Electronic effects in transition metal porphyrins. I. Reaction of piperidine with a series of para- and meta-substituted nickel(II) and vanadium(IV) tetraphenylporphyrins

Walker, F. Ann; Hui, E. T.; Walker, Janet M.

doi:10.1021/ja00842a014

Cited by 108 publications

(59 citation statements)

References 5 publications

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“…Consistent with its lower basicity, the K 1 values for the tetrabenzoporphyrins are larger than those measured for the octaethylporphyrins. As expected, Ni(II) [28] and Mg(II) [29] are the only compounds that bind two ligands. The weakly basic Ni(II)-tetra(2,3,5,6-tetrafluoro-N,-Ndimethyl-4-anilinium)porphyrin [30] in DMF gives…”

Section: Formation Constants With Pyridinesupporting

confidence: 81%

Tetrabenzoporphyrins: Metal Incorporation and Exchange Kinetics, Ligational Equilibria and Pulse Radiolysis Studies

Cromer

Hambright

Grodkowski

et al. 1997

J. Porphyrins Phthalocyanines

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The solution chemistry of tetrabenzoporphyrin ( TBP ) and several of its metal derivatives were compared with that of the corresponding octaethylporphyrins. Kinetic studies were done on zinc and cadmium ion incorporation and the exchange reactions of cadmium porphyrins with zinc. Formation constants of Cd (II), Cu (II), VO (IV), Ni (II), Zn (II) and Mg (II) porphyrins with pyridine were determined for both compounds. The spectra of the radical cations of Ni (II), Mg (II) and H 2- TBP were obtained, as well as that of the radical anion of Mg (II)- TBP . Aside from the new Ni (I)- TBP , no long-lived intermediates, as noted with other porphyrins, were observed upon reduction of the tetrabenzoporphyrins. The low basicity and rigidity of the tetrabenzoporphyrin nucleus may explain many of its relative reactivity properties.

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Section: Formation Constants With Pyridinesupporting

confidence: 81%

Tetrabenzoporphyrins: Metal Incorporation and Exchange Kinetics, Ligational Equilibria and Pulse Radiolysis Studies

Cromer

Hambright

Grodkowski

et al. 1997

J. Porphyrins Phthalocyanines

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“…[4] Walker et al observed a Hammett relationship of b (K 1S K 2 ) of piperidine with various porphyrins as a function of the meso substituent (R = p-C 6 H 4 R'). [5] A closer look reveals that the increase of the association constant induced by the electron deficiency of the porphyrin and the donor strength of the axial ligand is more pronounced for K 1S than for K 2 . In most combinations of porphyrins and nitrogen donor ligands K 2 is considerably larger than K 1S .…”

Section: Introductionmentioning

confidence: 97%

Coordination‐Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel–Porphyrins: σ‐Donor versus π‐Acceptor Effects

Thies

Bornholdt

Köhler

et al. 2010

Chemistry A European J

120

158

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Nickel-porphyrins, with their rigid quadratic planar coordination framework, provide an excellent model to study the coordination-induced spin crossover (CISCO) effect because bonding of one or two axial ligands to the metal center leads to a spin transition from S=0 to S=1. Herein, both equilibrium constants K(1S) and K(2), and for the first time also the corresponding thermodynamic parameters DeltaH(1S), DeltaH(2), DeltaS(1S), and DeltaS(2), are determined for the reaction of a nickel-porphyrin (Ni-tetrakis(pentafluorophenyl)porphyrin) with different 4-substituted pyridines by temperature-dependent NMR spectroscopy. The association constants K(1S) and K(2) are correlated with the basicity of the 4-substituted pyridines (R: OMe>H>CO(2)Et>NO(2)) whereas the DeltaH(1S) values exhibit a completely different order (OMeCO(2)Et>NO(2)). 4-Nitropyridine exhibits the largest binding enthalpy, which, however, is overcompensated by a large negative binding entropy. We attribute the large association enthalpy of nitropyridine with porphyrin to the back donation of electrons from the Ni d(xz) and d(yz) orbitals into the pi orbitals of pyridine, and the negative association entropy to a decrease in vibrational and internal rotation entropy of the more rigid porphyrin-pyridine complex. Back donation for the nitro- and cyanopyridine complexes is also confirmed by IR spectroscopy, and shows a shift of the N-O and C-N vibrations, respectively, to lower wave numbers. X-ray structures of 2:1 complexes with nitro-, cyano-, and dimethylaminopyridine provide further indication of a back donation. A further trend has been observed: the more basic the pyridine the larger is K(1S) relative to K(2). For nitropyridine K(2) is 17 times larger than K(1S) and in the case of methoxypyridine K(2) and K(1S) are almost equal.

