Transition Metal Hydrocarbyl Ligands

Higher 43-hydrocarbyl derivatives of transition metals can be obtained by partial protolysis of the bis(7i-allyl)metal compounds formed from cyclo-octa-1,5-diene metal complexes and 1,3-butadiene with one equivalent of the Bronsted acid in the presence of the proper ligand in a polar solvent at lowered temperature (e.g. — 40°C). For instance, Ni [43-(CxHn)l and Ni—[43-(Ci2Hig)] derivatives have been yielded by the reaction of Ni(CxH 2)2 [(Ni(Cod)2] with 1,3-butadiene (C4H6), followed by treatment with a Bronsted acid, according to scheme (1) [132] and scheme (2) [37] respectively ... 

Alkyne-substituted transition metal clusters have been reviewed,122,123 and other reviews of interest have discussed cyclopentadienyl metal clusters of group 9 transition metals124 and hydrocarbyl ligand derivatives of group 6 through group 9 heterometallic clusters.125... 

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. 

Transmetallafion transfers a hydrocarbyl or hydrido ligand from one metal to another. Since the transmetallation generates a new transition metal alkyl, it constitutes one of the most important elementary processes in molecular catalysis. 

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. 

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