368 1
Communications to the Editor Table 1. ' H NMR Spectral Parameters for [Pt(N,N,N',N'-Me4en)(Guo)~]*+ 0.05 , M in D2O
Chemical S h i f t s a T("C)
H(8)
H( 1 ' )
NCH3
NCH3
5.934 100.3
8.458
2.968
2.756
2.960
2.746
2.977
2.758
2.997
2.775
3.001
2.774
3.007
2.775
3.039
2.800
References and Notes (1) This paper is abstracted from a dissertation submitted to the Graduate Division of the University of Hawaii by P.L.D. in partial fulfillment of the requirements of a PhD. degree in chemistry. (2) Cramer, R. E.; Dahlstrom, P. L. J. Clin. Hematol. Oncol. 1977, 7, 330. (3) Mann, F.G.; Watson, H. R. J. Chem. SOC. 1958,2772.
Roger E. Crarner,* Phillip L. Dahlstrorn Department of Chemistry. 2545 The Mall University of Hawaii, Honolulu, Hawaii 96822 Received March 2, 1979
5.902 5.927 90.1
8.458 5.592 5.944
64.7
8.439 5.911 8.524
5.962
8.519
5.930
8.533
5.965
8.527
5.929
5.551
5.972
8.539
5.931
8.607
5.990
8.583
5.950
48.0
38.8
26.
0. Ppm downfield from DSS.
of base-stacking interactions between complexes. As a result of the temperature dependence of the chemical shifts, the two H(8) peaks merge at -55 "C. However the splitting of the H ( 1') peaks is larger and the H( 1') chemical shifts are less dependent on temperature so that two H ( 1') doublets remain a t 100 "C, confirming slow exchange between the diastereomers at this temperature. A lower limit to AG* for the interconversion between the diastereomers can be calculated from the chemical-shift difference between the two H( 1') resonances at I00 OC. This difference is 3.2 Hz at 100 "C so that AG* for the interconversion is >86 KJ mol-'. This value is large enough to allow the possibility of sep'arating the diastereomers, and we are attempting to do so. The chirality demonstrated for the platinum center of I I should be a general phenomenon for square-planar complexes. It will occur whenever a pair of large, planar ligands occupy cis positions i n the coordination sphere. I f these ligands are large enough, steric considerations will prevent their occupying the coordination plane and they will twist above and below it as observed for I. Isomers A, B, and possibly C will result. For exchange to occur among them, the ligands must rotate about the metal bond and in the transition state the ligand plane will lie in the metal coordination plane. This work demonstrates that it is possible, by increasing the steric bulk of the ligands, to destabilize the transition state so that a substantial barrier results between the A, B, and C stereoisomers. 0002-7863/79/I501-368 IS01 .OO/O
Bis(tetramethylammonium) Tris(sorbito1ato)manganate(IV), an EPR-Active Monomeric Complex of Manganese (IV) Sir: of the redox chemistry for During recent polyhydroxy complexes of manganese, we noted that certain of these ligands stabilize the +4 oxidation state as an apparent high-spin monomeric complex in aqueous alkaline solution. Previous examples of manganese( IV) species appear to be restricted to a series of di-p-oxo bridged dimers that contain the [Mn21v024f]unit.6-'0 Their low magnetic moments (ca. 6 2 . 5 p ~ are ) consistent with considerable antiferromagnetic coupling between the manganese centers.' A few unstable halide and pseudohalide monomeric complexes of the type [MnL612- (L = F,I' CI," IO3,I3or CNI4) have been reported, but they do not appear to exhibit appreciable distortion from octahedral symmetry and have not been fully characterized. A recent EPR study of a number of dioxygen adducts formed by manganese( I I ) porphyrins has been interpreted in terms of a manganese( IV)-peroxo formula ti or^.^^ We report here the isolation and characterization of (Me4N)2MnlV(c6Hl2 0 6 ) 3 (CsH1406= sorbital (D-glucitol)), which we believe to be the first authentic example of a high-spin tris(che1ate) monomeric complex of manganese( I V ) . I h The complex exhibits an EPR spectrum which is consistent with a ( ' / 2 -I/?) transition of the spin quartet ground state in an axially distorted octahedral ligand field. I n the formation reaction,I6 the manganese(l1)-sorbitol complex appears to reduce triplet-state dioxygen to hydrogen peroxide, with the yield dependent on the equilibrium constants K I and K l .
-
[Mn2"(Hz0)2(SH4)4I4-
+302
9[Mn~'11(OH)2(SH4)4]4-+ H 2 0 2 (8%)
(I)
7
(IIIA)?
