Borides protonation

Perhaps you are curious as to why absorptions are observed in the infrared spectrum of alcohols that correspond both to free and bydrogen-borided hydroxyl groups, whereas only one OH resonance is observed in their proton nmr spectra. The explanation is that the lifetime of any molecule in either the free or the associated state is long enough to be detected by infrared absorption but much too short to be detected by nmr. Consequendy, in the nmr one sees only the average OH resonance of the nonhydrogen-bonded and hydrogen-bonded species present. The situation here is very much like that observed for conformational equilibration (Section 9-IOC). 

In the case of the intermolecular frequencies, all the SCF values are too high, in comparison to experiment. These frequencies are further raised at the MP2 level. But when anharmonicity is included, they are lowered. As a result, the and shearing frequencies are quite close to experiment although the bending frequency of the proton acceptor remains too high. The authors considered the question as to whether a second-order perturbation treatment is appropriate for the case of H-borids. They concluded that terms higher than quairtic should typically be considered if possible. 

One likely geometry for a trimer would contain a pair of dimer structures as in Fig. 5.9a, where each H-bond is linear, or nearly so, and the H"X—H angle is in the 100-130° range. As in some of the cases already described, a third H-bond can be formed if the proton on the last molecule is brought near the X atom of the first, forming a cyclic structure as in Fig. 5.9b. Of course the price paid for this third H-borid is some angular distortion of all three. 

Imidazolines can exist as the 2-, 3-, or 4-isomers ((5)- 7)), and whereas (5) can exist as a pair of tautomers, any proton shift in (6) will give (7) by rearrangement. Hydrolysis of A(-unsubstituted 3-imidazolines (6) to a-aminoketones presumably occurs via (7). Nickel boride , prepared in situ, transforms 3-imidazolines into 2-imidazolines by double-bond migration <86H(24)287l>. 

Boron atoms in transition metal clusters Denuding the boron atom of B-H interactions in transition metal boron clusters Transition metal boride clusters at the molecular level Recent advances in the chemistry of carborane metal complexes incorporating d and /block elements The interplay of alkylidyne and carbaborane ligands at metal centres. I. Synthesis of electronically unsaturated mixed-metal complexes. II. Proton-mediated reactions... 

Other Reductions. The (porphinato)irons could realize the reduction of alkenes and alkynes with NaBILj. Various unsaturated carbon-carbon bonds were saturated by meso-tetraphenylporphinatoiron chloride (TPPFe Cl) derivatives (up to 81% yield). Ruthenium(III) complexes also pair with NaBH in the reduction of unsaturated carbon-carbon bonds (as does cobalt boride). In the presence of a catalytic amount of Ru(PPh3)4H2 (0.5-1 mol %) and NaBHj, unsaturated carbon-carbon bonds in a wide variety of alkenes and alkynes were saturated in toluene at 100 Addition of water was required to provide a proton source. Similar systems with RUCI3 in aqueous solution reduce unsaturated bonds under milder conditions. Various unactivated mono- or disubstituted olefins and activated trisubstituted olefins were reduced with RUCI3 (10 mol %) and NaBH4 in THF-H2O at 0 °C to room temperature (eq 36). When the RuCl3-catalyzed reductions of olefins were carried out in aqueous amide solution, unactivated trisubstituted olefins were also hydrogenated. ... 

---