The Zhan catalysts were inspired by previous work in the olefin metathesis field.
Robert H. Grubbs first reported the first and second generation of Ru catalysts in 1992, with good metathesis activity.
However, the catalysts containing the tricyclohexylphospine ligand were unstable to air and water, and the catalytic activity is not good enough for some multiple substituted olefin substrates.

In 1999, Amir H. Hoveyda showed that alkoxybenzylidene ligand based Ru catalysts offered higher activity and better stability than their Grubbs counterparts without these ligands.
Later, Grela (2002) and Blechert (2003) further improved catalyst activity by incorporating substitution to Hoveyda’s alkoxybenzylidene ligands.
Zhan’s catalysts were first reported in 2007, and include electron-withdrawing groups like dimethylsulfonamide on the aryl ring.
Zhan's second generation catalysts are also tethered to a resin or PEG-linked support via the sulfonamide group on the isopropoxystyrene.

As with other Grubbs-type catalysts with modified chelating benzylidenes, after one catalytic turnover, the chelate is no longer associated with the propagating catalyst, meaning that the initiate rate, the rate of o-alkoxystyrene rechelation, and the rates of various catalyst decomposition events are the factors that differ between the Zhan catalysts and the parent Hoveyda–Grubbs catalysts.
A mechanistic study by Plenio and coworkers in 2012 suggested that the Zhan compounds, like other Hoveyda-type catalysts, initiate by competing dissociative and interchange mechanisms, with the relative activation energies being a function of catalyst structure, olefin identity, and reaction conditions.
However, nobody had been able to rigorously establish through experimentation how the various changes to the structure affected catalytic activity of the complex.
In 2015, Engle, Houk, Grubbs, and coworkers developed a model that could rationalize initiation rates of ruthenium olefin metathesis catalysts with chelated benzylidenes, using a combination of organometallic synthesis, reaction kinetics, NMR spectroscopy, X-ray crystallography, and DFT calculations.
The Zhan catalysts were inspired by previous work in the olefin metathesis field. Robert H. Grubbs first reported the first and second generation of Ru catalysts in 1992, with good metathesis activity. However, the catalysts containing the tricyclohexylphospine ligand were unstable to air and water, and the catalytic activity is not good enough for some multiple substituted olefin substrates.
In 1999, Amir H. Hoveyda showed that alkoxybenzylidene ligand based Ru catalysts offered higher activity and better stability than their Grubbs counterparts without these ligands. Later, Grela (2002) and Blechert (2003) further improved catalyst activity by incorporating substitution to Hoveyda’s alkoxybenzylidene ligands. Zhan’s catalysts were first reported in 2007, and include electron-withdrawing groups like dimethylsulfonamide on the aryl ring. Zhan's second generation catalysts are also tethered to a resin or PEG-linked support via the sulfonamide group on the isopropoxystyrene.
As with other Grubbs-type catalysts with modified chelating benzylidenes, after one catalytic turnover, the chelate is no longer associated with the propagating catalyst, meaning that the initiate rate, the rate of o-alkoxystyrene rechelation, and the rates of various catalyst decomposition events are the factors that differ between the Zhan catalysts and the parent Hoveyda–Grubbs catalysts. A mechanistic study by Plenio and coworkers in 2012 suggested that the Zhan compounds, like other Hoveyda-type catalysts, initiate by competing dissociative and interchange mechanisms, with the relative activation energies being a function of catalyst structure, olefin identity, and reaction conditions. However, nobody had been able to rigorously establish through experimentation how the various changes to the structure affected catalytic activity of the complex. In 2015, Engle, Houk, Grubbs, and coworkers developed a model that could rationalize initiation rates of ruthenium olefin metathesis catalysts with chelated benzylidenes, using a combination of organometallic synthesis, reaction kinetics, NMR spectroscopy, X-ray crystallography, and DFT calculations.
Zhan catalyst