Feb. 5, 19G1
HALOGENATION O F blETAL CHELATES
531
stability and ease of dissociation of the oxime-metal ion bond are in keeping with expectations based on modern concepts of chemistry. Since both the metal ion and the acetyl group are electrophilic toward the oxime function, i t is not surprising to find the effects mutually deleterious. The apparent catalysis of the solvolysis of the oxime ester by metal ions provides an additional example of a type of observation which is rapidly 0 approaching the status of a generalization of ligand reactions. At this time, there exist no broadly established generalizations in this realm, despite the fact that certain seemingly obvious generalizal tions may soon find experimental justification. I n 0 the case a t hand, the acetyl group represents an (V 1 The reaction of [Pt(POX)2] with acetyl chloride uncoordinated bulky function adjacent to a coin chloroform solution produces a substance con- ordinated function. Further, this dangling group forming approximately to the formulation [Pt- is attached to the coordinated group by a link (POX-COCH3)2]C12. This compound is not so which is normally susceptible to solvolytic cleavage. easily purified as [Pd(POX-COCH3)Cls], and the In such circumstances, the lability toward solvolytic analyses are not ideal. The infrared spectrum of cleavage is expected to be enhanced by metal ion the product shows the band (at 1780 ern.-') char- coordination so long as the bond undergoing cleavacteristic of the oxime ester, and there seems to be age is not a part of a chelate ring. Eichhorn and Bailar13 first pointed out an example of this kind little question that acylation has taken place. On treatment with acetyl chloride the nickel(I1) among Schiff base complexes. Acknowledgments.-One of the authors (D. complex, [Ni(POX)z], undergoes decomposition. Insofar as the studies reported here reveal, the C. J.) wishes to thank the Research Corporation, effect of coordination of an oxime group to a metal while another (R. A. K.) wishes to thank the Naion on the ease of formation and solvolysis of oxime tional Institutes of Health, for financial assistance esters and, conversely, the effect of acylation on the during the course of this work.
by analysis and by its infrared spectrum, which exhibits a strong sharp carbonyl bandI2 near 1790 cm.-'. When this acylated palladium(I1) complex is treated with dilute, aqueous sodium hydroxide the ester is cleaved and the resulting compound appears to be [Pd(POX)Cl]. This compound probably is dimeric (Vj,
(12) 0. Exner and hf. Horak, Collection Czechoslov. Chem. Comms., 24, 2992 (1959).
[CONTRIBUTION FROM
THE
(13) G. L. Eichhorn and J. C. Bailar, Jr., THIS JOURNAL, 76, 2905 (1953).
DEPARTMENT OF CHEMISTRY, UXIVERSITY OF NORTHCAROLINA, CHAPELHILL, NORTHCAROLINA]
The Reaction of Metal Chelates. I. Halogenation of Metal Chelates of 1,3-Diketone~~,~ BY
JAMES
P. COLLMAN, ROBERTA.
HENRYMALTZ3bAND CLIFFORD c. HEINDEL
RECEIVED AUGUST1, 1960 Chlorine, bromine and iodine have been substituted directly on the chelate rings of metal chelates of 1,3-diketones. Bromine, iodine monochloride, and the N-halosuccinimides have been used as halogenating agents. Halogenated chelates containing chromium, cobalt, aluminum, iron and copper have been prepared by these direct substitution processes.
The chemical literature reveals many studies of metal acetylacetonates; however, these researches have focused on the physical properties, stereochemistry, bonding and synthesis of these chelates4 Very few reports record the chemical reactions of metal acetylacetonates. Of the scattered reports concerning the chemical reactions of metal chelates, only a few describe processes in which the chelate molecule was altered, but the chelate rings were not destroyed. Chlorination of copper phthalocyanine yielded a hexadeca(1) Presented a t the 137th Meeting of the American Chemical Society, Cleveland, Ohio, April, 1960. (2) This work was supported in part by the Petroleum Research Fund administered by the American Chemical Society, by the Research Corporation and by the Faculty Research Council of the University of North Carolina. (3) National Science Foundation Summer Undergraduate Fellows, (a1 1959; (b) 1960. (4) A. E. Martell and M. Calvin, "Chemistry of Metal Chelate Compounds," Prentice-Hall, Inc., New York, N. Y., 1952.
chlorinated copper phthal~cyanine.~The copper chelate of 2-hydroxy-1-naphthaldehydereacted with aqueous methylamine to form cis and trans isomers of the chelate of the N-methylimine.6 The first example of the direct substitution of a metal acetylacetonate is the reported bromination of chromium(II1) acetylacetonate (I) by the action of bromine in c h l ~ r o f o r m . ~The product of this reaction was reported to be tris-(3-bromo-2,4pentanedion0)-chromium(II1) (11), but this substance was not fully characterized. Another isolated example of this type of reaction was reported recently.* Treatment of copper acetylacetonate (XIII) with N204 yielded a complex which was (5) XI. Shigemitsu, J . Chem. SOL.J a p a n , l i d . Chem. Soc., 62, 112 (1959). (6) P . Pfeiffer and H. Glaser, J . punkl. Chem., 168, 265 (1939). (7) H. Reihlen, R. Illig and R . Wittig, Ber., 58B, 12 (1925). (8) C. Djoidjeric, J. Lewis and R. S. Nyholm, Chem. nnd Ind. (London), 122 (1959).
