Metal amido complex

Magnesium amides can form a wide range of mixed metal amido complexes with alkali metal ions (M2[Mg(NH2)4]) (M = K, Rb or Cs).These contain tetrahedral Mg-centered [Mg(NH2)4] ions connected in three-dimensional networks by coordination of the amido groups to the group 1 metal ions. The most common hetero metal is lithium and lithium amido magnesiates are readily accessible by the addition of a lithium amide to a magnesium amide. 

The extensive chemistry of amido complexes, and, more particularly, of alkylamido complexes, reveals that the planar form is almost invariably found, along with bridging amides (221). Much attention has been paid to the synthesis of metal amido complexes of early transition metals, lanthanides and actinides. The amido group, particularly where it is bulky, confers unusual low coordination numbers on the metals and can also produce materials with considerable kinetic stability toward attack by nucleophiles (42, 67). However, the relevance of this extensive and fascinating chemistry to nitrogen fixation is somewhat problematic. 

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. 

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]. 

Gribkov, D.V., Hultzsch, K.C., and Hampel, F. (2003) Synthesis and characterization of new biphenolate and binaphtholate rare-earth-metal amido complexes catalysts for asymmetric olefin hydroamination/cyclization. Chemistry - A European Journal, 9, 4796. 

The ruthenium-catalyzed reduction of polar bonds using H gas, rather than a sacrificial reductant such as isopropanol, is an atom-economical reaction that has been thoroughly explored. A key discovery by our laboratory was that neutral, stmctur-ally characterized metal-amido complexes such as 11 (Scheme 7) could cleave H heterolytically to yield the fran -dihydride complex 12, and that these are crucial intermediates during catalysis.R - Once the H-N-Ru-H moiety is in place, proton and hydride can then be transferred to the substrate. Having methyl groups instead of hydrogens on carbons alpha to the amido group (beta to the ruthenium) in this case and in the case of 1 (Scheme 4) was important to allow the isolation of an amido... 

Late-Metal-Amido Complexes (Written with Prof. Pinjing Zhao)... 

Overview of Metal-Amido Complexes of the Late Transition Metals... 

The reaction chemistry of late-transition-metal-amido complexes resembles that of organometallic complexes more than that of early-transition-metal amides. Thus, the chemistry of this class of amido complex is presented first. Several reviews of the chemistry of late-metal amido complexes have been published. -... 

The properties of late-transition-metal-amido complexes result, in part, from the mismatch of a hard ligand with a soft metal. This pairing of ligand and metal leads to a... 

Late-transition-metal-amido complexes have been prepared by metathetical substitution reactions, or-bonded ligand exchange, deprotonation of amine complexes, and oxidative addition of N-H bonds. Metathetical substitution is the most common route to late-metal-alkylamido complexes, whereas metathetical substitution and a-bonded ligand exchange have both been used commonly to prepare arylamido compounds. 

Finally, late-metal-amido complexes have been prepared by the oxidative addition of amines. These oxidative additions are included in Chapter 7. In brief, the oxidative addition of aniline is favored for several different types of metals. This reaction of electron-poor pentafluoroaniline to Pt(0) was reported many years ago by Stone (Equation 4.7), and the reaction of the parent aniline with Ir(PEt3)3Cl was reported later by Casalnuovo and Mil-stein. More recently, the oxidative addition of ammonia to an iridium(I) complex containing an electron-rich pincer ligand was observed (Equation 4.8). ... 

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... 

As noted in the introductory section to amido complexes, early-transition-metal-amido complexes have been used as catalysts for olefin polymerization, and they have been used as catalysts or precatalysts for alkyne and olefin hydroamination, olefin metathesis, - ... 

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