Amido complexes reactivity

When nitroalkenes were used as Michael acceptors, high yields and enantioselectivities of the desired Michael addition products were also obtained (Scheme 5.22). In these reactions, a well-defined chiral Ru amido complex (Figure 5.9) was an efficient catalyst. The mild reaction conditions and high reactivities and stereoselectivities allowed a large-scale reaction in the presence 1 mol% Ru catalyst. By using a chiral Pd(II) catalyst, an asymmetric allylic arylation was reported by Mikami and coworkers to give the cross-couphng product via the activation of both allylic C H and aryl C H bonds in moderate enantioselectivity (Scheme 5.23). ... 

This transformation is in contrast to the corresponding more sterically crowded [Mo N (Bu )Ar 3] which does not exhibit this type of behaviour. Initially it was assumed that the cyclometallated structure would inhibit the type of reactions (e.g. with N2 or N2O) shown by the t-Bu substituted tris-amido complex. Investigation of the chemistry, however, showed that this is not the case and the imine-hydrido product behaves as an effective source of [Mo N(Pr )Ar 3] which, because of its less sterically encumbered nature, exhibits reactivity not observed for its more hindered [Mo N(Bu )Ar 3] counterpart. A simple example is provided by complex formation with benzophenone to give [Mo N(Pr )Ar 3(r 2-OCPh2)], whereas the Bu analogue did not react with this reagent. ... 

Ligand deprotonation may result in some interesting ambiguities in oxidation state, which ultimately allow us to consider new patterns of reactivity. We begin by considering the iron(m) complex of a macrocyclic amine 5.18. Deprotonation of the amino group in the complex gives an iron(m)-amido complex 5.19 (Fig. 5-34). 

The cleavage of allcylamine N-H bonds by late transition metals to form metal amido complexes is also rare [69, 70]. When the transition metal is a low valent, late metal, the resulting amido complexes are highly reactive [71, 72]. It appears that the amination of aryl halides can involve an unusual N-H activation process by a palladium alkoxide to form a highly reactive palladium amide [65, 73]. 

In the course of a closely related study, a series of new functionalized amido complexes of ytterbium, [Cp2YbNHR]2 (R = 8-quinolyl (Qu), 2-pyridyl (Py), 2-aminophenyl, 3-amino-2-pyridyl, and Cp2Yb[NHC6H4(CH2NH2-2)], have been synthesized by metathesis of Cp2YbCl and the corresponding amido lithium salts. Their reactivity toward carbodiimides has been investigated, in which multiple N-H... 

Interestingly, by switching from bis(amidate) to bis(ureate) bis(amido) complexes, a broader scope of reactivity can be realized in intramolecular alkene hydroamination. [28] Reactivity studies indicate that the tethered zirconium bis(ureate) precatalysts are more reactive for intramolecular alkene hydroamination than the titanium analogs. 

Hydride addition to an E/Z mixture of the coordinated imine in [W(Tp )(CO)(PhC=CMe)(NH=CMeEt)][BArF] yields an amido complex with high diastereoselectivity through E/Z imine isomer reactivity differences.143 The amido species [W(Tp )(CO)(PhC=CMe)(NHCHRR/)] (R/R7 = Me/Me Et/Et) were synthesized according to literature methods.144 [W(Tp )-(CO)(PhC=CMe)(NHCHMeEt)] has been obtained in a 1 1... 

Re(V) oxo-amido complexes of the type TpRe( = 0)(NRR )Cl are formed upon reaction of 4 with several primary or secondary amines (NRR = NHEt, NH"Pr, NH Pr, NH2, NEt2, NHPh, NH-/ -tolyl or piperidyl) (Scheme 11). The Re complexes with secondary amido ligands are more robust and less reactive than the... 

Scheme 11. Reactivity of TpRe( = 0)Cl2 (4) with amines to produce Re(V) amido complexes.

Hydroamination is an atom-economical process for the synthesis of industrially and pharmaceutically valuable amines. The hydroamination reaction has been studied intensively, including asymmetric reactions, and a variety of catalytic systems based on early and late transition metals as well as main-group metals have been developed." However, Group 5 metal-catalysed hydroaminations of alkenes had not been reported until Hultzsch s work in 2011. Hultzsch discovered that 3,3 -silylated binaphtho-late niobium complex 69 was an efficient catalyst for the enantioselective hydroaminoalkylation of iV-methyl amine derivatives 70 with simple alkenes 71, giving enantioselectivities up to 80% (Scheme 9.30). Enantiomerically pure (l )-binaphtholate niobium amido complex 69 was readily prepared at room temperature in 5 min via rapid amine elimination reactions between Nb(NMe2)5 and l,l-binaphthyl-2-ol possessing bullqr 3,3 -silyl substituents. Since the complex prepared in situ showed reactivity and selectivity identical... 

Much of the organometallic reactivity of late-metal-amido complexes is presented in later chapters of this text. In general, these complexes are reactive toward many classic organometallic processes, such as reductive elimination, migratory insertion, and 3-hydrogen... 

Early-transition-metal amides are extremely reactive toward protic adds and are therefore useful precursors to a variety of M-X complexes (in which X is an anionic ligand less basic than an amide) by reaction of the amido complex with H-X (Equation 4.13). Common exchange processes that favor elimination of amine involve the reaction with alcohols, amides, amidines, and guanidines. However, weakly acidic hydrocarbons, such as cyclopentadiene derivatives, also react to form Cp complexes (Equation 4.14). ... 

Much of the reactivity of amido ligands involves proton exchange processes that eliminate amine. The exchange is believed to occur by an associative mechanism consequently, the rate of reaction decreases for sterically congested metal complexes. For example, treatment of V[N(CH3)2]j with terf-butanol at room temperature forms V(O-f-Bu) in good yield, while at this temperature the more encumbered complex W[N(CH3)2] reacts only slowly with methanol and ethanol, and not at all with tert-butanoV° The use of bulky N-alkyl substituents allows for the isolation of low-coordinate complexes, such as Cr[N( -Pr)2]3- Amido complexes derived from primary amines can also serve as precursors to imido complexes. In many cases, amido halide complexes form imido complexes by loss of hydrogen chloride in the presence of a base (Equation 4.17). ... 

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