Gentle, T.M.

Muetterties, E.L.

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Lawrence Berkeley National LaboratoryRecent WorkTitleSILANE SURFACE CHEMISTRY OF PALLADIUM: SYNTHESIS OF SILAETHYLENE, SILACYCLOBUTADIENE AND SILABENZENEPermalinkhttps://escholarship.org/uc/item/688866jmAuthorsGentle, T.M.Muetterties, E.L.Publication Date1982-10-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaLBL-15129 d-Preprint ~. ITtl Lawrence Berkeley Laboratory ~ UNIVERSITY OF CALIFORNI l:f ~ Materials & MolecularsERKEi.EY!ABfJR"TORY J!· Research Division JAN 111983 LIBRARY AND DOCUMENTS SECTION Submitted to the Journal of the American Chemical Society SILANE SURFACE CHEMISTRY OF PALLADIUM: SYNTHESIS OF SILAETHYLENE, SILACYCLOBUTADIENE AND SILABENZENE Thomas M. Gentle and E.L. Muetterties October 1982 TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed fo~ two weeks. For a personal retention copy~ call Tech. Info. Division~ E~t. 6782. Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098 " DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. , ... •"' ,. .• Silane Surface Chemistry of Palladium: Synthesis of Silaethylene, Silacyclobutadiene and Silabenzene Thomas M. Gentle and E.L. Muetterties* Materials and Holecular Research Division Law.rence Berkeley Laboratory and Department of Chemistry University of California Berkeley, California 94720 This work was supported by the U.S. Department of Energy under contract number DE-AC03-76SF00098. i. Abstract The clean surface of Pd(llO) proved effective in the dehydrogenation of organosilanes. After chemisorption of (cH3) 3SiH on Pd(llO) at -135°C, rapid heating of the crystal led to desorption of (CH3) 3SiH, (CH3) 2Si=CH2, H2 , and a minor amount of f(CH3) 2SiCHi12 • Silacyclohexane on Pd(llO) partially desorbed reversibly and partially dehydrogenated to give silabenzene, SiC5H6• Silacyclobutane on Pd(llO) yielded silacyclobutadiene H2Si=CH2 , and fH2S~Ch2t2 • (CH3) 2Si=CH2 was also partially formed in the thermal desorption of (CH3) 3Si0Si(CH3) 3 , (CH3) 3SiNHSi(CH3) 3, and (CH3) 3SiN3 • The azide also formed f(CH3) 2SiNCH3-t. ii. , ·-1-· Chemisorpt~on of cycloalkenes on metal surfaces are followed by dehydrogenation processes1 which oiten give chemisorbed C H specie's, e.g., cyclohexene + _____ n n 1-3 1 benzene and cyclooctadiene + cyclooctatetraene. Because these trans-formations are facile, w~ have been exploring the reactions of silaalkanes 4 with single crystal metal surfaces as routes to compounds in which there are Si-C -bonds of multiple bond order.· With platinum and nickel, we observed either no dehydrogenation or gross degradation of the silaalkane5• Palladium, however, has furnished dehydrogenation syntheses of silaethylenes, silabenzene and what appears to be silacyclobutadiene. 6 · Tetramethylsilane on Pd(llO) desorbed fully and intact at 'V-50°C analogous to neopentane on Pd(llO) which quantitatively desorbed with a T max of 'V-60°C. In sharp contrast, trimethylsilane after adsorption at -135°C underwent two. competing thermal processes: (i) reversible desorption with a maximum desorption rate at -20°C and. (ii) dehydrogenation to form (CH3) 2siaCH2 S, 9 which desorbed with maximum rates at -40 and +90°C (the· surface was essentially free of Si and C after the desorption experiment). The latter process was accompanied by H2 desorption which also exhibited maxima at -40 and +90°C. Minor dimerization of the· silaethylene also occurred: ~Si(CH3 ) 2cH2~2 desorbed to give a broad peak at "-'40°C. An unexpected feature here was desorption of silaethylene because most alkenes and alkynes irreversibly chemisorb on clean transition metal surfaces. Consistent with the organosilane surface chemistry, we have found that acetylene and ethylene chemisorb on Pd(llO) - -------------- -~------------- ----in a partially reversible fashion. 