Reactions Involving Isocyanide and Carbon Monoxide Ligands

REACTIONS INVOLVING ISOCYANIDE AND CARBON MONOXIDE LIGANDS 

Isocyanide ligands and carbon monoxide (C==X, where X = NBu, N-2,6-dimethylphenyl, and O) react in hydrocarbon solvents with (Pr 0)4W2-( i-CSiMe3)2 to give compounds of formula (PriO)(X=)W(/i-CSiMe3)-( i-fj2, j1-CCSiMe3)W(OPri)3 (50). The generic VB pictorial description of these molecules is shown in XVIII. 

Reactions employing CO give a product which is an oil at room temperature but a waxy crystalline product at low temperatures. Reactions employing CO, where C represents 92 g atom % 13C, show it is the resonance at approximately 250 ppm which is derived from CO. Moreover, there is 13C—13C coupling to the carbon signal at about 170 ppm of 35.4 Hz. 

Reactions employing C 0, where 0 represents 98 g atom % 18O, have allowed identification of v(W— lfiO) and v(W=180) absorptions at 945 and 900 cm-1, respectively. In the infrared spectra of the products derived from reactions involving CO (natural abundance) and CO, bands at 1722 and 1690 cm 1, respectively, can be assigned to v(C=C) of the r,7t-alkynyl ligand (57). 

It is possible to propose a scheme, based on the alkyne insertion/addition reaction, for reactions involving these C=X molecules. Whereas the alkynes give stable 1,3-dimetallated allyl derivatives, the analogs involving C—C bond formation with RNC and CO would be expected to be less stable and 

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