Organometallics 1996, 14, 1514-1517
1514
Synthesis and X-ray Structure of [(q5-CsH5)Fe(CO)C@)Me1 01-ql:q l-dppe)[(q4-exo-MeC6H5)Fe(CO)21 Lung-Shiang Luh and Ling-Kang Liu* Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 11529, ROC, and Department of Chemistry, National Taiwan University, Taipei, Taiwan 10767, ROC Received August 22, 1994@ Summary: The 1:l mixture of (r/5-CsHs)Fe(CO)Zrand (q5CsHs)Fe(CO)C(0)Me(ql-dppe) i n THF reacts with MeLi at -78 "Cto produce a novel complex [($-C5HdFe(CO)C(0)Me](~-q1:q1-dppe)[(q4-MeCsHs)Fe(CO)27 in which a dppe links two isomeric, methylated [(C&dFe(C0)27 units, one end being i n the form of (q5-C&JFe(C0)C(0)Me and the other end in the form of (q4-exo-MeCsHs)Fe(C0)z. The X-ray structure of the title complex exhibits a dppe-bridged unsymmetrical pseudooctahedral Fe(II) I pseudosquare pyramidal Fe(0) complex without any metal-metal bonding. The embedded structural parameters of Fe(II) and Fe(0) centers give evidence of a n Fe(II) smaller than Fe(O), as suggested by the Fe(II)-P length of 2.1 78(2)A simultaneously present with that of Fe(0)-P, 2.212(1) A. The shortening of 0.034 A is significant as it represents a difference greater than 10 ESDs. Introduction The diphosphine Ph2P(CH2)2PPh2 (dppe) has been regarded as a very good chelating 1igand.l Nevertheless, it is employed in this study as a bridging ligand to provide one of its PPh2 groups in assisting the methyl migratory insertion reaction of (q5-C5H5)Fe(C0)2Me2 and the other PPh2 in bringing up the ring alkylation reaction with (q5-C5H5)Fe(CO)21and MeLi,3 the ring methylation being a reverse in polarity-the (q5-C5H5) ligand of the iodide becomes the center for Me- nucleophilic addition.
Results and Discussion (q5-C5H5)Fe(CO)2Meis known to proceed with a PR3assisted methyl migratory insertion t o yield (q5-C5H5)Fe(CO)C(0)Me(PR3).2Accordingly, the unidentate complex (q5-C5H5)Fe(CO)C(0)Me(q1-dppe) (1) has been prepared by reacting (q5-C5H5)Fe(CO)2Mewith dppe in 1:l molar ratio to give both the unidentate product 1 (38%)and the bridging product [(q5-C5H5)Fe(CO)C(0)Me12(,n-q1:q1-dppe) (2; 49%). Since complex 1 is an intermediate to give complex 2, the reaction of (q5C5H5)Fe(C0)2Mewith dppe in 2:l molar ratio easily proceeds t o complex 2. The elaboration of the acetyl Me group in (q5-C5H5)Fe(CO)C(O)Me(PPha)by the nucleophile-electrophile sequence is of much use in organic ~ y n t h e s i s , taking ~-~
* To whom correspondence should be addressed at Academia Sinica.
