Cobalt and iron complexes of 2,3-quinoxalinedithiol

Notes

3579

of triphenylphosphine by Pt(PPha)a [11]. We also found that there was no catalytic oxidation ofparatolylisonitrile to the corresponding isocyanate at 40 ° in benzene or at 75 ° in toluene by Ru(PPha)3CI,, stable yellow Ru(PPha)z(RNC)2C12 being recovered from the solutions. This emphasizes the importance of a labile coordination of the substrate to the catalyst, in order to have an unsaturated catalytic centre. We have also carried out an investigation into the catalytic oxidation of cyclohexene by Ru(PPha) aCI2, this substrate being the object of a previous investigation with catalysts such as Rh(PPha)aCI or Pt(PPha)3 [12]. As in the preceding work, we found that the oxidation of cyclohexene at 60 ° and l atmosphere of oxygen pressure, is a radical reaction. In fact ~x-naphtoi inhibits the reaction, while the product distribution is typical of a free radical chain process [ 13]. The major reaction products are 2-cyclohexen-l one, 2-cyclohexen-l-ol, cyclohexene oxide and non volatile polymers. What we found interesting is that with peroxide-free cyclohexene, only a small induction period was detected, while catalysts such as trans-lrCICO(PPha)z requires nearly two hours before the oxidation starts[12]. This was interpreted in the latter case as the time required for the formation of small amounts of hydroperoxide by the thermal reaction with oxygen. It follows that Ru(PPh3)3Cl 2 has either a large effect on the decomposition of preformed hydroperoxide, or does not simply act as a generator of organic radicals. Work is in progress to elucidate these problems.

Acknowledgements - We wish to thank Italian C.N .R. for financial support and Engelhard S.P,A. for a loan of ruthenium.

lnstituto di Chimica G enerale Via Venezian 21-20133 Milano Italy

S. CEN IN 1 A. FUSI G. C A P P A R E L L A *

*Present address: Montecatini-Edison S.P,A., Centro di Ricerche di Bollate, Milano, Italy. 11. R. Ugo, Engelhard Tech. Bull. XI, 45 (1970); and references therein. 12. A. Fusi, R. Ugo, F. Fox, S. Pasini and S. Cenini,J. organometal. Chem. 26,417 (1971). 13. D. E. Van Sickle, F. R. Mayo and R. M. Aduck, J. Am. chem. Soc. 87, 4824 (1965).

J. inorg,nucl.Chem., 1971,Vol.33, pp. 3579to 3581. PergamonPress. Printedin Great Britain

Cobalt and iron complexes of 2,3-quinoxafinedithiol (Received 22 February 1971) RECENT investigations of cobalt and iron dithiolenes have revealed many complexities in the systems and also interesting physical properties. Here we wish to report the isolation and characterization of some new cobalt and iron dithiolenes with the ligand 2,3-quinoxalinedithiol. EXPERIMENTAL

Preparation of compounds 2,3-Quinoxalinedithiol was prepared as previously reported [l]. [n-Bu4N]2[Co(QDT)2]. lg of metallic sodium was dissolved in 100ml of methanol, 3.88g of 2,3-quinoxalinedithiol were added and to the filtered solution, 1-19g of COC12.6H20 dissolved in 30 ml of ethanol, were added slowly. The solution was stirred for 10 rain under a nitrogen atmosphere. The solution was then filtered under nitrogen. To the filtrate, 6.44g of n-Bu4N*Br- were added and stirred for 5 min. Water containing about l per cent of NHa was added slowly until precipitation started. I. L. J. Theriot, K. K. Ganguli, S. Kavarnos and I. Bernal, J. inorg, nucl. Chem. 31, 3133 (1969).

