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EXAFS STUDY OF SOLUBLE DINITROSYL IRON AND COBALT COMPLEXES CATALYSING SPECIFIC TRANSFORMATIONS OF OLEFINS
D. Ballivet-Tkatchenko, C. Esselin, J. Goulon
To cite this version:
D. Ballivet-Tkatchenko, C. Esselin, J. Goulon. EXAFS STUDY OF SOLUBLE DINITROSYL IRON AND COBALT COMPLEXES CATALYSING SPECIFIC TRANSFORMATIONS OF OLEFINS.
Journal de Physique Colloques, 1986, 47 (C8), pp.C8-343-C8-346. �10.1051/jphyscol:1986868�. �jpa- 00226190�
JOURNAL D E PHYSIQUE
Colloque C8, suppl6ment au n o 1 2 , Tome 47, decembre 1986
EXAFS STUDY OF SOLUBLE DINITROSYL IRON AND COBALT COMPLEXES CATALYSING SPECIFIC TRANSFORMATIONS OF OLEFINS
D. BALLIVET-TKATCHENKO, C. ESSELIN' and J. GOULON'~"
Laboratoire d e Chimie de Coordination du CNRS, 205, Route de Narbonne, F-31000 Toulouse, France
' ~ a b o r a t o i r e de Chimie Theorique, Universite de Nancy-I, U.A. 510 CNRS, BP 239, F-54506 Vandoeuvre-les-Nancy Cedex, France
* *
LURE, L.P. CNRS, MEN, CEA, Universit6 de Paris-Sud, Bdtirnent 2090, F-91405 Orsay Cedex, France
RBsumB
La spectroscopic EXAFS a permls de caract6riser en solution la structure des complexes cationiques dinitrosyles de fer/cobalt, utilis6s comme catalyseurs de la polym6risation des ol6fines. Les spectres EXAFS de leurs pr6curseurs neutres et ceux de compos6s modbles: Fe(NO),[PQ),]Cl, Fe(N01,[PQ3 , ont aussi Bt6 enregistres.
Pour le complexe cationique de fer, les resultats suggdrent une coordination du fer de type bipyramide B base trigonale impliquant trois mol6cules non 6quivalentes de solvant. Dans ce syst6me comme dans son pr6curseur, les groupes nitrosyles devraient &re 16gbrement coud6s.
Abstract
W S spectroscopy has been used in order to characterize in solution the structure of dinitrosyl iron/cobalt cationic complexes catalysing the polymerisation of olefins. W S spectra were also recorded on the inactive precursors of these systems and on relevant model compounds: Fe(NO)2[P43]C1, Fe(NO),[PQ),],. For the cationic iron species, the results are quite consistent with a trigonal bipyramidal coordination of iron implying three non equivalent solvent molecules. In this system as In its precursor, the nitrosyl groups are found slightly bent.
1 flOTIUATIONS
Specific transformations of olefins, e.g. polymerisation, oligomerisation or c~clodimerisation of dienes, can be catalysed in solutlon by soluble metal dinitrosyl complexes, but only after some appropriate activation:
1, by- -~enerat! on-of -cat!on!c-s?ec!esSaccor!!!~- to: [I-21
Solvent -4
1/2 [M(NO) pCl]e ---+ H(N0) ,CISD )- [M(NO) ,Sq I+ BF4-
- &Cl
I S ) (11 121
where S = MeCN. DMF. THF.... and M = Fe, Co. For instance the iron complex O is known to catalyse the polymerisation of styrene, while the cobalt complex 2 can also catalyse but at high temperature the oligomerisation of butadiene.
21 by monoelectronic reduction: [3] . . .
Recently the iron complex was indeed shown to catalyse at room temperature the cyclodimerisation of conjugated olefins.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986868
JOURNAL DE PHYSIQUE
X-ray Absorption Spectroscopy has been used in order to characterize in solution the structure of the solvated species 1, 2, and 3. In this paper we shall restrict our report to the major results obtained by EXAFS on the precursors 1 and the cationic species 2.
I 1 PRECURSORS AND HODEL COHPOUNDSo
EXAFS spectra of the precursors 1 [ M = Fe, Go] in various solvents were collected at L.U.R.E. on the EXAFS-I1 station. As illustrated by figure 1 which reproduces the FT spectra Im[ii,IR)] of 1 IM = Fe) in MeCN and D W , the coordination of the metal is quite identical in these two solvents. It is shown however by figure 2 that the coordinations of iron and cobalt are different for 1 in MeCN.
Details of the I.R. spectra susgest that this result could be explained - - by fast exchanges :
ColNO) , IMeCNI. . ' [GofNO),fMeCN),,, ]+ C1- MeCN
I
Figure 3 : FT spectra of :
4 = Fe(N0)2(P@3)C1 and 5 = Fe(No)2(P@3)2
Figure 4 : Comparison of the FT spectra of 1 (Fe / MeCN) and 4 .
