280
Organometallics 1986,5, 280-297
The Chemistry of (Fulva1ene)dimolybdenum Hexacarbonyl: A Rigidly Held Dinuclear Transition-Metal Complex James S. Drage and K. Peter C. Vollhardt' Department of Chemistry, University of California, Berkeley, and the Materials and Molecular Research Division, Lawrence Berkeley Laboratory, Berkeley, California 94 720 Received August 13, 1985
The X-ray structure of (fulva1ene)dimolybdenum hexacarbonyl [FvMoz(CO),] has been determined. Thermal, photolytic, and chemical treatment failed to yield the metal-metal triply bonded complex FVMO~(CO)~, either because it was not formed or because of its instability; this result may have been caused by excessive bond strain in the fulvalene ligand. Photolysis of FvMoz(CO)Gin the presence of alkynes afforded mono- and bis(a1kyne) complexes FVMO~(CO)~(RCSCR) and FVMO~(CO)~(RC=CR)~. Spectroscopic evidence indicated that the former bears as a ligand a cL-$-alkyne and that this ligand partially moved about the Mo-Mo bond in a rapid fluxional process: AG* = 15 f 0.5 kcal mol-'. The bis(a1kyne) systems contained uncoupled alkynes as determined by an X-ray diffraction study of one complex. This result is unusual in light of the frequent occurrence of alkyne coupling at a dinuclear center. Reduction of FVMO~(CO)~ with Na-Hg or LiBEt3H furnished the dianion FvMoz(CO)a-. The latter reacted with protic acids and haloalkanes to give the respective dihydride FVMO~(CO)~H~ and dialkyl complexes F V M O ~ ( C ~ ) ~ R ~ (R = CH3, CH2Ph, CH20CH3). A t 20 "C the dihydride eliminated Hzwith formation of FVMO~(CO)~. ~ C HBF4.(Et20) H~)~ at -20 "C (CD2Cl2)produced FVMO~(CO)~Treatment of F V M O ~ ( C O ) ~ ( C H ~with (CH20CH3)(=CH2)+,as determined by lH NMR spectroscopy. Warming to 0 "C gave the carbene-coupling product F V M O ~ ( C ~ ) ~ ( CThe ~ H bidcarbene) ~)~+. FVMO~(CO)~(=CH was ~ )not ~ ~ +detected. The dianion FvMo2(C0)2-reacted with I(CHz)31to give a metal-metal bonded 1-oxacyclopent-2-ylidenecomplex. An X-ray diffraction analysis showed that the Fischer-type carbene ligand was terminally bound. This complex exhibited fluxional behavior which may involve a bridging carbene species (AG* = 18 f 0.5 kcal mol-'). Thermolysis (100 "C) led to efficient generation of propene and FVMO~(CO)~ by a novel pathway. Organometallic compounds containing two transition metals, typically referred to as "dinuclear" complexes, have been intensively studied in recent years.l These materials have been regarded with considerable interest in part because they have been proposed as models for the interaction of organic molecules with metal surfaces. Dinuclear complexes are also attractive as potential catalysts for synthetic organic transformations.ld One of the rationales for the study of these systems is the anticipation that their chemical behavior may differ significantly from that of analogous mononuclear complexes.1c A common hypothesis is that concerted or cooperative interaction of two metal centers with a substrate might lead to transformations which do not occur when only one metal is invo1ved.l The validity of this idea has not been demonstrated unambiguously, for there have been few closely related mono- and dinuclear complexes suitable for comparison. Synthetically, a wide variety of ligands has been employed in order to anchor two metals in close proximity. The most common classes include diphosphines,2 diarsines,2 ortho-metalated aryl phosphine^,^ phosphide,* amido: alkoxido,6 alkyl sulfido,6 carbonate; and pyrazolate (1)(a) Muetterties, E. L.; Rhodin, R. N.; Band, E.; Brucker, C. F.; Pretzer, W. R. Chem. Reo. 1979,79,91. (b) Bruce, M. I. J . Organomet. Chem. 1983,242,147.(c) Bergman, R. G. Acc. Chem. Res. 1980,13,113. (d) Schore, N. E.; Ilenda, C. S.; White, M. A.; Bryndza, H. E.; Matturro, M. G.; Bergman, R. G. J . Am. Chem. SOC.1984, 106, 7451 and the references therein. (2)Maitlis, P.M.; Espinet, P.; Russell, M. J. H. In "Comprehensive Organometallic Chemistry"; Wilkinson, G., Stone, F. G. A,, Abel, E., Eds.; Pergamon Press: New York, 1982;Vol. 6,p 268. (3)Arnold, D. P.;Bennett, M. A.; McLaughlin, G. M.; Robertson, G. B.; Whittaker, M. J. J . Chem. SOC.,Chem. Commun. 1983,32. (4)(a) Puddephatt, R. J.; Thompson, P. J. J . Organomet. Chem. 1976, 117, 395. (b) Ebsworth, E. A. V.; Ferrier, H. M.; Henner, B. J. L.; Ranking, D. W. H.; Reed, J. F. S.; Robertson, H. E.; Whiteloch, J. D. Angew. Chem., Int. Ed. Engl. 1977,16,482. 15) Richter, U.; Vahrenkamp, H. J . Chem. Res., S ~ n o p .1977, 156.
