Alkylidynes bonding

Despite early reports on the addition of hydroxyl groups to tungsten-alkylidyne bonds [5-7], recent work has showed that the triple-bond remains untouched, at least in the cases involving the reaction of [Mo(=CEt)(N BuPh)3] [13], [W(=CCMe3) (CH2Me3)3] [26, 27] and [Mo(=CCMe3)(CH2Me3)3] with silica [28]. 

Alkynes insert into both metal-alkylidene and metal-alkylidyne bonds, as shown in reactions (s) and (t), respectively ... 

The stability of the metal-alkylidyne bond, especially for tungsten, induces other remarkable rearrangements fixtm a variey of systems. The high-yield s5mthesis of compound 49 upon photolysis of hexamethyltungsten(VI) in neat trimethylphosphine involves a methyl migration onto a proposed carbyne intermediate (Scheme 19).I 1... 

Although [Co3(w-CH)2Cp3] is Inert to CO at room temperature, the protonated cluster adds CO to give [Co3(M3-n -HOC-CH)(M3-CH)Cp3]t an overall Insertion of HCO Into a metal-alkylidyne bond NO similarly inserts into related neutral dialkylidyne clusters to form the novel clusters [Co3(M3-n -RC-NO)-... 

The alkene-W complexes used in this study are complexes 33, 166, and 168 (Schemes 5 and 31). The deprotonation of the W-alkene functionality has been carried out on 166, which has three methyl substituents at the C=C bond, in order to prevent any rearrangement of the 1-metallacyclopropene to the corresponding alkylidyne.22b The reaction of 166 with LiBu led to the 1-metallacyclopropene 169 (Scheme 32), which was isolated in quite good yield. The alkylidene 169, a very stable compound, was characterized both in solution and in the solid state.28 The h NMR spectrum shows a four-fold symmetry calixarene skeleton, while the 13C NMR spectrum contains a resonance at 271.0 ppm for the alkylidene carbon. 

A.J. Carty, Guelph-Waterloo Centre What are the frequencies of the metal-carbon (v(M=C)) stretching frequencies in the tungsten alkylidyne compounds One might expect these to be quite high in view of the x-ray data showing short M=C bonds and evidence of multiple bond reactivity. 

We referred earlier to the significance of reactions at the alkylidyne carbon atoms of the dimetal species. Our studies in this area are in a preliminary stage, but Schemes 1 and 2 summarise some chemistry at the bridged carbon centres for the compounds (1 ) and (3,)(12). It will be noted that protonation of the neutral bridged al ylidyne compounds yields cationic alkylidene species in which one C—C bond of the tolyl group is n2 co-ordinated to tungsten, a feature revealed by both n.m.r. and X-ray diffraction studies. 

W.L. Gladfelter, University of Minnesota What is the possibility of forming carbon-carbon bonds using two metal alkylidyne fragments ... 

F.G.A. Stone With increasing frequency, as our work in this area develops, we are observing reactions in which the metal alkylidyne fragments link to form C-C bonds Please refer to compounds (39) and (40), and the relevant references to these species. 

A corresponding Lewis-like picture can be developed for triply bonded metal alkylidynes (H MCH), such as the duodectet-rule-conforming examples... 

Finally, one can readily visualize various duodectet-rule-conforming alkyli-dene/alkylidyne complexes with more extensive multiple bonding, such as... 

For a general review of metal-ligand multiple bonds, see W. A. Nugent and J. M. Mayer, Metal-Ligand Multiple Bonds The Chemistry of Transition Metal Complexes Containing Oxo, Nitrido, Imido, Alkylidene, or Alkylidyne Ligands (New York, Wiley, 1988). 

W=W triple bond and formation of both nitrido and alkylidyne complexes of WV1. Crystal structure determination94 of [(OBu )3W=N] and [(OBu )3W IMe]2 has shown that the nitrido complex is polymeric with unsymmetrical W—N—W bridges. The alkylidyne complex is dimeric with a short W—C bond length of 1.76 A. As expected, this distance is significantly shorter than the one observed for the W—C double bond. 

Molybdenum(VI) compounds containing Mo—C bonds are a recent addition to the literature. These compounds include both oxo and non-oxo species. The latter have an alkylidyne (alternatively formulated as an alkylcarbido) group which is a bonding equivalent to the oxo group. 

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