J. Am. Chem. SOC.1993, 115, 127-137
127
intensity as observed in expt no. 60 and 66 (light intensity 3.06 monoxide by displacement of the chloride anion. (3) A two X 10” and 5.41 X einstein min-’ cm-2, respectively). The electron reduction of the Ir(II1) metal center generates the neutral WGSR of the [(qs-C5Mes)Ir111(bpy-4,4’-(COOH)2)Cl]+ system [(~S-CsMes)Irl(L)] complex 8 which has been isolated and fully characterized. (4) Reactivity studies have proved that 8 is the is surprisingly efficient given the many steps involved in the process key intermediate of the overall WGSR process. Oxidative addition (Scheme 11) and the requirement that the metal complex functions of the proton on 8 gives the hydride complex [($-C5Me,)Ir11*as both CO oxidation and H 2 0 reduction catalyst as well as photosensitizer. Its efficiency compares well with the highly (L)(H)]+ which has also been characterized. ( 5 ) The photospecific photoinduced reduction of C02to CO mediated by facchemical step of the catalytic cycle is the protonation of this Re’(bpy)(C0)3C1.63*64In this case also the quantum yield for hydride to give H2 and the starting complex. (6) Activation CO formation reaches values as high as 15% despite the mulenergies show that decarboxylation of intermediate B is the rate limiting step. Moreover, the presence of an electron withdrawing tielectron nature of the process. group on the bpy chelate halves the activation energy and thus SUmIMq favors the decarboxylation of B. Finally, this new family of The results of the present study lead to several conclusions iridium(II1) complexes provides excellent catalysts for the phoregarding the mechanism of the photochemical WGSR catalyzed toassisted WGSR. by the [(~s-CsMes)Irlll(L)C1]+ complexes. (1) The process is both Ackuowkdgmed. We thank Professor V. Balzani, Dr.D. Matt, specific and efficient for the photoinduced oxidation of CO and and Dr.K.J. Watson for helpful and stimulating discussions, Dr. reduction of H 2 0 . Quantum yields reach 12.796 with 410-nm C. de Bellefon for measuring FT-IR spectra, E. Piedmont for irradiation and may prove to be higher in the presence of even assistance in the determination of the quantum yields, M. Y. more electron withdrawing groups (like -S02CH3 or -CF3) on Guibert for performing the GC/MS analyses, P. Maltbe for the 2,2’-bipyridine chelate. (2) The initial thermal step in the determining 400 MHz NMR spectra, S.Lips for technical asoverall reaction squence involves the coordination of carbon sistance with the carbon dioxide GC analysis, A. Geyer for the glass blowing of the thermostated Schlenk cell, and D. Blitz for (63) Hawecker, J.; Lehn, J.-M.; Ziessel, R. Helu. Chim. A c u 1986, 69, help with the preparation of the manuscript. Financial support 1990 and references cited therein. for this work was provided by the Centre National de la Recherche (64) Kutal, C.; Weber, M. A.; Ferrandi, G.; Geiger, D. Organometallics 1985, 4, 2161. Scientifique.
