Insertion products from photolysis of Tp′(CO)3WH and alkynes

Irradation of Tp'(CO)(3)WH in the presence of alkynes produces a diverse array of products, including eta(2)-vinyl, eta(2)-acyl, metallafuran, and carbyne complexes. A common mechanistic feature consistent with the observed distribution of products is cis insertion of alkynes into a photogenerated "Tp'(CO)(2)WH" species. Initial cis 2,1-insertion of the alkynes leads to eta(2)-vinyl and eta(3)-allyl products, while cis 1,2-insertion ultimately produces eta(2)-acyl, metallafuran, and carbyne products. An X-ray structure of a metallafuran product, Tp'(CO)(2)W(eta(2)(C,O)C(Bu-n)CHC(=O)CH=CHBun), shows trans stereochemistry for the double bond of the pendant 1-hexenyl group, which indicates that cis 1,2-insertion of the first equivalent of alkyne forms an intermediate eta(1)-vinyl complex, additional support for eta(1)-vinyl intermediates is present in the eta(2)-acyl. product Tp'(CO)(2)W(eta(2)(C,O)-C(=O)CH=CHC(CH3)(3)), which evinces a trans double bond as assayed via H-1 NMR. Irradiation of Tp'(CO)(3)WH in the presence of Me3SiC=CCH3 produces two isomers of Tp'(CO)(2)W(eta(3)-syn-CH2CHCHSiMe3) which differ in the orientation of the allyl fragment relative to the metal center. Heating of the allyl complex results in an unusual eta(3)-allyl to carbyne rearrangement.