Product coordinates

When polymerizing dienes for synthetic rubber production, coordination catalysts are used to direct the reaction to yield predominantly 1,4-addition polymers. Chapter 11 discusses addition polymerization. The following reviews some of the physical and chemical properties of butadiene and isoprene. 

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Alternatively, the azide anion can be added to coordinated organic isonitrile (211) or nitrile (60) ligands to give the same products. Coordination of RCN ligands greatly increases their susceptibility to attack by azide anions reactions typically go to completion in 15 minutes at 25°C (60). 

A dependence of product coordination is also observed for reactions of heteroligands with peroxo and hydroxamido vanadates. Peroxide, which complexes as 022, is a much better electron donator than is hydroxamido, which complexes as H2N01. Bis complexes from these two ligand types can have very similar coordination, as depicted in Scheme 9.3. In fact, there are two distinct types of bishydroxamido... 

Vinylpyridine with [( 5-MeC5H4)Mn(CO)2(EtOH)] gives a mixture of products— ( -coordinated, 85, / -coordinated via the vinyl framework, 86, and rjl(N) -coordinated dinuclear species 87 (82JOM(231)C9). 

Immediately upon contact with air, the high-spin complex (g 6.1) attributable to Fe(III) TPP py (pentacoordinated complex) is observed together with the free radicals whose g values are 1.99-2.04 and the low-spin Fe(III) complex (see Figure 4). The formation of a pair of low-spin complexes attributable to the hexacoordinated Fe(III) TPP complexes (g = 2.66, 2.19, 1.80 and g = 2.31, 1.93) occurs with time. Of those, one should be the Fe(III) TPP py2 and another the product-coordinated Fe(III)-TPP complex. The appearance of ESR absorptions attributable to Fe(III) complexes (high-and low-spin) indicates that a part of the Fe(II)-TPP complex is converted to Fe(III) TPP by reaction with molecular oxygen. 

Treatment with base (usually LDA) at low temperature produces an enolate, and you can clearly see that the auxiliary has been designed to favour attack by electrophiles on only one face of that enolate. Notice too that the bulky auxiliary means that only the Z-enolate forms alkylation of the E-eno-late on the top face would give the diaster eoisomeric product. Coordination of the lithium ion to the other carbonyl oxygen makes the whole structure rigid, fixing the isopropyl group where it can provide maximum hindrance to attack on the wrong5 face. 

It is clear that 10 and 37 can be used to generate C—N bonds—a feature which is required for any catalytic synthesis of any organonitrogen compound however, the resulting organonitrogen product coordinated to titanium is much too stable. It is now apparent that any attempt at a catalytic synthesis of organonitrogen compounds has to involve a metal complex which can uniquely balance all of the features outlined in Section IV,B,2. 

As found with H2P20 and H2P30 hydrolysis of ATP and ADP can be accelerated by [Co(OH)(OH2)(N)4]2+ species570,571 and by the hydrolysis products of [Co(Cl)3(dien)].572 The (N)4 = (tn)2 complex shows no acceleration for a 1 1 ratio, but the 2 1 metal ATP mixture (0.1-0.01 mol dm 3 ATP) shows 105 enhancement at pH 7. Scheme 63 summarizes these findings. At high pH hydrolysis of the Coin complex predominates. [Co(cyclen)(H20)2]3+ also catalyzes the hydrolysis of [Co(NH3)4(ATP)] at pH 8-9, and (168) has been claimed as the reactive species.581 In all these studies however no intermediates have been positively identified, and the immediate products, coordinated or otherwise, also lack definition. 

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Reactions of transition-metal complex-coordinated ligands with protonic acids can yield N—H bond-containing products. Coordinated nitrosyl groups react with HCl ... 

After activation, the catalyst is intrcxiuced into the polymerization reactor as slurry in a saturated hydrocarbon such as isobutane. The precise mechanism of initiation is not known, but is believed to involve oxidation-reduction reactions between ethylene and chromium, resulting in formation of chromium (II) which is the precursor for the active center. Polymerization is initially slow, possibly because oxidation products coordinate with (and block) active centers. Consequently, standard Phillips catalysts typically exhibit an induction period. The typical kinetic profile for a Phillips catalyst is shown in curve C of Figure 3.1. If the catalyst is pre-reduced by carbon monoxide, the induction period is not observed. Unlike Ziegler-Natta and most single site catalysts, no cocatalyst is required for standard Phillips catalysts. Molecular weight distribution of the polymer is broad because of the variety of active centers. 

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