493 the odd ligand, the 0-donor, N-ethyl-N’-oxo-1,4-diazabicyclo[2.2.2]octonium cation, has a field strength much lower than triphenylphosphine but still appreciably greater than the bromide ligands. Finally, the [CO(L,+XNCS)~] complex is expected to have a very
small value for Dr (that is, no appreciable trigonal distortion), because the ligand field strength of the odd ligand, the N-donor, N-ethyl-1,4-diazabicyclo[2.2.2]octonium cation, does not differ substantially from that of the three isothiocyanato ligands, NCS.
Structural Characterization of Fe ( co) 3 ( C6H5CZC6H4 CZC6H5 ZFe ( co a Bimolecular Condensation Product of o-Bis(phenylethiny1)benzene : Steric Equivalence of Fe(CO)(cyclobutadiene) and Fe(CO), Groups 9
Earl F. Epstein’ and Lawrence F. Dahl
Contribution from the Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706. Receioed July 7, 1969 Abstract: An X-ray crystallographic investigation of Fe(C0)3(C6HsC2C6H4C2CeH6)2Fe(CO) was undertaken in order to determine the nature of one of the products, Fez(CO)4C4rH2s,of a reaction between o-bis(phenylethiny1)benzene and iron pentacarbonyl. The product forms crzstals with four forrnpla units in a monocJinic cell of symmetry P21/nandoflatticeparameters a = 13.56 f 0.02 A, b = 24.00 f 0.04 A, c = 11.32 f 0.02 A, /3 = 93’ 55’ z?= 10’.
Refinement of the determined structure by anisotropic-isotropic least squares yielded unweighted R1and weighted Rz values of 9.9% for the 1880 independent nonzero diffraction maxima collected photographically. The organoiron carbonyl complex was found to contain a Fe(CO)(cyclobutadiene) fragment which is coordinated to a ferracyclopentadiene ring system. This unusual molecular system originates from the intermolecular condensation of two molecules of o-bis(phenylethiny1)benzene with a Fe(C0)3and a Fe(C0) fragment. One pair of acetylenes forms a cyclobutadiene ring, while the other pair of acetylenes produces the five-membered ferracyclopentadienering by the incorporation of the Fe(C0)3 fragment. Molecular stabilization is achieved through the interaction of the cyclobutadiene ring with the Fe(C0) fragment, which is also coordinated to the ferracyclopentadiene ring via both a (cis-butadiece)-iron interaction and an iron-iron electron pair bond; the resulting iron-iron single bond distance is 2.494(5) A. The striking stereochemical principle which emerges from a detailed comparison of the molecular ~ H ~those ) ~ F of ~ ( Fe(C0)3(HOC2CH3)2Fe(C0)3 CO) is that the cycloparameters of F ~ ( C ~ ) ~ ( C B H ~ C ~ C B H ~ C ~ Cwith butadiene ligand may sterically behave as only a bidentate ligand by the effective occupation of two metal coordination sites in place of two terminal carbonyl groups. he reactions of alkynes with Fe(CO)5, Fez(C0)9, or T F e 3(CO)12have yielded a large number of organoiron complexes with a remarkable variety of configurations. 2, One such complex was isolated by Whitlock and Sandvick4r5 in low yields from the reaction of o-bis(phenyiethiny1)benzene with either iron pentacarbonyl or triiron dodecacarbonyl under vigorous conditions. Elemental analysis and molecular weight determination by vapor pressure osmometry6 indicated that the compound has the molecular formula Fe2(C0)4C44H28. (1) This manuscript is based in part on a dissertation submitted by Earl F. Epstein to the Graduate School of the University of Wisconsin in partial fulfillment of the requirements for the Ph.D. degree, Jan 1969. (2) Cf, W. Hiibel, “Organic Synthesis via Metal Carbonyls,” I. Wender and P. Pino, Ed., Interscience Publishers, New York, N. Y., 1968, pp 273-342, and references therein. (3) Cf.F. L. Bowden and A. B. P. Lever, Organometal. Chem. Rev., 3, 227 (1968), and references therein. (4) H. W. Whitlock, Jr., and P. E. Sandvick, J . Amer. Chem. Sac., 88, 4525 (1966). ( 5 ) P. E. Sandvick, Ph.D. Thesis, University of Wisconsin, 1968. (6) The empirical formula CasHzaOaFer was based on the following; Anal. Calcd: C, 73.87; H, 3.62; Fe, 14.31. Found: C, 74.14; H, 3.45; Fe, 14.04; mol wt: 750, 772, 790, 810 (vapor pressure osmometer).s
