Alkynes Metal-alkyne complexes

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. 

The vinyl metal intermediate arising from intermolecular nucleophilic addition of an oxygen nucleophile to a metal-alkyne complex has been harnessed for further transformations prior to protonation. An example is the ruthenium-catalyzed benzannulation of 1,5-enedyines that occurs through a tandem sequence involving hydroalk-oxylation, carbometallation, and protonation (Equation (82)).293... 

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... 

In fact, this approach constituted one of the earliest trials. One is introduction of a chiral ligand like glyphos on cobalt by replacing one of the carbon monoxides to obtain an enantiomerically enriched new metal-alkyne complex. The second approach is use of the propargyl alcohol bearing a chiral auxiliary. Replacement of only one carbon monoxide would lead to a mixture of diastereomers. In both cases, a I I mixture of products was obtained, and each diastereomer was separated before the... 

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. 

Carbometallation is a term coined for describing chemical processes involving net addition of carbon-metal bonds to carbon-carbon Jt-bonds [1] (Scheme 4.1). It represents a class of insertion reactions. Whereas the term insertion per se does not imply anything chemical, the term carbometallation itself not only explicitly and clearly indicates carbon-metal bond addition but also is readily modifiable to generate many additional, more specific terms such as carboalumination, arylpalladation, and so on. In principle, carbometallation may involve addition of carbon-metal double and triple bonds, that is, carbene- and carbyne-metal bonds, as well as those of metallacycles. Inasmuch as alkene- and alkyne-metal Jt-complexes can also be represented as three-membered metallacycles, their ring expansion reactions via addition to alkenes and alkynes may also be viewed as carbometallation processes (Scheme 4.1). 

Once an alkyne moiety is introduced into a peptide, e.g., as propargyl glycine (Pgl) in place of a simple glycine in Enk, it can of course be used directly for complexation to a metal complex. Along those lines, we have reacted Co2(CO)g with the peptide Ac-Tyr-Gly-Pgl-Phe-Leu-NH2, to yield the Co2(CO)6 complexed to the Pgl alkyne side chain [32]. In a real SPPS scheme with a pre-formed metal-alkyne complex, the amino acid building block [Tp WI(CO)(ri2-Fmoc-Pgl-OH)] was incorporated to yield the side-chain substituted Enk derivative H-Tyr-Gly-[Tp W(I)(CO)(r 2-Pgl)]-Phe-Leu-OH (Tp tris(3,5-dimethylpyrazolyl)-borate) [44]. 

Although many metal-alkyne complexes are known, probably the most thoroughly studied are those in which the alkyne is coordinated with a dicobalt unit. When this area was reviewed in 1974, more than 170 examples... 

Transition Metal Alkyne Complexes Containing Trifluorophosphine... 

Complexes containing coordinated tertiary phosphines or arsines of the type [Rh2(PF3)4L2(alkyne)] and [Rh2(PF3)2L2(alkyne)] (L = mono-dentate, L = bidentate ligand) are readily obtained by displacement of PF3 from [Rh2(PF3)6(alkyne)] under mild conditions (method D). There are also reports of displacement of CO by PF3 from an alkyne metal carbonyl complex (method E) e.g., 113). 

Chung CY. Transition metal alkyne complexes the Pauson-Khand reaction. Coord. Chem. Rev. 1999 188 297-341. Brummond KM, Kent JL. Recent advances in the Pauson-Khand reaction and related (2 + 2+1) cycloadditions. Tetrahedron 2000 56 3263-3283. 

Keun Chung, Y. Transition metal alkyne complexes the Pauson-Khand reaction. Coord. Chem. Rev. 1999, 188, 297-341. 

The preceding pair of resonance descriptions is called the Dewar Chatt Duncanson model of tt bonding. Similar pictures can be drawn for metal-alkyne complexes, regardless of whether the second tt bond is acting as a tt donor, and for metal-1,3-diene complexes. 

The Pauson-Khand reaction gives the same product as the group 4 metal-mediated reductive coupling and carbonylation, and both reactions proceed by essentially the same mechanism formation of an alkyne-metal tt complex, insertion of an alkene, insertion of CO, and reductive elimination. Some details differ, however. When an alkyne is added to Co2(CO)g, CO evolves, and an isolable, chromatographable alkyne-Co2(CO)6 complex is obtained. This butterfly complex contains four Co(II)-C bonds, and the Co-Co bond is retained. The formation of the alky n e-C o2 (C O) 6 complex involves the formation of an ordinary tt complex of the alkyne with one Co(0) center, with displacement of CO. The tt complex can be written in its Co(II) cobaltacyclopropene resonance structure. The tt bond of the cobaltacyclopropene is then used to form a tt complex to the other Co center with displacement of another equivalent of CO. This second tt complex can also be written in its cobaltacyclopropene resonance structure. The alkyne-Co2(CO)6 complex has two 18-electron Co(II) centers. 

Eor a recent review, see Schore NE (1995) Transition Metal Alkyne Complexes Pauson-Khand Reaction. In Louis Hegedus (vol ed), Abel EW, Stone EGA,Wlkmson G (eds) Comprehensive OrganometaUic Chemistry II. Pergamon, Kidlington, vol 12,703... 

The NLO properties of organometallic and coordination complexes are also rich (21, 184, 279-296). Metal-alkyne complexes were first reported 1960 (297) and have recently attracted significant interest because of their potential in materials applications (2, 298). Studies of these types (299) have resulted in the development of structure-NLO response relationships for quadratic optical nonlinearities (p-value), which increase with valence electron count and ease of oxidation of metal. The amplitude is also tunable by ancillary ligand modification and substitution. Select small alkynyl complexes have been shown to exhibit p values at 1064 nm > 2600 x 10 ° esu (299). 

The resulting expansiveness of this field prevents a comprehensive review. It is our intention, therefore, to highlight some of the most important and recent developments in the chemistry of metal-alkyne complexes. We will largely limit our coverage to that chemistry which clearly involves the intervention of metal- i-bonded alkyne complexes. We thus exclude the chemistry of metal-acetylide derivatives and mention only briefly the burgeoning number of metal-catalyzed reactions for which alkyne complexes are only presumed intermediates. Prior reviews of metal-alkyne chemistry may be consulted for more complete coverage of the older literature [3]. 

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