364
RICHARD J. HOEYAND ARTHURE. MARTELL
comparison of the coordination tendencies of ligands V and VIII. This conclusion is also supported by other comparisons made in a preliminary phase of this investigation, when it was observed that many bidentate ligands which were known to form 6-membered chelate rings with other metals were not effective with Zr(IV).
[CONTRIBUTION FROM
THE
VOl. 82
All of the results of this investigation are compatible with a maximum coordination number of S for aqueous Zr(1V) complexes. Because of the small radius of the Zr(1V) ion, however, complexes and chelates involving a lower coordination number of the metal are also possibly formed. U'ORCESTER,MASS.
DEPARTMENT OF CHEMISTRY, CLARKUNIVERSITY]
Dipole Moments of Metal Chelate Compounds. 111. Analogs and Polar Substituted Analogs of Bis-acetylacetoneethylenediimine1,2 BY RICHARD J. HOVEY AND ARTHURE. MARTELL RECEIVED MARCH19, 1959 The electric dipole moments of some quadridentate Schiff base chelating agents have been determined and interpreted in terms of the polar groups present and of rotation of the hydrogen-bonded chelate rings about the alkylene bridge. Dipole moment values indicate t h a t polar substituents such as p-bromophenyl, m-ntiro and trifluoroniethyl, occupy terminal positions in these molecules. In the benzoylacetonepolymethylenediirnirie series the dipole moments were found to increase with increasing number of methylene groups.
Earlier papers in this series3 have reported the results of dipole moment measurements on a series of quadridentate Schiff -base chelating agents and on the corresponding square planar chelates formed with transition metal ions. The present investigation describes similar studies of a number of closely related ligands. Its purpose was t o observe the changes in dipole moment resulting from : (1) structural changes in the diimine portion of the Schiff base molecules and (2) the introduction of polar groups into the ligands. The compounds measured are given in Table I and may be represented by formula I in which 13 is the alkyl (or aryl) radical of the diamine and R represents various polar and non-polar groups.
Experimental Procedure.-The syntheses and purification of the Schiff base ligands used in this investigation have been given pre~ i o u s l y . ~ The * ~ method of measuring the dielectric constants and a description of the cell and heterodyne oscillator were reported in the first paperS of this series. I n all determinations benzene solutions of the ligands were employed. Because of their low solubilities many of the ligands containing polar groups required heating t o obtain complete solution. All solutions employed had concentrations of 1y, ur less. Specific volumes were determined by means of liieschauer pycnometer. The cells used for the measurements were imniersed in a n oil-bath at 25"; for the determination of an individual dipole moment the temperature remained within rt 0.01'. (1) Abstracted from a dissertation submitted by Richard J. Hovey t o t h e Faculty of Clark University in partial fulfillment of the rcquirenients for the degree of Doctor of Philosophy, 1958. (2) This work was supported b y the Ofice of Ordnance Research under Contract No. DA-19-020-OKD-824:i. (3) P. J. McCarthy and A. E. Martell, THISJ O U R N A L , 78, 264 2106 (I9x;). ( 4 ) P. J. McCarthy. R. J. IIobey, K. Ueno and 4 . E. llartel!. ibid., 77, 5820 (1955). (5) K . J. Hovey, J . J. O'Conuell and A. E. Martell. ibid., 81, 3189 (1959).
