Synthesis of monomeric and dendritic ruthenium benzylidene cis-bis-tertiobutyl phosphine complexes that catalyze the ROMP of norbornene under ambient conditions

Abstract

The synthesis of monomeric and dendritic ruthenium benzylidene cis-bis-phosphine complexes that catalyze norbornene ROMP previously reported with dicyclohexyl bis-phosphines has now been extended to monomeric and dendritic bis-tertiobutyl phosphines. The reaction of Hoveyda's catalyst [RuCl 2(=CH- o-O-iPrC 6H 4)PPh 3] ( 1) with the diphosphine PhCH 2N(CH 2P tBu 2) 2 ( 2) gives the new air-stable green ruthenium carbene complex ( 3) in which ( 2) models a dendritic branch of poly(diphosphine) dendrimers DAB- dendr-[N(CH 2P tBu 2) 2] n (G 1, n = 4; G 2, n = 8; G 3, n = 16). Metallodendrimers DAB- dendr-[N(CH 2P tBu 2) 2Ru(=CHAr)(Cl) 2] n ( 4)–( 6) derived from the three first generations of DAB polyamines containing, respectively, 4, 8 and 16 ruthenium branches have been synthesized. These dendritic ruthenium–benzylidene complexes initiate the ROMP of norbornene at room temperature to form star-shaped metallodendritic polymers slightly more rapidly than the analogues with bis-cyclohexyl phosphines. Interestingly, the metallodendrimers G 1 ( 4) initiates the ROMP of norbornene much faster than the model ruthenium complex ( 3) the overall rate order being G 1 > G 2 > G 3 > model, these positive and negative dendritic effects being comparable with those found for the dicyclohexyl bis-phosphine complexes.