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ELECTRON TRANSFER AND HEAVY ATOM PERTURBATION IN SYSTEMS OF HALOGENATED TYROSINES AND MENADIONE’
the quinone which is expected in the region of the fine s t r u ~ t u r and e ~ ~greatly ~ enhanced by the spinorbit coupling effect of the iodine atoms. ConfirSir : mation is given by the set of reasonably well resolved Saturated aqueous solutions of menadione and bands also presented by the bromo analog without dissociated orthoiodinated phenols produce in- any spectral shift (Fig. 1). Phenolate does not stantaneously a pinkish color which is reversibly induce any absorption in this region. In acetoneweakened by warming. Spectroscopic examination aqueous KHCOg half saturated (1:5 v./v.) at 2 5 O , shows a new, wide band with a maximum near 520 the association constant and the molar extinction mp, whose short wave length side is overlapped by coefficient a t 520 mp for the 3,5-dibromotyrosinethe vitamin absorption. Despite the lability of the menadione complex are 1.1 1. mole-l and 850; system one seems to find that the band has a trace for the iodo complex the values are 1.4 1. mole-’ of fine structure. This point is confirmed by adding and 800. the menadione in acetone solution (Fig. 1). A Very interestingly also, the absorption band due clear example for purely aqueous solutions is fur- to the interaction of halogenated quinones with nished by p-benzoquinone and 3,5-diiodo-4-hy- hexamethylbenzene shows some fine ~ t r u c t u r e . ~ droxybenzoic acid. Acknowledgment.-We wish to thank the Rockefeller Foundation and the “Conselho Nacional de Pesquisas” for grants, and the latter also for a fellowship awarded to M. B. (3) J. W. Sidman, J . A m . Chcm. SOC.,78, 2363,4567 (1956). (4) A. Kuboyama, Bull. Chem. SOC.Japan, 8 6 , 295 (1962). (5) R. Foster, D. L. Hammick and P. J. Placito, J. Chem. Soc., 3881 (1956). T h e fine structure in t h e peak of t h e complex of p benzoquinone near 420 mp m a y be connected with another transition of t h e quinone; see for instance, ref. 4.
DEPARTMENT OF CHEMISTRY FACULDADE DE FILOSOFIA, CI~NCIAS E LETRAS DE S I 0 PAULO GIUSEPPECILENTO UNIVERSIDADE SXo PAULO,BRASIL MARCOSBERENHOLC RECEIVED AUGUST13, 1962 N.M.R. CONTACT SHIFTS IN PARAMAGNETIC NICKEL(I1: SALICYLALDIMINES
Sir: Distinct advantages in mapping unpaired electron distributions in paramagnetic species by n.m.r. contact shifts rather than by e.p.r. hyperfine splittings have been demonstrated by studies of the nickel(I1) chelates of the aminotroponeimines.’,*v8 It has now been found that large high and low field shifts are also observed in the proton n.m.r. of the paramagnetic4 nickel(I1) chelates of N-m-tolylsalicylaldimines, I. These shifts are attributed to
Fig. 1.-Absorption spectrum of a solution prepared by adding 0.22 ml. of a 1.5 X 10-2 M acetone solution of menadione to 1.0 mi. of a solution of the halogenated tyrosine in half saturated aqueous KHC08. The latter solution was 9.7 X 10-2 M in the case of 3,5-diiodotyrosine (upper curve) and 6.6 X 10-2 M i n the case of 3,5-dibromotyrosine. Blank: similar solutions omitting the vitamin; optical path, 1 cm.; room temperature. Readings were taken from right to left as fast as possible.
Since charge transfer bands are quite diffuse-as demanded by theory2-the fine structure must belong t o another band which is presumably overlapped by the electron transfer absorption. This band may be ascribed to the T+S transition in (1) A related, unpublished work was presented a t t h e International Biophysics Congress, Stockholm, 1961, Abstracts of Contributed Papers, p. 851 (2) S. P . McGlynn, Chem. Reus., 68, 1113 (1958). Several important references concerning t h e subject of this communication are given in t h a t review article.
