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

Reactions of the first-generation Grubbs' catalyst trans-[RuCl2(CHPh)(PCy3)(2)] (1) with the amidinatogermylenes Ge-((t)Bu(2)bzam)R (R = Bu-t (L-1), CH2SiMe3 (L-2); (t)Bu(2)bzam = 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)(L-1)(2)] (3) and cis-[RuCl2(CHPh)(L-2)(2)] (7), which curiously differ in the arrangement of their germylene ligands. DFT calculations have revealed that the different volumes of L-1 and L-2 (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 = L-1 (2), L-2 (5)) and their evolution to either the disubstituted final product (for L-1) trans-[RuCl2(CHPh)(L-1)(2)] (3) or the short-lived disubstituted intermediate (for L-2) trans-[RuCl2(CHPh)(L-2)(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.