Photochemistry and ligand substitution chemistry of (fulvalene)diruthenium(tetracarbonyl)

Studies of the scope and mechanism of the photoisomerization of (fulvalene)diruthenium(tetracarbonyl) (FvRu$\sb2$(CO)$\sb4$ 1) to ($\mu\sb2$-$\eta\sp1$:$\eta\sp5$-cyclopentadienyl)$\sb2$Ru$\sb2$(CO)$\sb4$ 37 and of the thermal reversal of the latter were performed ($\Delta$H$\sp\mp$ = 29.9 $\pm$ 0.02 kcal mol$\sp{-1}$ and $\Delta$S$\sp\mp$ = 17.2 $\pm$ 2.0 eu). A rate acceleration and external ligand incorporation was observed when the thermal reversion was performed under CO. Treatment of 1 with PR$\sb3$ (R = CH$\sb2$CH$\sb3$, CH$\sb3$, and OCH$\sb3$) yielded FvRu$\sb2$(CO)$\sb3$(PR$\sb3$) 52-54, the $\sp1$H and $\sp{13}$C NMR spectra of which indicated the presence of fluxional behavior in solution, probably by a process involving intramolecular terminal to bridging carbonyl exchange. The trialkylphosphine species 52 and 53 failed to detectably photoisomerize, while 54 (R = OCH$\sb3$) rapidly and reversibly afforded the P(OCH$\sb3$)$\sb3$-substituted analog of 37 upon irradiation with UV light. Heating 52 (R = CH$\sb2$CH$\sb3$) in the presence of CCl$\sb4$ regiospecifically generated a novel adduct containing a CCl$\sb3$ moiety instead of the expected dichloride complex.

Treatment of E-2,2$\sp\prime$,4,4$\sp\prime$-tetra-tert-butylfulvalene with Ru$\sb3$(CO)$\sb{12}$ provided the tetra-tert-butyl-substituted analog of 1, which did not photoisomerize. When irradiated in the presence of CCl$\sb4$, the dichloride derivative was rapidly formed. The diastereomers (S$\sp*$,S$\sp*$- and S$\sp*$,R$\sp*$- 3,3$\sp\prime$-di-tert-butylfulvalene)-Ru$\sb2$(CO)$\sb4$ 65a and b were prepared by exposing 3,3$\sp\prime$-di-tert-butyldihydrofulvalene to Ru$\sb3$(CO)$\sb{12}$. Each stereospecifically and reversibly transformed upon UV irradiation to different photoisomers. Derivatives of 1 containing one tert-butyl and one P(OCH$\sb3$)$\sb3$ substituent were synthesized by treatment of (3-tert-butylfulvalene)Ru$\sb2$(CO)$\sb4$ with P(OCH$\sb3$)$\sb3$. These complexes reversibly generated separate regioisomeric photoisomers upon UV irradiation, one of which (69a) was characterized by X-ray crystallography. The structure of the precursor 68a of the latter was determined using NMR techniques.

Treatment of 1 with an excess of P(CH$\sb3$)$\sb3$ at 120$\sp\circ$C afforded trans-Ru (P(CH$\sb3$)$\sb3$) $\sb2$(CO)$\sb3$ 95 and the novel "ring-slipped" FvRu (P(CH$\sb3$)$\sb3$) $\sb2$(CO) 96, which was characterized by an X-ray structural analysis. A variety of heterodi- and trinuclear complexes incroporating ruthenium were synthesized by exposure of 96 to mononuclear early (Ti, Zr) and late (Cr, Mo, W, Fe) transition-metal reagents. Preliminary studies of the reactions of some of these compounds with various organic substrates were performed.