I
contact interaction between protons and spin densities centered on ring carbon atoms. This spin density arises as a result of delocalization of the fractional unpaired electron placed on nitrogen and oxygen by dn-pn bonding with nickel. For this non-alternant system contributions to the ground state wave function from valence bond structures such as B and C are expected to place positive spin density a t C3and Cg. Negative spin densities aris(1) W. D. Phillips and K. E. Benson, J . Chem. P h y s . , 33, 607 (1960). (2) R. E. Benson, D. R. Eaton, A. D. Josey and W. D. Phillips, J . A m . Chcm. SOC.,8 3 , 3714 (1961). (3) D. R. Eaton, A. D. Josey, W. D. Phillips and R. E. Benson, J . Chem. P h y s . , 37, 347 (1962). (4) R. H. Holm and T. 51. McKinney. J . A m . Chem. SOL.,83, 5506 (1960).
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Oct. 20, 1962
TABLEI N.M.R. PROTON RESONANCE FREQUENCIES‘ FOR I Substituent X
- 1890 9.i7)” 307d - 1925
HC
(-
+
4-CH3 5-CH3
6
5
4
$275 (+4.64) +286 -917d
- 1292 5.79) - 1275
CH-N
.. ..
(-
-1258
.... N-3490 (broad)
ortho
msta
-+200 (broad)
- 810
...
-+250 (broad)
(-2.58) 792 - 799
-
mcl4 CHa
para
+96*vd
$181 (+4.01)‘
+91d +91d
+178 +186
+
- 772 102 -701d +272 - 1306 .... 96d +96d +179 - 1319 .,. . ~$250 +271 ortho -338 - 805 meta -461 -152.5 ... . -+250 S-CsHs-h’=i‘;- 1925 +92a $175 Para -300 (broad) In C.P.S. a t 60 Mc./sec. The chelate spectra were determined in CSI solution and were internally referred to tetramethylsilane. For the ligands in CDCla, these resonance frequencies are applicable: - 135 (CHI), -420 (aromatic protons) and Spin densities b Integration of the N-(m-CHa) resonance suggests that it includes the 3-H resoiiance 504 (-CH=N). X 108 are given in parentheses for this compound. Qc+: 4-CHa = +6.8 gauss, 5-CH3 = +25.3 gauss, N-(m-CH$) = +13.8 gauss, N-(p-CH8) = +21.2 gauss. * Data for bis-[N-(3’,4‘-dimethylphenyl)-salicylaldi1nine]-nickel(II),f Data -nickel(11). for bis- [ N-( 3’,5’-dimethylphenyl)-salicylaldimine] H“
- 1884
I1
- 1892
J
+
-
ing from electron correlation effects are expected a t C4 and Cs. Consistent with this prediction, protons attached to Cs and Cb exhibit high field resonances, and protons attached to Cq and CSexhibit low field resonances.
A
R
C
Although the proton resonances of the salicylaldimines are considerably broader than those of the aminotroponeimineates and nuclear spin-spin structure cannot be resolved, i t has been possible to make spectral assignments of the individual protons on the salicylaldehyde residue through substitution studies. The frequencies are given in Table I. For I, X = H,5 the spin densitys a t Cr is about 0.1 that of the y position of an aminotroponeimineate.203 On substituting CH, at Cg, proton shifts for methyl are observed that are in an opposite direction from that of the CS proton. Furthermore, the ratio ~UCH,/UCH/ of 1.125 is close to that observed in e.p.r. studies of methylquinonelquinone ion radicals’ and corresponds to QCH, = $25.3 gauss. This result indicates that, a t least a t the Cb position, the spin density is moving primarily through the x-system. Moreover, on substituting the phenylazo group for hydrogen a t CS an alternation of spin density signs on the phenyl ring is observed, and the attenuation from Co t o the para position is 6.8. The relative spin densities and the attenuation are comparable to those observed for ( 5 ) Initially prepared by L. Hunter and J. A. Marriott, J . Chcm. SOC.,2000 (1037). (6) Calculated by t h e method described in ref. 2. (7) A. D. McLachlan, Mol. Ph>s., 1, 233 (1968).
