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Experimental and Theoretical Study of Hyperfine Coupling of Vanadocene Complexes

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Experimental and Theoretical Study of Hyperfine Coupling of Vanadocene Complexes UNIVERSITY OF PARDUBICE FACULTY OF CHEMICAL TECHNOLOGY DEPARTMENT OF GENERAL AND INORGANIC CHEMISTRY EXPERIMENTAL AND THEORETICAL STUDY OF HYPERFINE COUPLING OF VANADOCENE COMPLEXES Annotation of the PhD Degree Thesis AUTHOR: Ing. Jan Honzíček SUPERVISOR: Doc. Petr Nachtigall, PhD. 2005 - 1 - The PhD degree Thesis was carried out at Department of General and Inorganic Chemistry of University of Pardubice in years 2002-2005. Candidate: Ing. Jan Honzíček Reviewers: The PhD Thesis will be defended at University of Pardubice in face of Commission for Defending Doctoral Thesis chaired by............................ on.............................. 2005. The PhD Thesis will by available to those interested in the central library of University of Pardubice. - 2 - 1. Introduction Metallocene complexes of the type Cp2MX2 (M = early transition metal; X - halide, pseudohalide) are currently largely investigated due to their biological [1, 2] and catalytic activity [3, 4]. Currently known studies show that such activity is closely connected with the metallocene complex structure [5, 6]. X-ray structure analysis and spectroscopic methods are useful for the structure investigation. X-ray analysis can be used only for single crystals of the compounds. The isolation of the compounds in the solid state and preparation of the single crystal is sometimes very is difficult or impossible. Therefore spectral methods are often used for structure investigation. NMR spectroscopy cannot be used for paramagnetic compounds therefore the interpretation of vibration spectra are in point of the interest. Infrared and Raman spectra give important information about the structure of the metallocene complexes. Based on such methods it is possible to find out the presence of the metallocene fragment with two η5-bonded cyclopentadienyl rings [7]. This work is attended especially for the study of vanadocene complexes by EPR 51 7 spectroscopy. The presence of the magnetic active nucleus ( V, I = /2, 99,8 %) causes the hyperfine coupling (HFC) that is very sensitive to changes in the coordination sphere of the central metal. Some problems occurs with the assignment of the obtained EPR parameters to the concrete species, when the particular structure is not known from another experimental technique. Such problems can be solved by theoretical calculations. Recently, EPR parameters of some 3d-metal compounds were theoretically investigated at the DFT level of the theory [8-12]. - 3 - 2. Results and Discussion 2.1 Synthesis and Vanadocene Complexes Metallocene complexes of the type Cp2VX2 and Cp'2VX2 (X = NCO, NCS, N3, CN, 5 5 dca, tcm, dcnm; Cp = η -C5H5, Cp' = η -CH3C5H4, Scheme 1), were prepared by reaction of vanadocene dichloride with the large excess of the sodium or potassium salt of the corresponding pseudohalide. R R Cl X V + NaX (KX) V + NaCl (KCl) Cl X R R 1a: R = H 2a: R = H X = NCO 2b: R = CH3 X = NCO 1b: R = CH 3a: R = H X = NCS 3 3b: R = CH3 X = NCS 4a: R = H X = N3 4b: R = CH3 X = N3 5a: R = H X = CN 5b: R = CH X = CN 6a: R = H X = dca 3 6b: R = CH X = dca 7a: R = H X = tcm 3 7b: R = CH X = tcm 8a: R = H X = dcnm 3 8b: R = CH X = dcnm 3 Scheme 1 Synthesis of pseudohalide complexes. Monosubstituted derivatives (Cp2VClX) are formed by ligand-exchange reaction. The EPR spectra measurements show that all prepared complexes are contaminated with disubstituted compounds (Scheme 2). Only complex Cp2VCl(tcm) (7c) was successfully separated from complex 7a by extraction, because these complexes show very different solubility in organic solvents. Cl Cl tcm V + Na(tcm) V + V +NaCl Cl tcm tcm 1a 7c 7a Scheme 2 Reaction of complex 1a with Na(tcm). - 4 - Complexes of carboxylic acids Cp2VX2 a Cp'2VX2 (X = OOCH, OOCCCl3, OOCCF3; 5 5 X2 = (OOC)2, (OOC)2CH2; Cp = η -C5H5, Cp' = η -CH3C5H4; Scheme 3), were prepared by reaction of vanadocene dichloride with corresponding carboxylic acid. R1 O R1 9a: R = H R = H R2 1 2 RCOOH O 10a: R = H R = CCl Cl 1 2 3 V V + HCl Cl O 11a: R1 = H R2 = CF3 R 2 9b: R = CH R = H R 1 3 2 1 R O 1a: R = H 1 10b: R1 = CH3 