10 Displacement of the silaethylene, (CH3) 2Si=CH2, from the Pd(llO) surface was effected with P(CH3) 3• On dosing the crystal face with P(CH3)3 at +25°C, there was immediate displacement of the silaethylene, the dimer, fSi(CH2 ) 3cH2~ 2 , and trimethylsilane. -2-The silaethylene, (ca3)2Si=CH2, was also produced in the thermal desorption experiments with (CH3)3Si0Si(CH3) 3, (CH3) 3SiNHSi(CHj) 3 , and (CH3) 3siN3 on Pd(llO). All three also exhibited partially reversible chemisorption. In the azide system, an additional and major ~reduct was f(CH3)2Si-N(CH3)~ 2 • Silacyclobutane displayed a complex Pd(llO) surface chemistry. After adsorption at -l35°C, silanes 1-4 were observed in the thermal desorption H2C SiH H2C SiH2 HC-SiH 2 H2Si=CH2 II II H2C CH2 H Si-2 CH2 HC CH l 2 3 4 with respective desorption maxima at 'V-65°, +65°, +50°, and+ 70°C, respectively. Ethylene and hydrogen were observed with similar T of 60-80°C. All these max species were observed in a chemical displacement reaction with P(CH3) 3 • Silacyclobutadiene is a new compound, and its characterization must be considered tentative in that it is based solely on mass spectrometric. data. The parent ion was less intense than the parent-minus-one ion as exPected for a species with one Si-H bond. Ostensibly, silaethylene was the precursor t.o the dimer, 2. Consistent with this presumption, the ratio of 4 to 2 increased when the heating rate was increased from 25° sec-l to 75° sec-1 • Silacyclohexane, initially adsorbed on Pd(llO) at -l35°C, also underwent two competing surface reactions: reversible desorption (Tmax = -25°C) and dehydrogenation to give silabenzene12 , SiC5H6 (two T of 90 and 190°C) and max H2 (two Tmax of 15 and 190°C). This chemistry parallels that of cyclohexene which gave benzene with a Tmax(c6a6) of 220°C and also ofpiperdinewhich gave pyridine with Tmax(NC5H5) of 115 and 155°C.10 Silabenzene was not displaced from the surface generated fromsDa~yclohexane at temperatures of 25-70°C. I .. ,, -3-'J;here are a number of remarkable features to this Pd(llO) chemistry. One is the extensive degree of reversible chemisorption of unsaturated hydrocarbons like acetylene, ethylene, and of course, silaethylene and silabenzene. Secondly, these results suggest a practical synthesis of silaethylenes, silacyclobutadienes, and silabenzenes by palladium catalyzed dehydrogenation of organosilanes, an aspect now under study in our laboratories. 13 Also, this technique of metal catalyzed dehydrogenation of readily available, saturated organometallic compounds should provide not only a useful route to new compounds 13 with multiple bonds to silicon but also to new very reactive monomers with multiple bonds based on other elements such as P, Ge, Al, etc. Thirdly, we note ·that the saturated organosilanes in which there is at least one Si-H bond are far more susceptible to dehydrogenation than are saturated hydrocarbons;for example, cyclohexane and tetramethylsilane unde·rgo fully reversible chemisorption on Pd.(llO) under ultrahigh vacuum conditions in contrast to silacyclohexane and ' '2 trimethylsilane. Apparently, a primary surface interaction bond of Si-H species is through a. three-center :Si-H-M f bond: note the substantially higher . sur -. desorption temperature for (cH3)3 SiH (T =-20°C) than for (CH3) 4si (T =-50°C). Acknowledgements. This work was supported by the National Science Foundation, by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098, and by a grant from the Dow Chemical Company. One of us (TI1G) also thanks the Dow Corning Corporation for a grant in the form of a graduate fellowship. We would also like to thank Professor Thomas Barton for the sample of monsilacyclobutane and Dr. Maher Elsheikh for the trimethylsilane and silacyclohexane. Supplementary Material. Thermal desorption spectra for Pd(llO)-trimethylsilane, Pd(llO)-silacyclobutane, and Pd(llO)-silacyclohexane (6 pages). Ordering information may be obtained from any current masthead page. -4-REFERENCES AND FOOTNOTES l. Tsai, M.C.; Stein, J.; Friend, C.M.; Muetterties, E.L. J. Am. Chem. Soc. 1982, 104, 3~33-3534. 2. Gates, B.C.; Katzer, J.R.; Schuitt, G.C.A.; Chemistry of Catalytic Processes, McGraw Hill Book Company, New York, 1979, pp. 222-247. 3. (a) Tsai, M.-c.; Friend, C.M.; Muetterties, E.L. J. Am. Chem. Soc. 1982, 104,2539-2543. (b) Tsai, M.-c.; Muetterties, E.L. J. Phys. Chem. 1982, 86, 0000. 4. See references in 3 for the equipment, techniques and procedures for these ultra high vacuum experiments. Adsorption was generally effected at -135°C. and desorption st.udies were done usually with -l 25°sec heating rates. 5. Tsai, M.