Imido complexes bonding

After cleavage of the N-N bond the parent dinitrogen complex has been converted to a Mo(IV) or W(IV) nitrido or imido complex... 

Table 4.21. Geometrical and NBO parameters for nitrido and imido complexes (4.65), showing bond angles, valence Lewis accuracy (%p f, and metal bond hybrid Qim) and polarization (%cyf) of omn, 7Tmn, and omh NBOs... 

With R = R = Ph and using complexes 1 or 2a, the central N -N single bond of the azine is cleaved by both metals. In this case, the bis(imido) complexes 81 were formed, treatment of which with complexes such as CpCo(C2H2)2 can give heterobimetallic bis(alkylideneamido)-bridged complexes such as 82. Mach has used this concept for the reaction of methyl-substituted titanocenes with acetoneazine. With 3, monomeric Ti(III) complexes 83 and, after activation of the methyl groups, coupled products such as 84 could be obtained [44],... 

The nudeophile is activated by the formation of a titanium(IV)-imido complex 19. The next step is a [2 + 2] cydoaddition with one of the jt-bonds of the allene, depending on the regioselectivity leading to either 20 or 22. Compound 20 then delivers 21 by twofold stepwise proto-demetallation and the latter enamine tau-tomerizes to the imine 24 (Scheme 15.3). Compound 22, on the other hand, should provide allylamines 23, but as we shall see, there are no examples of that mode of reaction known so far. 

Fig. 3.37. Insertion of nucleophilic carbene and imido complexes into aliphatic and aromatic C-H bonds [408,683,689,691].

The starting tantalum hydride(s) also cleave the dinitrogen triple bond at low pressure of hydrogen and at 250 °C to yield the surface Ta amido imido complex [(=SiO)2Ta(=NH)(NH2)] (Scheme 2.22) [60]. 

In summary, the tantalum hydride system adds to the few previously reported well-defined organometallic complexes capable of cleaving N-H bonds of ammonia to yield either an amido or an imido complex, and achieves unprecedented dinitrogen N=N triple bond cleavage with dihydrogen on isolated tantalum atoms to yield reduction of both N atoms. 

The Tc complex [TcI(N—Ar)s] (28) (see Section 5.2.2.1.2) can be reduced with Na° in THE to yield the green, nonbridged, dinuclear compound [Tc2(NAr)6] (46), in which three imido-ligands are bound to the Tc center and connected by a single bond to the second technetium. The molecule has a staggered, ethane-like structure and is diamagnetic. Reduction of (28) yields another homoleptic imido-complex of Tc, the imido-bridged, tetrahedral, dinuclear compound [Tc2(/u-NAr )2(NAr )4] (47) (Ar = 2,6-diisopropylphenyl). The conformation could be confirmed by X-ray structure analysis the assumption of a Tc Tc bond is confirmed by the... 

The complex (PPh4)[Os NC(CCl3)NCCl(CCl3) Cl5] may be regarded as an imido complex of osmium(VI), made by the reaction of OS2CI10 with trichloroacetonitrile and has been characterized by X-ray structural studies. The Os—N distance of 1.97 A is slightly shorter than that expected for a single bond. 

R(H)N—N ], and diazenido (R—N=N ) [68, 71, 72] ligands have been isolated and characterized. Among them, the amido/imido complexes are related by a reduction step. Also, cleavage of the N=N bond of diazene or isodiazene/hydrazido(2—) ligands, to produce imido or amido derivatives, requires several Fl+/e transfer steps. 

Isocyanate formation through multiple bond metathesis of C02 with carbodiimide has been also demonstrated [112]. This transformation can be promoted by titanium isopropoxide, at 383 K, in THF as solvent. It is worth noting that the reverse process, which opens an entry into carbodiimide synthesis, is a well-known process that is catalyzed by several other systems, including trialkylphosphine oxides [113] or vanadium-oxo or -imido complexes [114]. 

An excellent review of transition metal imido complexes appeared in 1980 (260). Transition metal imido complexes (NR R = H, alkyl, or aryl) are most common for Second and Third Row metals, but relatively rare for First Row metals. Three classes of imido complex are known. The majority of imido complexes are monomeric containing a terminal imido group which may adopt either a linear configuration (M=N—R) containing a formal metal-nitrogen triple bond as in [Os(N-fBu)03] and rans-[M(NH)X(dppe)2]+ (M = Mo or W X = CH30,... 

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