Amido complexes bonding

Nin-amido complexes such as (117) react with small electrophiles by insertion either in the Ni—N bond (e.g., with C02 to form (118)) or in the N—11 bond. With unsubstituted aryl groups (Ar = Ar = Ph), both a monomeric complex (117) or a dimeric species (119) is formed, depending on the amount of PMe3 added. Using bulky borylamide ligands, an almost linear, two-coordinate Nin complex could be obtained and structurally characterized.467 The N—Ni—N angle in (120) is 167.9°. 

Reaction of dpp-bian with Mg in THF for 30 min reflux gives complex 87 (Ar = 2,6-diisopropylphenyl) which undergoes oxidative addition via m-bond metathesis with PhC=CH to give the black alkynyl amido complex 88. The insertion reaction of 88 with Ph2CO in EtzO yields complex 89. Unexpectedly, hydrogen abstraction to give the radical anion occurs simultaneously with ketone insertion.268... 

Based on the established mechanism for titanium-catalyzed hydroamination, the authors propose a reversible reaction between a titanium imide complex and the alkyne to form metalloazacyclobutene 86, which in turn undergoes 1,1-insertion of the isonitrile into the Ti-C bond. The generated five-membered ring iminoacyl-amido complex 87 with the new C-C bond is protonated by the primary amine to afford the desired three-component coupling product, with regeneration of the catalytic imidotitanium species. Very recently, titanium-catalyzed carbon-carbon bond-forming reactions have been reviewed.122... 

Noyori and coworkers reported well-defined ruthenium(II) catalyst systems of the type RuH( 76-arene)(NH2CHPhCHPhNTs) for the asymmetric transfer hydrogenation of ketones and imines [94]. These also act via an outer-sphere hydride transfer mechanism shown in Scheme 3.12. The hydride transfer from ruthenium and proton transfer from the amino group to the C=0 bond of a ketone or C=N bond of an imine produces the alcohol or amine product, respectively. The amido complex that is produced is unreactive to H2 (except at high pressures), but readily reacts with iPrOH or formate to regenerate the hydride catalyst. 

Lactams Lactams represent a special type of C=N system due to the tautomerization between the lactam (keto amine) and lactim (hydroxyimine) forms. The lactim form is much more favored for cyclic than for non-cyclic amides of carbocyclic acids. In the reaction of complex 2b with N-methyl-e-caprolactam, a simple ligand exchange reaction occurs and complex 87 can be isolated. With P-propiolactam, the alkenyl-amido complex 88 is formed, which indicates an agostic interaction. The reaction of complex 1 with e-caprolactam gives, after elimination of the alkyne and of molecular hydrogen, complex 89 with a deproto-nated lactam in a r]2-amidate bonding fashion [47]. 

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). ... 

Figure 2.1 Illustration of the monomeric primary amido complex [Li(NHMes )(tmeda)f showing the distorted trigonal planar geometry at the lithium ion. Selected bond lengths Li-NI 1.895(8) A, Li-N2 2.137(9) A and Li-N3 2.165(9)A...

R = R = Cy R = 1-adamantyl, R = CfiH 5. Te2-3,5 5 ). The vanadium analogue of the latter [V N(l-Ad)(C6H3Me2-3,5) 3] " 4 has also been characterized. Furthermore, a more efficient route to [Cr N(SiMe3)2 3] and a new crystal structure determination has been described. Three-coordinate metal amides have been treated in a general review that covers three-coordinate transition metal species with hard ligands. The electronic structure and bonding in tricoordinate amido complexes of transition metals have also been detailed... 

The chemistry of indium complexes of aU types in metal oxidation states lower than +3 has been comprehensively reviewed. Few lower oxidation state mononuclear amido complexes of indium are well characterized, however, and no structure has been reported for an In(I) amide. The compound In N(SiMe3)2 n. which is unstable, " has been characterized NMR spectroscopy but its structure is unknown. The structures of several In(I) complexes, related to amides but outside our current scope, have been described. Like its aluminium and gallium counterparts, the p-diketuninate derivative [ In N(Dipp)C(Me) 2CH] has been characterized, as has the closely related species [ In N(Dipp)C(CF3) 2CH]. ° These feature V-shaped, two-coordination at the metal. The less bulky [(In N(Mes)C(Me) 2-CH)2] ° and 15-2.6-.Vlc,)( (Me) i are dimeric with long In In bonds of... 

