Rational Design and Evaluation of Upgraded Grubbs/Hoveyda Olefin Metathesis Catalysts: Polyfunctional Benzylidene Ethers on the Test Bench

The series of upgraded Grubbs/Hoveyda second-generation catalysts (H2IMes)(Cl)2Ru═C(H)(C6H4OR) (E2 (71% yield), R = CH(Me)(C(O)OMe); M2 (58% yield), R = CH(C(O)OMe)2; Kme2 (88% yield), R = CH2C(O)Me; Ket2 (63% yield), R = CH2C(O)Et); C2 (58% yield), R = C(Me)CN) were prepared by the reaction of the Grubbs second-generation catalyst (H2IMes)(Cl)2Ru(CHPh)(PCy3) (G2) with the appropriate ortho-substituted ether H(Me)C═CHC6H4OR in the presence of CuCl as a phosphine scavenger. The X-ray structures of these complexes reveal that the terminal oxygen of the ester, ketone, or malonate group installed as the terminal substituent of the benzylidene ether is coordinated to the metal, giving an octahedral structure. In contrast, the nitrile group of the complex C2 remains uncoordinated. Even more sophisticated complexes, incorporating both a coordinating group R (ester or ketone) as a terminal substituent of the ether and an electron-withdrawing group X (NO2 or C(O)Me) on the aromatic ring, were synthesized: (H2IMes)...