Amine titanium amide

The reaction of (EBI)H2 [EBI = ethylene-1,2-bis(indenyl)] and titanium amides did not give the expected ansa-titanocene products. Even with the azetidine complex, Ti(NC3H6)4 reacts with only a single amine elimination to give the mono(indenyl) derivative (C9H6CH2CH2C9H7)Ti(NC3H6)3. By contrast, -zirconocene and hafnocene are easily obtained by the amine elimination process. It is likely that increased steric crowding around the smaller Ti disfavors the second amine elimination.674... 

Reductive amination is historically defined as the combination of a Brpnsted acid, a ketone, an amine, and a coexisting reductant. The recent evolution of titanium (IV) alkoxides, as mild Lewis acid replacements for Brpnsted acids, owes its genesis to a clever modification of titanium amide chemistry demonstrated by Mattson et al. in 1990. By prestirring a ketone, amine, and Ti(OiPr)4 (neat), followed by the addition of EtOH and NaBH3CN, the desired reductive amination product was afforded (Scheme 8.8). The same authors suggested that these reductive aminations proceeded through a hemiaminal titanate intermediate, based on IR spectroscopy before addition of the reductant. 

Examination of the enantioselectivities in Table 7.5 indicates a striking difference in selectivity achieved in the reduction of cyclic (entries 1-8) vs. acyclic imines (entries 9-11). The former is very nearly 100% stereoselective. The simple reason for this is that the acyclic imines are mixtures of E and Z stereoisomers, which reduce to enantiomeric amines vide infra). The mechanism proposed for this reduction is shown in Scheme 7.11 [86]. The putative titanium(III) hydride catalyst is formed in situ by sequential treatment of the titanocene BINOL complex with butyllithium and phenylsilane. The latter reagent serves to stabilize the catalyst. Kinetic studies show that the reduction of cyclic imines is first order in hydrogen and first order in titanium but zero order in imine. This (and other evidence) is consistent with a fast 1,2-insertion followed by a slow hydrogenolysis (a-bond metathesis), as indicated [86]. Although P-hydride elimination of the titanium amide intermediate is possible, it appears to be slow relative to the hydrogenolysis. 

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. 

Arsenic and titanium amides have been used for the amination of 0X0 compds. to gem-diamines and enamines as well as for the amination of acid derivatives . Recently, the preparation of enamines, including sterically hindered compounds, with free amines and titanium tetrachloride has been reported . A Claisen-type rearrangement to form /,(3-unsatd. amines has been used for the preparation of 17-disubst. steroids . 

A more recent patent describes the production of titanyl nitrate by electrolysis of titanium tetrachloride or titanyl chloride (37). Other titanium nitrogen compounds that have been described include titanous amide [15190-25-9] Ti(NH2)3, titanic amide [15792-80-0] Ti(NH)2, and various products in which amines have reacted with titanium tetrachloride (38). 

Addition compounds form with those organics that contain a donor atom, eg, ketonic oxygen, nitrogen, and sulfur. Thus, adducts form with amides, amines, and A/-heterocycles, as well as acid chlorides and ethers. Addition compounds also form with a number of inorganic compounds, eg, POCl (6,120). In many cases, the addition compounds are dimeric, eg, with ethyl acetate, in titanium tetrachloride-rich systems. By using ammonia, a series of amidodichlorides, Ti(NH2) Cl4, is formed (133). 

Other Rea.ctlons, The anhydride of neopentanoic acid, neopentanoyl anhydride [1538-75-6] can be made by the reaction of neopentanoic acid with acetic anhydride (25). The reaction of neopentanoic acid with acetone using various catalysts, such as titanium dioxide (26) or 2irconium oxide (27), gives 3,3-dimethyl-2-butanone [75-97-8] commonly referred to as pinacolone. Other routes to pinacolone include the reaction of pivaloyl chloride [3282-30-2] with Grignard reagents (28) and the condensation of neopentanoic acid with acetic acid using a rare-earth oxide catalyst (29). Amides of neopentanoic acid can be prepared direcdy from the acid, from the acid chloride, or from esters, using primary or secondary amines. 

A similar dependence of the stereoselectivity on the solvent and reaction temperature was found with the x-oxo amides 9 derived from phenylglyoxylic acid (R = C6H5) and 2-oxopropanoic acid (R = CH3) with amine F (Table 23)15. Thus, the highest selectivity was observed under chelation-controlled conditions in the presence of the Lewis acid titanium(IV) chloride. 

The attempted amine exchange reaction to prepare metal amides can be complicated if primary amines are used. Hence, titanium dialkylamides will react with many primary amines to produce polymeric materials (equation 38).66... 

Nitrones, C=N" (R)=0, are generated by the oxidation of N-hydroxyl secondary amines with 5% aq. NaOCl. ° Secondary amines, such as dibenzylamine, can be converted to the corresponding nitrone by heating with cumyl hydroperoxide in the presence of a titanium catalyst. Imines are oxidized to amides with mcpba and BF3 OEt2. ° ... 

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