Unusual Electronic Effects Imparted by Bridging Dinitrogen: an Experimental and Theoretical Investigation

Hoffert, Wesley A.; Rappé, Anthony K.; Shores, Matthew P.

doi:10.1021/ic101528d

Cited by 18 publications

(12 citation statements)

References 68 publications

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“…163 From modeling of variable-temperature magnetic susceptibility data recorded on a solid sample of 88-Cr/ To test this hypothesis, Shores and co-workers studied the series [88-Cr/Si i Pr 3 ] n+ in which n = 0, 1, and 2. 164 Magnetic susceptibility data evidence S = 1 and 2 ground states for [88-Cr/Si i Pr 3 ] 0/2+ , and a quartet-to-doublet spin equilibrium for [88-Cr/Si i Pr 3 ] 1+ below 16 K. Despite the prior calculations, N−N bond lengths are within error and vibrational data indicate a marginal increase in N−N bond strength as one increases the metal formal oxidation state across the series. This trend suggests that oxidation is of a metal nonbonding d δ orbital rather than the M−N 2 or N−N π* orbital (Figure 68).…”

Section: Group 6: Cr Mo and Wmentioning

confidence: 99%

“…To test this hypothesis, Shores and co-workers studied the series [ 88-Cr/Si i Pr 3 ] n+ in which n = 0, 1, and 2 . Magnetic susceptibility data evidence S = 1 and 2 ground states for [88-Cr/Si i Pr 3 ] 0/2+ , and a quartet-to-doublet spin equilibrium for [88-Cr/Si i Pr 3 ] 1+ below 16 K. Despite the prior calculations, N–N bond lengths are within error and vibrational data indicate a marginal increase in N–N bond strength as one increases the metal formal oxidation state across the series.…”

Section: Dinitrogen Activation By Multimetallic Complexesmentioning

confidence: 99%

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Activation of Dinitrogen by Polynuclear Metal Complexes

et al. 2020

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Activation of dinitrogen plays an important role in daily anthropogenic life, and the processes by which this fixation occurs have been a longstanding and significant research focus within the community. One of the major fields of dinitrogen activation research is the use of multimetallic compounds to reduce and/or activate N2 into a more useful nitrogen-atom source, such as ammonia. Here we report a comprehensive review of multimetallic-dinitrogen complexes and their utility toward N2 activation, beginning with the d-block metals from Group 4 to Group 11, then extending to Group 13 (which is exclusively populated by B complexes), and finally the rare-earth and actinide species. The review considers all polynuclear metal aggregates containing two or more metal centers in which dinitrogen is coordinated or activated (i.e., partial or complete cleavage of the N2 triple bond in the observed product). Our survey includes complexes in which mononuclear N2 complexes are used as building blocks to generate homo- or heteromultimetallic dinitrogen species, which allow one to evaluate the potential of heterometallic species for dinitrogen activation. We highlight some of the common trends throughout the periodic table, such as the differences between coordination modes as it relates to N2 activation and potential functionalization and the effect of polarizing the bridging N2 ligand by employing different metal ions of differing Lewis acidities. By providing this comprehensive treatment of polynuclear metal dinitrogen species, this Review aims to outline the past and provide potential future directions for continued research in this area.

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Section: Group 6: Cr Mo and Wmentioning

confidence: 99%

Section: Dinitrogen Activation By Multimetallic Complexesmentioning

confidence: 99%

Activation of Dinitrogen by Polynuclear Metal Complexes

et al. 2020

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“…S ¼ 3 / 2 equilibrium was recently reported in the dinitrogen-bridged, mixed-valence dichromium complex [(dmpe) 4 Cr I Cr II (C 2 Si i Pr 3 ) 2 (m-N 2 )] + . 31 Regarding examples of trinuclear clusters exhibiting such a phenomenon, a family of linear Co 3 complexes was shown to display transitions between both integer 32 and non-integer 33 spin states, depending on oxidation state. Finally, trigonal trinuclear Co and mixed Co/Rh complexes featuring carbonyl or chalcogenide capped trinuclear cores have been shown to feature thermally induced spin state changes analogous to those reported here.…”

Section: Magnetic Propertiesmentioning

confidence: 99%

Modulation of magnetic behavior vialigand-field effects in the trigonal clusters (^PhL)Fe₃L^₃(L^= thf, py, PMe₂Ph)

