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Organometallics 2009, 28, 1014–1017
r-Metallocenylmethylium Ions and Their Isoelectronic Congeners: A Comparison Based on DFT Calculations Christian Bleiholder,†,#,‡ Frank Rominger,† and Rolf Gleiter*,† Organisch-Chemisches Institut der UniVersita¨t Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany, and Deutsches Krebsforschungszentrum (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany ReceiVed June 22, 2008
The geometrical parameters, net natural charges, and Wiberg bond indices of a series of R-metallocenylmethylium ions with 18 valence electrons were calculated using density functional theory. The transition metals considered were Cr, Mn, Fe, Mo, Re, W, Ru, and Os. As coligands to the fulvene-metal fragment we used benzene, cyclopentadienyl, and three CO units. We also examined the fulvene-metal fragments for Co, Rh, and Ir using a cyclobutadiene coligand. Trends in bond order between the exocarbon atom of the fulvene unit (C6) and the metal atom as well as the bending angle of C6, R, and the net charges at C6 and the metal centers were analyzed. We found good correlation between R and the metal-C6 distance (d1). A comparison of the calculated values of R and d1 with experimental data shows good agreement in cases where steric effects do not hamper the C6-metal interaction. Introduction Studies in the past 40 years on R-metallocenylmethylium ions and their isoelectronic fulvene congeners of d6 to d9 metals1,2 have shown that the properties in solution and the solid state are in agreement with a through-space interaction between the exomethylene carbon center of the fulvene unit (C6) and the metal. This interaction is most bonding when the C6 center is bent toward the metal, leaving the other five carbons of the fulvene ring in one plane. This metal-C6 interaction consequently distributes the positive charge over the ligands and the metal atom, leading to retention of configuration at the C6 atom during nucleophilic addition at C6. The structural motif of a bent R-metallocenylmethylium ion (1) is also found in systems with two metal centers such as 2 or 3,3,4 as shown in Figure 1. In the past 35 years several quantum chemical methods applying different approximations have been used to calculate the properties of 1 and related congeners.5 The geometrical parameters of 1 that were typically reported were those that characterize the distortions of the fulvene ligand with respect to a planar structure: the angles R, β, and γ and the distances ∆x, d1, and d2 (Figure 2).5a It turned out, by comparing the * To whom correspondence should be addressed. E-mail: rolf.gleiter@ oci.uni-heidelberg.de. † Universita¨t Heidelberg. # DKFZ. ‡ Current address: Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106. (1) (a) Rosenblum, M.; Abbate, F. W. AdV. Chem. Ser. 1967, 62, 532– 548. (b) Cais, M. Organomet. Chem. ReV. 1966, 1, 435–454. (c) Kerber, R. C.; Ehntholt, D. J. Synthesis 1970, 449–465. (d) Watts, W. E. J. Organomet. Chem. Library 1979, 7, 399–459. (2) (a) Kreindlin, A. Z.; Rybinskaya, M. A. Russ. Chem. ReV. 2004, 73, 417–432. (b) Rybinskaya, M. I.; Kreindlin, A. Z.; Kamyshova, A. A. Russ. Chem. Bull. Int. Ed. 2002, 51, 1616–1632. (c) Gleiter, R.; Bleiholder, C.; Rominger, F. Organometallics 2007, 26, 4850–4859. (3) (a) Sato, M.; Kudo, A.; Kawata, Y.; Saitoh, H. Chem. Commun. 1996, 2, 25–26. (b) Sato, M.; Kawata, Y.; Kudo, A.; Iwai, A.; Saitoh, H.; Ochiai, S. J. Chem. Soc., Dalton Trans. 1998, 2215–2224. (4) (a) Sato, M.; Watanabe, M. Chem. Commun. 2002, 1574–1575. (b) Sato, M.; Kubota, Y.; Kawata, Y.; Fujihara, T.; Unoura, K.; Oyama, A. Chem.-Eur. J. 2006, 12, 2282–2292.
Figure 1. Examples of bent R-metallocenylmethylium ions.