TABLE I L I G A N SDT R C C T U R E S €3
CH( CH3)CHa
R
Name of ligand
p-CeH4Br
Bis-p-bromobenzoylacetonepropylenediimine CFa Bis-trifluoroacetylacetonepropylenediimine m-C6H4KOz Bis-m-nitrobenzoylacetonetrimethylenediimine CHI Bis-acetylacetorietetramethylenediimine C6& Bis-benzoylacetonetetrametli>-lenediirnine CeIl.5 Bis-benzol lacetonepetitamcth ylenediirnine CsHs Bis-benzoylacetone-1,3diimino-2-propani 11 Bis-acetylacetone-nzCHs phenylenediimirie
Spectro-grade benzene, ubtained from the Eastman Kodak Co., was refluxed o x r %)-mesh calcium hydride (Metal Hydrides, Inc., Beverly, RIass.) for approximately 48 hours, and then was distilled through a Widmer column, the first and last 15(,4 being rcjected. In comparison with the previous method of purifying benzene this new procedure is much simpler and far less time consurning. The dielectric constant of the solvent purified in this manner agreed with the earlier values witliin the desired limits. Calculations .-The total molar polarization of tlie solute a t infinite dilution (P?,) W;LS calculated by the method o f Hnlverstadt and Kuinler.6 P 2 = was obtained by means of tlie equation
where CY and t, are tlie slope ;tiid intercept of the plot of e12 (the dielectric constant of a solution) against wz (the weight fraction), 4 and zll arc the slope and intercept of the plot of uI2 (tlic s p c c i h vi~lunie( i f a solution) against Z U Y , and M Z is the niolecular weiglit o f tlie solute. The leastsquares method wits iicetl i i i evaluat iiig the various slril)es and intercepts. The dipole nioinc~itp i3 equal to 0.01281 (P"l')'/z,where 1' is the absolute tenq~erature. The orientation polarization POwas obtained by subtracting PE,the electronic polariza(6) I. Halverstadt and W. Kumler, ibid., 64, 2988 (1942).
ANALOGS OF BIS-ACETYLACETONEETHYLENEDIIMINE
Jan. 20, 10GO
365
TABLE I1 DIPOLEMOMENTS AND RELATED PARAMETERS Compound
ei
ais-p-bromobenzoylacetonepropylenediimine Bis-trifluoroacet ylacetonepropylenediimine Bis-m-nitrobenzovlacetonetrimethvlenediimine Bis-acetylacetonetetramethylenediimine Bis-benzoylacetonetetramethylenediimine Bis-benzoylacetonepentamethylenediimine Bis-benzoylacetone-1,3-diimino-2-propanol Bis-acetylacetone-m-phenylenediimine
2 .2714 2.2687 2.2714 2.2736 2.2732 2,2726 2.2733 2.2735
tion, and P A ,the atom polarization, from Pzm. The methods of estimating PE and P A are the same as those described previously.a
VI
U
3,646 10.112 11.891 6,870 4.589 5.362 3.879 6.438
1.14690 1.14655 1.14478 1.14349 1,14380 1.14373 1.14360 1.14435
-@
0.4791 ,4058 ,3468 ,2029 .2852 .2691 .2793 .2535
PE (cc.)
123.7 67.9 120.9 73.9 112.9 117.6 109.8 79.5
P z m (cc.)
JI(D.)
461.1 737.3 1120.9 396.4 421.0 495.3 373.3 402.0
3,99 5.70 6.96 3.93 3.81 4.23 3.52 3.93
According to the suggestion of Eyring,lO there is
a van der Waals potential between the end groups,
which gives rise to attraction, and tends to increase the molecular moment. Superimposed on this effect are the electrostatic forces between the dipoles, which affect the positions of the polar end groups relative to one another in such a way as to reduce the resultant moment. In trimethylene bromide it is possible for the bromine atoms to approach each other closely enough so that van der Waals forces operate to compensate in part for the dipole repulsions, thus favoring to a greater extent configurations in which the dipoles point in the same directioms The effect of the relative stabilization of such rotational isomers of high dipole moment is to give trimethylene bromide a Discussion higher moment than one would expect if only For the bis-benzoylacetonepolymethylenediimine dipole forces were operative. Apparently the ligands having two t o five carbon atoms between same factors obtain in the Schiff bases derived from the nitrogen atoms, the observed increase of dipole trimethylenediamine. moment is 3.21, 3.71, 3.81 and 4.23 D,respectively. As expected, the dipole moment of bis-acetylSimilar results have been observed in other poly- acetonetetramethylenediimine (3.93 D),was found methylene series, such as the polymethylene di- to be larger than that of bis-acetylacetoneethylenebromides’~~ and d i c y a n i d e ~ . ~ diimine (3.16 D ) . It has been noted“ that the Rotation around the carbon-carbon and carbon- substitution of a benzoylacetone for an acetylnitrogen bonds makes it possible for the dipoles acetone residue in both copper(I1) and nickel(I1) associated with the terminal groups t o assume dif- Schiff base chelates has only a small effect on the ferent positions relative to one another. How- observed dipole moments. It seems reasonable, ever, all positions are not equally probable because therefore, to assume that the dipole moments of of steric factors and the mutual repulsion of the benzoylacetonyl and acetylacetonyl groups in dipoles. the ligands have the same relative values as those The large energy associated with the