25 °C. The reaction was monitored by NMR or TLC until completion. Yield
was determined by 1H-NMR spectroscopy. For isolated yields, the reaction
was quenched with a diluted solution of NaHCO3 and the mixture was
extracted with CH2Cl2. The organic solution was dried over MgSO4, filtered,
and evaporated. The crude was diluted with hexane and filtered over silica
gel; products were eluted with hexane and Et2O for dibutyl 2-methyl-
enesuccinate. The quality of the catalyst is again essential for the successful
completion of the reaction.
demonstrates the high versatility of fluorophosphonium cations
in catalysis providing a main-group catalyst for the transfer hy-
drogenation of olefins.
Methods
General Procedure for Dehydrocoupling Reactions. To a solution of the catalyst
[(C6F5)3PF][B(C6F5)4] (1.0–1.5 mol%) in C6D5Br or CD2Cl2 (0.34 M) was added
the corresponding silane (1.0–1.2 Eq) and RH (R = Ar2N, ArS, ArO, ArCO2) (1.0
Eq) at 25 °C. The reaction was monitored by NMR analysis until the reaction
was complete. Yield was determined by 1H-NMR spectroscopy. Freshly pre-
pared catalyst was used and resulted in the optimal yields.
Supplementary Data. Details of the syntheses, spectroscopic data are in-
ACKNOWLEDGMENTS. We thank the Natural Sciences and Engineering
Research Council (NSERC) of Canada for financial support. D.W.S. is grateful
for the award of a Canada Research Chair. C.B.C. is grateful for the award
of an NSERC Postgraduate Scholarship and a Walter C. Sumner Fellowship.
General Procedure for Olefin Transfer-Hydrogenation. To a solution of silane
(1.0 Eq), RH (R = Ar2N, ArS, ArO, ArCO2) (1.0 Eq) and olefin (1.0–1.2 Eq) was
added the [(C6F5)3PF][B(C6F5)4] (1.5 mol%) in C6D5Br or CD2Cl2 (0.5 M) at
1. Sabatier P (1926) How I have been led to the direct hydrogenation method by metallic
catalysts. Ind Eng Chem 18(10):1005–1008.
2. Hallman PS, Evans D, Osborn JA, Wilkinson G (1967) Selective catalytic homogeneous hy-
drogenation of terminal olefins using tris(triphenylphosphine)hydridochlororuthenium(II);
hydrogen transfer in exchange and isomerisation reactions of olefins. Chem Commun
1967(7):305–306.
26. Gevorgyan V, Rubin M, Benson S, Liu JX, Yamamoto Y (2000) A novel B(C6F5)3-cata-
lyzed reduction of alcohols and cleavage of aryl and alkyl ethers with hydrosilanes.
J Org Chem 65(19):6179–6186.
27. Grimme S (2006) Semiempirical GGA-type density functional constructed with a long-
range dispersion correction. J Comput Chem 27(15):1787–1799.
28. Chai JD, Head-Gordon M (2008) Long-range corrected hybrid density functionals with
damped atom-atom dispersion corrections. Phys Chem Chem Phys 10(44):6615–6620.
29. Blackwell JM, Foster KL, Beck VH, Piers WE (1999) B(C6F5)3-catalyzed silation of al-
cohols: A mild, general method for synthesis of silyl ethers. J Org Chem 64(13):
4887–4892.
30. Hermeke J, Mewald M, Oestreich M (2013) Experimental analysis of the catalytic cycle
of the borane-promoted imine reduction with hydrosilanes: Spectroscopic detection
of unexpected intermediates and a refined mechanism. J Am Chem Soc 135(46):
17537–17546.
31. Brook MA, Grande JB, Ganachaud F (2011) New synthetic strategies for structured
silicones using B(C6F5)3. Adv Polym Sci 235:161–183.
