Heteroscorpionate Rare-Earth Catalysts for the Hydroalkoxylation/Cyclization of Alkynyl Alcohols
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- 作者：Javier Martínez ; Antonio Otero ; Agustín Lara-Sánchez ; José Antonio Castro-Osma ; Juan Fernández-Baeza ; Luis F. Sánchez-Barba ; Ana M. Rodríguez
- 刊名：Organometallics
- 出版年：2016
- 出版时间：June 13, 2016
- 年：2016
- 卷：35
- 期：11
- 页码：1802-1812
- 全文大小：694K
- 年卷期：0
- ISSN：1520-6041
文摘
The chiral, enantiopure bis(pyrazol-1-yl)methane-based NNO-donor scorpionate ligands in the form of the alcohol compounds bpzbeH (bpzbe = 1,1-bis(3,5-dimethylpyrazol-1-yl)-3,3-dimethyl-2-butoxide), bpzteH (bpzte = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-p-tolylethoxide), and (R,R)-bpzmmH ((R,R)-bpzmm = (1R)-1-{(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl}-2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide) have been used to obtain new NNO-heteroscorpionate yttrium and lutetium complexes. The reactions of bpzbeH, bpzteH (racemic mixtures), and (R,R)-bpzmmH (enantiopure compound) with [M{N(SiHMe2)2}3(thf)2] (M = Y, Lu) in a 1:1 molar ratio in toluene afforded the mononuclear bis(silylamide) complexes [M{N(SiHMe2)2}2(κ3-NNO)(thf)] (M = Y, Lu; 1–6), respectively. When the reaction was carried out with a 2:1 molar ratio (ligand to metal precursor) or with excess ligand, homoleptic complexes of the type [Y(κ3-NNO)2(κ-O-NN)] (κ3-NNO = κ-O-NN = bpzbe (7), bpzte (8)) were obtained. Compounds 1 and 3 were used as convenient starting materials for the synthesis of the aryloxide and alkoxide yttrium compounds [Y(OR)2(κ3-bpzbe)] (OR = O-2,6-Me2C6H3 (9), O-CH2(2-CH≡C)C6H4 (10)) and [Y(OR)2(κ3-bpzte)] (OR = O-2,6-Me2C6H3 (11), O-CH2(2-CH≡C)C6H4 (12)). The structures of the complexes were determined by spectroscopic methods, and the X-ray crystal structures of 1, 2, and 7 were also established. Complexes 1–6 are efficient catalysts for the intramolecular hydroalkoxylation of alkynyl alcohols and give TOF values up to 19.4 h–1 at 90 °C for (2-ethynylphenyl)methanol (13) by using the single enantiopure complex 5 as catalyst, producing exclusively the exo-methylene products. The activation parameters ΔH⧧ = 19.93(0.2) kcal/mol, ΔS⧧ = −28.75(0.2) eu, and Ea = 18.61(0.2) kcal/mol are consistent with observations for other catalyst-mediated insertive hydroelementation processes.