Ferrous Wheels, Ellipse [(tBu₃SiS)FeX]_n, and Cube [(tBu₃SiS)Fe(CCSitBu₃)]₄

Abstract

The controlled aggregation of low-coordinate, transitionmetal complexes can lead to the generation of unusual oligomers, polymers or clusters. Inspired by Hoffmann's treatise on tetrahedral units as building blocks, [1,2] we sought "XMY" species as potential monomers for [M(m-X)(m-Y)] n , an oligomer or polymer based on the edge-connectivity of tetrahedra. Literature precedent [3] suggested the use of bulky thiolate and halide ligands as the m-X and m-Y linkages. [5,6] hence desymmetrization was viewed as one means toward oligomerization. FeX 2 (thf) 2 and one equivalent of tBu 3 SiSNa(thf) x (x = 1.4-1.7) were stirred for 18-24 h to provide yellow [(X 2 Fe)(m-SSitBu 3 ) 2 {FeX(thf)}]Na(thf) 4 (2 a, X = Cl, 74 %; 2 b, X= Br, 86 %) and cis-[{I(thf)Fe} 2 -(m-SSitBu 3 ) 2 ] (3, 75 %) upon isolation. The structures of 1, 2 b and 3 were determined by single-crystal X-ray crystallography, and quenching studies (D 2 O/DCl in D 3 COD) suggested that 2 a has the same thiolate:THF ratio (1:3.9) as 2 b. Elemental analyses were indeterminate, probably because of variable desolvation. Each complex has a m eff consistent with an S = 2 ground state (Evans' method [7] in [D 8 ]THF) and little orbital contribution: 2 a, 4.8 m B ; 2 b, 4.5 m B ; 3, 4.8 m B .If the solvent (THF) was removed after the above procedures, and the remaining solids were heated under vacuum (2 a, 808C, 1.5 h; 2 b, 798C, 2 h); 3, 117 8C, 5 h) and extracted into benzene, then desolvation and aggregation occurred, but not to the expected polymers. Instead, ferrous wheels [Fe(m-X)(m-SSitBu 3 )] n (C 6 H 6 ) m (X = Cl, n = 12, 4 a, 45 %;[8] X = Br, n = 12, 4 b, 72%) [9] and the ferrous ellipse [Fe(m-I)(m-SSitBu 3 )] 14 (C 6 H 6 ) m (5, 16%) [10] were isolated by crystallization. The structures of these complexes were determined by single-crystal X-ray crystallography, [11] but the benzene molecules of solvation, determined from quenching studies to be~0.5-1.0 equivalent per Fe atom, exhibited significant disorder, and were removed from the refinement by using PLATON methods.The chloride ferrous wheel, 4 a (Figure 1), packs in a tetragonal array of columns; the bromide derivative, 4 b, is isomorphous. The wheels consist of edge-shared tetrahedra, with the inner diameter comprises m-X ligands, and the periphery composed of m-SSitBu 3 linkages. The orientation of each shared tetrahedral edge alternates relative to the ring plane such that the three different transannular X···X separations are basically the same (4 a, 9.484 (29) av; 4 b, 9.483 (22) av) Because of the greater size of Br ion, the iron atoms in 4 b are slightly displaced towards the outside of the wheel relative to 4 a.The iodide ellipse, 5 (Figure 2) is constructed of tetrahedra linked on the perimeter by m-SSitBu 3 ligands, and internally by bridging iodides. Ellipse 5 also packs in columnar fashion, and has transannular d(I···I) of 11.101 (2), 11.499 (2), 12.402 (2) and 13.469 (2) . The tetrahedra form a ring with the iodides inside, despite the d(FeI) av = 2.672 (11) that is substantially long...

High-Spin Iron(II) Alkynyl Complexes with N-Heterocyclic Carbene Ligation: Synthesis, Characterization, and Reactivity Study

“…Complex 1 might initially react with four tert-butyl isocyanide molecules to afford cis-(Bu t NC) 4 Fe-(CCBu t ) 2 (A). While the attempts to isolate intermediate A were unsuccessful, the analogous complex cis-[(Bu t NC) 4 Fe-(CN) 2 ] is known. 19 Intermediate A undergoes migratory insertion to produce iron vinylidene species B.…”

Structure and reactivity studies of transition metals ligated by tBuSi3X (X = O, NH, N, S, and CC)

“…Twelve-membered wheels [(m-SSi t Bu 3 )M(m-X)] 12 (M = Fe, X = Cl (28-Cl, m eff B 18 at 300 K), Br (28-Br, m eff B 15 at 300 K); M = Co, X = Cl (29-Cl, m eff B 15 at 300 K); M = Ni, X = Br (30-Br)) were found for various combinations of Fe, Co, Ni, and Cl and Br, whereas the unique, 14-membered ellipse [(m-SSi t Bu 3 )Fe(m-I)] 12 (28-I, m eff B 14 at 300 K) was found for the combination of iron and iodide. 71,72 Initial excitement over these compounds as potential single molecule magnets was dampened by a discerned lack of intermetallic communication. Since each cyclic compound has at least two distinct pseudo-T d centers, modeling the coupling was difficult.…”

A 32 vertex polyhedron via supramolecular assembly of silanedithiolate silanolate units

“…the catalytic center of alcohol dehydrogenase or the heterocubane fragment of Fe-S proteins. 33,34 While there are several monofunctional silanethiols known in the literature, only a few reports have been made on compounds bearing two SH groups at the silicon center and compounds with three SH groups are hitherto unknown. 35,36 Some years ago, Komuro, and, more recently, Tokitoh reported on the synthesis and structural characterization of silanedithiolate complexes.…”