Organometallics 1995, 14, 269-273
269
Synthesis of Stable (q4-Vinylallene)ironTricarbonyl Complexes: Preparation, Fluxionality, and X-ray Crystal Structure Analysis Charles E. Kerr and Bruce E. Eaton* Department of Chemistry, Washington State University, Pullman, Washington 991 64-4630
James A. Kaduk Amoco Corporation, Naperville, Illinois Received August 16, 1994@ Some of the first examples of air stable y4-vinylallene-Fe(C0)3 complexes have been prepared by photochemical reaction of Fe(C0)b and vinylallenes. A high degree of diastereofacial selectivity was observed for iron coordination and the mfacial preference confirmed by X-ray crystallography. Comparison of NMR data (lH and 13C) for y4vinylallene-Fe(C0)3 complexes and y4-isoprene-Fe(C0)3 revealed many similarities but some important differences that may be attributed to different polarization of these conjugated z-systems. Consistent with these differences the y4-vinylallene-Fe(C0)3 complexes showed significantly higher AG* for interconversion of the carbonyl ligands as compared to q4-isoprene-Fe(C0)3. The X-ray data rule out intra- or intermolecular contacts as the cause of the increased barrier to carbonyl isomerization. The data clearly indicate that the central allene carbon is strongly backbonding to the iron center, which may account for observed NMR and X-ray results.
Introduction
A wide array of y2-allene-transition-metal complexes have been prepared and their structures studied.l In contrast very few examples of conjugated vinylallenes coordinated t o transition metals have been reported.2 Preparation of y4-vinylallene-Fe(CO)3 complexes had been accomplished previously by treatment of the corresponding y4-vinylketene-Fe(C0)3complexes with stabilized Wittig reagents.2b It was of interest to probe the chemistry of these "high energy" ligands and determine if any stable complexes could be prepared by simple complexation of Fe(C0)3, a method that in contrast to the Wittig reaction of vinylketenes might allow for the inclusion of a wide array of hydrocarbon substituents at the terminal allene carbons. In addition, previously it had been shown that conjugated d i a l l e n e ~allenyl ,~ ketones4 and allenyl imines5 react with CO and catalytic amounts of iron carbonyls t o give [4 11 cycloaddition products. The stereoselectivity of those cycloaddition reactions was attributed to a high degree of diastereofacial selectivity on coordination of the iron to one face of the allene n-system. Herein we describe a highly diastereoselective synthesis of (y4-vinylallene)iron-Fe(C0)3 complexes, related to 11 the putative intermediates in the proposed 14 cycloaddition mechanisms.
The fluxtionality of these new (y4-vinylal1ene)iron tricarbonyl complexes was also examined by variable temperature NMR revealing significant differences in the dynamic behavior of the carbonyl ligands as compared to their y4-dienecounterparts. An X-ray crystallographic study was performed to unambiguously determine the facial preference of iron coordination and to better understand the nature of the bonding in these air-stable complexes.
Results and Discussion Using the method of Nakanishi: the desired vinylallenes could be prepared in good yield starting from allenyl aldehydes.' Treatment of the vinylallenes with Fez(C0)g failed to give complete conversion. The best yields were obtained when the vinylallenes were treated with Fe(C0)5 under 350 nm irradiation (eq 1). After
+
+
Abstract published in Advance ACS Abstracts, November 1, 1994. (l)Bowden, F. L.;Giles, R. Coord. Chem. Rev. 1976,20, 81 and references cited therein. (2)(a)Trifonov, L.S.; Orahovats, A. S.; Prewo, R.; Heimgartner, H. Helv. Chim. Acta. 1988,71,551.(b) Hill, L.;Saberi, S. P.; Slawin, A. M. 2.;Thomas, S. E.; Williams, D. J. J. Chem. Soc., Chem. Commun. 1991,1290.(c) Saberi, S.P.; Thomas, S. E. J.Chem. Soc., Perkin Trans. 1 1992,259. (3)Eaton, B. E.; Rollman, B.; Kaduk, J. A. J.Am. Chem. Soc. 1992, 114,6245. (4)Sigman, M.S.; Kerr, C. E.; Eaton, B. E. J.Am. Chem. SOC.1993 115,7545. (5)Sigman, M.S.;Eaton, B. E. J. Org. Chem., in press. @
0276-733319512314-0269$09.0010
1842
2s-C
R
Cvield
la. 2n; COzCHzCHj
97
Ib, fb; COCHj
66
le. l e : CHzWHzCHj
77
careful isolation under air-free conditions it was found that complex 2a was in fact very robust and could be stored in the air a t ambient temperature for several days without any detectable decomposition. The rela(6)Nakanishi, K.;Yudd, A. P.; Crouch, R. K.; Olson, G. I.; Cheung, H.-C.; Govindjee, R.; Ebrey, T. G.; Patel, D. J. J.Am. Chem. Soc. 1976, 98,236. (7) Clinet, J. C.; Linstrumelle, G. Nouueau J. Chim. 1977,1, 373.
