Clusters oxidative addition

In the reactions described above, only the AuPR3 fragment of the gold phosphine precursor has added to the cluster. Oxidative addition of Au(PR3)X [where X = Cl (90,188, 191), Br (90, 188), I (179), SCN (104), NCO (231), C2R (92, 97), etc.] has also been observed to occur, yielding clusters in which the transition metal is in a higher oxidation state. This type of reaction was first investigated by Nyholm and coworkers (90, 232), and some examples are given below ... 

The metal-metal bond breaking may also take place as a result of ligand addition to the cluster, oxidative addition of XY molecule, or as a result of changes in bonding properties of the ligand itself, for instance, conversion of an n electron ligand into an fi 2 electron one, such as j -CO(2e)- f/ -CO(4e) [equations (3.54) and In contrast to mononuclear complexes, oxidative addition of an X —Y... 

In general, oxidative addition reactions of clusters are identified with dissociative chemisorption of heterogeneous solid-state catalysts. Therefore, studies of oxidative addition of clusters are useful in finding connections between these areas of chemistry. In the case of clusters, oxidative addition may be one-center if both fragments of the XY molecule add to the same metal atom or two-center if X and Y are coordinated to two... 

In some cases, typical only for clusters, oxidative addition of acetylenes involving C —C bond scission takes place and leads to carbyne complexes. ... 

When applied to molecular clusters oxidative addition may concern more than one metal atom. In fact this kind of activation may concern cleavage of H—bond, C—H bonds of olefinic or acetylenic compounds and various types of ligands. One of the unique aspects of oxidative addition in clusters is the ability of clusters to cleave bonds of a ligand in a very close vicinity to the original point of attachment of this ligand (Figure 32). Thus, the first oxidative addition of ethylene to an OS3 cluster is likely to be as in (A) (Figure 32) and that of pyridine as in B. Other mechanisms of vinylic... 

In contrast to chloride compounds, niobium oxides have a VEC of 14 electrons, due to an overall anti-bonding character of the a2u state, caused by a stronger Nb-O anti-bonding contribution. In some cases, the VEC cannot be determined unambiguously due to the uncertainty in the electron distribution between the clusters and additional niobium atoms present in the majority of the structures. The 14-electron compounds exhibit semiconducting properties and weak temperature-independent paramagnetism. Unlike niobium chlorides, the oxides do not exhibit a correlation between the electronic configuration and intra-cluster bond distances. 

In order to elucidate the causes of the increased stability of the hydrolyzed cluster ions compared with the unhydrolyzed ions, further studies were made of the behaviour of [Te2X8]3 (where X = Cl,Br, or I) in solutions of hydrogen halides [43,52,80,87]. The studies were performed mainly in relation to the most stable and most readily synthesized [Tc2C18]3- ion (Fig. la) kinetic methods with optical recording were employed. The identity of the reaction products was in most cases confirmed by their isolation in the solid phase. The studies showed that the stability of the [Tc2X8]3 ions (where X = Cl, Br, or I) in aqueous solutions is determined by the sum of competing processes acid hydrolysis complex formation with subsequent disproportionation and dissociation of the M-M bonds, and oxidative addition of atmospheric oxygen to the Tc-Tc multiple bond. 

Oxidative addition reactions have been observed also for the binuclear clusters of other d-transition elements with multiple M-M bonds [1,116,117]. The multiplicity of the M-M bonds must decrease in these reactions. It is known from organic chemistry that similar reactions are extremely characteristic of unsaturated organic compounds. We believe that the capacity for oxidative... 

Apart from reactions involving the oxidative addition of oxygen, the usual oxidation-reduction reactions have also been observed for binuclear technetium clusters with multiple M-M bonds (in this case they must be accompanied by a change in the multiplicity of the Tc-Tc bonds up to their complete dissociation)11 (15,16) [11,80],... 

In this chapter, we will study the elementary reaction steps of these mechanisms focusing primarily on the anthraphos systems. This chapter begins with a description of the impact of different methods (coupled cluster, configuration interaction and various DFT functionals), different basis sets, and phosphine substituents on the oxidative addition of methane to a related Ir system, [CpIr(III)(PH3)Me]+. Then, it compares the elementary reaction steps, including the effect of reaction conditions such as temperature, hydrogen pressure, alkane and alkene concentration, phosphine substituents and alternative metals (Rh). Finally, it considers how these elementary steps constitute the reaction mechanisms. Additional computational details are provided at the end of the chapter. 

Using as catalyst precursors the clusters Os3H2(CO)i0 and Os3(CO)12 [71, 72], Laine and coworkers found a deuteration pattern of quinoline hydrogenation similar to that shown in Scheme 16.16, except for the presence of more deuterium in the 4-position and less in the 2-position, which has been interpreted in terms of the occurrence of oxidative addition of the osmium cluster to C-H bonds in quinoline, and also 1,4-hydrogenation (Scheme 16.17). 

Cluster or bimetallic reactions have also been proposed in addition to monometallic oxidative addition reactions. The reactions do not basically change. Reactions involving breaking of C-H bonds have been proposed. For palladium catalysed decomposition of triarylphosphines this is not the case [32], Likewise, Rh, Co, and Ru hydroformylation catalysts give aryl derivatives not involving C-H activation [33], Several rhodium complexes catalyse the exchange of aryl substituents at triarylphosphines [34] ... 

Most of the chemistry performed on orthometallated ylides has been carried out with Pd and Pt as metal centers. Few examples dealing with other metals (Co, Ru, and Os mainly, see 62 and 63) have been reported. Complex (74) has been prepared by reaction of a Ru-vinylidene with PPh3 [153] while Os derivative (75) has been obtained after treatment of the methylimido complex with PPh3 [154]. Orthoruthe-nated indenyl complexes [155] have been synthesized by reaction of the halomethyl precursors with PPh3, and the oxidative addition of the yUde Ph3P=CHC(0)H to clusters of Ru and/or Os also allows the synthesis of orthometallated complexes... 

During the chemisorptions of Ru3(CO)i2 or Os3(CO)i2 on silica, the first step with the surface silanols was to produce a covalent bonding with the silica surface by oxidative addition of the silanol group to the metal-metal bond of the clusters. The nature of surface molecular species [=Si-0)(M3( x-H)(CO)io)j covalently linked to the silica surface (M = Ru, Os) was clearly defined and structurally characterized by a series of physical and chemical techniques, including mass balance taking into account the evolution of two molecules of CO and one molecule of hydrogen [27, 33, 35]. 

An HP IR study of the platinum catalysed carbonylation of methanol to methyl formate, revealed that the catalyst precursor, ds-[Pt(PEt3)2Cl2] is converted into cis-[Pt(PEt3)2(CO)2] along with a cluster species, [Pt3(PEt3)3(CO) ] (n = 3 or 4) [95]. A mechanism involving oxidative addition of methanol to Pt(0) followed by CO insertion into the Pt-OMe bond was suggested. 

AuCN fragment, oxidative addition, heteronu-clear gold cluster compounds, 39 335 lAu(dppe)j]Cl, 36 34-36 Aufhau reaction, 2 74 Auger... 

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