Metathetical Reactions of Re( VII) Alkylidene-Alkylidyne Complexes of the Type Re( CR’)( CHR’)[ OCMe(CF3)2]2(R’ = CMe3 or CMe2Ph) with Terminal and Internal Olefins Robert Toreki, G.Alan Vaughn, Richard R. Schrock,* and William M. Davis Contribution from the Department of Chemistry, 6-331,Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. Received June 25, 1992. Revised Manuscript Received September 24, I992 Abstract: 1-Deccne and methyl 9-decenoate react with syn- and anti-Re(C-t-Bu)(CH-t-Bu)(ORF6) to give syn- and anriR~(C-~-BU)[CH(CH~),M~](OR~~)~ and syn- and anti-Re(C-t-Bu)[CH(CH2)7C0zMel(OR& respectively (ORF6 = OCMe(CF3)2). The new alkylidene complexes are unstable in the presence of excess terminal olefin and decompose upon attempted isolation. However, vinylferrocene reacts relatively smoothly and reversibly with ~~~-R~(C-~-BU)(CH-~-BU)(OR~~)~ in a noncoordinating solvent to yield tert-butylethylene and primarily unti-Re(C-r-Bu)(CHFc)(ORF6), (Fc = ferrocenyl). ~nri-Re(C-t-Bu)(CHFc)(0R~~)~ (a = 9.769 (2) A, 6 = 30.746 (7) A, c = 10.140 (2) A, B = 116.78 (1)O, V = 2719 (2) A’, space group = R1/o,2 = 4, FW = 815.50, ~(calcd)= 1.992 g/cm3, R = 0.052, R, = 0.050) was shown to be a pseudotetrahedral spbcies with an unusually acute Re==C,-C, angle (1 14.8 (7)O) and short R e bond (1.70 (1) A). In the presence of THF or dimethoxyethane, complexes of the type syn- or anti-Re(C-I-Bu)(CHR)(oR~~)2s2 (R = Me, Et, Ph; S = THF or 0.5DME) and CHz=CHR. Heteroatom-substituted(0,S,or N) could be prepared in high yield from R~(C-~-BU)(CH-Z-BU)(ORF~)~ terminal olefins react more rapidly than ordinary olefins with Re(c-t-Bu)(cH-t-Bu)(OR~~)2 in the presence of THF to yield (X = OR, SR, NRz, or p-dimethylaminophenyl). The complexes of the type syn- or U~~~-R~(C-~-BU)(CHX)(OR~~)~(THF)~ ( a = 10.318 (1) A, 6 = 18.303 (2) A, c = 16.181 (2) A, B = X-ray structure of syn-Re C-t-Bu)(CHOEt)(ORF6)2(THF)z 96.98 (2)O, Y = 3033 (1) space group = R 1 / c ,Z = 4, FW = 819.74, p(ca1cd) = 1.795 g/cm3, R = 0.052, R, = 0.050) showed it to be a pseudooctahedral complex containing cis alkylidyne and alkylidene ligands and a THF ligand trans to each. The R e 0 bond to the THF trans to the neopentylidyne ligand is significantly longer than that trans to the ethoxymethylene ligand; presumably it is the THF ligand trans to the neopentylidyne ligand that exchanges more rapidly with free THF in and intermediate alkyidene solution. 2-Penteneor methyl oleate k metathesized in the presence of R~(C-~-BU)(CH-~-BU)(OR~~)~, followed by TMEDA yields complexes can be observed in each case. Addition of 3-hexene to R~(C-~-BU)(CH-~-BU)(OR~~)~ Re(C-r-Bu)(CHEt)(ORF6),(TMEDA). Internal olefins are metathesized only very Slowly by R~(C-~-BU)(CH-~-BU)(OR~~)~ in the presence of several equivalents of THF or DME or especially in neat THF or DME.
i3,
Introduction It is now well-established that many do alkylidene complexes of T i Nb, Ta, Mo, or W will react with olefins1-’ and that practical ( 1 ) Schrock, R. R. In Reactions of Coordimted Liguds; Braterman, P.
R.. Ed.; Plenum: New York, 1986. (2) Schrock, R. R. J . Orgunomer. Chcm. 1986, 300, 249.
0002-7863/93/1515-127$04.00/0
olefin metathesis or ring-opening metathesis polymerization (ROMP) catalysts can be d c p i e d rationally by ligand variation.a8 (3) Kress, J.; Aguero, A.; Osborn, J. A. J . Molec. Culul. 1986, 36, 1. (4) Kress, J.; Osbom, J. A.; Amir-Ebrahimi, V.; Ivin, K. J.; Rooney, J. J. J . Chem. Soc., Chem. Commun. 1988, 1164. (5) Grubbs, R. H.; Tumas, W. Science 1989, 243, 907.
