Dissociative ligand substitution reactions

Louie, J., Hartwig, J. F. Transmetalation, Involving Organotin Aryl, Thiolate, and Amide Compounds. An Unusual Type of Dissociative Ligand Substitution Reaction. J. Am. Chem. Soc. 1995,117,11598-11599. 

Fig. 4.31. Dissociative ligand substitution reactions of (L)(PR3)(X)2Ru=CHR (L = PR3 or NHC) phosphine/phosphine and phosphine/olefin substitutions.

Dissociative ligand substitution reactions of 18-electron Pd(0) complexes... 

Alternatively, bi- or multidentate ligands can also be used for support. As an additional benefit, the latter offer greater stability for the coordinatively bound metal center against leaching through ligand dissociation and substitution reactions. The first, somewhat remarkable, approach to this is shown in Figure 42.11, based on numerous examples of the support of bidentate phosphines on polymers [1-5]. 

Non-Marcusian linear free energy relationships (if I may again be permitted that barbarism) provide direct evidence for this type of potential surface in octahedral ligand substitution reactions. Both dissociative (e.g., the chloropentaamine of cobalt(III)) and associative systems (e.g., chloropentaaquo chromium(III)) may have values of slopes for the linear free energy relationships indicating non-Marcusian behavior. 

Langford and Gray proposed in 1965 (13) a mechanistic classification for ligand substitution reactions, which is now generally accepted and summarized here for convenience. In their classification they divided ligand substitution reactions into three categories of stoichiometric mechanisms associative (A) where an intermediate of increased coordination number can be detected, dissociative (D) where an intermediate of reduced coordination number can be detected, and interchange (I) where there is no kinetically detectable intermediate [Eqs. (2)-(4)]. In Eqs. (2)-(4), MX -i and... 

I propose to develop and apply such methods, based on ultrafast X-ray absorption spectroscopy, to study the ultrafast molecular motions of organometallics in solutions. In particular, initial studies will focus on photo-induced ligand dissociation and substitution reactions of transition metal carbonyls and related compounds in various solvent systems. 

Nickel(II) complexes with cryptands are still rare. In general the encapsulation of nickel(II) in this type of macrocyclic ligand makes the complexes extraordinarily resistant to dissociation and substitution reactions. 

Figure 5-38. The prototypical ligand substitution reaction in octahedral complexes. In principle, the reaction could proceed by associative or dissociative mechanisms.

The individual catalytic cycles generated by HRh(CO) L4 species will be coupled with each other by ligand substitution reactions. This is shown in Fig. 5.4, where only the possible equilibria between the catalyst precursors (i.e., analogues of 5.1), the dissociated species (i.e., analogues of 5.2), and the alkene coordinated species (i.e., analogues of 5.3) are shown... 

Substitution of several metal-carbonyl complexes Cr(CO)6 and Mn(CO)5 (amine) show a small dependence on the nature and concentration of the entering hgand. Under pseudo-first-order conditions, the rate laws for these substitutions have two terms, as shown for Cr(CO)6 (as for some substitution reactions with 16e complexes, see equation 5). The second-order term was always much smaller than the first-order term. A mechanism that ascribes the second-order term to dissociative interchange (U) has been suggested for the Mo(CO)5Am system (Am = amine) and involves a solvent-encased substrate and a species occupying a favorable site for exchange. Thus, the body of evidence for the simple metal carbonyls indicates that CO dissociation and is the mechanism of ligand substitution reactions. 

H. M. Marques, J. C. Bradley, and L. A. Campbell, J. Chem. Soc., Dalton Trans., 2019 (1992). Ligand Substitution Reactions of Aquacobalamin Evidence for a Dissociative Interchange Mechanism. 

The ligand-substitution reaction of M(tpps) (M2+ = Zn2+. Cd2+, Pb2+) with N,N -l,2-ethanediylbis[(N-carboxymethyl)glycine] (H4edta) and the acid-dissociation reaction of the metalloporphyrins are inhibited by the presence of 18-Crown (18C6).22 Jhe rate suppression by 18C6 was explttined by the formation of [M(tpps)(18C6)] as a precursor complex. The... 

The mechanism of ligand substitution reactions in the carbyne complexes /rar7.v-M(CR)X(CO)4 (M = Cr, W R = Me, Ph, NEtj X = Cl, Br, 1, SePh) was investigated by H, Fischer and co-workers (JOO). The influence of the metal center, the trans ligand, and the carbyne substituent on the M—CO dissociation step was determined. The reactions with PPhj in 1,1,2-trichloroethane [Eq. (62)] all follow first-order kinetics, with activa-... 

Almost all of the reactions of metals can be classified into just a few typical reactions, and the reactions that metals promote in organic chemistry are simple combinations of these typical reactions. If you learn these typical reactions, you will have no trouble drawing metal-mediated mechanisms. The typical reactions of metal complexes are ligand addition/ligand dissociation/ligand substitution, oxidative addition/reductive elimination, insertion/j8-elimination, a-insertion/ a-elimination, cr-bond metathesis (including transmetallations and abstraction reactions), [2 + 2] cycloaddition, and electron transfer. 

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