Figure 2. Definition of the structural parameters R, d1, and d2 as well as the carbon numbering of the fulvene moiety.
various structures, that the most relevant parameters are R, d1, and d2, whereas the others tend to show only rather small changes.2c In this paper we present the results of quantum chemical calculations on a series of model systems each containing a fulvene-metal segment with 18 electrons. The overall charge state of the fulvene-metal group was changed as needed to maintain this 18-electron count and allowed us to restrict our calculations to the corresponding singlets. We subdivided our systems according to the coligands used. In the first three classes (Figure 3) we employed coligands that provide formally six electrons to the valence shell (benzene, 4-6; cyclopentadienyl
10.1021/om800573u CCC: $40.75 2009 American Chemical Society Publication on Web 01/21/2009
R-Metallocenylmethylium Ions
Organometallics, Vol. 28, No. 4, 2009 1015 Table 1. Computed Wiberg Bond Order Indices (bond order) between the Metal Atom (M) and C6, Net Natural Charges at the Metal Centers and C6, and the Geometrical Parameters r, d1, and d2 of 4-15 formal bond compd metal ligand charge order
Figure 3. Definition of 4-15.
anion, 7-9; and three CO groups, 10-12). In the fourth class we used cyclobutadiene as a coligand (13-15).
Computational Details The geometrical parameters of 4-15 were optimized using the Gaussian suite of programs6 at the density functional theory (DFT)7 level of theory by applying the three-parameter hybrid functional by Becke (B3)8 and the correlation functional suggested by Lee, Yang, and Parr (LYP).9 The 6-31G(d,p)10 basis was used for the (5) (a) Gleiter, R.; Seeger, R. HelV. Chim. Acta 1971, 54, 1217–1220. (b) Albright, T. A.; Hoffmann, R.; Hofmann, P. Chem. Ber. 1978, 111, 1591–1602. (c) Kreindlin, A. Z.; Fedin, E. I.; Petrovskii, P. V.; Rybinskaya, M. I.; Minyaev, R. M.; Hoffmann, R. Organometallics 1991, 10, 1206– 1209. (d) Rybinskaya, M. I.; Kreindlin, A. Z.; Petrovskii, P. V.; Minyaev, R. M.; Hoffmann, R. Organometallics 1994, 13, 3903–3908. (e) Bandy, J. A.; Mtetwa, V. S. B.; Prout, K.; Green, J. C.; Davies, C. E.; Green, M. L. H.; Hazel, N. J.; Izquierdo, A.; Martin-Polo, J. J. J. Chem. Soc., Dalton Trans. 1985, 2037–2049. (f) Volland, M. A. O.; Kudis., S.; Helmchen, G.; Hyla-Kryspin, I.; Rominger, F.; Gleiter, R. Organometallics 2001, 20, 227–230. (g) Gleiter, R.; Schimanke, H.; Silverio, S. J.; Bu¨chner, M.; Huttner, G. Organometallics 1996, 15, 5635–5640. (6) (a) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W;. Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.;. Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople J. A. Gaussian 03, ReVision B.03; Gaussian, Inc.: Wallingford, CT, 2004. (7) (a) Kohn, W.; Sham, L. J. Phys. ReV. A: At. Mol. Phys. 1965, 140, 1133–1138. (b) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and Molecules; Oxford University Press: Oxford, U.K. 1989. (c) Koch, W.; Holthausen, M. C. A Chemists Guide to Density Functional Theory; WileyVCH: Weinheim, Germany, 2000. (8) (a) Becke, A. D. J. Chem. Phys. 1992, 96, 2155–2160. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (c) Becke, A. D. J. Chem. Phys. 1993, 98, 1372–1377. (9) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B, Condens. Matter 1988, 37, 785–789. (b) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623–11627. (10) (a) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639– 5648. (b) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650–654.