0 1993 American Chemical Society
128 J. Am. Chem. SOC.,Vol. 115, No.I , 1993
Toreki et 01.
For example, a variety of functional groups in norbornenes and norbomadienes are tolerated by living ROMP initiators of the type MO(CHR’)(NA~)(O-~-BU)~ (R’ = t-Bu or CMe2Ph, Ar = 2,6-C6H3-i-Pr2).+15 New types of ring-opening polymerizat i ~ n s and ~ Jring-closing ~ ~ r e a ~ t i o n sare ~ ~possible *~ with catalysts of this type, in some cases largely because they are active in the absence of Lewis acid cocatalysts. In comparison, metathesis catalyzed by well-characterized rhenium complexes is in its infancy. In a previous paperZSwe described the synthesis of some new Re(VI1) complexes of the type Re(CR’)(CHR’)(OR), (R’ = r-Bu or CMe2Ph; OR = a bulky alkoxide) that are related to Mo and W metathesis catalysts of the type M(CHR’)(NAr)(OR)2 by virtue of the isoelectronic relationship between the M-N- (M = Mo or W) and R e fragments and have reported their activity for the metathesis of olefins in a preliminary fashion.26 Potential advantages of homogeneous rhenium metathesis catalysts versus Mo or W catalysts, at least according to data accumulated using heterogeneous rhenium catalyst s y ~ t e m s , ~ ~are -~O a greater tolerance of functionalities and a dflerent and/or higher stereuselectivity in ROMP reactions. The possible trade-off for Re versus W or Mo catalysts is a decrease in reactivity and a greater tendency for rhenium to be reduced. In this paper, we report reactions of rhenium complexes of the type Re(CR’)(CHR)[OCMe(CF3)2]2 with some internal and terminal olefins, including those that lead to heteroatom-substituted do alkylidene complexes and productive metathesis of intemal olefins. Reactions involving ethylene, norbornenes, and norbornadienes will be reported separately. (e)
(6) Feldman, J.; Schrock, R. R. Prog. Inorg. Chem. 1991, 39, 1. (7) Wu, 2.;Wheeler, D. R.; Grubbs, R. H . J. Am. Chem. Soc. 1992,114, 146. (8) Schrock, R. R. Acc. Chem. Res. 1990, 23. 158. (9) Bazan, G.; Khosravi, E.; Schrock, R. R.; Feast, W. J.; Gibson, V. C.; ORegan, M.B.;Thomas, J. K.; Davis, W. M. J. Am. Chem. Soc. 1990,112, 8378. (10) Sankaran, V.; C u m “ , C. C.; Schrock, R. R.; Cohen, R. E.; Silky, R. J. J. Am. Chem.Soc. 1990, 112,6858. (1 1) Saunders, R. S.;Cohen, R. E.; Schrock, R. R. Macromolecules 1991, 24, 5599. (12) Bazan, G. C.; Oskam, J. H.;Cho, H.