Organometallics 1996, 14, 157-161
157
Photochemical Reimer-Tiemann Reactions of (? I ~ - C ~ H ~ ) ~ F ~ ~ ( I ~ - C O )and ~(I~-P~~PCH~P (?1~-C5H5)2Fe2(Ic-C0)201-Ph2PCH2CH2PPh2). Molecular Structures of ( ? I ~ - C ~ H ~ ) ~ F ~ ~ C ~ - C O ) ~ C ~ - P ~ ~ P C and
(q5-CHOC5H4) (?I~-C~H~)F~~C~-CO)~~~-P~~PC Joyce E. Shade,* Wayne H. Pearson,* and James E. Brown Department of Chemistry, U.S. Naval Academy, Annapolis, Maryland 21402-5026 Thomas E. Bitterwolf" Department of chemistry, University of Idaho, Moscow, Idaho 83844-2343 Received July 28, 1994@ Photolysis of either (175-C5H5)2Fe201-CO)201-DPPM) (DPPM = Ph2PCH2PPh21, I, or (r5C5H5)2Fe201-C0)201-DPPE)(DPPE = Ph2PCH2CH2PPh2), 11, in CHCl3 followed by chroma-
tography on wet alumina results in the formation of products in which one cyclopentadienyl ring has been formylated. In contrast, photolysis of (175-C5H5)2Fe201-CO)201-DPPP), 111,under analogous conditions gives the chloride derivative expected from Fe-Fe bond homolysis. Available evidence suggests that the reactions of I and I1 proceed via a photochemical Reimer-Tiemann reaction involving a n irreversible charge transfer to yield the respective radical cation and a dichloromethyl radical. Subsequent coupling of these radicals forms a ring-substituted dichloromethyl intermediate which is in turn hydrolyzed to the aldehyde upon workup. Formyl derivatives have been fully characterized by IR, lH, 13C,and 31PNMR, mass spectrometry, and elemental analysis. Reaction of [(175-C5H5)2Fe201-CO)201-DPPM)lPF6, I+PF6, with ICHzCOzCzH5, under conditions known to generate the alkyl radical, yielded providing the ring substituted compound (1;15-C5H4CH2C04C2H5)(C5H5)Fe201-C0)201-DPPM), additional support for a radical pathway to ring substitution in these compounds. The molecular structures of (175-C5H5)2Fez01-C0)201-DPPE), 11, and ( D ~ - C H O C ~ H ~ ) ( ~ ~ ~ - C ~ H ~ ) F ~ ~ b-C0)2@-DPPE), V,have been characterized by X-ray crystallogra hy: 11,rhombohedral, R3, a = b = c = 27.749(2) A, a = ,8 = y = 116.52(9)",V = 10104(15)i f3, Z = 12, R(F)= 4.1%; V , orthorhombic, Pna21, a = 13.988(10)A, b = 13.371(3)A, c = 17.358(6)A, V = 3246.5(41) A3,Z = 4,R(F) = 6.9%. The photochemical behavior of metal-metal bonded, metal-carbonyl complexes has been the subject of substantial investigati0n.l It is now well-established that two principle reaction modes are possible: metalmetal bond homolysis and carbonyl loss. We have been interested for some time in the behavior of bimetallic compounds in which the metal atoms are linked by either a bridging ligand such as a diphosphine, coupled cyclopentadienyl rings, or both. We hypothesized that these additional linkages between the metals would reduce the importance of the radical pathway by either eliminating homolysis or facilitating facile recombination of metal radicals. To test this hypothesis we examined the photolysis of (775-C5H5)2Fe2CU-CO)2CUDPPM), I, (q5-C5H5)2Fe2+-C0)2+-DPPE), 11, and (q5C ~ H ~ ) ~ F ~ ~ ( U - C O ) & - D11 P1P, in P )CHCl3, , anticipating that CHC13 would serve as an efficient radical scavenger for any long-lived iron-iron bond homolysis products. Abstract published in Advance ACS Abstracts, November 1,1994. (1)For major references, please see: (a) Zhang, S.; Brown, T. L. Organometallics 1992, 11, 4166. (b) Dixon, A. J.; George, M. W.; Hughes, C.; Poliakoff, M.; Turner, J. J. J . Am. Chem. SOC.1992, 114, 1719. (c) Bloyce, P. E.; Campen, A. K.; Hooker, R. H.; Rest, A. J.; Thomas, N. R.; Bitterwolf, T. E.; Shade, J. E. J . Chem. Soc., Dalton Trans. 1990,2833. @
0
1:" 11:"
I
-
Ill:"-
I
1v:
2
n
I
v n
I
I
,
VI
1
Ch2C02C'1&H,
Ph2P
'
PP\)
CH?'