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“…A similar shift is observed for the pyrrolidine-VO(OEP) complex, suggesting that both complexes have the metal in the porphyrin plane. This finding probably applies to the ρiperidine-VO(TpCH^PP) complex as well (19). …”

Section: Effects Of Environment On Vanadium-porphyriη Complexesmentioning

confidence: 75%

“…For example, Walker et a I . (19) noted a large red shift (578 •+ 605 nm) in the a band of the absorption spectrum of VO tetra-p-methyIphenyIporphyriη (VO(TpCH^PP)) in piperidine indicating formation of the piperidine adduct.…”

Section: Axial Ligation In Vanadium Porphyrinsmentioning

confidence: 99%

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Axial Coordination in Nickel and Vanadium Porphyrins: Transient and Difference Raman Spectroscopy

Shelnutt

Alston

Findsen

et al. 1987

ACS Symposium Series

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Nickel-and vanadium-porphyrin complexes and Ni(II)-reconstituted hemoglobin ( Ni Hb) and myoglobin ( Ni Mb) have been investigated using cw and transient resonance Raman spectroscopy.The state of axial coordination at the metal in these materials can be determined using the characteristic frequencies of the Raman marker lines arising from the porphyrin moiety.The state of axial ligation is highly sensitive to the molecular environment of these geoporphyrin analogs.Whether vanadium porphyrins are 5-or 6-coordinate depends on solvent and π-π aggregation and complexation. Similarly, nickel porphyrins exhibit 4-, 5-, or 6-coordination depending on the molecular environment.Nickel -reconstituted proteins provide well characterized models of hydrophobic cavities such as might exist in a heterogeneous petroleum environment.In the protein cavity a novel 5-coordinate Ni-porphyrin complex is observed. The existence of only one axial ligand is supported by identification of the axial ligand-Ni stretching vibration by isotopic substitution.The frequency of the Ni-ligand mode is consistent with histidine as the fifth ligand. The effects of the T->R change in quaternary structure of the protein environment of the Ni porphyrin are also observed in the Raman spectrum. The photoinitiated ligand-release and ligand-uptake processes in excited states of the Ni porphyrins and Ni-reconstituted proteins were also investigated. Laser excitation (~10-ns duration) of the complexes formed in coordinating solvents induces the release of axial ligands, but does not induce release of the histidine ligand of Ni-reconstituted hemoglobin and myoglobin. The results indicate that the protein matrix controls ligation dynamics by promoting rapid geminate recombination of the ligand.

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Electronic effects in transition metal porphyrins. I. Reaction of piperidine with a series of para- and meta-substituted nickel(II) and vanadium(IV) tetraphenylporphyrins

Cited by 108 publications

References 5 publications

Tetrabenzoporphyrins: Metal Incorporation and Exchange Kinetics, Ligational Equilibria and Pulse Radiolysis Studies

Tetrabenzoporphyrins: Metal Incorporation and Exchange Kinetics, Ligational Equilibria and Pulse Radiolysis Studies

Coordination‐Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel–Porphyrins: σ‐Donor versus π‐Acceptor Effects

Axial Coordination in Nickel and Vanadium Porphyrins: Transient and Difference Raman Spectroscopy

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