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VOl. 82
because the corresponding cobalt(II1) compounds rhodium(II1) complexes are almost identical are well defined and have been known for a long whereas the spectra of the cis differ from those of time.’ It is significant that the rhodium(II1) iso- the trans isomer^.^ Likewise the cis-chloride and mers now have been prepared because it will be pos- trans-nitrate salts are the less soluble forms for the sible to make quantitative comparisons between cobalt(II1) and also for the rhodium(II1) comthese systems and the analogous cobalt(II1) com- plexes. Finally, the rate of acid hydrolysis of cispounds. Work is now in progress on the kinetics [Rh(en)zCla]+ is faster than that of the trans-isomer and mechanism of hydrolysis, isomerization, and as is also true for the analogous cobalt(II1) comracemization of the rhodium(111) complexes. plexes. The method described by Meyer and Kienitz3 (9) Xl. L. Morris and D H. Busch. THISJOURNAL, 82, 1521 (1960). for the synthesis of IRh(en)2Cl?]Cl.HaO was tried DEPARTMEKT OF CHEYISTRY several times but without success. Other attempts NORTHWESTERS UNIVERSITY S.ANDERSON to prepare this compound also were unsuccessful.8 EVANSTON, ILLISOIS FREDBASOLO The cis- and trans- [Rh(en)zClz]NOa finally were JUSE 9, 1960 RECEIVED isolated from a reaction mixture obtained by gradually adding aqueous KOH to a refluxing water soluSPIN DISTRIBUTION IN ALIPHATIC KETYLS’ tion of RhC13.3HzO and ens2HCl. In a typical preparation 1.0 g. of RhCla.3HzO (0.0038 mole), Sir: Electron spin resonance experiments confirm the 1.0 g. of ena2HCl (0.0076 mole), 0.43 g. of KOH (0.0076 mole) and 50 cc. of H2O were heated to re- conclusion of Favorsky and Nazarov2 that hexflux. Over a period of 15 min. another 50 cc. of amethylacetone and pentamethylacetone react with H20 containing 0.43 g. of KOH (0.0076 mole) was alkali metals to form free radicals. Reduction of added to the refluxing reaction mixture in 10 cc. solutions of the ketones in tetrahydrofuran by increments. The color of this solution changed potassium yields products whose hyperfine splitfrom dark red to bright yellow. Since the chloride tings correspond to the free radicals containing the salts are rather soluble and difficult to separate from same numbers of protons as the original molecules. KC1, 20 cc. of HNOa (concd.) was added to the cold The spectrum of the ketyl of hexamethylacetone reaction mixture after concentration to one half has seventeen lines evenly spaced a t an interval of the original volume. Yellow-orange crystals of 0.12 oersted and symmetrically distributed about g trans- [ R h ( e n ) ~ c l ~ ] N Oseparated s in 33% yield = 2.003. The intensities correspond to hyperfine with eighteen equivalent protons. (0.45 g.). Anal. Calcd. for [ R h ( e n ) ~ C l ~ l N Ointeraction ~: C, 13.5; H, 4.53; C1, 19.9. Found: C, 13.9; Nineteen lines are expected, but the two weakest H , 4.63; C1, 20.1. Evaporation of this filtrate to ones, of expected intensity only 2 X l o p 5 as great 20-30 cc. a t room temperature yields 0.13 g. of as the strongest one, are not detected by our specbright yellow cis-[Rh(en)?C1%]NOa.Analysis of trometer. Pentamethylacetone yields a syrnmetrical doublet with splitting of 2.38 oe.; each member of this isomer shows C, 13.9; H , 4.31; C1,20.0. Although the chloride salts are fairly soluble, it the doublet is further split into incompletely rehas been possible to isolate cis- and trans- [Rh(en)?- solved components with interval about 0.1 oersted. The spectrum of each compound contains addiCLlC1 from a reaction mixture of the type described above. When the reaction is finished, instead of tional components whose intensities correspond adding “ 0 3 , the solution is concentrated. The well with those expected from splitting by CI3in its first crystals to separate are the cis isomer after natural abundance. In hexamethylacetone two which the more soluble trans form is obtained from replicas of the central pattern are found symmetrically disposed about i t (Fig. 1). The interval the mother liquor. Assignment of the geometric configuration to the between the replicas is 7.6 oe., the intensity of each two isomers was made on the basis of the resolu- 0.033 that of the central pattern. A second pair of tion of the asymmetric cis isomer. A solution of patterns, with intensity 0.1‘7 of the first pair is 0.45 g. of ~ i s - [ R h ( e n ) ~ C l ~and ] C l 0.9 g. of dextro- found with splitting -19.6 oe. The intensity of the ammonium a-bromocamphor-r-sulfonate in 13 cc. first pair corresponds to the G,CiYoof the molecules of H 2 0 was frozen in an ice-salt-bath. After melt- which have one C13 in any of six equivalent posiing, 0.23 g. of I-cis- [Rh(en)?Cl?] [d-C10H1404SBr] tions, of the second pair to the natural abundance mas collected on a filter and washed. This dia- of C13 in a single position. We conclude that the stereoisomer was thoroughly ground with 2 cc. of a splitting of 7.6 oe. arises from CI3 in the methyl 1: 1 : 1 mixture of ethanol: ether : HC1 (conccl.) position, the 49.G oe. from CI3 in the central carbon. and 0.19 g. of Z-cis-[Rh(en)J21z]C1was isolated. No splitting from the quaternary carbons is found. The specific optical rotation of a 0.4% aqueous solu- Similarly in pentamethylacetone the splitting by C13 in the central position is 49.8 oe. and by CI3 tion of this compound has values of [a]b,7mp -50” in a methyl position 13 oe. Splitting by the five and [ ~ ] W Z -58”. ~ Additional evidence in support of this structural methyl carbons are approximately equal. The large splittings by the central carbon atoms assignment is offered by a comparison of the rhodium(II1) isomers with the same cobalt(II1) com- are in the same range as those in methyl radical3 pounds of known structure. For example, the (1) This work was supported by the U. S. Air Force through the infrared spectra in the 3, G , and 9 1.1 regions for the Air Force Office of Scientific Research of the Air Research and Development Command under Contract A F 49.638-469. Reproduction in cis and for the trans isomers of the cobalt(II1) and whole or in part is permitted for any purpose of the U. S Government. (7) “Gmelins Handbuch der anorganischen Chernie,” 68B, 228 (1930). (8) G. XI Harris, private communication.