0 1995 American Chemical Society
Kerr et al.
270 Organometallics, Vol. 14,No.1, 1995 Table 1. Selected 'H and I3C NMR Data for Vinylallenes of the Corresponding Iron Carbonyl Complexes
1.-c
ld2a
3
Zs-C
lb/Zb
lC/ZC
0
314
lH Chemical shifts (6): H'
5.76/1.25
5.9211.24
5.5W1.34
5.041-0.22
H2
7.2M.68
6.88/5.70
6.08/4.98
6.3Y4.72
H3
5.64/4.46
5.64/4.48
5.72/4.48
H@
1.47/1.85
1.50/1.89
1.56/1.92
1-Bu
0.85/0.79
0.89/0.85
0.95/0.86
'H Coupling constants (Hz): H1 - H2
15.4/8.0
15718.1
15.Y8.5
H2. H3
11.0/4.7
10.U4.8
10.4/4.5
H3- H3C6
2.6/1.4
2.711.7
2.711.6
17.4/8.5
I3C Chemical Shifts (6): C1
119,6147.9
129.1m.3
127.7/61.6
I13.5/38.0
C2
143.2/89.9
141.4188.4
129.488.9
140.W84.8
c3
93.2/68.9
93.6169.3
93.9166.3
142.5/103.2
c4
208.6/152.2
208.9/152.5
204.3/153.2
116.9/43.8
c5
110.6/133.8
110.6/133.8
109,71132.4
C6
14.4120.7
14.4/20.8
14.9120.7
t-Bu
28.9D9.6
28.9129.6
29.U29.7
tive stability of the complexes in air was 2a I2b >> 2c. Complex 2c decomposed in air after several minutes and was handled and stored in an argon atmosphere. In all cases the substituents on the terminal allene carbons were methyl and tert-butyl. Excellent diastereoselectivity of iron coordination was observed. In all examples only one diastereomer was isolated as determined by lH NMR (Table 1). NMR Analysis. The assignments for the lH resonances were made on the basis of COSY NMR experiments. To make assignment of the 13CNMR resonances HETCOR experiments were performed on both free vinylallene ligands and iron complexes. What is the best structural description of these vinylallene-Fe(C0)3 complexes? Are the vinylallenes strictly q4-boundto the iron and how do they compare to 1,3-diene-Fe(CO)s complexes? We begin the analysis by comparing the resonances for the free vinylallene ligands (la-c) with the relevant isoprene (3)proton resonances. The endo proton H1 resonance is at lower field for all the vinylallenes studied as compared to 3. Regardless of whether the group R on the vinyl allene was electron withdrawing or donating, the H1 chemical shift was 0.5 to 0.8 ppm higher than for 3. The internal proton H2 (6.35 ppm) of isoprene is difficult to compare to the vinylallenes because of the methyl group a t C3, but the vinylallenes la-c span a range (7.21-6.08) that includes the frequency observed for 3. Larger differences exist between la-c and 3 in their 13C NMR spectra. On average C' is shifted down field for la-c as compared to 3. Both the 13C NMR resonances C1 and C2 appear to be changed by the substituent R, perhaps due to changes in polarization about the vinylallene n-system. The resonance most notably different for la-c versus 3 is C3, which is shifted ca.