VI,
As will be discussed in this paper, photolysis of I11 proceeds by the expected homolysis pathway while photolysis of I and I1 revealed a wholly unexpected, and previously unobserved, charge transfer pathway for the photolysis of metal-metal bonded complexes. Further evidence for a radical pathway to ring substitution of these compounds is presented.
0276-733319512314-0157$09.00/00 1995 American Chemical Society
158 Organometallics, Vol. 14, No. 1, 1995
Shade et al.
Table 1. WNisible Data for ( C S H S ) ~ F ~ ~ @ - Cand O ) ~Related L~ Complexes
A,,,. nm (6.Umol cm) L2 DPPM DPPE
(CsHMez@-C0)2Lza 634 (5.8 x lo2) 342 (7.4 x 103) 655 (5.7 x 376 (4.7 x 681 (5.5 x 376 (5.5 x
DPPP
lo2) 103) lo2) 103)
MezSi(CsH4)2Fe2Oc-CO)zLzb 616 (4.4 x lo2) 385 (3.9 x 103) 648 (4.0 x 385 (3.8 x 682 (4.3 x 389 (4.2 x
lo2) lo3) lo2) lo3)
C H ~ ( C ~ H ~ ) Z F ~ Z ~ ~ - C O ) ~ L(CsH4CHO)(CsHs)FezOc-CO)zLz' ~".' 580 (3.6 x lo2) 660 (3.7 x lo2) 332 (5.3 x 103) 390 (3.7 x 103) 330 (5.0 x lo3) 604 (2.5 x lo2) 670 (5.5 x lo2) 400 (4.7 x 103) 360 (3.7 x 103)
Spectra were recorded in benzene. Spectra were recorded in CH2Clz. Reference 9.
Results and Discussion (r5-C5H5)2Fe2CU-C0)2Cu-L2),where L2 = DPPM (I), DPPE (111, and DPPP (1111, were prepared as described by Haines.2 Photolysis of I or I1 in CHCl3 resulted in a change in color of the reaction mixture from green to brown. After solvent removal, the resulting oil was chromatographed on wet (6%water) alumina, grade 111, using petroleum ether:CHCl3. In each case, a single golden brown band was eluted from the column, yielding a brown solid after removal of solvent. Analysis of lH and 13C NMR spectra of the product compounds, IV and V, where L2 = DPPM and DPPE, respectively, revealed that one cyclopentadienyl ring had been substituted during the course of the reaction. Characteristic resonances in both the proton and carbon spectra and the appearance of new IR bands at 1658 and 1655 cm-l, respectively, strongly suggested the presence of a formyl group in the molecule. The IR spectra also contained bands which were almost identical in position in the p-CO stretching bands of the starting materials. We have been unable to locate the 13C bridging carbonyl resonances of these compounds. The 31PNMR spectrum of IV consisted of a clean AB pattern centering on 84.48 and 81.47 ppm which is upfield of the singlet resonance observed a t 86.56 ppm for I. V was found t o have two singlets at 68.52 and 64.11 ppm which are slightly upfield from the singlet resonance of I1 which is found at 69.82 ppm. Mass spectrometry of IV (EI/CI) and V (FAB) revealed a parent mass and fragmentation pattern consistent with formyl derivatives of I and 11. Final confirmation of the structure of V, and by inference IV,was provided by a molecular structure of V (vide infra). The color change from the green starting materials to the golden brown formyl products can be understood by examination of the Whisible spectra. The band positions of compounds I-V and representative, similar compounds are presented in Table 1. Compounds I and I1 have two bands in their electronic spectra. The lower energy bands are assigned to the Fe-Fe (0 a*)and the higher energy band to the Fe ring (MLCT) transitions. Introduction of a formyl group onto one ring causes the 0 u* bands to shift t o longer wavelength and splits the Fe ring charge transfer bands. In the case of IV, two charge transfer bands are clearly observed, while for V a broad plateau is observed that, presumedly, contains the two overlapping bands. We suggest that the two bands correspond t o Fe C5H5 charge transfer bands, respectively. and Fe CBH~CHO In both IV and V, the net effect of formylation is to shift the strongly absorbing charge transfer bands toward the
-. -
-
- -
-
(2)(a) Haines, R.J.; DuPreez, A. L. J . Orgunometal. Chem. 1970, 21,181.(b) Haines, R.J.; DuPreez, A. L. Inorg. Chem. 1970,1I,330.
