Amines hydride abstraction

Another route to the amido complexes originates from [(>j-Tp )W(CO) (PhC=CMe)(OTf)l and benzylamine and yields [(i -Tp )W(CO)(PhC=CMe) (NHCH2Ph)] (96JA6916). The latter can be protonated with tetrafluoroboric acid to give the amine derivative [(> -Tp )W(CO)(PhC=CMe)(NH2CH2Ph)](Bp4), and this process can be reversed by -butyllithium. Hydride abstraction by silver tetrafiuoroborate, molecular iodine, or PhsCPEe leads to the cationic imine derivatives [(> -Tp )W(CO)(PhC=CMe)(HN=CHPh)]". -Butyllithium deproto-nates the product and gives the neutral azavinylidene species [(> -Tp )W(CO) (PhC=CMe)(N=CHPh)]. The latter with silver tetrafiuoroborate forms the cationic nitrile species [(j -Tp )W(CO)(PhC=CMe)(N=CPh)](Bp4). 

Direct oxidation of diphenylmethanes is of little practical value as color formers. In liquid sulfur dioxide, leuco diphenylmethane 12 (Scheme 2) undergoes hydride abstraction by triphenylcarbenium perchlorate at the benzylic amine position to form immonium ion7 13, whereas in acetonitrile... 

Thermodynamics of complex formation of silver with several ligands such amines,368 hindered pyridine bases,369 nitrogen donor solvents,370 and azoles371 have been carried out. Other studies include the secondary-ion mass spectra of nonvolatile silver complexes,372 the relationship between Lewis acid-base behavior in the gas phase and the aqueous solution,373 or the rates of hydride abstraction from amines via reactions with ground-state Ag+.374... 

Most transition metal ions react with aliphatic amines by hydride abstraction and some second- and third-row metal ions react by dehydrogenation and de-methanation. This area has been adequately reviewed by Eller and Schwarz (9), but to highlight a specific example, the reaction of ammonia with bare Ti+ will be discussed. 

Allylammonium ylides can undergo 2,3-sigmatropic rearrangement [1234]. With weakly nucleophilic amines, C-H bond insertion or hydride abstraction can compete efficiently with ammonium ylide formation. 

Nucleophilic substitution occurs at C-2, and to a lesser extent C-4, as might be predicted from similar reactions with pyridine. Chichibabin amination occurs rather more readily than with pyridine, giving 2-aminoquinoline. A typical hydride abstraction process occurs when qninoline is heated with sodinm... 

Closely related to the phthalides, leucotriarylmethanes are converted into the coloured form by hydride abstraction, chemical and photooxidation and in some cases by acids. A class of pH sensitive lencotriarylmethanes that have fonnd nse in dark blue colour formers are (1.77). They are readily synthesised from Michler s Hydrol (1.73) by reaction with aromatic or heteroaromatic amines in the presence of an acid catalyst. 

Hydride abstraction from alkylamines forms the corresponding imi-nium ions, whose coordination to transition metals gives either a ir-complex or cr-bonded three-membered ring (Scheme 15) (26). Ligation of the cationic dehydro amines to Rh is aided by substantial electron donation from the metal to the electron-deficient carbon atom to produce the Rh(IH) complex with a covalent C—Rh bond and an N—Rh dative bond, consistent with the long C—N bond (1.467 A) and the small H— C( 1)-—N—C(2) dihedral angle (124.6°) as well as the noncoplanarity of the CH2—CH bond and a possible CH—NH2 plane seen in the allylam-ine oxidative addition product (24). 

Alkoxy substituted thiopyrylium compounds are obtained by hydride abstraction from the thiin precursor with trityl salts, or by elimination of halogen from a thiin. By contrast, alkylthio substituents may be generated in creating the cationic species as shown in equation (115), though of course only 2- and 4-substituents are available in this way (76CC899). Amino substituted compounds may be prepared by substitution of the methylthio groups, but the nature of the product is strongly dependent on the nature of the amine (see Section 2.25.3.4). 

The usefulness of 1,3-cyclohexadiene complexes is enhanced by their conversion to stable cationic complexes. The if -cationic complex 102 is prepared as a stable salt by the hydride abstraction from the neutral complex 66 via 101, and its highly regio- and stereoselective reaction with nucleophiles is used for synthetic purposes. Complex 102 reacts with nucleophiles such as amines, active methylenes, alkyl copper or alkoxides at C(l) or C(5) from the uncomplexed exo side. In other words, the nucleophilic attack occurs regioselectively at a dienyl terminus, and stereoselectively anti to Fe(CO)3 to give 103. Hydride abstraction from 103 affords 104, which reacts with a nucleophile to form 105. Decomplexation of 105 produces the 5,6-disubstituted-l,3-cyclohexadiene 106. 