Abstract published in Advance ACS Abstracts, January 15,1995. (1)Cotton, F.A,, Wilkinson, G., Eds. Advanced Inorganic Chemistry, 5th ed.; Wiley: New York, 1988;Section 2.4. (2)(a)Bibler, J . P.; Wojciki, A. Inorg. Chem. 1966,5,889.(b) Butler, I. S.; Basolo, F.; Pearson, R. G. Inorg. Chem. 1967,6,2074.(c) Green, M.;Westlake, D. J. J . Chem. SOC.A 1971,367. (3)(a) Luh, L.-S.; Liu, L.-K. Bull. Inst. Chem., Acad. Sin. 1994,41, 39. (b) Liu, L.-K.; Luh, L . 3 . Organometallics 1994,13,2816.(c) Liu, L.-K.; Luh, L.-S.; Eke, U. B. Organometallics, in press. @
advantage of the chiral Fe center. With similar bonding on the half-sandwich Fe center, the unidentate complex 1 had been expected to proceed with a deprotonation by MeLi, producing the anionic intermediate (q5-C5H5)Fe(CO)(q1-dppe)C(0)CH2-t o receive an electrophile, e.g., (q5-C5H5)Fe(C0)21,in this study. Treating complex 1 with MeLi and then trapping with (q5-C5H5)Fe(CO)21 in sequence produced very complex Fe-containing species which were not resolved. The reaction of equal amounts of (q5-C5H5)Fe(CO)21 and MeLi in the presence of 1 equiv of unidentate complex 1 at -78 "C followed the reaction pattern reported earlier3 and gave a novel complex (q5-C5H5)Fe(CO)C(0)Me(pq1:q1-dppe)(q4-MeC5H5)Fe(CO)2 (3;76%) that has been characterized with IR, NMR, melting point, MS, elemental analysis, and X-ray crystallograPhY * The molecular connectivity of 3 was readily derived from the spectroscopic data: the IR vco bands of 1910 and 1603 cm-' and 31PNMR chemical shift of 6 75.9 are typical of (q5-C5H5)Fe(CO)C(0)Me linked to dppe as exhibited in 1 and 2. On the other hand, the IR vco bands of 1963 and 1910 (overlapping) cm-l, 31PNMR chemical shift of 6 70.3 and lH NMR shifts at 6 4.88, 2.62, and 2.11 (integration 2:1:2) are indicative of the presence of a (q4-RC5H5)Fe(C0)2(PR3) fragment in 3 as well, in good comparison with (q4-MeC5H5)Fe(C0)2(PPh3I3,which shows relevant IR vco bands of 1964 and 1904 cm-l, chemical shifts at 6 73.2 (31P)and 5.03,2.72, and 2.41 PH, integration 2:1:2). Thus, for the first time a dppe linking two isomeric, methylated [(CsHs)Fe(C0)21 units was obtained, one end in the form of (q5-C5H5)Fe(CO)C(O)Me and the other end in the form of (r4MeC5HdFe(C0)2. In the absence of phosphines, the electrophile Fe(C0)2I is known to react with nucleophilic MeLi to give (q5-C5H5)Fe(CO)2Me,7where the halide exchange is indirect: the electrophile (q5-C5H5)Fe(C0)21initially receives RLi at the coordinated CO site rather than the Fe center or the (q5-C5H5)ligand,8 followed by Fe-I bond cleavage and CO deinsertion. A neutral (q5-C5H5)Fe skeleton is resistive to modification in the q5bondingag If a (q5-C5H5)ligand is the site of reaction, RLi usually deprotonates the (r5-C5H5)ring, evidenced (4)(a)Davies, S. G. Organotransition Metal Chemistry: Applications to Organic Synthesis; Pergamon: Oxford, U.K., 1982. (bj Davies, S. G. Aldrichim. Acta 1990,23,31,and references within. ( 5 ) For practical preparation of optical chiral auxiliaries: CaseGreen, s. C.; Costello, J. F.; Davies, S. G.; Heaton, N.; Hedgecock, C. J . R.; Prime, J. C. J. Chem. SOC.,Chem. Commun. 1993,1621. (6)Libeskind, L. S.;Welker, M. E.; Fengl, R. W. J . A m . Chem. SOC. 1986,108,6328. (7)(a) Piper, T. S.; Wilkinson, G. J . Inorg. Nucl. Chem. 1966,3, 104. (b) Li, H.-j.; Turnbull, M. M. J . Organomet. Chem. 1991,419, 245. ( 8 ) Wong, A.; Pawlick, R. V.; Thomas, C. G.; Leon, D. R.; Liu, L.-K. Organometallics 1991,1 0 , 530.
