CREATION AND CATALYTIC PROPERTIES OF ORGANOTRANSITION METAL COMPLEXES BEARING PHOSPHAALKENE LIGANDS

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(1)Electronic and steric properties of 1,2-diaryl-3,4-bis(2,4,6-tri-t-butylphenylphosphinidene)cyclobutene ligands [aryl=4-methoxyphenyl (DPCB-OMe) ; phenyl (DPCB) ; 4-trifluoromethylphenyl (DPCB-CF_3)] have been investigated using their methylplatinum(II) and palladium(II) complexes. It has been found that DPCB-Y ligands possess intermediate magnitude of σ-donating ability between common diimine and diphosphine ligands, but be much stronger π-acceptors than the other supporting ligands.(2)The mechanism of dehydrative condensation of allylic alcohols and aniline (i.e. N-allylation of aniline) catalyzed by palladium DPCB-OMe complex has been examined by model studies of possible intermediates as well as kinetic investigations. A novel process involving a hydridopalladium intermediate has been proposed for C-O bond cleavage of allylic alcohol to give (π-allyl)palladium complexes.(3)(π-Allyl)palladium triflate bearing DPCB-OMe ligand efficiently catalyzes deallylation of a variety of ally … More l ethers in aniline to give corresponding alcohols in high yields under mild conditions. The same complex serves as a highly active catalyst for cyclodehydration of cis-2-butene-1,4-diol with active methylene compounds to give 2-vinyl-2,3-dihydrofurans.(4)Cationic complexes of the formula [Pd(MeCN)_2(DPCB-Y)](OTf)_2 and [Rh(MeCN)_2(DPCB-Y)](OTf) have been prepared. The former shows high catalytic activity towards conjugate addition of benzyl carbamate to α,β-unsaturated ketones.(5)Palladium or copper complexes bearing DPCB catalyze cross-coupling of aryl halides with anilines, organotin reagents, or zinc cyanide.(6)Dichlororuthenium complex bearing DPCB-OMe ligand catalyzes highly stereoselective hydrosilylation of diethynylarenes with HSiMe_2Ph to give (Z,Z)-bis(2-silylethenyl)arenes. Treatment of the hydrosilylation products with NBS causes bromodesilylation in a stereospecific manner, giving (Z,Z)-bis(2-bromoethenyl)arenes with high geometrical purities (>98%). (Z,Z)-Bis(2-bromoethenyl)benzenes thus obtained have been applied to the synthesis of geometrically pure all-cis poly(phenylene vinylene)s (PPVs), which are synthesized by Suzuki-Miyaura-type polycondensation with 2,5-dioctyloxy-1,4-benzenediboronic acid. The all-cis PPVs undergo one-way photoisomerization to the corresponding trans-PPVs both in solution and in the solid. This phenomenon is applied to direct microscale patterning of PPVs onto a quartz substrate. Less