-N.; Park, L. Y.; Schrock, R. R. J. Am. Chem. Soc. 1991,113,6899. (13) Sankaran, V.; Cohen, R. E.; Cummins, C. C.; Schrock, R. R. Mucromolecules 1991, 24, 6664. (14) Cummins, C. C.; Beachy, M. D.; Schrock, R. R.; Vale, M. G.; Sankaran, V.; Cohen, R. E. Chem. Murer. 1991, 3, 1153. (15) Bazan, G. C.; Schrock, R. R.;Cho, H.-N.; Gibson, V. C . Mucromolecules 1991, 24, 4495. (16) Klavetter, F. L.;Grubbs. R. H . J. Am. Chem. Soc. 1989,110,7807. (17) Ginsburg, E. J.; Gorman, C. B.; Marder, S.R.; Grubbs, R. H. J. Am. Chem. Soc. 1989,111.7621. (18) Knoll, K.; Schrock, R. R. J. Am. Chem. Soc. 1989, I 1 I , 7989. (19) Sailor, M. J.; Ginsburg, E. J.; Gorman, C. B.; Kumar, A.; Grubbs, R. H.;Lewis, N. S . Science 1990, 249, 1146. (20) Wagener, K. B.; Nel, J. G.; Konzelman, J.; Boncclla, J. M. Mucromolecules 1990, 23, 5155. (21) Wagmer, K.B.; Boncella, J. M.; Nel, J. G. Mucromolecules 1991, 24, 2649. (22) Lautens, M.; Crudden, C. M.; Abd-El-Aziz, A. S.;Wada, T. Mucromolecules 1991. 24, 1425. (23) Fu, G. C.; Grubbs, R. H . J. Am. Chem. Soc. 1992, 114, 5426. (24) Fu, G. C.; Grubbs, R. H. J . Am. Chem. Soc. 1992, 114,7324. (25) Toreki, R.; Schrock, R. R. J. Am. Chem. Soc. 1992, 114, 3367. (26) Toreki, R.; Schrock, R. R. J. Am. Chem. Soc. 1990, 112, 2448. (27) Ivin, K. J. Olefin Merurhesis; Academic: New York, 1983. (28) Dragutan, V.;Balaban, A. T.;Dimonie, M. Olefin Merurhesis and Ring-Opening Polymerizurion of Cyclo-Olefins, 2nd 4.; Wiley: New York, 1985. (29) Mol,J. C. J. Mol. Curul. 1991, 65, 145. (30) Herrmann, W. A.; Wagner, W.; Flessner, U. N.;Volkhardt, U.; Komber, H . Angew. Chem., Inr. Ed. Engl. 1991, 30, 1636.
12.8
12.6
12.4
12.2
12.0
11.8
11.6
11.4
11.2
Figure 1. (a) Re(C-r-Bu)(CH-r-Bu)(ORFs)z (27 mM) in C6D6 plus 1 equiv of 1-decene. (b) Sample in part a plus 5 equiv of methyl acetate. (C) Re(C-r-Bu)(CH-l-Bu)(ORF,)2 (34 mM) in C6D6 PIUS methyl 9decenoate (0.7 equiv); spectrum recorded after 25 min. (d) Re(C-rBU)(CH-~-BU)(OR,)~(34 mM) in C6D6plus (i) 1-deccne (0.7 equiv) followed by (ii) methyl oleate (4.7 equiv); spectrum recorded after 15 min. (e) Sample in part d 14 h later; H, intensities had decreased by 30%.
Results R ~ c ~ ~Involving o M Termlnrl OIefins in the Abeenee of Coordinating Solvents .ad the X-ray Structure of rab’-Re(C-t-Bu)(CHFc)(OR& (Fc = Ferroceayl). Reactions between ordinary terminal olefins and complexes of the type Re(CR’)(CHR’)(OR), (R’ = t-Bu or CMe2Ph) in the absence of coordinating solvent (e.g., THF) are slow (hours) when OR = 0-r-Bu and fast (seconds) when OR = OCMe(CF3)2. For example, in Figure l a