Titanium-isocyanate complex

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... 

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... 

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. 

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. 

Gade and coworkers reported that titanium hydrazinediido complexes act as effective catalysts for hydrohydrazination reactions involving substituted hydrazines and carbodiimides giving rise to aminoguanidines in good yields. On the other hand, Sundermeyer developed titanium phthalocya-nine complexes as catalysts for the synthesis of highly pure carbodiimides from isocyanates under solvent-free reaction conditions. ... 

Also, switterionic titanium-imide complexes mediate the reaction of carbon dioxide with primary amines to give the corresponding isocyanates and symmetrical carbodiimides via a ligand metathesis reaction . 

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]. 

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. ... 

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

New monomers have been introduced which combine both unsaturation in with isocyanate groups. For example, 2-isocyanatoethyl methacrylate (Dow) has been reported to give a mixture of trimer and polymers using titanium complexes (Tyzor DC from DuPont) which still has unsaturation [2bj. The resulting polymer can possibly be crosslinked via the unsaturated part of the molecule. 

Figure 21.4 shows an example of the in situ Diffuse Reflection Infrared Fourier Transform (DRIFT) spectra observed when propene in heUum is fed at 330°C to an Rh-Ti02 catalyst with preadsorbed NO species. After addition of propene, an immediate decrease in the intensity of the band at 1925 cm (Rh-NO " ") and a simultaneous increase in the intensity of two bands at 1842 and 1755 cm (gem-dinitrosyl complex on Rh) was observed. For longer times on stream, the intensity of these bands also decreases, while new bands form at about 1720 and 1654 cm which could be attributed to vC=0 in coordinated acrylic acid and acrolein, respectively. When acrolein and acrylic acid started to be detected, bands near 2200 cm (2235 and 2200 cm attributed to isocyanate coordinated to titanium and rhodium ions, respectively) also were detected. 

The insertion of phenyl isocyanate into liganded titanium (m) alkyl complexes affords the expected products 310... 

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