[145381-23-3]  · C28H47Cl2PRu  · (MW 586.62)

(catalyst for ring-closing and -opening metathesis reactions; precursor to cationic ruthenium allenylidene complexes)

Alternate Name: p-cymene(tricyclohexylphosphine)ruthenium dichloride.

Solubility: limited data for the title compound are available, although related arene ruthenium(II) complexes are soluble in most chlorinated organic solvents (e.g. CHCl3, CH2Cl2) and toluene. Ring-closing metathesis reactions with the title reagent are usually performed in CH2Cl2.

Form Supplied in: brown or red-brown powder; not commercially available.

Analysis of Reagent Purity: 31P NMR (81 MHz, CDCl3) d = 26.0.

Preparative Methods: the title compound is readily prepared in 90% yield by cleavage of commercially available di-m-chlorobis[(1,2,3,4,5,6-h)-1-methyl-4-(1-methylethyl)benzene]chlororuthenium {[(p-cymene)RuCl2]2} with tricyclohexylphosphine in CH2Cl2.3,5b

Handling, Storage, and Precautions: specific data for the title compound are not available, although related arene ruthenium(II) complexes are air-stable solids.2

Ring-Closing Metathesis

Ring-closing metathesis (RCM) reactions with mononuclear 18-electron dichlororuthenium(II) arene complexes, such as the title reagent 1, are a convenient alternative to the more commonly used ‘Grubbs’ ruthenium carbenes (see dichlorobis(tricyclohexylphosphine)benzylideneruthenium) and dichloro[1,3-bis(2,4,6-trimethylphenyl)imidazolidine](tricyclohexylphosphine)benzylideneruthenium). Because of limited activity in its coordinatively saturated form, activation by irradiation is usually employed.

Fürstner and Ackermann have reported remarkably straightforward procedures for RCM using 1 activated by sunlight or common neon-tube light.4 Either previously prepared 1 can be used (1), or alternatively 1 can be formed in situ from commercially available tricyclohexylphosphine and [(p-cymene)RuCl2]2 (2). Comparable yields are obtained using these procedures to those observed with dichlorobis(tricyclohexylphosphine)benzylideneruthenium (3), although reaction times are typically longer.4,6 Further comparative data for the two procedures is available.1b

The functional group compatibility of 1 is also comparable to dichlorobis(tricyclohexylphosphine)benzylideneruthenium, and the in situ procedure has been applied to more complex substrates (4 and 5).5,4

RCM to form tri-substituted double bonds can also be achieved by this method (6).4 Allylic substitution, which is known to slow the rate of RCM reactions, is also well tolerated. As well as the example in 5, other macrocylizations by the in situ procedure have been reported.6

Synthesis of Cationic Ruthenium Allenylidene Complexes

Reagent 1 is also used to prepare cationic ruthenium allenylidene complexes with hexafluorophosphate and triflate counterions (7 and 8).3 Complexes with other counterions (e.g. BPh4- and BF4-) are also known. These complexes are active catalysts for RCM reactions,7 and yne-ene metathesis.8

Ring-Opening Metathesis Polymerization

Norbornene is polymerized by 1 after treatment with diazoalkanes such as ethyldiazoacetate,9 or upon irradiation.10 In situ-formed 1 has also been reported to be a highly active catalyst for the polymerization of functionalized norbornenes and cyclooctenes after activation with trimethylsilyldiazomethane.11

Related Reagents.

Dichlorobis(tricyclohexylphosphine)benzylideneruthenium; dichloro[1,3-bis(2,4,6-trimethylphenyl)imidazolidine]-(tricyclohexylphosphine)benzylideneruthenium; dichloro1,3-bis(2,4,6-trimethylphenyl)-2,3-dihydro-1H-imidazole](tricyclohexylphosphine)benzylideneruthenium; dichloro(3,3-diphenyl-2-propenylidene)bis(tricyclohexyl-phosphine)ruthenium; 2,6-di(1-methylethyl)phenylimidobis[1,1-(trifluoromethyl)ethoxido]-2-methyl-2-phenylpropylidenemolybdenum.

1. (a) Trnka, T. M.; Grubbs, R. H., Acc. Chem. Res. 2001, 34, 18. (b) Fürstner, A., Angew. Chem., Int. Ed. Engl. 2000, 39, 3012. (c) Armstrong, S. K., J. Chem. Soc., Perkin Trans. 1 2001, 371. (d) Schuster, M.; Blechert, S., Angew. Chem., Int. Ed. Engl. 1997, 36, 2036.
2. Bennett, M. A.; Smith, A. K., J. Chem. Soc. Dalton Trans. 1974, 233.
3. Fürstner, A.; Liebl, M.; Lehmann, C. W.; Picquet, M.; Kunz, R.; Bruneau, C.; Touchard, D.; Dixneuf, P. H., Chem. Eur. J. 2000, 6, 1847.
4. Fürstner, A.; Ackermann, L., Chem. Commun. 1999, 95.
5. Fürstner, A.; Thiel, O. R., J. Org. Chem. 2000, 65, 1738.
6. Fürstner, A.; Müller, T., J. Am. Chem. Soc. 1999, 121, 7814.
7. (a) Fürstner, A.; Picquet, M.; Bruneau, C.; Dixneuf, P. H., Chem. Commun. 1998, 1315. (b) Picquet, M.; Touchard, D.; Bruneau, C.; Dixneuf, P. H., New J. Chem. 1999, 141.
8. Picquet, M.; Bruneau, C.; Dixneuf, P. H., Chem. Commun. 1998, 2247.
9. (a) Demonceau, A.; Noels, A. F.; Saive, E.; Hubert, A. J., J. Mol. Catal. 1992, 76, 123. (b) Demonceau, A.; Stumpf, A. W.; Saive, E.; Noels, A. F., Macromolecules 1997, 30, 3127.
10. Hafner, A.; Mühlebach, A.; van der Schaaf, P. A., Angew. Chem., Int. Ed. Engl. 1997, 36, 2121.
11. Stumpf, A. W.; Saive, E.; Demonceau, A.; Noels, A. F., J. Chem. Soc., Chem. Commun. 1995, 1127.

Andrew J. Phillips

University of Colorado, Boulder, Colorado, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.