3580

Notes Table 1. Properties of metal complexes

Complex

M.P. (°C)

A

[n-Bu4N]2[Co(QDTh]

115

127"

[n-Bu4N]3[Co(QDT)3]

198-9

159"

[(C,Hs)4As]2 [Fe(QDT)3]

161-2

122"

E,~2 (V) 0.125 (CH~CN) 0-56 (DMSO) +0.31 (CH3CN)

/zen (B.M.T°K)

Band maxima (cm -1, c)

2-40(300 ° )

9,850(40) 11,970(295) 16,800(70) 20,000(863) 13,106(2170) 17,094(2700sh) 20,127(7460)

DIA 3.02(299)

*Obtained at room temperature in nitromethane; results expressed as cmZohm-'mole -1. The resulting solution was left under nitrogen for 15 rain and filtered. The black precipitate obtained was dissolved in methanol under nitrogen. Water containing 3 per cent NHa was added slowly until precipitation started. The black precipitate obtained was filtered and washed with water several times. A final washing was performed with 10ml of ethanol. Caic.: C, 62-14; H, 8.63; N, 9-06; S, 13'81. Found: C, 61.60; H, 8.78; N, 9-61; S, 14.88. [n-Bu4N]a [Co(QDT)3]. 2,3-Quinoxalinedithiol (4-85g) was added to a solution of sodium methoxide obtained from 2g of metallic sodium in 150ml of methanol. To the solution 3.02g of Na3[Co(CO3)3] "3H20 were added slowly over a period of 30 min with constant stirring. The solution was filtered and 8.06g ofn-Bu4N+Br - were added to the solution. Water containing 1 per cent NH3 was added slowly and left overnight. The orange colored crystalline precipitate was recrystallized from methanol and water. The product was filtered and dried at 60°C under vacuum for 12 hr. Caic.: C, 63.48; H, 8.82, N, 9.26; S, 14.11. Found: C, 62.40; H, 8.97; N, 9-63; S, 14.84. [(CeHs)4As]z[Fe(QDT)3]. 0.76g of sodium was dissolved in 40ml of methanol. 2.92g of 2,3quinoxalinedithiol was added to the solution followed by 1.08g of FeC13'6H20 and finally, 4.18g of Ph4AsCI.HC! were added to the green solution. A green precipitate formed which was filtered, washed with water, methanol, ether and air dried. Calc.: C, 61.8; H, 3.75; N, 5.99; S, 13.70. Found: C, 61.8; H, 3.90; N, 5.47; S, 12.89.

Physical measurements Electronic spectra were obtained with a Cary 14 recording spectrophotometer using spectral grade acetonitrile and solid spectra were obtained by using Nujol mulls supported on filter paper. Conductivities were determined on an Industrial Instrument Serfass Bridge, Model RCM 15BI using a standard dip type microcell whose cell constant was determined using aqueous 0.01M KCI solution. Polarograms were obtained with a Sargent Model XV recording polarograph. Potentials were measured relative to an aqueous calomel electrode saturated with KCI. A rotating platinum electrode was used as indicating electrode. Solutions were 10-aM in complex and 0.05M in tetra-n-butyl ammonium perchlorate as a supporting electrolyte. Magnetic susceptibilities were measured on solid samples by the Gouy method using HgCo(NCS)4 as standard. RESULTS AND DISCUSSION 2,3-Quinoxalinedithiol, which is of considerable interest in the analysis of various metals[2], is known to exist largely in the dithione form [3]. Therefore, the isolatable complexes are restricted to metals which can exist in the basic conditions necessary for syntheses. The complex [n-Bu4N]2 [Co(QDT)2] has a magnetic moment of 2.4B.M. which suggest a spin doublet ground state. This result is in agreement with other cobalt dithiolenes species studied since an authentic spin quartet is, thus far, unknown for dianionic planar species. Attempts to isolate an oxidized product have not resulted in analytically pure complexes~ The complex [n-BUAN]3[Co(QDT)a] is diamagnetic after 2. R.W. Burke and E. R. Deardorff, Talanta 17,255 (1970). 3. G. W. H. Cheesman, Advances in Heterocyclic Chemistry (Edited by A. R. Katritzky, J. M. Lagowskii and A. J. Boulton), Academic Press, New York (1963).

