Synthesis of coumarin derivatives by palladium complex catalyzed intramolecular Heck reaction: Preparation of a 1,2-cyclobutadiene-substituted CpCoCb diphosphine chelated palladium complex

A cobalt-sandwich diphosphine chelated palladium complex 2, [(eta(5)-cyclopentadienyl)(eta(4)-1,2-diphenyl-3,4-bis(diphenylphosphino-kappa P)cyclobutadiene)cobalt(I)]palladium(II)dichloride, was prepared from the reaction of a cyclobutacliene-substituted CpCoCb diphosphine 1, (eta(5)-cyclopentadienyl) (eta(4)-1,2-diphenyl-3,4-bis-diphenylphosphinocyclobutadiene)cobalt(I), with one molar equivalent of Pd(COD)Cl-2. Both compounds were characterized by spectroscopic means as well as single-crystal X-ray diffraction methods. Application of purified 2 as the catalytic precursor in intramolecular Heck cyclization reaction on 4-hydroxycoumarin resulted in the formation of several derivatives with intensity enhanced fluorescence property. (C) 2009 Elsevier B.V. All rights reserved.