Other Insertions

A series of cationic Pci catalysts such as [(phen)PdMe CO)J is known to copolymerize CO with an alkene such as ethylene to give a strictly alternating copolymer, (CH2CH2CO) . The polymer is interesting from a practical standpoint because it has carbonyl functionality and so lends itself to useful chemical modification. The polymerization reaction is also of mechanistic interest because of the essentially perfect alternation of alkene and CO insertions that is involved. 

Of the possible erroneous insertions, double carbonyl insertion is foibidden for the thermodynamic reasons discussed in Section 7.1, and double alkene insertimi is very rare because of the high affinity of the catalyst for CO together with the much slower intrinsic rate—by a factor of 2000 in a typical case—of alkene insertion versus CO insertion. 

Sulfur dioxide is a strongly electrophilic species with a vacant orbital on sulfur, which it can use to attack even 18e metal complexes. Wojcicki and co-workers have studied these reactions in detail and find that the SO2 can give electrophilic attack at the a carbon of the alkyl from the side opposite the metal, which leads to the formation of an alkyl sulfinate ion (RS02 ) with inversion at carbon. Since the anion has much of its negative charge on the oxygens, it is not surprising that the kinetic product of ion recombination is the 0-bound sulfinato complex. On 

An unusual insertion of SO2 has been reported in a Pd methyl complex where the resulting MeS02 ligand bridges between the two metals.  

Goldberg and co-workers have de.scribed a rare example of O2 insertion into a M—X bond their case, involving Pt(lV)-H, is shown below  

Insertion of the dienes CH2=CRCR =CH2 into the Fe—H bond in [Cp(OC)2FeH] occurs with rates first order in [complex] and [diene] but independent of An inverse primary H/D isotope effect is observed and 

Photolysis of [(HBPzJ)Rh(CO)(C2H4)] in benzene [HBPzf = tris-(3,5-di-Me-pyrazol-l-yl)borato] leads to approximately equimolar amounts of [(HBPz )Rh(CO)(H)Ph] and [(HBPzf )Rh(CO)(Et)Ph], probably via a common intermediate. The thermodynamic instability of M—Et bonds toward -elimination in some early transition metal compounds has been examined and discussed in terms of strong metallacyclopropane bonding of ethylene to the metals.  

Insertion of CO2 into Cu—H and Cu—Me bonds has been examined theoretically and the former is very different because of the ready formation of a Cu—H—CO2 adduct prior to formation of an 77or 17 -formato complex. Formation of a [(OC)5CrH—C02] adduct is calculated to be exothermic by - 8 kcal mor and this can be followed by concerted CO dissociation and formation of [(0C)4Cr(T7 -02CH)].( ) 

The invaluable help of Mr. Lezhan Chen and Ms. Ying Zheng in preparing this chapter is gratefully acknowledged. 

Metal-Alkyl and Metal-Hydride Bond Formation and Fission Oxidative Addition and Reductive Elimination 

Dienes As we saw in Sections 5.2-5.3, butadiene and allene react with a variety of hydrides by 1,2 insertion, but butadienes also react with HMn(CO)s to give an apparent 1,4 insertion. Since this 18e hydride has no vacant site and CO dissociation is slow, a different mechanism must be operating this is thought to be H atom transfer to give a 1,1-dimethylallyl radical that is subsequently trapped by the metal (Eq. 7.31). Only substrates that form especially stable radicals can react (e.g., 1,3-diene allyl radical), not simple alkenes. 

As expected for this mechanism, the reactivity falls off as the alkyl group becomes more bulky and as the substituents become more electron-attracting. By carrying out a crossover reaction on a mixture of RS and SR isomers of [CpFe (CO)L CH2C H(Me)Ph ], which is chiral at both Fe and the carbon shown, very little of the crossover products, the R,R and 5,5 isomers of the sulfinate complex, are seen. This shows that the postulated ion pairs must stay together, and that the intermediate iron cation also has stereochemical stability. Ion pairing is very common in organic solvents, and the ions probably rarely break free from the ion pair-  

In 16e complexes, a 2e site is usually available, except for Pd(II), and especially for Pt(II), which tend to avoid the 18e configuration. Yamamoto found that frani-[PdL2Et2] complexes (L = 3° phosphine), tend to decompose by reductive elimination via an 18e transition state, but Whitesides found that phosphine dissociation is required for p elimination of the corresponding platinum alkyls [PtL2Bu2] (7.7). The related metalacycle 7.8 -eliminates 10 -fold more slowly than 7.7, presumably because a coplanar M—C—C—H arrangement is harder to achieve  

Grubbs has studied the analogous nickel complexes and has found that there are three decomposition pathways, one for each of the different intermediates, 14e, 16e, and 18e, that can be formed (Eq. 7.36). An understanding of the reasons for this diversity has only come with a detailed m.o. study. 

