. . "Concrete examples are NH.sub.3.BH.sub.3, CH.sub.3NH.sub.2.BH.sub.3, (CH.sub.3).sub.2 NH.BH.sub.3, (CH.sub.3).sub.3 N.BH.sub.3, and (C.sub.2 H.sub.5).sub.2 NH.BH.sub.3.Such reducing agents as hydrazine, hypophosphorus acid, and hydrogenated boron compound which are generally used for the precipitation of other metals are invariably undesirable from the standpoints of practical reducing speed, catal" . .