The presence of only terminal carbonyl groups was indicated from its infrared absorption spectrum in solution.’ Attempts to characterize the structure further by chemical and physical methods were not successful. Since o-bis(phenylethiny1)benzene per se exhibits intramolecular interaction between the triple bonds on reaction with electrophilic, nucleophilic, or radical reag e n t ~ it, was ~ ~ ~of interest to determine whether this behavior is also exhibited on reaction with iron pentacarbony1 and triiron dodecacarbonyl. In order to resolve this question and ascertain the molecular geometry of the compound, a three-dimensional X-ray analysis of o-bis(phenylethiny1)benzene diirontetracarbonyl, Fe(C0)3(C6H6C2C6H4C2C6H&Fe(CO), was carried out. The determination of the molecular structure of this organodiiron complex instead revealed an intermolecular polymerization of two molecules of o-bis(phenylethiny1)benzene with two iron carbonyl fragments to give an unusual kind of transition metal complex. (7) The infrared spectrum in CCl4 shows strong absorption bands at 2070, 1996, and 1894 cm-1.6
494
Experimental Section Data Collection. Crystals of Fez(CO)4C44HZ8 were generously supplied to us by Professor Howard Whitlock and Dr. Paul Sandvick of the University of Wisconsin. Several crystals were mounted and used initially for the characterization of the symmetry of the crystal system. One of these crystals was selected for the collection of Weissenberg and precession intensity data with Zr-filtered Mo Ka radiation (A 0.7107 A). From Weissenberg data with a c axis rotation setting, eleven zones of nonintegrated, equiinclination data (hkn, n = 0-10) were obtained by the multiple film technique with packets of eight films and successive exposure times of 72, 12, and 2 hr (the latter only until the intensities of the reflections on higher reciprocal layers became too weak to be judged). Timedexposure precession photographs were taken of the h01, Okl, lkl, and 2kl reciprocal zones. The same crystal was used throughout the data collection with no apparent decay. All intensities were estimated visually by comparison with a calibrated set of spots obtained from the same crystal. The intensities were averaged,* and corrections for Lorentz polarization effects and nonzero spot extensions were applied. The averaging procedures excluded reflections which were so weak that they were observed on only one film of a given packet. Those individual judgings of intensity for a given reflection which did not statistically agree with the other judgings for this reflection were removed by the consideration of the “variance” for each estimated intensity. For a particular judging from the jth film, the “variance” is defined as I Zj*(hkZ)-Z(hkr)1 , where Z,*(hkl) is the scaled intensity of the reflection from the jth film and I(hkl) is the average of all the scaled intensities for this reflection. If the “variance” for the individual intensity estimation of a given reflection was greater than 2 0 z of the average intensity for that reflection, then the individual intensity value was discarded, and the average intensity was redetermined from the remaining judgings. No corrections for either absorption or anomalous dispersion were made. The crystal used for the data collection was close to a rhombohedron in shape, with approximately 0.025-cm sides and a 70” angle between edges. For Mo Ka radiation the linear absorption coefficient (p) is 8.65 cm-l, for which the maximum intensity variation on a given reciprocal layer due to absorption was estimated to be less than 11%. For Mo K& radiation the value of the dispersion corrections to the atomic scattering factor for iron are Af’ = 0.4 and Af” = 1.0.lo Since the crystal possesses centrosymmetric space group symmetry, these relatively small dispersion corrections are presumed not to affect significantly the atomic coordinates. lo A variance was assigned to the intensity of each reflection according to the following relation: if Z > .