Cationic Zirconium Dialkyl and Alkyl Complexes Supported by DAC (Deprotonated 4,13-Diaza-18-crown-6) Ligation

The synthesis, characterization, and reactivity of a series of neutral and cationic Zr alkyls supported by DAC (deprotonated 4,13-diaza-18-crown-6) ligation are reported. Reaction of H 2 DAC with Zr(CH 2 Ph) 4 affords a 1:4 mixture of cis - and trans -Zr(DAC)(CH 2 Ph) 2 ( cis-/trans -1a ). The pure isomers undergo slow cis − trans isomerization in solution to regenerate the 1:4 cis:trans equilibrium mixture. X-ray crystallographic results are reported for both cis - and trans - 1a . Reaction of Zr(CH 2 Ph) 2 Cl 2 with H 2 DAC, followed by treatment with LiR (2 equiv), gives cis -Zr(DAC)R 2 (R = CH 2 SiMe 3, cis -1b; R = CH 2 CMe 3, cis - 1c ) exclusively. Alkyl abstraction from cis - or trans -1a using B(C 6 F 5 ) 3 (1 equiv) produces the stable cation [Zr(DAC)(CH 2 Ph)] + [B(CH 2 Ph)(C 6 F 5 ) 3 ] - ( 2a ) as a yellow oil. NMR studies on 2a in CD 2 Cl 2 show no evidence for η 2 -benzyl formation or anion coordination. Protonation of cis - or trans -1a with [ n -Bu 3 NH] + [BPh 4 ] - similarly yields [Zr(DAC)(CH 2 Ph)] + [BPh 4 ] - ( 2b ). Cation 2a reacts with t -BuNC to form the vinyl amide complex [Zr(DAC){N( t -Bu)CH CHPh}] + [B(CH 2 Ph)(C 6 F 5 ) 3 ] - ( 3 ). p -Tolylacetylene undergoes catalytic dimerization to ( Z )-1,4-di- p -tolyl-1-buten-3-yne in the presence of 2a .