Titanium isocyanates

Izumi used Pd(OAc)2 to effect the bis-alkoxylation of o-nitrostyrenes to form the corresponding o-nitrophenylacetaldehyde acetals, which, upon treatment with Fe/HOAc/HCl, give a variety of indoles (4-OMe, 5-OMe, 4-Me, 4-C1, 4-C02Me, 6-Me) in 63-86% yields [465]. Mori and coworkers employed a titanium-isocyanate complex to construct tetrahydroindolones 373 from cyclohexane-1,3-diones [466],... 

Using a strategy of lactam synthesis with a combination of carbonylation and nitrogenation, 2-methyl- and 2-benzylquinazolin-4(3i/)-one 17 are obtained in 54 and 40% yield, respectively, on treatment of corresponding 2-bromoacetanilides 16 with tetrakis(triphenylphosphane)-palladium [Pd(Ph3P)J, potassium carbonate, and a titanium isocyanate complex in A-methyl-pyrrolidone under a carbon monoxide atmosphere. ... 

Mori and Shibasaki s group described the use of a special titanium-isocyanate complex for a novel one-step synthesis of isoindolinones and quinazolinones starting from o-halophenyl alkyl ketones [260]. As shown in Scheme 2.35, this reaction proceeds through the oxidative addition of the enol lactone, generated by palladium-catalyzed carbonylation of o-halophenyl alkyl ketones, to the titanium-isocyanate complex A. 

In 1991, a new C-N-C bond formation reaction using a nitrogenation-transmetalation process was described. Ketones and aryl or vinyl halides couple to give divinyl or arylvinyl amines in the presence of the titanium isocyanate complex [3THF MgaClaO TiNCO] and a palladium catalyst, via transmetallation of the titano imine complex with aryl or vinyl palladium bromide. Moderate to good yields of the desired products were observed (Scheme 2.176). 

In Yamamoto s report, an interesting Ti-N complex 1 was produced from TiCl4 or TiCls and Mg as a reducing agent (Scheme 1.6a) [54]. Later, Sobota reported that the treatment of complex 1 with CO2 afforded titanium-isocyanate complex 2 (Scheme 1.6b) [60]. Because of the handling of complex 2 is easier than complex 1, the employment of 3.0 equivalent of complex 2 to construct nitrogen-containing... 

Zirconium alkoxides are used for cross-linking and hardening of isocyanate, epoxy, siUcon, urea, melamine, and terephthalate resins in the sol-gel process as catalysts in condensation and as water repellents. Zirconium alkoxides hydroly2e in moist air, but more slowly than titanium alkoxides. 

The anionic polymerization of isocyanates using NaCN as an initiator was first reported in I960.998 The living coordinative polymerization of n-hexylisocyanate has been described using the titanium(IV) complexes (345) (348).999-1001 A trifunctional initiator has also been used to prepare star polyisocyanates.1002... 

There are also chemicals that can generate corrosive or irritant agents, when reacting with other species such as water. They could be called pro-irritant or pro-corrosive agents. For instance, it is the case of titanium s salts (See Sect 3.4.3.1, Figs. 3.65), bore, silane, alkyl aluminium, isocyanates, or Lewis acid (Figs. 3.16 and 3.17). 

Comparison of the titanium-pseudohalide complexes (86) and (88) shows nicely the different bonding of the pseudohalide, i.e. bent Ti—N—N vs. linear Ti—N—C of the N-bonded isocyanate and isothiocyanate. Table 9a shows that in isostructural M(tj5-Cp)2(NCO>2 (M = Ti, Zr)222 the N—C (b) bonds tend to be shorter than the C—O (c) bonds. This may point to a larger contribution of canonical structure (89) which has some C—O triple bond character in the bonding. 

The alkoxides of titanium and zirconium will undergo reaction with both phenyl isocyanate and carbodiimide.253-255 Both types of reaction were shown to be reversible (equation 69).253... 

