Reaction Control of Dynamic Complexes Relevant to Catalysis

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(1)1,2-Diaryl-3,4-diphosphinidenecyclobutenes (DPCB-Y) as low-coordinate phosphorus compounds have been found to serve as extremely strong x-acceptors towards transition metals. Structures and catalytic properties of several organo- palladium(II) and-platinum(II) complexes bearing DPCB-Y ligands have been examined. The DPCB-Y-coordinated palladium complexes provide highly efficient catalysis with hitherto unknown reactivity and selectivity. Representative examples include dehydrative allylation of aniline and active methylene compounds with allylic alcohols, deallylation of allylic esters, amination and cyanation of aryl halides, and hydroamidation of enones. Detailed catalytic mechanisms have been examined for dehydrative allylation of aniline.(2)Dichlororuthenium(II) complexes bearing DPCB-Y ligands efficiently catalyze stereoselective hydrosilylation of diethynylarenes with HSiMe2Ph to afford (Z,Z)-bis(2-silylethenyl)arenes, which undergo bromodesilylation with NBS in a stereospecif … More ic manner giving (Z,Z)-bis(2-bromoethenyl)arenes in high geometrical purity (>98%). The products are good staring materials for the synthesis of geometrically pure all-cis poly(arylene vinylene)s (PAVs), which rapidly undergo photoisomerization to trans-PAVs both in solution and in the solid. This phenomenon has been applied to direct microscale patterning of PAVs onto a quartz substrate.(3)The Fischer-type ruthenium carbenes bearing heavier chalcogen atoms RuCl_2(=CHER)(PCy_3)_2 (E = S, Se, Te) catalyze ring-opening/cross-metathesis of norbornene derivatives with alkenyl chalcogenides to give heterodifunctionalized poly(norbornenes) in high selectivities.(4)The vinylideneruthenium complexes bearing bulky phosphine ligands RuCl_2(=C=CHPh)L_2 (L = PPr^i, PCy_3) serve as good catalyst precursors for (Z)-selective cross-dimerization between arylacetylenes and silylacetylenes in the presence of N-methylpyrrolidine.(5)The platinum complexes having unsymmetrical heteroatom ligands cis-Pt(ER_n)(ER_m)(PMe_2Ph)_2 (E, E' = B, Si, Ge, Sn) have been prepared, and their reactivity towards alkyne-insertion has been examined by kinetic experiments. The reactivity decreases in the order : Pt-B > Pt-Si > Pt-Sn > Pt-Ge. The mechanisms of C-B, C-Si, and C-Ge reductive elimination from platinum(II) centers have also been investigated. Less