+
+
[Mn2111(OH)z(SH4)4]4- 302 2SH6 (IIIA)2
+
K2
G 2 [ M n 1 V ( S H 4 ) 3 ] 2 - H202 (60%) SHh
E
(2)
CsH 1 4 0 6
The yields of hydrogen peroxide have been estimated by means of cyclic voltammetry in aqueous 0.5 M N a O H and 0.5 M sorbitol. The low yield in the ( 1 1 111) step is due to a further reaction between manganese(l1) and hydrogen peroxide above pH 7 . 5 . ' , 5Such a process yields manganese(l1l) and may produce -OH by a process analogous to Fenton's reaction.l8.Iy The equilibrium constant (K2) has been estimated, from the concentration of hydrogen peroxide at 1 atm in 0.5 M NaOH and 0.5 M sorbitol, to be 3.44X 10' m M atm-' at 298 K. The infrared spectrum of the solid complex, as a KBr disk, exhibits bands due to the 0 - H , C-H. and C - 0 stretching vibrations of sorbitol and a band at 560 cm-', which is assigned
-
0 1979 American Chemical Society
3682
Journal of the American Chemical Society
/ 10I:IS /
June 20, 1979
Table I. Absorption spectral Properties for t h e (Me4N)2Mniv(ChH I 2Odi Complex conditions ( A ) methanol ( S A r ) ( B ) A 100-fold MQNOH
+ ( C ) B + 100-fold sorbitol
(D)dimethyl sulfoxide (hO2,
265 265 265 265
6 700 10800 13000 I O 170
500 500 500 500
186 314 400 400
275
15 000 500
400
excess ble4iVOH or sorbitol)
( E ) aqueous M n ( I I I )
+
K3Fe(CN)6 (+500-fold O H - / sorbitol)
,
The electrochemical behavior of the poly01 complexes of manganese ions in aqueous solution has been described in detail previously.'-5 Cyclic voltammograms in dimethyl sulfoxide and dimethylformamide for the present manganese(1V)sorbitol complex have been recorded, but these are difficult to interpret. An irreversible reduction wave at - 1.3 V vs. SCE is observed in all cases and disappears upon reduction to manganese( I l l ) . Controlled potential coulometry at - 1.45 V results in an apparent one-electron reduction to give a solution of manganese(1ll). The absorption spectrum of the resulting manganese(ll1) solution (Table I ) is characteristic of the dimeric species ( 1 1 1 * ) 2 which has a 2:l 1igand:metal stoichiometry.' Such a structural change during reduction in dimethyl sulfoxide may account for the irreversibility of the redox process.
I
+ + + 2 H 2 0 E - -1.3 '/r[Mn,"'(OH)2(C6H1206)4]~- + O H - -I- c b k j 1 4 0 6
[Mn'V(C6H1206)3]2- e0
V. MezSO
I.o
2.0
3.0
4.0
H(Kgauss)
(3)
( 1 11,412 6
4
3
2
g- values Figure 1. First derivative EPR spectra for the (Me4N)*Mn'"(C6HI206)3 complex in various solvents: (a) aqueous 20% NaOH at 77 ti; (b) methanol a t 4.5 and 77 ti; (c) dimethyl sulfoxide a t 4.5 and 77 ti or solid complex at 4.5.77, or 298 K; (d) hexaaquo manganese( 11) ion a t 77 K in methanol; and (e) 0.1 M manganese(lI), 0.3 M sorbitol, 0.4 'VI Me4NOH in methanol at 77 K . Spectrometer settings: microwave frequency. -9.5 GHz: modulation amplitude, 4 X IO2, gain 4-400; scan time. 5 min. and attenuation. 5 dB.
