SYNTHESIS AND APPLICATIONS OF RUCL2(=CHR')(PR(3))(2) - THE INFLUENCE OF THE ALKYLIDENE MOIETY ON METATHESIS ACTIVITY

The reactions of RuCl2(PPh(3))(3) with a number of diazoalkanes were s urveyed, and alkylidene transfer to give RuCl2(=CHR)(PPh(3))2 (R = Me (1), Et (2)) and RuCl2(=CH-p-C(6)H(4)X)(PPh(3))(2) (X = H (3), NMe(2) (4), OMe (5), Me (6), F (7), Cl (8), NO2 (9)) was observed for alkyl d iazoalkanes RCHN(2) and various para-substituted aryl diazoalkanes p-C (6)H(4)XCHN(2). Kinetic studies on the living ring-opening metathesis polymerization (ROMP) of norbornene using complexes 3-9 as catalysts h ave shown that initiation is in all cases faster than propagation (k(i )/k(p) = 9 for 3) and that the electronic effect of X on the metathesi s activity of 3-9 is relatively small. Phosphine exchange in 3-9 with tricyclohexylphosphine leads to RuCl2(=CH-p-C(6)H(4)X)(PCy(3))(2) 10-1 6, which are efficient catalysts for ROMP of cyclooctene (PDI = 1.51-1 .63) and 1,5-cyclooctadiene (PDI = 1.56-1.67). The crystal structure o f RuCl2(=CH-p-C6H4Cl)(PCy(3))(2) (15) indicated a distorted square-pyr amidal geometry, in which the two phosphines are trans to each other, and the alkylidene unit lies in the Cl-Ru-Cl plane. The benzylidenes R uCl2(=CHPh)(PR(3))(2) (R = Cy (cyclohexyl) (10), Cp (cyclopentyl) (17) , i-Pr (18)) are quantitatively available via one-pot synthesis with R uCl2(PPh(3))(3), PhCHN(2), and PR(3) as reaction components. 10 is an efficient catalyst for metathesis of acyclic olefins: On reaction with excess ethylene, the methylidene complex RuCl2(=CH2)(PCy(3))(2) (19) is formed quantitatively and various alkylidene compounds RuCl2(=CHR)( PCy(3))(3) (R = Me (20), Et (21), n-Bu (22)) are isolated as the kinet ic products from the reaction of 10 with an excess of the correspondin g terminal or disubstituted olefins. Metathesis of conjugated and cumu lated olefins with 10 results in the formation of vinylalkylidene and vinylidene complexes, as shown by the synthesis of RuCl2(=CHCH=CH2)(PC y(3))(2) (23) and RuCl2(=C=CH2)(PCy(3))(2) (24) from 1,3-butadiene or 1,2-propadiene, respectively. Also, functional groups such as -OAc, -C l, and -OH can be introduced into the alkylidene moiety via cross meta thesis with the appropriate alkene.