Preferably the alkylated borohydride is of formula VI; M is an alkali metal ion such as lithium, sodium, potassium, or cesium, particularly lithium, sodium or potassium, although metallic elements in the second row of the Periodic Table such as barium, magnesium or calcium may be useable, as may transition metals such as copper, iron or cobalt; R10-R12 may suitably be the same or different alkyl g