Ligand nucleophilic substitution

Imidazole with [Re(CO)3(phen)Cl] or [Re(CO)3(phen)(CF3S03)] in the presence of sulfuric acid gives [Re(CO)3(phen)(im)]2SO (95ICA(240)169). Imidazole with [Mri2(CO) g] gives [Mn2(CO)g(imH)] (84P707). This path involves the nucleophilic substitution of the carbonyl ligand. However, it is complicated by some redox... 

A further factor which must also be taken into consideration from the point of view of the analytical applications of complexes and of complex-formation reactions is the rate of reaction to be analytically useful it is usually required that the reaction be rapid. An important classification of complexes is based upon the rate at which they undergo substitution reactions, and leads to the two groups of labile and inert complexes. The term labile complex is applied to those cases where nucleophilic substitution is complete within the time required for mixing the reagents. Thus, for example, when excess of aqueous ammonia is added to an aqueous solution of copper(II) sulphate, the change in colour from pale to deep blue is instantaneous the rapid replacement of water molecules by ammonia indicates that the Cu(II) ion forms kinetically labile complexes. The term inert is applied to those complexes which undergo slow substitution reactions, i.e. reactions with half-times of the order of hours or even days at room temperature. Thus the Cr(III) ion forms kinetically inert complexes, so that the replacement of water molecules coordinated to Cr(III) by other ligands is a very slow process at room temperature. 

Ru—C(carbene) bond distances are shorter than Ru—P bond lengths, but this can simply be explained by the difference in covalent radii between P and The variation of Ru—C(carbene) bond distances among ruthenium carbene complexes illustrates that nucleophilic carbene ligands are better donors when alkyl, instead of aryl, groups are present, with the exception of 6. This anomaly can be explained on the basis of large steric demands of the adamantyl groups on the imidazole framework which hinder the carbene lone pair overlap with metal orbitals. Comparison of the Ru—C(carbene) bond distances among the aryl-substituted carbenes show... 

Helquist et al. [129] have reported molecular mechanics calculations to predict the suitability of a number of chiral-substituted phenanthrolines and their corresponding palladium-complexes for use in asymmetric nucleophilic substitutions of allylic acetates. Good correlation was obtained with experimental results, the highest levels of asymmetric induction being predicted and obtained with a readily available 2-(2-bornyl)-phenanthroline ligand (90 in Scheme 50). Kocovsky et al. [130] prepared a series of chiral bipyridines, also derived from monoterpene (namely pinocarvone or myrtenal). They synthesized and characterized corresponding Mo complexes, which were found to be moderately enantioselective in allylic substitution (up to 22%). 

In this article, special attention has been paid to cyclopropanations, Diels-Alder reactions, and nucleophilic substitutions, for which numerous works have been devoted to the use of Ar,N-containing ligands. Other classical reactions allowing the formation of a new C - C bond have been omitted here (e.g., Michael-type additions or aldol reactions) where they have also been, to a lesser extent, efficiently performed using nitrogen-containing ligands. 

The outer ligands in M3Q4L9 (type-I) and M3Q7L6 (type-II) clusters can be easily replaced through nucleophilic substitution reactions. These reactions are discussed separately for each cluster type. 

The ease of dehalogenation of C H X by Ni(ll)/ IMes HCl 1/NaO Pr decreased in the order 1 > Br > Cl F. Subsequent work showed that a 1 1 combination of Ni and NHC in the presence of NaOCHEt resulted in enhanced reactivity towards aryl fluorides [6], Again, the A-mesityl substituted ligand IMes HCl 1 imparted the highest level of catalytic activity. Table 8.2 illustrates that hydrodefluorination is sensitive to both the nature of the substituents on the aromatic ring and the specific regioisomer. Thus, 2- or 4-fluorotoluene (Table 8.2, entry 2) proceeded to only 30% conversion after 15 h, whereas quantitative conversion of 2-fluoroanisole (Table 8.2, entry 3) and high conversion of 3-fluoropyridine (Table 8.2, entry 5) was achieved in only 2-3.5 h. The reactivity of 2-fluoropyridine was compromised by more efficient nucleophilic aromatic substitution. 

Sulfoximines bearing a chiral sulfur atom have recently emerged as valuable ligands for metal-catalysed asymmetric synthesis.In particular, C2-symmetric bis(sulfoximines), such as those depicted in Scheme 1.51, were applied to the test reaction, achieving enantioselectivities of up to 93% ee. The most selective ligand (R = c-Pent, R = Ph) of the series was also applied to the nucleophilic substitution reaction of l,3-diphenyl-2-propenyl acetate with substituted malonates, such as acetamido-derived diethylmalonate, which provided the corresponding product in 89% yield and 98% ee. 

Almost no attention has been paid to diphosphine sulfides employed as chiral ligands for palladium-catalysed nucleophilic substitution reactions. In this context, enantiomerically pure diphosphine sulfides derived from 2,2 -biphosphole, which combined axial chirality and phosphorus chiralities, were synthesised, in 2008, by Gouygou et al. through a four-step synthetic sequence. Among various palladium catalytic systems derived from this type of ligands and evaluated for the test reaction, that depicted in Scheme 1.62... 

A general mechanistic description of the copper-promoted nucleophilic substitution involves an oxidative addition of the aryl halide to Cu(I) followed by collapse of the arylcopper intermediate with a ligand transfer (reductive elimination).140... 

The boranediyl insertion with BC13 and BBr3 gives products with 1-haloboratabenzene ligands which easily undergo nucleophilic substitution at boron complex 6 has been made in this way (57,79). However, these reactions have never been published in detail. 

Compound (39) reacts with Pt(II) and Pd(II) chlorides at room temperature in CH3CN and CHC13, respectively. But in both cases coordination of two ligands with the metal atom was accompanied by nucleophilic substitution at the exocyclic carbon atom. Complexes (210) and (211) having a novel chelate bicyclic ligand with Pt(II) and Pd(II) have been formed in the course of template processes [Eq. (149)] (92IZV335,92MI1). 

The enormous number of coordination compounds undergo many reactions, but a large number of reactions can be classified into a small number of reaction types. When one ligand replaces another, the reaction is called a substitution reaction. For example, when ammonia is added to an aqueous solution containing Cu2+, water molecules in the coordination sphere of the Cu2+ are replaced by molecules of NH3. Ligands are held to metal ions because they are electron pair donors (Lewis bases). Lewis bases are nucleophiles (see Chapter 9), so the substitution of one nucleophile for another is a nucleophilic substitution reaction. Such a reaction can be illustrated as... 

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