0276-733319512314-1514$09.0OlO 0 1995 American Chemical Society
Notes
Organometallics, Vol. 14,No. 3, 1995 1515 Scheme 1
ea I Me',
sa I
8"
I - - +
I
by the RLi-induced migration reactions of (r5-C5H5)Fe(C0)2E (E = alkyl, silyl, germyl, stannyl, etc.) being transferred from Fe-E to (y5-C5H4-E).10J1In the presence of PPh3, however, (r5-C5H5)Fe(C0)21is reduced by RLi via the cationic intermediate [(q5-C5H5)Fe(C0)2(PPh3)1+, which is more electrophilic toward RLi, to produce (y4~o-RC5H5)Fe(C0)2(PPh3).3 Within reasonable extension, Scheme 1 is a plausible mechanism toward the preparation of 3-the dangling PPhz group of 1 coordinates to (r5-C5H5)Fe(C0)21t o first form a cationic intermediate that is attacked by MeLi, the methylation of (v5-C5H5)occurring via an ex0 direction, which is consistent with the results of an X-ray structure analysis. Figure 1 shows the ORTEP plot of the molecule in which an exo-Me group is seen on the cyclopentadiene ring, indicating retrochemically no Fe mediation. Shown in Figure 1,dppe is a bridging ligand. To the best of our knowledge, the compound is the first to (9) Wilkinson, G.,Stone, F. G. A., Abel, E. W., Eds. Comprehensive Organometallic Chemistry: The Synthesis, Reactions, and Structures of Organometallic Compounds; Pergamon: Oxford, U.K., 1982; Vol. 4, pp 491-2. (10) Abbott, S.;Baird, G. J.;Davies, S. G.; Dordor-Hedgecock, I. M.; Maberly, T.R.; Walker, J. C.; Warner, P. J . Organomet. Chem. 1985, 289, C13. (11) (a) Berryhill, S.R.; Clevenger, G. L.; Burdurlu, F. Y. Organometallics 1985,4, 1509. (b) Pannell, K. H.; Cervantes, J.;Hernandez, C.; Cassias, J.; Vincenti, S. Organometallics 1986, 5, 1056. ( c ) Cervantes, J.; Vincenti, S. P.; Kapoor, R. N.; Pannell, K. H. Organometallics 1989, 8, 744.
Figure 1. Molecular plot of [(r15-CsHs)Fe(CO)C(0)Mel~y1:r11-dppe)[(r14-MeC5H5)Fe(CO)~l (3). Selected bond lengths, bond angles, and torsion angles: Fe(l)-P(l) 2.212(1), Fe(l)-C(l) 2.102(3), Fe(l)-C(2) 2.043(3), Fe(l)-C(3) 2.054(3),Fe(l)-C(4) 2.124(3),Fe(l)-C(7), 1.768(4),Fe(1)C(8) 1.746(4),Fe(2)-P(2) 2.178(1), Fe(2)-C(23) 2.103(4), Fe(2)-C(24) 2.123(4), Fe(2)-C(25) 2.120(3), Fe(2)-C(26) 2.098(4), Fe(2)-C(27) 2.115(4), Fe(2)-C(28) 1.735(4), Fe(2)-C(29) 1.928(4), 0(7)-C(7) 1.144(5), 0(8)-C(8) 1.150(4),0(28)-C(28) 1.140(5),0(29)-C(29) 1.193(6),C(1)C(2)1.414(5),C(l)-C(5) 1.504(5),C(2)-C(3) 1.403(5),C(3)C(4) 1.408(5), C(4)-C(5) 1.508(5), C(23)-C(24) 1.398(7), C(23)-C(27) 1.396(8),C(24)-C(25) 1.385(6),C(25)-C(26) 1.389(6), C(26)-C(27), 1.403(7) A; P(l)-Fe(l)-C(7) 97.8(1), P(l)-Fe(l)-C(8) 89.8(1), C(7)-Fe(l)-C(8) 100.1(2), P(2)-Fe(2)-C(28) 91.6(1), P(2)-Fe(2)-C(29) 92.7(1), C(28)-Fe(2)-C(29) 89.6(2)";Fe(l)-P(l)-C(21)C(22)-175.7(2), Fe(2)-P(2)-C(22)-C(21) -59.7(1), P(1)C(21)-C(22)-P(2) -162.9(2), C(28)-Fe(2)-C(29)-0(29) -125.4(3)".