0276-7333/86/2305-0280$01.50/0
anions.* Linkage of two dissimilar metals has been achieved by using heterodifunctional ligands, cyclopentadienylphosphido dianions being recent example^.^ Most of the neutral ligands, such as diphosphines, suffer the disadvantage of forming relatively weak bonds to transition metals, with the result that bridged compounds have limited thermal stability. In contrast, ligands which contain cyclopentadienyl (Cp) rings should form more robust connections to dinuclear metal systems. Typical dissociation enthalpies of trialkylphosphine-metal bonds fall in the range of 30-40 kcal mol-', whereas q5-cyclopentadienyl metal bond energies have been estimated to vary between 60 and 70 kcal mol-'.lo In a few cases, two Cp rings connected by methylenell or dimethylsilene12 units have been employed as bridging ligands. Thus far, none of these compounds has exhibited reactivities significantly different from those of the analogous cyclopentadienyl complexes. Strong divergence from the chemistry of Cp metal dimers might exist in dinuclear complexes in which the (6)(a) Kopf, H.; Rathlein, K. H. Angew. Chem., Int. Ed. Engl. 1969, 8, 980. (b) Braterman, P.S.; Wilson, V. A.; Joshi, K. K. J . Chem. SOC. A 1971, 191.
(7) Hughes, R. P. In "Comprehensive Organometallic Chemistry"; Wilkinson, G., Stone, F. G. A., Abel, E., Eds.; Pergamon Press: New York, 1982;Vol. 5,p 277. (8)Weiss, J. C.;Beck, W. Chem. Ber. 1972,105,3203. (9)Casey, C. P.; Bullock, R. M.; Nief, F. J. Am. Chem. SOC.1983,105, 7574 and references therein. (10)Connor, J. A. Top. Curr. Chem. 1976, 71, 71. (11) (a) Bryndza, H.E.; Bergman, R. G. J. Am. Chem. SOC.1979,101, 4766. (b) Mueller-Westerhoff, U.T.; Nazzal, A.; Tanner, M. J . Organo-
met. Chem. 1982,236,C41. (12)(a) Day, V. W.; Thompson, M. R.; Nelson, G. 0.; Wright, M. E. Organometallics 1983,2,494.(b) Nelson, G.0.;Wright, M. E. Ibid. 1982, I , 565. (c) Nelson, G.0.;Wright, M. E. J. Organomet. Chem. 1982,239, 353. (d) Wegner, P.A.; Uski, V. A.; Kiester, R. P.; Dabestani, S.; Day, V. W. J . Am. Chem. SOC.1977,99,4846. (e) Weaver, J.; Woodward, P. J . Chem. Soc., Dalton Trans. 1973,1439. (f) Wright, M. E.; Mezza, T. M.; Nelson, G. 0.; Armstrong, N. E.; Day, V. W.; Thompson, M. R. Organometallics 1983,2,1711.
