Pergamon Tetrahedron Letters, Vol.38, No. 45, pp. 7879-7882, 1997 0 1997Publi~edby Elsevier Science Ltd All rights r--~erved. Printedin Great Britain PII: S0040~039(97)I0154-X oo4o~39~7 SD.oo + o.oo Cyclopropanation Reactions Catalysed by Rhodium(I) Complexes with New Anionic Carborane Phosphine Ligands A. Demonceau,*? F. Sinai, and A.F. Noels Laboratory of Macmmolecular Chemistry and Organic Catalysis, C.E.R.M. University of Liege, Sart-Tilman (B.6a), B-4000 Liege, Belgium C. Vifias,*~ R. Nufiez, and F. Teixidor Institut de CiSncia de Materials de Barcelona, CSIC, Campus de Bellaterra, Cerdanyola, 08193 Barcelona, Spain Abstract : The first set of rhodium(I) complexes 1-3 has been shown to be active for the cyclopropanation of olefins with diazoacetates. © 1997 Publishedby ElsevierScience Ltd. Cyclopmpanation is currently an area of significant research activity.1 To date, direct tramition-metal- catalysed carbene transfer from a diazo compound to an olefm remains the most straightforward route to cyclopropanes (Eq. 1).2 Dirhodium(ID carboxylates and earboxamidates have been proved to be outstanding R R CO2Et R H + (1) ~ + N2CHCO2Et _N2 \CO2E t cis (endo ) trans ( exo ) catalysts for this reaction.3 Other rhodium complexes (e.g., Rh6(CO)16, 4 Rh2(BF4)4,5 and rhodium(IH) porphyrins6) have also been introduced as cyclopmpanation catalysts but none of them has been demonstrated to be superior to rhodium carboxylates and carboxamidates. To the best of our knowledge, attempts with rhodium(l) complexes have never been successful. For instance, Rh2(CO)4C12 and Rh2(C2I-I4)4C12 were inefficient for the cyelopropanation of l,l-dichloro-4-methylpenta-l,3-diene with ethyl diazoacetate at 83°C, 4 while the former catalysed the cyclopropanation of n-butyl vinyl ether with ethyl diazoacetate in 58% yield at room temperature.7 In the same vein, RhCI(PPh3)3 cyclopropanated styrene in only 12% yield.8 We have recently reported on the use of novel ruthenium complexes with anionic phosphine figands as efficient catalysts for olefin cyclopropanation with ethyl diazoacetate.9 In continuation of these studies, we envisaged rhodium(l) analogues as potential candidates for the desired cyelopropanation, on the basis of the exceptional activity of related complexes in hydrogenation reactions.lO We now wish to report the first set of rhodium(I) catalysts (1-3)1 ! whose effectiveness for olefin cyclopropanation is noteworthy. Preliminary results are summarised in Table 1. t Fax :++32-4-366 34 97. E-mail : A.Dcmonccau@ulg.ac.bc ~ Fax : ++34-3-580 57 29. E-mail :clara@icmvax.icmab.es 7879