Nucleophiles transition-metal complexes attacked

A transition metal complex such as bpyNi(COD), generalized as LjNi, reacts with NCA in a complex reaction sequence that generates a propagating species XLV whose active center is a 5-membered amido-amidate metallacyclic complex. Propagation involves a nucleophilic attack by the amido nitrogen of the amido-amidate at the C-5 carbonyl of NCA. The... 

The excellent ability of late transition metal complexes to activate alkynes to nucleophilic attack has made them effective catalysts in hydroamination reactions. The gold(l)-catalyzed cyclizations of trichloroacetimidates 438, derived from homopropargyl alcohols, furnished 2-(trichloromethyl)-5,6-dihydro-4f/-l,3-oxazines 439 under exceptionally mild conditions (Equation 48). This method was successfully applied to compounds possessing aliphatic and aromatic groups R. With R = Ph, cyclization resulted in formation of 439 with complete (Z)-stereoselectivity <2006OL3537>. 

In certain early transition metal complexes and in metal clusters, organic nitriles can insert into metal-hydrogen or metal-carbon bonds (equations 92 and 93). Similarly, nucleophilic attack at coordinated nitrile can yield methyleneamido complexes (equation 94). 

Palladium(II) salts, in the form of organic solvent soluble complexes such as PdCl2(RCN)2, Pd(OAc>2 or Li2PdCU, are by far the most extensively utilized transition metal complexes to activate simple (unactivated) alkenes towards nucleophilic attack (Scheme 1). Alkenes rapidly and reversibly complex to pal-ladium(II) species in solution, readily generating alkenepalladium(II) species (1) in situ. Terminal monoalkenes are most strongly complexed, followed by internal cis and trans (respectively) alkenes. Geminally disubstituted, trisubstituted and tetrasubstituted alkenes are only weakly bound, if at all, and intermolecular nucleophilic additions to these alkenes are rare. 

As noted in the introduction, in contrast to attack by nucleophiles, attack of electrophiles on saturated alkene-, polyene- or polyenyl-metal complexes creates special problems in that normally unstable 16-electron, unsaturated species are formed. To be isolated, these species must be stabilized by intramolecular coordination or via intermolecular addition of a ligand. Nevertheless, as illustrated in this chapter, reactions of significant synthetic utility can be developed with attention to these points. It is likely that this area will see considerable development in the future. In addition to refinement of electrophilic reactions of metal-diene complexes, synthetic applications may evolve from the coupling of carbon electrophiles with electron-rich transition metal complexes of alkenes, alkynes and polyenes, as well as allyl- and dienyl-metal complexes. Sequential addition of electrophiles followed by nucleophiles is also viable to rapidly assemble complex structures. 

The transition metal complex-catalyzed formation of 1,3-dioxepanes from vinyl ethers has also been described. For example, reaction of allyl vinyl ether 157 with a nonhydridic ruthenium complex at higher temperatures and without any solvent produced 1,3-dioxepane 159 whereas, the use of a hydridic ruthenium complex resulted in the formation of vinyl ether 158 by double-bond isomerization (Scheme 43). It was suggested that cyclic acetal formation proceeds via a 7i-allyl-hydrido transient complex, which undergoes nucleophilic attack of the OH group at the coordinated Jt-allyl <2004SL1203>. 

HC1, giving MgCl2, and it is practically impossible to reduce the generated Mg(II) to Mg(0) in situ, and hence the Grignard reaction is stoichiometric. In other words, Mg(0) is oxidized to Mg(II) by the Grignard reaction. However, reactions involving transition metal complexes proceed with a catalytic amount of the metal compounds in many cases whenever they are attacked by nucleophiles. 

A phosphenium ligand can be considered to have a vacant p orbital and a positive charge on the phosphorus to some extent even in a transition metal complex (see below). Thus, it serves as a 7i-acceptor resulting in the activation of other 7i-acceptor ligands existing on the same transition metal, and is susceptible to both intermolecular and intramolecular nucleophilic attack causing migration. 

An attack of a nucleophilic transition metal hydride on coordinated CO has also been observed by Labinger and Wong, who treated carbonyls of Ct, Mo, W, Mn, Fe, Ku and Co with Cpi Nbllj. which is of a lower hydridic nature than the main group hydrides or group IV hydridic complexes (54]. Small amounts of C C3 hydrocarbons are formed. However, when the reaction of CpjNbH with Cr(CO)(( is carried out under H], only ethane t formed. Carbene intermediates are proposed to account for this selectivity (Scheme 14). 

Transition metal complexes are used as catalysts and as reagents in the synthesis of imides. Molybdenum hexacarbonyl activates strained aziridines and allows the nucleophilic attack of caibanions. Intramolecular rearrangement and a final oxidation yields imides completely stereospecifically (equation 59).38> Dicobalt octacarbonyl catalyzes the conversion of 3,7-unsaturated amides to imides in the presence of carbon monoxide (equation 60). ... 

Utilizing the processes involving the allylic C-0 bond cleavage promoted by transition metal complexes and combining them with subsequent other processes, such as nucleophilic attack, CO insertion, hydrogenolysis, etc., one can de-... 

Finding ways to make nonactivated haloarenes susceptible to nucleophilic attack has always been a great challenge for chemists. Catalysis with transition metal complexes has proven to be efficient in activating inert aryl-halogen bonds and performing various nucleophilic displacement reactions (Eq. 25) [ 178]. The... 

A number of transition metal complexes containing weakly basic (5-member ring) HDN-related ligands are known. The authenticated bonding modes of pyrrole (Pyr) and pyrrolyl ions (Pyl) -or their alkylated analogues- in mononuclear metal complexes are summarized in Fig. 6.1. Pyrrole is a 5-member aromatic heterocycle in which the lone pair is delocalized over the n system of the ring, and it is therefore an electron rich molecule that reacts readily with electrophiles but is not susceptible to nucleophilic attack. 

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