Synthesis and Characterization of Tetra(pyridyl)cyclo­butadiene Iron Complexes [Cp*Fe(C₄py₄)]^– (py = 3‐pyridyl and 4‐pyridyl, Cp* = C₅Me₅)

Abstract

Abstract. The tetra(pyridyl)cyclobutadiene complexes [K([18]crown-6){Cp*FeC 4 (3-py) 4 }] (2) (3-py = 3-pyridyl) and [K([18]crown-6){Cp*FeC 4 (4-py) 4 }] (3) (4-py = 4-pyridyl) were synthesized by reacting two equivalents of bis(3-pyridyl)acetylene and bis(4-pyridyl

Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis

“…220,221 The complexes [K( [18]crown-6){Cp*Fe(η 4 -C 4 py 4 )}] [py = 2-pyridyl (205), 3-pyridyl (206), 4-pyridyl (207)] present structural differences, as determined by X-ray diffraction; while the 2-pyridyl isomer 205 is monomeric with a contact ion pair, 220 the 3-pyridyl (206) and 4-pyridyl (207) analogues form coordination polymers with alternating cation−anion sequences. 221 The neutral complex {Cp*Fe[η 4 (2-py) 4 ](ZnCl 2 ) 2 ] (211) in which the anionic complex acts as a bidentate chelate (see Figure 6). 221 [K( [18] 222 Along with the mixture of the phosphorus cations, the oxidized cationic complex [Cp*Fe(η 6 -naphthalene)]Cl (215) was identified.…”

“…221 The neutral complex {Cp*Fe[η 4 (2-py) 4 ](ZnCl 2 ) 2 ] (211) in which the anionic complex acts as a bidentate chelate (see Figure 6). 221 [K( [18] 222 Along with the mixture of the phosphorus cations, the oxidized cationic complex [Cp*Fe(η 6 -naphthalene)]Cl (215) was identified. The relative ratio in which the phosphorus cations were obtained depended strongly on the reaction temperature and order of addition of the reagents.…”

“…217 Follow-up studies demonstrated that the cyclodimerization of bis(pyridyl)acetylene (pyridyl = 2-pyridyl, 3-pyridyl, 4-pyridyl) at 201 was also possible, generating potentially redox-active multitopic substituted cyclobutadiene ligands with potential to form supramolecular assemblies. 220,221 The complexes [K( [18]crown-6){Cp*Fe(η 4 -C 4 py 4 )}] [py = 2-pyridyl (205), 3-pyridyl (206), 4-pyridyl (207)] present structural differences, as determined by X-ray diffraction; while the 2-pyridyl isomer 205 is monomeric with a contact ion pair, 220 the 3-pyridyl (206) and 4-pyridyl (207) analogues form coordination polymers with alternating cation−anion sequences. 221 The neutral complex {Cp*Fe[η 4 (2-py) 4 ](ZnCl 2 ) 2 ] (211) in which the anionic complex acts as a bidentate chelate (see Figure 6).…”

“…Also, when 201 is treated with t BuCP, a cyclodimerization of the phospha­alkyne occurs, affording the 1,3-diphospha­butadiene iron(0) sandwich compound 204 (Scheme b, top) . Follow-up studies demonstrated that the cyclodimerization of bis­(pyridyl)­acetylene (pyridyl = 2-pyridyl, 3-pyridyl, 4-pyridyl) at 201 was also possible, generating potentially redox-active multitopic substituted cyclobutadiene ligands with potential to form supramolecular assemblies. , …”

“…The complexes [K([18]­crown-6)­{Cp*Fe­(η 4 -C 4 py 4 )}] [py = 2-pyridyl ( 205 ), 3-pyridyl ( 206 ), 4-pyridyl ( 207 )] present structural differences, as determined by X-ray diffraction; while the 2-pyridyl isomer 205 is monomeric with a contact ion pair, the 3-pyridyl ( 206 ) and 4-pyridyl ( 207 ) analogues form coordination polymers with alternating cation–anion sequences . The neutral complex {Cp*Fe­[η 4 -C 4 (2-py) 4 ]} ( 208 ) was also obtained after oxidizing 205 with [CuBr­(tht)] (1 equiv; tht = tetrahydro­thiophene).…”