Hydrogen-bonded assemblies of two organically templated borates: syntheses and crystal structures of [(1,10-phen)(H3BO3)2] and [2-EtpyH][(B5O6(OH)4]

Wang, Yanjing; Jia, Ai‐Quan; Chen, Xing-Shun; Shi, Hua‐Tian; Zhang, Qian‐Feng

doi:10.1515/znb-2014-0277

Cited by 2 publications

(3 citation statements)

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“…The bond distances between the Cp* ring carbons and rhodium are elongated to 2.190(3)–2.228(3) Å in 3 from 2.141(3) to 2.171(3) Å in [Cp*Rh(phen)Cl]OTf ( 5 ), while those from the phen nitrogens to rhodium are markedly shortened to 2.006(3) and 2.004(2) Å in 3 from 2.121(2) and 2.100(2) Å in 5 . The C5–C6 linkage in the phen ligand is shortened to 1.394(4) Å in 3 , from a value of 1.422(3) Å in 5 and 1.449 Å in free phen . This bond contraction is indicative of extensive delocalization of electron density in the highest occupied molecular orbital (HOMO) of 3 onto the phen ligand .…”

Section: Results and Discussionmentioning

confidence: 93%

“…The C5−C6 linkage in the phen ligand is shortened to 1.394(4) Å in 3, from a value of 1.422(3) Å in 5 and 1.449 Å in free phen. 19 This bond contraction is indicative of extensive delocalization of electron density in the highest occupied molecular orbital (HOMO) of 3 onto the phen ligand. 20 This phenomenon can be understood to arise from the accessible π* orbitals on phen that can mix with electron-rich rhodium(I) centered orbitals.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Structural and Electrochemical Consequences of [Cp*] Ligand Protonation

et al. 2017

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There are few examples of the isolation of analogous metal complexes bearing [η-Cp*] and [η-Cp*H] (Cp* = pentamethylcyclopentadienyl) complexes within the same metal/ligand framework, despite the relevance of such structures to catalytic applications. Recently, protonation of Cp*Rh(bpy) (bpy = 2,2'-bipyridyl) has been shown to yield a complex bearing the uncommon [η-Cp*H] ligand, rather than generating a [Rh-H] complex. We now report the purification and isolation of this protonated species, as well as characterization of analogous complexes of 1,10-phenanthroline (phen). Specifically, reaction of Cp*Rh(bpy) or Cp*Rh(phen) with 1 equiv of EtNHBr affords rhodium compounds bearing endo-η-pentamethylcyclopentadiene (η-Cp*H) as a ligand. NMR spectroscopy and single-crystal X-ray diffraction studies confirm protonation of the Cp* ligand, rather than formation of metal hydride complexes. Analysis of new structural data and electronic spectra suggests that phen is significantly reduced in Cp*Rh(phen), similar to the case of Cp*Rh(bpy). Backbonding interactions with olefinic motifs are activated by formation of [η-Cp*H]; protonation of [Cp*] stabilizes the low-valent metal center and results in loss of reduced character on the diimine ligands. In accord with these changes in electronic structure, electrochemical studies reveal a distinct manifold of redox processes that are accessible in the [Cp*H] complexes in comparison with their [Cp*] analogues; these processes suggest new applications in catalysis for the complexes bearing endo-η-Cp*H.

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Section: Results and Discussionmentioning

confidence: 93%

Section: ■ Results and Discussionmentioning

confidence: 99%

Structural and Electrochemical Consequences of [Cp*] Ligand Protonation

et al. 2017

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“…With the Fe(phen) 3 core intact, we reluctantly considered the possibility of the protonation of anions aggregated with the catalyst. While counteranions have not been traditionally considered in the Belousov–Zhabotinsky reaction, there is a wealth of evidence in the crystallographic record that cationic transition metal complexes of 1,10-phenanthroline interact strongly with anionic and neutral polar outer sphere ligands (OSLs). − In fact, a number of cocrystals of phenanthrolines with anions and other neutral polar species have been reported. − In light of this evidence, it is certainly warranted to postulate that similar interactions would occur in solution, and we have chosen to consider outer sphere aggregation in our investigation into the proton dependence. The aggregation of a cationic transition metal complex with anionic counterions provides stabilization due to electrostatic interactions, hydrogen-bonding, and van der Waals interactions. The stabilization is expected to increase with the charge of the transition metal complex, with the charge of the counterion, and with the number of counterions.…”

Section: Introductionmentioning

confidence: 99%

Origin of the Second-Order Proton Catalysis of Ferriin Reduction in Belousov–Zhabotinsky Reactions: Density Functional Studies of Ferroin and Ferriin Aggregates with Outer Sphere Ligands Sulfate, Bisulfate, and Sulfuric Acid

McCauley

Glaser

2022

J. Phys. Chem. A

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The detailed mechanisms of Belousov−Zhabotinsky oscillating reactions continue to present grand challenges, even after half a century of study. The origin of the pH dependence of the oscillation pattern had never been rigorously identified. In our recent kinetic study of one of the key Belousov−Zhabotinsky reactions, the iron-catalyzed bromate oxidation of malonic acid, compelling agreement between experiments and kinetic simulations was achieved only with the inclusion of second-order proton catalysis of the reduction of the [Fe(phen) 3 ] 3+ species. After exhausting all other avenues in search of an explanation of this proton catalysis, we considered the possibility that the parent iron−phenanthroline complexes could aggregate with neutral and anionic outer sphere ligands (OSLs) in the highly concentrated sulfuric acid solution, and we hypothesized that OSL protonation would increase the capacity of the aggregated complex to oxidize the organic fuel. We performed potential energy surface analyses at the SMD(APFD/6-311G*) level of complexes of the types [Fe(phen) 3 (SO 4 2− ) m (HSO 4 − ) n (H 2 SO 4 ) o ] (c-2m-n)+ for ferriin (c = 3) and ferroin (c = 2) aggregated with m sulfate, n bisulfate, and o sulfuric acid OSLs. We present structures of the OSL aggregates, develop a nomenclature for their description, and characterize their electronic structure. The structural chemistry provides the foundation to discuss the ferroin/ferriin redox couple with emphasis on the relationship between the vertical electron affinities of ferriin aggregates and their OSL protonation states. For proton catalysis to manifest itself, double-protonation paths that are slightly endergonic should be present, and proton affinities of aggregated OSLs allow the identification of such double-protonation chains. As a first test of our mechanistic proposal for the second-order proton catalysis of the Belousov−Zhabotinsky reaction, the results presented here provide compelling evidence in support of the importance of outer sphere ligation of the iron catalyst.

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Hydrogen-bonded assemblies of two organically templated borates: syntheses and crystal structures of [(1,10-phen)(H₃BO₃)₂] and [2-EtpyH][(B₅O₆(OH)₄]

Cited by 2 publications

References 23 publications

Structural and Electrochemical Consequences of [Cp*] Ligand Protonation

Structural and Electrochemical Consequences of [Cp*] Ligand Protonation

Origin of the Second-Order Proton Catalysis of Ferriin Reduction in Belousov–Zhabotinsky Reactions: Density Functional Studies of Ferroin and Ferriin Aggregates with Outer Sphere Ligands Sulfate, Bisulfate, and Sulfuric Acid

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