Alkylidynes synthesis

Scheme 2. Oxide-abstraction as a route to alkylidyne synthesis.

Scheme 8. High-valent Tp -alkylidyne synthesis from ligand substitution.

Bailey BC, Fan H, Huffman JC, Baik M-H, Mindiola DJ. Intermolecular C—H bond activation reactions promoted by transient titanium alkylidynes. Synthesis, reactivity, kinetic, and theoretical studies of the Ti C linkage. J Am Chem Soc. 2007 129 ... 

Two commonly used synthetic methodologies for the synthesis of transition metal complexes with substituted cyclopentadienyl ligands are important. One is based on the functionalization at the ring periphery of Cp or Cp metal complexes and the other consists of the classical reaction of a suitable substituted cyclopentadienyl anion equivalent and a transition metal halide or carbonyl complex. However, a third strategy of creating a specifically substituted cyclopentadienyl ligand from smaller carbon units such as alkylidynes and alkynes within the coordination sphere is emerging and will probably find wider application [22]. 

Byers, P.K, Carr, N. and Stone, F.G.A. (1990) Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M ( CR)(CO)2 (C6F5)AuC(pz)3 j (M = W or Mo, R — alkyl or aryl, pz — pyrazol-l-yl) crystal structure of pjC PtAu(C6F5)( l3-CMe)(CO)2(PMe2Ph)2 (C6F5)AuC(pz)3 ]. Journal of the Chemical Society, Dalton Transactions, (12), 3701—3708. 

B. The Synthesis and the Chemistry of Metal-Alkylidene and -Alkylidyne Functionalities... 

The alkylidyne tricobalt nonacarbonyl complexes (2) are produced from the reaction of the cobalt tetracarbonyl anion with 1,1,1-trihaloalkanes [4], under conditions analogous to those used for the synthesis of the n-allyl complexes. Although the yields for (2) appear to be low (Table 8.3), they are better than, or comparable with, those obtained by the traditional procedures [8] and are obtained under more amenable conditions. 

Further developments are likely as the chemistry of the compounds described above is explored. Moreover, entirely new dimensions may be added. For example, the synthesis of tungsten-alkylidyne complexes with carba-borane ligands with cage structures smaller than the icosahedral C2B9 fragment should result in the isolation of new electronically unsaturated metal cluster and electron-deficient molecules of types as yet unknown. 

The reversible [2+2] cycloaddition of metal alkylidyne or Fischer-type metal carbyne complexes remains the only general methodology for the synthesis of metallacyclobutadiene complexes. Recent literature revolves principally around the heavier group 6 metals and the investigation of intermediates in catalytic alkyne metathesis (Scheme 25 Equation 45) <1996CHEC-II(lb)887> (W <2005OM4684>, Mo <2003JOM56>). 

Our interest in dimetallacyclobutadienes was triggered when Schrock reported the synthesis of alkylidyne tungsten compounds in a metathesis-like reaction involving W=W bonds [Eq. (2)] (18). 

See also Scheme 17 for the template synthesis of tri(te/t-butyl)-Cp from a dimeric tantalum alkylidyne complex and 3,3-dimethyl-1-butyne. Schemes 8 and 9 show the syntheses following method 2. The 1,3,5-substi-tuted tri(/m-butyl)cyclopentadiene is obtained as the single isomer from both routes. 

Although it may be said that alkylidyne clusters do not contain an unsaturated organic fragment, the chemistry of these compounds is related to that of the alkyne and alkene derivatives, and their synthesis will be discussed briefly. 

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