Regioselective Synthesis of 1,2- and 1,3-Di(silylamido)cyclopentadienyl Zirconium Complexes

Regioselective methods to synthesize [Zr{η5-C5H3-1,3-(SiMe2-η-NtBu)2}R] and [Zr{η5-C5H3-1,2-(SiMe2-η-NtBu)2}R] have been investigated. Selective formation of 1,3- and 1,2-di(silylamido)cyclopentadienyl zirconium complexes is controlled by the generation of the intermediate lithium salts Li[C5H3-1,3-(SiMe2NHtBu)2] (2) and Li2[C5H4-1,1-(SiMe2NtBu)2] (3). Experimental data and ab initio calculations justify the formation of 2 and 3 starting from C5H4(SiMe2NHtBu)2 (1). The structural characterization of the lithium salt 3 shows the cyclopentadiene ring unaltered, while the two deprotonated 1,1-di(silylamido) groups are bridging both lithium atoms with one additional coordinated THF molecule. The X-ray diffraction studies of 1,2- and 1,3-di(silylamido)cyclopentadienyl zirconium complexes show a remarkably different coordination site in these molecules.