0 1986 American Chemical Society
Organometallics, Vol. 5, No, 2, 1986 281
Chemistry of (Fulva1ene)dimolybdenum Hexacarbonyl
entry 1 2 3
Table I. Correlation of Metal-Metal Distance with the Dihedral Angle B (deg) compd M-M, A e (s5:s5-C~oHdzFez 3.984 2.6 3.329 13.6 (s5:s5-CloH8)2V(NCCH3)22+ 3.371 3.347 3.227 3.053 2.821 2.719
Figure 1. ORTEP drawing of 1 with labeling scheme. View is from the “side” of the molecule. The ellipsoids are scaled to represent the 50% probability surface. Hydrogen atoms, where shown, are given as arbitrary small spheres, and are labeled according to the carbon to which they are attached.
metals are bridged by two joined Cps as in the fulvalene ligand, shown in generalized form in A. In the absence
15.3 16.1 17.5 18.1 28.5 31.6
ref 20c 20b
this work 20d 20a 20e 16 18a
W Figure 2. “End”-viewof 1. The ellipsoids are scaled to represent the 50% probability surface.
chemistry of 1 and compare it with that of (a5C6H5)zMoz(C0)6,which differs in its reactivity both quantitatively and qualitatively.l8 In the subsequent discussion the fulvalene ligand will be abbreviated Fv.
Results and Discussion X-ray Structural Analysis of F V M O ~ ( C O(I). ) ~ In LnM--M
Ln
A
of a metal-metal bond, the fulvalene should hold the metal centers relatively closely together and thereby enforce stronger interactions between them. It may also be expected that novel reactivity in these compounds could arise from a bending distortion of the n-ligand in metal-metal bonded systems. Indeed, the intermetal distance in a planar q5:q5-bridgingfulvalene complex has been estimated to be about 4.0 A,13 whereas most M-M bonds are less than 3.5 A. Strain energy resulting from this distortion may cause the metal-metal bonds to be weaker and more reactive as compared to those of the Cp analogues. Fulvalene might also exert novel electronic effects on its environment. The metal atoms in fulvalene complexes should be more electron-rich compared to the metals in Cp metal dimen.’* In addition, fulvalene should provide electronic communication between the two metal centers regardless of whether there is a metal-metal bond or not. Electrochemical evidence for this phenomenon has already been observed in a dirhodium system.15 We have recently reported a new entry into the class of “half-sandwich” fulvalene systems based on the discovery that dihydrofulvalene is relatively stable when pure and can therefore be reacted with metal carbonyls at elevated temperatures to give a number of fulvalene dimetal carbonyls,16including ( l ) . I 7 In this paper we describe the (?5:q5-CloH,)(CO)6M02 (13) Smart, J. C.; Curtis, C. J. J. Am. Chem. SOC.1977, 99, 3518. (14) For an MO diagram of fulvalene see: Streitwieser, A., Jr.; Brauman, J. I. “Supplemental Tables of Molecular Orbital Calculations”; Pergamon Press: London, 1965; Vol. I, p 87. (15) Connelly, N. G.; Lucy, A. R.; Payne, J. D.; Galas, A. M. R.; Geiger, W. E. J. Chem. SOC.,Dalton Trans. 1983, 1879. (16) Vollhardt, K. P. C.; Weidman, T. W. Organometallics 1984,3,82; J . Am. Chem. SOC.1983, 105, 1676. (17) Smart, J. C.; Curtis, C. Inorg. Chem. 1977, 16, 1788.
order to ascertain the surmised presence of strain in 1, an X-ray structural investigation was perf~rmed.’~Figures 1 and 2 show two views of the molecule, clearly confirming the molecular structure. As in other fulvalene dimetal systems which have been characterized in this way (Table I), the metals are nearly symmetrically bound to all five Cp carbons. The bonds linking the two Cps in 1 and other systems vary only slightly (1.43-1.47 A). Perhaps the most interesting feature with respect to structure-activity relationships is the enforced bend of the fulvalene ligands from planarity because of the metal-metal bond. The bend angle 6 (the “dihedral angle” between the two Cp planes) generally increases with decreasing metal-metal bond length (Table as might be expected. Similar to the tungsten analogue of 1,20dfor which a “stretched” metal-metal bond was invoked, the Mo-Mo distance (3.371 A) in 1 is unusually long compared with models, such as ( C ~ M O ) ~ ((3.235 C ~ ) A) ~ ~or~ (qlO-dihydroheptalene)dimolybdenum hexacarbonyl (3.193 A) ,23 boding well for unusual chemistry. The bond distances and angles in the molecule are given in Table 11. (18) Preliminary reports of some of the aspects of this work have appeared (a) Drage, J. S.; Tilset, M.; Vollhardt, K. P. C.; Weidman, T. W. Organometallics1984,3,812. (b) Drage, J. S.; Vollhardt, K. P. C. Ibid. 1985,4, 191. (19) We thank M. Tilset for providing crystals suitable for X-ray
diffraction. (20) (a) Bashkin, J.; Green, M. L. H.; Poveda, M. L.; Prout, K. J. Chem. SOC.,Dalton Trans. 1982, 2485. (b) Smart, J. C.; Pinsky, B. L.; Frederich, M. F.; Day, V. W. J. Am. Chem. SOC.1979, 101, 4371. (c) Churchill, M. R.; Wormald, J. Inorg. Chem. 1969, 8, 1970. (d) Abrahamson, H. B.; Heeg, M. J. Inorg. Chem. 1984,23,2281. (e) Cooper, N. J.; Green, M. L. H.; Couldwell, C.; Prout, K. J. Chem. SOC.,Chem. Commun. 1977, 145. (21) Guggenbarger, L. J.; Tebbe, F. N. J. Am. Chem. SOC.1976, 98, 4137. (22) Adams, R. D.; Collins, D. M.; Cotton, F. A. Inorg. Chem. 1974,13, 1086. (23) Lindley, P. F.; Mills, 0. S. J. Chem. SOC.A 1969, 1286.
