Hydride ligands abstraction

Abstract Organic syntheses catalyzed by iron complexes have attracted considerable attention because iron is an abundant, inexpensive, and environmentally benign metal. It has been documented that various iron hydride complexes play important roles in catalytic cycles such as hydrogenation, hydrosilylation, hydro-boration, hydrogen generation, and element-element bond formation. This chapter summarizes the recent developments, mainly from 2000 to 2009, of iron catalysts involving hydride ligand(s) and the role of Fe-H species in catalytic cycles. 

In the transition metal-catalyzed reactions described above, the addition of a small quantity of base dramatically increases the reaction rate [17-21]. A more elegant approach is to include a basic site into the catalysts, as is depicted in Scheme 20.13. Noyori and others proposed a mechanism for reactions catalyzed with these 16-electron ruthenium complexes (30) that involves a six-membered transition state (31) [48-50]. The basic nitrogen atom of the ligand abstracts the hydroxyl proton from the hydrogen donor (16) and, in a concerted manner, a hydride shift takes place from the a-position of the alcohol to ruthenium (a), re-... 

HCHO under carbonyl loss conditions (prolonged heating) to generate the cluster anion [Ru3lrH2(CO)i2] The hydride ligand is likely to be abstracted from the cluster by OH" (this step, of course, is not observed in the mass spectrometer). The resulting cluster will be short of one CO ligand, but as two have been lost, there will be plenty of CO present in solution for the unsaturated cluster to pick up. 

In most cases, the immediate product of a-hydrogen elimination is not observed. Instead, reductive elimination of a hydride and an alkyl group to form an alkane frequently occius (Equation 10.30). In other cases, a carbene forms from a dialkyl complex of a d metal that cannot accommodate the additional valency required to form an alkylidene and a hydride ligand. In these cases, an alternative four-center pathway involving the transition state shown in Equation 10.31 that does not involve formation of a metal-hydride complex is followed. When the valency of the metal allows either pathway to occur, it is difficult to distinguish between the a-elimination and a-hydrogen abstraction pathways. ... 

As noted in the introductory sections to this chapter, olefin polymerization occurs by catalyst initiation, chain propagation, and chain transfer. Catalyst initiation occurs by the generation of an alkyl or hydride ligand, or abstraction of one alkyl ligand from... 

ABSTRACT. The redox properties of a variety of isocyanide, rutrile arvj alkyne-derived vinylidene and phenylatlene complexes, commonly with an electron-rich Re(l) or Fe(ll)-phosphinic centre, as well as of the derived protonated species (with aminocarbyne, methyteneamido, carbyne, i vinyl or hydride ligands), as studied by < dic voltammetry and controlled potential electrolysis in aprotic media, are discussed in terms of ligand and metal site effects on the redox potential, and the values of the electrochemical parameter which measures the ligand net etectron-donor/acceptor character are also presented for these ligands. Expressions are indicated which allow to predict the oxidation potential for the octahedral-type 18-electron complexes or 3) or [MsU-1-... 

As discussed above, an 18e metal hydride complex can activate CO2 through a direct hydride abstraction (4). During the abstraction process, the hydride ligand nucleophilically attacks the CO2 carbon. We expect that a simultaneous hydrogen bonding interaction of one of the CO2 oxygens with a protic hydrogen would promote the abstraction process. Indeed, it was found that... 

Triphenylmethyl tetrafluoroborate abstracts a hydride ligand RuH2(PPh3)4 + (Ph3C)Bp4 [RuH(PPh3)4] BF4 + Ph3CH... 

The resulting macrocyclic ligand was then metallated with nickel(II) acetate. Hydride abstraction by the strongly electrophilic trityl cation and proton elimination resulted in the formation of carbon-carbon double bonds (T.J. Truex, 1972). 

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