proximity reported for acetophenone and acetone (2.88 and of the end groups in the ethylenediimine Schiff 2.72 D, respectively12). If this assumption is base tends to keep the dipoles near a trans-configura- correct, then the relative dipole moment values of tion thus causing the moment of bis-benzoylace- bis-acetylacetonetetramethylenediimine (3.93 0) toneethylenediimine t o be considerably less than and bis - benzoylacetylacetonetetramethylenedithose of the compounds having longer polymethyl- imine (3.81 D) are quite reasonable, since the ene bridges. As the bridge length increases, greater polarity of the aromatic ketone would there is a relative decrease in the potential energy result in the subtraction of the component of its for cis positions of the two end groups, so that their dipole moment increment from the group moments dipoles tend gradually to assume an average ori- of the hydrogen bonded chelate rings. The effect entation in which all possible configurations contrib- would be further decreased by a possible slight ute. While this explanation may account for steric factor which would change the statistical the increase in dipole moment with increasing distribution of rotatory isomers slightly in favor bridge length, by itself it does not satisfactorily of the trans forms. The apparent reversal of account for the closeness in the moments of the these effects for bisbenzoylacetoneethylenediimine trimethylene and tetramethylene derivatives. A (3.21 0)and bisacetylacetoneethylenediimine is similar situation occurs in the polymethylene di- within experimental error and is not considered bromides, the dipole moments of which increase in significant. As indicated above, the trans forms the order 1.50, 1.07, 2.00 and 2.25 D , for two, contribute proportionately more in the ethylenethree, four and five carbons between the bromine (10) H. Eyring, THISJ O U R N A L , 64, 3101 (1932). atoms, respectively.
Results For each dipole moment determination dielectric ) specific volumes ( ~ ~ 2 )were constants ( ~ ~ 2 and measured for five or six solutions of varying concentration. Plots of these values against weight fraction (w2) of the solute yielded straight lines in all cases. In Table I1 are listed the HalverstadtKumler parameters and dipole moment values of the eight ligands studied. As indicated in the earlier papers the dipole moment values are believed to be accurate t o about 0.1 D.
*
J O U R N A L , 54, 2261 (1932). (7) C . P. Smyth and W S.Wall, THIS ( 8 ) C P. S m y t h and W. S. Wall, J. Chem. P h y s . , 1, 200 (1933). (9) P. Trunel. A n n . chim. ( P o ~ ~ [s l)l,]18, 93 (1939).
(11) P. J. McCarthy, Ph.D. Dissertation, Clark University, Worcester, Mass., 1955. (12) “The Structure of Molecules,” Y.K.Syrkin and M. E: Dyatkina, Butterworths Scientific Pubftcations, London, 1950, p. 248.
T. A. MANUEL AND F. G. A. STONE
3 66
Vo!. 82
diamine derivatives, and the benzene rings therefore have very little influence, both sterically and electronically, on the molecular moment. The differences between the behavior of the ethylene and trimethylene compounds, with respect t o the replacement of methyl by phenyl, is outside experimental error, and is in the direction that would be observed if the increased van der Waals forces between the phenyl groups favored rotational forms having the cis configuration. The structure of bis-acetylacetone-m-phenylenediimine differs considerably from those of the other ligands discussed here. As can be seen H 111, from structures IIa,b,c rotation is restricted to the two carbon-nitrogen single bonds. The bulky and relatively rigid %-phenylene bridge should likewise limit the number of configurations of the end groups favoring trans forms and a relatively low dipole moment. However, the relatively high moment observed seems to indicate a constiI1 I3 tutional factor which favors a higher moment. IIC This factor may well be the tendency of the aromatic ring to conjugate with the hydrogen bonded are several Debye units higher than the corchelate rings to stabilize three forms, cis-cis, responding unsubstituted ligands. This effect is cis-trans and trans-trans, as is indicated by for- probably the result of the fact that the polar group moments lie in an average direction such mulas IIa, I I b and IIc. The contributions of two of these, IIa and IIc, that they add t o the moments due t o the hydrowhich have high moments, could easily account gen-bonded chelate rings. As expected, this factor outweighs the tendency for the average orientafor the high observed moment. The dipole moments of bis-trifluoroacetylacetone- tion of the end dipoles in the more polar ligands to IxopyIenediiinine (5.70 D),bis-p-bromobenzoyl- be somewhat closer to the trans form because of acetonepropylenediimine (3.99 0 ) and bis-m- the mutual repulsive forces between them. nitrobenzoylacetonetrimethylenediimine (6.96 D ) WORCESTER, MASS.
