Tetranuclear Zirconium and Hafnium Polyhydride Complexes Composed of the “CpMH2” Units

A series of tetranuclear group 4 transition metal octahydride complexes [(C5Me4R)4M4(μ-H)8] (2-Zr, M = Zr, R = SiMe3; 2-Hf, M = Hf, R = SiMe3; 3, M = Zr, R = Me) were synthesized by the hydrogenolysis of the half-sandwich tris­(trimethylsilylmethyl) complexes [(C5Me4R)­M­(CH2SiMe3)3] (1-Zr, M = Zr, R = SiMe3; 1-Hf, M = Hf, R = SiMe3; 1-Zr′, M = Zr, R = Me). X-ray diffraction studies revealed that these hydride clusters possess a tetrahedral M4 framework which is connected by two μ3-H and six μ2-H ligands. Such bonding modes have been further clarified by DFT studies. The reaction of 2-Zr with SePPh3 resulted in oxidation of two of the four Zr­(III) ions in 2-Zr to Zr­(IV) and reduction of SePPh3 to Se2–, yielding the selenium-capped hydride cluster [(C5Me4SiMe3)4Zr4(μ3-Se)­(μ-H)8] (4) with release of PPh3.