( 2 ) Favorsky and Nazarov, B u l l . SOC. chiin., [ 5 ] 1, 40 (1934). (3) T. Cole, H. 0. Pritchard, N. R . Davidson and H . A I . McConnell, M o l . P h y s . . 1,406 (1958).
COMMUNICATIONS TO THE EDITOR
Aug. 20, 1960
Fig. 1.-dX"/dH
Fig. 2.-dX"/dH
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vs. H for potassium ketyl of hexamethylacetone in THF.
vs.
H for sodium ketyl of hexamethylacetone in THF.
and suggest structure I as the major ingredient in the ground state of each of the ketyls. 0-
somewhat more complex because of the presence of the isotopes Li6 and Li7. The complexes with sodium and lithium are under further investigation. DEPARTMENT OF CHEMISTRY WASHINGTON UNIVERSITY h-OBORU HIROTA S. I. WEISSMAK SAINTLOUIS,MISSOURI RECEIVED JULY 11, 1960 N.M.R. SPECTRA AND STRUCTURE OF ALUMINUM METHYL CHLORIDES
Sir:
I1 0 -
I
CH,-C=C-C(
CHI)
(111)
Splittings by the methyl carbons and by the unique proton in pentamethylacetone could be accounted for by admixture of conjugated structures such as I1 and 111. (In view of the recent proliferation in names of conjugations we don't know which kind we are reporting.) '4dmixture of two or three per cent. of each of structure I1 and of about 0.5 per cent. of structure I11 could account for the observed splittings. The absence of splittings by the quaternary carbons is not easily explained. Spin polarization of the u bond between them and the central carbon might be expected to produce observable splittings. Probably other structures which produce spin density of opposite sign to that produced by I must be included. When sodium or lithium is used as reducing agent, the splittings by protons and CI3in the ketyls are almost identical with those described in the preceding paragraphs. In addition, splittings by two equivalent alkali metal nuclei per paramagnetic molecule are found. The sodium compound in tetrahydrofuran yields seven evenly spaced lines a t interval 1.58 oe. with intensities 1 : 2 : 3 : 4 : 3 : 2 : 1 (Fig. 2 ) . The spectrum of the lithium ketyl is
Recently Brownstein, et uL,l have published n.m.r. data on Ah(CH3)6, Alz(CH3)4C12 and Alz(CHa)zC14. The interpretation of their results for .412(CH3)4C12and Alz(CHs)zC14is based on the methyl bridge model for these two molecules deduced from Raman Spectra by Van der Kelen and Herman.2 However, for Alz(CH3)& a chlorine bridge structure was deduced from electron diffraction measurements by Brockway and D a ~ i d s o n from , ~ the infrared spectrum by S c h o m b ~ r g ,and ~ from infrared and Raman ~ o r k . ~The , ~ vibrational spectrum of AlZ(CH3)aC14 gives evidence of a centrosymmetrical structure6 but subsequent Raman work did not yet allow of a definite choice between the chlorine bridge model (Czb symmetry) and the methyl bridge model ( D z h symmetry). The n.m.r. spectra of Brownstein, et ul., were (1) S. Brownstein, B. C. Smith, G. Ehrlich and A. W. Laubengayer, THIS J O U H N A L , 83, 1000 (1960). (2) G. P. Van der Kelen and M. A. Herman, Bull. SOC. Chim. Belges, 66,350 (1956). (3) L. 0. Brockway and N. R. Davidson, THISJOURNAL, 68, 3287 (1911) (4) G. Schomburg, "Infrarot spektroskopische Untersuchungen a n aluminum-organischen Verbindungen," Diss., Aachen, 1956. ( 5 ) M. P. Groenewege, 2. physik Chemie, Neue Folge, 18, 147
(1958). ( 6 ) M.P . Groenewege, Revue Universe& des Mines ( L i e g e ) , 9 S6rie. 16,461 (1959).
