Ambidentate Thiocyanate and Cyanate Ligands in Dinitrosyl Iron Complexes

Abstract

To explore the effect of delocalization in the Fe(NO)(2) unit on possible linkage isomerism of ambidentate ECN(-) ligands, E = S and O, anionic DNICs, dinitrosyl iron complexes, (SCN)(2)Fe(NO)(2)(-) (1) and (OCN)(2)Fe(NO)(2)(-) (2) were synthesized by the reaction of in situ-generated [Fe(CO)(2)(NO)(2)](+) and PPN(+)ECN(-). Other {Fe(NO)(2)}(9) (Enemark-Feltham notation) complexes, (N(3))(2)Fe(NO)(2)(-) and (PhS)(2)Fe(NO)(2)(-), were prepared for comparison. The X-ray diffraction analysis of 1 and 2 yielded the typical tetrahedral structures of DNICs with two slightly bent Fe-N-O oriented toward each other, and linear FeNCE units. The ν(NO) IR values shift to lower values for 1 > 2 > (N(3))(2)Fe(NO)(2)(-) > (PhS)(2)Fe(NO)(2)(-), reflecting the increasing donor ability of the ancillary ligands and consistent with the redox potentials of the complexes, and the small trends in Mössbauer isomer shifts. Computational studies corroborate that the {Fe(NO)(2)}(9) motif prefers N-bound rather than E-bound isomers. The calculated energy differences between the linkage isomers of 1 (Fe-NCS preferred over Fe-SCN by about 6 kcal/mol) are smaller than those of 2 (Fe-NCO preferred over Fe-OCN by about 16 kcal/mol), a difference that is justified by the frontier molecular orbitals of the ligands themselves.

Reactivity of Cyanide and Thiocyanate Towards the Nitrosyl Carbonyl [Co(CO)3(NO)]

“…= 178.9(2)°. [11] Beside the characteristic CO and NO vibration bands in the IR spectrum of 3, which are comparable to the corresponding pattern of 1 and 2, a strong band at 2097 cm -1 was found. This vibration we assigned to the CϵN moiety of the thiocyanato ligand which is in good agreement with the reported data of PPN[Fe(NO) 2 (SCN-κN) 2 ] (2076sh, 2056vs, THF).…”

“…PPN[Fe(NO) 2 (XCN) 2 ] (X = O, S) were reported by Darensbourg and co-workers. [11] The latter were prepared by the reaction of [Fe(CO) 2 (NO) 2 ] with cyanate and thiocyanate, respectively, in THF at room temperature and their molecular structures in the crystal were confirmed by X-ray diffraction. The bonding parameters concerning the Co-NCS unit of 3 are comparable to the ones found for PPN[Fe(NO) 2 (SCN-κN) 2 ].…”

Structural and Electronic Responses to the Three Redox Levels of Fe(NO)N2S2‐Fe(NO)2

“…[23] The most selectiver oute to the Fe(NO)N 2 S 2 ·Fe(NO) 2 + complex,t hree o'clock positioni nF igure 1, is found to be the reaction of an N-heterocyclic-carbenestabilized, trinitrosylironc omplex (TNIC), [(IMes)Fe-(NO) 3 ] + , [24] with Fe(NO)N 2 S 2 as nucleophile, displacing an NOC radical, as well as the NHC, to form oxidized diiron complex 1 + + .A to ne o'clock in Figure 1, the "one-pot" synthesis, involved in situ generation of NOC and the putative [Fe(CO) 2 (NO) 2 ] + to serve as a Fe(NO) 2 + source, [25] derived from [Fe(CO) 3 (NO)] À and two equivalents of [NO] [BF 4 ]. [23] The most selectiver oute to the Fe(NO)N 2 S 2 ·Fe(NO) 2 + complex,t hree o'clock positioni nF igure 1, is found to be the reaction of an N-heterocyclic-carbenestabilized, trinitrosylironc omplex (TNIC), [(IMes)Fe-(NO) 3 ] + , [24] with Fe(NO)N 2 S 2 as nucleophile, displacing an NOC radical, as well as the NHC, to form oxidized diiron complex 1 + + .A to ne o'clock in Figure 1, the "one-pot" synthesis, involved in situ generation of NOC and the putative [Fe(CO) 2 (NO) 2 ] + to serve as a Fe(NO) 2 + source, [25] derived from [Fe(CO) 3 (NO)] À and two equivalents of [NO] [BF 4 ].…”

Dioxygen controls the nitrosylation reactions of a protein-bound [4Fe4S] cluster

“…IR data are available for a range of model compounds featuring the DNIC Fe(NO) 2 motif, with the ν NO bands varying with co-ligand and solvent. [44][45][46][47][48][49][50][51][52][53][54] No bands in the spectra for nitrosylated HiPIP resemble a DNIC species.…”