Early carbon-carbon double-bond metathesis catalysts were notoriously sensitive to moisture and air, catching fire upon the slightest atmospheric contact; Robert Grubbs engineered a stable ruthenium carbene catalyst that performs bond-swapping reactions smoothly on the open benchtop. This Nobel Prize-winning catalyst transformed green polymer manufacturing and pharmaceutical synthesis of Hepatitis C antiviral therapies.
In industrial plastic synthesis and pharmaceutical manufacturing, stitching carbon-carbon double bonds together required harsh, dangerous chemicals that destroyed delicate therapeutic molecules. Early catalysts were so violently sensitive to air and water that they burst into flames outside specialized vacuum boxes.
Robert Grubbs engineered an air-stable ruthenium catalyst that works like a molecular square dance caller. When added to a reaction flask on an open laboratory bench, the catalyst coordinates reacting carbon molecules, breaks their double bonds, and swaps their partners smoothly without producing toxic chemical waste.
Grubbs catalysts became a cornerstone of green, sustainable chemistry. By enabling commercial self-healing materials, by synthesizing life-saving antiviral medicines for Hepatitis C, and by manufacturing bio-based plastics from vegetable oils, ruthenium metathesis reshaped industrial chemistry.
Synthesis and Applications of RuCl 2 (CHR‘)(PR 3 ) 2 : The Influence of the Alkylidene Moiety on Metathesis Activity
The reactions of RuCl 2 (PPh 3 ) 3 with a number of diazoalkanes were surveyed, and alkylidene transfer to give RuCl 2 ( CHR)(PPh 3 ) 2 (R = Me ( 1 ), Et ( 2 )) and RuCl 2 ( CH- p -C 6 H 4 X)(PPh 3 ) 2 (X = H ( 3 ), NMe 2 ( 4 ), OMe ( 5 ), Me ( 6 ), F ( 7 ), Cl ( 8 ), NO 2 ( 9 )) was observed for alkyl diazoalkanes 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 have 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 metathesis activity of 3 − 9 is relatively small. Phosphine exchange in 3 − 9 with tricyclohexylphosphine leads to RuCl 2 ( CH- p -C 6 H 4 X)(PCy 3 ) 2 10 − 16, 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 of RuCl 2 ( CH- p -C 6 H 4 Cl)(PCy 3 ) 2 ( 15 ) indicated a distorted square-pyramidal geometry, in which the two phosphines are trans to each other, and the alkylidene unit lies in the Cl−Ru−Cl plane. The benzylidenes RuCl 2 ( CHPh)(PR 3 ) 2 (R = Cy (cyclohexyl) ( 10 ), Cp (cyclopentyl) ( 17 ), i -Pr ( 18 )) are quantitatively available via one-pot synthesis with RuCl 2 (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 RuCl 2 ( CH 2 )(PCy 3 ) 2 ( 19 ) is formed quantitatively, and various alkylidene compounds RuCl 2 ( CHR)(PCy 3 ) 3 (R = Me ( 20 ), Et ( 21 ), n -Bu ( 22 )) are isolated as the kinetic products from the reaction of 10 with an excess of the corresponding terminal or disubstituted olefins. Metathesis of conjugated and cumulated olefins with 10 results in the formation of vinylalkylidene and vinylidene complexes, as shown by the synthesis of RuCl 2 ( CHCH CH 2 )(PCy 3 ) 2 ( 23 ) and RuCl 2 ( C CH 2 )(PCy 3 ) 2 ( 24 ) from 1,3-butadiene or 1,2-propadiene, respectively. Also, functional groups such as −OAc, −Cl, and −OH can be introduced into the alkylidene moiety via cross metathesis with the appropriate alkene.
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