Imido transfer

The Cp Ti(amidinate) fragment provides a particularly useful platform for the synthesis of novel titanium imido complexes and the study of their unusual reactivity. Numerous single-, double-, and cross-coupling and imido-transfer reactions were investigated using these compounds. The synthetic routes leading to CpTi and Cp Ti amidinate derivatives are outlined in Scheme... 

Based on a most simple analysis, one might approach the design of a metal-im-ido transfer catalyst by considering the corresponding reactivity of metal-carbe-noid complexes or metal-oxo complexes (Fig. 2). It is interesting, in fact, that all of the imido transfer catalysts identified thus far fall into the general category of olefin epoxidation or cycloprop anation catalysts. 

All of the examples described above involve stoichiometric imido transfer to the alkene substrate. A crucial advance in the area of catalytic oxidation was made by Mansuy, who disclosed the first example of catalytic aziridination of alkenes in 1984 [10]. Both iron- and manganese-based porphyrin complexes were found... 

The catalytic transfer of carbenes to imines (Fig. 4) represents a method for the preparation of aziridines complementary to the imido transfer strategies summarized above. The synthetic accessibility of imines and diazocarbonyl compounds, combined with the relative cleanliness of diazo chemistry and the inherent convergence associated with the coupling of two potentially complex reaction partners offer considerable incentive for developing this approach. 

Imido transfer. Aldehydes are converted into RCH=NAr on reaction with ArN=S=0, using catalysts such as VOCI3, M0OCI3, and M0O2CI2. 

Analogous to 0-atom transfer from Ru-oxo species, imido transfer can occur from Ru (porp)( imido) and Ru (porp)(imido)2 species. 

Application of the more electron deficient complex Ru(TPFPP)CO as a catalyst for such imido transfer reactions with PhINTs as donor, in the absence of pyrazole, led to reasonable yields of the corresponding aziridines and amides ". For example, aziridination of allylbenzene, cyclooctene and... 

Baneijee et al. reported a number of soluble poly-imido [134], polyazomethine [135], and polyazoxy phos-phonates [136] by the two phase polycondensation method with or without any phase transfer catalyst. Resulting polymers exhibit high thermal stability and fire retardancy. 

Over the last decade a number of high oxidation state ruthenium porphyrin complexes containing 0x0 or imido ligands have been reported and have been thoroughly studied for their role in oxidation and atom-transfer chemistry. Although comparisons can be drawn with organometallic species (carbene, imido. and 0x0 ligands are formally isolobal) the chemistry of the 0x0 and imido complexes is beyond the scope of the review and will not be covered here. 

Besides, iron(IV) imides have also been implicated as reaction intermediates in nitrogen atom/group transfer reactions [36]. The first structurally characterized iron-imide complex was reported by Lee and coworkers [37] through the reaction of FeCls with 2 equiv. of LiNH Bu in THF, giving one of the products as a stable site-differentiated cubane having three Fe(lll) and one Fe(IV) centers and the Fe(IV) center has a terminally bonded imido ligand (Scheme 4). 

Iron-nitrene/imido complexes are proposed to be the reaction intermediates in nitrogen group transfer reactions. The nitrene group can be transferred to organic substrates. Aziridination and amination are the well-known nitrogen atom/group... 

A first terminal imido complex of nickel (121) was prepared according to Equation (3).468 The synthesis goes via the Ni11 amido compound (122) and uses the steric bulk of the arylimido group for stabilization. The Ni11 center in (121) is planar and three-coordinate. Reaction of (121) with CO or benzyl isocyanide leads to formal nitrene transfer with formation of (124) and (125), respectively. Further reaction with CO liberates the isocyanate and carbodiimide (Equation (4)). 69... 

Ostensibly minor variations of a synthetic procedure sometimes can have significant consequences. For example, substituting KOCMe(CF3)2 for LiOC-Me(CF3)2 is believed [85] to lead to formation of the alkylidyne complex shown in Eq. 16 instead of the known [83] Mo(CH-f-Bu)(NAd)[OCMe(CF3)2]2 (Ad=ad-amantyl). A proton is likely to be transferred before formation of the final product, since it has been known for some time that both W(CH-f-Bu)(NAr)[OC-Me(CF3)2]2 and W(C-f-Bu)(NHAr)[OCMe(CF3)2]2 are stable species that cannot be interconverted in the presence of triethylamine [41]. In such circumstances the nucleophilicity of the alkoxide ion and the nucleophilicity and acidity of the alcohol formed upon deprotonation of the alkylidene will be crucial determinants of whether the imido nitrogen atom is protonated at some stage during the reaction. At this stage few details are known about side reactions in which amido alkylidyne complexes are formed. 

Compounds of the composition [ReOCl3(N N)] have also been isolated with pyridine-2-aldi-mine and rr-acidic arylazopyridine and arylazoimidazole ligands." The products (101) are readily reduced by oxygen atom transfer reactions from Re to phosphorus atoms of phosphines which results in the formation of rhenium(III) complexes. Depending on the reaction condition and the phosphines used either mononuclear or binuclear compounds are formed." " Azo splitting reactions with arylazopyridines give access to arylimido and binuclear oxo/imido com-plexes. "" ... 

The unstable species [RuX4-Bu -TPP)(NR) is prepared by the oxidation of [Ru (4-Bu -TPP)(NR)] (Section 5.6.6.2) using Ag+ or Ce. This complex can transfer the imido group to PMe2Ph at a rate 60 times faster than that its Ru analog. 

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. 

The imido complex [Mo2(cp)2(/r-SMe)3 (/u.-NFl)]" " 25+ undergoes an irreversible one-electron (EC) reduction [70]. Controlled potential electrolysis afforded the amido analog [Mo2(cp)2(/x-SMe)3(/x-NH2)] 26 almost quantitatively after the transfer of IF mol 25+. The amido complex was not the primary reduction product the latter was assigned as a rearranged imide radical (Sch. 18), which is able to abstract a FI-atom from the environment (supporting electrolyte, solvent, or adventitious water) on the electrolysis timescale. In the presence of protons, the reduction of 25+ became a two-electron (ECE) process. This is consistent with the protonation at the nitrogen lone pair of the primary reduction product, followed by reduction of the resulting amido cation... 

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