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EDITOR
1701. 84
cal Society (Grant 48s-C) and to the National Science Foundation (G-14289) for financial support.
the systems approached epimeric equilibrium. This was measured by oxidizing each sample to KEDZIECHEMICAL LABORATORY JAMES L. CORBIU sulfone I, whose rotation and deuterium content MICHIGASSTATEUSIVERSITV HAROLD HART were measured by methods previously reported.?b EASTLANSING, MICHIGAS CHARLES K. LVAGSER LVith phosphine oxide, the polarimetric rates were RECEIVED MARCH15, 1962 measured in a conventional manner, and the deuterium content measured through use of the infraCONFIGURATIONAL STABILITY OF CARBANIONS red bands a t 10.98 and 14.29 p present in the deuterated and absent in the undeuterated compounds. STABILIZED BY &ORBITALS' Comparison of the steric courses of the exchange Sir: In an earlier investigation, the stereochemical reactions of sulfoxides I1 and phosphine oxide III course of base-catalyzed hydrogen-deuterium ex- with that of 2-phenylbutane indicates that the change of sulfone I was studied through deter- d-orbital containing functional groups exercise mination of k e l k , , in which k e was the rate constant even less stereochemical control over the course of for exchange and k , for racemization. Values of the exchange reaction than does a phenyl group this ratio varied between a high of about 2000 with Indeed, the data suggest t h a t what stereospecificity tert-butyl alcohol as solvent to a low of 10 with is observed with the sulfoxide and phosphine oxide systems is associated with asymmetric solvation dimethyl sulfoxide.2 rather than with carbanion asymmetry. This CH1 CHJ conclusion is in striking contrast to that drawn for *I *I sulfone system I, which provided high though PZ-C~H~~-C-H( U) PZ-C~H~~-C-H(I>) differing retention for exchange in all solvents. I SOC6Hj Two different hypotheses could account for the I1 difference in behavior of carbanions derived from CH3 sulfone I and oxides I1 and 111. (1) Non-stabilized *' carbanions probably have sp" hybridization similar n-CtiHia-C-H( D) to amines. Carbanions stabilized by d-orbitals 111 PO( CtiHj)? might have a tendency to rehybridize to sp'-p IVe have now prepared by conventional reactions since p-d overlap might be more favorable than both diastereomers of sulfoxide 113and phosphine sp3-d overlap. However, many investigators have oxide I I I ? in optically pure states, and have concluded that d-orbital stabilization of carbanions determined approximate values of the ratio of does not have rigid geometric requirements, although kelk, for the three substances in a number of dif- different geometries provide different stabi1ities.j ferent solvents (see Table I). Since the configura- Superimposed on overlap effects are electrostatic
---CompoundNat.
TABLEI EXCHAXGE STERICCOURSEOF HYDROGES-DEUTERIUX ~BaseConcn. .\-
IIa-11 Ila-d IIb-11 111-h 111-d IIa-d 111-d 111-h 111-d 111-d 995; deuterated
0.17 0.17 0.17 0.20 0.20 0.17 0.20 0.20 0.21 0.21 (ref. l b ) .
Solvent
( CH3)3CODU
*
(CH3)jCOH (CHa)3COD" (CH3)aCOD" (CHa)aCOH ( CH3)2S06 (CH3)2SOh DOCH2CH?ODa HOCH2CHzOH CH30H 1.2 -11 in methanol.
tion a t sulfur of I I a and I I b was unaltered during the exchange at carbon, k , for these compounds actually is associated with the rate a t which 11) W e are pleased t o acknowledge financial support of t h e research reported here by t h e National Science Foundation. ( 2 ) (a) r). J. Cram, W. D. Nielsen and B. Rickborn, J . A n t . Chem. S u r . . 82, 6415 (1960); (b) 13. J. Cram, D. A . Scott a n d W. D. Sielsen, i b i d . , 83, 3696 (1961). (3) Carbon, hydrogen, sulfur and phosphorus analyses deviated from theory by a maximum of 0.2870. Deuterated I I a , I I b and I11 contained 9 7 4 8 % deuterium in t h e position indicated (combustion analysis and falling drop method by J . S e m e t h ) . Isomer I I a had m . p 20.7-21.54, [a]% -192 i 3' ( c 2 , 9.5% ethanol), and isomer 1 I b mas an oil which was separated from I I a b y chromatography o n silica gel, [ e ] % b + I 6 6 i :j0 i t 2 , 95;; ethanol). These isomers possessed the Dame configuration a t carbon, hut dibered a t sulfur. Compound I11 possessed m.p. 94-9S3, [e]%t. - 14.7' i c 0 . carbon tetrachloride). All three compounds uere prepared frc,m optically illire h i c t y l to%yl:it?
