Heteroscorpionate Rare-Earth Catalysts for the Hydroalkoxylation/Cyclization of Alkynyl Alcohols

Martinez, Javier; Otero, Antonio; Lara-Sanchez, Agustin; Antonio Castro-Osma, Jose; Fernandez-Baeza, Juan; Sanchez-Barba, Luis F.; Rodriguez, Ana M.


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-dimethylpyr az ol- 1-y1)-3,3- dim e thy1-2-but oxide), bpzteH (bpzte = 2,2-bis(3,5-dimethylpyrazol-l-y1)-1-p-tolylethoxide), and (R,R)-bpzmmH ((R,R)-bpzmm = (1R)-1-{(1R)-6,6dimethylbicydo [3.1.1]-2-hepten-2-yl}-2,2-bis (3,5-climethylpyrazol-1-yl)ethoxide) have been used to obtain new NNOheteroscorpionate yttrium and lutetium complexes. The reactions of bpzbeH, bpzteH (racemic mixtures), and (R,R)bpzmmH (enantiopure compound) with [M{N(SiH.Me-2)(2)}(3)(thf)(2)] (M = Y, Lu) in a 1:1 molar ratio mononuclear bis(silylamide) complexes [M{N(SiHMe2)(2)}(2)(x(3)-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(kappa 3NNO)(2)(x-O-NN)] (kappa(3)-NNO = x-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)(x(3)-bpzbe)] (OR = 0-2,6-Me2C6H3 (9), O-CH2(2-CH C)C6H4 (10)) and [Y(OR)(2)(kappa(3)-bpzte)] (OR = O-2,6-Me2O6H3 (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 at 90 degrees C for (2-ethynylphenyl)methanol (13) by using the single enantiopure complex 5 as catalyst, producing exclusively the exo-methylene products. The activation parameters Delta H-double dagger = 19.93(0.2) kcal/mol, Delta S-double dagger = 28.75(0.2) eu, and E-a = 18.61(0.2) kcal/mol are consistent with observations for other catalyst-mediated insertive hydroelementation processes.

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Título según WOS: ID WOS:000377925600026 Not found in local WOS DB
Título de la Revista: ORGANOMETALLICS
Volumen: 35
Número: 11
Fecha de publicación: 2016
Página de inicio: 1802
Página final: 1812


Notas: ISI