blue end of the visible range, resulting in a color change from green to golden-brown. IR spectra of the reaction mixture of I prior to chromatographic purification contains bands which are similar in position to those of the product although the shoulder assigned to the formyl group was not observed. No bands were observed that might be attributable to a CpFe(C0)LCl product. Several attempts to obtain NMR spectra of these reaction mixtures were unsuccessful, due, apparently, to the presence of paramagnetic decomposition products. Ultraviolet photolysis of I in Nujol at 77 K yielded no change in the IR spectrum after 1h, ruling out the possibility of photochemical carbonyl bridge opening. Similarly, photolysis of I in benzene resulted in some decomposition with no isolable product. Photolysis of I11 proceeds similarly to that of I and I1 with a color change from green to brown although chromatography of the resulting product required a more polar solvent mixture (20:1 dichloromethane: methanol) for elution of the brown product, VI, which is unstable in solution and upon storage. It was not possible to record an NMR spectrum of VI. VI has a single carbonyl stretching band at 1967 cm-l. No bands which might be associated with either bridging carbonyl or formyl groups were observed. The observed IR band is similar in position to that of an authentic sample of (r5-C5H5)Fe(CO)(PPh3)C1 which has a terminal carbonyl stretching band at 1963 cm-'. These observations suggest that photolysis of I11 proceeds by homolysis of the Fe-Fe bond followed by reaction of the iron radicals with the chlorinated solvent. The reactions of I and I1 are reminiscent of those reported by Sugimori and co-workers3 involving the photochemistry of ferrocene in halocarbon solvents in which formyl, carboxylic acid, and ester (alcohol solvolysis) derivatives were isolated. Similar studies involving electron rich arene compounds) have been r e p ~ r t e d .These ~ authors suggested that the observed products could be explained by a photochemical Reimer-Tiemann reaction whose initiating step is the photoinduced transfer of an electron from the ferrocene t o CHCl3, yielding a ferrocinium ion, a chloride ion, and the CHCl2 radical. Exo attack of the CHC12 radical on a cyclopentadienyl ring of the 17-e- ferrocinium ion gives a protonated ferrocene intermediate. Deprotonation and hydrolysis of this species upon workup yields the formyl derivative. The literature on photooxidation of metal complexes has been r e v i e ~ e d . ~ We propose that photolysis of I and I1 proceeds by a (3)Hoshi, Y.; Akiyama, T.; Sugimori, A. Tetrahedron Lett. 1970, 1485. (4) (a)Hirao, K.; Ikegame, M.; Yonemitsu, 0. Tetrahedron 1974,30, 2301. (b) Kurz, M.E.; Lapin, S. C.; Mariam, K.; Hagen, T. J.; Qian, X. Q. J . Org. Chem. 1984,49,2728.