4a 4b 4c 5a 5c 6a 6b 6c 7a 7b 7c 8a 8c 9a 9b 9c 10a 10b 10c 11a 11c 12a 12b 12c 13 14 15
Cr Mn Fe Mo Ru W Re Os Cr Mn Fe Mo Ru W Re Os Cr Mn Fe Mo Ru W Re Os Co Rh Ir
C6H6 C6H6 C6H6 C6H6 C6H6 C6H6 C6H6 C6H6 C5H5 C5H5 C5H5 C5H5 C5H5 C5H5 C5H5 C5H5 (CO)3 (CO)3 (CO)3 (CO)3 (CO)3 (CO)3 (CO)3 (CO)3 C4H4 C4H4 C4H4
0 1 2 0 2 0 1 2 -1 0 1 -1 1 -1 0 1 0 1 2 0 2 0 1 2 1 1 1
0.57 0.43 0.20 0.64 0.36 0.68 0.59 0.43 0.59 0.53 0.36 0.65 0.43 0.68 0.63 0.50 0.39 0.28 0.15 0.40 0.19 0.42 0.32 0.21 0.24 0.27 0.37
R
d1
d2
35.85 34.31 16.88 35.30 31.89 36.94 37.58 34.87 37.84 39.50 35.73 37.96 36.49 40.26 40.90 38.72 32.45 27.96 10.60 30.19 20.02 31.74 29.38 22.74 30.26 27.92 33.32
2.27 2.35 2.82 2.33 2.48 2.31 2.32 2.42 2.24 2.21 2.31 2.31 2.34 2.30 2.27 2.31 2.38 2.49 2.94 2.51 2.77 2.49 2.54 2.72 2.39 2.49 2.37
1.41 1.39 1.38 1.43 1.39 1.44 1.42 1.40 1.43 1.41 1.39 1.44 1.41 1.46 1.44 1.42 1.40 1.38 1.38 1.41 1.38 1.42 1.40 1.39 1.38 1.39 1.41
charges q (C6) q(M) -0.45 -0.33 -0.09 -0.51 -0.24 -0.55 -0.42 -0.29 -0.57 -0.44 -0.31 -0.57 -0.35 -0.61 -0.50 -0.39 -0.42 -0.30 -0.07 -0.44 -0.17 -0.47 -0.36 -0.20 -0.31 -0.34 -0.38
0.16 0.29 0.52 0.05 0.23 0.27 0.24 0.35 0.20 0.30 0.46 -0.02 0.21 0.17 0.21 0.34 -0.61 -0.34 0.08 -0.48 -0.07 -0.26 -0.18 0.06 0.54 0.39 0.50
main atoms. For the transition metals we used the Dunning/ Huzinaga valence double-ζ basis (D95)11 supplemented with the Stuttgart/Dresden effective potentials MDF10 (Mn, Cr, Fe, Co), MWB28 (Mo, Ru, Rh), and MWB60 (Re, W, Ir, Os),12 denoted as SDD. This level of theory was chosen after considering the B3LYP/ Lanl2dz, B3LYP/SDD, and B3LYP/SDD,6-31G(d,p) levels of theory. These computations indicated an overall agreement among the latter two as well as to experimental structures. The B3LYP/ SDD,6-31G(d,p) level of theory was then used for the computations presented in this work. Similar benchmark calculations had also been carried out for population analysis (Merz-Kollman,13 CHelpG,14 natural population analysis15 (NPA), Mulliken16), from which the net charges presented in Table 1 were derived. Here, NPA was chosen for analysis of bond orders as well as atomic charges (see Supporting Information for details). Frequency calculations were performed in order to confirm the minima. The NAO density was used to analyze bond orders (Wiberg bond order index).17
Results and Discussion In Table 1 the calculated distances between the metal center and C6 (d1), the distances between C1 and C6 (d2), and the (11) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical Chemistry; Schaefer, H. F., III, Ed.; Plenum: New York, 1976; Vol. 3, pp1-28. (12) (a) Fuentealba, P.; Preuss, H.; Stoll, H.; Szentpaly, L. v. Chem. Phys. Lett. 1982, 89, 418–422. (b) Szentpaly, L. v.; Fuentealba, P.; Preuss, H.; Stoll, H. Chem. Phys. Lett. 1982, 93, 555–559. (c) Fuentealba, P.; Stoll, H.; Szentpaly, L. v.; Schwerdtfeger, P.; Preuss, H. J. Phys. B 1983, 16, L323–L328. (d) Stoll, H.; Fuentealba, P.; Schwerdtfeger, P.; Flad, J.; Szentpaly, L. v.; Preuss, H. J. Chem. Phys. 1984, 81, 2732–2736. (13) (a) Besler, B. H.; Merz, K. M., Jr.; Kollman, P. A. J. Comput. Chem. 1990, 11, 431–439. (b) Singh, U. C.; Kollman, P. A. J. Comput. Chem. 1984, 5, 129–145. (14) Breneman, C. M.; Wiberg, K. B. J. Comput. Chem. 1990, 11, 361– 373. (15) (a) Carpenter, J. E.; Weinhold, F. J. Mol. Struct. (THEOCHEM) 1988, 46, 41–62. (b) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211–7218. (16) Mulliken, R. S. J. Chem. Phys. 1955, 23, 1833–1840. (17) Wiberg, K. B. Tetrahedron 1968, 24, 1083–1096.
