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Potassium tris(perfluoropinacolato)ferrate(III) deposited as very pale yellow crystals from water. Anal. Calcd for C18F3606FeK3:C, 18.49; F, 58.50. Found: C, 18.36; F, 58.38; magnetic moment, 6.0 BM. Rolf Huisgen, Peter Otto Potassium tris(perfluoropinacolato)aluminate(III) deInstitut fiir Organische Chemie der Uniuerstat posited as colorless crystals from water. Anal. Calcd Munich, Germany for C18F3606A1K3:C, 18.95; F, 59.97. Found: Receiued Ju/y 22, 1968 C, 19.03; F, 59.54. Potassium bis(perfluoropinaco1ato)m a n g ana t e ( I I) formed brown crystals from water, dehydrating in vacuo Fully Fluorinated Alkoxides. 111. to a pale yellow solid. Anal. Calcd for C I Z F ~ ~ O ~ M ~ K ~ : Perfluoropinacol, a Useful Bidentate Ligand C, 18.08; F, 57.20; Mn, 6.89. Found: C, 18.12; Sir: F, 57.02; Mn, 6.85; magnetic moment, 5.2 BM. Potassium bis(perfluoropinacolato)nickelate(II)formed The perfluoropinacol molecule, (CF&C(OH)C(OH)a yellow aqueous solution giving purple crystals of a (CF3)2, is known to form the basis of a number of five7 1 dihydrate, dehydrating in vacuo to deep blue-purple membered heterocycles of type OC(CF3)2C(CF&0M, anhydrous compound (diamagnetic). Anal. Calcd for where the element M is Si, Ge, Sn, B, or S. C12F2404NiK2: C, 17.99; F, 56.93; Ni, 7.33. Found: Previously reported compounds of this type have C, 17.56; F, 56.71; Ni,7.28. been made by the reaction of the appropriate dihalides Potassium bis(perfluoropinacolato)cuprate(II) formed with the ionic alkoxides of perfluoropinacol in anhya deep blue aqueous solution giving deep blue crystals drous donor solvent, such as tetrahydrofuran. Howof stable dihydrate. Anal. Calcd for Cl2H4Fz4O6CuK2: ever, the stability of perfluoropinacol in water, comC, 17.12; H, 0.48; F, 54.16; Cu, 7.55. Found: C, bined with its acidic nature (pK = 5.959, suggests that 16.92; H, 0.64; F, 54.10; Cu, 7.61; magnetic moit should be possible to prepare complexes in which the ment, 2.0 BM. pinacol ion is acting as a bidentate ligand to a metal Potassium bis(perfluoropinacolato)zincate(II) deposion. ited as colorless crystals from water. Anal. Calcd This we have found to be the case, and we now refor CI2Fz4O4ZnK2:C, 17.84; F, 56.46. Found: port that stable complexes with a variety of metals may C, 17.88; F, 56.49. readily be made in aqueous solution. Complex ions A brief investigation was made of some complexes of the type [M(PFP),I3-, where PFP represents the percontaining other cations. When perfluoropinacol was fluoropinacolato ion, [OC(CF3)2C(CF3)20]2-,have been added to an aqueous stirred suspension of iron(II1) made where M = Fe3+.or A13+,while complexes of the hydroxide and silver oxide, reaction occurred to give type [M(PFP)2]2- are formed where M = Mn2+, Ni2+, silver tris(perfluoropinacolato)ferrate(III), as pale yelCu2+,or Zn2+. low crystals from water, rapidly darkening on exposure The most general method of preparation was to add Anal. Calcd for C18F3606FeAg3:C, 15.71; to light. the aqueous metal ion (as the metal sulfate) to the calcuF, 49.72. Found: C, 15.65; F, 49.60. lated amount of perfluoropinacol in a 1:l methanol/ Metathetical reaction of the aqueous silver salt with water mixture (the pinacol having only limited solutris(ethylenediamine)cobalt(III) iodide gave aqueous bility in water). No reaction was observed, but the tris(ethylenediamine)cobalt(III) tris(perfluoropinacointroduction of aqueous potassium hydroxide produced lato)ferrate(III), [ C O ( ~ ~ ) ~ ] [ F ~ ( P F Anal. P ) ~ ] . Calcd for immediate color changes in those solutions which were C 2 4 H 2 4 F 3 6 0 6 N 6 C ~ C, F e : 22.32; H, 1.87; F, 52.97; colored, and, by addition of base to a pH of about 7.5, N, 6.51. Found: C, 22.01; H, 2.08; F, 52.68; N, the complex ions were formed according to the equa6.18. tion The cesium salts appeared to be much less soluble nH2PFP + M"+ + 2nOH- +[M(PFP)*p- + 2nHz0 than the potassium salts. With the bis(perfluor0pinacolato)cuprate(II), for example, addition of aqueous where n = 2 or 3. cesium chloride to an aqueous solution of the potassium In some cases, e.g., iron and manganese, it was possalt gave an immediate precipitate of the deep blue sible to prepare the complex ions by dissolving the cesium salt, which was then recrystallized from methafreshly precipitated metal hydroxide in partially neutraC S 14.51; ~: nol. Anal. Calcd for C I ~ F ~ ~ O ~ C UC, lized pinacol F,45.89. Found: C, 14.45; F,45.62. 3HzPFP + Fe(0H)s 30H- --f [Fe(PFP)3]a- + 6 H 2 0 In the iron and aluminum compounds described above, where the metal atom is chelated by three pinacol but this route was not suitable for all the metals studied. ligands, there is no reason to doubt that the structure is Solid products were obtained by filtration of the basically octahedral, similar to the well-known triabove solutions to remove any metal hydroxides, foloxalatoferrate or -aluminate ions, and the magnetic lowed by crystallization by evaporation at 25 O of aquemoment of the iron complex is that to be expected from ous or methanolic solutions and drying at 25O in vacuo. a high-spin d5 species. Similarly, the magnetic moment The following compounds were characterized. of the ion [Cu(PFP)2I2- is within the range usually found for d9 species of copper(II), and that of the ion [Mn(1) C. L. Frye, R. M. Salinger, and T. J. Patin, J. Am. Chem. SOC.,88, (PFP),I2- is consistent with d6 manganese(I1). With 2343 (1966). (2) M. Allan, A. F. Janzen, and C. J. Willis, Chem. Commun., 55 the nickel complex [Ni(PFP)2]2-, the diamagnetism ( 1 9 68). would suggest a square-planar configuration, but more (3) W. J. Middleton and R.V. Lindsey, J. Am. Chem. SOC.,86, 4948 detailed interpretations of the structures of all these (1 9 64).
of I1 in benzonitrile: AH* = 10.8 kcal mol-' and AS* = -42 eu. Large negative activation entropies are consistent with highly ordered transition states.
+
Communications to the Editor
5344
species must await the results of work now in progress on their electronic absorption spectra. From the species described above, it would appear that perfluoropinacol is a valuable addition to the range of bidentate oxygen-containing ligands and may be expected to form a variety of complexes with many metal ions. Acknowledgment. We gratefully acknowledge financial support from the National Research Council of Canada. Microanalyses were performed by Alfred Bernhardt Laboratories, Mulheim (Ruhr) Germany.