Photochemical Reimer-Tiemann Reactions
Organometallics, Vol. 14, No. 1, 1995 159
Scheme 1. Postulated Mechanism for Formylation of I +
I
2 1 ’
l P*,P
o
‘
1
I
I
O
I
I
PPh,
C”>’
L
J
similar mechanism (Scheme 1)involving photoinduced electron transfer from the bimetallic compound to the solvent, followed by radical attack to form a protonated intermediate containing a p-H. Hydrolysis upon workup yields the isolated formyl derivative. The good yields of formyl products suggest that the bimetallic radical cation and the dichloromethyl radical are formed within a solvent cage, enhancing the likelihood of a favorable attack of the dichloromethyl radical onto one of the cyclopentadienyl rings. Since formylcyclopentadienyl iron compounds have proven to be particularly difficult to prepare by other strategies, this reaction provides an attractive synthetic entry t o this class of compounds. We are presently exploring the organic reaction chemistry of these compounds. Previous studies have shown that I and I1 can be oxidized to the corresponding stable radical cations both chemically and electrochemically.2bs6Additionally, (q5C~H~)~F~Z@-CO)Z@-P~~PN(E~)PP~~) undergoes oneelectron charge transfer oxidation with 7,7,8,8-tetracyanop-quinodimethane to yield a product which has been crystallographically characterized.’ Generating the monocations of I and I1 by photochemical charge transfer is entirely reasonable under the conditions of our reactions. In order to provide further support for the proposal that these reactions proceed via radical attack on the ring of a bimetallic radical cation, we have carried out the reaction of I+PF6under conditions that are reported to involve alkyl radicals. Floris and co-workerss have described the reactions of ferrocene and ferrocinium ions with alkyl radicals generated by reaction of alkyl iodides with Fe+2, H202, and DMSO. Directly adopting the reported protocol, I+PF6was reacted with ICHzCOzCzH5. Upon workup and careful chromatography, a small quantity of green product was obtained that was shown to be free of I by HPLC. IR confirmed the presence of both ester and p-CO bands, and lH, 13C,and 31PNMR spectra were consistent the expected ring substituted (5)Giannotti, C.;Gaspard, S.; Kramer, P. In Photoinduced Electron Transfer. Part D. Photoinduced Electron Transfer Reactions: Inorganic Substrates and Applications; Fox, M. A.; Chanon, M., Eds.; Elsevier: Amsterdam, 1988;p 200-240. (6) (a) Furguson, J. A,; Meyer, T. J. Inorg. Chem. 1971,10, 1025. (b)Furguson, J. A.; Meyer, T. J. Znorg. Chem. 1971,11,631. (7) Bell, S. E.;Field, J. S.; Haines, R. J. J . Chem. SOC.,Chem. Commun. 1991,489. (8)Baciocchi, E.; Floris, B.; Muragila, E. J. Org. Chem. 1993,58, 2013. See also, Minisci, F.; Vismara, E.; Fontana, F. J . Org. Chem. 1989,54,5224.
product, VII. Mass spectrometry (EYCI) yielded the required parent mass and a fragmentation pattern diagnostic of an ethyl ester. As found in the mass spectrum of IV and V, fragmentation of these asymmetrically substituted compounds gives rise to (C5H5)FeL2+ and (CsH4R)FeLz+species that provide further confirmatory evidence for the identity of the compounds. The ultimate yield of VI1 was insufficient to permit elemental analysis. The differences in behavior among compounds I, 11, and I11 are probably attributable to the effect of the increasing length of the phosphine bridge upon the stability of the Fe&-C0)2 core of the molecule. Several physical properties of these and related compounds support this argument. Iron-Iron bond lengths are found to increase with increasing bridge length. The Fe-Fe bond length in I has been found t o be 2.516 A,9 while the same bond length in I1 is 2.527 A. Wright and co-workers1° have found the Fe-Fe bond lengths in the compounds (CH3)2Si(C5H4)2Fe2CU-CO)01-X),where X = DPPM and DPPP, to be 2.497 and 2.521 A, respectively. It should be noted that introduction of the (CH3)2Si bridge between the rings in the DPPM derivative compresses the Fe-Fe bond relative to