REACTIVITY OF COMPLEXES OF THE TYPE RE2X4(LL)2 TOWARDS BIS(TRIPHENYLPHOSPHINE)IMINIUM CARBOXYLATES - A CONVENIENT, NONREDOX SYNTHETIC ROUTE TO CIS AND TRANS ISOMERS OF RE2(O2CR)2X2(LL)2 (R = CH3, C2H5, C6H5 OR 4-C5H4N - X = CL OR BR - LL = PH2PCH2PPH2 OR PH2ASCH2ASPH2)