ORIGINAL PAPER Electrochemical and spectral properties of some tantalocene derivatives with one pentamethylated cyclopentadienyl ligand: Cp*(Cp-R)TaCl 2 , R = H, SiMe 3 or (CH 2 ) 3 NC 4 H 4 Mikhail A. Vorotyntsev & Magdalena Skompska & Magdalena Graczyk & Jürgen Heinze & Jerome Goux & Pierre Le Gendre & Claude Moise Received: 24 January 2007 / Revised: 6 May 2007 / Accepted: 31 May 2007 / Published online: 21 September 2007 # Springer-Verlag 2007 Abstract Three tantalocene dichloride complexes, Cp* (Cp-R)Ta(IV)Cl 2 , with one pentamethylated cyclopenta- dienyl ligand, Cp* = η 5 –C 5 Me 5 , Me = CH 3 , and one monosubstituted cyclopentadienyl ligand, Cp-R, Cp = η 5 –C 5 H 5 , R = H, SiMe 3 or (CH 2 ) 3 NC 4 H 4 , have been studied in acetonitrile solutions with cyclic voltammetry in the ranges of the Ta(IV) oxidation to Ta(V) or of its reduction to Ta(III). The former transition is reversible, while the latter one gives an irreversible wave due to the dissociation of the reduced complex with the loss of one chloride ligand. The redox transformation from the initial state of complex Cp*CpSiMe 3 TaCl 2 to its oxidized state, Cp*CpSiMe 3 TaCl 2 + , and back was monitored by spectroelectrochemical mea- surements in a thin-layer acetonitrile solution. Kinetic data for the evolution of the UV-visible spectrum of the system in the course of the double potential step experiment were treated on the basis of two theoretical models as the reactant diffusion across the solution layer without or with taking into account ohmic losses. The values of the diffusion coefficients of the complex in its initial and oxidized (cationic) states have been estimated. It was demonstrated that this complex in each of two oxidation states, Ta(IV) or Ta(V), is represented by a single molecular form. An attempt to deposit a conducting polymer film by oxidation of the tantalocene complex containing a pyrrole group attached to the Cp ring, Cp*Cp(CH 2 ) 3 PyTaCl 2 , led to a thin insulating layer at the electrode surface because of an inhibiting effect of chloride anions. Keywords Tantalum . Metallocene . Pentamethylated tantalocene complexes . UV-visible spectra . Spectroelectrochemistry . Redox transition . Thin layer voltammetry and chronoamperometry . Diffusion coefficient . Ohmic potential drop Abbreviations AN acetonitrile THF tetrahydrofuran DCM dichloromethane TBAPF 6 tetrabutylammonium hexafluorophos- phate (C 4 H 9 ) 4 NPF 6 Cp cyclopentadienyl ligand, η 5 –C 5 H 5 Cp* pentamethylated cyclopentadienyl li- gand, η 5 –C 5 Me 5 , Me = CH 3 Cp*CpTaCl 2 tantalocene dichloride complexes: (η 5 –C 5 Me 5 )(η 5 –C 5 H 5 )TaCl 2 Cp*CpSiMe 3 TaCl 2 (η 5 –C 5 Me 5 )(η 5 –C 5 H 4 SiMe 3 )TaCl 2 Cp*(Cp(CH 2 ) 3 Py)TaCl 2 (η 5 –C 5 Me 5 )(η 5 – C 5 H 4 (CH 2 ) 3 NC 4 H 4 )TaCl 2 J Solid State Electrochem (2008) 12:421–435 DOI 10.1007/s10008-007-0402-5 Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24th, 2007. M. A. Vorotyntsev (*) : M. Graczyk : J. Goux : P. Le Gendre : C. Moise ICMUB–UMR 5260 CNRS, University of Bourgogne, Bat. Mirande, 9 avenue A. Savary, BP 47 870, 21078 Dijon Cedex, France e-mail: mv@u-bourgogne.fr M. Skompska Department of Chemistry, Warsaw University, ul. Pasteura 1, 02 093 Warsaw, Poland J. Heinze Inst. Physik. Chemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse, 21, 79104 Freiburg, Germany