532
J. P. COLLMAN, R.A.
MOSS,
H. M.%LTZ .4ND
c. c. HEINDEL
Vol. 83
TABLE I HALOGENATION O F METALCHELATES OF 1,3-D I K I i T O N E S
Unsubstit. chelate
I I
Halogenated chelate
I1 I1 I11 I11
M
n
x-y"
Solvent
Yield. h v
Infrared band of halogenated chelate, cm - 1
Cr Cr Cr Cr Cr co co co co co Cr Cr cu A1
3 Rr? HOXc 61 1540 H0.h 3 NBS 60 1540 I I c1 HOAc 3 72 1030 I H0.h 3 NI s 62 1530 I IV scs HOilc 3 65 1550 V VI Brz 3 HOAc 1545 53 V VI NBS 3 CHClj 84 1545 V VI1 3 IC1 H0.k 97 1535 V VI1 NI s 3 CHC13 42 1535 V VI11 NCS 3 H0.k 49 1545 IX X 3 NBS CHCl3 46 1530 XI XI1 3 NBS 65 1520 CHC13 XI11 XIV 2 1-cs 78 1555 CHC13 xv XVI 3 SBS CHCl3 58 1560 XVII XVIII Fe 3 55 1545 SBS CHC13 X-Y is the halogenatinp agent; NCS, NBS and N I S represent S-chloro, N-bromo and N-iodosuccinirnide. This yield is based on the unsubstituted chelate. Only the strong bands from 1600 t o 1500 crn.-l are indicated.
designated as bis- (3-nitro-2,4-pentanediono)-copper Adams catalyst a t 50 p.s.i. of hydrogen, and the (11); however, the structure of this chelate was not chelate is not adsorbed on activated alumina. rigorously established. Such stability seems to be associated with complete I n this Laboratory, a detailed investigation of the saturation of the coordination sphere and coordinareactions of metal chelates, particularly acetylace- tion of the inner orbital type. tonates, has begun. These chelates will be conTreatment of a glacial acetic acid solution of sidered as sensitive organic heterocycles and the chromium(II1) acetylacetonate (I) with bromine in effect of coordination on the chemical properties of the presence of acetate ion afforded tris-(3-bromothe organic ligand will be investigated. It is hoped 2,4-pentanediono)-chromium(III)(11)in good yield. that such studies will lead to the fabrication of a Uptake of bromine was rapid until three moles of wide variety of new chelates. In particular, studies bromine were consumed per mole of chelate. Addiof the elaboration of stable chelates may make tion of more bromine did not result in further reacpossible the preparation of monomers containing tion. In the absence of acetate ion, evolution of coordinated metal atoms. HBr was evident and some decomposition of the Consideration of the proposed aromaticityg*l0of chelate occurred. Cobalt (111) acetylacetonate (V) certain metal acetylacetonates suggested that these behaved in a similar manner. These and other molecules might undergo electrophilic substitution. halogenation reactions are outlined in Table I . In order to extend the bromination reaction to Halogenation seemed the best starting point to investigate this hypothesis. The halogenation of chromiurn(II1) chelates of other 1,3-diketones, metal acetylacetonates and the properties of the tris - (1 - phenyl - 1,3 - butanediono) - chromium (111) (IX) and tris-(l,3-diphenyl-l,3-propanediono)halogenated chelates are described below. The instability of copper(I1) acetylacetonate chrornium(II1) (XI) were prepared. The chelates (XIII) precludes the use of this and similarly acid I X and X I were synthesized by a modification of labile chelates in the presence of such strongly elec- the standard preparation of chromium acetylacetrophilic media as bromine. The copper(I1) com- tonate. l 3 Gtilization of 9670 dimethylformamide, plexes of 3-ketoaldehydes have been reported to 47, water as a solvent affords a general method for break down in the presence of bromine in chloro- the preparation of chromium chelates of water inform." Aryl acid halides also break down copper soluble 1,3-diketones. Under conditions that had caused facile brominaacetylacetonate in chloroform. l 2 Chromium(II1) acetylacetonate (I) is much tion of chromium(II1) acetylacetonate (I),the chromore stable. Whereas dilute mineral acids slowly mium chelates I X and X I failed to react with broattack this chelate, glacial acetic acid has no effect mine. Attempted brominations employing the on this compound even a t 50". Chromium(II1) dioxane-bromine complex and pyridine perbromide acetylacetonate (I) is also stable to reduction over resulted in destruction of the chelates I X and X I . N-Bromosuccinimide unexpectedly provided the (9) M. Calvin and K . W. Wilson, THISJOURNAL, 67, 2003 (1945). best route to tris-(2-bromo-l,3-diphenyl-l,3-pro(10) R. H. Holm and F. A . Cotton, ibid., 80, 5658 (1958); this panediono) -chromium (111)(XII) and tris- (2-bromoreference gives strong arguments against such aromaticity. l-phenyl-l,3-butanediono)-chromium(III) (X). In (11) H. G. Garg, Y .Singh and M. M. Bokadia, J. I n d i a n Chem. Soc., SS, 3.53 (1966). (12)
