Influence of Sulfur Metalation on the Accessibility of the Ni^II/I Couple in [N,N‘-Bis(2-mercaptoethyl)-1,5-diazacyclooctanato]nickel(II):  Insight into the Redox Properties of [NiFe]-Hydrogenase

Abstract

A redox model study of [NiFe] hydrogenase has examined a series of five polymetallics based on the metalation of the dithiolate complex [1,5-bis(mercaptoethyl)-1,5-diazacyclooctane]Ni(II), Ni-1. Crystal structures of three polymetallics of the series have been reported earlier: [(Ni-1)(2)()Ni]Cl(2)(), [(Ni-1)(2)()FeCl(2)()](2)(), and [(Ni-1)(3)()(ZnCl)(2)()]Cl(2)(). Two are described here: [(Ni-1)(2)()Pd]Cl(2)().2H(2)()Ocrystallizes in the monoclinic system, space group P2(1)/c with cell constants a = 12.212(4) Å, b = 7.642(2) Å, c = 16.625(3) Å, beta = 107.69(2) degrees, V = 1443.230(0) Å(3), Z = 2, R = 0.051, and R(w) = 0.056. [(Ni-1)(2)()CoCl]PF(6)() crystallizes in the triclinic system, space group P&onemacr;, with cell constants a = 8.14(2) Å, b = 13.85(2) Å, c = 15.67(2) Å, alpha = 113.59(10) degrees, beta = 101.84(14) degrees, gamma = 94.0(2) degrees, V = 1561.620(0)Å(3), Z = 2, R = 0.072, and R(w) = 0.077. In all Ni-1 serves as a bidentate metallothiolate ligand with a "hinge" angle in the range 105-118 degrees and Ni-M distances of 2.7- 3.7 Å. The most accessible redox event is shown by EPR and electrochemistry to reside in the N(2)S(2)Ni unit and is the Ni(II/I) couple. Charge neutralization of the thiolate sulfurs by metalation can (dependent on the interacting metal) stabilize the Ni(I) state as efficiently as methylation forming a thioether. The implication of these results for the heterometallic active site of [NiFe]-hydrogenase as structured from Desulfovibrio gigas (Volbeda, A., et al. Nature, 1995, 373, 580), the generality of the Ni(&mgr;-SR)(2)M hinge structure, and a possible explanation for the unusual redox potentials are discussed.

Self-Assembly of Dinitrosyl Iron Units into Imidazolate-Edge-Bridged Molecular Squares: Characterization Including Mössbauer Spectroscopy

“…The patterns of the cyclic voltammograms are consistent with previously studied polymetallics that have multiple redox events. 36,37 …”

The Construction of (N2S2)Ni−Pd Clusters: A Slant‐Chair, a Basket and a C4‐Paddlewheel Structure

“…However, the slant-chair trimetallic molecular structure was evident in the isolated crystalline material; it had no significant differences in metric parameters from those found for the chloride salt of [(Ni-1) 2 Pd] 2ϩ (Scheme 1). [9] Likewise, the Ni-1Ј moiety was treated with NiCl 2 , which resulted in a trimetallic complex of composition [(Ni-1Ј) 2 NiCl][Cl]. As shown in Figure 3, this trimetallic com- …”

“…[2Ϫ7] The most common composition is a trimetallic cluster complex with a slant-chair structure made of two square-planar N 2 S 2 Ni complexes, which flank a central planar S 4 [8,9] A 2:3 ratio of ZnCl 2 or CuBr to Ni-1 results in a C 3 -paddlewheel cluster with three Ni-1 units performing as bidentatebridging ligands, placing either Zn II or Cu I atoms in tetrahedral S 3 X coordination geometry (B, Scheme 1). [10,11] With an excess of Cu I Cl, an adamantane-like Ni 2 Cu 4 cluster C results; four CuCl units bridge two (bme*-daco)Ni II moieties [Ni-1*, bme*-daco ϭ N,NЈ-bis(2-mercapto-2-methylpropyl)-1,5-diazacyclooctane], engaging all available lone pairs on all sulfurs for coordinating to the soft Cu I metal centers.…”

Synthetic, spectral, thermal and antimicrobial studies on some mixed 1,3-dithia-2-stannacyclopentane derivatives with dialkyldithiocarbamates

“…Interest in main group metal complexes with dithiocarbamate ligands arises in part because of their varied structural possibilities ( Fig. 1) and biological activities [2,3].…”