2012

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Utilizing a hexadentate ligand platform, a series of trinuclear iron clusters ( Ph L)Fe 3 L * 3 ( Ph LH 6 ¼ MeC (CH 2 NPh-o-NPh) 3 ; L * ¼ tetrahydrofuran (1), pyridine (2), PMePh 2 (3)) has been prepared. The phenyl substituents on the ligand sterically prohibit strong iron-iron bonding from occurring but maintain a sufficiently close proximity between iron centers to permit direct interactions. Coordination of the weak-field tetrahydrofuran ligand to the iron centers results in a well-isolated, high-spin S ¼ 6 or S ¼ 5 ground state, as ascertained through variable-temperature dc magnetic susceptibility and lowtemperature magnetization measurements. Replacing the tetrahydrofuran ligands with stronger s-donating pyridine or tertiary phosphine ligands reduces the ground state to S ¼ 2 and gives rise to temperature-dependent magnetic susceptibility. In these cases, the magnetic susceptibility cannot be explained as arising simply from superexchange interactions between metal centers through the bridging amide ligands. Rather, the experimental data are best modelled by considering a thermallyinduced variation in molecular spin state between S ¼ 2 and S ¼ 4. Fits to these data provide thermodynamic parameters of DH ¼ 406 cm À1 and T c ¼ 187 K for 2 and DH ¼ 604 cm À1 and T c ¼ 375 K for 3. The difference in these parameters is consistent with ligand field strength differences between pyridine and phosphine ligands. To rationalize the spin state variation across the series of clusters, we first propose a qualitative model of the Fe 3 core electronic structure that considers direct Fe-Fe interactions, arising from direct orbital overlap. We then present a scenario, consistent with the observed magnetic behaviour, in which the s orbitals of the electronic structure are perturbed by substitution of the ancillary ligands.

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“…Interestingly, 4 could also be prepared directly by the reaction of chloride 1 in Et 2 O with 1 equiv of NaBAr F 4 under a nitrogen atmosphere. Apparently, the combined donor strengths of the permethylated cyclo- 19 These authors assigned high spin triplet and quintet states to their Cr I Cr I and Cr II Cr II complexes, respectively, while the mixed-valent Cr I Cr II species exhibited a doublet-quartet spin equilibrium. We have not carried out temperature-dependent magnetic measurement to pursue these apparent parallels.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…One possible interpretation of this result is to postulate ferromagnetic coupling of the two Cr(II) sites in 4 . It is notable that the room temperature effective magnetic moments of 2 – 4 measured by us are similar to those of a closely related set of compounds, viz., [{RCC(dmpe) 2 Cr} 2 (μ-N 2 )] n + ( n = 0, 1, 2), characterized by Hoffert et al These authors assigned high spin triplet and quintet states to their Cr I Cr I and Cr II Cr II complexes, respectively, while the mixed-valent Cr I Cr II species exhibited a doublet-quartet spin equilibrium. We have not carried out temperature-dependent magnetic measurement to pursue these apparent parallels.…”

Section: Resultsmentioning

confidence: 99%

The Intrinsic Barrier for N≡N Bond Cleavage or Formation Mediated by the Cp*Cr(dmpe) Fragment Is Insurmountable

2023

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We report the synthesis and characterization of a series of related chromium dinitrogen and nitrido complexes supported by the Cp*Cr(dmpe) fragment. Reduction of Cp*(dmpe)CrCl (1, Cp* = η5-C5Me5, dmpe = 1,2-bis(dimethylphosphino)ethane) with sodium metal under a nitrogen atmosphere yielded Cr(I) dinitrogen complex {Cp*(dmpe)Cr}2(μ-N2) (2). Reaction of the latter with 1 or 2 equiv of HBArF4 (HBArF 4 = [H(OEt2)2][(B(3,5-(CF3)2C6H3)4]) at room temperature did not effect protonation but rather gave mixed-valent [{Cp*(dmpe)Cr}2(μ-N2)]BArF 4 (3) and Cr(II) dinitrogen complex [{Cp*(dmpe)Cr}2(μ-N2)](BArF 4)2 (4), apparent products of oxidation by H+. 4 can be prepared independently by the reaction of [Cp*(dmpe)CrCl] with 1 equiv of NaBArF 4 under N2. The Cr(IV) nitride Cp*(dmpe)CrN (5) was synthesized by the reaction of 1 with an excess of NaN3. The cationic Cr(V) nitride [Cp*(dmpe)CrN]BArF 4 (6) is the product of oxidation of 5 with 1 equiv of FcBArF 4. DFT calculations were performed to suggest that the dinitrogen complexes are the thermodynamic products of the relevant interconversion processes. However, no NN bond cleavage or nitride coupling was observed under any circumstances.

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Unusual Electronic Effects Imparted by Bridging Dinitrogen: an Experimental and Theoretical Investigation

Cited by 18 publications

References 68 publications

Activation of Dinitrogen by Polynuclear Metal Complexes

Activation of Dinitrogen by Polynuclear Metal Complexes

Modulation of magnetic behavior vialigand-field effects in the trigonal clusters (^PhL)Fe₃L^₃(L^= thf, py, PMe₂Ph)

The Intrinsic Barrier for N≡N Bond Cleavage or Formation Mediated by the Cp*Cr(dmpe) Fragment Is Insurmountable

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Unusual Electronic Effects Imparted by Bridging Dinitrogen: an Experimental and Theoretical Investigation

Cited by 18 publications

References 68 publications

Activation of Dinitrogen by Polynuclear Metal Complexes

Activation of Dinitrogen by Polynuclear Metal Complexes

Modulation of magnetic behavior vialigand-field effects in the trigonal clusters (PhL)Fe3L*3(L*= thf, py, PMe2Ph)

The Intrinsic Barrier for N≡N Bond Cleavage or Formation Mediated by the Cp*Cr(dmpe) Fragment Is Insurmountable

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Modulation of magnetic behavior vialigand-field effects in the trigonal clusters (^PhL)Fe₃L^₃(L^= thf, py, PMe₂Ph)