Addition of diazoalkanes to alkyne(pentacarbonyl) /chromium and /tungsten */ formation of 3H-pyrazole complexes
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چکیده
Photolysis of [M(CO)6] (M /Cr, W) in CH2Cl2 at /78 8C generates [(CO)5M(CH2Cl2)]. Subsequent sequential reaction of [(CO)5M(CH2Cl2)] with terminal alkynes, HC /CR (R /COOMe, Ph, p -Tol), and diazoalkanes, R (R)CN2 (R 1 /Me, Et, Ph; R2 /Me, Et) affords 3H -pyrazole complexes, [(CO)5M / N N C(R) C(H) C /(R)(R)]. These complexes are derived from addition of diazoalkanes to alkyne complex intermediates, [(CO)5M(HC /CR)]. Their vinylidene tautomers, [(CO)5M /C /C(R)H], present in solution in equilibrium with the alkyne complexes, do not react. Likewise, isolable disubstituted vinylidene complexes, [(CO)5M /C / C(R‘)R*], do not add diazoalkanes. # 2002 Elsevier Science B.V. All rights reserved.
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