Imido titanium

Amidinato-amido chloro complexes, with Ti(IV), 4, 335-336 Amidinato-imido titanium complexes, synthesis, 4, 431 -32 Amidinato ligands... 

See, e.g.. Fix, R. M. Gordon, R. G. and Hoffman, D. M., Synthesis of thin films by atmospheric pressure chemical vapor deposition using amido and imido titanium(IV) compounds as precursors. Chem. Mater. 2 (1990) 235-241. 

The imido titanium complex supported by a diamido-pyridine framework Ti(=NBut)[(2-C5H4N)C(R)-(CH2NSiMe3)2](py) (R = H, Me) reacts with 2,6-xylyl isocyanide to give the double insertion of the isocyanide into the imido titanium bond and formation of the corresponding four-membered titanacycle with one cr-Ti-C bond the... 

Imido titanium complexes of the type TiX2(=NR)( -L3) (L3 = six-electron donor peralkylated triazacyclic ligand) have been considered as isolobal analogs of corresponding bis-Cp derivatives (Scheme 74). 

The amidinato-imido titanium complexes shown in Scheme 246 have been obtained by salt metathesis methods.90,656 Complexes containing a Gp and the N-alkylated benzamidinato ligands have been synthesized by treatment... 

Reaction of the Cp-amidinato imido titanium complexes Cp Ti[MeC(NPr1)2](NR) (R = But, 2,6-C6H3Me2) with C02 proceed via initial cycloaddition reactions to give N-O-carbamato complexes. The Buc derivative does not react with an excess of C02 and it undergoes a retrocyclization process with the formation of BuNCO and the binuclear fi-oxo compound Cp Ti[MeC(NPr1)2] 2(/i-0). The aryl derivatives exhibit a double CO2 insertion process to give Cp Ti[MeC(NPri)2][0(C0)N(Ar)(C0)0] (Scheme 248).661... 

The ansa-Xmk d macrocycle imido titanium complexes have been described. They are isolobal analogs of ansa-Xmkcd bis-Gp complexes and relatives of Cp-amido olefin polymerization catalysts.1685... 

The insertion products of diphenylcarbodiimide into Ti(0-i-Pr)4 carry out metathesis reactions at elevated temperatures by insertion of an equivalent of carbodiimide in a head to head fashion followed by an extrusion reaction Also, insertion into a Ti-C bond is observed in the reaction of CpTiMcs with carbodiimides to form CpTiMe2[NRC(Me)NR] Insertion into Ti-C bonds is also observed in the reaction of diisopropylcarbodiimide with imido titanium cations Carbodiimides also insert into Ta-N bonds in a mixed tantalium amido/imido complex... 

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. 

The chemistry of titanium has been reviewed in COMC (1982) and COMC (1995)40 41 as well as in Comprehensive Coordination Chemistry II. 2 Since then, several contributions have covered the coordination chemistry of cyclopenta-dienyltitanium carboxylates and related complexes,43 new titanium imido chemistry,44 the use of titanium(iv) chloride45 and isopropoxide46 in stereoselective synthesis, the preparation and synthetic applications of l, -dicarba-nionic titanium intermediates47 and organotitanium complexes,48 49 and titanium-catalyzed enantioselective... 

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. 

Alkoxides and imido are used as anionic ligands in zirconium and titanium catalysts for the polymerisation of alkenes, sometimes as the only anions, but often in combination with cyclopentadienyl ligands. Imides linked to cyclopentadienyl groups form part of the single-site catalyst developed by Dow (Chapter 10) (Figure 1.9, 1). In very different titanium catalysts, namely those used for epoxidation of alkenes, also alkoxide ligands are used (Chapter 14). 

Inter- and intramolecular (cyclometallation) reactions of this type have been ob-.served, for instance, with titanium [408,505,683-685], hafnium [411], tantalum [426,686,687], tungsten [418,542], and ruthenium complexes [688], Not only carbene complexes but also imido complexes L M=NR of, e.g., zirconium [689,690], vanadium [691], tantalum [692], or tungsten [693] undergo C-H insertion with unactivated alkanes and arenes. Some illustrative examples are sketched in Figure 3.37. No applications in organic synthesis have yet been found for these mechanistically interesting processes. 

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]. 

Bis(cyclopentadienyl) titanium complexes with imido groups, 4, 419-420 with indenyls, 4, 428... 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

Whereas Groups 5-7 metals form numerous complexes with M=E double bonds, this feature has been less prominent in Group 4. However, an increasing number of titanium imido compounds have recently been prepared 41... 

Bulky titanium alkylamido complexes are capable of equilibrating with aliphatic and aromatic hydrocarbons via concerted 1,2-elimination/l,2-addition processes a Ti=NR imido species is formed as a transient intermediate. Kinetic parameters suggest a four-center transition state with an almost linear NHR arrangement 122... 

The metathesis of symmetrical aliphatic carbodiimides is also catalyzed by tungsten imido complexes above 140 Other carbodiimide metathesis catalysts include Cr(ll)/Si02/ iminophosphoranes, imido circonocenes, guanidine supported titanium complexes and group 14 amide complexes. ... 

Imido zwitterionic titanium complexes, Ti=NAr[CH3B(C6F5)3], undergo reaction with carbon dioxide to give isocyanates and symmetrical carbodiimides via a ligand metathesis... 

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