COMMUNICATIONS TO THE EDITOR
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Table I: Comparison of Spectra B and C with Those Obtained from CHsCHOH and CH8.
B CH~HOH
a
Hyperfine splitting, oersteds
Source
Spectrum
(CHsCHO-HzOZ) CHsCH20H
+ Ticla
+ T i c & + HzO, +
ai
a value
15.1 fO.3O 22.6f0.3
2 0033
ai UHOH
15.0 f 0 . 1
2.0033
I
de 22.5 f 0 . 3
C
(CH~CHO-HZOZ) TiCla
22.5 f 0 . 2
2.0028
CHaa
1-BuOzH
+ TiCls
22.3 & 0 . 2
2.0028
Standard deviation of splitting over the whole spectrum, after correction for nonlinearity of field sweep rate.
to be present at pH 0.7, the usual condition in the aqueous flow system. Alternatively, Russell5 has pointed out that the septet A may arise from the uncharged species V if one assumes that the proton transfer is acid catalyzed, CH$(OH)CO CH3
CH&O(?(OH)CHa
V
and fast enough at pH 0.7 to give equivalent methyl groups. Also, our observation’ that the septet A shows an alternating line-width effect, with incipient collapse to a quartet ( a H = 17 oersteds) as the pH is raised from 0.7 to 2.0 could be explained by assuming a decrease in proton transfer rate in V with increase in pH. We agree that all the facts now known can be more simply explained by assigning septet A to a structure such as V with rapid proton exchange taking place. Turkevich, et aL16have recently published a spectrum, obtained by injecting acetaldehyde into the titanous-peroxide flow system, which consists mainly of a doublet of quartets and a quartet, assigned by them to [CH&H-O]+ and CH&O, respectively. We have attempted to reproduce their spectrum, but succeeded only when the acetaldehyde and peroxide were premixed. The hyperfine splittings and g values were identical with those attributed previously’ to spectra B and C. Moreover, careful measurements showed them to be indistinguishable from those of the spectra given by ethanol-titanous-peroxide and tbutylhydroperoxide-titanous, respectively, and these systems are generally accepted7 as giving uncomplicated spectra of the CH3CHOH and CH3- radicals. The various spectra were run consecutively, with repetition to check the constancy of the field sweep rate, FrBmy’s salt being used as a standard ( a H = 13.07 oersteds, g = 2.0055). The results are given in Table I. The correspondence of the splittings and g values may be taken, in the absence of positive evidence to the contrary, to imply the identity of the radicals. The Journul of Physicol Chsmiatry
Reasonably straightforward mechanisms are available’ for the production of both CHaCHOH and CH3. in the acetaldehyde-titanous-peroxide system. Further evidence of the production of RCHOH radicals from aldehydes was obtained by Dixon, et a1.,* who reported CHzOH from formaldehyde, and even detected a splitting of 1.0 oersted from the hydroxyl proton (which is not present in CHzO+). The assignment of spectrum C to CHI. rather than CH&O is supported by the spectra obtained from the reaction of other aldehydes RCHO with the titanous-peroxide system: spectra corresponding to R - have also been found for R = CBHS,~ and for R = n-CaH7, i-C3H7; and t-C4H0.0 It is improbable that in all five cases RCO would give rise to the same spectrum as Re. (5) G. A. Russell, private communication.
(6) Y. S. Chiang, J. Craddock, D. Mickewich, and J. Turkevich, J . Phys. Chem., 70,3509 (1966). (7) H. Fischer, “Landolt-Bornstein Numerical Data and Functional Relationships in Science and Technology,” New Series, Group 11,
Vol. I, Springer-Verlag, Berlin, 1965. (8) W. T. Dixon, R. 0. C. Norman, and A. L. Buley, J . Chem. Soc., 3625 (1964). (9) J. R. Steven and J. C . Ward, Australian.J . Chem., in press.
DIVISIONOF COALRESEARCH CSIRO CHATSWOOD NEW SOUTHWALES,AUSTRALIA
J. R. STEVEN J. C. WARD
RECEIVED MARCH 2, 1967
Comments on the Nuclear Magnetic Resonance Spectrum of Diethyldipyridylnickel
Sir: In a recent paper Saito, et al.,l have described the preparation and characterization of diethyldipyridylnickel (I).