32. Cella J, Rubinsztajn S (2008) Preparation of polyaryloxysilanes and polyaryloxysiloxanes
by B(C6F5)3 catalyzed polyetherification of dihydrosilanes and bis-phenols. Macro-
molecules 41(19):6965–6971.
33. Greb L, Tamke S, Paradies J (2014) Catalytic metal-free Si-N cross-dehydrocoupling.
Chem Commun (Camb) 50(18):2318–2320.
34. Sadow AD, Tilley TD (2005) Synthesis and characterization of scandium silyl complexes
of the type Cp*2ScSiHRR’. sigma-Bond metathesis reactions and catalytic dehydro-
genative silation of hydrocarbons. J Am Chem Soc 127(2):643–656.
35. Waterman R (2013) Mechanisms of metal-catalyzed dehydrocoupling reactions. Chem
Soc Rev 42(13):5629–5641.
36. Hill MS, Liptrot DJ, MacDougall DJ, Mahon MF, Robinson TP (2013) Hetero-dehy-
drocoupling of silanes and amines by heavier alkaline earth catalysis. Chem Sci 4(11):
4212–4222.
3. Boerner A, Holz
J (2004) Homogeneous hydrogenations: Olefin hydrogenations.
Transition Metals for Organic Synthesis, eds Beller M, Bolm C (Wiley, New York), 2nd
Ed, Vol 2, pp 3–13.
4. Pettinari C, Marchetti F, Martini D (2004) Metal complexes as hydrogenation catalysts.
Comprehensive Coordination Chemistry II, eds McCleverty JA, Meyer TJ (Elsevier,
Oxford), Vol 9, pp 75–139.
5. Friedfeld MR, et al. (2013) Cobalt precursors for high-throughput discovery of base
metal asymmetric alkene hydrogenation catalysts. Science 342(6162):1076–1080.
6. Trovitch RJ, Lobkovsky E, Bill E, Chirik PJ (2008) Functional group tolerance and
substrate scope in bis(imino)pyridine iron catalyzed alkene hydrogenation. Organo-
metallics 27(7):1470–1478.
7. Zuo W, Lough AJ, Li YF, Morris RH (2013) Amine(imine)diphosphine iron catalysts
for asymmetric transfer hydrogenation of ketones and imines. Science 342(6162):
1080–1083.
8. Jagadeesh RV, et al. (2013) Nanoscale Fe2O3-based catalysts for selective hydroge-
nation of nitroarenes to anilines. Science 342(6162):1073–1076.
9. Bullock RM (2013) Chemistry. Abundant metals give precious hydrogenation perfor-
mance. Science 342(6162):1054–1055.
10. Hantzsch A (1881) Condensationprodukte aus Aldehydammoniak und Ketoniartigen
Verbindungen. Chem Ber 14:1637–1638.
11. Birch AJ (1944) A new reagent for primary and secondary aliphatic amines. J Chem
Soc 1944:314–315.
12. Stephan DW, Erker G (2013) Frustrated lewis pair mediated hydrogenations. Top Curr
Chem 332:85–110.
13. Gudat D (2010) Diazaphospholenes: N-Heterocyclic phosphines between molecules
and Lewis pairs. Acc Chem Res 43(10):1307–1316.
14. Burford N, Ragogna PJ (2002) New synthetic opportunities using Lewis acidic phos-
phines. Dalton Trans (23):4307–4315.
15. Yoshifuji M (2009) Product class 3: Phosphenium salts. Sci Synth 42:63–69.
16. Guerret O, Bertrand G (1997) Trigonal planar phosphorus cations. Acc Chem Res
30(12):486–493.
17. Dunn NL, Ha M, Radosevich AT (2012) Main group redox catalysis: Reversible P(III)/P(V)
redox cycling at a phosphorus platform. J Am Chem Soc 134(28):11330–11333.
18. Wittig G, Schöllkopf U (1954) Über Triphenyl-phosphin-methylene als Olefinbildende
Reagenzien I. Chem Ber 87:1318–1330.
