Insertion of olefin

The propagation centers of the catalysts of olefin polymerization contain the active transition metal-carbon olefin polymerization may be divided into two vast classes according to the method of formation of the propagation center two-component and one-component.1... 

The acrylate complex 10 was suggested to be the major solution species during catalysis, since the equilibrium in Scheme 5-11, Eq. (2) lies to the right (fQq > 100)-Phosphine exchange at Pt was observed by NMR, but no evidence for four-coordinate PtL, was obtained. These observations help to explain why the excess of phosphine present (both products and starting materials) does not poison the catalyst. Pringle proposed a mechanism similar to that for formaldehyde and acrylonitrile hydrophosphination, involving P-H oxidative addition, insertion of olefin into the M-H bond, and P-C reductive elimination (as in Schemes 5-3 and 5-5) [11,12]. 

In view of the extensive and fruitful results described above, redox reactions of small ring compounds provide a variety of versatile synthetic methods. In particular, transition metal-induced redox reactions play an important role in this area. Transition metal intermediates such as metallacycles, carbene complexes, 71-allyl complexes, transition metal enolates are involved, allowing further transformations, for example, insertion of olefins and carbon monoxide. Two-electron- and one-electron-mediated transformations are complementary to each other although the latter radical reactions have been less thoroughly investigated. 

In the propagation process of Ziegler-Natta polymerization, the insertion of olefin into a metal-carbon bond is the most important basic step, but many questions concerning to this process remained unanswered for a long time. 

Polymerization occurs by repeated migratory insertion of olefin into the (Tv-oriented metal-carbon bond by the generally accepted Cossee mechanism [5, 60]. This mechanism is believed to be shared by all transition metal coordination polymerization... 

This scheme is shown with ethylene as the olefin substrate. If the olefin is substituted, i.e., RCH=CH2, the possibility exists for the formation of the isomers RCH2CH2Co(CO)3 or RCH(CH3)Co(CO)3 in Eq. (8). These isomers, which result from the insertion of olefin into the Co—H bond, then produce the isomeric aldehydes RCH2CH2CHO and RCH(CH3)CHO. The understanding of the factors which determine these pathways and control the desired product, has been the motivation for much study. 

Many discoveries changed human life in the last fifty years, and the polymerization of olefins catalyzed by transition metals certainly can be considered among them. At first glance, the job requested to polymerization catalysts seems rather trivial. It consists in the enchainment of monomeric units by insertion of olefins into Mt-P (P = Polymeric chain) bonds. Despite its simplicity and the amount of work by many research groups both in the... 

We are currently trying to answer specifically the question of whether ir-bonded complexes do occur in certain cases where insertion reactions are observed. I think they do because I believe that the same factors which favor stabilization of this type of transition state will also tend to favor formation of 7r-bonded olefin complexes, which are only slightly removed from this. At the moment Bern Tinker is examining the insertion of olefins in mercuric complexes to see whether there is any indication of 7r-bonded intermediates. In his paper, Dr. Heck referred to some unpublished work relevant to this theme. I would certainly be interested in anything more he can tell us about that. 

A special case is addition of trifluoromethyl- and bis(trifluoFomethyl)phos-phorus radicals to alkenes, referred to as insertion of olefins into phosphorus-carbon bond [6] (equations 8 and 9)... 

It is not easy to distinguish between these alternatives since they give rise to such a similar kinetic pattern. It is possible that each may occur under appropriate conditions analogies for both possibilities exist in metal carbonyl chemistry (96). Subsequent steps such as the insertion of olefin to give the alkylcobalt carbonyl are also susceptible to SN1 or SN2 interpretations. Carbon monoxide insertion does occur in the absence of an atmosphere of carbon monoxide but the reaction could be assisted here by the presence of olefin (73). 

The insertion of olefins and conjugated dienes between carbon-bound metals has been well documented in the literature (8-10). Hanford and co-workers (//) prepared polyethylenes of molecular weight 1400 by using phenyllithium in ether solvent at high temperatures and under high pressures of ethylene. The propagation reaction was in competition with termination of the active lithium ends. 

Activation of vinyl C-H bonds with RuH2(CO)(PPh3)3 catalyst has allowed the formal insertion of a,/l-unsaturated ketones or esters into the C-H bond of vinylsilanes and led to a regioselective C-C coupling at the -position [9] (Eq. 6). Activation of the sp2 C-H bond occurred with the aid of chelation of a coordinating functional group and provided vinylruthenium hydride 14. Insertion of olefin afforded the tetrasubstituted alkene 13. The ruthenium activation of a variety of inert C-H bonds has now been performed by Murai [10]. 

Intramolecular insertion of olefins and acetylenes into the Zr-C bonds of zirconaaziridines can lead to annulation reactions. Livinghouse showed that alkyl-, silyl-, and aryl-substituted C-C multiple bonds readily insert into the Zr-C bonds of zirconaaziridines derived from the hydrazones 28 and 29, yielding cyclic products [28]. 

