Ruthenium Carbene Complexes Analogous to Grubbs-I Catalysts Featuring Germylenes as Ancillary Ligands

Abstract

Reactions of the first-generation Grubbs’ catalyst trans-[RuCl2(CHPh)(PCy3)2] (1) with the amidinatogermylenes Ge(tBu2bzam)R (R = tBu (L1), CH2SiMe3 (L2); tBu2bzam = N,N′-bis(tertbutyl)benzamidinate) have allowed the isolation and full characterization of the first specimens of Grubbs-type carbene complexes featuring heavier tetrylenes as ancillary ligands, namely, the disubstituted derivatives trans-[RuCl2(CHPh)(L1)2] (3) and cis-[RuCl2(CHPh)(L2)2] (7), which curiously differ in the arrangement of their germylene ligands. DFT calculations have revealed that the different volumes of L1 and L2 (the former is larger than the latter) are responsible for the different stereochemistry of 3 and 7. NMR-monitoring of the reaction solutions has allowed the observation of the monosubstituted intermediates trans-[RuCl2(CHPh)(L)(PCy3)] (L = L1 (2), L2 (5)) and their evolution to either the disubstituted final product (for L1) trans-[RuCl2(CHPh)(L1)2] (3) or the short-lived disubstituted intermediate (for L2) trans-[RuCl2(CHPh)(L2)2] (6). Complex 7 arises from a trans-to-cis isomerization of intermediate 6. As olefin metathesis catalysts, both 3 and 7 promoted the ring-closing metathesis of diethyl 2,2-diallylmalonate and the ring-opening metathesis polymerization of norbornene, but their catalytic activity decreased with the reaction time, indicating catalyst decomposition.