Polycyclic systems transition metals

Virtually all types of metal ions have been complexed with macrocyclic ligands. " Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22). Macrocyclic ligands derived from the Schiff base and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions. The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems. Transition metd complexes with thioether and phosphorus donor macrocycles are also known. ... 

Transition metal catalyzed intermolecular carbocyclization has been used in the construction of six-membered ring systems (10, 352) and provides a powerful approach to the construction of complex polycyclic systems. The rhodium-catalyzed intermolecular [2 - - 2 - - 2] carbocychzation of heteroatom-tethered 1,6-enynes with symmetrical and unsymmetrical alkynes affords the corresponding bicyclohexadienes in a highly efficient and regioselective... 

As demonstrated throughout this review, rapid progress has been made in the field of the total synthesis of polycyclic ether natural products. Particularly, most of these accompUshments were concentrated over the last five years. Convergent assembly of the polycycUc ether fragments is, of course, the key to successful construction of the large ladder-shaped polycycUc ether system. In this context, the completed total syntheses have benefited enormously from the transition-metal catalyzed carbon-carbon bond forming reactions, such as olefin metathesis and cross-coupUng reactions. These powerful tools will imdoubtedly enable even more impressive accompUshments in this field. 

PO can be made degradable by means of additives. The types of additives include aromatic ketones (benzo-phenone and substituted benzophenones [47], qui-none), aromatic amines (trisphenylamine), polycyclic aromatic hydrocarbons (anthracene, certain dyes such as xanthene dyes), or transition metal organic compounds. The transition metal compounds of Fe, Co, Ni, Cr, Mn are widely used. Organo-soluble acetyl acetonates of many transition metals are photooxidants and transition metal carboxylates are also thermal pro-oxidants. Co acetylacetonate appears to be an effective catalyst for chemical degradation of PP in the marine environment. The preferred photoactivator system is ferric dibutyldithiocarbamate with a concentration range of 0.01. 1%. Scott has patented the use of organometallic compounds hke iron (ferric) dibutyldithiocarbamate or Ni-dibutyl-dithiocarbamate [48]. Cerium carboxylate [49] and carbon black are also used in such materials [50]. 

Chatani N, Kataoka K, Mural S, Furukawa N, Seki Y. Con-stmction of novel polycyclic ring systems by transition-metal-catalyzed cycloisomerization of ene-ene-ynes. Interception of a carbenoid intermediate in skeletal reorganization of enynes. J. Am. Chem. Soc. 1998 120 9104-9105. 

The transition metal catalyzed cycloaddition-carbocyclization reaction is an effective technique for the formation of complex polycyclic systems [4]. Various versions of these reactions are described below, including [2+2+2+1] [154], [4+2+2] [155], [5+1+2+1] [156], [3+3+1] [157] and [5+2+1] [158] cycloaddition. These reactions are often used for the synthesis of complex molecules and natural products [158]. On the other hand, the discovery of natural 5-7-6-S tetracyclic condensed system, such as Caribenol A [159], contribute to the development of highly efficient synthetic methods for the creation of polycyclic cores in one step starting with the enediynes [160]. 

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