Preparation by Reduction with Simple Hydrides and Their Derivatives

Preparation by Reduction with Simple Hydrides and Their Derivatives 

The initial experiments carried out by Hurd (158) were complicated because hydrogen was admixed with the boron halides passed through the reduction chamber. 

In general, the simple metal hydrides are less reactive toward boron halides than the complex aluminum hydrides. Thus LiH gives very little, if any, diborane on direct interaction with, for example, BF3 or BBr3 at temperatures as high as 180 C (279). [It has recently been claimed that at still higher temperatures 

Although Schlesinger and his co-workers did not publish this observation until 1953 (279), it had in fact been mentioned in an unpublished report dated 1943, and this gave other American workers the opportunity to study it further and make improvements in the meantime. Thus it was reported in 1952 (87) that the addition of small quantities of such ether-soluble, active-hydrogen-containing promoters as LiBH or LiBH(0Me)3 causes the reaction to take a different course and proceed in two stages via LiBH as an intermediate 

This results in a considerable saving of boron trifluoride, since (as already mentioned) LiBH reacts further to give not LiBFi but LiF, so that the overall reaction is now 

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