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Figure 4. Correlation diagram between the frontier orbitals of a planar (left) and a bent (right) R-metallocenylmethylium ion.
bending angle R are given as defined in Figure 2. Furthermore, net charges q at the metal center and at C6 as well as the Wiberg bond order index17 between the metal and C6 are compiled. A comparison of the Wiberg bond order index (bond order) between the metal atom and C6 within the triads 4a to 4c, 6a to 6c, 7a to 7c, 9a to 9c, 10a to 10c, and 12a to 12c as well as the dyads 5a/5c, 8a/8c, and 11a/11c shows a decrease on going from left to right in the periodic table, i.e., from a to c. The bond order increases within a period when the ligand is kept the same, e.g., in 4a-5a-6a, 4b-5b-6b, and 4c-5c-6c, as well as 13-14-15. These variations are independent of the coligands (benzene, cyclopentadienyl, CO, or cyclobutadiene) attached to the metal atom. In most cases the trend found for the bond order is also found for the bending angle R (cf. Figure 2). Exceptions are 10a-11a-12a, where R is 32.45°, 30.19°, and 31.74°, respectively, and 13-14-15, where R is 30.26°, 27.92°, and 33.32°. For d2, the exo-double bond of the fulvene moiety, a slight decrease is found when going from left to right in the periodic table and also a slight increase within one period. The distances between the metal center and carbon atoms of the fulvene ring (C1 to C5) vary much less than the distance M-C6 (see Supporting Information), and no clear trend can be established here. However, we note a relationship between the distances C1-C6 and C2-C3 (for details, see Supporting Information). There is a good correlation (r2 ) 0.96) between the computed values for R and d1. We find satisfactory correlations between the charge at C6 (q(C6)) and R (r2 ) 0.70), the bond order and R (r2 ) 0.76), and q (C6) and d1 (r2 ) 0.68). The predicted bending of the C6 atom of the fulvene unit toward the metal and the accompanying increase of the C1-C6 distance, together with the increase of negative charge at C6 with increasing R, can be rationalized by considering the frontier orbitals of a planar metallocenylmethylium ion or their isoelectronic neutral fulvene complexes. In Figure 4 we have correlated the frontier orbitals of a planar (left) with a bent structure (right). By bending C6 toward the metal (i.e., increasing value of R) the LUMO is destabilized and the HOMO is stabilized. The resulting splitting in energy of both levels can be understood in terms of an increased bonding interaction of the p-orbital located at the C6 atom with the metal d-orbital of the HOMO and an increased antibonding interaction between the same atomic orbitals of the
Figure 5. List of R-metallocenylmethylium ions and neutral fulvene complexes whose molecular structures have been determined by X-ray analysis.
LUMO. As a result, electron density is transferred into an orbital antibonding between C1 and C6, resulting in an increased bond length between C1 and C6 with an increased value for the bending angle R. Figure 5 displays R-metallocenylmethylium ions and neutral fulvene complexes whose molecular parameters have been determined by X-ray investigations in the solid state. Two of these are the unsubstituted species 8c18 and 10a,19 which have been examined here theoretically. The others (16-30) are substituted at the C6 atom of fulvene with either alkyl or aryl groups and can be correlated to one of our model compounds shown in Figure 3 based on the metal and ligand types. (18) Barlow, S.; Cowley, A.; Green, J. C.; Brunker, T. J.; Hascall, T. Organometallics 2001, 20, 5351–5359. (19) Koch, O.; Edelmann, F.; Behrens, U. Chem. Ber. 1982, 115, 1313– 1324.