[COSTRIHLJTIOK
FRO31 TIIE
MALLINCKRODT CHEMICAL LABORATORY A T HARVARD UXIVERSITY]
Cyclooctatetraene Iron Tricarbonyl and Related BY
T. -1. l f A N U E L 3 AND F. G .
STONE
RECEIVEDJUNE29, 1959 Froin the reaction between iron pentacarbonyl and cyclobctatetraene the three solid conipounds CaH8.Fe(C0)3(I)! CsHs[ F e ( C O ) 3 ](11) ~ and CaHa.Fez(CC)?(111) have been isolated and characterized. Compound I is appreciably volatile and essentially air stable. Its nuclear magnetic resonance spectrum shows a single proton resonance, and it cannot be hydrogenated under coiiditions under which other metal-cyclooctatetraene complexes (e.g., CsHs.PtI2) readily absorb hydrogen. These and other properties suggest t h a t all four double bonds of the C8HBring in I are involved in the bonding to iron. Compound I may also be prepared by heating cycloheptatriene-iron dicarbonyl with cyclooctatetraene. Compound I1 has no bridging carbonyl groups, and the Fe(CO), groups must be on either side of the CsHs ring. Compound 111, however, is a derivative of Fep(CO)s, possessing bridging carbonyl groups. Certain aspects of the infrared and ultraviolet spectra of I, I1 and I11 are discussed. The reaction between iron pentacarbonyl and a mixture of cyclooctatrienes has been investigated. X yellow-orange liquid complex CsHlo.Fe(CO)a(IV)was isolated. Its infrared and ultraviolet spectra and its probable constitution are discussed. The reaction between I and the compounds ( C O H ~ ) ~ (M M = P, As and Sb) has been studied. The compounds [(CeH~)sP]2Fe(C0)3,(c~H5)34s(CsH~)Fe(CO)z and ( C O H ~ ) ~ S ~ ( C ~ H ~ ) have F ~ ( Cbeen O ) *isolated. Triphenylphosphine and IV, and triphenylphosphine and Ci”.Fe(C0)3 afforded [ ( C B ~ H S ) ~ P ] ~ F ~ (The C Olatter ) ~ . material was also obtained, together with [(CaH&P]2Fe( CO)a, when cycloheptatriene-iron dicarbonyl was heated with triphenylphosphine.
The chemistry of the transition elements has been greatly expanded during the last decade by the preparation of derivatives of the metal carbonyls, in which carbon monoxide groups are replaced to some extent by other ligands. For the synthesis of these substituted metal carbonyls two ( I ) Presented before t h e 130th Meeting of t h e American Chemical Society in Atlantic City, N.J , September 1939. (2) For a preliminary communication see: T. A. hlanuel and F. G. A. Stone, Proc. C h c m . Soc., 90 (1959). ( 8 ) National Science Foundation predoctoral fellow 1958-1959.
main preparative routes have been used : treatment of a metal carbonyl with the appropriate ligand and treatment of a compound of the metal with carbon monoxide. At this time perhaps the most remarkable of all the ligands occurring bonded t o a metal simultaneously with CO are the unsaturated hydrocarbons which do so by means of their rr-electrons. One extreme of such behavior is found in the sandwich bonds4 of the cyclopenta(4) H. H. Jaffe, J . Chrrn. P h y s , 21, 157 (1953); W. Moffitt, THIS 76, 3386 (1951). J D Dtlnitz and L. E. Orgel, J . Chenc.
JOURNAL,