exhibit the dppe bridge between a pseudooctahedral, formally Fe(I1) center of (q5-C5H5)Fe(CO)C(0)Me(PR3) skeleton and a distorted square-pyramidal, formally Fe(0) center of (r4-MeC5Hs)Fe(CO)2(PR3) skeleton. There is no Fe-Fe bond between the Fe(I1) and Fe(0) centers. The coordination geometry of Fe(I1) can be described as a piano stool with the (v5-C5H5)ring occupying the fac sites and the three legs being orthogonal.12 That of Fe(0) can be described as a square-pyramid with the diene group occupying the cis sites of the basal plane as joined by CO and PR3, the remaining CO being at the apical position. In the literature, the Fe(I1)-P lengths and the Fe(0)-P lengths are very scattered in their numerical values. For PMe3, the hexacoordinated Fe(I1)-P length is seemingly shorter than the pentacoordinated Fe(0)-P length, 2.230(37) us 2.265(42)A.13 For other phosphines, the Fe-P lengths have been tabulated only collectively. Figure 2 reveals a histogram summarizing the Fe(I1)-P and the Fe(0)-P lengths, with values retrieved from the Cambridge Structural Database14 for structures containing a fragment of Fe(C0)2(PR3) (R = alkyl, aryl) with no differentiation toward the identity of the PR3. The structures with (12) Seeman, J.I.; Davies, S. G. J . A m . Chem. SOC.1985,107,6522. (13)Orpen, A.G.; Brammer, L.; Allen, F.H.; Kennard, 0.; Watson, D. G.; Taylor, R. J . Chem. SOC.,Dalton Trans. 1989,S1.
Notes
1516 Organometallics, Vol. 14, No. 3, 1995
2.35
2.30
i
-
i 1I I I
2.25
- 1
+
I
2.20
2.159
10
0
10
20
30
(0.796 g, 2 mmol) were dissolved in CH3CN (50 mL) and refluxed for 12 h. The solution was then cooled to room temperature. Filtration followed by removal of the solvent and then column chromatography (SiOz, eluting with 1:2 EtOAd n-hexane) yielded three bands. The first band was the starting materials. The second band was the orange-yellow compound (q5-C5H5)Fe(CO)C(0)Me(y1-dppe)(1;0.438 g, 38%). The third band was the orange compound [(115-C5H5)Fe(CO)C(0)Me12(p-ql:ql-dppe) (2; 0.386 g, 49%). 1: gummy solids, no well defined mp; IR (CH2C12) vco 1916 (s), 1600 (m) cm-'; 31P{1H}NMR (CDC13) 6 75.3 (d), -12.1 (d), 3 J p p = 40.6 Hz; MS (mlz) 591 (M+ 1). Anal. Calcd for C34H32FeO~Pz: C, 69.17; H, 5.46. Found: C, 69.18; H, 5.68. 2: mp 106-110 "C; IR (CH3CN) 1912 (s), 1591 (m) cm-'; 31P{1H)NMR (CDC13) 6 76.33 (s), 76.27 (s), presumably due to the meso and D,L forms; MS (mlz)782 (M+). Anal. Calcd for C4zH40Fe~04Pz: C, 64.47; H, 5.15. Found: C, 64.09; H, 5.02. Reaction of 1:l (r,P-C5He)Fe(CO)zIand MeLi in the Presence of 1. (q5-C5H5)Fe(CO)zI(0.225 g, 0.74 mmol) and 1 (0.437 g, 0.74 mmol) were dissolved in THF (100 mL) and maintained at -78 "C. MeLi (1.6 M, 0.5 mL, 0.8 mmol) in 15 mL of ether at -78 "C was added dropwise to the solution. The mixture was stirred for an additional 1 h before being warmed to room temperature and stirred overnight. The solution was then quenched with water. The organic layer was combined with the benzene extracts of the HzO layer, dried over MgS04, and then evaporated to dryness under vacuum. The resulting oillike concentrates were mixed with 10 mL of CHzClz and 5 g of silica gel and pumped dry before being loaded on top of the column. Purification