Titanium nitrogen complexes

Regioisomers of pyrrolizines 255 and their dihydroanlogues 256 were obtained as a mixture, in moderate yield, by reacting the 1,4,7-triketones 254 with titanium-nitrogen complexes (ClTi=NTMS, Cl2TiN(TMS)2, and N(TMS)3) prepared by reduction of TiCU with lithium under a nitrogen atmosphere (Scheme 69) <2004BCJ1655>. 

The synthesis of aromatic primary amides through aminocarbonylation of aryl halides with ammonia is not well documented due to the technical difficulty in using gaseous ammonia. To resolve this problem, methods using ammonia equivalents such as hexamethyldisilazane (HMDS), " formamides, and a titanium-nitrogen complex have been developed. 

A new method for nitrogen fixation involved the treatment of titanium tetraisopropoxide with lithium metal and trimethylsilyl chloride in the presence of a nitrogen atmosphere to give either a titanium-nitrogen complex and/or N(TMS)3 9 (proposed structures) <04BCJ1655>. This reagent was utilized to prepare pyrrole, indoles, and other nitrogen heterocycles. For example, treatment of preformed 9 with enol triflate 8 led to fused pyrrole 10. 

As the importance of primary amides, Morera and Ortar used hexamethyldi-silazane (HMDS) as a source of ammonia in the carbonylation of aryl iodides and triflates to primary amides (Scheme 2.12) [131]. The desired products were isolated in high yields after hydrolysis. In addition, Indolese et al. reported the efficient aminocarbonylation of aryl bromides with formamide at 5 bar of carbon monoxide. Here, using 4-(dimethylamino)pyridine (DMAP) as a base was the key factor for success [132]. Primary benzamides were also prepared from aryl bromides using CO and a titanium-nitrogen complex in conjunction with NaO Bu [133],... 

Scherer A, Kollak K, Liitzen A, et al. Low-valent titanium—pentafulvene complexes— formation of dinuclear titanium-nitrogen complexes. Eur J Inotg Chem. 2005 2005 1003-1010. 

Scheme 1.6 Titanium-nitrogen complex and its application in heterocycle synthesis...

A remarkable process was reported by Mori that forms aniline from dinitrogen (Equation (26)).106 Titanium nitrogen fixation complexes were generated from reactions of titanium tetrachloride or tetraisopropoxide, lithium metal, TMS chloride, and dinitrogen. These complexes generated a mixture of aryl and diarylamines in yields as high as 80% when treated with aryl halide and a palladium catalyst containing DPPF ... 

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. ... 

Nitrogen gas may serve as an ammonia equivalent by first capturing nitrogen with TiXVLi/TMSCl, which gives a LnTi-N(SiMe3)2 complex 50.93 (DPPF)Pd or (BINAP)Pd catalyze the amination of aryl bromides and triflates with this titanium amide complex in low yields after an acidic workup. Di-arylation is the major byproduct. 

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). 

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