Highly efficient regio- and stereoselective dimerization of (hetero)aromatic terminal alkynes by organo rare-earth metal catalysts

The yttrium dialkyl complex [(L)Y(CH2SiMe3)(2)] (1, L = 1, 4, 6-trimethyl-N-(2-pyrrolidin-1-ylethyl)-1, 4-diazepan-6-amine), activated by (PhNMe2H)(B(C6F5)(4)), catalytically dimerizes a range of (hetero)aromatic alkynes to Z-enynes with 100% selectivity and high rates. Catalyst turnovers up to 2000 were readily achieved in preparative scale (5-10 mmol) reactions. For comparison, the related E-enynes were produced with a permethyl lanthanocene catalyst.