is shown the reaction of 1 equiv of 1-decene with a mixture of anti (Ha at 12.48 ppm) and syn (Ha at 11.05 ppm) isomers of Re(C-~-BU)(CH-~-BU)(OR~~)~~~ in benzene-d6 (ORF6 = OCMe(CF3)2). New resonances for anti (Ha at 12.54 ppm; J H H = 7 Hz) and syn (Ha at 11.19 ppm; J H H = 5 Hz) rotamers of Re(C-~-BU)[CH(CH~)~M~](ORF~)~ are clearly observable in equilibrium with those of syn- and anti-Re(C-t-Bu)(CH-1Bu)(0RF6),. (syn and anti assignments for Re(C-r-Bu) [CH( C H ~ ) ~ M ~ ] ( O are R F based ~ ) ~ on the known upfield shift for Ha in syn rotamers vs Ha in anti rotamers for Re(C-1-Bu)(CH-rBu)(OR& and other compounds of this tvpe that are discussed later.25) If several equivalents of 1-decene are added, the H, resonances for syn- and anti-Re(C-r-Bu)[CH(CH2)7Me](ORF6)2 lose intensity and all Re( C-1-Bu)(CH-t-Bu) (ORF& eventually is consumed, consistent with decomposition of syn- and antiRe(C-t-Bu) [ C H ( C H ~ ) ~ M ~ ] ( O R in Fthe ~ ) ~presence of excess 1-decent. We show later that terminal allcylidene complexes of this type are relatively stable in dilute solution when they are prepared from an internal olefin. Therefore their instability in the presence of excess 1-decene can be ascribed either to some adverse reaction involving 1-decene or to one involving ethylene
J. Am. Chem. SOC.,Vol. 115, No. 1. 1993
Re( VU) Alkylidene-Alkylidyne Complexes
129
Tabk I. Pertinent NMR Data for New Re(C-t-Bu)(alkylidene) [OCMe(CF3)2]2Complexes in C6D6 complex
~~~~
bCHR' 6CHR' 12.49 254.0 12.30 261.2 13.02 249.8 Re(C-r-Bu) [CH@-C6H4NMe2)]( O R F ~ ) ~ ( D M E ) ~ 12.94 ~~~-R~(C-~-BU)(CHE~)(OR,,)~(TMEDA) 12.20 273.3 ~~~-R~(C-~-BU)(CHOE~)(OR,~)~(THF)~ 11.56 265.7 u~~~-R~(C-~-BU)(CHOE~)(ORF~)~(THF)~11.93 266.7 ~~~-R~(C-~-BU)(CHOE~)(OR~~)~" 11.03 syn-Re(C-r-Bu) [CH(CH2)7Me](ORF6)2LI 11.19 mi-Re(C-r-Bu) [ C H ( C H ~ ) , M ~ ] ( O R F ~ ) ~ " 12.54 syn-Re(C-r-Bu) [CH(CH2)7C02Mel(ORF6)20 11.97 anti-Re(C-r-Bu) [CH(CH2)7C02Me]( O R F ~ ) ~ " 12.64 ~~~-R~(C-~-B~)(CHOS~M~,)(ORF~)~(THF)~ 12.50 259.5 ~~~~-R~(C-~-BU)(CHOS~M~,)(OR~~)~(THF)~ 12.82 264 ~~~-R~(C-~-BU)(CHSP~)(OR~~)~(THF)~ 12.31 238.6 onri-Re(C-r-Bu)(CHSPh)(oR~6)2(THF)2 12.50 224.3 ~~~-R~(C-~-BU)(CHSP~)(OR~~)~(~-BUNH~)~~ 13.55 262.2 anri-Re(C-r-Bu)(CHSPh)(OR~6)2(t-BuNH2)2~ 13.76 258.5 213.3 anti-Re(C-r-Bu) [CHN(CH2),CO](ORF6)2 10.92 syn-Re(C-r-B~)(cHFc)(oR~~)~ 11.72 228.9 U~I~-R~(C-~-BU)(CHFC)(OR~~)~ 13.15 232.3 "Observed in situ; I3C NMR data were not obtained. bsyn/anti assignment is uncertain.