I. These changes in bond length are reflected in changes in the Fe-Fe (a a*)band positions as presented in Table 1 for compounds 1-111 and analogous ring-coupled derivatives. As the diphosphine ligand bridge grows, this band moves to lower energy, reflecting the increasing strain on the Fe-Fe bond. Similarly, Wright has found that the first oxidation potentials for the series (CH3)2S ~ ( C ~ H ~ ) ~ F ~ Z ~ ~ - C where O ) C UX- X=)DPPM, , DPPE, and DPPP, undergo a negative shift with increasing bridge length.1° These various trends are consistent with a gradual weakening of the Fe-Fe bond with increasing bridge length, but do not explain why only ring substitution is observed for compounds I and I1 and only bond homolysis is observed for 111. The X-ray crystallographic results for both I1 and V were obtained. Crystallographic data for I1 and V appear in Table 2 and selected bond lengths and angles appear in Tables 3 and 4, respectively. The solid state structure of I1 contains a racemic mixture resulting from the C2 symmetry of the compound. The two independent molecules in the unit cell are chemically indistinguishable. The structures of compounds I1 (Figure 1)and V (Figure 2) are also effectively superimposable with no chemically significant differences in bond lengths or angles arising from the presence of the formyl group. The Fe-Fe bond length of 2.527(1)A for V and 2.516(1) and 2.512(1) A for the two independent molecules of I1 indicate a slight weakening of the FeFe bond, as reflected in the electronic spectra. The observation of photochemical charge transfer for one class of bimetallic complexes raises the possibility that similar reactions might be possible for other complexes such as (q5-C5H,=,)2Fe2(C0)4and (q5-C5H&Moz(CO)s. Recent elegant work by Bullock et al.ll examined the electrochemical formation of the [(q5C5H5)2Fe2(CO)411+radical cation and provided detailed
-
(9)Bitterwolf, T. E.; Shade, J. E.; Pearson, W. H.; Brown, J. E., Unpublished results, 1994. (10) Wright, M. E.; Mezza, T. M.; Nelson, G. 0.; h s t r o n g , N. R.; Day, V. W.; Thompson, M. R. Organometallics 1983,2,1711. (11)Bullock, J. P.; Palazotto, M. C.; Mann, K. R. Inorg. Chem. 1991, 30, 1284.
Shade et al.
formula crystal system space group a b c
a
P Y volume, A 3 Z
D(calc), g/cm3 D(obs), g/cm3 p(Mo Ka),cm-' temp, K crystal size, mm crystal color diffractometer monochromator radiation wavelength 28 limits, deg scan technique standards decay (max), % octants collcd no. of reflns collcd no. of independt rflns no. of independt rflns I2 3a(Z) R(Z) on averaging, % T(max)/T(min)
R(F), % RdF), % GOF
Ab A(@),e k3 NdNv
(i) Crystal Data C38H3402PzFe2 trigonal
C39H3403PzFez orthorhombic
R3 (No. 148) 27.749 (2) 27.749(2) 27.749(2) 116.52(9) 116.52(9) 116.52(9) 10109(15) 12b 1.373 1.410 10.5 296 0.30 x 0.20 x 0.25 dark green
Pna21 (No. 33) 13.988 (10) 13.37l(3) 17.358(6) 90 90 90 3246.5(41) 4 1.481 1.463 10.5 296 0.25 x 0.25 x 0.20 dark brown
(ii) Data Collection Enraf-Nonius CAD4 oriented graphite Mo Ka 0.71073 2-50 3 stdl00 refls 4.2 1h,k,&l(1-30° 28)d h,k,fl(30-50" 28) 17970 11832
Enraf-NoniusCAD4 oriented graphite Mo Ka 0.71073 2-50 8-28 3 stdl00 rfls 1.6 fh,fk+l(O-24° 28) h,k,fl(24-50' 28) 5360 4704
5413 3.8 1.02
3368 1.7 1.35
(iii) Refinement 4.1 5.9 1.936 0.01 1.03 6.83
5.4 6.3 1.667 0.01 2.75 8.13
0
C15
c9
Figure 1. c3 4
c3
ClO
*A
c4 y j A __ c s LL
P2
C 6
R-
c21-
Figure 2. Table 4. Selected Bond Angles (deg) for I1 and V atoms II V
Cell parameters for the idealized cells were determined from 25 reflections in the range 20" < 28 -= 35" followed by least-squares refinement. Setting angles for the 25 reflections were based upon 100 reflections (four settings of each reflection including 1 2 8 values). This is the number of molecules in the unit cell. The number of asymmetric units per unit cell is six, with two molecules per asymmetric unit. Same as 11. dData were collected with hexagonal setting and converted to rhombohedral for structure solution and refinement.