by chromatography (SiOz, eluting with ethyl acetateln-hexane) gave the q4-e3co-MeC5H5)yellow [(q5-C5H5)Fe(CO)C(0)Me)Ol-yl:rl'-dppe)[( Fe(CO)z(PPh3)](3;0.439 g, 76%), the orange 2 (0.017 g, 3%), and a trace of yellowish (q5-C5H5)Fe(CO)zMe. 3 could also be obtained as a byproduct (6.7%)in the reaction of 1:l (q5-C5H5)Fe(C0)ZI and MeLi in the presence of d ~ p e . ~ ' 3: mp 159-160 "C; IR (CHZC12) vco 1963 (s), 1910 (s), 1603 (m) cm-'; 'H NMR (CDC13) 6 0.28 (d, 3 J =~15 ~Hz, 3H, Me), 1.83, 2.39 (b, 4H, CpFePCHZCHzP), 2.04, 2.16 (b, 2H, CH=CHCHMe), 2.51 (s, 3H, C(O)Me), 2.63 (b, l H , CH=CHCHMe),4.31(s, 5H, Cp), 4.83,4.95 (b,2H, CHSCHCHMe), 7.18-7.37 (m, 20H, Ph); 13CNMR (CDCl3) 6 25.28 (d, I J p c = 24.7 Hz, CpFePCHZCHzP),27.23 (d, lJpc = 22.0 Hz, CpFePCHZCHzP), 28.21 (d, 4 J p = ~ 5.5 Hz, Me), 51.0 (s, C(O)Me), 51.58 (d,3Jpc= 4.8 Hz,CH=CHCHMe),57.8 (s,lC,CH=CHCHMe), 82.05 (d, 3 J p = ~ 4.9 Hz, CH=CHCHMe), 84.7 (s, C5H5), 128.0138.4 (m, phenyl region), 219.49 (d, Vpc = 14.0 Hz, CO), 219.5 (d, 'Jpc = 10.1 Hz, CO), 220.7 (5, CO), 275.32 (d, 'Jpc = 21.9 Hz, COMe); 31P(1H}NMR (CDC13) 6 75.9 (d, 3 J p p = 41.6 Hz), p 41.6 Hz); MS (mlz)782 (M+). Anal. Calcd for 70.3 (d, 3 J ~ = C4~H40Fez04Pz: C, 64.47; H, 5.15. Found: C, 64.09; H, 5.02. X-ray Structure Analysis. The single-crystal X-ray diffraction measurements were performed on a Nonius CAD-4 automated diffractometer using graphite monochromated Mo Ka radiation. Twenty-five high-angle reflections were used in a least-squares fit to obtain accurate cell constants. Diffraction intensities were collected up to 20 < 45" using the 8/28 scan technique, with background counts made for half the total scan time on each side of the peak. Three standard reflections, remeasured every hour, showed no significant decrease in intensity during data collection. The reflections with 1, > 2.541,) were judged as observations and were used for solution and structure refinement. Data were corrected for Lorentz and polarization factors. An empirical absorption correction based on a series of li, scans was applied t o the data. The structure was solved by direct methods17 and refined by a full-matrix least-squares routine18with anisotropic thermal parameters for all non-hydrogen atoms (weight = l/[dF,)2 +
I
I
40
50
Figure 2. Histogram of Fe(0)-P lengths (filled bar) and Fe(I1)-P lengths (open bar) with a step size of 0.01 A for crystal structures containing a molecular fragment of Fe(C0)dPRd.
disordering problems, and those with an R factor greater than 0.10 were discarded. The structures were then sorted into Fe(O), Fe(I), and Fe(I1) complexes by hand. The results indicate that the average Fe(0)-P length is 2.242(34)A for 68 structures totaling 235 fragments whereas the average Fe(I1)-P length is 2.270(35)8, for 21 structures and 55 fragments. Statistically, the Fe(I1)-P length and the Fe(0)-P length are not different. The structure analysis of the novel complex 3 gives one rare chance for direct com arison. The Fe(I1)-P length of 2.178(2) A is 0.034 shorter than that of Fe(0)-P, 2.212(1)A. Being greater than 10 ESDs, this difference is small yet significant, giving experimental support for Fe(I1) smaller in size than Fe(0).