49 ppm. This is undoubtedly the effect of the sp carbon C4in la-c. These data suggest that conjugated vinylallenes are different from conjugated dienes in the way their n-systems are polarized and that vinylallenes may adopt other bonding interactions with Fe(C013. The complexes 2a-c and 4 show some similarity in their lH and 13CNMR spectra. Beginning with the lH NMR data, as seen for q4-1,3-diene-Fe(CO)3structures, the chemical shift of the endo proton H1 (Table 1)is shifted upfield > 4 ppm on iron coordination while the H2 and H3 protons are shifted between 1 and 2 ppm upfield. The allenyl H3 proton is virtually a t the same chemical shift for all the complexes studied and is upfield 0.44 to 0.46 ppm as compared to the internal proton H2 in the isoprene complex, possibly indicating more electron density at this location in the vinylallene complexes. All CH3 groups of 2a-c are shifted > 0.4 ppm downfield on complexation of Fe(C0)3 indicating that they are positioned within the deshielding region of the iron and/or the carbonyl ligands. For both isoprene and the vinylallene complexes the 'H-lH couplings are decreased by approximately 50%. This decrease in 'H-lH coupling is consistent with iron backbonding into the antibonding n*-orbital of the ligand. A small but measurable coupling is still present between the CH3 groups and the allenyl H3-proton of 2a-c indicating that there is electronic communication through the allenyl n-system accounting for the presence of a 5-bond coupling. Consistent with iron coordination anti to the less sterically hindered n-face of the allene, the resonance of the t-butyl group is shifted only slightly (0.09-0.04 ppm) upfield. The 13CNMR data shows some interesting differences between the complexes 2a-c and 4. First, the resonance assigned t o C1 is shifted 5-24 ppm downfield for the complexed vinylallenes 2a-c relative to 4. Interestingly, the order of the magnitude of downfield shift is strongly affected by the group R, where ester (2a) < ketone (2b) < ether (2c). The internal carbon, C2 of 2a-c all have a chemical shift very similar to the corresponding carbon in complex 4. In contrast, C3 of 2a-c is shifted approximately 34-37 ppm upfield as compared to 4. Notably, the central allene carbon in all the vinylallene complexes, for which there is no counterpart in the isoprene complex, is shifted upfield more than 50 ppm on coordination of Fe(C0)3,consistent with a change in hybridization because of extensive back-bonding into the allene n-system. Concomitant with this shift of the central carbon of the allenes, the terminal carbon is shifted t o lower field, possibly due t o the electron withdrawing effect of the metal. In contrast to 4, all of the complexes 2a-c show slow exchange of the carbonyl ligands. Variable temperature 13C NMR experiments revealed a trend in the coalescence temperature for the different substituents R attached to C1 of the vinylallene (Table 2). The energy barrier t o interconversion of carbonyl ligands in the vinylallene complexes 2a-c increases with the degree of electron withdrawing character of the R group. For the vinylallene-Fe(C0)3 complexes studied AG* is 2025 kJ/mol higher than for isoprene-Fe(C0)3 (41, representing a difference in T, of between 80-100 "C. It was of interest to determine if this higher barrier to interconversion of carbonyl ligands was because of steric, electronic or coordinating interactions of the
Stable (y4-Vinylallene)ironTricarbonyl Complexes
Organometallics, Vol. 14,No. 1, 1995 271
Table 2. 13C N M R Coalescence Temperature and Chemical Shift Data of Carbonyl Ligands of 2a, 2b, 2c, and 4 in Toluene4 2a
2c
4
78.3(1)/314 211.2 209.0 210.8 216.1
57.7(1)/234 211.8 210.2 215.9
2b
A& (kJ/mol)/T, (K) 83.3(1)/333 86.3(1)/342 chem shift (6)" 209.1 209.6 chem shiftsb(6) 206.2 205.5 209.5 209.4 214.9 215.5
At coalescence. Below coalescence. AG* (kJ/mol) = 9.62RTc(10.32 where Av is the difference between resonances.