which have methyl groups on their azomethine carbons, the pattern of the C D bands in the d-d region is reversed, compared to N i ( ~ a l )-)pn. ~( In addition, the magnitude of the CD bands is greater for the methylsubstituted compounds. Such sign reversals may be observed in previously reported O R D ~ p e c t r a . ~The reversal in the CD spectra is more definitive, however, since in these closely related complexes it is reasonably certain that the low-energy C D bands correspond to the same transitions. A number of crystallographic investigations have shown the central ring of these tetradentate Schiff base M. Allan, C. J. Willis chelates to be nonplanar. The C D results given above Chemistry Department, Uniaersity of Western Ontario may be interpreted by assuming that the sign of the London, Ontario, Canada Cotton effect of a given d-d transition is determined Receioed June 19, I965 by the preferred conformation of the central chelate ring. If, by analogy with coordinated 1,2-diaminopropane5 (pn), it is assumed that in Ni(~al)~(-)pnthe An Anomalous Sign Reversal in the Circular Dichroism X conformation,e with the methyl group pseudoSpectra of Tetradentate Schiff Base Complexes of equatorial, is favored, then the sign reversal in the CD is Nickel(I1) and Copper(I1) explained by a preference for the 6 (methyl-axial) conSir: formation in Ni(7-CHa~al)~( -)pn and N i ( a ~ a c )-)pn. ~( This methyl-axial preference in these compounds is In the course of an investigation of the circular reasonable, owing to the severe interaction between the dichroism (CD) spectra of a series of square-planar methine methyl and an equatorial pn methyl group. metal complexes with tetradentate Schiff base ligands, The increase in magnitude of the C D is a consequence of we have found a correlation between the sign of the the stronger conformational preference in the case of Cotton effects in the d-d transition region and the the methyl-substituted complexes. presence of substituents at the azomethine carbon The assumption of a X conformation for the central atoms. This observation suggests that the chelate ring ring in N i ( ~ a l )-)pn ~ ( may be questioned, however, since conformation, rather than the absolute configuration those interactions which favor an equatorial orientation of the amine, is of primary importance in the induction for the methyl group in chelated pn are absent in these of optical activity in the metal ion chromophore by Schiff base chelates. The crystal structure' of Cu(~a1)~these asymmetric ligands. These results may be (-)pn.H20 in fact shows the pn methyl to be pseudorationalized by assuming a corresponding inversion in axial, although this may be due to interaction with the the conformation of the central chelate ring, similar to coordinated water molecule. Inspection of a model of that employed to detect apical coordination in tridenN i ( ~ a l )-)pn ~( suggests that the only appreciable steric tate amino acid chelates. interaction is that between the methine hydrogen and The d-d band in the visible absorption spectrum pn methyl, and should tend to favor the methyl-axial, of N,N '-bis(salicy1idene)-R-( -)-propane- 1,2-diamino6 conformation. Similar conformational reasoning nickel(I1) (Ni(sal)*( -)pn)z occurs as a shoulder at can also be used to explain the fact that the complexes 18,500 cm-I (emax 150) on the more intense chargeC~(gly)~S(+)pn and Cu(gly),RR( - )chxn (gly = glycyl, transfer band. The spectra of the corresponding comchxn = 1,2-diaminocyclohexane) have low-energy CD plexes derived from o-hydroxyacetophenone (Ni(7-CH3sal)z(-)pn) and 2,4-pentanedione ( N i ( a ~ a c ) ~ - bands with the same sign.8 In-plane methyl-oxygen interaction may favor the axial position for the pn (-)pn) also exhibit single d-d bands3 at 18,080 cm-' will have a central ring methyl, so that C~(gly)~(+)pn ,,,E( 170) and 17,730 cm-' ,,E( 65), respectively. The C D spectra of these chelates in the d-d region are presented in Table I. For the latter two complexes, Table I. Circular Dichroism Spectra of Nickel(I1) Chelates
N i ( ~ a l )-)pn2 ~( Ni(7-CH8sal)2(- )pn Ni(acac)p( -)pn
17,570 20,700 17,670 20,410 (sh) 17,360 20,200 22. 420a
+O. 6 -0.4 -5.3 +1.0 -2.1 +O. 6 -2.0
a This band obscured by charge-transfer bands in the other compounds.
(1) K . M. Wellman, W. Mungall, T. G. Mecca, and C. R . Hare, J. Amer. Chem. Soc., 89, 3647 (1967). (2) B. Bosnich, ibid., 90,627 (1968). (3) A. P. Terent'ev, E. G. Rukhadze, G . V. Panova, and N. M. Viktorova, Rum. J . Gen. Chem., 34,3060 (1964); 35,1109 (1965).
Journal of the American Chemical Society
1 90:19
(4) R. H. Holm, G. N. Everett, and A . Chakravorty, Progr. Inorg. Chem., 7.83 (1966). (5) J. Dunlop and R. D. Gillard, Adunn. Inorg. Chem., Rndiochem, 9., 185 . - - - (19hh) ,- - - _, . (6) Proposed IUPAC nomenclature. (7) T. J. Llewellyn and T. N. Waters, J . Chem. Soc., 2639 (1960). ( 8 ) M. Parris and A. E. Hodges, J . Amer. Chem. Soc., 90,1909 (1968).
September 11, 1968