282 Organometallics, Vol. 5, No. 2, 1986
Drage and Vollhardt
Photoinduced Reactions of 1. As mentioned earlier, an investigation of the chemistry of F V M O ~ ( C O ) ~was (1) initiated with the intent of discovering new processes distinct from those seen for Cp2M02(CO)G.In light of the extensive and varied transformations observed for the metal-metal triple-bonded complex C ~ , M O ~ ( C O )we ,,~~ sought the preparation of the fulvalene analog FVMO~(CO)~ by both photochemi~al~"~~ and thermal means. It was of interest whether a (presumably higher strained) triplebonded dinuclear system bridged by the fulvalene ligand was accessible. On the basis of the reactivity of Cp2M02(CO),in the presence of we anticipated an equal plethora of reactions with 1. Cp2Moz(CO),can be prepared in high yield by heating Cp2M02(CO)6in boiling m - ~ y l e n e . ~ ~ In~ contrast, J~~ we found that F v M o ~ ( C O(1) ) ~ possessed remarkable thermal stability. Heating it in toluene to 110 "C or in triglyme to 216 "C for several days lead only to slight decomposition. Flash torr) gave only starting vacuum pyrolysis at 550 "C material (55 % yield) and intractable decomposition materials at the site of sublimation and in the hot zone of the pyrolysis tube. Higher temperature pyrolyses were not carried out. Turning to irradiative techniques,28awe attempted the photochemical synthesis of FvMo2(CO), from 1. The UV-visible spectrum of 1 in THF shows absorptions at 378 and 558 nm which are assigned to u ---* u* and d r u* excitations associated with metal-metal bonding and metal nonbonding electrons.'' The Cp2M02(C0)6complex in THF exhibits the correspondingtransitions at 388 and 512 nm.25 Irradiation of 1 in THF (0.001 M, 20 "C) with 250-, 300-, or 350-nm light led within an hour to extensive decomposition to intractable materials. After 5 h in bright sunshine the same result was observed. Purging the so-
-
(24) Davis, R.; Kane-Maguire, L. A. P. In "Comprehensive Organometallic Chemistry"; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: New York, 1982; Vol. 3, p 1149. (25) Geoffroy, G. L.; Wrighton, M. S. "Organometallic Photochemistry"; Academic Press: New York, 1979; Chapter 2. (26) Stiegman, A. E.; Tyler, D. R. Acc. Chem. Res. 1984, 17, 61. (27) (a) Wrighton, M. S.; Ginley, D. S. J. Am. Chem. SOC. 1975, 97, 4246. (b) Laine, R. M.; Ford, P. C. Inorg. Chem. 1977, 16, 388. (c) Hughey J. L., IV; Bock, C. R.; Meyer, T. J. J . Am. Chem. Soc. 1975,97, 