W. J . Barry, J . Cbein. Soc., 070 (19CiO).
(13) W. C . Fernrlius and J . E . Einnch, InorR. Syn.,
V, 130
(1957).
Feb. 5 , 1961
HALOGENATION OF METALCHELATES
533
The ultraviolet spectra" of the halogenated the absence of a radical initiator, N-bromosuccinimide in chloroform solution rapidly brominated the chelates and the unsubstituted chelates are listed in Table 11. Comparison of the spectrum of each chelates I X and X I . The N-halosuccinimides were found to be eff ec- unsubstituted chelate with that of the correspondtive halogenating agents for all of the other acetyl- ing halogenated chelate clearly illustrates an extenacetonates examined. Even the acid labile copper sion of conjugation. Only introduction of halogen (11) acetylacetonate (XIII) is efficiently chlorinated at the central carbon of the chelate ring would proby N-chlorosuccinimide. These halogenations can duce this spectral shift to longer wave lengths. be carried out in glacial acetic acid or in chloroform. TABLE I1 The latter solvent is better with acid labile chelates such as IX, XI, X I I I , XV and XVII. ULTRAVIOLET DATAFOR CHELATES5 Iodine monochloride in glacial acetic acid bufCompound X max., mp c (I./mole-cm.) fered with acetate ion also proved to be an efficient [HCAcz13Cr 335 15,800 iodinating agent of chromium(II1) acetylacetonate [ CICAcZ].Xr 357 11,700 (I) and cobalt(II1) acetylacetonate (V). [BrCAc213Cr 358 13,070 The structures assigned to the halogenated che[ICACZ] Xr 362 11,900 lates are based on several arguments. First, the [HCAC~I~CO 25gb 38,800' chlorinated copper chelate XIV is identical to the [CICAc2]3Co 258 25,800 chelate14 prepared from 3-chloro-2,4-pentanedione. 343 6,900 Thus, one halogenated chelate has been synthesized 26 1 27,700 [B~CAC~]~CO by an independent method. The structures of the 343 7,760 other halogenated chelates are inferred by analogy. [ICACZI3 c O 275 43,800 Second, the chromiuni(II1) chelate I reacted with [HCAczlsAl 286 42,900 one mole of bromine per chelate ring, releasing [BrCAcz]3Al 310 36,800 hydrogen bromide. In every instance, the ele[ HCBzAcI3CrC 358 24,050 mental analyses of the halogenated products indi[BrCBzAc]&r 3 73 16,750 cate one atom of halogen per chelate ring. If the [HCBzzlaCr 385 33,300 methyl groups had been undergoing halogenation, [ BrCBz2]3Cr 392 20,300 more than one mole of halogen per chelate ring These spectra were measured a t about lo-' ;Vi' in chlorowould have been taken up. That these methyl form. *These values were taken from ref. 10. BZ groups do not take part in the reaction is especially represents benzoyl. evident when one considers the bromination of the A number of attempts to carry out reactions on chelates I X and X I . The infrared spectra of the halogenated chelates tris - (3 - bromo - 2,4 - pentanediono) - chromium provide further evidence supporting the assigned (111) (11) have failed, but the results are interesting structures. The spectra of the halogenated che- inasmuch as they reflect on the chemical nature of lates are very similar, and the same pattern of the bromine atoms on the chelate ring. The analochanges appears when these spectra are compared to gous iodo chelate behaved in a similar manner. Treatment of the brominated chromium chelate the infrared spectra of the unsubstituted chelates. All metal acetylacetonates possessing a hydrogen I1 with magnesium or lithium in tetrahydrofuran, atom on the central carbon atom of the chelate ring benzene or ether failed to initiate any reaction even after extended periods at the boiling points of these exhibit two infrared bands in the 1500 to 1600 cm.-' solvents. In each case, the starting material was region. Acetylacetonates having a group other than hydrogen a t the central carbon exhibit a singlet at recovered. displacements of the bromine from about 1550 cm.