This account provides a comprehensive overview of the development of gold and platinum catalysis of the enyne cycloisomerization. The use of these soft, alkynophilic metals enables mild, chemoselective and efficient transformations of a variety of readily available acyclic enynes to a wide range of synthetically useful carbocyclic and heterocyclic products. The review is organized according to diverse structural types of enynes that undergo skeletal cycloisomerizations. The account begins with an overview of transformations of primarily 1,6-enynes to 1-alkenylcyclopentenes, bicyclo[4.1.0]heptenes, methylenecycloalkenes, bicyclo[4.3.0]nonadienes and bicyclo[3.2.0]heptenes. This section is followed by the discussion of cycloisomerizations of 1,5-enynes, which enable a rapid access to a range of other cyclic products, including bicyclo[3.1.0]hexenes, cyclohexadienes, heterobicycloalkenes, methylenecyclopentenes, naphthalenes and methyleneindenes. In addition, the [3,3] rearrangement of 1,5-enynes provides efficient access to the corresponding allenes. The account concludes with an overview of the most recent studies on gold- and platinum-catalyzed cycloisomerizations of 1,4- and 1,3-enynes. Due to the rapidly increasing interest in this area during the past three to five years, we believe that this review provides a timely and comprehensive discussion of the development gold- and platinum-catalyzed cycloisomerization starting from the initial pioneering investigations to the latest advances in the field. A significant emphasis is placed on the mechanistic discussion of the observed manifolds of skeletal reorganizations.

Gold and platinum catalysis of enyne cycloisomerization

Interest in therapeutic applications of carbon monoxide release to physiological targets has led us to explore a photochemical strategy for such CO delivery. Here, we describe the photoactivated carbon monoxide releasing moiety (photoCORM), W(CO)(5)(TPPTS)(3-) (1), an air-stable, water-soluble tungsten(0) carbonyl complex of the trianionic ligand tris(sulphonatophenyl)phosphine. Near-UV photolysis of 1 in an aqueous buffer solution leads to the high quantum yield release of a single CO, the formation of which has been verified by three analytical methodologies. Furthermore, in aerated media, additional CO is slowly released from the W(CO)(4)(H(2)O)(TPPTS)(3-) photoproduct owing to autoxidation of the tungsten center. Thus, 1 serves as a carbon monoxide releasing moiety both in the primary photochemical reaction and in the secondary reactions of the initially formed photoproduct. The three methodologies for quantifying CO release under these physiologically relevant conditions are also described.

A Photochemical Precursor for Carbon Monoxide Release in Aerated Aqueous Media

Molybdenum η3-Allyl Dicarbonyl Complexes as a New Class of Precursors for Highly Reactive Epoxidation Catalysts with tert-Butyl Hydroperoxide

The fortuitous discovery of the seven-coordinate complexes [MI2(CO)3(NCMe)2] (M = Mo or W) is described; the wide- ranging chemistry of these compounds is discussed together with the use of the effective atomic number rule in predicting their reactions. The four structural types of seven-coordinate halocarbonyl complexes derived from [MI2(CO)3(NCMe)2] are described. The applications of the [MXY(CO)3(NCMe)2] (X = Y = Br, I; X = Cl, Br, Y = I; X =Cl, Y = GeCl3, SnCl3) system in both alkene metathesis catalysis and nitrogen fixation are also discussed. The synthesis of organometallic complexes containing six different ligands together with the preparation and stereochemical properties of the first structurally characterised {MABCDEF}2 dimer, [Cl(CO)(PPh3)(η2-MeC2Me)Mo(µ-NCS)(µ-SCN)MoCl(CO)(PPh3)(η2-MeC2Me)] are described.

Seven-coordinate halocarbonyl complexes of the type [MXY(CO)3(NCMe)2] (M = Mo, W; X, Y = halide, pseudo halide) as highly versatile starting materials

A Four-Electron π-Alkyne Complex as Precursor for Allenylidene Derivatives: Preparation, Structure, and Reactivity of [Os(η5-C5H5)(CCCPh2)L(PiPr3)]PF6 (L = CO, PHPh2)

Paul K. Baker

Papers

The Organometallic Chemistry of Halocarbonyl Complexes of Molybdenum(II) and Tungsten(II)

The Organometallic Chemistry of Halocarbonyl Complexes of Molybdenum( II) and Tungsten(II)