4440. (d) Mahmoud, K. A.; Rest, A. J.; Alt, H. G. J. Organomet. Chem. 1983,246,C37. (e) Hooker, R. H.; Mahmoud, K. A.; Rest, A. J. Ibid. 1983, 254, C25. (0 Haines, R. J.; Nyholm, R. S.; Stiddard, M. H. B. J . Chem. SOC.A 1968,43. (g) Klinger, R.; Butler, W.; Curtis, M. D. J . Am. Chem. SOC.1975,97,3535. (h) Stiegman, A. E.; Tyler, D. R. J. A m . Chem. SOC. 1982,104,2944. (i) Stiegman, A. E.; Stieglitz, M.; Tyler, D. R. Ibid. 1983, 105, 6032. ti) Ginley, D. S.; Wrighton, M. S. Ibid. 1975, 97, 3533. (k) Hackett, P.; ONeil, P. S.; Manning, A. R. J . Chem. SOC.,Dalton Trans. 1974,1625. (1) Goldman, A. S.;Tyler, D. R. J. Am. Chem. SOC. 1984,106, 4066. (28) (a) Ginley, D. S.; Bock, C. R.; Wrighton, M. S. Inorg. Chim. Acta 1977,23, 85. (b) Bailey, W. I., Jr.; Chisholm, M. H.; Cotton, F. A.; Rankel, L. A. J. Am. Chem. SOC.1978,100,5764. (c) For comparison, the Mo-Mo distance in C ~ , M O ~ ( Cis O 3.235 ) ~ A, see ref 22. (29) (a) Knox, S. A. R.; Stansfield, R. F. D.; Stone, F. G. A.; Winter, M. J.; Woodward, P. J. Chem. SOC.,Chem. Commun. 1978, 221; J . Chem. SOC.,Dalton Trans. 1982, 173. (b) Boileau, A. M.; Orpen, A. G.; Stansfield, R. F. D.; Woodward, P. Ibid. 1982, 187. (c) Beck, J. A.; Knox, S.
A. R.; Stansfield, R. F. D.; Stone, F. G. A.; Winter, M. J.; Woodward, P. Ibid. 1982,195. (d) Curtis, M. D.; Klingler, R. J. J . Organomet. Chem. 1978, 161, 23. (e) Adams, R. D.; Katahira, D. A.; Yang, L. Organometallics 1982, 1, 231. (0 Brunner, H.; Buchner, H.; Wachter, J. J. Organomet. Chem. 1983,244, 247. (9) Alper, H.; Petrignani, J.; Einstein, F. W. B.; Willis, A. C. J . Am. Chem. SOC. 1983,105,1701. (h) Brunner, H.; Wachter, J.; Wintergerst, H. J . Organomet. Chem. 1982,235,77 and references therein. (i) Alper, H.; Einstein, F. W. B.; Nagai, R.; Petrignani, J.; Willis, A. C. Organometallics 1983, 2, 1291. (i) Alper, H.; Einstein, F. W. B.; Petrignani, J.; Willis, A. C. Ibid. 1983,2, 1422 and references therein. (k) Endrich, K.; Korswagen, R.; Zahn, T.; Ziegler, M. L. Angew. Chem., I n t . Ed. Engl. 1982, 21, 919. (1) Green, M.; Orpen, A. G.; Schaverien, C. J.; Williams, I. D. J . Chem. Soc., Chem. Commun. 1983, 181. (m) Herrmann, W. A.; Ihl, G. J. Organomet. Chem. 1983,251, C1. (n) Messerle. L:Curtis, M. D.J . .4m.Chem. Soc. 1980. 102, 7789; 1982, 104, 889,.
-3O'C
0 '
Figure 3. Dynamic IH NMR behavior of diphenylethyne complex 3 between -20 and +60 "C. Coalescence of the two low field fulvalene signals occurred at +35 "C.