\/lo I,,,, then u(F) = 0.05F; if I 2 I,,,, then u(F) = 0.05F[101,,,/I]2, where I,i, represents the minimum observed intensity for each reciprocal Weissenberg or precession layer. The intensity data were placed on a single relative scale by a consideration of the 344 reflections common t o the 1753 Weissenberg and 41 1 precession data. The Sutton-Glick data correlation program” was used, and the resulting discrepancy factor for the merging of data was 3.5 Crystal Data. The dark red, approximately rhombohedral crystals of Fe2(C0)4C44H28 crystallize in the monoclinic system with dimensionsa = 13.56=t00.02,b=24.00=t0.04,~=11.32+0.02 A, p = 93” 55’ f 10’. These cell parameters were obtained from NaC1-calibrated precession photographs of the OkO and h01 reciprocal zones taken at room temperature. Errors in the lattice parameters were estimated from the precision of the measurements and from experience with the precession camera used. All measurements were made with Zr-filtered Mo KZ radiation (A 0.7107 A). The cell volume is 3648 A3; F(000), the total number of electrons in the unit cell, is 1600. Weissenberg and precession photographs exhibited systematic absences for { hot] with h I odd, and for { OkO) with k odd. These extinctions uniquely indicate the centrosymmetric space group P2Jn [nonstandard setting of P2’/c (Czh’, No. 14)]12which was confirmed
.\/G
z.
+
(8) J. F. Blount, Ph.D. Thesis, University of Wisconsin, 1965. (9) D. C. Phillips, Acta Cryst., 7, 746 (1954). (10) D . H. Templeton in “International Tables for X-Ray Crystallography,” Vol. 111, The Kynoch Press, Birmingham, England, 1962, p 215; Acta Cryst., 8, 842 (1955). (11) P. W. Sutton and M. D . Glick, “A Crystallographic Data Correlation Program for the C D C 1604,” University of Wisconsin, 1964. (12) “International Tables for X-Ray Crystallography,” Vol. I, The Kynoch Press, Birmingham, England, 1952, p 99.
Journal of the American Chemical Society
/ 92:3 /
by the structural determination. The experimental density, obtained by the flotation technique from mixtures of l-bromonaphthalene and diethyl malate, gave a value of 1.40 =t0.02 g/cm3; for four molecules in the unit cell, Poalcd = 1.42 g/cm3. No molecular symmetry is imposed by the crystallographic symmetry. All independent nonhydrogen atoms were found from the structural analysis to occupy the following fourfold set of positions: k ( x , y , z ;
+
+
x , ‘ 1 2 - Y , ‘/z 2). Solution of the Structure. The structural problem consisted of the location of the coordinates of 2 iron, 4 oxygen, 48 carbon, and
‘iz
28 hydrogen atoms which correspond t o one molecule. A calculated three-dimensional Patterson function’ based on corrected intensities yielded the expected eight metal-metal double weighted peaks of approximately equal magnitude plus the two metal-metal peaks of single weight. An interpretation of these vector positions provided initial coordinates for the two independent iron atoms. A Fourier synthesis phased on these iron atoms was computed, and an interpretation of this map gave initial positions for 3 oxygen and 15 carbon atoms. Another Fourier synthesis phased on the positional parameters of these 20 atoms was calculated, and the remaining nonhydrogen atoms were located. Full matrix isotropic least-squares refinement14 was begun with individual atomic thermal parameters for nonphenyl atoms. The scattering factors obtained by Hanson, et a/.,15 from Hartree-Fock-Slater wave functions were used for all atoms. The six phenyl groups were treated as rigid bodies in the refinement