Hydrocarbyl complexes reactions

Hydrocarbonyl compounds, lanthanide complexes, 4, 4 ( -Hydrocarbyl)bis(zirconocene), preparation, 4, 906 Hydrocarbyl-bridged cyclopentadienyl-amido complexes, with Zr(IV), 4, 864 Hydrocarbyl complexes bis-Cp Ti hydrocarbyls reactions, 4, 551 structure and properties, 4, 551 synthesis, 4, 542 cobalt with rf-ligands, 7, 51 cobalt with rf-ligands, 7, 56 cobalt with ]4-ligands, 7, 59 cobalt with rf-ligands, 7, 71 heteroleptic types, 4, 192 homoleptic types, 4, 192 into magnetic metal nanoparticles via ligand stabilization, 12, 87 via polymer stabilization, 12, 87 into noble metal nanoparticles... 

Carbon monoxide insertion reactions in hydrocarbyl complexes of group VIII are particularly relevant because several industrial processes involving carbonylation of an organic substrate are catalyzed by metals belonging to this group. In the subsections that follow, reference to catalytic processes is made on each specific occasion. 

The Tpx ligands can mimic the coordination environment created by three imidazolyl groups from histidine residues, which is frequently found in the active sites of metalloenzymes. Higher valent bis(ix-oxo) species, [(Tpx)M( i-0)2M(Tpx)] via 0-0 cleavage of [(Tpx)M( x-r 2 r 2-02)M(Tpx)] intermediates, but also peroxo, hydroperoxo, and alkylperoxo species, active species undergoing oxidative C-C cleavage reaction, stable hydrocarbyl complexes, and dinuclear xenophilic complexes, [(Tpx)M-M L71], are all relevant to chemical and biological processes, most of which are associated with transition metal catalytic species. 

N-heterocyclic carbenes (NHC) are considered extremely effective hgands for homogeneous catalysis (Figure 6.2). These specific carbenes often lead to high efficiencies in metal-catalyzed reactions compared to traditional phosphines [49, 50). NHC complexes are usually considered to be very stable, due to their electronic properties and the unusually high bond dissociation energies (BDE) associated with NHCs [51]. Previous work has shown that Ni-hydrocarbyl complexes of NHCs readily decompose by reductive elimination to yield the 2-substituted imidazohum salts [52, 53). Later studies have shown that the reverse reaction, oxidative addition of imidazohum salts to zerovalent Group 10 metals, is feasible [53]. 

Hydrocarbyl ligands, such as those shown in Figure 3.1, lie at the heart of transition metal organometallic chemistry. Virtually all reactions catalyzed by transition metals, such as hydrogenation (Chapter 15), cross-coupling (Chapter 19), hydroformylation (Chapter 16), and olefin polymerization (Chapter 22), involve the formation of such complexes. Stable hydrocarbyl complexes are known for all transition metals, and the early work in organometallic chemistry focused on their synthesis. 

A vacant coordination site is created during the forward insertion reaction of Equation 9.1, and a vacant coordination site must be present for the reverse reaction to occur. This mechanism makes it necessary for coordinatively saturated (18-electron) metal-alkyl complexes to dissociate a ligand prior to 3-hydrogen and 3-hydrocarbyl elimination reactions. 

Simpler p-halide eliminations occur from late transition metal catalysts for olefin polymerization (Equations 10.25 and 10.26). Reactions of the cationic palladium-alkyl complexes occur in a similar fashion to the reactions of the cationic group 4 complexes, despite the softer nature of these species. In this case, propylene and the metal chloride are formed. Even a neutral nickel-hydrocarbyl complex (the salicaldimine complex in Equation 10.26) undergoes reactions with vinyl chloride that involve insertion followed by P-chloride elimination. 

The formation of a Th(C5H5)3 complex was suggested because the subsequent thermal reaction of the photogenerated thbrium monohydride with unreacted starting hydrocarbyl complexes, gives the binuclear reductive elimination of alkane ... 

The triruthenium pentahydrido complex Cp Ru(jU-H) 3(/i3-H)2 7 shows remarkable reactivity toward hydrocarbons, such as diene, alkyne, alkene, and even alkane, and various hydrocarbyl complexes have been synthesized in good yields. From the reaction of 7 with 1,1-disubstituted alkene, a /i3-methylidyne-/tt3- ( )-alkyne complex 45 was obtained as a result of the C=C bond cleavage of a /i3-77 -vinylidene intermediate 44 (Equation (15)). The /r3-methylidyne-jU3- 7 ( )-alkyne complexes were alternatively synthesized by the thermolysis of /tt3-diruthena-allyl complexes 3Sa and 3Sb, which were obtained by the reaction of 7 with butadiene and isoprene, respectively (Equation (16)). 

Some of hydrocarbyl complexes mentioned above undergo skeletal tearrangement of the ligand upon thermolysis or oxidation. As shown in Scheme 2, such sequential skeletal rearrangement on the triruthenium cluster provides mechanistic insight into the reaction performed on a metal surface. In this regard, many studies have been performed using carbonyl clusters. 

Interest in iridium hydrocarbyl complexes has been fueled by the higher thermodynamic stability of both Ir-C and Ir-H bonds in comparison to related compounds of rhodium. Therefore, iridium alkyl and aryl complexes have been frequently and successfully used as kinetically inert models for a variety of rhodium-catalyzed reactions allowing to collect intriguing mechanistic information on important industrial processes and organometallic reactions of academic interest. 

Following the synthesis of the first methyl-palladium NHC complexes it was subsequently found that the complexes undergo a facile thermal decomposition process in which the NHC is lost as 2-methylimidazolium salt and the Pd is rednced to Pd(0) (Scheme 13.1) [15-17]. In ensuing studies investigating the reaction behavionr of a range of hydrocarbyl Pd and Ni carbene complexes, it was found that the decomposition reaction is ubiquitous. It occurs with varying ease, for mono-NHC, bis-NHC and donor functionalised-NHC complexes [16-23]. 

Insertion of carbon monoxide and alkenes into metal-carbon bonds is one of the most important reaction steps in homogeneous catalysis. It has been found for insertion processes of platinum [16] that the relative positions of the hydrocarbyl group and the unsaturated fragment must be cis in the reacting complex [17], The second issue concerns the stereochemical course of the reaction, insertion versus migration as discussed in Chapter 2.2. 

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