Nature
(CH,),COK (CHa)aCOK (CHahCOK (CH3hCOK (CH3)sCOK CHaOK CH30K DOCHzCHzOK HOCHzCHzOK CHaOIi
Concn \
0 78 I1 79
0 78 0 34 0 34 0 23 0 21 0 28 0 29 0 30
I ,
oc.
60 00 00 100 100 60 75
176 175 175
k,lka
2 3 3 3 3 1 1 1 1 1
effects. In the most favorable conformations, repulsion between the negative charge on carbon and the partial charges on oxygen attached to sulfur or phosphorus would be less for sp8 than for sp2-p hybridization a t carbon. Thus the overlap and electrostatic effects might oppose one another and a continuous spectrum of configurations a t carbon ranging from trigonal t o tetrahedral can be envisioned. Possibly no configurational stability is associated with trigonal carbon, whereas (1) I n tevl-butyl alcohol, k , ' k , > 10 lor t h e exchange of 2-phenylbutane-2-d [ref. l a and 11. J. Cram, C. A . Kingsbury and B. Rickborn, J . A m r h e i n . S o c . , 83, 3688 (196111. ( S ) ( a ) W. E. I h e r i n p and I,. K . l.evy, ibid., 77, 511 (19,X)); (1)) H E. Zimmerman and B. S. Thyagarajan, ibid., 82, 2505 (1960); ( c ) K. Breslon and Is. hfohacii, i b i d , 8 3 , 4100 (1961): (d) S . One, 8'.Tapaki :ind .4. Ohno, i h i d , 83,30.:T (1981).
hIay 5 , 1962
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COMMUXICATIONS TO THE EDITOR
tetrahedral carbon might maintain degrees of configurational stability due to electrostatic inhibition of inversion. Electrostatic effects in the anion of sulfone I should be much greater than in the anions of either sulfoxide I1 or phosphine oxide 111, and therefore the sulfone anion might exhibit configurational stability and the oxide anions lack of stability, as has been observed. (2) m'hen free from constrictions due to ring systems, carbanions stabilized b y d-orbitals might provide better p-d overlap when trigonally hybridized. Several conditions would have to be fulfilled before stereospecificity for exchange reactions involving such species was observed. (a) The rotomer t h a t gave the best p-d overlap would have to be asymmetric. (b) The rotomer would have t o be formed and consumed through a transition
state that involved only one particular conformation.6 (c) The carbanion would have to undergo proton capture faster than the carbanion equilibrated (by rotation) with its enantiomer. These conditions might come closer to fulfillment with the sulfone than with the oxide anions. The d-orbitals of the sulfone group are more stabilizing than those of the oxide groups, and might impose more severe geometric requirements with respect to conformation than do the d-orbitals of the two oxides. Attempts are being made to test these notions in other systems t h a t involve d-orbital-stabilizing groups.
