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

AbstractReaction of one equivalent of H2(acen), H2(cis‐Cyacen) or H2(trans‐Cyacen) with [Zr(CH2SiMe3)4] at room temperature afforded [Zr(acen)(CH2SiMe3)2] (1), [Zr(cis‐Cyacen)(CH2SiMe3)2] (2) or [Zr(trans‐Cyacen)(CH2SiMe3)2] (3), respectively (acen=C2H4(NCMeCHC(O)Me)2; Cyacen=1,2‐C6H10(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 H2(cis‐Cyacen) and SiMe4 as the soluble products. Compound 2 reacted cleanly with two equivalents of tBuOH to afford [Zr(cis‐Cyacen)(OtBu)2] (4), but excess tBuOH caused both SiMe4 and H2(cis‐Cyacen) elimination. The 1 : 1 reaction of H2(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(SiMe3)2}2] (7) was synthesized via the reaction of [Zr(acen)Cl2] with two equivalents of Li{N(SiMe3)2}, but was also thermally unstable as a solid and in solution at room temperature. Compounds 1–3, 5 and 7 were crystallographically characterized.