+ log TJk,), kc = ( ~ A v / 2 ) - 's-l, ~
c11
013
P
-
Figure 1. Ortep plot of the X-ray crystal structure of 2b. Table 3. Selected Bond Lengths (A) and Angles (deg) for 2b Cl-C2 C2-C3 C2-013 c3-c4 c4-c5 C5-C6 C6-C7 C7-C8 C7-Cl2 Fe-C3 Fe-C4 Fe-C5 Fe-C6 Fe-C14 Fe-C16 Fe-C18
1.499(6) 1.470(5) 1.222(5) 1.419(5) 1.398(5) 1.418 ( 5 ) 1.324(5) 1.538(5) 1.513(6) 2.136(3) 2.050(3) 2.071(4) 2.042(3) 1.81l(4) 1.781(4) 1.793(4)
Cl-C2-C3 C1 -C2-013 C3-C2-013 c2-c3-c4 c3-c4-c5 C4-C5-C6 C5-C6-C7 C6-C7-C8 C6-C7-C12 C8-C7-C12 C14-Fe-C16 C14-Fe-C18 C16-Fe-C18 Fe-C14-015 Fe-C16-017 Fe-C18-019
117.6(3) 120.8(4) 121.5(4) 121.2(3) 118.4(3) 115.4(3) 144.9(4) 122.1(3) 120.5(3) 117.3(3) 90.5(2) 101.6(2) 98.3(2) 177.3(3) 178.3(4) 179.6(3)
substituent R. In addition, we wanted more definitive structural information on how the iron was bound to the vinylallene, including the selectivity of n-face coordination. Fortunately, we were able to crystallize 2b and perform an X-ray crystal structure analysis. X-ray Crystal Structure Analysis 2b. The crystal structure consists of discrete molecules of complex 2b (Figure 1). Selected bond lengths and angles are provided in Table 3. The bond distances and angles of the ends of the vinylallene ligand fall within normal ranges for y4-diene-Fe(C0)3 complexes. There are several structural features in the center of the complexed ligand that are significantly different. The Fe-C vinylallene distances [2.136(3), 2.050(3), 2.071(4)and 2.042(3) AI are similar to the average Fe-C distance of 2.09(6) A, obtained from X-ray studies on 163 y4-diene-Fe(C0)3 complexes.8 The Fe-CO dis~
~~
(8)Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, 0.;Kennard, 0.; Macrae, C. F.; Mithchell, E. M.; Smith, J. M.; Watson, D. G. J. Chem. Inf. Comp. Sci. 1991,31,187.
A
B
C
Figure 2. Three resonance forms of vinylallene-Fe(C0)s complexes. tances of 1.781(4),1.811(4)and 1.793(4)A are also close to the average value of 1.81(9) A observed in the diene complexes. The orientation of the vinylallene in 2b with respect to the carbonyl ligands is very similar to that observed in several y4-diene-Fe(C0)3 complexes having a conjugated carbonyl The Fe-C-0 angles [177.3(3),178.3(4)and 179.6(3)"1are very close to linear. Both the molecular and crystal structure data rule out coordination or steric interaction of the carbonyl oxygen 013 as the cause of the slow interconversion of the carbonyl ligands. 013 is not oriented toward the Fe in the molecule, nor to the Fe in an adjacent molecule. The closest intermolecular contacts for 013 are 2.75 A, too far away to account for the slow interconversion of the CO ligands. Taken together the NMR and X-ray data suggest that it is best to view vinylallene-Fe(C0)3 complexes 2a-c as n-bound but with a significant degree of a-character between the iron and central allene carbon as shown by resonance structures A and B of Figure 2. The X-ray data rule out any significant contribution from resonance contributor C because the terminal vinyl carbon is close to sp2 hybridized and the vinylallene ironcarbon distances are all very similar. The iron appears to have little interaction with the terminal allene n-bond since this bond length is on the order of a typical C-C double bond. Conclusions. The y4-vinylallene-Fe(CO)3 