R2 = CCl3 11b: R = CH R = CF 1b: R = CH3 1 3 2 3 HOOC A COOH R 1 O 12a: R1 = H A = O 13a: R = H A = CH V A 1 2 O 12b: R1 = CH3 A = O 13b: R1 = CH3 A = CH2 R1 Scheme 3 Synthesis of carboxylic acid complexes 2.2 X-ray structures The structures of the complexes Cp'2V(NCO)2 (2b), Cp2V(NCS)2 (3a), Cp2V(N3)2 (4a), Cp2V(dca)2 (6a), Cp'2V(dca)2 (6b), Cp2VCl(tcm) (7c), Cp'2V(dcnm)2 (8a), Cp2V(OOCCCl3)2 (10a), Cp'2V(OOCCF3)2 (11b) and Cp2V(OOC)2 · 0.5(COOH)2 (12a) were determined by X-ray diffraction analyses. Complexes have typical bent metallocene structure with two η5-bonded Cp (Cp') rings and two donor atoms of other ligands around the vanadium(IV) center. The substitution of chloride ligands does not change the geometric parameters of the vanadocene moiety (Cg- V 1.95-1.98 Å, Cg-V-Cg 133-136°). 1,1'-dimethyl substituted complexes show different location of methyl groups. Complex Cp'2V(NCO)2 (2b) has one methyl group bellow the X–V–X moiety and the second one at the side (Fig. 1a). Complexes Cp'2V(dca)2 (6b) and Cp'2V(dcnm)2 (8b) have methyl groups above and bellow the X–V–X moiety (See Figs. 2b and 3b, respectively). The methyl groups of the compound Cp'2V(OOCCF3)2 (11b) are positioned at the opposite sides of the molecule, directed away from each other (Fig. 4b). - 5 - a) b) C1 C2 C16 C12 C5 C4 C13 C11 S1 C11 C3 N1 C15 O1 V1 C14 N1 C1 V1 N2 C7 C25 S2 C12 N2 C2 O2 C6 C24 C21 C10 C8 C23 C9 C22 C26 c) C6 C7 N6 C10 N5 C9 C8 N4 N1 V1 N2 N3 C3 C5 C1 C2 Fig. 1 X-ray structure of the complexes: a) Cp'2V(NCO)2 (2b); b) Cp2V(NCS)2 (3a); c) Cp2V(N3)2 (4a). The results of X-ray structure analyses show that pseudohalide ligands are bonded via nitrogen atom to the vanadocene moiety in compounds 2a, 3a a 4a (Fig. 1). The bond distances V–N were found in narrow range from 2.03 to 2.08 Å. Complexes Cp2V(dca)2 (6a) and Cp'2V(dca)2 (6a) have both bent dca ligands bonded via terminal nitrogen atom (V–N = 2.04 - 2.05 Å). The geometry of dca ligands are affected by coordination to vanadium(IV). Although the coordinated and non-coordinated C≡N bond lengths is the same (1.145(3) - 1.157(2) Å), the N–C bonds beside coordinated cyano-groups are significantly shorter ([1.286(3) - 1.301(3) Å] than beside non- coordinated groups [1.308(3)-1.322(3) Å]. Such distortions can be explained by two possible resonance structures, see Scheme 4. - 6 - a) b) N10 N10 C9 C25 C24 C22 C26 C9 C23 C21 N8 N8 C25 C7 C21 N6 C7 C23 N6 C22 C24 V1 V1 N5 N1 C13 N1 C4 C2 C14 C2 N3 C12 C13 N3 C4 C15 C11 N5 C14 C11 C15 C12 C16 Fig. 2 X-ray structures of the complexes: a) Cp2V(dca)2 (6a); b) Cp'2V(dca)2 (6b). O- O- N N N N N N N N O- O- N N N N N N O- O O O- N N N N Scheme 4 Resonance structures of non-linear pseudohalides. The unit cell of the compound Cp2VCl(tcm) 7c consists of four crystallographically independent but essentially the same molecules. One of them is shown in the Figure 3a. The planar tcm ligand is bonded to the vanadocene moiety through the nitrogen atom. The bond distances V–N (2.054(3) - 2.071(4) Å) are comparable with dca compounds 6a and 6b. The geometry of planar tcm ligand shows significant distortions that can be explained in similar way as for dca complexes. Two possible resonance structures are depicted in Scheme 4. The contribution of second resonance structure causes significant contraction of C-C bonds that are beside coordinated cyano-groups (C-C = (1.387(6) - 1.400(6) Å). The C-C bond that are positioned beside non-coordinated cyano-groups were found in the range - 7 - from 1.399(8) to 1.1414(6) Å. The bond distances of the cyano-groups are not affected by coordination (C≡N = 1.144(6) to 1.159(5) Å). a) b) N2 C8 C48 C49 C6 C7 N42 C9 C2 C1 N3 C410 N1 C47 C46 C413 C3 C5 C4 O1 C412 V1 V4 Cl4 N41 C411 O1a C41 C45 C414 C44 C43 C42 C43 Fig. 3 X-ray stuctures of the complexes: a) Cp2VCl(tcm) (7c); b) Cp'2V(dcnm)2 (8b). Complex Cp'2V(dcnm)2 (8b) have two planar dcnm ligands bonded via oxygen atoms of nitroso groups to the Cp'2V moiety (V–O = 2.035(1) Å, O–V–O = 74.78(5)°). The dcnm ligands were found in one plane with vanadium atom (Pldcnm-PlO1VO1a = 4.81(5)°). a) b) C4 C5 C6 C3 F2A C1 C2 C1 F1A C5 C2 C8 F3A V1 O1 C4 C7 O1' C3 O1 V1 O2 C6 C7 O1' Cl3 O2 Cl2 Cl1 Fig. 4 X-ray structure of the complexes: a) Cp2V(OOCCCl3)2 (10a); b) Cp'2V(OOCCF3)2 (11b).
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