r? Y
v
i
0
0
c
o
Fig. 1.-[OOl] Molecular projection of [C&( CsHj)3CO]Fe(CO)3: bond distances for the tropone ring are 1.45 and 1.49 A. for C I - C ~and C&7, respectively; 1.38 f i . for CL-CE, 1.34 A. for the normal double bond C2-C3, 1.44 A. ( a v . ) for the other three bonds, and 1.26 8. for C1-0 (all with e , s , f , =kO.O2 A , ) . Fe-C distances are 2.17, 2.00, 2.09, and 2.13 A. t o carbon atoms C4 , , . C;, respectively; iron distances t o the midpoints of C,-Cj, cj-c6 and C S - C ~are 1.96, 1.93 and 1.98 (6) Application of t h e principle of micruscopic reversibility indicates A,, respectively. Other non-bonding iron-tropone distances t h a t if a carbanion is formed by loss of a proton from a particular side are F e . . . C1 = 2.97 A,, F e Cz =03.46 A,, and Fe , . , of t h e molecule, the same side will be involved when the proton is re= 3.12 A. Fe-C (carbonyl) = 1.73 A . (av.), C-0 = 1.18 A . captured. DEPARTMEXT OF CHEMISTRY D. J . CRAM (av.) (all with e.s.d. 1 0 . 0 2 A), C-C bond lengths in phenyl UNIVERSITY OF CALIFORNIA RICHARD D. PARTOS rings range from 1.31 to 1.51 A. (e.s.d. 1 0 . 0 3 ) with average AT Los XSGELES,Los STANLEY H. PINE length 1.40 .A,). Bond angles are ( C ~ H ~ ) - C J - C =~ 118.2', ANGELES 21, CALIF. HERBJ A C E R (CCHj)-CI-Ca 112.2', CZ-Ca-Cj = 122.4", Cd-Cj-Ce RECEIVEDFEBRUARY 5, 1962 124.3', cj-cg-c7 = 116.2', (CgHa)-C6-Cj = 126.0", ( C ~ H ~ ) - C G -= C ~117.5', c&-ci 129.5', C ~ - C I - C ~= 125.O", Cl-C+23 = 121.8', (C~H~)-CS-CI= 117.3', T H E MOLECULAR CONFIGURATION O F = 119.9", Cy-Ca-C~ = 127.7' (all with e.s.d. (C&-c2-C3 2,4,6-TRIPHENYLTROPONE-IRON TRICARBONYL 3 1.6'). The dihedral angle between t h e two planes in the Sir: tropone ring is 139".
S3
T h e recent syntheses of several cycloheptatrienone (tropone) complexes b y Hiibel and coworkers' --4 have stimulated discussion about their molecular geometry and the type of bonding between the metal orbitals and the n-orbitals of the organic ring system. On the basis of simple molecular-orbital theory and the presumed similarity of these compounds to the cyclopentadienonemetal complexes, Brown5suggested a planar tropone ring with the iron bonding equally to all three double bonds of the ring. Hiibel and co-worker9 later found t h a t one of the double bonds could be hydrogenated and this together with the existence of isomers for each tropone complex led them (1) W. Hiibel, E. H . Braye, A. Clauss, E. Weiss, V. Kriierke, D. A. Brown, G. D . S. King, and C. Huogzand, J. Inorg. X u c l . C h e m . , 9, 204 (1959). (2) W. Hubel and E. H . Braye, i b i d . , 10, 250 (1959). (3) W. Hubel and E. Weiss, Chem. aizd I n d . , 703 (1959). ( 4 ) E. H . Braye, C . Hoogzand, W. Hubel, V. Kriierke, R . h l e r h y i , and E. Weiss, "Advances in t h e Chemistry of t h e Coordination Compounds," edited b y S. Kirschner, T h e Slacmillan Co., S e w York, N. Y., 1961, pp. 190-198. ( 5 ) D. A . Brown, J . Znorg. S u c l . C h e w . , IS, 212 (1960). (6) W. Hiibel, private communication, 1960.
to postulate interaction of the iron atom with only two of the three double bonds.4 T o resolve this conflict we have carried out an X-ray structural analysis of one isomer of a substituted tropone, 2,4,6-triphenylcycloheptatrienoneiron tricarbonyl, [ C & ( c & ~ ) & o ] F e (CO)8. The dark red crystals3 are orthorhombic with lattice parameters a = 19.53 pi., b = 7.62 A., and c = 15.03 A. Systematic absences show P 2 1 2 ~ 2as~ the probable space group. For four molecules per unit cell the calculated density is 1.31 g..'cc. in agreement with the density, 1.31 g./cc., measured by the flotation method. X-Ray intensity data obtained with MoKa radiation by the usual equi-inclination Weissenberg techniques were estimated visually. A. three dimensional structural analysis of the data including isotropic least squares refinement7 and error analysis8 has yielded the molecular configuration (7) W. R . Busing and H . A. Levy, "A Crystallographic Least Squares Refinement Program for t h e I B M 704," ORXLS, 19.59. ( 8 ) W . R. Busing and H . A . I x v y . "A Crystallographic Function and Error Program for the I B M 704," O R X F E , 1959.