COMMUNICATIONS TO THE EDITOR
As nmr evidence in support of structure I, the authors have reported: (a) the ratio (10:8) between the areas of the signals corresponding to the aliphatic and aromatic protons of the complex; (b) the high-field part of the proton spectrum of I, consisting of a triplet and a quartet centered a t 8.85 and 9.18, respectively; (c) the low-field part of the same spectrum, whose pattern is formed by two doublets and a quartet centered, in order, a t r 0.93, 1.95, and 2.45; the areas of these multiplets were reported to be in the ratio 1:2:1. Evidences (a) and (b) are self-explanatory, and the deductions by Saito, et al., from these data are reasonable. The interpretation of the low-field part of the spectrum (c) may, however, be questioned. Saito, et al., have assigned the chemical shifts of the aromatic protons by a direct comparison of the pattern of the spectrum of I with those of the spectrum of the complex [Fe11(C10H8N2)3]C12 (11), which has been completely analyzed and published earlier.2 In the latter, the chemical shifts of protons 3, 4, 5, and 6 occur a t r 1.15, 1.74, 2.41, and 2.42 in that order, and the whole spectrum may be very roughly described,a as done by Saito, et al., as t,he sequence of a doublet, a quintet, and a doublet with intensity ratio 1:1:2. It must be pointed out that the high-field shift of proton 6 in I1 has been explained, in our paperj2in terms of the magnetic anisotropy of the aromatic ring of an adjacent ligand in the octahedral complex and the low-field shift of proton 3 in terms of the dispersion forces arising because of the cis coplanar conformation of each ligand in 11. By matching the pattern of the two spectra, Saito, et al., assigned the low-field doublet of the spectrum of I to the resonance of proton 3, the next doublet to the resonances of protons 5 and 6, and the high-field multiplet to the resonance of proton 4. According to these assignments, the resonance of proton 6 in diethyldipyridylnickel would still occur a t a higher field than in the free 2,2’-bipyridyl molecule; since I contains only one bipyridyl ligand, Saito, et al., concluded that our interpretation of the high-field shift of proton 6 in I1 was wrong, and attributed the observed effect to the proximity of the metal atom. We believe, however, that another interpretation of the nmr spectrum of I is more consistent with the experimental data and that the assignments made by Saito, et al., are very likely incorrect. By inspection of the spectrum published in Figure 3 of their paper, it is
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evident that the splitting of the low-field doublet falls in the range 4.5-5.5 cps, which is the correct order of magnitude for the coupling constants between CY and p protons in pyridine4l5and in CY- and p-monosubstituted pyridines.2+’0 This doublet must be assigned, therefore, to the resonance of proton 6 and not to the resonance of proton 3. In the latter case, the splitting of the doublet should have been of the order of 8.0 cps, as found in the spectrum of I1 as well as in the spectrum of any a-monosubstituted pyridine so far analyzed.6-*0 The assignment of the resonances of the other protons then follows naturally. The intense doublet a t T 1.95 is assigned to protons 3 and 4 which are very strongly coupled and interact, to the first approximation, with the other protons as a particle of spin 1. They will split each component of the lowfield doublet in triplets which are not seen in the spectrum because of the poor resolution and the smallness of the splitting [(J46 J36)/2 N 1.18 cps]; the same splitting should also be present in each component of the intense doublet. The high-field quartet is then assigned to the resonance of proton 5; its multiplicity arises from the overlapping of a doublet (J56 N 4-5 cps) further split into triplets [(J35 Jd5)/2 N 4.3 cps] by interaction with protons 3 and 4; the latter spacing represents also the separation between the components of the main doublet a t r 1.95. According to these assignments, the experimental data of Saito, et al., fully support our conclusions about the strong shielding effect exerted by the other ligand groups on the resonance of proton 6 in 11. On the basis of the results obtained from the analysis of the nmr spectrum of the latter molecule, one would anticipate that the resonance of proton 3 should occur in I at a r value lower than 1.95; a small deviation from a coplanar arrangement of the two aromatic nuclei
+
+
(1) T. Saito, Y. Uchida, A. Misono, A. Yamamoto, K. Morifuji, and S. Ikeda, J. Am. C h m . Soc., 88, 5198 (1966). (2) S. Castellano, H. Glinther, and S. Ebersole, J. Phys. Chem., 69’ 4166 (1965). (3) Actually, in the spectrum of 11, much more fine structure is present. Both the experimental and calculated spectra of I1 are reported in ref 2. (4) J. A. Pople, W. G. Schneider, and H. J. Bernstein, “HighResolution Nuclear Magnetic Resonance,” McGraw-Hill Book Co. Inc., New York, N. Y., 1959, p 266. (5) S. Castellano, C. Sun, and R. Kostelnik, J . Chem. Phys., 46, 327 (1967). (6) W.Bragel, 2. Elektrochem., 66, 159 (1961). (7) V. J. Kowalewski and D. G. de Kowalewski, J . Chem. Phys., 36, 266 (1962). (8) V. J. Kowalewski and D. G. de Kowalewski, ihid., 37, 2603 (1962). (9) S. Castellano and A. A. Bothner-By, ihid., 41, 3863 (1964). (10) H. Glinther and 9. Castellano, Ber. Bunsenges. Physik. Chem. 70, 913 (1966).