lution with N2 during irradiation in order to expel carbon monoxide accelerated the decomposition. Photolysis with 300-nm light at -30 "C gave roughly the same rate of decomposition as at 20 "C. Attempts to detect any photogenerated intermediates by use of IR or 'H NMR spectroscopywere unsuccessful. In all cases only residual starting material was observed. Treatment of 1 with trimethylamine oxide30did not give any new characterizable products. The failure to generate FvMo2(CO),was attributed to steric constraints associated with the fulvalene ligand. Considering that the triple bond in Cp2M02(CO),is 2.448 A 10ng,~~g the fulvalene ligand in FvMo2(CO), would be severely strained. In the photolysis of 1 it is not known whether FvMo,(CO)~was produced with subsequent decomposition, or if some other unstable species was formed. The hexacarbonyl 1 was then irradiated in the presence of various ligands with the expectation that the latter would attack a transiently photogenerated fulvalene complex, possibly FvMo,(CO),. Reagents such as phosphines [PPh,, P(OMe),], hexamethylbenzene, and cyclooctatetraene did not react at all, whereas acetonitrile, pyridine, 2,2'-bipyridine, thiophenol, and diphenyl disulfide gave only intractable undefined materials. However, alkynes were found to smoothly displace CO ligands from 1 to form mono- and bis(a1kyne) complexes. For example, photolysis (300 nm) in the presence of 10 equiv of dimethyl ethynedicarboxylate in THF at 20 "C with a slow N2 purge caused a gradual color change from the purple of 1 to orange-red. After 5 h about 90% of the starting material had disappeared, and two new compounds were present which were subsequently formulated as FvMo&CO)~(RCCR) and FVMO~(CO)~(RCCR),. These products were cleanly separated by chromatography. The first product isolated from this reaction was the mono(alkyne)2 (orange crystals, mp 164-165 "C dec, 14% yield). The C, H analysis and mass spectrum (M+ at m/e
,
R 2 C 2 . T H F . 20'C.
5 h . N 2 purge, h v ( 3 0 0 n m )
+kco
@TQ \ --Ma Ma-
oc 3 u ( P ) were R = 1.77%, W R = 3.27%, and GOF = 2.08. The R value for all 2411 data was 1.97%. The quantity minimized by the least-squares program was Cw(lFoI - lFc1)2,where w is the weight of a given observation. The p factor, used to reduce the weight of intense reflections, was set to 0.025 throughout the refinement. The analytical forms of the scattering factor tables for the neutral atoms were used, and all non-hydrogen scattering factors were corrected for both the real and imaginary components of anomalous dispersion. Inspection of the residuals ordered in ranges of (sin 6')/A, IF,,], and parity and value of the individual indexes showed the absence of unusual features or trends. Examination of the high-intensity, low-angle data just prior to the final cycles of least squares revealed indications of secondary extinction. An isotropic extinction parameter was included in the last cycles of refinement. The largest peak in the final difference Fourier map had an electron density of 0.25 e/W3. The positional and thermal parameters of the refined atoms and a listing of the values of F, and F, are available as supplementary material. ( l-Oxacyclohex-2-ylidene)FvMo2(CO)6(21). A THF solu(1;) ~300 mg, 0.615 mmol) tion of 10 was prepared from F V M O ~ ( C O and 1,4-diiodobutane (97 pL, 0.738 mmol) added by syringe to the reaction mixture a t 20 OC. After 1 day the color had turned dark brownish red, and there was a large amount of insoluble material. In an Nz atmosphere glovebox a sample of the solution was transferred to an infrared liquid cell, which was then closed tightly. The IR spectrum indicated the presence of only 21. Solvent removal from the reaction mixture by rotary evaporation and chromatography (alumina, acetone-pentane) afforded red crystalline 21 (mp 187-188 OC dec; 29 mg, 7%): 'H NMR (300 MHz, C,D,) 6 5.08 (m, 2 H), 4.44 (m, 2 H), 4.04 (m, 2 H), 3.55 (m, 2 H), 3.47 (t, J = 6.1 Hz, 2 H), 3.24 (t,J = 6.9 Hz, 2 H), 1.26 (apparent quintet, J = 6.3 Hz, 2 H), 1.04 (apparent quintet, J = 6.3 Hz, 2 H); IR (THF) 2018,1987,1962,1928,1908 cm-'; MS, m / e (relative intensity) 544 (M', 2), 5.16 (17), 488 (3), 460 (7),