complexes of this study are air-stable when electronwithdrawing carbonyl groups are in conjugation with the vinylallene. They can be prepared easily be treating the vinylallenes with Fe(C0)S and irradiating a t 350 nm. The complexation of iron occurs preferentially to the n-face of the vinylallene ligand that is anti with respect to the tert-butyl group. On complexation of Fe(CO)3,vinylallenes show changes in chemical shifi and H1-H1 coupling similar to those observed in y4-is0prene-Fe(CO13. In contrast to known y4-diene-Fe(C0)3 complexes, the CO ligands of y4-vinylallene-Fe(C0)3 complexes show slow exchange by 13C NMR. One explanation is that the apparent strong interaction of the iron with the central allene carbon distorts the geometry of the vinylallene complexes so that they are not exclusively n-bound but posses a significant amount of u character, thereby increasing the barrier for interconversion of the CO ligands. The structure of 2b does show a significant rehybridization from sp t o sp2 of the central allene carbon consistent with strong backbonding from the iron into the allene n-system. X-ray (9)Mason, R.; Robertson, G. B. J. Chem. SOC.A . 1970,1229. (b) Messager, J. C.; Toupet, L. Acta Cryst. 1986,B42, 371. (c) Morey, J.; Gree, D.; Mosset, P.; Toupet, L.; Gree, R. Tetrahedron Lett. 1987,28, 2959. (d) Balde, L.; Rodier, N.; Bidaux, N.; Brion, J. D.; Le Baut, G. Acta Cryst. 1988,C44, 1394. (e) Adams, C. M.; Ceroni, G.; Hafner, A,; Kalchhauser, H.; von Philipsborn, W.; Prewo, R.; Schwenk, A. Helu. Chim. Acta 1988,71, 1116. (0Le Gall, T.; Lellouche, J.-P.; Toupet, L.; Beaucourt, J.-P. Tetrahedron Lett. 1989,30, 6517. (g) Rohde, W.; Fischer, J.; De Cian, A. J . Organomet. Chem. 1990, 393, C25. (h) Benvegnu, T.; Martelli, J.;Gree, R.; Toupet, L. Tetrahedron Lett. 1990 31, 3145.
272 Organometallics, Vol. 14, No. 1, 1995
Kerr et al.
l-Ethogy-6,7,7-trimethylocta-2,4,S-triene (IC). 6,7,7Trimethylocta-2,4,5-trien-l-o1 (2 mL, 10.48 mmol), THF (90 mL distilled from Na/K benzophenone) and 90 mL hexanes (freshly distilled from K)were combined and cooled to 0 "C. Butyllithium (7.4 mL, 1.5M in hexanes, 11.1"01) was added dropwise at 0 "C. The reaction mixture turned yellow imExperimental Section mediately, then gradually turned green over several minutes. After 10 m DMSO (45 mL, distilled off CaH2) were added, All reactions and manipulations were conducted under a dry followed by bromoethane (3.95 mL, 52.40 mmol). The reaction argon atmosphere either using an inert atmosphere glovebox mixture was then allowed to warm to ambient temperature or standard Schlenk techniques. The Wittie reagents and and stirred for 21 h. After standard aqueous work up the 4,5,5-trimethylhexa-2,3-diena17 were prepared as described in residue was vacuum distilled to give 1.85 g (91%) of IC as a the literature. The silica gel used was 230-400 mesh ASTM. pale yellow oil. 'H NMR (300 MHz: CDC13) 6 1.01 (s, 9H), Vacuum distillations, and freezelpumplthaw cycles were per1.18 (t,J = 7 Hz, 3H), 1.66 (d, J = 2.7 Hz, 3H), 3.45 (9, J = 7 formed on a vacuum line ('1 pmHg). A minimum of three Hz, 2H), 3.94 (dd, J = 6.3, 1.2 Hz, 2H), 5.64 (dtd, J = 15.3, freezelpump/thaw cycles were used when degassing samples. 