with an isotropic thermal parameter for each phenyl ring, After five cycles, all positional and thermal parameter shifts were less than 2/3 their respective standard deviations. The discrepancy values were Rl = 2 I ( 1 F, 1 - 1 F, 1 )I/Z ! F, 1 = 0.103 and RP = [Zw(,lF,/ 7 IF,1)2/ZwlFoIz]1/2 = 0.104. At this point an individual isotropic thermal parameter was assigned to each phenyl carbon atom and allowed to vary in subsequent leastsquares cycles. All shifts in positional parameters in these latter cycles were less than one standard deviation. The final value of both R1and R2 is 0.099 for the 1880 independent nonzero reflections. During the process of least-squares refinement, reflections were removed from the list of observations because the observed and calculated values of these data disagreed considerably, and reexamination of the films indicated that the reflections which corresponded to these data were affected by white-radiation streaks from other reflections. The value of the standard deviation of an observation of unit magnitude (i,e.,the error of fit function [ Z w 1 1 F, I - ! F,I 1 2/ ( N o - N,)]‘/2 wh2re (No - N,) is the difference between the number of observed refle-tions and the number of variables in the leastsquares process), which corresponds to the weighting scheme described here, was 1.68. Examination of the final variance-covariance matrix revealed 19 covariances greater than 0.400. Two of these related the overall scale factor to the thermal parameters of the two heavy atoms. No attempt was made to reduce this correlation by means of anisotropic thermal parameters for the heavy atoms, because a three-dimensional difference Fourier synthesis based on the final parameters gave residualopeaks in the vicinity of the iron atoms of less than 1.5 electrons/A3; no other remaining peaks were greater than +0.6 electron/A3. The remaining 17 covariances related one of the angles, which defined the orientation of a rigid body, to one of the origin parameters of the same rigid body. In order to verify the overall correctness of the structure, unobserved but experimentally accessible data (i.e., those reflections either too weak to be judged or actually observed) for which sin 0 2 0.40 were assigned an intensity equal to the minimum observed intensity for the given reciprocal level. After correction of these intensities for Lorentz polarization effects and spot extension, a comparison of the derived structure factors Fo(min) with the corresponding calculated ones showed that no F, exceeded 1.5F0(min). The positional parameters along with the isotropic temperature factors from the output of the last least-squares cycle appear in Table I. 16 Intramolecular distances and angles with estimated (13) All Patterson and Fourier syntheses were carried out with the Blount program: J. F. Blount, Ph.D. Thesis, University of Wisconsin, 1965. (14) W. R. Busing, K . 0.Martin, and H. A. Levy, “ORFLS, A Fortran Crystallographic Least Squares Program,” ORNL-TM-305, Oak Ridge National Laboratory, 1962. (15) H. P. Hanson, F. Herman, J . D . Lea, and S . Skillman, Acta Crysf., 17, 1040 (1964). (16) Calculated and observed structure factors utilized in the leastsquares refinement are deposited as Document No. NAPS-00773, with the ASIS National Auxiliary Publication Service, c/o CCM Information Corp., 909 3rd Ave., New York, N. Y . 10022. A copy may be secured
February 11, I970
495
E
standard deviations (which include the effect of the estimated errors in lattice parameters) as calculated with the Busing-Martin-Levy function and error programl7 are given in Table 11. Equations of least-squares planes determined by a weighted least-squares methodl8 along with distances of atoms from these planes and angles between the normals of these planes are given in Table 111. The orientations of the various phenyl groups are given in Table IV.
