CYCLOADDITION BETWEEN A TRANSITION-METAL PHENYLALLENYLIDENE COMPLEX AND ALLYL ALCOHOL

The allenylidene complex [Ru(eta(5)-C5H5)(C=C=CPh2)(CO)((PPr3)-Pr-i)]B F4 (1) reacts with allyl alcohol to give the alpha,beta-unsaturated al koxycarbene derivative )-C5H5){C(OCH2CH=CH2)CH=CPh2}(Co)((PPr3)-Pr-i)] BF4 (2), which affords the alkoxyallenyl compound ta(5)-C5H5){C(OCH2CH =CH2)=C=CPh2}(CO)((PPr3)-Pr-i) (3) by deprotonation at -78 degrees C. At room temperature, in solution, complex 3 undergoes an intramolecula r Diels-Alder reaction to form the tricyclic tetraenyl complex rahydro naphthol[2,3-c]-1-furanyl)(CO)((PPr3)-Pr-i) (4). This isomerization is highly stereospecific due to the chiral nature of 3 and gives a singl e pair of enantiomers of 4. For this reaction, first-order constants k (obs) were obtained in toluene-d(8), which gave activation parameters of Delta H double dagger = 18 +/- 2 kcal mol(-1) and Delta S double da gger = -18 +/- 3 cal K-1 mol(-1). The structure of 4 was determined by an X-ray investigation, revealing a Ru-C(tricyclic) distance of 2.088 (3) Angstrom. Complex 4 reacts with HBF4 to give the tricyclic carbene compound aphtho[2,3-c]-1-furanylidene)(CO)((PPr3)-Pr-i)]BF4 (5). Simi larly, the reaction of 4 with DBF4 affords phtho[2,3-c]-1-furanylidene )-(CO)((PPr3)-Pr-i)]BF4 (5-d(1)). At room temperature with chloroform and tetrahydrofuran as the solvents, complex 5 is unstable and evolves into the cationic acyclic alkoxycarbene derivative yl-3,4-dihydro-3-n aphthyl])H}(CO)((PPr3)-Pr-i)](+) (6), which was isolated as the PF6 sa lt by addition of NaPF6. For the isomerization of 5 into 6, first-orde r constants K-obs were obtained in chloroform-d, which gave activation parameters of Delta H double dagger = 20.8 +/- 0.9 kcal mol(-1) and D elta S double dagger = -10.6 +/- 0.7 cal K-1 mol(-1). At room temperat ure with methanol as the solvent, complex 6 loses the alkoxy group to afford the alcohol 3-hydroxymethyl-1-phenyl-3,4-dihydronaphthalene (7) and the organometallic methoxycarbene [Ru(eta(5)-C5H5){C(OCH3)H}(CO)( (PPr3)-Pr-i)]PF6 (8).