Table 3. Selected Bond Distances (A) for 11 and V atoms II V atoms I1 V
Fe2-Fe 1-P 1 Fel -Fe2-P2 Fel-Pl-C37 Fe2-P2-C38 Fel-C36-Fe2 Fe 1-C35 -Fe2 03-C39-C25
105.64(6) 105.65(7) 117.6(3) 119.5(2) 83.3(3) 82.1(2)
104.83(6) 106.24(7) 117.7(2) 118.0(2) 82.4(3) 82.6(3) 124.(1)
work will be necessary to establish whether photochemical charge transfer reactions compete with the more familiar radical formation processes and contribute t o the photochemistry of these bimetallic complexes.
Experimental Section
information on its reactions with nucleophiles. Earlier work by Kadish12demonstrated that the [(v5-C5H&Mo2(CO)&+ cation radical is an intermediate in the oxidation of the bimetallic molybdenum compound. Bullock and co-workers have demonstrated that reactions of the cation radicals with nucleophiles yield products which are similar to those observed by Tyler and attributed to an intermediate 19-electron species.13 Additional
Compounds I,2 11: III? and I+PFe,2b,S were prepared by literature procedures. Crystals of I1 and V for X-ray crystallography were grown from CHCl3:pentane mixtures. IR spectra were recorded on a Perkin-Elmer 1750 FT-IR spectrometer. NMR spectra were recorded on a GE-QE300 NMR spectrometer and referenced to solvent resonances. Mass spectra of IV were recorded by Dr. Mark Ross of the Naval Research Laboratory and Dr. Gary Knerr of the University of Idaho. Elemental analyses were performed by Desert Analytics, Inc. Tucson, AZ. Synthe~iSOf (tlS-C~CHO)(~S.C~)F~~-CO)~~-DPPM IV. I(0.50 g, 0.73 mmol) is taken up in 125 mL of CHC13 in a Pyrex water-jacketed reaction vessel and photolyzed using a 250 W General Electric sun lamp for 4 h. During this time the solution changes color from olive green to brown. After the reaction is complete, the solvent is removed and the oily residue is chromatographed on a grade I11 alumina column
(12)Kadish, K. M.; Lacombe, D. A,; Anderson, J. E. Inorg. Chem. 1986,25,2246.
(13)Avey, A.; Tyler, D. R. Organometallics 1992, 1 1 , 3856, and references therein.
Fei-Fe2 Fel-PI Fe2-P2 Fel-C36 Fel-C35 Fe2-C36 Fe2-C35
2.516(1) 2.172(2) 2.180(2) 1.884(8) 1.922(4) 1.902(6) 1.908(8)
2.527(1) 2.198(2) 2.186(2) 1.917(7) 1.925(6) 1.919(7) 1.903(7)
C36-02 C35-01 Pl-C37 P2-C38 C37-C38 C25-C39 03-C39
1.202(8) 1.181(8) 1.825(4) 1.838(8) 1.51(1)
1.187(8) 1.171(8) 1.817(7) 1.833(8) 1.55(1) 1.41(1) 1.25(2)
Organometallics, Vol. 14, No.