t
0
c -G I ,
Discussion Figure 2. The arrangement of the four molecules of Fe(C0)3(C~HSCZCBH~CZC~H~)ZF~(CO) in the monoclinic unit cell (of symDescription of the Structure. The molecular structure metry P21/n) viewed down the [loo] direction. shown in of Fe(C0)3(C6H5C2C6H4C2c6~~)2Fe(co) Figure 1 consists of an Fe(CO)(cyclobutadiene) fragment coordinated t o a ferracyclopentadiene ring system. Fe(C0)3(HOC2CH3)2Fe(C0)3,19 Fe(C0)3(C6H4CHThis configuration is achieved by the intermolecular CC6Hb)Fe(C0)3,20and Fe3(C0)10(C2H2)5.21The one condensation of two molecules of o-bis(phenylethiny1)remaining carbonyl group in Fe(C0)3(C6H5C2CBH4benzene with an Fe(CO), and an Fe(C0) fragment C2C6H5)2Fe(CO) is oriented in an analogous manner as (from iron pentacarbonyl) such that one pair of acetone of the three carbonyl groups of the nonring iron ylenes forms a cyclobutadiene ring while the other pair tricarbonyl fragment in these three stereochemically reof acetylenes produces the heterocyclic ferracyclopentalated compounds. The planar cyclobutadiene ring is diene ring system by the incorportation of the Fe(CO), symmetrically inclined with respect to the lone carbonyl group. Stabilization of this polymerization product group and the metal-metal direction, such that pseudo occurs through the interaction of the cyclobutadiene mirror plane symmetry is preserved for the geometry of ring with the Fe(C0) fragment, which also is coorthe Fe(C0)3(C2CgHlC2)2Fe(CO) fragment (Le., without dinated to the five-membered heterocyclic iron ring the four terminal phenyl groups). The angle between system aia both a (cis-butadiene)-iron linkage and an the normals of the cyclobutadiene and ferracyclopentairon-iron electron pair bond. diene planes is 47 ’. Both iron atoms in this diamagnetic compound conThe three carbonyl groups and the two terminal form to the 18-electron “noble gas” rule by a formal diene carbon atoms comprise a square-pyramidal-like contribution to the nonring zerovalent iron atom of polyhedron about the ring iron atom; besides a linkage four electrons from the cyclobutadiene group, two elecwith the other iron atom, there is an indication that the trons from the one terminal carbonyl group, and four ring iron atom forms a weak positive interaction with electrons from the butadiene part of the ferracyclothe lone carbonyl carbon atom of the nonring iron pentadiene ring; and by a formal donation to the ring atom (aide infra). For the nonring iron atom there is iron atom of six electrons from its three terminal caran ambiguity concerning the kind of coordination, debonyl groups, two electrons from the two a-bonding pending upon whether the cis-butadiene portion is asdiene carbon atoms of the ferracyclopentadiene ring, sumed to occupy two or three coordination sites. Based and the remaining two electrons from the nonring iron on the presumption that it occupies only the two double atom by a coordinate covalent iron-iron bond. bond sites and that the cyclobutadiene ring in this moleThe crystal arrangement of the four molecules per cule sterically takes up two coordination sites (due to its monoclinic unit cell is illustrated in Figure 2. The formal replacement of the two terminal carbonyl closest intermolecular distances given in Table 11 indigroups), the nonring iron atom may be formally concate that the separations between molecules correspond t o normal van der Waals contacts. sidered to possess a trigonal prismatic-like environment with the one terminal carbonyl and the other iron The angular placement of the Fe(CO)(cyclobutaatom occupying the other two coordination sites. If diene) fragment in Fe(C0)3(C6HjC2C6H1C2C6H5)2Fethe cis-butadiene part is alternatively assumed to oc(CO) is not unlike that of the nonring iron tricarbonyl fragments relative to the ferracyclopentadiene rings in cupy three sites (cia the other limiting bonding representation, consisting of two a-alkyl bonds from the iron by citing the document number and by remitting $1.00 for microfiche or to the terminal diene carbon atoms and a p bond to the $3.00 for photocopies. Advance payment is required. Make checks or money orders payable to: ASIS-NAPS. (17) W. R . Busing, I
