Alkylamine-boranes

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

N-Trialkyl-B-trihaloborazines can be prepared without difficulty from alkylammonium halide or alkylamine and trihaloborane 4> when the resulting alkylammonium tetrahaloborate or alkylamine-trihalo-borane is refluxed in chlorobenzene. Yields are nearly quantitative in most cases. This same observation holds true for N-triaryl-B-trihalo-borazines. Extensive studies using thermogravimetric methods in addition to preparative methods did not provide for the isolation or identification of any intermediates between the amine-trihaloborane and the borazine stage of the reaction 45 4fl>. 

The reaction of trialkylboranes with A-chloro- or A-(benzoyloxy)alkylamines afforded secondary amines via an anisotropic 1,2-shift of the alkyl group from boron atom to nitrogen in the B-N complex intermediate.519-521 Alkylation of A-chlorodimethylamine with primary trialkylboranes to give A,A-dimethylalkylamines was conducted in the presence of galvinoxyl to avoid the formation of alkyl chlorides via free radical process.522,523 A convenient approach to mixed secondary amines is alkylation of alkyl azides with relatively unhindered trialkylboranes in refluxing xylene followed by hydrolysis with water. The reaction smoothly took place at low temperature when trialkylboranes were replaced by alkyl(dichloro)boranes (Equation (108)).524 Intramolecular amination furnished cyclic amines (Equation (109)).400,525-528... 

Tris(mono-n-alkylamine),B5H9 adducts decompose thermally by the following scheme, via p-monoalkylaminodiboranes(6), with the final formation of NN N -trialkylborazines, polymeric solid boranes, (BH) , and H2 284... 

Bp3-OEt2 followed hy DiisobutyUduminum Hydride is used for the 1,2-reduction of y-aimno-Q, -unsaturated esters to give unsaturated amino alcohols, which are chiral building blocks for a -amino acids. Q , -Unsaturated nitroalkenes can be reduced to hydroxylamines by Sodium Borohydride and BF3-OEt2 in THF extended reaction times result in the reduction of the hydroxylamines to alkylamines. Diphenylamine-borane is prepared from sodium borohydride, BF3-OEt2, and diphenylamine in THF at 0 °C. This solid is more stable in air than BF3-THF and is almost as reactive in the reduction of aldehydes, ketones, carboxyhc acids, esters, and anhydrides, as well as in the hydrob-oration of alkenes. 

---