Monomeric oxygen adducts of some cobalt(II)-schiff base complexes

INORG.

NUCL.

CHEM. LETTERS

Vol. 7, pp. 901-904,

1971.

Pergamon

Press. Printed in

Great

Britain.

MONOMERIC OXYGEN ADDUCTS OF SOME COBALT( II )-SCHIFF BASE CDMPLEXES E.W. Abel, J.M. Pratt and R. Whelan Department of Inorganic Chemistry, The University, Bristol BS8 ITS, Eng~land. Imperial Chemical Industries Limited, Petrochemical & Polymer Laboratory, P.O. Box ll, The Heath, Runcorn, Cheshire. (Received 28 May 1971)

It has been known for some time that cobalt(II) Schiff base complexes react with oxygen. 1

Renewed interest in these reactions has led to the

recent discovery of additional binuclear and mononuclear adducts (see, for example, refs. 2-6).

The latter complexes are paremagnetic and their

electron spin resonance (e.s.r.) spectra show characteristics which suggest that the unpaired electron is located mainly on the 02 moiety, i.e. the complexes are best described as cobalt(Ill) species coordinated to a superoxide anion (02-). Bayston et al. 3 have studied the effect of changing the second axial ligand (X) on the e.s.r, parameters of the cobalt corrinoid oxygen adduct, and have shown that the 59Co coupling constants (x i04 cm-I) vary with the nature of X, e.g. cyanide (8.9 and ii.i), pyridine (12.1 and 15.4), methanol (14.9, 18.4).

We have been

interested in the effect of changing the equatorial ligand on these parameters and report here an e.s.r, study of the monomeric o~jgen adducts of cobalt(ll) complexes containing ligands related to N,N'bis(salicylidene)ethylenediamine (salen). In order to observe thc effect of various changes (noted in brackets) in the structure of the equatorial ligand, cobalt(ll) cozplexes were prepared

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902

MONOMERIC OXYGEN ADDUCTS

Vol. 7, No. 9

by known methods with the following ligands in their anionic form:

N,N'-bis-

(s all cylidene )-ethylenedi amine or s alen I ; N ,N '-bi s (4,6-dimethyls all cylidene )ethylenediamine or h,6-dimethylsalen 7 (substituents in aromatic ring); N,N '-his (salicylidene)-ortho-phenylenediamine or s aloph 8 (increase in conjugation within the equatorial ligand) ; N,N'-bis(2-hydroxyl-l-naphthylmethylene)-ethylenediamine or napsalen and N,N'-bis(2-hydroxyl-l-napthylmethylene)-ortho-phenylenediamine or napsaloph 8 (increase in aromaticity of equatorial ligand);

and N,N'-bis(orthoaminobenzylidene)-ethylenediamine or

amben 9 (substitution of N202 donor group by N4). Monomeric oxygen adducts of Co(ll) salen and Co(II) saloph are already known. ~'5

Adducts of complexes containing the other ligands were prepared

as follows : Fresh solutions of the Co(ll) species were prepared in fully deoxygenated methylene chloride/pyridine (i:i).

Oxygen was passed through these solutions

for 10-20 secs. at ambient temperatures and the solutions were frozen immediately to -175°C.

E.s.r. spectra were recorded both at this temperature

and at -70°C in fluid solution.

The formation of the oxygen adducts was

found to be reversible (02 removed by evacuating or flushing the solutions with nitrogen below room temperature). All the solutions showed e.s.r, spectra characteristic of monomeric oxygen adducts, i.e. eight hyperfine lines associated with both the g

l and g ~ a n d s

due to interaction with a single 59Co nucleus. 3

Since the

presence of a nitrogeneous base co-ordinated in the second axial position trans to the 02- ligand does not give rise to nitrogen hyperfine structure, 3 the presence or absence of co-ordinated pyridine cannot be established. The tabulated results show that the e.s.r, parameters (including the

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59Co coupling constants) are relatively insensitive to these changes in the structure of the equatorial liGand, even when the four co-ordinated atoms are changed from N202 (e.g. salen) to N~ (amben).

This contrasts with the

great sensitivity to a change in the single axial ligand in the transposition (e.g. from methanol to pyridlne), observed in the corrino~ds.

(1947).

i.

R.H. BAILES and M. CALVIN, J.Amer.Chem.Soc., 69, 1886

2.

C. FLORIm~I and F. CALDERAZZ0, J.Chem.Soc.(A), 946 (1969).

3.

J.H. BAYSTON, N.K. KING, F.D. LOONEY and M.E. WINFIELD, J.Amer.Chem.Soc., 91, 2775 (1969).

4.

B.M. HOFFM~, D.L. DIEMENTE and F. BASOLO, J.Amer.Chem.Soc., 92, 61 (1970).

5.

S.A. COCKLE, H.A.O. HILL and R.J.P. WILLIAMS, Inorg.Nucl.Chem.Letters, 6, 131 (1970).

6.

E.W. ABEL, J.M. PRATT and R. WHELId~, Chem.Cozm., 1971, hhg.

7.

G.L.P. RANDALL, Unpublished results.

8.

J. BOOTH, P.J. CRAIG, B. DOBBS, J.M. PRATT, G.L.P. RA~DALL and A.G. WILLIAMS, J.Chem.Soc.(A), 1971, in press.

9.

M. GREEN and P.A. TASKER, J.Chem.Soc.(A), 3105 (1970).