It is also preferred that R.sup.8 is alkyl or substituted alkyl, especially preferred that it is alkyl, and more preferred that R.sup.8 is methyl.Another useful catalyst is ##STR53## wherein: R.sup.2 and R.sup.5 are hydrocarbyl or substituted hydrocarbyl, provided that the carbon atom bound directly to the imino nitrogen atom has at least two carbon atoms bound to it; R.sup.3 and R.sup.4are each i