MeHAlHR.sub.2 in which Me has the same meaning as previously, R is an alkyl or alkoxy radicalpossibly substituted by an alkoxy radical, Al represents an aluminum atom and in particular sodium dihydro-bis(2-methoxy-ethoxy) aluminate NaAlH.sub.2 (OCH.sub.2 CH.sub.2 OCH.sub.3).sub.2, sodium diethyl aluminum hydride, NaAlH.sub.2 (C.sub.2H.sub.5).sub.2 or else a combination of organic polar agents and