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Reactions at the N 2 Ni(μ 2 ‐SR) 2 NiN 2 Core in Dinuclear Nickel(II) Amine‐Thiolate Complexes
Author(s) -
Kersting Berthold,
Steinfeld Gunther,
Hausmann Julia
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199901)1999:1<179::aid-ejic179>3.0.co;2-5
Subject(s) - chemistry , nickel , ligand (biochemistry) , crystallography , protonation , amine gas treating , stereochemistry , crystal structure , octahedron , ion , organic chemistry , biochemistry , receptor
A discrete dinickel complex with a central N 2 Ni II (μ 2 ‐SR) 2 Ni II N 2 core has been synthesized and investigated in the context of ligand binding and oxidation state changes. Reaction of the hexadentate amine‐thiolate ligand N , N ′‐bis‐[2‐thio‐3‐aminomethyl‐5‐ tert ‐butylbenzyl]propane‐1,3‐diamine ( 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 determined by X‐ray crystallography. Complex 9 contains a central N 2 Ni(μ 2 ‐SR) 2 NiN 2 core with two approximately 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 nickel atom forms a six‐membered chelate ring with the two secondary amine nitrogen atoms of 8 whereas the other nickel atom is bound to the remaining primary nitrogen atoms. Complex 9 binds a variety of substrates. Binding of 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 because of a slightly weaker ligand‐field strength. This is demonstrated by X‐ray structure determination of the isothiocyanate complex [Ni II 2 8 (NCS) 2 ] · MeOH ( 10 ) formed by the reaction of 9 with 2 equiv. of KSCN in methanol. Complex 10 is the first example of a complex with adjacent 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 retained in 10 , except for trans ‐axially bound isothiocyanate ions at Ni(1) and an as yet unexplained inversion of configuration at both secondary amine nitrogen atoms. In DMF solution both complexes undergo two successive 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 [Ni I 2 8 ] 0 species, respectively. The similar electrochemical properties of 9 and 10 suggest that the trans ‐axially bound isothiocyanate ions in 10 are replaced by DMF molecules in DMF solution. Upon reduction, these solvent molecules decoordinate to produce an unsolvated [Ni I Ni II 8 ] 1+ species with two planar N 2 S 2 Ni units.