Alkyne complexes chemistry

Melikyan GG, Nicholas KM (1995) The Chemistry of Metal-Alkyne Complexes. In Stang... 

Schore, N. E. Transition Metal Alkyne Complexes Pauson-Khand Reaction. In Comprehensive Organometallic Chemistry II Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. Elsevier Oxford, 1995 Vol. 12, pp 703-739. 

Schore NE (1991) Org React 40 1 Schore NE (1991) The Pauson-Khand reaction. In Trost BM (ed) Comprehensive organic synthesis, vol 5. Pergamon Press, Oxford, p 1037 Pauson PL (1985) Tetrahedron 41 5855 Schore NE (1995) Transition metal alkyne complexes Pauson-Khand reaction. In Abel EW, Stone EGA, Wilkinson G (eds) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford, p 703 Iwasawa N (1992) Chem Lett 473... 

The transformation predominates in Group 9 (Rh, Ir) chemistry. Reactions of RhCl(L)2 2 with 1-alkynes give the q -alkyne complexes which slowly convert to the hydrido(alkynyl)s at room temperature. The latter are sensitive to air and not often isolated. Addition of pyridine affords RhHCl(C=CR)(py)(L)2, which readily lose pyridine in hydrocarbon solvents to give square-planar fran.s-RhCl(=C=CHR)(L)2. Alternatively, the Cp complexes Rh(=C=CHR)(L)Cp can be obtained by reaction of the chloro complexes vdth TlCp. In the iridium series, heating for 36h in refluxing toluene afforded the vinylidenes in 80-90% yields. Table 1.2 lists several examples of reactions in which the q -alkyne complexes have been detected. 

Suitable oxidizing agents are [FeCp2] or Ag, while the cationic species may be reduced back to the alkyne complexes using CoCp2. Some of this chemistry has been reviewed [216]. 

The chemistry of alkyne complexes is somewhat more complicated than that of alkene complexes because of the greater possibilities for -n bonding by alkynes and the tendency of some of die complexes to act as intermediates in the formation of other organometallic compounds. 

As with alkenes, alkynes coordinate to platinum in both the zerovalent and divalen oxidation states. Since the chemistry of platinum alkyne complexes is less extensive than that c alkene complexes, this section is not subdivided into complexes of the two types. The divalen compounds of platinum will be covered first, followed by the complexes of platinum in a forms zerovalent oxidation state. 

Hexafluorobutyne-2 will add to platinum(II) complexes. The insoluble complex PtMe HB(pz)3 reacts with dissolution and the five-coordinate alkyne complexes can be isolated (equation 269).815 The coordination about platinum(II) is essentially trigonal bipyrami-dal. The C C triple bond is lengthened on coordination to 1.292(12) A and the alkyne bend-back angle is 34.4(4)°.816 These complexes have a -bonded alkyne ligand, and show different structural and reaction chemistry than platinum(II) acetylide complexes.817-821... 

An earlier review treated the organometallic derivatives, including alkyl, aryl, vinyl, alkynyl, carbonyl, carbene, alkene and alkyne complexes,16 and these will not be treated here (see Table 1 for other books and reviews on organogold chemistry). Two important articles dealing with [AuCl(CO)], including its structure and catalytic properties, have been published recently.97,381... 

In contrast to many stable transition metal-alkyne complexes, cationic cyclopentadienyliron-alkyne complexes are reactive toward a range of nucleophiles. However, since most of the nucleophiles studied were carbanions, discussion of this chemistry is deferred to Volume 4, Chapter 3.2, Section 3.2.3. 

A second populous class of T/2-vinyl complexes has resulted from addition of phosphines, phosphites, isonitriles, and thiolates to neutral d4 alkyne complexes. In particular, recent extensive work by the Davidson group with CpM(CF3C=CCF3)2X (97,176) and other hexafluorobutyne reagents has clarified much of this chemistry. We turn to this realm of Tj2-vinyl chemistry after first considering the one class of dithiocarbamate alkyne complexes known to form tj2-vinyl ligands. 

In 1974, Dickson and Fraser reviewed the already substantial area of cobalt-alkyne complexes.1 Since then the number of examples and applications of this class of organometallic compounds, especially dinuclear complexes, has increased enormously. This review will present the chemistry of polynuclear cobalt-alkyne complexes, with emphasis on the more recent developments. Although there have been many exciting fundamental discoveries, this is a maturing area of research that is finding many important applications in organic synthesis,2 such as the use of [Co2(jU-alkyne)(CO)6] complexes in the synthesis of enediyne antitumor antibiotics.3-4... 

Continuing expansion of the chemistry of polynuclear cobalt-alkyne complexes is expected, especially in the areas of reactivity and synthetic applications, in the coming years. 

The best example of chemical activation in cluster chemistry is the use of Me3NO which results in CO replacement under mild conditions (129). In an interesting example taken from alkyne-cluster chemistry, when Me3NO is used dry a monosubstituted cluster derivative is obtained, but with damp Me3NO a tetranuclear vinylidene complex is isolated (130, 131), as illustrated in Eqs. (4) and (5), respectively. 

Steric differences have been shown to affect the regio-chemistry of cyclization, as the CO inserts in the a-position of the larger alkynyl snbstitnent. However, theoretical stndies on dicobalt hexacarbonyl alkyne complexes have snggested that electronic differences in alkyne substitnents may also exert control over the regiochemistry of cyclizationd Calculations have also provided information on geometries and configurational stabilities of these complexes. 

An important and extensively investigated application of CpCo complex chemistry is the catalyzed synthesis of pyridines from alkynes and nitriles. Dissociation of the L ligands liberates the CpCo fragment to react with alkyne to form a cobaltacyclopentadiene complex. The nitrile coordinates to this intermediate and subsequently undergoes insertion to form a seven-membered cobaltacycle. Reductive coupling gives pyridine and reforms CpCo. Asymmetric alkynes add to the carbon with the bulkier substituent adjacent to the nitrile carbon. 

Athene complexes of platinnm have been well established since the middle of the nineteenth centnry (see Zeise s Salt), bnt TT-complexes of gold were only discovered by Htittel in 1965, with alkyne complexes following in 1972. All of these complexes have very limited stability, and therefore their chemistry is still poorly developed, even today. 

Transition metal carbenes constitute a very important class of molecules that have found a multitude of applications. With reference to manganese, a number of new carbene complexes have been reported recently. The ) -alkyne complex (18) was found to undergo oxidation by dimethyldioxirane to afford the a-keto carbene (19). The fascinating aspect of this reaction is the likely existence of an oxirene intermediate (20). Stable oxirene complexes have never been reported, imdoubtedly because of the extreme instability of the antiaromatic oxirene ring. The possibility of trapping an oxirene by epoxidation of a coordinated alkyne is intriguing. Scheme 10 summarizes the chemistry involved. 

Some of the most prolific reactants in organometallic chemistry are alkynes." At some time or the other every new cluster is reacted with an aUcyne. Not surprisingly, alkyne complexes dominate the C2-containing clusters. Alkynes most commonly bridge the triangular face of the cluster, either as (18) or as (19) ligands. In tetrametallic and... 

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