Multiple C−H Bond Activation in Group 3 Chemistry:  Synthesis and Structural Characterization of an Yttrium−Aluminum−Methine Cluster

Complete donor-induced alkylaluminate cleavage of halfmetallocene complex Cp*Y(AlMe4)2, that is, treatment of Cp*Y(AlMe4)2 with 2 equiv of diethyl ether, produces [Cp*Y(μ2-Me)2]3 in high yield (95%). In contrast, the equimolar reaction of Cp*Y(AlMe4)2 with diethyl ether reproducibly formed complex [Cp*4Y4(μ2-CH3)2{(CH3)Al(μ2-CH3)2}4(μ4-CH)2] in low yield (10−30%) via a multiple C−H bond activation. The synthesis of the heterooctametallic yttrium−aluminum−methine cluster was also accomplished in moderate yield (47%) by the equimolar reaction of discrete Cp*Y(AlMe4)2 and [Cp*Y(μ2-Me)2]3 in the absence of any donor solvent and “free” AlMe3. This gives strong evidence that preformed heterometal-bridged Y−CH3−Al moieties are prone to multiple hydrogen abstraction in the presence of a highly basic reagent such as [Cp*Y(μ2-Me)2]3. The monocylopentadienyl complexes [Cp*Y(μ2-Me)2]3 and [Cp*4Y4(μ2-CH3)2{(CH3)Al(μ2-CH3)2}4(μ4-CH)2] were structurally characterized.