Photochemical Reimer-Tiemann Reactions
I, 1995 161
(m, ipso-Ph), 131.7 (m, o-Ph), 128.4 (s, m-Ph), 127.0 @-Ph), using 6:l petroleum ether:CHCla as a n eluant. A green band 95.7 (ipso-cp),86.2 (CpR), 85.8 (Cp), 83.7 (CpR), 59.3 (CpCHzof I is eluted first from the column followed by a golden band. COz), 32.4 (CHzCHs), 27.5 (t, Jp-c = 21.7 Hz), 13.2 (CHzCH3). Removal of solvent from the golden band and recrystallization 31PNMR: (C&) 83.8 and 81.1 (AB q, JPa-Pb = 91.9 Hz). Mass from dich1oromethane:pentane yields 0.19 g of IV as a brown spectrometry: (EI/CI) 768 (M+), 740 (M+ - CzH4 or CO), 712 solid. Mp: 224-225 "C. Yield 37%. IR: (CHCl3): 1690 (m), (M+ - 2CO or CO and cZH4), 696 (M+ - CzH4 and COz), 682 1682 (sh), 1658 (sh). lH NMR: (CDCld 9.15 ( 8 , 1 H, CHO), (M+ - CJ&02), 654 (M+ - CJ3702 and CO), 591 ((q57.44-7.22 (m, 20 H, Ph), 4.70 and 4.66 (AA'BB,4 H, C5H4C5H4C3H,02)FeDPPE+), 505 ((CsHdFeDPPE+), 440 (Fe~ Hz, CHO), 4.37 (8, 5 H, C a s ) , 1.89 (t, 2 H, 2 J ~ =- 10.06 DPPM+). PCHZP). '3C NMR (CDC13) 191.2 (CHO), 136.28 (dd, ipsoX-rayStructure Determination. Crystal data are prePh, 'Jp-c = 32.6 Hz, Vp-c = 4.8 Hz), 135.75 (dd, ipso-Ph', 'JP-c sented in Table 1. Crystals of both I1 and V were grown by = 33.6 Hz, 3Pp-c = 6.3 Hz), 132.35 (d, 0-Ph, Vp-c = 9.6 Hz), 132.22 (d, o-Ph', 'Jp-c = 9.1 Hz), 129.96 (d,p-Ph and -Ph', 4 J ~ - ~evaporation of chloroform:pentane solutions. Suitable crystals were chosen from each compound and mounted in random = 8.0 Hz), 128.26 (d, m-Ph, 3 J p - ~= 9.4 Hz 128.22 (d, m-Ph', orientations on glass fibers. Rotation photographs were used 3Pp-c = 9.0 Hz), 94.28 (Zp~o-Cp),90.37 (CHOCp), 86.91 (Cp), to locate reflections which were then indexed to obtain the unit 85.31 (CHOCp), 28.29 (t, 'Jp-c = 22.8 Hz). 31PNMR (CDCld cells for both crystals, Axial photographs confirmed axial 84.48 and 81.47 (AB, V p - p = 92.38 Hz). Mass Spectrometry: lengths for both unit cells and mmm Laue diffraction sym710 (M+), 682 (M+ - CO), 658 (M+ - 2CO), 589 (CHOC5H4metry for V. Compound I1 was originally indexed in the FeZDPPM), 561 (CsHtjFezDPPM),533 (CHOC&f$eDPPM), 505 hexagonal cell for which a = 47.2 A and c = 15.7 (C~HSF~DPPM), 440 (FeDPPM). Calcd for C ~ ~ H ~ Z F ~C, Z O ~ Pnonprimative ~: A. Data were collected in the hexagonal cell but were later 64.25; H, 4.55; P, 8.72. Found: C, 64.36; H, 4.55; P, 8.63. Synthesis of (q5-C5~CHO)(C5Ha)Fe2(lr-CO)z(lr-DPPE), transformed to the primitive rhombohedral cell for structure solution and refinement. Conditions of reflection of h k 1 V. I1 (0.50 g, 0.72 mmol) was photolyzed and purified as = 3n confirmed space group R3 for 11. Conditions of reflection described above. V was recovered as a brown solid. Mp: 243OkZ (k 2 = 2n) and h01 (h = 2n) for V were not sufficient t o 244 "C dec. Yield: 40%. IR: (CHC13) 1687 (m), 1655 (sh). 'H choose between the centrosymmetric Pnam and the noncenNMR: (CDC13) 8.90 (s, 1H, CHO), 7.89 (m, 8 H, Ph), 7.45 (m, trosymmetric Pna2l. Intensity statistics indicated a noncen12 H, Ph), 4.57 and 4.53 (AA'BB', 4 H, CHOCEH~),4.72 ( 8 , 5 trosymmetric structure. A linear decay correction was applied H, C5H5), 1.35 (m, 4 H, P-Cd&-P). I3C: (CDCld 191.23 (CHO), to both data sets. Empirical absorption corrections for both 136.67 (br, ipso-Ph), 132.87 (br s, 0-Ph), 130.04 (d, 4Jp-c = 12.8 crystals were based on ly scans of three reflections at 10" yj Hz,p-Ph), 128.37 (pseudo t, 3 J p - ~= 8.3 Hz, m-Ph), 95.26 (ipsointervals. CHOCp), 90.37 (CHOCp), 86.88 (Cp), 84.55 (CHOCp), 22.54 (d, 'Jp-c = 25.23 Hz, PCZH~P), 22.30 (d, 'Jp-c = 25.72 Hz, Both structures were solved via direct methods and comP C z W ) . 