4259
J . Am. Chem. SOC.1984, 106, 4259-4261
Communications to the Editor Decaphenylstannocene, [q5-(C&15)5C5]2Snn:The First Symmetrical Main-Group Sandwich Compound Mary Jane Heeg, C. Janiak, and J. J. Zuckerman*
Department of Chemistry, University of Oklahoma Norman, Oklahoma 73019 Received November 23. I983 The lone-pair electrons in subvalent fourth main-group compounds reveal their VSEPR-expected stereochemical activity in distortions from high-symmetry geometries to give voids in the central-atom coordination sphere' and bent, two-coordinated species. Certain rare exceptions, e.g., CsSnBrp,*form perfect polyhedra in highly colored, conducting solids. We have synthesized3 penta- and decaphenylstannocene (Scheme I). The latter, [q5-(C6&)5]2Sn"$ is the first example of a molecular, main-group subvalent species in which the lone pair is stereochemically inert. Here the tin atom sits on an inversion center between symmetry-related, equidistant 2.401 (6) A to the ring center; d[Sn-Cri,,(av) = 2.692 (8) 1) cyclopentadienes that are planar, staggered, and exactly parallel (Figure 1, Table I). The attached phenyl groups are canted to each cyclopentadienyl ring oppositely in a double-opposed paddlewheel fashion to give molecules of Slosymmetry (Figure 2). There are no short intermolecular contacts (Figure 3). Phase changes to give the high-dielectric, intensely colored solids in which tin(I1) atoms are at sites of cubic symmetry are accompanied by isotropic lattice expansion.' The lone pairs are said to be delocalized in a conduction band. Where, then, are the 5s2 electrons in our bright-yellow decaphenylstannocene? Comparison solid-state data are available for the (q5-R5C&E derivatives for E = Sn, R = H5 and CH3,6 as well as for E = Ge, R = H,' and E = Pb, R = Ha and CH3.5 In addition, gas-phase data are available for E = Sn,Pb, R = H,9 and for the l,l'-(CH3)2derivativesI0of E = Ge, Sn. All are severely bent, e.g., the tin-nter
Figure 1. Decaphenylstannocene, [?s-(C6Hs)sC5]2Sn", viewed parallel to the plane of the cyclopentadiene rings.
a
(1) Our review of these structures is in preparation (Ng,S.-W.; Zuckerman, J. J.). (2) Donaldson, J. D.; Silver, J.; Hadjiminolis, S.; Ross, S. D. J. Chem. Soc., Dalton Trans. 1915, 1500. (3) Pentaphenylcyclopentadiene and its bromide have been known for nearly 60 years (Ziegler, K.; Schnell, B. Justus Liebigs Ann. Chem. 1925,445, 266). See also: Braye, E. H.; Hiibel, W.; Caplier, I. J . Am. Chem. Soc. 1961, 83, 4406. (4) Decaphenylstannocene,[qS-(C6H~)sC,]2Sn",C70H5&n,forms brightyellow parallelopipeds, mp >300 OC dec, in the monoclinic space. group P Z , / n with a = 10.458 (2) A, b = 13.462 (3) A, c = 18.130 (3) A, ,9 = 97.81 (1)O, V = 2529 (1) A3, Z = 2, = 1.326 g ~ m - ~ The . structure was determined by difference Fourier techniques from 4779 reflections measured at 138 f 2 K on an Enraf-Nonius CAD/4 automatic diffractometer with monochromatized Mo K a radiation to a final conventional R value of 0.058 and R, of 0.053 for the 2560 reflections included in the least-squares sums. Computations were performed by using local modifications of SHELX-76 programs (Sheldrick, G. M. University Chemical Laboratory: Cambridge, U.K., 1976). Scattering factors are from: "International Tables for X-ray Crystallography"; Kynoch Press: Birmingham, U.K., 1974; Vol. IV, p 72. ( 5 ) Atwood, J. L.; Hunter, W. E.; Cowley, A. H.; Jones, R. A,; Stewart, C. A. J. Chem. Soc., Chem. Commun. 1981, 925. (6) Jutzi, R.;Kohl, F.; Hofmann, P.; Krtiger, C.; Tsay, Y . H. Chem. Ber. 1980,113,757. (7) Grenz, M.; Hahn, E.: duMont, W.-W.; Pickardt, J. Angew. Chem. 1984, 96, 69. (8) Panattoni, C.; Bombieri, G.; Croatto, U. Acta Crystallogr. 1966, 21, 823. (9) Almenningen, A.; Haaland, A.; Motzfeldt, T. J. Organomet. Chem. 1961, 7 , 97. (IO) Almlof, J.; Fernholt, L.; Faergri, K.; Haaland, A,; Schilling, B. R.; Seip, R.;Taugbal, K. Acta Chem. Scand., Sect. A 1983, A37, 131.