Full details42 have been published on the conversion of enynes into iminocyclopentenes using a titanium precatalyst in the presence of BuLi and TESCN (equation 9) the resulting iminocyclopentenes can be hydrolysed to cyclopentenones or reduced to allylic silyl-amines. In a related protocol43, the tandem insertion of TMSCN and alkenes, alkynes, ketones or isocyanates into zirconacyclo-pentanes or -pentenes leads to cyclopentylamines carrying an a-alkyl, -alkenyl, -1-hydroxyalkyl or -carboxamide substituent, respectively (equation 9). 

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]. 

Reactions with Isocyanates, TYZOR TPT catalyzes the trimerization of isocyanates and polyisocyanates to isocyanurates and polyisocyanurates (38). Titanium alkoxides of the type Cl3TiOR initiate the living polymerization of isocyanates. Polyisocyanates possessing controlled molecular weights and narrow polydispersities can be synthesized using these catalysts (39) ... 

It is quite remarkable that with all the effort on dinitrogen fixation with the titanium metallocene systems very little is known about the reactions of these complexes with the oxides of nitrogen. Salzmann (119) reported the formation of a polymeric complex [(tj-CsHs TiNO] from the reaction of 3 and NO in toluene solutions. Later, Bottomley and Brintzinger reported that (T7-C5H )2Ti(CO)2 (39) reacts with NO to yield [( -CsHs TiO] as well as an apparent isocyanate complex (112). With an excess of (tj-C5H5)2Ti(CO)2 to nitric oxide, CO, C02, N2, and a Ti-isocyanate species were observed. With N20, (T -C5H5)2Ti(CO)2 yields N2, CO, and various Ti-oxo species. In contrast to our studies with 37 and CO, (tj-C5H5)2Ti(CO)2 and NH3 did not generate an isocyanate species. 

The alkyl-, alky laryl- and diarylcarbodiimides are the diimides derived from carbon dioxide, however, no direct formation of carbodiimides from amines and carbon dioxide is known. Interestingly, carbodiimides can be obtained from amines and carbon dioxide via a switteri-onic titanium complex (see Section 2.2.8). The major starting materials for the synthesis of carbodiimides are isocyanates, 1,3-disubstituted ureas or 1,3-disubstituted thioureas. The synthesis of isocyanates requires the use of the toxic carbonyl chloride or its oligomers. A book on the synthesis and reactions of isocyanates appeared in 1996. ... 

Other catalysts effective in the conversion of isocyanates into carbodiimides include the naphthenates of Mn, Fe, Co, Cu and Pb, derivatives of metallic acetylacetonates, the alkoxides of titanium, zirconium and niobium and vanadium oxides or chlorides. Sterically hindered isocyanates are readily converted into carbodiimides upon heating in the presence of a catalytic amount of a strong base. For example, heating of... 

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

NITRILES Glutaronitrile. Succinonitrile. Hexamethylphosphoric triamide. Methyl cazboazate. Methyl isocyanate. Phospho-nitrilic chloride. Titanium(IV) chloride. p-Toluenesulfonylhydrazine. Trichloroiso-cyanuric acid. 

Tetrakis(dimethylamino)titanium converts DMF to tris(dimethylamino)methane (529 equation 236). This compound is also formed in the reaction of V-tetramethyloxamide with the titanium reagent, whereas amides which have a-CH bonds are converted to ketene aminals. Cyclic and spitocyclic compounds, containing the substitution pattern of a trisamino compound, are formed in the reaction of IVA -dialkylformamides or A/ -aryl-(VJV-dialkylformamidines with aryl isocyanates. Similar compounds, e.g. (530 equation 237), are produced in the reaction of imidazolines or lactamid-ines with isocyanates. 

In the petrochemical industry sulfuric acid is utilized, for example, in the alkylation of isoalkanes with alkenes, in the chemical industry in the manufacture inorganic chemicals (e.g. hydrofluoric acid, chromic acid, aluminum sulfate) and organic products (e.g. dyes, explosives, isocyanates, soaps, detergents, fibers and pharmaceuticals). Sulfuric acid is also utilized in the manufacture of titanium oxide pigments, uranium and copper extraction, in steel pickling and in batteries. 

---