Reactions of Ruthenium Acetylide Complexes with Isothiocyanate

Treatment of Cp(PPh3)[P(OMe)3]RuC⋮CPh (2; Cp = η5-C5H5) with PhNCS at room temperature affords the [2 + 2] cycloaddition (3a), containing a four-membered ring, and the neutral vinylidene phosphonate complex Cp(PPh3)[P(O)(OMe)2]RuCC(Ph)C(SH)NPh (4a) in a 9:1 ratio. Formation of 4a results from an Arbuzov-like dealkylation reaction possibly after addition of PhNCS. The same reaction at 40 °C affords a higher yield of 4a (5a; R = Ph) which results from addition of a second isothiocyanate to the four-membered ring of 3a. The reaction of 2 with PhCH2NCS at room temperature directly affords the six-membered-ring product 5b (R = CH2Ph). Trimerization of phenyl isothiocyanate is catalyzed by Cp(dppe)RuC⋮CPh (1‘; dppe = Ph2PCH2CH2PPh2) in refluxing CH2Cl2. This catalytic reaction proceeds through a pathway in which the first two steps are the same as those observed in the reaction of 2a. An attempt to purify the precursor of the trimerization product gave the cocrystallization of 1‘ and (PhNCS)3 (8). The structure...