A Study of a New Catalytic System for the Metathesis o f Functionalized Olefins *

Efetuou-se o estudo sobre um novo sistema catalítico WCI6.PMHS. Curvas de conversão, números de rotação e freqüências de rotação foram comparados àqueles para os sistemas já conhecidos na literatura. Os resultados mostram que o novo sistema tem atividades análogas nas reações de metátese do 1 0-undecenoato de meti la e 1 0-undecenonitrila que os sistemas conhecidos para esse tipo de reações, com a vantagem de utilizar como catalisador um composto menos tóxico e de menor custo que SnMe4 e Ph2SiH2.

Since the discovery ofthe olefin-metathesis reaction for non-functionalized olefins, this research field has grown greatly and efficient systems have been developed 1 • 2 .However, the recently discovered, well-defined alkylidene complexes markedly improved the yields of the metathesis reactions offunctionalized olefins 6 • 7 • 8 • This was also the case for the Ah03/SiOz supported MeRe03 (MT0) 8 .A drawback ofthe use ofthe "classical systems" is the toxicity ofSnMe4, whereas the well-defined systems are problematic because they are somewhat difficult to synthesize andlor are expensive.
For functionalized olefins, this kind of reaction provides the synthesis of di-functional derivatives with welldefined structures.However, low tolerance for heteroatoms has been observed through the use of the same type of catalytic system as for non-functionalized olefins.The few systems which gave satisfactory results were those based on the use of WC16 associated with either SnMe4 or PhzSiHz (the so-called homogeneous systems), and also those based on RezO? associated with SnMe4 on a solid support (the heterogeneous systems) 3 • 4 • 5 .
The purpose of the present work is to study the new catalytic system WCkPMHS, where PMHS = Me3SiO(MeHSiO)nSiMe3, n = 35 (polymethyl-hydrosiloxane ), which avoids the use o f the toxic SnMe4 and the expensive PhzSiHz, in the metathesis reaction o f methyl-1 0-undecenoate and 1 0-undecenonitrile.Therefore, direct comparison o f this system to the known systems was carried out.

Results
The ester:PMHS.WC16 ratio chosen for the present study was 25:4:1, which gave the best conversion factors in the pre1iminary study 10 .
The se1ectivity ofthe ester reaction was approximate1y 100%.On1y when the reaction was performed on a 1arge sca1e were traces ofCH3CHC1(CH2)sCOOCH3 detected in addition to the expected product, as a resu1t ofthe addition of HC1, formed in the reaction, to the doub1e bond.The reactions were followed by 1 H-NMR spectroscopy since the o1efinic pro tons gave signa1s at 4. 8 ( m) and 5. 7 ( m) ppm, for the starting ester, and at 5.25 (m) ppm for the diester.Integration of these signa1s directly gave the conversion factors.The reaction carried out on the nitri1e was ana1yzed according to the same criteria, taking into account the formation ofthe HC1-addition product.
With either WC16 or PMHS taken separate1y no reaction took p1ace.The conversion factors, tumover numbers and frequency numbers for the ester reaction with the cata1ytic system studied in this work are shown in Fig. 1.All o f the systems were very active at the beginning o f the reaction, but were deactivated after 2 h, probab1y as a result o f the interaction ofthe cata1ytic species with the heteroatoms.
The resu1ts for the nitri1e are shown in Tab1e 1.The se1ectivity was poorer than for the ester reaction, in agreement to the 1iterature for other cata1ytic systems.Ana1ysis of the products, separated by si1ica-ge1 chromatography showed that in addition to 10-eiCosenodinitri1e, 10-unde-canonitri1e ch1oride was a1so formed, as a resu1t of the addition ofHC1 to the doub1e bond.

Experimental
WC16, SnMe4, Ph2SiH2 and PMHS were purchased from A1drich Chemica1 Company.Methy1-1 0-undecenoate was kind1y supp1ied by A TO Chimie (F rance). 1 O-unde-cenonitri1e was synthesized from the corresponding amide by refluxing it with thiony1e ch1oride in benzene.The product was purified by vacuum distillation.The yie1d was 60%.10-undecenonitrile: 1  All o f the metathesis reactions were performed under an argon atmosphere in a g1ove box.In a typica1 reaction, 127 mg ofWC16 was added to a flask containing 1.59 g of degassed methy1-10-undecenoate at 75 °C, followed by the addition of 0.081 g of degassed PMHS, making the ester:WCkPMHS, ratio 25:1:4.Forthenitri1e, theratio was 10:1:4 and the temperature was 100 °C.The bubb1ing o f argon in to the so1ution was necessary in order to carry the HC1 and C2H4 and drive the reaction to the product.The samp1es collected for ana1ysis were di1uted with EhO, filtered in microco1umns with ce1ite 545 and ana1yzed by All NMR spectra were performed on a V ARIAN CXR 200 MHz spectrometer using CDCb or CCl4 as solvents.The IR data were taken on a Perkin-Elmer 1430 coupled with a 483 data station.The spectra were obtained as liquid films in Csi cells.The mass spectra were made on a HP 5988 A mass spectrometer coupled to a HP 590 GC.
The conversion factors (C) were estimated from the integration ofthe olefinic proton signals by the equation C = 2D/(Ez + 2D), where D = integration of the diester or dinitrile olefinic proton signals and Ez = integration of the two terminal ester or nitrile olefinic proton signals.Tests with a calibrated solution confirmed an error of 4%.Tumover numbers were calculated by TN = 25C/2 for the ester, assuming a selectivity close to 100%, and TN = excess olefin X (Cdinitrile/2 + Cchloride product), for the nitrile, as the selectivity was not close to 100%.The Cchloride product was estimated from the 1 H-NMR signal of the proton at 3.9 ppm.Frequency numbers were given by FN = TN/t.All the reactions were repeated at least three times, and all the data points reflect the average o f the reactions.

Discussion
The new co-catalyst PMHS is a reductor under mild conditions, but does not reduce esters, amides o r nitriles per se 11 • The results obtained show that the new system WCkPMHS has activities strictly comparable to those of the other systems known to metathesize esters and nitriles.Previous observations demonstrated that a prere-quisite for the formation o f an active catalyst is the presence of one or more Si-H bonds in the co-catalyst, and also, that upon the interaction of PhzSiHz with WC16, reduction takes place, forming HC1 4 .The present results confirm these observations.Moreover, the presence of Si-O bonds does not hinder the formation o f the active species, the structure o f which has yet to be established.

Conclusion
Optimal working conditi~ns for the very easy to use and inexpensive WCkPMHS system were established for the metathesis reaction of functionalized olefins.The results can be favorably compared to the "classical" systems for the metathesis of this type o f olefin, and indicate that it is particularly well-suited to the synthesis of simple starting difunctionalized olefins.
1H-NMR spectroscopy.All products were characterized by mass spectroscopy, IR and