An Air-Stable, Reusable, Bimetallic Version of Grubbs’ Catalyst for Alkene Metathesis

Abstract

RCM, cross-metathesis and ring-opening cross-metathesis are efficiently catalyzed by a new, air-stable, bimetallic analog of Grubbs’ Ru-based metathesis catalyst, which can be recovered and recycled.

metathesis - ruthenium - carbene complexes - catalysis - organometallic reagents

References

<A NAME="RG22802ST-1">1</A>

Current address: Department of Organic Chemistry, Indian Association for the Cultivation of Science, Kolkata - 700 032, India. E-mail: [e-mail].

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Recycling catalyst:

<A NAME="RG22802ST-4A">4a</A> Kingsbury JS. Harrity JPA. Bonitatebus PJ. Hoveyda AH. J. Am. Chem. Soc.  1999,  121:  791 

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<A NAME="RG22802ST-4E">4e</A> For a survey of Ru-based initiators with other alkylidene groups, see: Frenzel U. Nuyken O. J. Polym. Sci. A  2002,  40:  2895 

We have followed the procedures described in

<A NAME="RG22802ST-5A">5a</A> Schwab P. Grubbs RH. Ziller JW. J. Am. Chem. Soc.  1996,  118:  100 

<A NAME="RG22802ST-5B">5b</A> Trnka TM. Day MW. Grubbs RH. Angew. Chem. Int. Ed.  2001,  40:  3441 

<A NAME="RG22802ST-6">6</A>

Vinylferrocene (61 mg, 0.29 mmol) in 1 mL dichloromethane was added to a solution of Ru-benzylidene complex, I, (200 mg, 0.243 mmol) in dichloromethane (5 mL). The reaction mixture was stirred at room temperature for 40 min when color of the solution turned from purple to red-violet. Volume of the solvent was reduced followed by addition of dry methanol at 0 °C, which afforded (Pcy₃)₂Cl₂Ru=C(H)Fc, III, as dark brown solid powder in 87% yield (198 mg). ¹H NMR (CD₂Cl₂): δ 19.00 (s, 1 H, Ru=CH), 4.70 (s, 2 H, Cp), 4.43 (s, 2 H, Cp), 4.14 (s, 5 H, Cp), 2.54 (broad s, 6 H, Pcy₃), 1.21-1.74 (m, 60 H, Pcy₃). ¹³C NMR (CD₂Cl₂): δ 292.14, 104.23, 71.55, 71.21, 69.77, 32.66, 32.04, 30.11, 28.40, 26.98. ³¹P NMR (CD₂Cl₂): δ 34.4 (s, Pcy₃). Details of preparation and complete characterization including crystal structure will be reported separately.

<A NAME="RG22802ST-7">7</A>

Reactions were performed in 1-2 mmol scale in dichloromethane. Yields represent isolated yields of products after purification by chromatography. All compounds were characterized by their IR, ¹H and ¹³C NMR spectra, and satisfactory elemental analyses were obtained for all new compounds.

For examples of RCM on organometallic substrates, see:

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<A NAME="RG22802ST-8C">8c</A> Licandro E. Maiorana S. Vandoni B. Perdicchia D. Paravidino P. Baldoli C. Synlett  2001,  757 

<A NAME="RG22802ST-8D">8d</A> Maity BC. Swamy VM. Sarkar A. Tetrahedron Lett.  2001,  42:  4373 

<A NAME="RG22802ST-9">9</A>

The Ru=CH₂ complex, IV, does not readily react with vinylferrocene at room temperature. However, on heating under reflux in dichloromethane with 1.2-1.5 equivalent of vinylferrocene, complex IV affords >80% yield of complex III.

<A NAME="RG22802ST-10">10</A> Maishal TK. Sinha-Mahapatra DK. Paranjape K. Sarkar A. Tetrahedron Lett.  2002,  43:  2263