Heterotrimetallic isopropoxides

Although many heterobimetallic alkoxides were characterized structurally (cf. Section III. A), the crystal structure of the first homoleptic heterotrimetallic isopropoxide [Ba Zr2(0-/-Pr)9 (/i-0-(-Pr)2Cd(/t-0-/-Pr)]2 was recently elucidated (39a). 

The first crystallographically characterized heterotrimetallic isopropoxide was synthesized (39a) by the following reactions ... 

The first clue to the formation of a heterotrimetallic alkoxide was, however, detected in 1985 in the case of beryllium. Its stability was initially ascribed to the small size of beryllium, which hindered the disproportionation of the species. The heterobimetallic isopropoxide (Pr-f-0)Be(/i-0-/-Pr)2Al(0-z-Pr)2 was found on the basis of NMR studies to dimerize on ageing (8) into a product that could be reported as [(0-f-Pr)2Al( -0-/-Pr)2Al(0-i -Pr)2]. This observation led to the feasibility of reactions of the following types, which resulted for the first time in 1985 in the synthesis and characterization of heterotrimetallic isopro-poxides. 

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