| This thesis describes the preparation and photochemistry of a series of low-valent carbyne complexes, CpL{dollar}sb1{dollar}L{dollar}sb2{dollar}M{dollar}equiv{dollar}C-R (M = Mo, W; L{dollar}sb1{dollar}, L{dollar}sb2{dollar} = CO, P(OMe){dollar}sb3{dollar}; R = aryl, alkyl). Photophysical studies on these complexes have led to an additional class of reaction for excited state metal carbynes in which photooxidation produces highly reactive 17 e{dollar}sp-{dollar} radicals. Photolysis of CpL{dollar}sb1{dollar}L{dollar}sb2{dollar}M{dollar}equiv{dollar}C-R in chlorinated solvents in the presence of PMe{dollar}sb3{dollar} results in the formation of the cationic complexes (Cp(PMe{dollar}sb3)sb2{dollar}M{dollar}equiv{dollar}C-R) (Cl). The formation of (Cp(PMe{dollar}sb3)sb2{dollar}M{dollar}equiv{dollar}C-R) (Cl) is postulated to involve electron transfer from the metal to ligand charge transfer (MLCT) excited states of the carbynes to the chlorinated solvent. The resulting 17 e{dollar}sp-{dollar} species then undergo ligand exchange followed by halogen atom abstraction to afford the observed complexes. UV-visible spectroscopy has established that electron transfer occurs upon MLCT excitation rather than from charge transfer to solvent transitions while EHMO calculations on model systems are in agreement with the MLCT band being d-{dollar}pisp*{dollar} in nature. For the cases L{dollar}sb1{dollar} = CO, L{dollar}sb2{dollar} = P(OMe){dollar}sb3{dollar}, R = Ph or tolyl, the MLCT state was also responsible for emission in fluid solution at room temperature.; Photooxidation of CpL{dollar}sb1{dollar}L{dollar}sb2{dollar}M{dollar}equiv{dollar}C-R (R = alkyl) in chloroform in the absence of strong donor ligands results in a switch in reactivity from the metal atom to the carbyne ligand and leads to the formation of free organic products. Acyclic substituents generally lead to olefins, while the cyclopropyl carbynes Cp(CO){dollar}{lcub}{dollar}P(OMe){dollar}sb3{rcub}{dollar} M{dollar}equiv{dollar}C-(c-C{dollar}sb3{dollar}H{dollar}sb5{dollar}) undergo a ring expansion/carbonylation sequence to yield cyclopentenone. The cyclopropyl rearrangements are very sensitive to the nature of the ancillary ligands and substituents of the cyclopropyl ring. 2-substituted cyclopropyl carbynes result in regioselective formation of 4-cyclopentenones while 2,3-disubstituted cyclopropyl carbynes rearrange to form trans-4,5-dimethylcyclopentenones as a result of a rapid photoisomerization prior to generation of the 17e- intermediate. Substitution at the Cl position by alkyl groups causes a bifurcation in the reaction pathway, leading to pentadienal complexes. Substitution at Cl by acyl or ester moieties leads to formation of oxymetallacycles and, in some cases, cyclopentenones. Mechanistic studies of cyclopentenone formation are presented and are consistent with initial hydrogen atom abstraction from the photolytically generated 17e- intermediate, followed by ring expansion, carbonyl insertion, and then reductive elimination. An intermediate on the reaction pathway, a cyclopentenone complex, was isolated and a crystal structure obtained.; The last section describes work performed on related bis(phosphite) cyclopropyl carbynes. Protonation of these complexes results in a ring opening reaction and rearrangement to form 1,3 diene complexes. This occurs through initial formation of the cationic carbene complex followed by ring expansion, {dollar}beta{dollar}-hydride shift, and reductive elimination. Evidence for attack of chloride early in the mechanism is presented as is evidence for reversible migration of hydrogen from the carbyne carbon to the metal center. |
