Cross metathesis allowing the conversion of a ruthenium indenylidene complex into Grubbs' catalyst

The active metathesis catalyst (PCy3)(2)Cl2Ru(3-phenylinden-1-ylidene) (4) was obtained in high yield using a simple one-pot procedure. The initial reaction of RuCl2(PPh3)(3) with 1,1-diphenyl-2-propyn-1-ol gave (PPh3)(2)Cl2Ru(3-phenylinden-1-ylidene) (6). In situ exchange of PPh3 with PCy3 led to the isolation of 4 in>90% yield. Whereas complex 6 did not show any activity in the cross metathesis reaction with styrene, reaction of compound 4 with excess styrene gave Grubbs' catalyst, (PCy3)(2) Cl2Ru=C(H)Ph (1), dichloro(phenylmethylene)bis(tricyclohexylphosphane)ruthenium(II), in nearly quantitative yield. This two-step procedure yielded complex 1 in 88% overall yield starting from inexpensive and commercially available materials. The widely used metathesis catalyst I was also obtained in good yield in one single step, that is, without isolation of compound 4, making this a simple and safe synthetic route to Grubbs' catalyst.