0002-786318411506-4259$01 S O / O
Figure 2. Decaphenylstannocene, [~5-(C,Hs)sCs]2Sn",viewed perpendicular to the plane of the cyclopentadienyl ring. Table I. Interatomic Distances [?5-(C6H5)~C~lzSn11 Sn-Cl 2.686 (6) Sn-C2 2.687 (7) Sn-C3 2.689 (7) Sn-C4 2.705 (7) Sn-C5 2.688 (7) Sn-Cpc 2.401 (6) Cl-c2 1.426 (9) C2-C3 1.450 (10)
(A)" for Decaphenylstannocene, c3-c4 c4-c5 C1-C5 C1-Cll C2-C21 C3-C31 C4-C41 C5-C51
1.424 (9) 1.414 (10) 1.425 (9) 1.506 (8) 1.489 (8) 1.485 (8) 1.497 (8) 1.494 (7)
"All phenyl carbon atoms were refined as a part of rigid bodies with d(C-C) = 1.395 (7) A. bEstimated standard deviations are in parentheses. 'Cp refers to the centroid of the cyclopentadienyl ring. Table 11. Interatomic Angles (Deg) for Decaphenylstannocene, InS-(CsHAC5l,Sn" " Cl-C2-C3 108.2 ( 5 ) C4-C5-C1 107.5 (5) Cl-C2-C21 127.7 (6) C4-C5-C51 124.4 ( 5 ) C2-C3-C4 106.1 (6) C41-C4-C5 128.4 ( 5 ) C2-C3-C31 125.8 (5) C5-Cl-C2 108.2 (6) C21-C2-C3 124.0 (6) C5-C1-C11 128.2 ( 5 ) C3-C4-C5 109.9 (6) C51-C5-C1 128.0 (5) C3-C4-C41 121.7 (6) Cll-Cl-C2 123.6 (5) C31-C3-C4 128.1 (6) "Estimated standard deviations for the last digit are in parentheses.
