Two, bifunctional side-chain cyclopentadienylmanganese tricarbonyl complexes, 7 (pyridine and ketone side chain) and 14 (thioamide and pyridine side chain), were prepared and converted to chelates following CO dissociation by UV irradiation. Both pyridine (8) and carbonyl (9) chelates are observed following irradiation of 7. In contrast, only thioamide chelate ( 16) is observed following irradiation of 14 even though a pyridine group was available. Visible irradiation isomerizes the pyridine chelate 8 to the carbonyl chelate 9, which thermally isomerizes back to 8 at 25 °C in a few minutes, demonstrating a photochromic response from a cyclopentadienyl-manganese complex based on a linkage isomerization of a tethered functional group. DFT calculations predicted that the activation enthalpy of thermal linkage isomerization would be 20.8 kcal/mol and that the mechanism is likely an associative process that does not involve a simple dissociation of the manganese bond to the side-chain ketone. The DFT calculations were supported by subsequent dynamic NMR experiments that yielded an activation enthalpy and entropy of 21.4 ( 0.8 kcal/mol and 3.5 ( 0.1 eu, respectively. The studies indicate that a compound with a tethered, coordinated functional group, which is otherwise not labile, can isomerize by a low-energy pathway if there is an appropriate "conduit" to another functional group with a stronger metal-ligand bond. Thus, the preparation of photochromic organometallic complexes based on linkage isomerization will require a bridge that inhibits an associative walk between functional groups if they are to be bistable.

2-Triethoxysilyl-substituted 1,3-butadiene has been prepared in 30-g quantities from chloroprene via a simple synthetic procedure. Silatrane- and catechol-substituted analogues of this main group element substituted diene were then prepared on a 10-g scale by ligand exchange and characterized by X-ray crystallography in addition to standard spectroscopic techniques. 2-Dimethylphenylsilyl-1,3-butadiene has also been prepared from chloroprene on an 8-g scale. Diels-Alder reactions of these dienes are reported as well as subsequent TBAF-assisted/Pd-catalyzed Hiyama cross-coupling reactions of those Diels-Alder adducts. Silicon-substituted cycloadducts and cross-coupled products were also characterized by NMR spectroscopy and, in two cases, by X-ray crystallography.

An ene-yne cross methasis of silyl-substituted alkynes and alkenes has been developed as a route to 4-aryl- and 4-alkyl-2-silyl-substituted 1,3-dienes. The dienes prepared were used to affect highly diastereoselective Diels-Alder reactions and then the silicon-substituted Diels-Alder cycloadducts were used in Hiyama cross-coupling reactions. The cross-coupling reactions enable these silicon dienes to be used as synthons for a variety of other dienes one might prepare and need access to. Two of the silicon-substituted Diels-Alder cycloadducts and one of the Hiyama cross-coupling products were also characterized by X-ray crystallography.