether the presence of an endo functionality would change the insertion stereochemistry. Because of the relative instability of the catalytically active palladium species, detailed studies encompassing the coordination and insertion of norbornene derivatives were carried using the model... 

The reaction of Co( t-Cp)(CO)2 and of [Co(7i-Cp)NO]2 with nitric oxide in the presence of norbomene has been reported. In both cases the species shown in Figure 14 may be isolated in high yield.The mechanism of these three component syntheses could well be relat to that of the NO insertion reactions (Scheme 2) in that here NO insertion might occur into the metal-carbon n-bond of a cobalt—norbomene intermediate. 

Examples of the insertions of alkenes or alk5mes into metal-amido bonds are also rare. Examples of the insertions of alkenes into tihe M-N bonds of isolated amido complexes include the reaction of a rhodium anilide complex with alkenes to form imines witii kinetic behavior that is consistent with migratory insertion,and the formal insertion of the strongly electrophilic acrylonitrile into a platinum anilide. Additional examples include reactions of a lanthanide-amido complex generated in situ, a catalytic carboamination process in which the stereochemistry implies insertions of olefins into amides, and a catalytic hydroamination that appears to occur through an aminoalkyl complex generated by S3m addition of the iridium and amido groups across the C=C bond of norbomene. 

Equation 9.84 depicts the reaction of aniline, norbomene, and [Ir(PEt3)2(CjH )jCl] to form an iridium-aminoalkyl complex. This process is thought to occur by oxidative addition of the aniline to form an amido hydride complex, followed by insertion of the strained alkene into the iridium-nitrogen bond. Products from oxidative addition of aniline to the same iridium species were shown to form in the absence of the olefin. The syn stereochemistry of the aminoalkyl product indicated that a migratory insertion pathway was followed. 

As discussed in Chapter 9, the insertion of olefins and alk)nes into metal-amido complexes is limited to a few examples. Such insertion reactions are proposed to occur as part of the mechanism of the hydroamination of norbomene catalyzed by an iridium(I) complex and as part of the hydroamination of alkenes and alkynes catalyzed by lanthanide and actinide metal complexes. This reaction was clearly shown to occur with the iridium(I) amido complex formed by oxidative addition of aniline, and this insertion process is presented in Chapter 9. The mechanism of the most active Ir(I) catalyst system for this process involving added fluoride is imknown. 

Table 12 shows the temperature dependence of the copolymerization parameters r and V2 and of the influence of the catalyst systems. Metallocene catalysts show low r values, which increases with the temperature and allows the easy incorporation of bulky cycloolefins into the growing polymer chain. Surprisingly, the copolymerization parameter ri = 1.8 3.1 for cyclopentene and norbomene is surprisingly low. The r value of 2 means that ethylene is inserted only twice as fast as norbomene. 

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