Synthesis, Characterization, and Catalytic Reactivity of Dithiolate-Bridged Diiron Complexes Supported by Bulky Cyclopentadienyl Ligands

Abstract

Coordinatively unsaturated sulfur-supported iron complexes are conceived as suitable functional models for probing the potential biomimetic reactivity. In this regard, it is of continuous interest to construct this class of metallic complexes and investigate their unique properties for prospective applications. Here, we describe synthesis, characterization, and reactivity of a series of thiolate-bridged di-or multinuclear iron complexes supported by bulky 1,2,4-tri(tert-butyl)cyclopentadienyl (Cp′) ligands. Especially, detailed studies on variable-temperature solidstate magnetic susceptibility measurement and zero-field 57 Fe Mossbauer spectroscopy at different temperatures reveal that the two iron centers in desirable [Fe II (μ-SR) 2 Fe II ]-type complexes are all in intermediate-or high-spin configurations. Notably, when the substituent in the bridging thiolate ligand is the isopropyl group, the corresponding diiron complex exhibits temperature-induced reversible phase transition phenomenon. Its temperature-dependent magnetic susceptibility under successive cycles exhibits an 8 K wide hysteresis of magnetization caused by the reversible phase transition. Moreover, its single-crystal X-ray diffraction analyses at different temperatures clearly demonstrate the existence of phase transition accompanied by obvious thermal expansion upon heating, during which the corresponding space group varied from non-central tetragonal P4̅ 2(1)c below the inflection point temperature to central tetragonal P4(2)/mbc above the inflection point temperature. In addition, these new iron complexes bearing sulfur donors are all proved to be good catalysts for the reductive silylation of N 2 .

Construction and Function of Thiolate-Bridged Diiron NxHy Nitrogenase Model Complexes

“…Through the modification of steric effects, several new [Fe 2 S 2 ]type complexes 4a, 4b, and 5 were constructed and can catalyze the reductive silylation of N 2 and further acidolysis to afford NH 3 (Figure 7). 41…”

“…However, upon employing multidentate thiolates, such as redox noninnocent benzene-1,2-dithiolate (bdt) and 3-thiapentane-1,5-dithiolate (tpdt), we successfully isolated coordinatively unsaturated [Fe 2 S 2 ]-type complexes [Cp*Fe­(μ-η 2 :η 4 -bdt)­FeCp*] ( 2 ) and [Cp*Fe­(μ-1 κ 3 SSS ′:2 κ 2 SS -tpdt)­FeCp*]­[PF 6 ] ( 3­[PF 6 ] ) . Besides, we also modulated Cp* to other bulky strong electron-donating carbon-based ligands such as Me 2 -cAAC (Me 2 -cAAC = :C­(CH 2 )­(CMe 2 ) 2 N-2,6- i Pr 2 C 6 H 3 ) or 1,2,4-tri­( tert -butyl)­cyclopentadienyl (Cp ‡ ), and obtained several [Fe 2 S 2 ]-type complexes [Cp ‡ Fe­(μ-SR) 2 FeCp ‡ ] ( 4a , R = Et; 4b , R = i Pr), [Cp ‡ Fe­(μ-pdt)­FeCp ‡ ] ( 5 , pdt = 1,3-propanedithiolate) and [(Me 2 -cAAC)­Fe­(μ-SR)­(Br)] 2 ( 6a , R = Me; 6b , R = Et) by the same strategy. , Second, [Fe 2 S 2 ]-type complexes [Cp † Fe­(μ-SR)­(MeCN)] 2 [PF 6 ] 2 ( 8a­[PF 6 ] 2 , Cp † = Cp*, R = Et; 8b­[PF 6 ] 2 , Cp † = Cp′ = C 5 Me 4 H, R = Et; 8c­[PF 6 ] 2 , Cp † = Cp′, R = i Pr) containing two labile MeCN ligands were generated through a sequential oxidation strategy (Scheme b), using zerovalent Fe­(CO) 5 as a precursor . Third, we adopted a modular assembly strategy between mononuclear iron precursors with different coordination environments to afford unsymmetrical [Fe 2 S 2 ]-type complexes [Cp*Fe­(MeCN)­(L)­FeCl]­[PF 6 ] ( 9­[PF 6 ] , L = N , N ′-dimethyl-3,6-diazanonane-1,8-dithiolate) and [Cp*Fe­(MeCN)­(L CH 2 )­FeCl]­[PF 6 ] ( 10­[PF 6 ] ) (Scheme c) …”

Light‐Driven Dinitrogen Activation with Transition Metal Complexes: Mechanisms and Applications†

“…[ 10‐13 ] Hence, a variety of strategies have been developed to achieve dinitrogen reduction more efficiently and in an environmentally‐friendly manner. [ 14‐37 ]…”

One Ligand to Bind them All: S~C~S2− Carbon‐ and Sulfur‐Based Gem‐Dianion as Structuring Ligand for Iron Polymetallic Assemblies

“…Another system was proposed by Yang, Qu et al, using the bulky Cp''' ligand to stabilize dimetallic and trimetallic iron sulfur clusters (Figure 1B, IV). [10] Interestingly, these complexes presented some catalytic activity in the functionalisation of dinitrogen into silylamines. In this series, the carbon atoms of Cp''' ligands interact with a single iron center on the edge of the structure, which would not be relevant to discuss the role of a carbon-based ligand for the close interaction and spin couplings in iron sulfur clusters.…”

“…presented tetranuclear iron sulfur cubanes obtained from a monomeric Fe(I) thiolate complex (Figure 1B, III) [9] However, the initial η 6 ‐Ar−Fe interaction modelling the “C” ligand was not maintained upon the increase of nuclearity. Another system was proposed by Yang, Qu et al ., using the bulky Cp’’’ ligand to stabilize dimetallic and trimetallic iron sulfur clusters (Figure 1B, IV) [10] . Interestingly, these complexes presented some catalytic activity in the functionalisation of dinitrogen into silylamines.…”