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ABSTRACT The doubly charged Lewis acid precursors [P(2-Py)3W(
CO)(NO)2](SbF6)2 ( 5 ) and [P(2-Py)3W(CO)(NO)2](BF4)2 are
conveniently synthes-ized by reactions of P(2-Py)3W(CO)3 and 2
equiv. of NOBF4 and NOSbF6 respectively. This kind of
organotungsten Lewis acids have been demonstrated to catalyze
Diels-Alder reactions between the dienes cyclopentadiene,
cyclohexadiene, and the enones methyl vinyl ketone, and
crotonaldehyde. The best catalysis conditions were provided when
0.3 mol % of [P(2-Py)3 W(CO) (NO)2](BF4)2 was used as Lewis acid
catalyst in CH2Cl2 solvent at reaction time of 0℃. There were >
99 % substrate conversion with the Diels-Alder reaction products
of 97 % endo selectivity. Catalytic polymerization of styrene,
isoprene, cyclopentadiene, and cyclohexadiene can also be
promoted by the same Lewis acids. The best reaction conditions
were observed, when CH3NO2 was used as a solvent, and when the
catalysis was performed at room temperature. The catalysis shows
strong solvent, temperature, and catalyst loading effects. The
kinetic behaviors of these Lewis acid catalyzed reactions have
been examined by 1H-NMR spectroscopy. Both the Diels-Alder
reactions and styrene polymerization follow the first-order
kinetics on substrate conc-entration. The long chain bidentate
ligand [ CH2CH(CH2)9N(H)P(O)(2-Py)2 ( 3 ) ] was also synthesized
by treating [ CH2CH(CH2)9N3 ( 1 ) ] with P(2-Py)3 in the
presence of water moisture.
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