Preparative, structural, and electrochemical investigations on peralkylated niobocene dichlorides and difluorides

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urn:nbn:de:bvb:355-epub-230179 Copy

Brunner, Henri ; Gehart, G. ; Meier, Walter ; Wachter, Joachim ; Riedel, Astrid ; Elkrami, S. ; Mugnier, Y. ; Nuber, B.

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Date of publication of this fulltext: 03 Jan 2012 08:34

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Item type:	Article
Journal or Publication Title:	Organometallics
Publisher:	American Chemical Society (ACS)
Volume:	13
Number of Issue or Book Chapter:	1
Page Range:	pp. 134-140
Date:	1994
Institutions:	Chemistry and Pharmacy > Institut für Anorganische Chemie > Alumni or Retired Professors > Arbeitskreis Dr. Joachim Wachter
Identification Number:	Value Type 10.1021/om00013a023 DOI
Dewey Decimal Classification:	500 Science > 540 Chemistry & allied sciences
Status:	Published
Refereed:	Unknown
Created at the University of Regensburg:	Unknown
Item ID:	23017

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Abstract

CP(dagger)2NbCl2 (CP(dagger) = 175-C5Me4Et) (1b) was synthesized from NbCl5 and a slight excess of Cp(dagger)Li and NaBH4. Its electrochemical (2 e-, E1/2 = -1.6 V) and chemical reduction (2 equiv of Na/Hg) was studied showing that peralkylation of the Cp ligand facilitates two-electron reduction compared to less substituted CP2NbHal2 derivatives. The reduced solutions of CP*2NbCl2 (CP* = C5Me5) ...

Abstract

CP(dagger)2NbCl2 (CP(dagger) = 175-C5Me4Et) (1b) was synthesized from NbCl5 and a slight excess of Cp(dagger)Li and NaBH4. Its electrochemical (2 e-, E1/2 = -1.6 V) and chemical reduction (2 equiv of Na/Hg) was studied showing that peralkylation of the Cp ligand facilitates two-electron reduction compared to less substituted CP2NbHal2 derivatives. The reduced solutions of CP*2NbCl2 (CP* = C5Me5) (1a) and of lb were shown by means of EPR spectroscopy to contain two new paramagnetic species 1A,B for which bent niobocene (A(Nb) = 100 G) and fulvene-like structures (A(Nb) = 55 G) are proposed. The high reduction potential of these species led in their reaction with HPF6 to the first stable difluoroniobocene derivative, [CP(dagger)2NbF2]PF6 (2), in good yield. The molecular structures of 2 and a cocrystallizate of 2 and [CP(dagger)2NbCl2]PF6 (3), analyzing as [CP(dagger)2NbCl(Cl,F)]PF6 (4), were studied by X-ray diffraction techniques. Comparison with the structure of 1b shows a marked decrease of the angle Hal-Nb-Hal from 102.3(4)-degrees (2) to 85.2(1)-degrees (1b). Electrochemical 1 e- reduction of 2 gave rise to the formation of CP(dagger)2NbF2, which exhibits a much lower potential (E1/2 = -2.38 V) than other niobocene dihalides. Reaction of 2 with Li2S2 gave CP(dagger)2Nb(eta-S2)F, whereas 3 was reduced by Li2S2 to give 1b.

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