The insertion of olefins and hetero-alkenes and -alkynes (ketones, nitriles) into the M—C bonds of metallacyclopropenes, as present in metal alkyne and particularly benzyne complexes, leads to five-membered metallacycles.193,194 This reaction has widespread synthetic applications 195... 

Palladium complexes figure prominently as well in the copolymerization of Q -olefins with carbon monoxide. Unlike the low molecular weight photodegradable random copolymers of ethylene and CO produced from a free-radical process, olefin/carbon monoxide copolymers produced from homogeneous palladium catalysts are perfectly alternating, the result of successive insertions of olefin and CO (Figure 19). Consecutive insertion of two similar monomers is either slow... 

The catalytic C-C bond cleavage of cydobutenedione by Ru3(CO)j2 in the presence of PEts followed by insertion of olefin produces cydopentenone frameworks (Eq. 14.2) [47]. 

In the course of a study on the insertion of olefins into metal-metal bonds, Clark et al. (115) have obtained, as a yellow oil, an ethylene Tt complex (CH3)3Sn-Mn(CO)4(C2H4) (42), by UV irradiation of (CH3)3Sn-Mn(CO)5 under ethylene pressure. Although the NMR spec-... 

Insertion of Olefins into the Transition Metal-Carbon Bond.78... 

A comparative study of the insertion of olefins into transition metal- and non-transition metal-carbon bonds is essential for the clarification of the specific role of transition metals in catalytic reactions. 

Mechanism of stereoregulation on the basis of the data on polyolefin stereoregularity. The structure of a polymer chain is the recording of events proceeding in the insertion of olefin molecules into an active metal-carbon bond. To understand the stereochemistry of the propagation reaction, the data on the stereoregular structure of polymer chains are important. Recently, for this purpose, C-NMR spectroscopy has been extensively used... 

Apparently, the reactivity of organometallic compounds in the addition of olefins to Mt—C bonds is determined by the capability of these compounds to coordinate olefins. The formation of intermediate n-complexes ensures further insertion of olefin by a concerted mechanism with a low activation energy. Thus, a high reactivity of active centers, containing a transition metal, comparable to the reactivity of the radical active centers, is achieved. The activation energy of the propagation in olefin polymerization on catalysts containing transition metals (2-6 kcal/mol) does not exceed its value for the radical polymerization (Table 10). 

ROCCHaCHaOR + Pd(0) or by insertion of olefin into the carbalkoxypalladium(II) followed by decomposition,... 

Stoichiometric study of the Ru(SiMe2Ph)Cl(CO)(PCy3)2 with vinylboronate confirms the insertion of olefin into the Ru-Si bond and supports the non-metallacarbene mechanism of this reaction [25]. 

Vinyl and allyl sulfides undergo an unusual cross-metathesis transformation with vinylsilane and vinylsilsesquioxane in the presence of the 2nd generation Grubbs catalyst (IV) to yield 1,2-silylvinyl sulfide or 1,3-silylpropenyl sulfide, respectively. The SC reactions of these substrates performed in the presence of Ru-H (I) and Ru-Si (II) give no products, which is explained by formation of the ruthenium sulfide species - inactive in the SC reactions since there is no insertion of olefin into the Ru-S bond. 

The similarity in the mechanisms of the two carbonylations is apparent. In the / -chloroacyl chloride formation, the first step is the insertion of olefins into the palladium-chlorine bond. For the catalytic carbonylations, the insertion of olefins takes place to the palladium hydride complex formed in situ. In both cases, divalent palladiums react with olefins. 

This mechanism is quite general for this substitution reaction in transition metal hydride-carbonyl complexes [52]. It is also known for intramolecular oxidative addition of a C-H bond [53], heterobimetallic elimination of methane [54], insertion of olefins [55], silylenes [56], and CO [57] into M-H bonds, extmsion of CO from metal-formyl complexes [11] and coenzyme B12- dependent rearrangements [58]. Likewise, the reduction of alkyl halides by metal hydrides often proceeds according to the ATC mechanism with both H-atom and halogen-atom transfer in the propagation steps [4, 53]. 

Another reaction of some synthetic utility is the insertion of olefins into aromatic C-H bonds [9d]. This reaction is catalyzed by ruthenium compounds and requires a coordinating group (typically, ketone) on the aromatic ring. The group binds to the metal and the ortho C-H bonds are activated due to the resulting chelate effect. 

Insertions of olefins into metal-carbon bonds are thought to occur by cis or 1,2-syn addition, as found for analogous insertions into metal-hydride bonds. Unfortunately, few well-documented examples exist among these are reactions (a)-(j) " . 

C5H5)Ti(CH2)(Cl)Al(CH3)2 insertion of olefins into bridging methylene 11.3.3.1 CisHisNi... 

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