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Amines, coordinated Acidity

Studies of the transfer of Br+ and I+ from amine-coordinated halonium ions to acceptor l-co-alkenols have been undertaken to determine the mechanism in an effort to assist in the development of chiral transfer reagents. Transfer of Br+ and I+ from two commercially available dimeric hydroquinine and hydroquinidine ligands ((DHQ)2PHAL and (DHQD)2PHAL) to various 1, (o-alkenols and l,co-alkenoic acids is shown to provide enantiomeric excesses of 4-47% depending on the acceptor alkene. [Pg.471]

Amine-terminated, full-generation PAMAM and PPI dendrimers, as well as carboxylate-terminated half-generation PAMAM dendrimers, can directly bind metal ions to their surfaces via coordination to the amine or acid functionality. A partial hst of metal ions that have been bound to these dendrimers in this way includes Na+, K+, Cs+, Rb+, Fe +, Fe +, Gd +, Cu+, Cu +, Ag+, Mn +, Pd, Zn, Co, Rh+,Ru +,andPt + [18,19,27,36,54,82-96]. Tuxro et al.have also shown that the metal ion complexes, such as tris(2,2 -bipyridine)ruthenium (Rulbpylj), can be attached to PAMAM dendrimer surfaces by electrostatic attraction [97]. A wide variety of other famihes of dendrimers have also been prepared that bind metal ions to their periphery. These have recently been reviewed [3]. Such surface-bound metal ions can be used to probe dendrimer structure using optical spectroscopy, mass spectrometry, and electron paramagnetic resonance (EPR) [86-88,90,97-99]. [Pg.92]

The fact that complex 38 does not react further - that is, it does not oxidatively add the N—H bond - is due to the comparatively low electron density present on the Ir center. However, in the presence of more electron-rich phosphines an adduct similar to 38 may be observed in situ by NMR (see Section 6.5.3 see also below), but then readily activates N—H or C—H bonds. Amine coordination to an electron-rich Ir(I) center further augments its electron density and thus its propensity to oxidative addition reactions. Not only accessible N—H bonds are therefore readily activated but also C—H bonds [32] (cf. cyclo-metallations in Equation 6.14 and Scheme 6.10 below). This latter activation is a possible side reaction and mode of catalyst deactivation in OHA reactions that follow the CMM mechanism. Phosphine-free cationic Ir(I)-amine complexes were also shown to be quite reactive towards C—H bonds [30aj. The stable Ir-ammonia complex 39, which was isolated and structurally characterized by Hartwig and coworkers (Figure 6.7) [33], is accessible either by thermally induced reductive elimination of the corresponding Ir(III)-amido-hydrido precursor or by an acid-base reaction between the 14-electron Ir(I) intermediate 53 and ammonia (see Scheme 6.9). [Pg.161]

Borazole (borazine), derivatives of, from boron halide-amine coordination compounds, 5 28 Boric acid, H3BO3, esters of, 6 29 Boron bromide, 3 27, 29 Boron chloride, 3 27, 28, 29 Boron chloride-trimethylamine, 6 27... [Pg.227]

It is likely that the Lewis acidity of the/ac-[99mTc(CO)3]+ moiety is the reason for cleavage. It is assumed that one remaining water molecule is acidified and attacks intramolecularly the tertiary N-C bond, resulting in a hydroxo group on the cleaved carbon and a secondary amine coordinated to technetium. [Pg.28]

The starting material is an 18-electron nickel(O) complex which is protonated forming a divalent five-coordinate nickel hydride [41]. This can react further with alkenes to give alkyl groups, but it can also react as an acid with hard bases to regenerate the nickel(O) complex. Similar oxidative addition reactions have been recorded for phenols, water, amines, carboxylic acids, mineral acids (e.g. HCN), etc. [Pg.115]

The ttaha ligand is heptadentate (Hgttaha = tris(2-aminoethyl)amine hexaacetic acid) but nine-coordination is attained in [C(NH2)3]3[Gd(ttaha)] 3H20 in the solid state by coordination of two... [Pg.149]

The actual catalyst is believed to be a complex (A) of the three components since it is soluble in CH2CI2 even though none of the components is. The amine-coordinated tin(ll) triflatc acts as a lewis acid to activate the aldehyde, and the tin(IV) fluoride or acetate interacts with the silyl enol ether. [Pg.342]