The initiation mechanism for cationic polymerization of cyclic ethers, vinyl amines, and alkoxy styrenes has been investigated by A. Ledwith. He used stable cations, like tropylium or triphenylmethyl cations with stable anions, like SbCl6, and distinguished between three initiation reactions cation additions, hydride abstraction, and electron transfer. One of the typical examples of cationic polymerization, in which the propagating species is the oxonium ion, is the polymerization of tetra-hydrofuran. P. and M. P. Dreyfuss studied this polymerization with the triethyloxonium salts of various counterions and established an order of... 

Note that in 9.33 hydride abstraction generates quaternary nitrogen containing conjugated allyl amine ligand. This prochiral molecule coordinates to the... 

In Fig. 9.6, conversion of 9.32 to 9.33 involves coordination by allyl amine followed by hydride abstraction. Modify the catalytic cycle to show this additional step, as well as conversion of 9.14 to 9.28 to 9.32. 

Hydride abstraction from tertiary amines by arylmethyl cations leads to iminium ions which can be hydrolyzed or trapped with nucleophiles. For example, r-butyldimethylamine reacts with triphenylmethyl perchlorate to give a 93% yield of the iminium salt. This can be trapped with acetophenone to give Ae Mannich product (Scheme 1). 

Hydride abstraction of 1-(cycloprop-2-enyl)indenes and 9-(cycloprop-2-enyl)fluorenes 15 (obtainable by the reactions of 1,2-disubstituted cyciopropenylium ions and the indenyl or fluorenyl anion) with the tritylium cation, followed by treatment with tertiary amines, is one of the earliest calicene syntheses affording 1,2-benzocalicenes and 1,2 3,4-dibenzocalicenes 16. ... 

Although LiAlH4 is stable in ethers, amine solvents can abstract A1H3 to give the amine hydrides discussed below, e.g.,... 

Mechanism of the arylamine formation is the following. Oxidative addition of aryl halide generates the arylpalladium 6, to which an amine coordinates. Abstraction of proton from the coordinated amine with a base (BM) affords the arylpalladium amide 7, and its reductive elimination yields the arylamine 8. Reductive elimination of 7 is a rate-determining step. A path, competitive to the path from 7 to 8, is jS-H elimination to give the imine 9 and the Pd hydride 10, and the reduced arene 11 is formed by reductive elimination of 10. This is a serious side reaction. The elimination of jS-H may be minimized by the use of chelating ligands. 

Because the reactions of related in -cyclohexadienyl complexes are synthetically valuable, the reactions of this ligand have been studied extensively. An outline of how this chemistry can be conducted on the Fe(CO)j fragment is shown in Equation 11.51. A variety of cyclohexadienes are readily available from Birch reduction of substituted aromatics. Coordination and abstraction of a hydride, typically by trityl cation, leads to cationic cyclohexadienyl complexes. These cyclohexadienyl complexes are reactive toward organolithium, -copper, -cadmium, and -zinc reagents, ketone enolates, nitroal-kyl anions, amines, phthalimide, and even nucleophilic aromatic compounds such as indole and trimethoxybenzene. Attack occurs exclusively from the face opposite the metal, and exclusively at a terminal position of the dienyl system. This combination of hydride abstraction and nucleophilic addition has been repeated to generate cyclohexa-diene complexes containing two cis vicinal substituents. The free cyclohexadiene is ttien released from the metal by oxidation with amine oxides. ... 

Protonated amine arm-assisted direct hydride abstraction... 

C-H activation can also lead to C-C bond formation. Irena S. Akhrem of the Nesmeyanov Institute, Moscow, described (Tetrahedron Lett. 2008, 49,1399) a hydride-abstraction protocol for three-component coupling of a hydrocarbon 13, an amine 14, and CO, leading to the homologated amide 15. Hua Fu of Tsinghua University, Beijing, showed (J. Org. Chem. 2008, 73, 3961) that oxidation of an amine 16 led to an intermediate that could be coupled with an alkyne 17 to give the propatgyUc amine 18. 

The formation of 88 is postulated to be occurring by the nucleophilic attack of a hydride ion (47), abstracted from the secondary amine, on the a-carbon atom of the iminium salt (89). The resulting carbonium ion (90) then loses a proton to give the imine (91), which could not be separated because of its instability (4H). In the case of 2-methyIhexamethylenimine, however, the corresponding dehydro compound /l -2-methylazacyclo-heptene (92) was isolated. The hydride addition to the iminium ion occurs from the less hindered exo side. 

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