6.3, 0.3 Hz, lH), 5.69 (dq, J = 10.4, 2.7 Hz, lH), 6.01 (ddt, J Irradiations were performed using a Rayonet photochemical = 15.3, 10.3, 0.3 Hz, 1H); I3C {'H} (75 MHz; CDCI3) 6 14.73, reactor (350 nm, 10 bulbs). NMR data was acquired on a 15.11,28.94,33.57,65.39,70.95,92.99,109.58,126.07,130.36, Bruker AMX (300 MHz lH). Infrared data was acquired from 204.09; IR (neat) 1945.1, 1644.1, 1461.5 cm-l; MS m l z (M+) a Perkin-Elmer 1600 I?TIR. Mass spectral data were obtained 194. HRMS m l z for C13H2201, calcd 194.1671;found 194.1675. from the departmental facility at Washington State University. (q4-Ethyl-6,7,7-trimethylocta-2,4,S-trienoate)iron TriElemental analysis was obtained from Desert Analytics, carbonyl (2a). Ethyl-6,7,7-trimethylocta-2,4,5-trienoate (177 Tuscon, AZ. Melting points were recorded on a Mel-Temp mg, 85 pmol) was placed in a vacuum Schlenk tube and apparatus and are uncorrected. freeze-pump-thawed. The tube was charged with Fe(C0)5 Ethyl-6,7,7-trimethylocta-2,4,5-trienoate (la). Sodium (223 pL, 1.70 mmol, 2 equiv) and THF (5 mL distilled from hydride (1.5 g, 63 mmol) and THF (75 mL dried over Na/K/ Na/K benzophenone) were added. The reaction bomb was then benzophenone) were placed in a flask under argon and cooled irradiated at 350 nm with stirring for 24 h. The resulting t o 0 "C. Triethylphosphonoacetate (11.54 mL, 57.1 mmol) was mixture was washed into a flask with ether and concentrated added gradually. Evolution of hydrogen gas was observed. The onto silica gel. The crude product was eluted from the silica mixture was stirred for 15 m and added to 4,5,5-trimethylhexawith ether and concentrated. The residue was then eluted 2,3-dienal (7.5 mL, 51.9 mmol) and stirred at ambient temwith benzene through a Pasteur filter pipette of silica gel perature for 12 h. The reaction mixture was submitted t o yielding 287 mg (97%) of 2a as an amber oil. 'H NMR (300 standard aqueous work up using diethyl ether. The ether MHz: CsDs) 6 0.79 (9, 9H), .93(t,J = 7.1 Hz, 3H), 1.25 (d, J = layer was concentrated and applied to silica gel using ether 8.1 Hz, lH), 1.85 (d, J = 1.4 Hz, 3H), 3.91 (MX, 2H), 4.46 as eluant. Removal of the ether followed by short-path vacuum (m, lH), 5.68 (dd, J = 4.7,7.9 Hz, 1H); 13C{'H} (75 MHz; CsDs) distillation gave 8.44 g (78%) of la pale yellow oil. lH NMR 6 14.17,20.66,29.57,36.84,47.91,60.42,68.97,89.88,133.77, (300 MHz; CDC13) 6 0.96 (8,9H), 1.17 (t,J = 7.1 Hz, 3H), 1.62 152.17, 171.41, 205.94 209.25, 214.36; IR (neat) 2058, 1980.2, (d, J = 2.5 Hz, 3H), 4.07 (9, J = 7.1 Hz, 2H), 5.71 (d, J = 15.4 1706.6 cm-l. Anal. Calcd for C16H~005Fel:C, 55.19; H, 5.79; Hz, lH), 5.74 (dq, J = 11.0,2.5 Hz, lH), 7.04 (dd, J = 15.4, 11 Hz, 1H); '3C {lH} (75 MHz: CDC13) 6 14.01,14.10,28.64,33.49, Fe, 16.04. Found C, 55.17; H, 5.64; Fe, 15.92: MS m l z (M+) 348. 59.72, 92.47, 110.23, 118.39, 143.39, 166.48, 208.41; IR (neat) (q4-7,8,8-Trimethylnona-3,5,6-triene-2-one)iron Tricar1941.5, 1719.8 cm-l; MS m l z (M+) 208. HRMS m / z for bony1 (2b). 7,8,8-Trimethylnona-3,5,6-trien-2-one (208 mg, C13H2002 calcd 208.1463, found 208.1478. 1.17 mmol) and THF (10 mL distilled from Na/K benzophe7,8,8-Trimethylnona-3,5,6-triene-2-one (lb). 