to the Mn-O(L) stretching vibration, in agreement with similar assignments for other manganese( IV) The absence of bands between 600 and 700 cm-' confirms the absence of the [Mn20>l4+p-oxo bridging unit in this complex. The results from a conductivity study i n freshly prepared methanol solutions over the concentration range 0.5-2.0 mM indicate an equivalent conductance ( A M )of 170-210, which confirms that the complex is essentially a 2: 1 electrolyte in this solvent.20Similar findings are obtained for dimethyl sulfoxide solutions. Freshly prepared solutions of the complex in methanol or dimethyl sulfoxide are deep reddish orange with an intense absorption band at 265 nm, which is assigned to a ligand to metal charge-transfer transition. A shoulder a t -500 nm is assigned to a d-d transition.' In methanol, the E values for both bands (Table I ) are dependent upon the concentrations of sorbitol and hydroxide ions in the solution. This appears to be due to partial solvolysis rather than reduction to manganese(lll), which is observed in aqueous media.' Slow reduction to a yellow-brown manganese(l1 I ) species does occur over a period of 24 h and is accelerated in the presence of U V light or elevated temperatures, and in the presence of excess ligand.?l-24
Figures la-c illustrate EPR spectra for the manganese(1V) complex in various solvents. The spectrum from the frozen dimethyl sulfoxide solution (Figure IC) is identical with that obtained from a powdered sample and is almost certainly due to a precipitation of the solid complex rather than the production of a "glass". I n aqueous 20% NaOH (Figure I C ) , however, a clean six-line hyperfine pattern at g = 2 is clearly observable together with a stronger and broader resonance at g = 4. The spectrum from methanol (Figure I b) apparently contains a mixture of the solid and solution species, but allows the resolution of a six-line hyperfine pattern on the broad g = 4 resonance. The anisotropy of the resonances is unusual for S = 3/z metal ion systems. However, similar properties have been reported for several chromium(ll1) tris(chelates)." Their powder and frozen glass spectra have been to be due to a field of axial symmetry that has a large value for the zero field splitting parameter ( D ) such that D >> hu and, hence, g P H / 4 D 95% manganese(1V) on the basis of polarographic analysis and by titration with ferrous ion in aqeous 0.5 M ~ "alternative method of preparation involved NaOH and 0.5 M ~ o r b i t o l . ~An permanganate oxidation of manganous(l1) perchlorate. 2KMn04
+ 3Mn"(C104)2 + 14Me4NOH
15CsH1406
aqueous
5[(Me4N)2Mn'V(C6H,206)3]
MeOH
+ 2KC1041 + 4Me4NC1041+ 24H20
In each case the complex was isolated as a hygroscopic red-brown powder after filtration of the reaction solution and recrystallization from methanol-ethyl acetate (1:5) and was dried (0.01 Torr) for 6-8 h (yield 93%). C, 36.66; H, 8.46; N, 3.29; Microanal. Calcd for (Me4N)2Mn(C6H,206)3.6H20: Mn, 6.46. Found: C, 35.90; H, 8.23; N, 3.07; Mn, 6.50. The isolated complex exhibited a room-temperature bulk magnetic moment of 4.0 f 0.1 pg, in agreement with that for a high spin d3 center (pet,3.89 p g ) . (17) 6.L. Velikov and J. Dolezal, J. Electroanal. Chem., 71, 91 (1976). (18) G. Czapski, A. Samuni, and D. Meisel, J. Phys. Chem., 75, 3271 (1971). (19) C. Walling, ACC.Chem. Res., 8, 125 (1975). (20) D. A. Skoog and D. M. West, "Fundamentals of Analytical Chemistry", Holt. Rinehart and Winston, New York, 1966. A 2: 1 electrolyte in methanol should have &, values in the range of 160-220 for concentrations around 1.0 mM. (21) 6. Long Poh and R. Stewart, Can. J. Chem., 50, 3432 (1972). (22) C . F. Wells and C. Barnes, J. Chem. SOC.A,, 430, 1405 (1971). (23) T. J. Kemp and W. A. Waters, J. Chem. SOC.,339 (1964). (24) P. Levesley and W. A. Waters, J. Chem. SOC.,21 7 (1955). (25) L. S. Singer, J. Chem. Phys., 23, 379 (1955). (26) R. F. Ferrante, J. L. Wilkerson, W. R . M. Graham, and W. Weltner, J. Chem. Phys., 67, 5904 (1977). (27) J. A . Fee, Methods Enzymol., 49, 512 (1978). (28) N. R. Orme-Johnsonand W. H. Orme-Johnson, "Methods of Enzymology", Vol. 52, Academic Press, New York, 1978, p 252. (29) M. L. Randolph, "Biological Applications of Electron Spin Resonance", H. M. Swartz, J. R. Bolton, and D. C. Borg. Eds., Wiley-lnterscience, New York, 1972, p 119. (30) R. Aasa and T. Vanngard, J. Magn. Reson., 19, 308 (1975). (31) L. L. Landucci and N. Sanyer, Tappi, 57, 97 (1974); also 58, 60 (1975).
David T. Richens, Donald T. Sawyer* Department of Chemistry. linicersitp of California Ricerside. California 9252 I Receiced Februar), 26, 1979
Water-Soluble Complexes of Tertiary Phosphines and Rhodium(1)as Homogeneous Catalysts' Sir: The low solubility of common phosphine-transition metal complexes in water has inhibited their application to catalytic transformations in aqueous solutions. Recent experiments have established that complexes derived from Ph2P(m-C6H4S 0 3 N a ) 2 are catalytically active in homogeneous olefin hydrogenation and hydroformylation reactions in ~ a t e r . ~ - ~ Complexes derived from bidentate ligands can have useful differences in chemical stability and catalytic activity from analogous complexes containing only monodentate ligands.6 Here we report the development of coupling reactions which permit the facile conversion of (bis(2-diphenylphosphinoethyl)amine ( l)7,sto a wide variety of water-soluble diphosphines
0 1979 American Chemical Society