Chemistry of (Fulva1ene)dimolybdenumHexacarbonyl 432 (lo), 404 (lo), 376 ( 5 ) ,43 (100). Magnetization Transfer Experiments Applied to 20. A solution of 20 (5 mg) in toluene-d8 (0.5 mL) was transferred t o an NMR tube fitted with a 14/20 joint. The solution was degassed by three freeze-pumpthaw cycles, and then the tube was sealed under vacuum. Samples prepared in this way were used t o acquire the variable-temperature spectra (Figure 6) and to carry out the magnetization transfer experiments. The latter employed the presaturation pulse sequence: D3; D4; P2; DE; AT; D5. During D3, a selective decoupling pulse was activated for a variable period of time. The decoupler was turned off a t D4, and then the normal sequence for proton observation began. A standard proton pulse P2 was followed by a short delay DE, and then by the acquisition time AT, a final delay D5 was also included. The theory of magnetization transfer and the methods for calculating rate constants have been discussed elsewhere.53 In practical terms, magnetization transfer can occur between two exchanging sites A and B; thus, irradiation of the latter will cause a decrease in the intensity of A. When B has been irradiated for a time, t , the magnetization of A, MA@),can be defined as the intensity of A expressed as a fraction of the normal intensity of A. The intensities are measured by integrating the signal for A against another signal which is not involved in the exchange process. In the experiments on 20 the fulvalene peak a t 6 5.14 was irradiated for a time, t , and the diminished area of the fulvalene peak at 6 4.47 was integrated against the signal a t 6 4.00. Measurements were carried out in this way a t 20 "C for 15 different values oft. By methods described in the l i t e r a t ~ r e ?these ~ data were applied to the calculation of a first-order rate constant; a t 20 "C k = 0.22 s-l and AG* = 18 & 0.5 kcal mol-'. Two control experiments were performed to support the results of this study. The selective decoupling frequency used in D3 of the pulse sequence was moved to a point downfield from the peak a t 6 5.14 where no signals appear. The frequency difference between this point and the peak a t 6 5.14 was the same as that between the latter signal and the peak a t 6 4.47. Irradiation a t this downfield position did not affect the intensity of the peak a t 6 5.14. Thus, there was no artificial saturation of the resonance a t 6 4.47 when the peak a t 6 5.14 was irradiated. In addition, it was necessary to show that nuclear Overhauser effects were not modifying the intensity of the observed signals. Lowering of the sample temperature should decrease the rate of proton site exchange, but it should not change the degree of NOE enhancement. Thus, a t -20 "C all four fulvalene signals were irradiated in succession. In each case there was no change in the intensity of the other signals. Evidently no NOE processes were occurring a t -20 "C, and presumably also not a t 20 "C. Thermal Extrusion of Propenes from 20. A solution of 20 (53 mg, 0.10 mmol) in 20 mL of benzene or toluene was added to a flask equipped with a 14/20 outer joint and a Teflon vacuum needle valve. The solution was degassed by three freezepump-thaw cycles, and the flask was immersed in a 100 "C oil bath. After 24 h all of the volatile contents were vacuum transferred to a flask fitted with a side-arm stopcock. Gas chromatographic (20% SE30 on Chromosorb WHP, 10 ft X 1/4 in.) analysis of the solution showed the presence of only one major component, which was assigned to propene based on its retention time. T o verify this finding, a sample of propene was condensed into the reaction mixture. The GC peak for the major reaction product was found to coincide precisely with the propene peak. The only other gaseous product of the reaction was a trace of ethene which was identified in the same way as propene. Cyclopropane was not detected. In a separate experiment, isobutane (0.10 mmol) was condensed into the reaction mixture in order to provide an internal standard for quantitative analysis of the gaseous products. By comparing the integrated GC peaks for propene and isobutane, the yield of propene was found to be 80%. A correction was applied for the different detector response factors of propene and isobutane. Chromatography (alumina, acetone) of the nonvolatile material gave F V M O ~ ( C O(1; ) ~40 mg, 80%) as the only product. Half-Life of the Thermal Extrusion of Propene from 20. Complex 20 (5.0 mg, 0.010 mmol) and ferrocene (2 mg, 0.010 mmol), which was employed as an internal standard, were dissolved in toluene-d8 (0.50 mL). The solution (0.020 M) was transferred to an NMR tube attached to a 14/20 outer joint. After