Notes

3581

r.i,p, corrections in agreement with low spin cobalt(Ill) octahedral complexes. The first spin allowed transition at 16,800 cm -t does not occur at the same energy as that of [n-Bu4N]2[Ni(QDT)~] which has an absorption band[l] at 11,300 cm -1. This seems to be the case with dithiolenes though the correlation works fairly well with dithiocarbamates, 1,1-dicyanoethylene-2,2-dithiolates and dithiooxalates [4]. The complex is presumably octahedral and the electronic spectrum compares closely with that of [Co(MNT)3]~-[4, 5]. The extinction coetticients are however lower in this case. The magnetic properties (/~ = 3-02B.M.) of [(CeHs)4As]2 [Fe(QDT)3] suggest a spin triplet ground state. The spectral and magnetic properties are similar to [(C~Hs)4As]2[Fe(MNT)3] for which a trigonally distorted octahedral structure is reported [8]. The intensities of the visible-u.v, bands of the tris dianionic iron species are considerably greater than those of the tris trianionic cobalt species, as has been found for other dithiolenes [4, 5]. A c k n o w l e d g e m e n t s - T h i s study was supported by The Robert A. Welch Foundation and the N.T.S.U. Faculty Research Fund. K. K. G A N G U L I G. O. C A R L I S L E H. J. HU L. J. T H E R I O T I. B E R N A L

Chemistry Department North Texas State University Denton, Texas 76203 Brookhaven National Laboratory Upton, N e w York 11973 U.S.A.

4. J. A. McCleverty, J. Locke and E. J. Wharton, J. chem. Soc. A, 816 (1968). 5. E. I. Stiefel, L. E. Bennett, Z. Doff, T. H. Crawford, C. Simo and H. B. Gray, lnorg. Chem. 9, 281 (1970). 6. W.C. Hamilton and I. Bernal, lnorg. Chem. 6, 2003 (1967). 7. A. D. Balch, I. Dance, and R. H. Holm, J. Am. chem. Soc. 90, 1139 (1968). 8. I. Bernal and A. Sequeira, In press.

J. inorg,nucl.Chem., 197I, Vol.33, pp. 3581to 3586. PergamonPress. Printedin Great Britain

The kinetics of the formation of cobalt(IH) products from the cobalt L-histidine and L-lysine oxygen carriers (Received 24 February 1971 )

COBALT(II) complexes of histidine, lysine and many other amino acids have been found to absorb molecular oxygen [ 1-8]. Oxygen absorption to form the complex with two cobalt atoms per 02 unit has been found to be a two step process[2,9-10]. First CoL.O2 (L-amino acid anion) forms and then 1. J. Z. Hearon, D. Burk and A. L. Schade, J. Natl. Cancer Inst. 9,337 (1949). 2. J. Simplicio and R. G. Wilkins, J. A m. chem. Soc. 89, 6092 (1967). 3. A. G. Sykes and J. A. Well, Progress in Inorganic Chemistry, Vol. 13, pp. 1-106. Interscience, New York (1970). 4. L.J. Zompa, C. S. Sokol and C. H. Brubaker, Jr., Chem. Commun. 701 (1967). 5. C. Tanford, D. C. Kirk,Jr. and M. K. Chantooni, Jr., J. Am. chem. Soc. 76, 5325 (1954), 6. J. B. Gilbert, N. C. Otey and V. E. Price, J. biol. Chem. 190, 377 (1951). 7. V. Caglioti, P. Silvestroni and C. Furlani, J. inorg, nuel. Chem. 13, 95 (1960). 8. M.T. Beck, Naturwiss enschaften 45, 162 (1958). 9. J. Simplicio and R. G. Wilkins, J. Am. chem. Soc. 91, 1325 (1969). 10. F. Miller, Jr. Simplicio and R. G, Wilkins,J. Am. chem. Soc. 91, 1962 (1969).