X-ray Structures and Homolysis of Some Alkylcobalt(III) Phthalocyanine Complexes

Galezowski, Wlodzimierz; Kubicki, Maciej

doi:10.1021/ic051078p

Cited by 11 publications

(10 citation statements)

References 67 publications

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“…), which may leave the M–C bond susceptible to thermolysis. Indeed, Galezowski and Kubicki reported that the Co(III)Pc–Me analogue (the phthalocyanine analogue of cobalamin) had a BDE of 126 kJ/mol and could be effectively broken by thermolysis (80 °C) . Thus, for applications that allow for phototriggered bond cleavage but must at the same time be relatively thermally stable (100–300 °C), the axial Si–C bond in Si phthalocyanines can provide essential specific control.…”

Section: Results and Discussionmentioning

confidence: 99%

NIR Photocleavage of the Si–C Bond in Axial Si-Phthalocyanines

et al. 2014

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The use of light-triggered photolysis provides a powerful tool for unique syntheses and for applications that require remote operation such as drug delivery or molecular switches. Here, we describe the photochemistry of a recently developed alkylsilicon phthalocyanine Pc 227, which undergoes an exchange of the alkyl ligand for a ligand derived from the solvent when the axial Si-C bond is photolyzed in a solvent with low-energy visible light. In this work with methanol as the solvent, we investigate the formation of the methoxy analogue of the therapeutic drug Pc 4, (termed Pc 233) upon irradiation. Using steady-state spectroscopy and characterization of the photoproducts, the competing pathways between direct ligand exchange on the central silicon atom and delocalization of the radical produced by homolysis on the phthalocyanine ring is observed. The delocalized radical intermediate is quite long-lived. At long times this intermediate decomposes without significant formation of Pc 233. The results of this investigation provide insights into recent work utilizing Pc 227 for drug delivery applications and for future work on the use of phthalocyanines as long-wavelength phototriggers.

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Section: Results and Discussionmentioning

confidence: 99%

NIR Photocleavage of the Si–C Bond in Axial Si-Phthalocyanines

et al. 2014

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“…From the structures, the complexes exhibit an overall octahedral geometry with a Co−C bond length similar to other alkyl-Co(III) complexes. 16,25,27,28 In particular, the metrical data of 2-Me is comparable to that of MeCbl with a Co−C bond length of 1.987 (4) vs 1.99 for MeCbl and Co− N1 of 2.072 (3) vs 2.19 in MeCbl. 29 Notably, the axial Co−N1 bond of 2-Me is shorter than the Co−N py bond using the pyN 4 platform (2.018(2)), showing how the pyrazole arms impose a more rigid environment around the cobalt center in comparison to alkylamines.…”

Section: ■ Results and Discussionmentioning

confidence: 75%

“…In addition, three of the 2-R derivatives were characterized using X-ray crystallography (Figure ). From the structures, the complexes exhibit an overall octahedral geometry with a Co–C bond length similar to other alkyl-Co(III) complexes. ,,, In particular, the metrical data of 2-Me is comparable to that of MeCbl with a Co–C bond length of 1.987 (4) vs 1.99 for MeCbl and Co–N1 of 2.072 (3) vs 2.19 in MeCbl . Notably, the axial Co–N1 bond of 2-Me is shorter than the Co–N py bond using the pyN 4 platform (2.018(2)), showing how the pyrazole arms impose a more rigid environment around the cobalt center in comparison to alkylamines.…”

Section: Resultsmentioning

confidence: 79%

Synthesis, Characterization, and Reactivity of Neutral Octahedral Alkyl-Cobalt(III) Complexes Bearing a Dianionic Pentadentate Ligand

