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( h 5 -Cyclopentadienyl)( h 4 -di- and tetra-phosphorylcyclobutadiene)cobalt( I ): Synthesis, structure, and formation of 1-D coordination polymer† Shigeru Sasaki,* Yoshihiro Tanabe and Masaaki Yoshifuji* Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan. E-mail: yoshifj@mail.cc.tohoku.ac.jp; Fax: +81 22 217 6562; Tel: +81 22 217 6558 Received (in Cambridge, UK) 17th May 2002, Accepted 11th July 2002 First published as an Advance Article on the web 25th July 2002 ( h 5 -Cyclopentadienyl)( h 4 -di- and tetra-phosphorylcyclobu- tadiene)cobalt( I ) complexes were synthesized by the reaction of mono- and diphosphorylacetylenes with CpCo(CO) 2 , respectively. The tetraphosphoryl derivative has proved to work as a bis-bidentate ligand affording a one-dimensional coordination polymer with Ce( III ). Cyclic p -conjugated systems fully substituted by heteroatoms have attracted considerable attention, since they are expected to have a unique structure due to intramolecular interaction between the adjacent functional groups, unique physical properties due to intermolecular interaction between p -conju- gated systems and the functional groups, and ability for coordination or hydrogen bonding to form a novel molecular assembly. However, the number of cyclic p -conjugated systems carrying neighbouring phosphorus functional groups is still limited. Pentaphosphinocyclopentadienyl complex, 1 1,2,3,4-tetraphosphinobenzene, 2 tetraphosphorylbenzoqui- none 3 have been reported so far. Oligomerization of acetylenes by ( h 5 -cyclopentadienyl)cobalt( I ) complexes 4 is a general method to prepare p -conjugated systems such as benzenes, ( h 4 - cyclobutadiene)( h 5 -cyclopentadienyl)cobalt( I ), and cobaltacy- clopentadienes, depending on the substrates and conditions. In fact, hexaborylbenzene was synthesized by the reaction of diborylacetylene with CpCo(CO) 2 . 5 Herein, we report synthesis of ( h 5 -cyclopentadienyl)( h 4 -di- and tetra-phosphorylcyclobuta- diene)cobalt( I ) complexes by the reaction of phosphorylacety- lenes with CpCo(CO) 2 , and their structures, together with redox properties and unique transition metal complex formation. Acetylene 1a 6 was allowed to react with CpCo(CO) 2 in refluxing xylene and the reaction was monitored by 31 P NMR spectroscopy (Scheme 1). Formation of the cyclobutadiene complex 3a as a single isomer without significant side reactions was confirmed by disappearance of the signal of alkynylphos- phoryl group of 1a ( d P = 2 5.3) and growing signals due to the phosphoryl group of 3a ( d P = 20.6) attached to the cyclobuta- diene. Acetylene 1b 7 afforded complex 3b as a main product similarly to 1a except for the formation of a significant amount of a side product. 8
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