of the ring angles for the R = H, CH,, and C6H5 solids is 143.7' and 148.0', 143.6' and 144.606 (two independent molecules in each), and 180' (Table 11). Thus our structure represents a sharp discontinuity from previous results.1',12 However, our R = C6H5 0 1984 American Chemical Society
Communications to the Editor
4260 J. Am. Chem. SOC.,Vol. 106, No. 1.5, 1984
R = H [av 2.422 (13) A; range 2.410-2.436 %.I6 homologues. The fortuitous formation of qJ-pentaphenylcyclopentadiene derivatives of the transition metals is evidence for the stabilizing power of this ligand. The qS-(C6H5)5CSMsystem first unexpectedly turned up from diphenylacetylene with M o ( C O ) ~ , ~ ' diglyme1s-Mo(C0)3,or W(CO)s and subsequently with Pd(02CCH3)2,19but pentaphenylaluminole, (C6H5)5C4A1,also irrationally yields an M = N i derivative from lithium metal and NiBr2.20 Other, directed syntheses yield the alkali-metal salts21*22 and derivatives in which M = Fe,22,23Ni ,24 Cr,22 Mo,22 W 22 C0,22 RqZ2Ti,22Zr,22 L U , and ~ ~ PdaZ6 Aside from imparting high kinetic stability through its large volume, the q5-(C6H,)5C5system is also less basic. Electron withdrawal by the phenyl groups makes low-oxidation transition-metal states more accessible as measured by increased potentials of the redox an effect opposite to that wrought by methyl substitution, which makes reduction more difficult.28 Since the tin 5s2 electrons are not occupying a nonbonding orbital and all of the bonding orbitals are filled, then these electrons must occupy an orbital with antibonding character. The phenyl groups, which are not antiparallel to the cyclopentadiene rings, can help delocalize these electrons. For stannocene itself, initial, semiempirical M O calculations assigning the lone-pair electrons to the HOMO6 have been replaced by SCF x,-SW result^^^*^^ placing the lone pair in a strongly directional, fifth-occupied orbital, ca. 2 eV more stable than the HOMO. However, M N D O calculations on the hypohomologues predict D5h thetical E = Si and [~5-(CsHs)2P]+ ground-state geometries with the lone pairs distributed among the third and fifth M O ' S . ~An ~ ab initio SCF-MO calculation on the E = Ge analogue gives a DSdground state (the DShform is less than 0.2 kJ/mol higher) with the lone pair in the HOMO.'O In solid (q5-CSH5)2Snthere are eclipsed and staggered molecule^.^ In [qS-(CH3)sC5]2Sn both independent molecules are staggered.6 For E = Ge a rather flat well makes large amplitude ringmetal-ring bending with slippage of E away from the ring centroid accessible, but the bent form is more stable at shorter E-ring distances. lo Bending our decaphenylstannocene, as studied using space-filling models and nonbonded contact radii sums, may require further separating the cyclopentadienyls and slipping the tin vectors from the ring centroids. Rotation about the linear tin vectors, on the other hand, seems easier. Assessing the severity of the intramolecular n,n'-phenyl steric interference is difficult since the rings approach perpendicularly in an H atom-r-system contact. We note that the alternative isomeric 9'- or spirostannacyclohexatriene or stannacyclohexatrienyl cation-cyclopentadienyl anion combination structures are not adopted. Other internuclear distances and angles in decaphenylstannocene are unexceptional. The range of d(C-C) values, 1.414 (10)-1.450 (10) A and their average, 1.428 (1 3) A, resemble those 1