Due to the anticancer activity of some amine-coordinated Pt compounds, there has been extensive interest in the complexes of Pt with oligonucleotides and nucleotides. These Pt complexes normally have square planar geometry and, in the case of bases and dinucleotides, can template more extensive supramolecular structures. Certain cw-Pt complexes are highly effective anticancer agents, the most famous being cisplatin or d5-diamminedichloroplatinum(II) and a related compound, carboplatin, cM-diammine(cyclobutane-l,l-dicarboxylato)platinum(II). There have been extensive studies of the coordination properties of Pt compounds with nucleic acid bases to further understand the effect of these drugs on DNA structure and function. ... [Pg.805]

The catalysts for cationic polymerization can be strong anhydrous acids, Lewis acids, salts of primary and secondary amines, carboxylic acids, and salts of amines with carboxylic acids that split off water at elevated temperatures. The initiators react by coordinating with and fonrung rapid pre-equilibrium lactam cations. These cations are the reactive species in the polymerizations. Initiations of this type are also possible with weakly acidic compound, but such compounds ate not able to transfer protons to the lactam. They are capable, however, of forming hydrogen bonds with the lactams. The high reactivity of the lactam cations may be attributed to the decreased electron density at the carbonyl carbon atoms. This makes them more subject to nucleophilic attacks. Protonations of the amides occur at the oxygens, but small fractions of N-protonated amides are also presumed to exist in tautomeric equilibrium. To simplify the illustrations, all lactams will be shown in this section as... [Pg.190]

The adsorption of neutral molecules on smectites is driven by various chemical interactions hydrogen bonds, ion-dipole interactions, coordination bonds, acid-base reactions, charge transfer, and van der Waals forces. Several polar molecules, such as alcohols, amines, and acids, form intercalation complexes with montmorillonites. The intercalation can be performed from the vapor, liquid, or even solid state. In intercalation from solution, solvent molecules are generally coadsorbed in the interlayer space. Guest molecules may be intercalated in dried clay minerals or may displace the water molecules of hydrated montmorillonite. [Pg.58]

Telomerization of 1,4-butadiene with water, alcohols, amines, and acids is an extremely useful reaction since it leads to the formation of practically important products. (179,180). For example, the telomer with water, 2,7-octadiene-l-ol can be further hydrogenated to 1-octanol which is a raw material for plasticizers for poly(vinyl chloride). In fact, this reaction was among the processes disclosed in the first patents on the use of TPPTS in biphasic solvent mixtures (58). The catalyst for such telomerizations usually consists of palladium(O) and an excess of TPPTS, TPPMS, or other water-soluble phosphines (eg, with quaternary ammonium substituents). The telomerization of 1,4-butadiene with water was developed into an industrial process by Kuraray Ind. (Scheme 26). Interestingly, the best ligand was the phosphonium salt shown in (Scheme 26) and the catalyst could be prepared in situ from this ligand and [Pd(OAc)2] (179). It is assumed that under the reaction conditions the corresponding tertiary phosphine can be formed to some extent and coordinates to palladium. In any case with a large excess of... [Pg.485]

This was soon supplanted by a more powerful spectroscopic method, wherein the IR behavior of chemisorbed amines onto acidic surfaces was found to distinguish the relative amounts of Lewis and Bronsted sites. The first report, for ammonia on a silica-alumina cracking catalyst, occurred in 1954 (61). Bands for NH3 and NH4+ were observed upon addition of water, the NH4 bands increased at the expense of NH3 bands. These results indicated two types of acid sites (1) NH3 chemisorbed by coordinate bond formation between the Lewis base (NH3) and a Lewis acid site, and (2) transfer of a proton from a Bronsted site to the base forming NH4" bound via coulombic forces. [Pg.36]


See other pages where Amines, coordinated Acidity is mentioned: [Pg.808]    [Pg.234]    [Pg.15]    [Pg.89]    [Pg.192]    [Pg.163]    [Pg.163]    [Pg.26]    [Pg.261]    [Pg.53]    [Pg.85]    [Pg.88]    [Pg.270]    [Pg.154]    [Pg.170]    [Pg.471]    [Pg.240]    [Pg.463]    [Pg.88]    [Pg.128]    [Pg.982]    [Pg.86]    [Pg.122]    [Pg.974]    [Pg.363]    [Pg.330]    [Pg.435]    [Pg.1060]    [Pg.20]    [Pg.837]    [Pg.297]   
See also in sourсe #XX -- [ Pg.320 ]




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