-l in their infrared ~ p e c t r a . ' ~ , ~ Nucleophilic ~ The halogenated chelates each exhibit a singlet the brominated chelate I1 by azide, acetate, nitrite and iodide ions failed in hot (100') dimethylaround 1550 cm.-l. formamide. In each instance the chelate I1 was The upper frequency band of the doublet at 1550 recovered unchanged. Sodium ethoxide in cold cm.-l in the spectra of acetylacetonates has been ethanol and zinc powder in boiling ethanol caused attributed to the chelated carbonyl group; whereas, decomposition of the brominated chelate 11. the lower band has been assigned to the partial The mechanism of chelate halogenation will be double bonds of the chelate ring.16 This lower the subject of a future publication. It should frequency band is thought to disappear upon sub- suffice here to state that the chelate molecule must stitution of the acetylacetonate ring because of a exhibit a high electron density a t the central carbon mass effect. I t seems reasonable that the doublet atom. Whether or not this occurs through partial may arise from a coupling of the chelated carbonyl ionization and ring opening is an interesting quesgroups. The carbonyl groups in the diketo form of tion fundamental to all reactions of chelates of acetylacetone give rise to two carbonyl stretching 1,3-diketones. An obvious extension of these halobands-a result that can only arise from coupling.I4 genation studies is the investigation of reactions such as nitration, mercuration and the Friedel(14) H . F. Holtzclaw, Jr., and J. P. Collman, THISJOURNAL, 79, Crafts processes. Preliminary investigations of 3318 (1937). these reactions are currently being carried out in (15) R. .'1 Dryden and A. Winston, J . Phys. Chein., 62, G3R (1958). this Laboratory. (16) For a review of t h e infrared spectra of metal acetylacetonates see F. A. Cotton in "Modern Cotkdination Chemistry," edited by J. Le*-is and R. G. Wilkins, Interscience Publishers, Inc., New York, N. Y . , 1960, p. 378.
(17 For a review of t h e ultraviolet spectra of metal acetylacetonates see ref. 10.
534
J . P. COLLXAN, K. A. Moss, H. XILTZ AND C. C.HEINUEL Experirnental18,19
Vol. 53
Anal. Calcd. for C ~ S H & T O ~ BC, ~ ~56.37; : H, 3.13; Br, 25.05. Found: C, 56.89; H , 3.51; Br, 24.75. Tris-( 3-iodo-Z,4-pentanediono)-chromium(III)(111) .(.I)A solution of bromine (12.1 g., 0.076 mole) in 20 ml. (.i) -1 solution of iodine monochloride (4.5 g., 0.028 mole) of acetic acid was added slowly, with stirring, t o a solution in 20 nil. of acetic acid mas added slowly with stirring to a of tris-(2,4-pentanedioiio)-chromiurn(III)( I ) ( 6 g . , 0.017 mole) and potassium acetate (5.1 g., 0.052 mole) in 150 solution of tris-(2,4-pentanediono)-chromium(III)( I ) (3 g., 0.0086 mole) and potassium acetate ( 2 . 5 g., 0.025 mole) ml. of acetic acid a t 30". After five minutes the precipitate was collected, washed with water, sodium bicarbonate solu- in 70 ml. of acetic acid a t 35'. ;\fter five minutes the precipitate was collected, washed with water, sodium bition, sodium bisulfite solution and again with water. carbonate solution, sodium bisulfite solution and again The brown substance was recrvstallized from benzeneheptane. The yield of brown crystals was 6 . 5 g. (64TL), with water. The brown solid was recrystallized froin benzene-heptane yielding 4.5 g. (72yc) of black crystals, 11i.p.228-229". Anal. Calcd. for C1SH10CrOGBr3: C, 30.74; H, 3.10; 1n.p. 224-225O. Anal. Calcd. for C ~ S H ~ ~ C T Oc&, : 24.77; H, 2.50; I , Br, 40.91. Found: C, 30.95; H, 3.35; Br, 10.72. ( B ) ,-Isolution of S-bromosucciniinide (0.4 g., 0.023 52.37. Found: C, 24.18; H, 2.72; I , 51.65. (B)-The iodo chromium chelate(II1) was prepared inole) in 10 nil. of acetic acid WAS added slowly, with stirring, from S-iodosuccinimide in glacial acetic acid in the usual to J. solution of tris-(2,4-pentanediono)-chromium(III j (I)