1-Triphnone) were combined and freeze-pump-thawed. Iron penenylphosphoranylidene-2-propanone (8.7 g, 27 mmol), p-dioxtacarbonyl (750 pL, 5.7 mmol) was added and the solution ane (150 mL freshly distilled from Wbenzophenone) and 4,5,5irradiated for 5 h at 350 nm. The resultant mixture was trimethylhexa-2,3-dienal(3.0mL, 20.8 mmol) were combined concentrated onto silica gel. The dried residue was added to under argon and refluxed for 20 h. The dioxane was removed the top of a pad of silica gel and the product was eluted with under reduced pressure. After percipitation of the tri1:1 benzene:pentane. The concentrated eluent was eluted phenylphosphine oxide from pentane and filtration of the through a Pasteur pipet of silica gel, first with benzene, then solvent was removed by reduced pressure. Fractional vacuum again with ether as the eluant. Removal of solvent gave 244 distillation gave 1.93 g (75%)of lb a pale yellow oil. 'H NMR mg (66%)of 2b as an orange oil. Crystallization from pentane (300 MHz; CDC13) 6 0.91 (s, 9H), 1.58 (d, J = 2.7 Hz, 3H), gave amber crystals (Mp 55.5-58 "C, vacuum sealed capillary); 2.07 (6, 3H), 5.69 (dq, J = 10.8, 2.6 Hz, lH), 5.92 (d, J = 15.6 'H NMR (300 MHz; CsDs) 6 0.85 (9, 9H), 1.24 (d, J = 8.1 Hz, Hz, lH), 6.83 (dd, J = 10.8, 15.7 Hz, 1H); 13C ('H} (75 MHz; lH), 1.68 ( 8 , 3H), 1.89 ( 8 , 3H), 4.48 (m, lH), 5.70 (dd, J = 8.0, CDC13) 6 14.0, 26.7, 28.6, 33.4, 92.8, 110.26, 128.0, 142.4, 4.8 Hz, 1H); I3C {lH} (75 MHz; CsDs) 6 20.70, 29.04, 29.62, 197.34, 208.92; IR (neat) 1939.6, 1663.2 cm-l; MS m l z (M+) 36.90,55.31,69.33,88.40,133.65,152.33,201.01,205.2,209.2, 178. HRMS mlz for C12HlsO1, calcd 178.1358, found 178.1374. 215.4; IR (neat) 2057.1, 1982.1, 1679.0 cm-l. MS m l z (M+) 6,7,7-Trimethylocta-2,4,5-triene-l-ol. la (500 pL, 2.23 318. HRMS m l z for C~Hle04Fe1,calcd 318.0559, found mmol) was dissolved in THF (25 mL distilled from NaW 318.0532. benzophenone) and cooled to 0 "C pending addition of DIBAL (11.1mL, 1M in THF, 11.1mmol). After addition, the reaction (q4-1-Ethoxy-6,7,7-trimethylocta-2,4,5-triene)iron Tricarbonyl (24. l-Ethoxy-6,7,7-trimethylocta-2,4,5-triene (171 was allowed to warm to ambient temperature and stirred for mg, 879 pmol) was freeze-pump-thawed and THF (from 10 20 h. Workup by extraction with ether/HCl, followed by mL NdK benzophenone) and Fe(C0)5 (578 pL, 4.39 mmol) concentration of the organic residue gave a yellow oil. The were added. ARer 18 h irradiation at 350 nm, the reaction product was dried with MgS04 in dichloromethane to yield 350 mixture was concentrated onto silica gel. The crude product mg (94%)of 6,7,7-trimethylocta-2,4,5-triene-l-o1 as a colorless was eluted with ether, concentrated, and then purified by oil. 'H NMR (300 MHz; CDC13) 6 .99 (s, 9H), 1.64 (d, J = 2.7 Hz, 3H), 3.37 (s, lH), 4.04 (dd, J = 6.0, .9Hz; 2H), 5.7 (m, 2H), column chromatography ( 1 : l O hexanes:toluene, flash silica) to yield 2c 294 mg (77%). 'H NMR (300 MHz; CsD6) 6 0.86 ( 8 , 5.97 (ddt, J = 15.4,10.3,1.3Hz; 1H); 13C{lH} (75 MHz; CDC13) 9H), 1.03 (t,J = 6.99 Hz, 3H), 1.34 (m, lH), 1.92 (d, J = 1.63 6 14.51, 28.26, 33.34, 62.44, 92.90, 109.22, 128.49, 128.62, Hz, 3H), 3.14 (m, 2H), 3.22 (m, 2H), 4.48 (m, lH), 4.98 (dd, J 203.76; IR (neat) 3322.4, 1944.9 cm-l; MS m l z (M+) 166. = 4.5, 8.5 Hz, 1H);13C ('H} (75 MHz; CsDs) 6 15.22, 20.69, HRMS m l z for C11HISOlrcalcd 166.1358, found 166.1346.