19. Terada M, Kouchi M (2006) Novel metal-free Lewis acid catalysis by phosphonium
salts through hypervalent interaction. Tetrahedron 62(2-3):401–409.
20. Sereda O, Tabassum S, Wilhelm R (2010) Lewis acid organocatalysts. Top Curr Chem
291:349–393.
21. Hudnall TW, Kim YM, Bebbington MWP, Bourissou D, Gabbaï FP (2008) Fluoride ion
chelation by a bidentate phosphonium/borane Lewis acid. J Am Chem Soc 130(33):
10890–10891.
37. Motokura K, Baba T (2012) An atom-efficient synthetic method: Carbosilylations of
alkenes, alkynes, and cyclic acetals using Lewis and Bronsted acid catalysts. Green
Chem 14(3):565–579.
38. Farrell JM, Heiden ZM, Stephan DW (2011) Metal-free transfer hydrogenation catal-
ysis by B(C6F5)3. Organometallics 30(17):4497–4500.
39. Nishiguchi T, Fukuzumi K (1971) Homogeneous transfer-hydrogenation of olefins
catalyzed by FeII, CoII, and NiII complexes: o- and p-dihydroxybenzene as hydrogen
donors. Chem Commun 1971(3):139–140.
40. Ohkubo K, Aoji T, Hirata K, Yoshinaga K (1976) Enantioselective dehydrogenation
of secondary carbinols by ruthenium(II) chiral phosphine complexes in the transfer
hydrogenation of olefins. Inorg Nucl Chem Lett 12(11):837–842.
41. Jiang Y, Hess J, Fox T, Berke H (2010) Rhenium hydride/boron Lewis acid cocatalysis of
alkene hydrogenations: Activities comparable to those of precious metal systems.
J Am Chem Soc 132(51):18233–18247.
42. Lin TP, Peters JC (2013) Boryl-mediated reversible H2 activation at cobalt: Catalytic
hydrogenation, dehydrogenation, and transfer hydrogenation. J Am Chem Soc
135(41):15310–15313.
43. Leitao EM, Jurca T, Manners I (2013) Catalysis in service of main group chemistry
offers a versatile approach to p-block molecules and materials. Nat Chem 5(10):
817–829.
22. Caputo CB, Hounjet LJ, Dobrovetsky R, Stephan DW (2013) Lewis acidity of organo-
fluorophosphonium salts: Hydrodefluorination by
a saturated acceptor. Science
341(6152):1374–1377.
44. Johnstone RAW, Wilby AH, Entwistle ID (1985) Heterogeneous catalytic transfer hy-
drogenation and its relation to other methods for reduction of organic-compounds.
Chem Rev 85(2):129–170.
23. Pérez M, Hounjet LJ, Caputo CB, Dobrovetsky R, Stephan DW (2013) Olefin isomeri-
zation and hydrosilylation catalysis by Lewis acidic organofluorophosphonium salts.
J Am Chem Soc 135(49):18308–18310.
45. Blaser HU, et al. (2003) Selective hydrogenation for fine chemicals: Recent trends and
new developments. Adv Synth Catal 345(1-2):103–151.
46. Pieber B, Martinez ST, Cantillo D, Kappe CO (2013) In situ generation of diimide from
hydrazine and oxygen: Continuous-flow transfer hydrogenation of olefins. Angew
Chem Int Ed Engl 52(39):10241–10244.
24. Parks DJ, Blackwell JM, Piers WE (2000) Studies on the mechanism of B(C6F5)3-cata-
lyzed hydrosilation of carbonyl functions. J Org Chem 65(10):3090–3098.
25. Rendler S, Oestreich M (2008) Conclusive evidence for an SN2-Si mechanism in the
B(C6F5)3-catalyzed hydrosilylation of carbonyl compounds: Implications for the re-
lated hydrogenation. Angew Chem Int Ed Engl 47(32):5997–6000.
Pérez et al.
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