et al. 2020

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A variety of neutral alkyl-cobalt(III) complexes bearing a dianionic tetrapodal pentadentate ligand B2Pz4Py are reported. Compounds 2-R (R = CH3, CH2SiMe3, CH2SiMe2Ph, i Bu, CH2(c-C5H9) and (CH2)4CH=CH2) are synthesized in 58-90% yield. These diamagnetic, octahedral complexes are thermally stable up to 110˚C and are also remarkably stable to ambient atmosphere. They were fully characterized by spectroscopic techniques, and in three cases, X-ray crystallography. Evidence for reversible homolytic cleavage of the Co-C bonds was found in their reactions with the hydrogen atom donor 1,4-cyclohexadiene and the radical trap TEMPO, as well as the observed cyclization of the 5-hexenyl group to the methylcyclopentyl derivative over the course of several hours. Despite these observations, it can be concluded that the diborate B2Pz4Py ligand provides a very stable platform for these Co(III) alkyls. Reduction by one electron to a Co(II) alkyl can accelerate bond homolysis, but in this instance, using cobaltocene as the reducing agent leads to ejection of an alkide anion through bond heterolysis, an unusual reaction for Co(III) alkyls. Finally, protonation of compound 2-Me with the strong acid HNTf2 leads to divergent reactivity in which the major protonation site is the pyridyl nitrogen of the ligand as opposed to protonation of the methyl group. The produce of protonation at nitrogen is the dimeric species 4 which was prepared via separate synthesis and characterized by X-ray crystallography. Introduction. In Nature, two types of cobalamins, also known as Vitamin B12, exhibit a Co-C bond, methylcobalamin (MeCbl) 1 and adenosylcobalamin (AdoCbl), 2 featuring-CH3 and-CH2R groups in the axial position, respectively (Figure 1). In both stable forms of Vitamin B12, the cobalt center bears a +III oxidation state. During catalysis, however, the Co-C bond of MeCbl, can undergo heterolytic cleavage to give Co(I) and CH3 + , while for AdoCbl the bond can cleave homolytically to provide a source of Co(II) and organic radical. 3 Thus, the alkyl groups in these Co(III) alkyls exhibit divergent reactivity in the in vivo function of Vitamin B12. Although both MeCbl and AdoCbl bear the same functionalized corrin L3X supporting

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“…From the structures, the complexes exhibit an overall octahedral geometry with a Co-C bond length similar to other alkyl-Co(III) complexes. 16,25,27,28 In particular, the metrical data of 2-Me is comparable to that of MeCbl with a Co-C bond length of 1.987 (4) vs 1.99 for MeCbl and Co-N1 of 2.072 (3) vs 2.19 in MeCbl. 29 Notably, the axial Co-N1 bond of 2-Me is shorter than the Co-Npy bond using the pyN4 Hydrogen ).…”

Section: Synthesis and Characterization Of 2-rmentioning

confidence: 66%

Synthesis, Characterization and Reactivity of Neutral Octahedral Alkyl-Cobalt(III) Complexes Bearing a Dianionic Pentadentate Ligand

Nurdin

Piers

Lin

et al. 2020

Preprint

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<div>A variety of neutral alkyl-cobalt(III) complexes bearing a dianionic tetrapodal </div><div>pendadentate ligand B2Pz4Py are reported. Compounds 2-R (R = CH3, CH2SiMe3, </div><div>CH2SiMe2Ph, i Bu, CH2(c-C5H9) and (CH2)4CH=CH2) are synthesized in 58-90% yield. These </div><div>diamagnetic, octahedral complexes are thermally stable up to 110˚C and are also </div><div>remarkably stable to ambient atmosphere. They were fully characterized by spectroscopic </div><div>techniques, and in three cases, X-ray crystallography. Evidence for reversible homolytic </div><div>cleavage of the Co-C bonds was found in their reactions with the hydrogen atom donor 1,4-</div><div>cyclohexadiene and the radical trap TEMPO, as well as the observed cyclization of the 5-</div><div>hexenyl group to the methylcyclopentyl derivative over the course of several hours. </div><div>Despite these observations, it can be concluded that the diborate B2Pz4Py ligand provides a </div><div>very stable platform for these Co(III) alkyls. Reduction by one electron to a Co(II) alkyl can </div><div>accelerate bond homolysis, but in this instance, using cobaltocene as the reducing agent, </div><div>leads to ejection of an alkide anion through bond heterolysis, an unusual reaction for </div><div>Co(III) alkyls. Finally, protonation of compound 2-Me with the strong acid HNTf2 leads to </div><div>divergent reactivity in which the major protonation site is the pyridyl nitrogen of the ligand </div><div>as opposed to protonation of the methyl group. The produce of protonation at nitrogen is </div><div>the dimeric species 4 which was prepared via separate synthesis and characterized by Xray crystallography.</div>

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X-ray Structures and Homolysis of Some Alkylcobalt(III) Phthalocyanine Complexes

Cited by 11 publications

References 67 publications

NIR Photocleavage of the Si–C Bond in Axial Si-Phthalocyanines

NIR Photocleavage of the Si–C Bond in Axial Si-Phthalocyanines

Synthesis, Characterization, and Reactivity of Neutral Octahedral Alkyl-Cobalt(III) Complexes Bearing a Dianionic Pentadentate Ligand

Synthesis, Characterization and Reactivity of Neutral Octahedral Alkyl-Cobalt(III) Complexes Bearing a Dianionic Pentadentate Ligand

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