-C.; Friend, C.M.; Johnson, A.L.; Muetterties, E.L., unpublished data. 6. The contrasting behavior of palladium with respect to platinum might 7. 8. 9. 10. 11. . be traced to a uniquely low Pd-Si bond energy. 7 Auwiera-Matieu, A.V.; Peeters, "R.; Mcint~re, N.S.; Drowart, J. Trans. Faraday Soc., 1970, 66, 809-816. This compound was characterized only by its mass spectrum. The essential absence of a parent minus one ion clearly indicated that this species contained no Si:-H bo.nd. This silaethylene molecule has been prepared by thermolysis of tetramethylsilan~ and trimethylsilane. 9 (a) Fritz, G., Grobe, J.; Kummer, D. Adv. Inorg. and Radiochem., 1965, z, 364. (b) Davidson, I.M.T.; Lamberty, C.A. J. Chem.Soc. (A) 1977, 882. Gentle, T.M.; Muetterties, E.L. J. Phys. Chem. 1983, 86, 0000. References to the generation of thermal processes, mass spectrum and· trapping of silabenzene is given in ref. 12. ,. '• -5-12. (a) Solouk, B.; Rosmus, P.; Bock, H.; Maier, G. Angew. Chem. Int. Ed. Engl. 1980, 19, 51. (b) Barton, T.J.; Burns, G.T. J. Am. Chem. Soc. 1978, 100, 5246. 13. Since compounds with Si-C multiple bonds readily dimerize or polymerize, the ultra high vacuum reaction conditions are ideal for observation of such compounds. However, this technique is impractical for the generation of sufficient quantities for chemical trapping experiments. We plan to examine Pd catalyzed organosilane dehydrogenation reactions under flow condit~ons using very short contact times and matrix or chemical trapping conditions. -6-Figure 1. Shown above are the mass spectrometric intensity traces for the four compounds that thermally desorb from the Pd(llO)-(CH3) 3SiH surface (heating rate of 25° sec-1). The silaethylene (parent mass of 72) does not show an ion of mass 71 clearly indicating that this silicon species doE!s not have an Si-H.bond. Also the dimer -f(CH3) 2SiCH2~2 does not in electron impact mass spectrometry show an ion of mass 72 nor does it show substantial intensity ions for parent-minus-one or -two. ., c..J 0• 0 ::r N ~ -~ .·~ ~ a.n X -7-N :z::: i-f X AliSN3ltH Ll"\ X r5 -~ -cr -:X: -(I) l't'\ • -l't'\ :X: u -Ll"\ . N X -~ 0 0 -L1. c:: t-<l 0: LJ. 0. ::E LJ. ..... -8-Figure 2. In the thermal desorption experiment for Pd(llO)-silacyclobutane (initial adsorption of -l35°C), there were detectably six molecules that desorbed •. Shown above are the mass spectral intensities of the ion characteristic of these species with exception of ethylene (ethylene desorbed at ~60-80°C). In these plots, mass 2 is for H2 , mass 67 for-silacyclobutadiene, mass 86 for fSiH2cH2-t2 and mass 44 for the parent ion of H2Si=CH2 ~ a fragmentation ion for a sila-cyclobutane. The low temperat.ure (-65°C) maximum is ascribed to silacyclobutane reversibly desorbing and the high temperature (+75°C) maximum to silaethylene. In this experiment, the heating rate was 75°C -l sec • -l In an experiment performed with a heating rate of 25°C sec ,. more dimer -fSiH2cH2:1 2 and less silaethylene were formed. In the case of the dimer -fSiH2cH2:12 , the parent ion intensity is less than those for the parent ion-minus-one, -two,-three and -four. I u • 0 00 I 0 c.o .. .... X u ... 0 " ... -9-.... X A!ISN3!NI 0 .... X 0 .... X -(..; 0 --10-Figure 3. Illustrated above is the results of a thermal desorption experiment (heating rate of 25°C sec-1) for Pd(llO)-silacyclohexane. u ., 0+ 0' u o§l (.0 :: U'\ u -Cl) 0 ~ X -11-u .. 0 0'+ ~ u •· U'\+· N ~ X A!ISN3!NI N ...... ::: a.n u -Cl) 0 ~ X -u This report was done with support from the Department of Energy. Any 'conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley La~oratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department _of Energy to the exclusion of others that may be suitable. 'i;. -- ... ,. TECHNICAL INFORMATION DEPARTMENT LAWRENCE BERKELEY LABORATORY UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA 94720 , I ~- "" . ·.' ~ : 

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SILANE SURFACE CHEMISTRY OF PALLADIUM: SYNTHESIS OF SILAETHYLENE, SILACYCLOBUTADIENE AND SILABENZENE

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SILANE SURFACE CHEMISTRY OF PALLADIUM: SYNTHESIS OF SILAETHYLENE, SILACYCLOBUTADIENE AND SILABENZENE

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