Reduction by diimine

Gaylord, Reduction with Complex Metal Hydrides, Interscience Publishers, Inc., New York, 1956 (b) A. Haj6s, Komplexe Hydride und ihre Anwendung in der organischen Chemie, VEB Verlag der Wissenschaften, Berlin, 1966. 

Unsymmetrical double bonds, as in N02, —N=C, S=0, also —C=N, are hardly attacked at all, nor are bonds that are susceptible to other reducing agents. For instance, diallyl sulfide can be converted into dipropyl sulfide without fission of the S—S linkage.110 Carbonyl groups are, however, reducible (see page 62). 

trans-Olefins are reduced faster than ds-olefins. For example, under standard conditions fumaric acid reacts ten times as fast as maleic acid.101 In some special cases these differences are so great as to control completely the course of the reaction, cis-trans-trans-cyclododzca.-triene affords a mixture of 95 % of cis-dodecene and 5 % of dodecane without a detectable trace of /ra/w-dodecene.111 

The rate of reaction decreases with increase in the number of substituents on the doubly bonded atoms. However, not all substituents have the same influence. Terminal double bonds react faster than those in the interior of a chain 112 and with further increase in the number of substituents on the double bond there may be no reduction at all. Relative rates of reaction measured by Hiinig et al.106 are maleic acid 10, methylmaleic acid 0.7, dimethyl-maleic acid 0, and ethylenetetracarboxylic acid (dicarboxymaleic acid 0.3). Nevertheless, under other conditions dimethylmaleic acid also can be reduced.109 

/ tfra-Substituents in the benzene ring of cinnamic acid have practically no influence on the rate of reduction. 

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