Amine-boron interactions

The tertiary amine boronic add (N-B) interaction in a boronic acid-based PET sensor has strength in the range of 15-25 kJ mol ... 

The introduction of a carefully located tertiary amine proximal to the boron centre of a fluorescent sensor permits the sensor to function at lower pH and introduces an off on optical response to the system via photoinduced electron transfer (PET). The tertiary amine boronic acid (N-B) interaction in a boronic acid-based PET sensor has strength in the range of 15 25 kJ mol . In an aprotic solvent, the N B dative bond is usually present. However, in a protic media, solvent insertion of the N-B occurs to afford a hydrogen-bonded zwitterionic species. 

Hydroboration of allylic amines.1 Hydroboration of primary and secondary allylic amines presents problems because amino groups interact with boron reagents. Hydroboration proceeds normally when the amino group is protected by trimethylsilyl groups, and deprotection can be effected by protonolysis in CH,OH. 

James TD, Sandanayake KRAS, Iguchi R et al (1995) Novel saccharide-photoinduced electron-transfer sensors based on the interaction of boronic acid and amine. J Am Chem... 

Appropriate combinations of boronic acid and fluorophores lead to a remarkable class of fluorescent sensors of saccharides (Shinkai et ah, 1997, 2000, 2001). The concept of PET (photoinduced electron transfer) sensors (see Section 10.2.2.5 and Figure 10.7) has been introduced successfully as follows a boronic acid moiety is combined intramolecularly with an aminomethylfluorophore consequently, PET from the amine to the fluorophore causes fluorescence quenching of the latter. In the presence of a bound saccharide, the interaction between boronic acid and amine is intensified, which inhibits the PET process (Figure 10.42). S-l is an outstanding example of a selective sensor for glucose based on this concept (see Box 10.4). 

The reaction is initiated by addition of the amine 2 to the a keto acid 3, catalyzed by the vinyl boronic acid derivative 1. Use orbital interaction theoretical arguments to explain the following features of this synthesis ... 

Interestingly, the propensity of the boron atom to engage in secondary interactions was also examined by Jacobsen. The interaction of the rhodium complex 60 with a model substrate, namely 5-hexen-l-amine, was monitored by 1H NMR spectroscopy.62 The stronger upheld shifts of the alkene resonances compared to those observed upon coordination of the same substrate to the related boron-free salt [Rh(cod)(DIOP)][ClC>4] (cod = cycloocta-1,5-diene) were attributed to a cooperative behavior of the boron and metal centers of 60 that concomitantly interact with the nitrogen atom and alkene moiety, respectively (Figure 20). 

A third basic procedure of synthesizing 1,3,2-diazaboracyloalkanes involves the interaction of aliphatic a, co-diamines with boron trihalides in the presence of a tertiary amine as hydrogen halide acceptor as is illustrated by Eq. 5 15>17). 

In addition to pyrolysis, transamination, and dehydrohalogenation with tertiary amines several other reactions have been described which yield access to the 1,3,2-diazaboracycloalkane system. For example, Abel and Bush 19> reported the ready replacement of silicon by boron in certain heterocyclic systems as illustrated in Eq. (6). It seems quite likely that this procedure can be developed into a general synthesis. On the other hand, the interaction of trialkylboranes with bis(l,3-diphenylimidazolid-... 

The BH3 adduct of 2-aminopyridine seems to be very stable to internal hydroboration and polymerisation compared to borane pyridine. We attribute the extra stability to hydride-proton interactions these together with those of fluorine-proton were reported for other amine borane compounds16 (Figure 5). The MM models for the two boron complexes shown in Figure 6, present atomic distances... 

Another chiral bimetallic Lewis acid 56 prepared from phenylboronic acid and l-tartaric acid by azeotropic distillation selects 1,6-diaminohexane over 1,2-diami-noethane by using two boron centers and two carbonyl oxygens (Fig. 22) [64b]. In the interaction with l,2-diamino-l,2-diphenylethane, 56 chooses a different complexation pattern by recognizing the chirality of the amines. In both examples the carbonyl groups in 56 play essential roles as Lewis basic sites. 

Isotactic vinyl polymers often possess a helical conformation in the solid state however, without bulky substituents present (vide infra) in solution at room temperature, helix—helix reversal takes place fast and no optical activity is observed. Ortiz and Kahn reported a borderline case in which a non-bonded interaction between the monomers leads to the formation of isotactic 39 (Chart 7) by anionic polymerzation at —78 °C. Optically active polymers can be isolated, but in solution the proposed one-handed helicity is lost in less than 1 h.148 An intriguing class of polymers formed by polycondensation of diboronic acid and chiral tetraalcohols has been studied by Mikami and Shinkai and is exemplified by polymer 40 (Chart 7). In this D-mannitol-based polymer, the noncovalent intramolecular interaction between the amines and the boron atoms imposed a sp3-hybridization on boron, which, according to calculations, results in a helical conformation of the macromolecule.149... 

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