Synthesis and interconversions of reduced, alkali-metal supported iron-sulfur-carbonyl complexes

We report the synthesis, interconversions and X-ray structures of a set of [mFe-nS]-type carbonyl clusters (where S = S^2-, S₂^2- or RS^-; m = 2-3; n = 1-2). All of the clusters have been identified and characterized by single crystal X-ray diffraction, IR and ¹³C NMR. Reduction of the parent neutral dimer [μ₂-(SPh)₂Fe₂(CO)₆] (1) with KC₈ affords an easily separable ∼1 : 1 mixture of the anionic, dimeric thiolate dimer K[Fe₂(SPh)(CO)₆(μ-CO)] (2) and the dianionic, sulfido trimer [K(benzo-15-crown-5)₂]₂[Fe₃(μ₃-S)(CO)₉] (3). Oxidation of 2 with diphenyl-disulfide (Ph₂S₂) cleanly returns the starting material 1. The Ph-S bond in 1 can be cleaved to form sulfide trimer 3. Oxidation of sulfido trimer 3 with [Fc](PF₆) in the presence of S₈ cleanly affords the all-inorganic persulfide dimer [μ₂-(S)₂Fe₂(CO)₆] (4), a thermodynamically stable product. The inverse reactions to form 3 (dianion) from 4 (neutral) were not successful, and other products were obtained. For example, reduction of 4 with KC₈ afforded the mixed valence Fe(i)/Fe(ii) species [((FeS₂)(CO)₆)₂Fe^II]^2- (5), in which the two {Fe₂S₂(CO)₆}^2- units serve as bidendate ligands to a Fe(ii) center. Another isolated product (THF insoluble portion) was recrystallized in MeCN to afford [K(benzo-15-crown-5)₂]₂[((Fe₂S)(CO)₆)₂(μ-S)₂] (6), in which a persulfide dianion bridges two {2Fe-S} moieties (dimer of dimers). Finally, to close the interconversion loop, we converted the persulfide dimer 4 into the thiolate dimer 1 by reduction with KC₈ followed by reaction with the diphenyl iodonium salt [Ph₂I](PF₆), in modest yield. These reactions underscore the thermodynamic stability of the dimers 1 and 4, as well as the synthetic and crystallization versatility of using the crown/K⁺ counterion system for obtaining structural information on highly reduced iron-sulfur-carbonyl clusters.

Two Fe3(μ3-S)2(CO)8 clusters with terminal N-heterocyclic carbenes

The title compounds with terminal N-heterocyclic carbenes, namely octacarbonyl(imidazolidinylidene-κC(2))di-μ3-sulfido-triiron(II)(2 Fe-Fe), [Fe3(C3H6N2)(μ3-S)2(CO)8], (I), and octacarbonyl(1-methylimidazo[1,5-a]pyridin-3-ylidene-κC(3))di-μ3-sulfido-triiron(II)(2 Fe-Fe), [Fe3(C8H8N2)(μ3-S)2(CO)8], (II), have been synthesized. Each compound contains two Fe-Fe bonds and two S atoms above and below a triiron triangle. One of the eight carbonyl ligands deviates significantly from linearity. In (I), dimers generated by an N-H···S hydrogen bond are linked into [001] double chains by a second N-H···S hydrogen bond. These chains are packed by a C-H···O hydrogen bond to yield [101] sheets. In (II), dimers generated by an N-H···S hydrogen bond are linked by C-H···O hydrogen bonds to form [111] double chains.