In migratory insertion reactions

Dihalocarbene ligands, like other neutral 2-e donor carbon ligands, are expected to participate in migratory-insertion reactions when bound adjacent to a rx-bound alkyl or hydride ligand. An example is provided by the following reaction (119) ... 

CN Li-CH(Me) Cl Ph3Si LI-V7 Ll O Ph LjA-7 Ll O NC R1 uV ples of a-hetero-substituted or-ganolithiums used in migratory insertion reactions of organyizirconocene derivatives. 

Experimental and theoretical studies on the intermediacy of a cyclic intermediate in migratory insertion reactions... 

Organometallic Compounds. Mononuclear carbon monoxide complexes of palladium are relatively uncommon because of palladium s high labihty, tendency to be reduced, and competing migratory insertion reactions in the presence of a Pd—C bond (201). A variety of multinuclear compounds... 

The migratory insertion reactions of the Ta-C functionalities in complexes 113-115 are presented in Scheme 22.9 In the reaction of 113-115 with both CO or Bu NC, the migration, under mild conditions (i.e., room temperature), of both alkyl or aryl groups to form r 2-ketones 116-118 and T 2-imino derivatives, 119-121, has been observed. Unlike the case of [Cp2M] or polyphenoxo derivatives of Ta, migration of the second alkyl or aryl group to the intermediate r 2-acyl or T 2-iminoacyl derivatives is very fast, which prevents the interception of the... 

The osmium hydroxycarbene complex 18 is formed in an acid-assisted migratory-insertion reaction of OsClEt(CO)2(PPh3)2. This alkyl compound results from reaction of the ethylene adduct 19 with one equivalent of acid 46). 

The main steps in the catalytic MeOH carbonylation cyde which were proposed for the Co catalysed process [2] have served, with some modification perhaps in the carbonylation of MeOAc to AC2O, to the present day and are familiar as a classic example of a metal catalysed reaction. These steps are shown in Eigure 5.1. They are of course, (i) the oxidative addition of Mel to a metal center to form a metal methyl species, (ii) the migratory insertion reaction which generates a metal acyl from the metal methyl and coordinated CO and (iii) reductive elimination or other evolution of the metal acyl spedes to products. Broadly, as will be discussed in more detail later, the other ligands in the metal environment are CO and iodide. To balance the overall chemistry a molecule of CO must also enter the cycle. 

Compared with Rh systems, where the two principal species are well resolved, it can be seen that as well as more Ir species the bands also overlap, making quantification more difficult. Qualitatively some conclusions can be drawn from the spectra. Forster identified for example that in the presence of I", a potent catalyst poison, much of the Ir could still be present as [IrMe(CO)2l3] . Similarly, as [H2O] is increased the carbonylation rate falls. This is consistent with increased [T] since equilibrium [HI] increases with [H2O] as described above, inhibiting the migratory insertion reaction of [IrMe(CO)2l3] . 

The first study of the energy barriers associated with the migratory insertion reactions occurring in the initiation and propagation steps was carried out with Pd" complexes stabilised by structurally rigid dinitrogen ligands such as bipyridine (bipy), phenanthroline (phen) and bis(arylimino)acenaphthene (Ar-BIAN) [22, 26, 27]. 

Kinetic studies of migratory insertion reactions of the ligands that are involved as (P-P)Pd" fragments in either the propagation cycle of ethene/CO copolymerisation or ethene dimerisation to butenes have been reported by Brookhart [28] and Bian-chini [5e, fj. 

In contrast to theoretical results reported by Morokuma [29] and Ziegler [30], as well as previous studies with Pd"-phen model compounds [26], the lowest experimental energy barrier was found for the migratory insertion of the acyl (ethene) complex (Eq. (10)). The relative rates of alkyl to CO and alkyl to ethene migratory insertion reactions allowed one to estimate that sequential ethene insertions occur once for every ca. 10 insertions of CO into the Pd-alkyl bond [18]. 

Bianchini has reported that the migratory insertion reactions of [Pd(R)(CO)(P-P)]+ complexes (R = Me, Et) are reversible and follow first-order kinetics irrespective of the chelating diphosphine (P-P = dppp, dppe, meso-dppb, rac-dppb, meso-bdpp, rac-bdpp) [5e, f]. The free energies of activation for these reactions were calculated from the half-life times (tj 2) obtained by P( H HP NMR spectroscopy as all the rates of conversion of the methyl carbonyl complexes were independent of the CO pressure. Therefore, the AG values associated with the migratory insertion of the methyl carbonyl complexes could be straightforwardly calculated from the values using the equation AG = RT(ln k -ln kT/h) with = In First-order... 

Organometallic Compounds. Mononuclear carbon monoxide complexes of palladium are relatively uncommon because of palladium s high lability, tendency to be reduced, and competing migratory insertion reactions in the presence of a Pd—C bond (201). A variety of multinuclear compounds are known (202), including [Pd2Cl4(CO)2] [75991-68-3], [Pd3(P(C6H5)3)3(CO)3] [36642-60-1], and [Pd7(P(CH3)3)7(p3-CO)3(p2-CO)4] [83632-51-3]. 

Extrusions are the reverse of migratory insertion reactions. These are a- and -eliminations, decarbonylations, and fragmentations of metallacycles with more than five members. Their general descriptions are given in Table II by Reactions 13 through 17. The evaluation table is given by Matrix 7. 

Fig. 8.3 Warren R. Roper (born in 1938) studied chemistry at the University of Canterbury in Christchurch, New Zealand, and completed his Ph.D. in 1963 under the supervision of Cuthbert J. Wilkins. He then undertook postdoctoral research with James P. Collman at the University of North Carolina at Chapel Hill in the US, and returned to New Zealand as Lecturer in Chemistry at the University of Auckland in 1966. In 1984, he was appointed Professor of Chemistry at the University of Auckland and became Research Professor of Chemistry at the same institution in 1999. His research interests are widespread with the emphasis on synthetic and structural inorganic and organometallic chemistry. Special topics have been low oxidation state platinum group metal complexes, oxidative addition reactions, migratory insertion reactions, metal-carbon multiple bonds, metallabenzenoids and more recently compounds with bonds between platinum group metals and the main group elements boron, silicon, and tin. His achievements were recognized by the Royal Society of Chemistry through the Organometallic Chemistry Award and the Centenary Lectureship. He was elected a Fellow of the Royal Society of New Zealand and of the Royal Society London, and was awarded the degree Doctor of Science (honoris causa) by the University of Canterbury in 1999 (photo by courtesy from W. R. R.)...

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