Synthesis and Characterization of Sterically Hindered Group IV Metallocenes

• Published in: Organometallics Vol. 18; no. 3; pp. 404 - 412
• Main Authors: Grimmond, Brian J, Corey, Joyce Y, Rath, Nigam P
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.02.1999; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; CYCLOPENTADIENYL LIGANDS; SILYL COMPLEXES; POLYSILANE HIGH POLYMERS; <2-(DIISOPROPYLAMINO)ETHYL>CYCLOPENTADIENYL LIGAND; NMR-SPECTROSCOPY; OLEFIN POLYMERIZATION; TITANOCENE DERIVATIVES; TITANIUM COMPLEXES; BOND METATHESIS MECHANISM; SECONDARY SILANES
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om9808615

Three new C 2 symmetric heteroannular dialkyl substituted group IV metallocene dichlorides (CpR)2MCl2 [CpR = C5H4C(Me)2CHMe2; M = Zr (2), Hf (3), Ti (4)] were synthesized as potential catalytic precursors for the dehydropolymerization of silanes to polysilanes. The hindered complexes were generated in fair yield by reaction of 2 equiv of the alkyllithium reagent CpRLi (1) and the corresponding metal halide, MCl4·2THF for 2 and 3 and MCl3·3THF for 4. Crystal structures for compounds 2−4 were obtained and established a pseudotrans configuration of the ancillary ligands in the solid state. The structural features adopted by these compounds to accommodate the large substituents are described with comparisons to known metallocenes. Monoalkyl-substituted metallocenes Cp(CpR)MCl2, M = Ti (5), Zr (6), were also synthesized from 1 and the corresponding monocylopentadienyltrihalide species CpMCl3. Characterization of 2−6 by various NMR techniques in conjunction with solid-state analysis of 2, 3, and 4 permitted interpretation of an interligand mechanism for the observed NOE signals involving the distal protons of the substituted cyclopentadienyl ligand and portions of the alkyl cyclopentadienyl substituent.