Schrock has found an interesting case of a and p elimination taking place competitively in a tantalum complex, the two tautomers of which can be observed in solution by H NMR. 

---

Where it is required to use metal or other inserts for fastening of upholstery elements or coverings. 

Another consideration is the ability of a material to provide a surface that is compatible with the requirements of the application a smooth finish for extruded profiles, molded-in colors, textured surfaces, etc. The compatibility of the major processes with in-mold coating and other insert-surfacing materials, and their compatibility with surface decoration secondary processes, could also be important. 

Inserts are any parts of any material located into another plastic part during or after its processing. The best known are metal inserts for assembly by screwing but there are numerous other insert types (plastic parts, films. ..) for numerous other applications. 

Other insertions may involve isonitriles, alkynes, alkadienes, CO2, and SO2. They will not be dealt with here. 

Metal complexes of heterocyclic compounds display reactivities changed greatly from those of the uncomplexed parent systems. All of the -electron system(s) of the parent heterocycle can be tied up in the complex formation, or part can be left to take part in alkenic reactions. The system may be greatly stabilized in the complex, so that reactions, on a heteroatom, for example, can be performed which the parent compound itself would not survive. Orbital energy levels may be split and symmetries changed, allowing hitherto forbidden reactions to occur. In short, a multitude of new reaction modes can be made possible by using complexes dimerization of azirines with a palladium catalyst serves as a typical example (Scheme 81). A variety of other insertion reactions, dimerizations, intramolecular cyclizations, and intermolecular addition reactions of azirines are promoted by transition metals. 

In addition to serving as ligands, organostannylenes can also insert into metal-ligand bonds (cf. Fig. 10). In the reaction shown in Eq. (50) (78), two moles of the divalent tin compound react, one forming a terminal stannylene complex, and the other inserting into the Pt—Cl bond. 

This is the second chapter of a two-part review concerned with insertion reactions of transition metal-carbon a-bonded compounds. The first chapter, which appeared in Volume 11 of this series (137), provided a broad introduction to the subject of insertion reactions in general and a detailed treatment of the carbon monoxide insertion and decarbonylation. Presented herein are the insertion and elimination reactions of sulfur dioxide and of a few other unsaturated molecules. The reactions of sulfur dioxide are accorded a complete literature coverage, whereas those of the other inserting species are treated selectively. Metal-carbon a-bonded compounds of the main group elements are discussed only in the context of comparisons with their transition metal analogs. 

The CO insertion reaction into the metal hydride bond is in fact a member of the class of ligand insertion reactions to which much theoretical work has been devoted (28,29-35). Some years ago we analyzed the ethylene insertion into the rhodium hydride bond of a Rh(III) hexacoordinated complex (. We later focused our attention on the CO insertion reaction into the Mn-H bond ofHMn(CO)5 (37-39) and very recently we have undertaken the study of the CO2 insertion reaction into the Cr-H bond of HCr(CO)5 (C. Bo and A. Dedieu, Inorg. Chem., in press). We will concentrate here on the CO insertion reaction and compare it to the two other insertion reactions. The study of the reaction (1) was carried out at both the SCF and... 

This section considers only the direct insertion reactions represented by equation (a), although many other insertion-type products can be prepared by other routes. For example CpFe(CO)2SnCl2CO(CO)4 (Cp = cyclopentadienyl) can be prepared by the reaction of CpFe(CO)2SnCl3 with Co2(CO)s, but not by the direct insertion of SnCl2 into the Fe-Co bond of CpFe(CO)2Co(CO)4. ... 

Insertion Reactions into Metal-Metal Bonds 11.7.5. Other Insertion Reactions... 

After oxidative addition of an unsymmetrical cr bond (E-H) to the metal, an unsaturated compound can insert into either the M-E or the M-H bond. In some cases, such as the hydrosilylation of carbonyl compounds, the 7r bond of the substrate inserts into the M-E bond, whereas, in others, insertion of the ir bond of the substrate into the M-H bond occurs faster. In any case, either pathway gives the same product after reductive elimination. 

Particularly if pellets with high density or strength and small diameter must be produced, the necessary die thickness and effective hole length may be rather incompatible. In such cases replaceable insert plates with short bores may be used (Figure 328(a)). Other inserts may be used as replacements in the case of wear and to salvage the overall die body (Figure 328(b) ) or to fulfill process requirements, such as cooling of the dies. ... 

OTHER INSERTION METERS. Modified forms of magnetic meters, turbine meters, ultrasonic meters, thermal mass flowmeters, and other types are available as insertion meters. They all have advantages for certain services. Insertion meters are generally cheaper than full-bore meters and are usually the most cost-effective method of measuring flow in large pipes. 

---