A combined experimental and theoretical study of dinitrosyl iron complexes containing chelating bis(diphenyl)phosphinoX (X=benzene, propane and ethylene): X-ray crystal structures and properties influenced by the presence or absence of π-bonds in chelating ligands

Holloway, Lauren R.; Clough, Andrew J.; Li, Jessica Y.; Tao, Emily L.; Fang, Tao; Li, Lijuan

doi:10.1016/j.poly.2013.12.019

Cited by 14 publications

(4 citation statements)

References 53 publications

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“…In both the oxidized and reduced NHC-DNICs, deviation from linearity is in the form of the NO ligands bending symmetrically toward each other within the coplanar Fe(NO) 2 unit. Interestingly, such an “attracto” orientation ,, is maintained in bimetallics and clusters that were previously discussed.…”

Section: Structural and Spectroscopic Standardssupporting

confidence: 58%

Synthetic Advances Inspired by the Bioactive Dinitrosyl Iron Unit

Pulukkody

Darensbourg

2015

Acc. Chem. Res.

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Resulting from biochemical iron-NO interactions, dinitrosyl iron complexes (DNICs) are small organometallic-like molecules, considered to serve as vehicles for NO transport and storage in vivo. Formed by the interaction of NO with cellular iron sulfur clusters or with the cellular labile iron pool, DNICs have been documented to be the largest NO-derived adduct in cells, even surpassing the well-known nitrosothiols (RSNOs). Continuing efforts in biological chemistry are aimed at understanding the movement of DNICs in and out of cells, and their important role in NO-induced iron efflux leading to apoptosis in cells. Intrigued by the integrity of the unique dinitrosyl iron unit (DNIU) and the possibility of roles for it in human physiology or medicinal applications, the understanding of fundamental properties such as ligand effects on its ability to switch between two redox levels has been pursued through biomimetic complexes. Using metallodithiolates and N-heterocyclic carbenes (NHCs) as ligands to Fe(NO)2, the synthesis of a library of novel DNICs, in both the oxidized, {Fe(NO)2}(9), and reduced, {Fe(NO)2}(10), forms (Enemark-Feltham notation), offers opportunity to examine structural, reactivity, and spectroscopic features. The raison d'etre for the MN2S2·Fe(NO)2 synthesis development is for the potential to exploit the ease of accessing two redox levels on two different metal sites, a property presumably required for achieving two electron redox processes in base metals. Hence such molecules may be viewed as synthetic analogues of [NiFe]- or [FeFe]-hydrogenase active sites in nature, both of which use bridging thiolates for connection of the two centers. A particular success was the development of an Fe(NO)N2S2·Fe(NO)2(+/0) redox pair for proton reduction electrocatalysis. Monomeric, reduced NHC-DNICs of the L2Fe(NO)2 type are synthesized via the Fe(CO)2(NO)2 precursor, and oxidized thiolate-containing forms are derived from the dimeric (μ-RS)2[Fe(NO)2]2. Monomeric NHC-DNICs are four coordinate, pseudotetrahedral compounds with planar Fe(NO)2 units in which the slightly bent Fe-NO groups are directed symmetrically inward at both redox levels. They serve as stable analogues of biological histidine binding sites. In agreement with IR data, Mössbauer spectroscopic parameters, and DFT computations, the prototypic NHC-DNICs indicate extensive delocalization of the electron density of iron via π-backbonding. Such π-delocalization presents an unusual reaction path for the one electron process of RS(-)/RSSR interconversion. Comparisons with imidazole-DNICs find NHCs to be the "better" ligands to Fe(NO)2 and prompted investigations in (a) possible relationships between such imidazole- and NHC-containing DNICs, (b) systems that might mimic the reactivity of DNICs with the endogenous gaseotransmitter CO, and (c) mechanistic details of such processes. In a broader context, these studies aim to further describe the behavior of the {Fe(NO)2} unit as a single molecular entity when subjected to various ligand environments and r...

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Section: Structural and Spectroscopic Standardssupporting

confidence: 58%

Synthetic Advances Inspired by the Bioactive Dinitrosyl Iron Unit

Pulukkody

Darensbourg

2015

Acc. Chem. Res.

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“…Table summarizes key crystallographic structural parameters and the corresponding scalar-relativistic DFT (OLYP , /STO-TZP) optimized values for a set of exemplary, four- and five-coordinate complexes. − The choice of the OLYP functional for this study was based both on the generally excellent performance of GGA functionals based on the OPTX exchange functional for transition metal systems − and on extensive calibration studies on nitrosyls. − The assembled data suggest that the attracto conformation is most characteristic for four- and five-coordinate {M(NO) 2 } complexes, while the less common repulso conformation is largely limited to pseudotetrahedral {M(NO) 2 } complexes. That said, far from all {M(NO) 2 } complexes are repulso ; like the {Fe(NO) 2 } DNICs, certain {Fe(NO) 2 } derivatives are also attracto.…”

Section: Resultsmentioning

confidence: 99%

Stereochemistry of Transition-Metal Dinitrosyl Complexes. A Molecular Orbital Rationale for the Attracto and Repulso Conformations

Ghosh

Conradie

2019

Inorg. Chem.

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Transition metal dinitrosyl complexes constitute a fairly large class of compounds, exemplified by some 500 structures in the Cambridge Structural Database. While many of the complexes exhibit a claw-like cis-attracto conformation, a handful of them exhibit a peculiar repulso conformation, in which the two NO groups are splayed outward and away from each other. Surprisingly, no computational study to date has attempted to explain the existence of these two limiting conformations of cis-dinitrosyl complexes. Careful examination of the large body of structural data and DFT-based molecular orbital analyses have identified both specific Enemark-Feltham electron counts and metal-ligand orbital interactions as crucial to each of the two conformations. Thus, the common attracto conformation, which is favored by as many as four metal(d)-NO(π*) orbital interactions, is observed most characteristically in four-and fivecoordinate cis-{M(NO) 2 } 8 complexes. The rarer repulso conformation, characterized by an unusually wide NMN´ angle, appears to be typical of pseudotetrahedral {M(NO) 2 } 10 complexes involving 4d and 5d transition metals. These complexes exhibit an a 1-symmetry (under a C 2v molecular point group) metal(d)-NO(π*) orbital interaction that uniquely favors a repulso geometry. This orbital interaction, however, appears to be weaker for 3d orbitals, which are significantly smaller than 4d and 5d orbitals. Pseudotetrahedral {M(NO) 2 } 10 complexes involving a 3d transition metal accordingly thus tend to exhibit an attracto conformation for hard, nitrogenbased supporting ligands but repulso-like/borderline conformations for soft phosphine and thioether-type supporting ligands.

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“…All harmonic frequencies obtained were compared with real values to confirm each of the equilibrium geometries calculated corresponding to a minimum on the potential energy surface. 56 Additionally, some of the calculated harmonic frequencies, particularly the NO stretch frequencies, were directly compared with the experimental frequencies. The assignment of the calculated wave numbers was aided by the animation option of Gauss View 5.0 graphical interface for Gaussian programs, which gives a visual presentation of the shape of the vibrational modes.…”

Section: Methodsmentioning

confidence: 99%