Insertion-deinsertion reactions ligand

Equations 8.1 and 8.2 describe the general process of insertion of a ligand into an M-Y bond. The former shows a process known as 1,1-insertion and the latter its 1,2 counterpart. The reverse reactions are known interchangeably as deinsertion, extrusion, or elimination. 

It has been suggested that intermolecular incorporation, i.e. oxidative addition and complexation of a substrate by a metal should be favored, intramolecular reactions, i.e. insertion, migration and deinsertion reactions should be invariant, and extmsion reactions such as reductive elimination or decomplexation should be disfavored by pressure [13], However, decomplexation reactions are in most cases ligand exchange reactions, which can proceed by associative mechanisms, and indeed, there is ample evidence that ligand exchange reactions can be accelerated by pressure [2]. 

Behind the interest manifested in binuclear complexes stands the expectation that they will display fundamentally new modes of reactivity. Naturally, we also expect that they can show the patterns of reactivity known for mononuclear complexes. These include Lewis base associ-ation/dissociation, Lewis acid association/dissociation, ligand migration (insertion/deinsertion), oxidative addition/reductive elimination, and oxidative ligand coupling/reductive ligand uncoupling, as well as electron-transfer. While these reaction patterns do occur with binuclear... 

Insertion-Deinsertion. An unsaturated ligand such as an alkene can undergo insertion into a bond between the metal of a complex and a hydrogen or a carbon. These reactions are reversible, and the reverse reaction is called deinsertion. 

Platina-/3-diketone 6 reacts with 2 equiv. of phosphine ligand to give a 50% yield of acyl complex 7, with half the starting 6 remaining over time this reaction mixture evolves to give a mixture of f/s- and /r< //.f-isomers of methyl carbonyl complexes 8 (Scheme 2). One of the isomers of 8 exhibits a reversible CO insertion/deinsertion, which may be brought about by the simple expedient of solvent removal or addition. 

These reactions resemble those described in section 2.2.1 because both types involve insertion of the transition metal into the Si-H or Ge-H bond. However, here the molecule eliminated is not a neutral ligand but is formed by deinsertion of two ligands which are sigma bonded to the transition metal after the addition of R3MH. 

The product of this reaction appears to have formed by insertion of a CO group into an Mn—CHj bond. The reverse of this reaction is called decarbonylation but may also be called deinsertion or, more broadly, elimination. Infrared studies with CO have revealed that the reaction actually proceeds by migration of the methyl ligand rather than by CO insertion. 

Compared to the CO insertion into the M — tr-carbyl bond, the reaction of this type for isocyanide ligands proceeds more readily, giving iminoacyl groups which are thermodynamically more stable than the acyl ligands. Thus, in contrast to the acyl groups, they do not undergo the reverse reaction, i.e., deinsertion. 

An NMR study of the reaction mixtures of ethene and CO in the presence of some Pt complexes revealed the presence of hydride, alkyl, and acyl ligands, 167-169. The complexes are interconverted reversibly by insertion and deinsertion of ethene and CO. They are involved in Pt-complex-catalyzed methoxycarbonylation of ethene. 

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