Synthesis, Structures, and Thermal Stability of Dialkyl and Bis(amido) Zirconium(IV) Acen Complexes

Abstract

Reaction of one equivalent of H 2 (acen), H 2 (cis-Cyacen) or H 2 (trans-Cyacen) with [Zr(CH 2 SiMe 3 ) 4 ] at room temperature afforded [Zr(acen)(CH 2 SiMe 3 ) 2 ] (1), [Zr(cis-Cyacen)(CH 2 SiMe 3 ) 2 ] (2) or [Zr(trans-Cyacen)(CH 2 SiMe 3 ) 2 ] (3), respectively (acen = C 2 H 4 (NCMeCHC(O)Me) 2 ; Cyacen = 1,2-C 6 H 10 (NCMeCHC(O)Me) 2 ). These alkyl compounds are trigonal prismatic in the solid state, and whereas 1 and 3 decomposed without sublimation above 120 °C (5-10 mTorr), 2 sublimed in > 95 % yield at 85 °C (5-10 mTorr). However, heating solid 2 at 88 °C under static argon for 24 hours resulted in extensive decomposition to afford H 2 (cis-Cyacen) and SiMe 4 as the soluble products. Compound 2 reacted cleanly with two equivalents of t BuOH to afford [Zr(cis-Cyacen)(O t Bu) 2 ] (4), but excess t BuOH caused both SiMe 4 and H 2 (cis-Cyacen) elimination. The 1 : 1 reaction of H 2 (acen) with [Zr(NMeEt) 4 ] did not proceed cleanly, and 8-coordinate [Zr-(acen) 2 ] (5) was identified as a by-product; this complex was isolated from the 2 : 1 reaction. A zirconium amido complex, [Zr(acen)(NMeEt) 2 ] (6) was accessed via the reaction of 1 with two equiv. or excess HNMeEt, but decomposed readily in solution at room temperature. More sterically hindered [Zr-(acen){N(SiMe 3 ) 2 } 2 ] (7) was synthesized via the reaction of [Zr(acen)Cl 2 ] with two equivalents of Li{N(SiMe 3 ) 2 }, but was also thermally unstable as a solid and in solution at room temperature. Compounds 1-3, 5 and 7 were crystallographically characterized.