Molybdenum Catalyst with a Stereogeneic Metal Center

Flook, M. M.; Jiang, A. J.; Schrock, R. R.; Müller, P.; Hoveyda, A. H. Z-Selective olefin metathesis processes catalyzed by a molybdenum hexaisopropylterphenoxide monopyrrolide complex. J. Am. Chem. Soc. 2009, 131, 7962-7963. There aren’t many interuniversity partnerships out there that have been more productive than the one between Richard Schrock and Amir Hoveyda. Recently, this […]

Cross Metathesis Reaction Planning

There’s nothing more frustrating to a synthetic chemist than a reversible reaction. We incur great expense to prepare reactive reagents (MeMgBr, LiAlH4, Br2, PhI(OAc)2, etc.) that do their thing and then just stand by and watch after they’re done. I think this is in part why RCM was so quickly adopted by the synthetic community. […]

Selectivity in Olefin Cross Metathesis

Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. A general model for selectivity in olefin cross metathesis. J. Am. Chem. Soc., 2003, 125, 11360-11370. When well-defined olefin metathesis catalysts started to come on scene, the majority of initial interest was in ring opening metathesis polymerization (ROMP), and subsequently ring closing metathesis (RCM). […]

Mechanism of Ring Closing Metathesis: Oligomers as Intermediates

Conrad, J. C.; Eelman, M. D.; Silva, J. A. D.; Monfette, S.; Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E. Oligomers as Intermediates in Ring-Closing Metathesis. J. Am. Chem. Soc. 2007, 129, 1024-1025. Reading this communication changed the way I think about ring closing metathesis (RCM) reactions. Fogg and coworkers studied the pre-equilibrium product […]

2nd Generation Hoveyda Catalyst

2ndGeneration Hoveyda Catalyst1 – CAS#: [301224-40-8] – FW: 626.62 – Color: Green – Initiation temperature: >0 °C Process Strengths Weaknesses CM2 -Compatible with most olefins, including highly electron-deficient (i.e. acrylonitrile) -Incompatible with hindered substrates RCM -Forms di- and trisubstituted olefins rapidly (5- & 6-membered rings) -Excels at macrocycle formation -Tetrasubstituted olefin formation is slow and […]

Grubbs Triblock Copolymers

Careful combination of multiple polymerization mechanisms can generate truly unique architectures. Incorporation of chain-segments generated by metathesis polymerizations have been explored by a number of researchers (particularly the Matyjaszewski group at Carnegie Mellon University), typically by terminating the ROMP reaction with a functionality that could later be used as an initiator for atom transfer radical […]

Identifying the Best Ruthenium Catalyst

Bieniek, M.; Michrowska, A.; Usanov, D. L.; Grela, K. In an Attempt to Provide a User’s Guide to the Galaxy of Benzylidene, Alkoxybenzylidene, and Indenylidene Ruthenium Olefin Metathesis Catalysts. Chem. Eur. J. 2008, 14, 806-818. There are a number of ruthenium metathesis catalysts out there, and if you squint just enough, they all look the […]

Inhibiting Olefin Isomerization

Olefin isomerization/migration can be an annoying side reaction of olefin metathesis, in no small part because the side products are usually difficult to separate from the desired product. The isomerization is catalyzed by metal hydride species formed in the decomposition of the catalyst (see Schmidt, Eur. J. Org. Chem. 2004, 1865 for a review). General […]

Low Polydispersity ROMP Catalyst

Although their increased functional-group tolerance has made the ruthenium-based metathesis catalysts extremely attractive for use as polymerization catalysts, these catalysts have typically struggled to match the “living” polymerizations of the molybdenum- and tungsten-based catalysts. The advent of 2nd generation N-heterocyclic carbene ruthenium catalysts increased the overall activity to match other systems, but polymers generated still […]

ROMP Catalysts: Key Fundamentals

Buchmeiser M. R. Homogeneous Metathesis Polymerization by Well-Defined Group VI and Group VII Transition-Metal Alkylidenes: Fundamentals and Applications in the Preparation of Advanced Materials. Chem. Rev. 2000, 100, 1565. This 2000 review article by Michael Buchmeiser is actually two reviews in one:  (i) part catalyst survey and (ii) part summary of specialty polymers and materials […]

2nd Generation Grubbs Catalyst

2nd Generation Grubbs Catalyst1 (Ph = phenyl; PCy3 = tricyclohexylphosphine) – CAS#: [246047-72-3] – FW: 848.97 – Color: Orange-brown – Initiation temperature: >10 °C. Process Strengths Weaknesses CM2 -Applies to most olefins -Deactivated olefins (e.g. vinyl phosphonates, α, β-unsaturated carbonyls) -Typically forms the thermodynamic E/Z ratio -Highly electron-deficient substrates -Very Hindered substrates RCM -Synthesis of […]