Sulfur Bridging Interactions of Cis-Planar Ni^II−S₂N₂Coordination Units with Nickel(II), Copper(I,II), Zinc(II), and Mercury(II):  A Library of Bridging Modes, Including Ni^II(μ₂-SR)₂M^I,IIRhombs

Abstract

Sulfur bridging interactions between three cis-planar NiII-S2N2 complexes and NiII, CuI,II, ZnII, and HgII reactants were investigated by synthesis and X-ray crystal structures of some 24 complexes. This work was stimulated by recent crystallographic structures of the A-cluster of carbon monoxide dehydrogenase/acetylcoenzyme A synthase. This bridged biological assembly has the minimal formulation [Fe4S4]-(micro2-SCys)-[M((micro2-SCys)2Gly)Ni] with M = NiII, CuI, and ZnII at sites distal and proximal, respectively, to the iron-sulfur cluster. Bridges supported by representations of the distal nickel site were sought by reactions of the complexes [NiII(LH-S2N2)]2- and [NiII(LR-S2N2)], with 5-5-5 chelate ring patterns. Reaction products implicate the bridges Ni-(micro2-S)1,2-M in a variety of molecular structures, some with previously unknown connectivities of bridge atoms. The most frequently encountered bridge units are the nonplanar rhombs Ni(2-S)2M involving both sulfur atoms of a given complex. Those with M = NiII are biologically relevant inasmuch as the catalytic metal at the proximal site is nickel. The complex [Ni(L-655)]2-, containing the 6-5-5 ring pattern and coordination sphere of the distal nickel site, was prepared and structurally characterized. It was shown to sustain Ni2(micro2-S)2 rhombic interactions in the form of trinuclear [[Ni(L-655)]2Ni]2- and [[Ni(L-655)]Ni(R2PCH2CH2PR2)] (R = Et, Ph) in which the second NiII simulates the proximal site. Bridging interactions of NiII-S2N2 complexes are summarized, and geometrical features of Ni2(2-S)2 rhombs in these complexes, as dependent on ring patterns, are considered (LH-S2N2 = N,N'-ethylenebis(2-mercaptoisobutyramide)(4-); LR-S2N2 = trans-rac-N,N'-bis(2-mercapto-2-methylprop-1-yl)-1,2-cyclohexanediamine(2-); L-655 = N-(2-mercaptopropyl)-N'-(2'-mercaptoethyl)glycinamide(4-)).

Synthesis of MFe3S4Clusters Containing a Planar MIISite (M = Ni, Pd, Pt), a Structural Element in the C-Cluster of Carbon Monoxide Dehydrogenase

“…Related research in this laboratory is directed toward the attainment of analogues of the A-cluster of bifunctional CODH. 18,19 Experimental Section…”

Nickel Thiolate Complexes as Ligands for Copper and Zinc: Novel Additions to a Library of Binding Modes

“…Structures have been reported of [{Ni(N 2 S 2 )} 2 Cu 2 ] 2+ , which have the same nickel/copper ratio as [{Ni(xbsms)CuI} 2 ] but which do not contain coordinated halides and in which the sulfur binding is different. [5,7] The reaction of NiN 2 S 2 complexes with copper and zinc halides has been shown to result in similar structures in some cases, [12] although different topologies have also been reported. [7] Our new nickel-zinc complexes [Ni 2 (bsms) 3 -ZnBr 3 ] and [Ni 3 (xbsms) 2 (ZnBr 3 ) 2 ] are noticeably different from these earlier reported structures, and are also quite different from each other, as a result of dissociation of the didentate bsms ligand from part of the mononuclear complex and re-assembly to form a dinuclear core similar to that of the nickel ethanedithiolate compound [Ni 2 (edt) 3 ].…”

“…[5,7] The reaction of NiN 2 S 2 complexes with copper and zinc halides has been shown to result in similar structures in some cases, [12] although different topologies have also been reported. [7] Our new nickel-zinc complexes [Ni 2 (bsms) 3 -ZnBr 3 ] and [Ni 3 (xbsms) 2 (ZnBr 3 ) 2 ] are noticeably different from these earlier reported structures, and are also quite different from each other, as a result of dissociation of the didentate bsms ligand from part of the mononuclear complex and re-assembly to form a dinuclear core similar to that of the nickel ethanedithiolate compound [Ni 2 (edt) 3 ]. [30] The binding of the ZnBr 3 -group to one thiolate sulfur atom is similar to the binding observed in the dinuclear complex [Ni(N 2 S 2 )ZnCl 2 (dmf)].…”

“…[1] However, due to the earlier reports of Cu-or Zn-containing structures, [2,3] attempts to synthesise structural models of the A-cluster have resulted in reports of several new heteronuclear clusters. [4][5][6][7][8][9][10][11] In most of these investigations, discrete mononuclear nickel complexes of tetradentate N 2 S 2 ligands have been used as building blocks, and their reactivity towards transition metals such as Fe, Ni, Cu, Zn, Ag, Pd and Hg have been studied. The nickel complexes can be considered to react as didentate S ligands.…”

“…A wealth of structures has become available, and a range of possible bridging modes for the thiolate sulfur atoms have been reported. [7] The two cis-thiolate sulfur atoms in the parent nickel complex may form single bridges to two different metal ions in, for example, Ni 3 Cu 2 , Ni 3 Ag 2 or Ni 3 Zn 2 clusters [4,10,12,13] or Ni 4 Pd 2 paddle wheels; [10,14] they can act as a chelating ligand to one metal ion to form ion and the other one µ 3 -bridging to two copper ions. The complex is located on a crystallographic twofold axis and the complex in a single crystal is enantiomerically pure.…”