Imido complex

A series of new Tc(VII) imido complexes has been recently synthesized and characterized. When a hexamethyldisiloxane solution of [Tc03(0SiMc3]°. which can be prepared as a white solid by reaction of AgTc04 with chlorotrimcthylsilane [26], is treated with 2.6-diisopropylphcnylisocyanate at 100 C, deep green [TeCNAr), (OSiMc3)]° (Ar = 2,6-diisopropylphcnyl) is formed  

Some structural data of Tc(VII) complexes are reviewed in Table 12.1.A. 

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Reactions with Transition-Metal Compounds. The numerous pubhshed products of reactions of transition-metal compounds with a2iridines can be divided into complexes in which the a2iridine ring is intact, compounds formed by reaction of a2iridine with the ligands of a complex, and complexes in which the a2iridine molecule is fragmented (imido complexes). 

Imido Complexes. The reaction of azitidines with tungsten(II) complexes leads to the formation of tungsten(IV) imido complexes (332) ... 

Titanium imido complexes supported by amidinate ligands form an interesting and well-investigated class of early transition metal amidinato complexes. Metathetical reactions between the readily accessible titanium imide precursors Ti( = NR)Cl2(py)3 with lithium amidinates according to Scheme 84 afforded either terminal or bridging imido complexes depending on the steiic bulk of the amidinate anion. In solution, the mononuclear bis(pyridine) adducts exist in temperature-dependent, dynamic equilibrium with their mono(pyiidine) homologs and free pyridine. 

A range of chloride metathesis reactions of the monomeric titanium N,N -bis(trimethylsilyl)benzamidinato-imido complexes have been described. These... 

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... 

The formation of a bis(guanidinate)-supported titanium imido complex has been achieved in different ways, two of which are illustrated in Scheme 90. The product is an effective catalyst for the hydroamination of alkynes (cf. Section V.B). It also undergoes clean exchange reactions with other aromatic amines to afford new imide complexes such as [Me2NC(NPr )2]2Ti = NC6F5. ... 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

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. 

The rates of reaction vary with the isomer in the order 3 > 4 > 2. The imido complex may then be hydrolyzed under more vigorous acid conditions to give ammonium ion and the carboxylic acid, probably via the intermediate formation of the acyl complex. In this case the 2-isomer reacts more rapidly than the others. Treatment of the imido complexes with alkali, however, liberates the nitrile (see also Seetion B,l,e) ... 

With the same tactic, a meta-stable 3-coordinate iron(III) imido complex was reported by Holland and coworkers [40]. Using the diketiminate-supported dinitrogen iron(I) complex [L T eNNFeU ] as a source of iron(I) precursor [L = 2,4-bis (2,6-diisopropylphenylimino)pent-3-yl], the addition of adamantyl azide (AdN3) in... 

High-valent iron-imido complexes have also been proposed as reaction intermediates in several reactions of the iron catalysis. Que and coworkers have provided evidence for Fe(IV) imide as a reaction intermediate in the reaction of [(6-PhTPA)-Fe°(CH3CN)2] " with PhI=NTs. Borovik and coworkers have also reported the formation of an amide product involving the generation of a putative iron(IV) imide [36] (Scheme 7). 

An iron(lV)-imido complex was reported by Que and coworkers in 2006 [35]. The starting iron(ll) precursor is [Fe(N4Py)] (N4Py = V,V-bis(2-pyridylmethyl)bis... 

Other iron-imido complexes have also been reported. Holland and coworkers reported the synthesis of the imidoiron(III) complex [L FeNAd] [40, 41]. This imidoiron(III) complex has not been isolated and was found to convert to a purple high-spin iron(III) complex. It has an S = 3/2 ground state from EPR measurement. Based on the results of QM/MM computations, [L EeNAd] is a three-coordinated complex with an Fe-N distance of 1.68 A and has a nearly linear Fe=N-C unit with Fe-N-C angle of 174.1°. Chirik and coworkers made use of liable ligands to prepare iron-imido complexes by treatment of C PDI)-Fe(N2)2 ( PDI = (2,6- Pr2CgH3N = CMe)2C5H3N) with a series of aryl azides [47]. 

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... 

The proposed catalytic cycle is based on that reported by Bergman et al. with zir-conium-imido complexes (see above, Scheme 4-15). 

The monomeric terminal imido complexes cp IrNR (R = tBu, SiMe2 Bu, 2,6-Me2C6H3, 2,6-1Pr2C6H3) were prepared from [cp IrCl2]2 and four equivalents of LiNHR in THF.104 All four product species were structurally characterized by X-ray diffraction and exhibit short Ir—N distances (1.712(7)—1.759(3) A) and nearly linear Ir—N C (Si) angles. Some reactions of cp IrN Bu are highlighted in Reaction Scheme 9. Complexes (77) and (78) have been studied by single-crystal X-ray diffraction. 

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... 

A very interesting study of the reaction of methyl Grignard reagents with homoleptic imido complexes of Tc(VI) has been performed [104]. Reduction of 91 with Na in THF gave the first homoleptic Tc(VI)-imido complex [Tc2(N-Ar)6] (Ar = 2,6-dimethylphenyl) [105], Under more vigorous conditions dimerization to the second homoleptic Tc(VI)-imido complex [Tc2(N-Ar)4(/i-N-Ar)2] (94)... 

Scheme 22. Reaction of homoleptic dinuclear Tc-imido complex 94 with methyl Grignard reagent...

Organometallic complexes of the /-elements have been reported that will perform both intra-and intermolecular hydroamination reactions of alkenes and alkynes, although these lie outside of the scope of this review.149-155 Early transition metal catalysts are not very common, although a number of organometallic systems exist.156-158 In these and other cases, the intermediacy of a metal imido complex LnM=NR was proposed.159,160 Such a species has recently been isolated (53) and used as a direct catalyst precursor for N-H addition to alkynes and allenes (Scheme 35).161,162... 

Reversible pyridine dissociation yields the non-Lewis base stabilized imido complex [Cp(NHAr) Ti=NAr] (54). This coordinatively unsaturated species undergoes a [2 + 2] cycloaddition reaction with allene to give an azatitanocyclobutane (55), which is then protonated to the /mamido complex. Elimination of enamine occurs followed by isomerization to the energetically more favorable imine. 

Equation 44).57 The amide hydrogen is acidic in these compounds and can be deprotonated with standard organometallic bases such as raBuLi to give the imido complex 28 (Equation 44). 

The N-N and metal-N force constants resulting from normal coordinate analysis of the N2-, NNH-, NNH2-, and NNH3-complexes l ppe, 2 ppeF, 34ppeF, and 4 epeF as well as the nitrido and imido complexes 5, Ns and 6 pe C1 are graphically represented in Fig. 4 (15-17). Upon protonation of l pe to the NNH complex 2 peF, the N-N force constant decreases from... 

C. Electronic Structure and Reactivity of Molybdenum Nitrido and Imido Complexes... 

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... 

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