Reactions at the N2Ni(mu(2)-SR)(2)NiN2 core in dinuclear nickel(II) amine-thiolate complexes

discrete dinickel complex with a central N2NiII(mu(2)-SR)(2)(NiN2)-N-II cor e has been synthesized and investigated in the context of ligand binding an d oxidation state changes. Reaction of the hexadentate amine-thiolate ligan d N,N'-bis-[2-thio-3-aminomethyl-5-tert-butylbenzyl]propane-1,3-diamine (8) with Ni(ClO4)(2) . 6 H2O in methanol affords [Ni(2)(II)8][ClO4](2) . 3 CH3 OH (9), the structure of which has been determined by X-ray crystallography . Complex 9 contains a central N2Ni(mu 2-SR)(2)NiN2 core with two approxima tely planar cis-N2S2Ni coordination polyhedra bridged at the thiolate sulfu r atoms. The cis-N2S2Ni units differ in that one nickel atom forms a six-me mbered chelate ring with the two secondary amine nitrogen atoms of 8 wherea s the other nickel atom is bound to the remaining primary nitrogen atoms. C omplex 9 binds a variety of substrates. Binding of anions to the N2Ni(mu(2) -SR)(2)NiN2 core in 9 occurs selectively at the Ni atom bound to the second ary nitrogen atoms because of a slightly weaker ligand-field strength. This is demonstrated by X-ray structure determination of the isothiocyanate com plex [Ni(2)(II)8(NCS)(2)] . MeOH (10) formed by the reaction of 9 with 2 eq uiv. of KSCN in methanol. Complex 10 is the first example of a complex with adjacent octahedral cis-N4S2Ni and planar cis-N2S2Ni sites. The overall di nuclear structure of the parent complex 9 is retained in 10, except for tra ns-axially bound isothiocyanate ions at Ni(1) and an as yet unexplained inv ersion of configuration at both secondary amine nitrogen atoms. In DMF solu tion both complexes undergo two successive reductions at potentials of -0.9 5 V and -1.53 V vs SCE, assigned to the formation of mixed-valent [Ni(I)Ni( II)8](1+) and [Ni(2)(I)8](0) species, respectively The similar electrochemi cal properties of 9 and 10 suggest that the trans-axially bound isothiocyan ate ions in 10 are replaced by DMF molecules in DMF solution. Upon reductio n, these solvent molecules decoordinate to produce an unsolvated [Ni(I)Ni(I I)8](1+) species with two planar N2S2Ni units.