Trimethylamine, complex with boron

Borane, which is used as a complex with tetrahydrofuran [992] or dimethyl sulfide [611, 992] or generated in situ from lithium borohydride with boron trifluoride etherate [646] or sodium borohydride with aluminum chloride [184], reacts with 3 mol of an alkene to form a tertiary borane. The oxidation with alkaline hydrogen peroxide [183, 992, 1201] or with trimethylamine oxide [991, 992] yields an alcohol (equations 598 and 599). 

Since the boron trifluoride adduct is the most stable adduct of the boron complexes of methylenetriphenylphosphorane 121>, it might be expected that this Lewis acid would also form a stable nitrogen ylid adduct. Treatment of the ylid with boron trifluoride gave a white crystalline solid whose properties were consistent with the proposed adduct 11 °>. The adduct decomposes to trimethylamine trifluoroborane... 

In a molecule of 2-phenyl-l-boraadamantane there are two markedly different types of B-C bonds two of them are boron-alkyl and one is boron-benzyl. On treatment of THF complex 34 with 8-hydroxyquinoline at 20 °C, mpture of the 1-boraadamantane core takes place, resulting in a mixture of boron chelates 52-54 (Scheme 16). When trimethylamine adduct 16 is used as the starting compound, reaction takes place only in boiling toluene. Interestingly, all the products result from the protolysis of B-CH2 bonds only <2006UP1>. 

Evidence for the reverse process, donation of electron density from the nucleophilic dimer atom to an electron-deficient molecule, also exists. Konecny and Doren theoretically found that borane (BH3) will dissociatively adsorb on Si(100)-2x1 [293]. While much of the reaction is barrierless, they note an interaction between the boron atom and the nucleophilic atom of the Si dimer during the dissociation process. Cao and Hamers have demonstrated experimentally that the electron density of the nucleophilic dimer atom can be donated to the empty orbital of boron trifluoride (BF3) [278]. XPS on a clean Si(100)-2 x 1 surface at 190 indicates that BF3 dissociates into BF2(a) and F(a) species. However, when BF3 is exposed on a Si(100)-2 x 1 surface previously covered with a saturation dose of trimethylamine, little B-F dissociation occurs, as evidenced by the photoelectron spectrum. They conclude that BF3 molecularly adsorbs to the nucleophilic dimer atom and DFT calculations indicate that the most energetically favorable product is a surface-mediated donor-acceptor complex (trimethylamine-Si-Si-BF3) as shown in Figure 5.19. 

Figure 5.19. Illustration of the formation of a donor-acceptor complex by the sequential adsorption of trimethylamine and boron trifluoride. The Lewis-basic trimethylamine forms a dative bond with the electrophilic Si dimer atom, and the Lewis-acidic boron trifluoride bonds to the nucleophilic Si dimer atom [278].

A series of metal complexes containing trimethylamine boranecarboxylato ionligand [103904-11-6], (CH3)3N BH COO, have been prepared with Co (III), Co (II), Zn(II), Ca(II), Cr(III), and Fe(III) (39,40). This ligand, derived from the boron analogue of the amino acid glycine, behaves similady to organic carboxylato ligands. 

A review of the chemistry of Group III complexes shows that many of the concepts of Werner s coordination chemistry may be applied to these elements. Furthermore, the differences observed in the complexing behavior between ammonia and trimethylamine refiect fundamental differences in the amines. Ammonia tends to give ionic compounds, whereas trimethylamine tends to give non-ionic products. Trends observed with the metal halides can be extrapolated into hydrides of boron, aluminum, and gallium. An extension of Werner s concepts provides a significant... 

The acid—base properties of the five-membered heterocyclic dioxa— and dithia-boron systems (similar to 20) with trimethylamine and tri-methylphosphine have been considered,and it was claimed " that there was a reversal of base strength. In this work Shore et al. did not make use of the AB values, although these did in fact correspond to the relative acid—base strengths found from the study of homogenous displacement reactions and from dissociation tendencies. Similarily, from dissociation pressures it was concluded ° that the five-membered dioxaborolane (42) was a stronger Lewis acid than the corresponding six-membered compound (43) the AB values obtained for the complexes of (42 AB= -I-21-2) and (43 AB= -I-9-3) are in agreement with this conclusion. 

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