crystal structure analysis did not reveal steric or coordinating interactions for either the carbonyl or CO ligands that could account for the relatively slow exchange of the CO ligands.
Stable (q4-Vinylallene)iron Tricarbonyl Complexes 29.73,36.80,61.63, 66.26,66.39, 71.08,88.98, 132.42, 153.18, 334. HRMS 210; IR (neat) 2044.2,1962.4 cm-l; MS mlz (M+) m l z for C~H2204Fe1,calcd 334.0867, found 334.0864. X-ray Crystal Structure Analysis. A clear yellow crystal aproximately 0.75 x 0.58 x 0.38 mm was wedged in a 0.3 mm capillary and optically centered on a NicoleUSiemens R3m single crystal difFractometer. The dimensions of the primative monoclinic unit cel were determined from the setting angles of 23 strong reflections having 25 < 20 .c 32". The refined lattice parameters, derived from a Rietveld refinementlo of a powder sample mixed with NIST 640b Si internal standard are as follows: a = 10.7875(8),b = 13.1067(13),c = 11.5274(10) A, and ,f3 = 95.598(5)". A search of the Crystal Data database yielded no plausable hits. The details of the data collection are reported in supplementary material. Both UJ and 20lw scans indicated that the crystal was of high quality. The intensities of four check reflections varied by f l %during data collection. A n empirical absorption correction, derived from yj-scans of 15 strong reflections well-distributed in reciprocal space, was applied. The maximum and minimum transmission were 0.268 and 0.227. The systematic absences unambiguously determined the space group to be P21lc. Data processing was carried out using the SHELXTL Plus, version 3.4 system of programs (Nicolet Instrument Corp.). The structure was solved by direct methods, which indicated the position of the iron atom, 6 carbons and three oxygens. The remaining heavy atoms were located by difference Fourier techniques. The hydrogen atoms were included in the calculated positions. (10)Larson, A. C.; Von Dreele, R. B. GSAS, The General Structure Analysis System; Los Alamos National Laboratory, Feb 1993 version.
Organometallics, Vol. 14, No. 1, 1995 273 All non-hydrogen atoms were refined anisotropically. All C-H distances were fixed at 0.96 A. A common isotropic displacement coeficient was refined for the three vinyl hydrogens. The methyl groups were treated as rigid bodies. A common isotropic displacement coeficient was refined for the hydrogens on C 1 and C12, and another common thermal parameter for the tert-butyl hydrogens on C9, C10 and C11 (Figure 1). The final refinement of 184 variables using 2135 observations yielded the residuals R = 0.0427 and WR = 0.0545. The R factor expected from counting statistics is 0.0198. The atomic coordinates and the equivalent isotropic displacement coeficients of the heavy atoms, bond angles, bond lengths, anisotropic displacment coeficients and the observed and calculaed structure factors are reported in supplementary material.
Acknowledgment. Support from the donors of the Petroleum Research Fund and a Grant-in-Aid from Washington State University is gratefully appreciated. NMR data were obtained from the WSU NMR Center supported in part by the NIH (Grant RR0631401) and NSF (Grant CHE-9115282). Special thanks to Matt Sigman for preparation of this manuscript. Supplementary Material Available: X-ray crystal structure determination data for 2a including tables of solution and refinement parameters, atomic coordinates,bond lengths, bond angles, and isotropic and anisotropic displacement coefficients and stereo ORTEP plots (10 pages). Ordering information is given on any current masthead page. OM9406512
