Triene complexes reactions

The insertion reaction between alkenylcarbene complexes and electron-rich alkynes such as 1-alkynylamines (ynamines) leads to mixtures of two regioi-someric cyclopentyl derivatives [78]. Thus, if the insertion occurs on the carbon-metal bond a new aminocarbene complex is produced which evolves to a cyclopentenylmetal derivative. On the other hand, if the insertion reaction occurs on the carbon=carbon double bond of the alkenyl complex, the reaction gives a l-metala-4-amino-l,3,5-triene complex which finally generates a different regioisomer of the cyclopentenylmetal derivative (Scheme 31). 

The metal-mediated and metal-catalyzed [6 + 2]- and [6 + 4]-cycloaddition reactions, pioneered by Pettit and co-workers105 106 and Kreiter and co-workers,107 respectively, involve the cycloaddition of metal-complexed cyclic trienes with 7r-systems such as alkenes, alkynes, and dienes. The [6 + 2]-reactions produce bicyclo[4.2.1]nonadiene derivatives and the [6 + 4]-reactions produce bicyclo[4.4.1]undecatrienes (Scheme 32). Trienes complexed to chromium, which can be prepared on large scale (40 g) as reported by Rigby and co-workers,108 react with 7r-systems upon thermolysis or irradiation.109-111 Chromium and iron-catalyzed [6 + 2]-reactions of cycloheptatrienes and disubstituted alkynes... 

If the profile of the observed or the intrinsic rate constant plotted against pH resembles the profile for an acid-base titration curve, this strongly suggests that one of the reactants is involved in an acid-base equilibrium in that pH range. Such behavior is ftiirly common and is illustrated by the second-order reaction between the Co(II)-trien complex and O2 (Fig. 1.12). The limiting rate constants at the higher and low acidities correspond to the acidic and basic forms of the Co(II) reactant, probably. 

Fig. 1.12 The pH dependence of the first stage of the reaction between Co(II)-trien complex and Oj. The solid line represents Eqn. (1.207) with = 6 X which is a spectrally determined...

Reaction of CrCl3-6H20 with trien gives a blue-violet mixture from which some chromium(III)-trien complexes (electronic spectra given in Table 56) may be isolated as indicated in Scheme 53. While the conversion of cis-ar-[Cr(0H)(trien)H20]Cl2 to the cis-fi isomer in the temperature range 160-225 °C is reversed on cooling, the process is irreversible if the reaction is carried out above 225 °C. 

A number of complexes of the general type (CoN4(OH)(OH2)]2+ (N4 = a system of four nitrogen donors) stoichiometrically cleave the N-terminal amino acid from di-or tri-peptides. Reactions have been described for N4 = en2,164-165 trien166 167 and tren.168,186 In the case of trien complexes, the proposed mechanism for peptide hydrolysis is shown in Scheme 7. Hydrolysis can occur by two pathways (a) attack by external hydroxide on the O-bonded chelated peptide, and (b) intramolecular attack of coordinated hydroxide on the N-bonded peptide. 

Triene complexes of rhodium have been prepared by a crossed aldol condensation with acetophenone (211) or by Wittig reactions [Eq. (29)] (212). 

Steric influences on the heats and entropies of chelate formation may arise from the difficulty encountered by the ligand in assuming the conformation most suitable for effective coordination of a metal ion. Examples of this effect may be seen in the data given in Table V for tetra-coordination of Cu Ni+2 and by polyamines (12, I4). Probable structures of these complexes are represented by Formulas XIV-XVII. It is interesting that the main differences between the stabilities of the tren and trien complexes are due to differences in enthalpies, rather than in entropies, of reaction. Of the two sets of chelate compounds, those of Zn(II) represent the more nearly normaP situation because all four donor groups of each ligand can coordinate to the metal ion with little strain. The remarkable difference between the enthalpies of formation of Chelates... 

Compounds 33 and 34 are readily formed from 31 by direct reaction with CpCo(CO)2. A possible reaction sequence is formation of the triene, 31, from alkyne dimerization followed by reaction with the cobalt species to give the three complexes. Reaction of 34 with alkynes yielded only cyclobutadiene complexes alkyne metathesis was not observed, probably since the carbon-to-metal bonds are too strong. 

The base hydrolysis of the carbonyl bonded amides and peptides display a first order dependence on the hydroxide ion concentration up to a pH of ca. 10, but then become independent of the hydroxide ion concentration due to the formation of the unreactive deprotonated amide (pK = 11 to 12). Some typical kinetic data for these reactions are summarised in Table 7.6. The p2-Co(trien) complexes have the configuration shown in (7.12). Similar studies have been carried out with complexes of the general type trans-[Co(dien)X(peptideOR)] (7.13). Typical kinetic results... 

A small number of concerted cycloadditions of trienes are known, but the reaction is not common. A more versatile process is the formal cycloaddition of Ti -triene complexes with alkynes, alkenes and dienes. Heating or photolysis of an T -triene complex 11.174 with a diene results in the formation of the bicyclo[4.1.4]... 

The 77 -cyclohepta-l,3,5-triene complex Ee(77 -CHT)(r7 -COD) has been evaluated as a catalyst precursor in several reactions, including hydroformylation of 1-hexene and cyclotrimerization of acetylenes. It is found to be more active than other iron catalysts. 

Protonation of complexes of cyclo-octa-1,3,5-triene and reaction with nucleophiles is discussed. 

The photochemistry of the complex [(trien)Co(/i-OH 02)Co(trien)] has been studied in basic aqueous solution. The photoinduced cobalt(II)-trien complexes, [Co(trien)(OH2)2] and [Co(OH)trien(OH2)], react with dioxygen in basic solution to give the intermediates [(OH)(trien) Co-02-Co(trien)(OH2)] " and [(OH)(trien)Co-02-Co(trien)(OH)]2+, which are transformed reversibly into the starting complex. The transient absorption spectra of the monobridged //-peroxo complexes, which have an absorption maximum near 313 nm, were measured by a flash photolysis method. Rate constants for the reaction of the cobalt(II )-trien complexes with dioxygen were also determined as a function of pH, and are compared with the constants obtained using stopped flow methods. 

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. 

In 2008, Grisi et al. reported three ruthenium complexes 65-67 bearing chiral, symmetrical monodentate NHC ligands with two iV-(S)-phenylethyl side chains [74] (Fig. 3.26). Three different types of backbones were incorporated into the AT-heterocyclic moiety of the ligands. When achiral triene 57 was treated with catalysts 65-67 under identical reaction conditions, a dramatic difference was observed. As expected, the absence of backbone chirality in complex 65 makes it completely inefficient for inducing enantioselectivity in the formation of 58. Similarly, the mismatched chiral backbone framework of complex 66 was not able to promote asymmetric RCM of 57. In contrast, appreciable albeit low selectivity (33% ee) was observed when the backbone possessed anti stereochemistry. 

Reaction of trietylenetetraamine (trien) with H [AuCU] at low pH leads to the water soluble dinuclear complex [Au2(trien-H)Cl3]Cl2, which features a deprotonated amino nitrogen bridging the two gold centers (Figure 2.10) [69]. 

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