the same substituent on an aminotroponeimineate, substantiating that the electron is moving through the ?r-system in both of these structures. For I, X = 4-CHs, the shifts for CH3 a t Cc and C m e t a of the N-phenyl substituent, which are sites of negative spin density, are opposite those of the protons a t these positions, in accord with the direct contact interaction mechanism (hyperconjugation). The ratios ~UCH, / UCHI are less than those found for the Cs position, a site of positive spin density, and correspond to QCH, values of -1-6.8 gauss (C4) and f13.8 gauss ( C m e t a of phenyl ring).* The results imply a stronger hyperconjugation effect a t the latter position. Magnetic susceptibility studies in carbon disulfide solution a t room temperature of several of the N-m-tolyl derivatives have given magnetic moments of -3.4 B.M. in accord with two unpaired electrons on nickel. In chloroform, the magnetic moment of I, X = 4-CH3, has been found to be temperature independent over -60 to $50’. A simple valence bond calculation was carried out for I , X = H, assuming one electron delocalized. Comparison of calculated with experimental spin density distributions suggests that approximately one-sixtieth of an unpaired electron has transferred from nickel to each salicylaldimine ligand. This value of spin transfer in the nickel(I1) salicylaldimines is to be compared with the transfer of onetenth of an electron to each ligand in the nickel(I1) aminotroponeimineates. 3 As found independently by molecular weight studies on I, X = H, have shown that this compound is associated in solution. Similar studies in the case of I, X = 3-CH3, indicate that essentially no association is occurring up to 0.042 molal concentration in benzene, presumably due to steric hindrance. Furthermore, the latter compound is diamagnetic (pes Q 0.1 B.M.) and, as expected, iio contact shifts are observed. The magnetic susceptibility of the nickel chelate of N-methylsalicylaldimine is reported to vary with (8) A similar observation has been made in nickcl(I1) aminotroponeat t h e para imineates. F o r t h e N-phenyl derivatives, a t~ position corresponds t o QCH* = +27.7 gauss, whereas ~ U C E J ~ C H t h e meta position corresponds t o Q C E ~= +8.3 gauss (unpublished results). (9) We wish t o thank Dr. Holm for making his result available t o us prior t o publication.
~OCB,/UCHI
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concentration.10 In accord with these observations, we have noted large proton shifts for this compound that are concentration dependent. Finally, we have observed large changes in the n.m.r. spectra of several nickel chelates of salicylaldimines on the addition of pyridine together with corresponding shifts in the proton resonances of pyridine. Such effects are consistent with a coordination of pyridine to nickel and studies are being continued. The chelates prepared for this study were obtained either by treating the Schiff base phenolate ion with nickel acetate or, more conveniently, by treating a suspension of the bis-(salicylaldehyde)nickel(I1) in boiling ethanol with an excess of the substituted aniline.11,12 The chelates were obtained as anhydrous solids and had satisfactory C, H, N and Ni analyses.
crystallizes in a packing arrangement similar to that of the diester. It was therefore of interest to test its photo-behavior, which had not been reported by Griffin. Ultraviolet irradiation of a powdered sample of monomethyl fumarate produced a progressive change in the X-ray powder pattern. After several days of exposure the irradiated sample was washed free from starting material with diethyl ether; the less soluble residue showed no hydrogen uptake on attempted catalytic hydrogenation. After recrystallization from din-butyl ether this material melted a t 153-154' ; elemental analysis gave: C, 46.5; H, 4.4; (0) CH3, 11.5. Calcd. for C1~HI2O8:C, 46.2; H, 4.7; (0)CH3,11.6. A convenient method of isolation of the dimeric material treats the irradiated sample with excess boiling thionyl chloride which removes the monomer a t the water pump as the volatile p-(chloro(10) R . H. Holm, J . A m . Chem. SOL., 83, 4683 (1961). (11) F. Basolo and W. R. Matoush, ibid., 76, 5663 (1953). formyl) methylacrylate. The anhydride of the (12) L. Sacconi, P. Paoletti and G. Del Re, ibid., 79, 4062 (1957). dimer (m.p. 144' from chloroform) gives an COXTRIBUTION No. 808 E. A. LALANCETTE infrared spectrum characteristic of a five-membered CENTRAL RESEARCH DEPARTMENT D. R. EATON cyclic anhydride. Hydrolysis with hot water EXPERIMESTAL STATION R . E. BENSON regenerates the diacid diester of m.p. 153-154'. E. I. DZi POST D E h-EMOURS AND COMPANY WILMISGTOS,DELAWARE W. D PHILLIPS The photodimer as well as its anhydride were AUGUST6, 1962 converted by methanolic hydrogen chloride to a RECEIVED compound identical with cyclobutane 1,2,3,4tetracarboxylic acid tetramethyl ester of n1.p. 144145' obtained by Grifin and co-workers by the THE PHOTODIMERIZATION OF MONOMETHYL photodimerization of dimethyl fumarate.2 The FUMARATE conformation of the dimer of monomethyl fumaSir: Through the courtesy of Dr. G. W. Griffin we rate is therefore established as I. Thus, the crystal have had access to his work (since published1$2) structures of the three monomers have in common on the photodimerization in the solid state of a shortest axis of 4 A. and dimerization to dimers HOgC fumaric acid derivatives to the corresponding cyclobutanes. Following our own interest in the photodimerization of cinnamic acids to a-truxillic and @-truxinic acids and the dependence of the stereochemical course of this reaction on the lattice geometry of the m ~ n o m e r ,we ~ have extended TABLE I fyans-Compound
hIe02CCH=CHC0&e4 SCCH=CHCS6 Me02CCH=CHC02H $PhCH=CHCO2H Me02C(CH=CH)2C02Me MeO?CfCH=CH)rC02ble
a,.&.
3.92 3.89 14.14 6.05 T .74 7.60
b,A.
c,A.
9.24 3.60 3.99 4.04 5.81
5,93 11.34 5.60 31.3 5.82 13.06
.i.RR
OL
101'47' ...
72.6" ... 88 0"
81.1"
B
1120 49' 121.9' 98.8" 90.3" 121.Xo
1n.i.;"
Y
109' 20' ... 83.8" ... 106.1" 105.9"
Space group
Pi P21/n Pi P2,/c
Pi Pi
n
1
2 3
I
4 1
-
1
Griffin's work on the fumaric derivatives by crystallographic studies. As Griffin, et al., have already noted the packing arrangements of dimethyl fumarate4 and of fumaronitrile5 (see Table I) favor the formation of dimers of symmetry 2/m through the contact of parallel omoleculesalong the shortest translation period of 4 A. A crystallographic survey of other fumaric acid derivatives shows that monomethyl fumarate
of symmetry m; they are completely analogous to the @-modification of substituted ci;namic acids defined by shortest axes of 4.0 * 0.1 A . and photodimerization to p-truxinic acids. The next higher homologs, dimethyl trans,transmuconate and dimethyl all-trans-hexatriene dicarboxylate, do not belong to this structure type (see Table I); work on their photochemical behavior is under way.
(1) G. W. Griffin, G. E. Basinski and A. F. Vellturo, Telvahedvon Lelters, S o . S , 18 (1960). ( 2 ) G. W. Griffiu, A. F. L'ellturo and K. Furukawa, J . A m . Chem. S o i . , 83, 2725 (1961). (3) G. ?VI.J. Schmidt, Acfa C v y s f . , 10, 783 (1967); M. D. Cohen and G. M . J. Schmidt in J. H. de Boer, Ed., "Reactivity of Solids," Elsevier Publishiug Co., .4rnstrrdum, 1961, p. 556. ( 4 1 I. E. Knagys and K. Lonsdale, J . C h e w . Sa.,417 (1942). ( 2 ) B. peal, private cururuunication.
Acknowledgment.-\i?e wish to thank N r . L. Leiserowitz and h4r. D. Rabinovich for measuring some of the crystallographic constants reported here. DEPARTMEST OF X-RAYCRYSTALLOGRAPHY INSTITCTE OF SCIENCE .r.SADEH WEIZMANN G. IT.J. SCHMIDT KEHOVOTH,ISRAEL K E C E I V U u d U G L J b r 16, 1962