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Organometallics, Vol. 28, No. 4, 2009 1017
Table 2. Comparison between the Experimental Parameters r, d1, and d2 (see Figure2) Derived for 8c, 10a, and 16-30 with Those of the Calculated Values for the Corresponding Model Systems 5-10 and 13 in Brackets compd
model
R [deg]
8c18 10a19 165e 175e 185e 195e 2020 2121 2222 2323 2424 2525 2626 2727 2828 295f 305g
(8c) (10a) (5a) (5a) (6a) (6a) (7c) (7c) (7c) (7c) (8c) (9c) (8c) (10a) (10a) (10b) (13)
39.9 34.4 35.0 34.4 33.8 35.3 6.8 24.0 21.1 22.7 38.2 40.8 33.9 28.4 23.9 7.7 9.5
d1 [Å] (36.5) (32.5) (35.3) (35.3) (36.9) (36.9) (35.7) (35.7) (35.7) (35.7) (36.5) (38.7) (36.5) (32.5) (32.5) (28.0) (30.3)
2.27 2.35 2.31 2.38 2.39 2.33 2.96 2.69 2.72 2.66 2.27 2.24 2.41 2.55 2.63 3.05 2.99
d2 [Å] (2.34) (2.38) (2.33) (2.33) (2.31) (2.31) (2.31) (2.31) (2.31) (2.31) (2.34) (2.31) (2.34) (2.38) (2.38) (2.49) (2.39)
1.40 1.36 1.42 1.43 1.45 1.44 1.44 1.39 1.42 1.37 1.40 1.43 1.40 1.45 1.40 1.41 1.41
(1.41) (1.40) (1.43) (1.43) (1.44) (1.44) (1.39) (1.39) (1.39) (1.39) (1.41) (1.42) (1.41) (1.40) (1.40) (1.38) (1.38)
In Table 2 the molecular parameters R, d1, and d2 (cf. Figure 2) derived experimentally for these species are compared to those calculated for the corresponding model compound. An excellent correlation between the experimental and computed values are found for 8c and 10a and those species with small substituents at C6 (17-19, 24, and 25). Large differences between the experimental and computed values are particularly observed for 20, 29, and 30, in which cases bulky groups at the C6 atom prevent a close approach of C6 to the metal center.
Conclusions Theoretical calculations of the structural parameters for a series of R- metallocenylmethylium ions and related neutral fulvene complexes predict an increase of the metal-fulvene interaction on going from the lighter to the heavier metals. A comparison of the results obtained for these model compounds with experimental results obtained for a group of related compounds reveals good agreement when steric effects at the fulvene C6 atom are small. Besides R-metallocenylmethylium ions of CpRu and CpOs as well as the benzene(Mo) and benzene(W) complexes with fulvene, there are no other R-metallocenylmethylium ion species known with heavier elements. Also congeners of 2 and 3 with heavier metals and ligands other than Cp have not yet been investigated and should be promising candidates regarding their electronic properties.
Acknowledgment. Dedicated to Prof. Dr. Zvonimir B. Maksic on the occasion of his 70th birthday. We are grateful to the Deutsche Forschungsgemeinschaft for financial support. We thank Mrs. P. Kra¨mer for typing the manuscript and for the drawings. C.B. is grateful to the Deutsches Krebsforschungszentrum for a Ph.D. Fellowship. Supporting Information Available: Electronic energies and zero-point vibrational energies for all calculated species, comparison of various schemes for population analysis, additional bond lengths, and tables of Cartesian coordinates. This material is available free of charge via the Internet at http://pubs.acs.org. OM800573U
(20) Sime, R. L.; Sime, R. J. J. Am. Chem. Soc. 1974, 96, 892–896. (21) Cais, M.; Dani, S.; Herbstein, F. H.; Kapon, M. J. Am. Chem. Soc. 1978, 100, 5554–5558. (22) Behrens, U. J. Organomet. Chem. 1979, 182, 89–98. (23) Kreindlin, A. Z.; Dolgushin, F. M.; Yanovsky, A. I.; Kerzina, Z. A.; Petrovskii, P. V.; Rybinskaya, M. I. J. Organomet. Chem. 2000, 616, 106– 111. (24) Kreindlin, A. Z.; Petrovskii, P. V.; Rybinskaya, M. I.; Yanovsky, A. I.; Struchkov, Y. T. J. Organomet. Chem. 1987, 319, 229–237.
(25) Rybinskaya, M. I.; Kreindlin, A. Z.; Struchkov, Y. T.; Yanovsky, A. I. J. Organomet. Chem. 1989, 359, 233–243. (26) Watanabe, M.; Motoyama, I.; Takayama, T. J. Organomet. Chem. 1996, 524, 9–18. (27) Andrianov, V. G.; Struchkov, Y. T.; Setkina, V. N.; Zdanovich, V. I.; Zhakaeva, A. Z.; Kursanov, D. N. Chem. Commun. 1975, 117–118. (28) Lubke, B.; Edelmann, F.; Behrens, U. Chem. Ber. 1983, 116, 11– 26.