The reaction of PtX and liquid ammonia gives mixtures of haloammine complexes [PtX (NH3)6 ]X4 n (X = Cl, Br, I n = 3, 2, 1, 0). The salts Pt(NH3)6]X, may be isolated as the main product only after several weeks of reaction. Interactions at room temperature of PtCl -and PtBr salts with liquid ammonia yield the dinuclear p-amido ammine complex [(NH3)4Pt(/i-NH2)2Pt(NH3)4]X6 quantitatively.1033 The structure shows a Pt-Pt separation of 3.16(1) A. 34 Interaction of PtXg with liquid or gaseous ammonia followed by addition of excess KNH2 yields the hexakis(amido) complex K2[Pt(NH2)6] (equation 333).1033 Complexes of the anionic ligand NC12 bonded to platinum(IV) have also been prepared. One method is by treatment of [PtCl(NH3)s]CI3 with chlorine (equation 334).1035... 

When aqueous solutions of the complexes [Co(NH3)5(N=CR)]3+ (R=Me or Ph) are treated with an excess of NaN3 at pH 5-6 (to prevent base hydrolysis to the amido complex) tetrazole complexes are formed (Scheme 17).32 The formation of 5-methyltetrazoIe from sodium azide and acetonitrile requires a reaction time of 25 h at 150 °C323 compared with only 2 h at ambient temperature for coordinated acetonitrile. The subsequent conversion of the N -bonded complex to an N2-bonded complex has been confirmed as the latter complex has been prepared and its crystal structure determined.324... 

However, the iron(m)-amido complex could also be written as an iron(n) amido radical complex 5.20. These two representations are, of course, simply limiting valence bond descriptions of the complex (Fig. 5-35). The difference simply involves the transfer of one electron from the lone pair on the nitrogen in 5.19 to the iron(ni) centre. 

Acyl(phosphido) complexes, with Pt(II), 8, 458 Acyl radicals, via selenium precursors, 9, 477 Acylsilanes, applications, 9, 319 Acylstannanes, preparation, 3, 822-823 l-Adamantyl-2-pyridyl amido complexes, with Zr(IV), 4, 782 Adaptive quantum control, for selective bond cleavage, 1, 247 Addition reactions... 

Another mechanistically interesting example was reported by Ikariya et al. in 2003 (Scheme 10) [12], The authors focused on the basic character of the Ru-amido complex 21. The reaction of dimethyl malonate with 21 afforded a C-bound Ru-enolate, the structure of which was supported by X-ray analysis. It was considered that the N-H moiety plays a role in bringing the enones to the optimum position by hydrogen bonding, as shown in 22 C-C bond formation then occurs at relatively high reaction temperature, affording the desired adduct in 97 % ee. Before this report appeared, a related catalyst system had been examined by Suzuki et al. for the Type I reaction [4f]. 

The amination chemistry depends on the absence of irreversible P-hydrogen elimination from the amido complexes before reductive elimination of amine. At the early stages of the development of the amination chemistry, it was remarkable that the unknown reductive elimination of arylamines could be faster than the presumed rapid [57,58] P-hydrogen elimination from late metal amides. In fact, directly-observed P-hydrogen elimination from late metal amido complexes was rare, and no examples were observed to occur irreversibly from a simple monomeric amido species [69], At this point, it is clear that C-N bond-forming reductive elimination of amines and ethers can be rapid, and that P-hydrogen elimination can be slow. 

The transition metal catalyzed synthesis of arylamines by the reaction of aryl halides or tri-flates with primary or secondary amines has become a valuable synthetic tool for many applications. This process forms monoalkyl or dialkyl anilines, mixed diarylamines or mixed triarylamines, as well as N-arylimines, carbamates, hydrazones, amides, and tosylamides. The mechanism of the process involves several new organometallic reactions. For example, the C-N bond is formed by reductive elimination of amine, and the metal amido complexes that undergo reductive elimination are formed in the catalytic cycle in some cases by N-H activation. Side products are formed by / -hydrogen elimination from amides, examples of which have recently been observed directly. An overview that covers the development of synthetic methods to form arylamines by this palladium-catalyzed chemistry is presented. In addition to the synthetic information, a description of the pertinent mechanistic data on the overall catalytic cycle, on each elementary reaction that comprises the catalytic cycle, and on competing side reactions is presented. The review covers manuscripts that appeared in press before June 1, 2001. This chapter is based on a review covering the literature up to September 1, 1999. However, roughly one-hundred papers on this topic have appeared since that time, requiring an updated review. 

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