Figure 3. Packing Diagram of decaphenylstannocene, [$(C~HS)&IZS~'*. Scheme I synthetic route
Ph
J J
I.
PhLi or PhMgBr 2. H 2 0
Ph
* Ph QPh
83%
0
1. BuLi 2. SnC12 4'
58%
Ph
Ph
1 1. BuLi I
Ph
1. BuLi 2. CpSnCl
ph*ph Ph
Sn
Ph
1. BuLl
(15)Dory, T. S.;Zuckerman, J. J., unpublished results. (16)Bos, K. D.; Bulten, E. J.; Noltes, J. G.; Spek, A. L. J . Organomet. Chem. 1975,99,71. i (17) Hubel, W.; Merenyi, R. J . Organomet. Chem. 1964,2, 213. (18) Diglyme = diethylene glycol dimethyl ether, CH30C2H40C2H40CH3. (19) Jack, T. R.;May, C. J.; Powell, J. J. Am. Chem. SOC.1977,99,4707. Krause-Going, R.; Kriiger, C.; Sekutowski, J. C. Angew. (20)Hoberg, H.; Chem., Int. Ed. Engl. 1977, 16, 183. tin-ring centroid distance [2.401 (6) A] is greater than that in (21)Zhang, R.;Tsutsui, M.; Bergbreiter, D. E. J. Organomet. Chem. the R = CH3 [av 2.396 (5) A; range 2.388-2.400 A], but not the 1982,229, 109. (22)Slocum, D. W.; Johnson, S.; Matusz, M.; Duraj, S.; Cmarik, J. L.; Simpson, K. M.; Owen, D. A. Abstr. Pap.-Am. Chem. SOC.1983,186th, (1 1) The germanium (Molloy, K. C.; Zuckerman, J. J. Adu. Inorg. Chem. PMSE 75. Radiochem. 1983,27, 113)and tin (Zubieta, J. A.; Zuckerman, J. J. Prog. (23)McVey, S.,Pauson, P. L. J . Chem. SOC.1965,4312. Inorg. Chem. 1978,24,251.Smith, P. J. J . Organomet. Chem. Libr. 1981, (24)Schott, A,; Schott, H.; Wilke, G.; Brandt, J.; Hoberg, H.; Hoffmann, 12,97)structures have been reviewed, as well as those of bivalent germanium, E. G . Justus Liebigs Ann. Chem. 1973,508. tin, and lead (Harrison, P. G. Coord. Chem. Rev. 1976,20, 1). (25) Zhang, R.; Tsutsui, M. Youji Huaxue 1982,435;Chem. Abstr. 1983, (12)Other related structures also show severe bending at the tin(I1) atom, 98, 198374q. e.g., in (q5-[(i-C3H,)2N]ZPCSH4)zSn,13 (qS-C5HSCo[4,5-(C2H5)2-l,~; (26)Powell, J.; Dowling, N. I. Organometallics 1983,2, 1742. (CH,)f2BC-1,3]-qSjSn,'4 ([BF4]~(p-qS-C5H5)zSn[p-q5-C5H5Sn]tTHF},, (27)Broadley, K.; Lane, G. A,; Connelly, N. G.; Geiger, W. E. J . Am. and (q -C5HS)SnC1.' Chem. SOC.1983,105, 2486. (13) Cowley, A.H.; Lasch, J. G.; Norman, R. C.; Stewart, C. A,; Wright, (28) Koelle, U.;Khouzami, F. Angew. Chem., Int. Ed. Engl. 1980,19,640. T. C. Organometallics 1983,2, 1691. (29)Baxter, S.G.; Cowley, A. H.; Lasch, J. G.; Lattman, M.; Sharum, (14) Wadepohl, E.;Pritzkow, H.; Siebert, W.Organometallics, 1983,2, W. P.; Stewart, C. A. J . Am. Chem. SOC.1982,104, 4064. 1899. (30)Lattman, M.; Cowley, A . H. Inorg. Chem. 1984,23,241.
J . Am. Chem. Sot. 1984, 106, 4261-4263
426 1
in [115-(C6H~)~C~)Ni-(?3-c3(c6Hs)3)-Ni(C4(c~H5)4-114)Table I. Et,AICl-Promoted Diels-Alder Reactions of Dienophiles 1-3 and Cyclopentadiene (Scheme I)6 (1.41-1.48 and 1.44 A).2o The average d(Sn-C) values are 2.67 and 2.70 A for R = HS and 2.675 and 2.678 A for R = CH? (two diastereoindependent molecules in each) vs. 2.692 (8) A for decaphenylselection' purified isolated stannocene. enendo ratio yield, We are now attacking the opposite problem, that of producing try dienophile endo:exo (4:5) (4:s) %* mp, "C a severely bent angle so that the lone-pair electrons will be both >99:1 81 59.2-61 >100:1 93:7 A la. R , = H chemically (as a base) as well as stereochemically active. Our 97:3 78 120-121 B 24 R; = H >ioo:i 95:5 recent metallocenophane ~ y n t h e s e s ~are ~ *steps ~ * in this direction. C 3a, R , = H 1OO:l 5:95 99:1 55:l 97:3 99:l 83 60:l 2:98