Volume 71, Number 7 June 1967
COMMUNICATIONS TO THE EDITOR
2370
would, however, account for this discrepancy.” Furthermore, the high-field shift of r 0.2 observed for the chemical shift of proton 4 in I seems to indicate that, for the outermost protons in the molecule, solvent and concentration effects may also be very effective in altering the position of the resonance. (11) In 11, the main contribution to the low-field shift of proton 3 (and 3’) is due to the van der Waals interaction between the two protons. This effect decreases with the 6th power of the distance, and a small deviation from the coplanar arrangement of the two aromatic rings may, therefore, cause very large effects.
MELLON INSTITUTE PITTSBURGH, PENNSYLVANIA INSTITUT FC% ORGANISCHE
DER KOLN,
CHEMIE
UNIVERSIT~~T KOLN
Found: C, 63.3; H, 7.4; N, 8.3; Ni, 19.3. The crystalline complex is dark green and is very airsensitive. It decomposes at 125” in vucuo, evolving ethane and ethylene. The nmr spectra were recorded in dimethoxyethane solutions by use of a 60 Mc/sec spectrometer. As tetramethylsilane could not be used, the chemical shifts were measured by using a methyl signal of the solvent as an internal reference and then were converted into a r scale.
S. CASTELLANO
Table I: Chemical Shifts of the Ring Protons of the Ligands and Their Complexes in Dimethoxyethane Solutions. (The H. G ~ T H E R Figures in Brackets Are the Intensity Ratios.)
GERMANY
-Chemical
RECEIVED MARCH16, 1967
The Nuclear Magnetic Resonance Interpretation
Ha
H4
1.62 (1) doublet
2.29 (1) triplet
1.95 (2 ) doublet
of Diethylnickel Complexes of
shifta, H6
HE
2.80 1.46 (1) (1) quartet doublet 2.45 0.93 (1) (1) quartet doublet
Substituted Dipyridyl
Sir: In the previous paper,‘ we reported the preparation and characterization of diethyldipyridylnickel (I).
1.64 (1) singlet
, ,
.
2.80
1.45
(1)
(1)
doublet doublet
CH,
5
Ni
(1)
During the course of our study of the analogous nickel complexes of 4,4’-disubstituted 2,2’-dipyridyl, we found that our previous nmr assignments of the ring protons were incorrect. We wish to report in this communication the synthesis and the nmr interpretation of diethyl(4,4’-dimethyl 2,2’-dipyridyl)nickeI (11) , and to correct the nmr assignments of the ring protons of I.
(11)
The complex (11) was prepared by the reaction of nickel acetglacetonate, 4,4’-dimethyldipyridyl, and diethylaluminum monoethoxide in ether. Anal. Calcd for C16H22N2Ni: C, 63.8; H, 7.4; N, 9.3; Nil 19.5. The Journal of Phyeical Chemistry
w7 -
N c
OCH,
, /
2.16 (1) singlet
...
2.66
1.17 (1) doublet doublet
1.97 (1) doublet
...
3.03 1.53 (1) (1) quartet doublet
2.33 (1) doublet
. .
2.84 1.30 (1) (1) quartet doublet
,
(1)
c,H/N‘c2Hs
In Figure 1, the signal a t r 2.16, which is a singlet due presumably to the small J35and J36 and/or to the poor resolution of the spectrum, is assigned to H3, because the adjacent carbon has no proton. It is most reasonable to assign the doublet a t r 1.17 t o Heand the doublet a t r 2.66 to Hg, because it is very improbable that the coordination of the ligand to nickel exerts such an effect to deshield the H5 to shift the signal to the field as low as r 1.17, and because the J M estimated G signal is ca. 6.0 cps. from the splitting of the H (1) T.Saito, Y. Uchida, A. Misono, Y. Yamamoto, K. Morifuji, and S. Ikeda, J . Am. Chem. SOC.,88, 6198 (1966).