K
Experimental Section General Procedures. All manipulations were performed under an atmosphere of prepurified nitrogen with standard Schlenk techniques. All solvents were distilled from an appropriate drying agent.15 Infrared spectra were recorded in CHzClz using CaFz optics on a Perkin-Elmer 882 spectrophotometer. The IH NMR and 13CNMR spectra were obtained on Bruker AC200lAC300 spectrometers, with chemical shifts reported in 6 values relative t o the residual solvent resonance of CDC13 (IH 7.24 ppm, 13C 77.0 ppm). The 31P{1H} NMR spectra were obtained on Bruker AC200lAC300 spectrometers using 85% H3PO4 as an external standard (0.00 ppm). The melting points (uncorrected) were determined on a Yanaco MPL melting point apparatus. (q5-C5H5)Fe(CO)zIwas prepared according t o the literature procedure.l6 Other reagents were obtained from commercial sources, e.g., Aldrich and Merck, and used without further purification. Reaction of 1:l (+A.HdFe(CO)zMeand PPhz(CH)zPPhz (dppe). (q5-C5H5)Fe(CO)zMe(0.384 g, 2 mmol) and dppe (14) (a) Cambridge Structural Database; the associated software, Cambridge Structural Database System; Cambridge Crystallographic Data Centre: Cambridge, U.K., Release April 1994. (b) Buergi, H.B., Dunitz, J. D., Eds. Structural Correlation; VCH: Weinheim, Germany, 1994; pp 71-110. (15) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals; Pergamon Press: Oxford, U.K., 1981. (16) (a) Dombek, B. D.; Angelici, R. J. Inorg. C h i n . Acta 1973,7, 345. (b) Meyer, T.J.;Johnson, E. C.; Winterton, N. Inorg. Chem. 1971, 10, 1673. ( c )Inorg. Synth. 1971,12, 36. (d) Inorg. Synth. 1963,7, 110.
(17) Main, P. In Crystallographic Computing 3: Data Collection, Structure Determination, Proteins and Databases; Sheldrick, G . M., Krueger, C., Goddard, R., Eds.; Clarendon Press: Oxford, U.K., 1985; pp 206-215.
Notes 0.0001(F,)21, d F 0 )from counting statistics). All of the hydrogen atoms were placed isotropically at their calculated positions (C-H = 1.00 A) and fmed in the calculations. Atomic scattering factor curves fo, A?, and Af" of Fe, P, 0, and C, and fo of H were taken from ref 19. Selected bond distances and angles were given in the caption of Figure 1. Crystal data of 3: C42H40Fe204P2, triclinic, space group P -1; a = 11.967(2), b = 12.066(1), c = 14.855(4) A; a = 106.51(1),/3 = 97.84(2), y = 108.20(1)"; V = 1893.1(6)A3;fw = 782.42, 2 = 2, F(OO0) = 811.88; pcalc= 1.373 g/cm3, p = 0.89 (18)(a)Gabe, E. J.; Le Page, Y.; White, P. S.; Lee, F. L. Acta Crystallogr. 1987,43A, S294. (b) Gabe, E. J.; Le Page, Y.; Lee, F. L. In Crystallographic Computing 3: Data Collection, Structure Determination, Proteins and Databases; Sheldrick, G. M., Krueger, C., Goddard, R. E., Eds.; Clarendon Press: Oxford, U.K., 1985; pp 167174. (19) Ibers, J. A., Hamilton, W. C., Eds. International Tables forX-ray Crystallography; Kynoch: Birmingham (Current distributor D. Reidel, Dordrecht, The Netherlands), 1974; Vol. 4,Tables 2.2A, 2.3.1D.
Organometallics, Vol. 14, No. 3, 1995 1517 mm-l, Mo K a 1 = 0.7093 A, Nonius CAD-4, 28 I50", -12 I h 5 1 1 , O 5 k 4 12, -15 5 I 5 15; transmission factors 0.9350.999, 90 atoms, 451 parameters, 4052 observations [Io > 2.5a(Zo)],R = 0.031, R, = 0.037, GOF = 1.81, A/a = 0.020.
Acknowledgments. The authors take this chance to thank Academia Sinica and the National Science Council, ROC, for their kind financial support. Thanks are due to Mr. Y.-S. Wen for assistance with the singlecrystal X-ray diffraction data collection. Supplementary Material Available: For Figure 2, listings of the retrieved crystal structures with bibliographic data and, for the structure of 3,listings of crystallographic data, positional and anisotropic thermal parameters, and bond distances, angles, and structural parameters (23 pages). Ordering information is given on any current masthead page. OM940672W
