A discrete dinickel complex with a central N 2 Ni II (µ 2 -demonstrated by X-ray structure determination of the isothiocyanate complex [Ni II 2 8(NCS) 2 ] • MeOH (10) formed SR) 2 Ni II N 2 core has been synthesized and investigated in the context of ligand binding and oxidation state changes.
by the reaction of 9 with 2 equiv. of KSCN in methanol.
Complex 10 is the first example of a complex with adjacent Reaction of the hexadentate amine-thiolate ligand N, NЈ-bis-[2-thio-3-aminomethyl-5-tert-butylbenzyl]propane-1,3-di-octahedral cis-N 4 S 2 Ni and planar cis-N 2 S 2 Ni sites. The overall dinuclear structure of the parent complex 9 is amine (8) with Ni(ClO 4 ) 2 • 6 H 2 O in methanol affords [Ni II 2 8][ClO 4 ] 2 • 3 CH 3 OH (9), the structure of which has been retained in 10, except for trans-axially bound isothiocyanate ions at Ni(1) and an as yet unexplained inversion of determined by X-ray crystallography. Complex 9 contains a central N 2 Ni(µ 2 -SR) 2 NiN 2 core with two approximately configuration at both secondary amine nitrogen atoms. In DMF solution both complexes undergo two successive planar cis-N 2 S 2 Ni coordination polyhedra bridged at the thiolate sulfur atoms. The cis-N 2 S 2 Ni units differ in that one reductions at potentials of -0.95 V and -1.53 V vs SCE, assigned to the formation of mixed-valent [Ni I Ni II 8] 1+ and nickel atom forms a six-membered chelate ring with the two secondary amine nitrogen atoms of 8 whereas the other [Ni I
2 8] 0 species, respectively. The similar electrochemical properties of 9 and 10 suggest that the trans-axially bound nickel atom is bound to the remaining primary nitrogen atoms. Complex 9 binds a variety of substrates. Binding of isothiocyanate ions in 10 are replaced by DMF molecules in DMF solution. Upon reduction, these solvent molecules anions to the N 2 Ni(µ 2 -SR) 2 NiN 2 core in 9 occurs selectively at the Ni atom bound to the secondary nitrogen atoms decoordinate to produce an unsolvated [Ni I Ni II 8] 1+ species with two planar N 2 S 2 Ni units. because of a slightly weaker ligand-field strength. This is early example of such a system involved the template syn- [a] Institut für Anorganische und Analytische Chemie, Universität Freiburg dentate amine-thiolate ligand 1 (see Scheme 1). [15] The di-