The EXAFS spectra of reference compounds of known crystal structure: 4 = Fe(N0) ,[PcS3 JC1 and 5 = FelNO) ,[PO3 I, were also recorded. Their FT spectra Im[ii, (R) ] are displayed in figure 3, whereas the FT spectra of 1 M Fe;S = MeCN] and 4 are directly compared in fi ure 4. It is noteworthy that ail if these FT spectra were implicitly corrected [ 4 7 in the same way, using standard phase shifts and amplitude functions relevant to the first coordination shell, 1.9. the nitrogen atoms of the
nitrosyl groups. Indeed in all of these F'T spectra, the first peak can be unambiguously assigned to these nitrogen atoms and it is well enough resolved to make possible accurate determinations of the M...N bond lengths (table 1).
table 1 R IFe.. .N)
1 ( S = HeCN) 4
5
The signatures of the oxygen atoms of the NO groups can also be easily assigned.
However as the sequence M. .. N. ..O is either quasi linear or only slightly bent, multiple scattering paths and focusing effects are expected to affect these signatures and preclude accurate direct determinations of the M. ..O distances.
Typically the phase of the signal is inverted whereas the amplitude enhancement factor is critically dependent upon the H N 0 angle. A direct comparison suggests
(figure 3/41 that in the precursor 1 the nitrosyl ligand should be slightly bent (N N 0 < 165O). Refined multiple scattering calculations taking into account all vibrational modes and disorder effects are in progress.
111 CATIONIC SPECIES.
The W S spectra of the cationic species 2 [M = Fe, Co, S = MeCN] were recorded on freshly prepared solutions i.e. shortly after production of these active species. Their spectra and thoke of the relevant precursors 1 are compared in figures 5/6. The results are consistent with the exchange of the chlorine atom with at least one solvent molecule. Here again the coordinations of iron and cobalt are obviously different (q = 3 for Fe; q 2 for Col as illustrated by the relative intensities of the M...N (solvent) pealts observed at ca. 2.1 A and which are to be compared to the M...N (NO groups] signals.
EXAFS 1.69 * 0.01 A
1.67, + 0.01 A 1.64, + 0.01 A
Figure 5 : Comparison of the FT Figure 6 : Comparison of the FT spectra of 2 and 1 (M=Fe /MeCN) spectra of 2 and 1 (M = Co / MeCN)
As regards 2 [ M = Fe], chan e in the geometry of the NO group can be at the FT differentdial spectrum 2 - 1 detected.Thus it makes sense t w
reproduced in figure 7: specific signatures characteristic of coordinated MeCN molecules are unambiguously detected. If one substracts now from the original data the fitted contribution of the Fe . . . N (NO groupsl signal, one is left (figure 81 with an as mmetrical signal supporting the probable coordination of q = 3 non e uivalen& mo eeules. A quite reasonable fit was generated for one t i g n
d moF:culel at R[Fe ... NI = 2.0 R ( G ~= 0.0014 A 1 and two more loosely Cryst. struct.
---
1.68. A 1.65, A
bound solvent molecules at R(Fe ... N) = 2.1 A ( ~ ~ = 0 . 0 0 4 5 A ~ ) . S u c h s m a l l differences in bond lengths fall below the resolution capability of the technique and it is difficult to ascertain whether the proposed solution is unique. It is however quite consistent with the trigonal bipyramid structure which was recently roposed for this radical cation on the basis of ESR spectra and EHMO calculations
f71.
Fe N 0 ( 5 165O)
166O 178O
References this work
1 2 3
CS-346 JOURNAL DE PHYSIQUE
n W I E R SUBTPACTIC4 OF THE
F1(10l2 (bO1)a 1.) D DIIIITRmn Ft..II SHELL 1
Figure 7 : FT differential spectrum of Figure 8 : Contribution of the 2 - 1 (M = Fe , S = MeCN) solvent molecules MeCN in the
coordination of iron.
IU FURTHER DEUELOPHENTS.
Our efforts are now directed towards the characterization of 3 and related complexes.0n the other hand, details of the e d g e / W S spectra are consistent with a noticeable increase of the effective charge of iron in species i! with respect to its inactive precursor 1. The larger electrophilic character of i! might thus explain its catalytic activity. A continuation of such E X A F S / M S investigations should help us to define the driving force which permits a selective orientation of the catalytic polymeri sation.
References.
[I] D. BALLIVET-TWrTCHENKO and I . TKATCHENKO Inorg. Chem. 16, 945 (1977)
[2] D. B A L L I W - T K W 3 E N K O 0 C. BILLARB and A. W I L L O N J.Polymer Sci. 19, 1697 (1981)
[3] D. BALLIIIET-WXTCHENKO, M. RIVECCIE and N. El MURR J. Am. Chem. Soc. &,3 2763 (19791
[4] J. CiOULON and C. WULON-GINET Pure 8r Appl. Chem. 2 , 2307 119821
KOPF and J. SCHMIDT Naturforsch. g , 149
[ 6 ] V.G. AL.BAN0, A. -0, P.L. BELLON, G. GIANI and M. HANASSERO J.0rganometall. Chem. 67, 413 11974)
[7] D. BALLIVET-TKf.ITCHENK0, B. NICKEL, A. WlSSAT and J. VINCEW-VAUQUELIN Inorg. Chem. (in press.)