syn-Re(c-r-B~)(cHMe)(oR,~)~(DME) syn-Re(c-r-B~)(cHEt)(oR~~)~(DME) syn-Re(c-r-Bu)(CHPh)(oR~~)2(DME)
that is formed by productive metathesis. The latter possibility is suggested by the fact that decompition is induced upon adding in benzethylene to a sample of Re(C-t-BU)(CH-t-BU)(OR,,), ene-d6. (Reactions involving ethylene will be reported separately.") It is important to note that methyl acetate does not react readily with the sample whose spectrum is shown in Figure la. However, some of the Ha resonance-sshift downfield (Figure lb). A 1-15 ppm shift in the Ha resonance of an alkylidene ligand upon formation of an adduct of a well-characterized four-coordinate alkylidene complex is norma1.7-32*33 Therefore the shift in Ha correlates roughly with the extent of adduct formation. In this vein it is interesting to note that the H, resonance for U~~~-R~(C-~-BU)(CH-Z-BU)(OR,~)~ doesn't Shift at all, While that for syn-Re(C-t-Bu)[CH(CH,)7Me](ORF6)2 Shifts the mOst Of any (ca. 0.8 ppm). These results suggest that methyl acetate binds weakly to anti-Re( C-t-Bu) (CH-t-Bu) (OR,,) but relatively (OR,),. Five-coorstrongly to ~~~-R~(C-~-BU)[CH(CH,)~M~] dinate adducts of well-characterizedfour-coordinate alkylidene complexes have been found to be relatively unreactive toward 0 l e f i n s , 7 - presumably ~~~~~ because the donor ligand blocks olefin access to the metal. In Figure IC is shown the result of adding 0.7 equiv of methyl 9-decenoate to a mixture of syn- and anti-Re(C-2-Bu)(CH-tBu)(ORF6),;new Ha resonances for anti- and syn-Re(C-t-Bu)[CH(CH2)7C02Me](ORF6)2 can be Observed at 12.64 and 11.97 ppm, respectively. If a similar reaction is carried out with an unequal mixture of 1-decene and methyl 9-decenoate (less than 1 equiv total), then it is found that the Ha resonances for antiand syn-Re(C-1-Bu)[CH(CH2)7Me](OR,), can be resolved from (OR,), those for anti- and syn-Re(C-t-Bu)[CH(CH2)7C02Me] at 500 MHz, the H, resonances for anti- and syn-Re(C-1-Bu)[CH(CH2)7Me](ORF6),coming downfield from those for antiand syn-Re(C-2-Bu) [CH(CH2)7C02Me] (ORF6),, The exact chemical shift for H, in each compound depends on conditions, as chemical shifts are sensitive to the presence of the ester group, as noted above. The ability to observe all four of these terminal akylidenecomplexes will prove important later in a study involving the metathesis of methyl oleate. Addition of excess methyl 9also leads to loss of decenoate to Re(C-t-Bu)(CH-t-Bu)(ORF6), intensity for the Ha resonances in syn- and anti-Re(C-t-Bu)[CH(CH2)7C02Me](ORF6),, consistent with sample decomposition.
,
(31) Vaughan, G. A.; Toreki, R.; Schrock, R. R.; Davis, W. M. Submitted. (32) Schrock, R. R.; Rocklage, S.M.; Wengrovius, J. H.; Rupprecht, G.; Fellmann, J. J . Mol. Caral. 1980, 8, 73. (33) Schrock, R. R.; Crowe, W. E.;Bazan, G. C.; DiMare, M.; ORegan, M.B.;Schofield, M. H.Organomrrallics 1991, 10, 1832.
129 128 127
bcR 290.6 290.8 291.2
125 135 163
287.1 295.9 301.3
135 166 143 184 151 145 173 132 173
295.6 299.7 297.3 300.8 286.8 289.4 301.5 298.5 304.2
JP"
Table 11. Intramolecular Distance (A) and Angles (deg) for the Non-Hydrogen Atoms in anti-Re(C-I-Bu)(CHFc)[OCMe(CF1)*]* Bond Distances 1.39 (1) Re-O(l) 1.916 (6) O ( l ) C ( l l ) Re-O(2) 1.928 (6) 0 ( 2 ) C ( 2 1 ) 1.40 (1) Rd(1) 1.70 (1) C(l)C(lO) 1.51 (1) Re-C(2) 1.88 (1) C(2)C(201) 1.45 (1) 0(1)-Re-0(2) O(l)-RtC(l) O(l)-RtC(2) 0(2)-R&(l) 0(2)-RtC(2)
Bond Angles 120.4 (3) C(l)-RtC(2) 111.9 (4) R4(1)