Organometallics, Vol. 5, No. 2, 1986 297 it had been degassed by three freeze-pump-thaw cycles, the tube was sealed under vacuum. In an oil bath the tube was heated t o 100 "C, and periodically removed and cooled t o 20 "C prior t o analysis by 'H NMR spectroscopy. The disappearance of 20 proceeded with a half-life of about 12 h. In a nearly identical experiment, a 0.002 M solution of 20 was heated to 100 "C, and the half-life for disappearance of starting material was found to be about 12 h as in the previous case. Deuteration of 20 at (2-3. Sodium methoxide (1 mg, 0.02 mmol) was added to a solution of 20 (52 mg, 0.10 mmol) in T H F (7 mL) and CH30D (3 mL). After 5 min the solution was filtered through a short column of alumina which had been partially deactivated with D20. The product was eluted with THF. Removal of the solvent by rotary evaporation gave red crystalline 2 0 4 (52 mg, 100%); 'H NMR (200 MHz, toluene-d8) 6 5.15 (m, 2 H), 4.49 (m, 2 H), 3.97 (m, 2 H), 3.69 (t, J = 7.2 Hz, 2 H), 3.55 (m, 2 H), 1.10 (t, J = 7.2 Hz, 2 H). Deuterium incorporation in the C-3 position was >98%. Deuteration of 20 at C-4. A T H F solution ( 5 mL) of 10 prepared from 1 (50 mg, 0.10 mmol) was treated with ICH2CD z C H 2 P(45 mg, 0.15 mmol) as described for the synthesis of 20. Solvent removal by rotary evaporation and chromatography (alumina, acetone) afforded 2 0 - 4 labeled a t C-4 (47 mg, 90%); 'H NMR (250 MHz, C & j ) 6 5.14 (m, 2 H), 4.47 (m, 2 H), 4.00 (m, 2 H), 3.61 (s, 2 H), 3.57 (m, 2 H), 3.30 (s, 2 H). Deuteration of 20 at C-5. A T H F solution (10 mL) of Ph3C+BFc(62 mg, 0.19 m o l ) was slowly added to a THF solution (10 mL) of 20 (50 mg, 0.094 mmol) a t -78 "C. As the reaction mixture warmed to room temperature the color changed from red to a dark brownish red. Next, a T H F solution (5 mL) of LiA1D4 (8 mg, 0.19 mmol) was added t o the reaction mixture a t -78 "C. The mixture was allowed to warm to 20 "C, and then the solvent was removed by rotary evaporation. Chromatography of the crude product (alumina, acetone-pentane) gave 2 0 4 labeled a t C-5 (16 mg, 32%); 'H NMR (250 MHz, CsDs) 6 5.14 (m, 2 H ) , 4.47 (m, 2 H), 4.00 (m, 2 H), 3.61 (t, J = 7.2 Hz, 1 H), 3.57 (m, 2 H), 3.30 (t, J = 7.6 Hz, 2 H)8 1.03 (dt, J = 7.6, 7.2 Hz, 2 H). Thermolysis of 20-d2Labeled at C-3. A degassed toluene-d8 solution of 20-d2labeled at C-3 ( 5 mg, 0.010 mmol) was heated in a sealed 'H NMR tube for 24 h a t 100 "C. The NMR tube was placed in a long cylindrical vessel which was fitted with a 14/20 outer joint a t the top and a Teflon vacuum needle valve in the middle. The NMR tube was positioned in such a way that it would be broken by an inward movement of the needle valve. With this arrangement in place, the vessel was fitted to a vacuum line through the 14/20 joint. Under high vacuum the NMR tube was broken, and the volatile contents were allowed to condense into another NMR tube which was attached to the vacuum line and cooled in liquid N2. The tube was then sealed with a flame. Propene-I,I-d2was the only product observed; lH NMR (200 MHz, toluene-d8) 6 5.70 (4, J = 6.4 Hz, 1 H), 1.57 (d, J = 6.4 Hz, 3 H). Thermolysis of 20-dzLabeled at C-4. Thermolysis of 20-d2 labeled at C-4 was carried out in the same manner as described above. At 100 "C the reaction was complete within 24 h. Propene-2,S-d2was the only volatile product; 'H NMR (200 MHz, toluene-dJ 6 4.90 (m, 1 H), 4.79 (m, 1 H), 1.57 (m, 2 H). Thermolysis of 20-d2Labeled at (2-5. Thermolysis of 2 0 4 labeled a t C-5 was carried out in the same manner as described above. Propene-3-dl was the only volatile product observed; 'H NMR (200 MHz, toluene-d8) 6 5.70 (m, 1 H), 4.83 (m, 2 H), 1.57 (m, 2 HI.
Acknowledgment. This work was s u p p o r t e d b y the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division of the U.S. Department of Energy, under C o n t r a c t DE-AC03-76SF 00098. The crystal structure analyses of 1 and 20 were carried o u t b y Dr. F. J. Hollander, U. C. Berkeley X - r a y Crystallographic Facility. K.P.C.V. was a Camille and Henry Drefus Teacher-Scholar (1978-1983).
Supplementary Material Available: Tables of positional and thermal parameters and the values for F, and F, for 1 and 20 (33 pages). Ordering information is given on any current masthead page.
