Synthesis and Solid State Structures of Sterically Crowded d⁰-Metallocenes of Magnesium, Calcium, Strontium, Barium, Samarium, and Ytterbium

Abstract

The base-free metallocenes [1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Ca, [1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Sr, and [1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Ba have been prepared by reaction of MI 2 and the sodium or potassium salt of the substituted cyclopentadiene anion in THF, while [1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Mg was prepared from the cyclopentadiene, 1,2,4-(Me 3 C) 3 C 5 H 3, and dibutylmagnesium. The structures of the magnesocene and calcocene as well as those of the previously prepared ytterbium and samarium analgoues have been determined by X-ray crystallography. The metallocenes are slightly bent in the solid state with centroid−metal−centroid angles ranging from 163° to 173°. Adducts of the strontocene and samarocene with THF and of the barocene, samarocene, and ytterbocene with 2,6-Me 2 C 6 H 3 NC have also been prepared and characterized. The massive bulk of the [1,2,4-(Me 3 C) 3 C 5 H 2 ] - ligand leads to behavior quite different from that previously observed for base-free metallocenes of the alkaline earths and divalent lanthanides.