31PNMIk (CDC13) 68.52 and 64.11. MS: (FAB) 724 pleted with difference Fourier synthesis. Structure solutions (M+),696 (Mf - CO), 668 (M+ - 2 CO), 640 (M+ - 3 CO), 575 for V were attempted in both Pnam and Pna21 but could only [CHOC5H3e(DPPE)(CO)1,547 [CHOCd&Fe(DPPE)I or tC&be obtained in Pna21. The absolute configuration of the, space Fe(DPPE)(CO)], 519 [C5HsFe(DPPE)l, 454 [Fe(DPPE)I. group was assigned on the basis of the difference in R(F) Synthesis of (q5-C5HaCH2C04C2Ha)(CaHs)Fe2(lr-CO)2(lr-between refinements of both hands without hydrogen atoms. DPPM), VIII. I+PFs(0.51 g, 0.61 mmol) and FeS04.7Hz0 "he two forms refined to R(F) of 0.066 for the correct structure (0.28 g, 1.0 mmol) were taken up in DMSO, 35 mL of ICHzand RQ of 0.072 for the incorrect structure. All non-hydrogen COzCzHs, and 5.0 mL of a 0.20 M solution in DMSO (1.0 atoms were refined with anisotropic temperature factors in mmol), and the solution stirred for 15 min, at which time the both structures. Hydrogen atoms were located in the differsolution was green. Freshly prepared HzOz in DMSO (0.140 ence Fourier maps but were calculated at idealized positions mL of 30% solution in 10 mL of DMSO, 1.0 mmol) was added and assigned a temperature factor 30% larger than the dropwise t o the solution during which the solution changes to corresponding carbon isotropic temperature factor. Hydrogen reddish brown. Note: addition of excess HzOz results in atom positions were updated throughout the final cycles of refinement. Examination of strong, low-angle reflections complete decompositionof the metal compounds. After stirring for 15 min, the solution was diluted with brine and an excess revealed no extinction effects. of ascorbic acid was added. The solution immediately produces An interesting feature of I1 is the existence of both enana green suspension that was stirred for at least 30 min. tiomers of the compound in the asymmetric unit. CocrystalExtraction with benzene (30 mL) gave a green solution that lization of both enantiomers accounts for the usually large unit was washed with brine and dried with MgS04. Removal of cell with six asymmetric units per cell. solvent gave a green solid that was taken up in minimal benzene and chromatographed on a 40 x 2 cm alumina (grade Acknowledgment. We thank Prof. Barbara Floris 111)column using benzene as the eluant. Slow elution resulted for providing us with preprints of her manuscript in the partial separation of two green bands. The first band describing alkyl radical reactions with ferrocene and was shown by IR and HPLC to be I. The second band ferrocnium. J.E.S.thanks the United States Naval recovered in this way was consistently contaminated with I Academy Research Council for generous support. J.E.B. and had to be rechromatographed to obtain a small amount thanks the Naval Academy for a Trident Scholarship. of VI1 as a dark green solid. VI1 appears to decompose slowly on the column to a purple product resulting in a reduction of the total yield. IR: (CHzClz) 1728 (m), 1676 (s), 1095 (m) cm-' Supplementary Material Available: Tables of bond (m). IH NMR: (C&) 7.50 (8H, Ph), 7.00 (12 H, Ph), 4.59 (t, distances and angles, positional parameters, and general 2H, CpR), 4.39 (s, 5H, Cp), 4.09 (m, 2H, CpR), 3.92 (9, 2H, J displacement parameters for I1 and V (36 pages). Ordering = 7.1 Hz, CHzCHs), 3.59 (9, 2H,CpCHzCOz), 1.76 (t, 2H,JP-H information is given on any current masthead page. = 10 Hz, PCHzP), 0.93 (t, 3H, J = 7.1, CHzCH3). 13C NMR OM9406660 (CsDs)295.1 (t,Jp-c = 14.6 Hz,,u-CO), 170.6 (COzCzHd, 136.3
+ +
+
