28110-70-5Relevant articles and documents
Laser photolysis of chromium(III) porphyrins with axial pyridines in dichloromethane and toluene solutions. Novel effects of a hydrogen bond in the ligand exchange reaction
Inamo, Masahiko,Nakaba, Hideyuki,Nakajima, Kiyohiko,Hoshino, Mikio
, p. 4417 - 4423 (2000)
Laser photolysis studies were carded out for (chloro)(pyridine)(5,10,15,20-tetraphenylporphyrinato)chromium-(III), [Cr(TPP)(Cl)(Py)], in both dichloromethane and toluene containing water. The five-coordinate [Cr(TPP)(Cl)] produced by the photoinduced dissociation of pyridine from [Cr(TPP)(Cl)(Py)] initially reacts with H2O to give [Cr(TPP)(Cl)(H2O)], which eventually exchanges the axial H2O with Py to regenerate [Cr(TPP)(Cl)(Py)]. The rate for the ligand exchange of [Cr(TPP)(Cl)(H2O)] with exogenous Py is found to exhibit a bell-shaped pyridine-concentration dependence. Kinetic studies revealed that at a high Py concentration, the exogenous Py probably makes a hydrogen bond with the axial H2O of [Cr(TPP)(Cl)(H2O)] to yield [Cr(TPP)(Cl)(HO-H···Py)] as a dead-end complex. A similar structure of the Cr-TPP complex having 2-methylpyridine molecules bound to the coordinated H2O ligand by a hydrogen bond was determined by X-ray structure analysis. The exchange reaction of the axial HO-H···Py in [Cr(TPP)(Cl)(HO-H···Py)] by Py follows the dissociative mechanism: The first step is the dissociation of Py from [Cr(TPP)(Cl)(HO-H···Py)], and the second step is the dissociation of H2O. The five-coordinate [Cr(TPP)(Cl)] thus produced reacts with Py to regenerate [Cr(TPP)(Cl)(Py)]. The direct ligand exchange reaction of the axial HO-H···Py in [Cr(TPP)(Cl)(HO-H···Py)] with exogenous Py does not occur. Probably, the hydrogen bond, HO-H···Py, increases the basicity of H2O, and thus, the bond energy between Cr and O in [Cr(TPP)(Cl)(HO-H···Py)] becomes much stronger than that in [Cr(TPP)(Cl)(H2O)]. The mechanism of the ligand substitution reaction of the chromium(III) porphyrins has been examined in detail on the basis of the laser photolysis studies of [Cr(TPP)(Cl)(L)] (L = pyridine, 3-cyanopyridine, and H2O).
Binding of propylene oxide to porphyrin- and salen-M(III) cations, where M = Al, Ga, Cr, and Co
Chen, Peter,Chisholm, Malcolm H.,Gallucci, Judith C.,Zhang, Xiangyang,Zhou, Zhiping
, p. 2588 - 2595 (2005)
The binding of propylene oxide (PO) to a series of metal cations LM(III)+, where for L = tetraphenylporphyrin (TPP) M = Al, Ga, Cr, and Co, and for L = (R,R)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexenediamine (salen) M = Al and Cr, was studied in the gas phase by electrospray tandem mass spectroscopy, and the relative stabilities of LM(PO)2+ and LM(PO)+ cations were determined. The chromium(III) and aluminum(III) cations most tenaciously bind PO, and for M = Al, coordination to the TPP ligated metal center was favored relative to salen. For (TPP)M(PO)2+, the dissociation of PO followed the order M = Al > Cr, but for (TPP)M(PO)+ the dissociation was M = Cr > Al. The single-crystal structural determinations on (R,R-salen)AlOCHMe(S)CH2Cl-0.5PO and (R,R-salen)AlO 2CMe-1.5py grown in neat PO and pyridine, respectively, reveal five-coordinate aluminum(III) centers with the alkoxide/acetate ligands in the axial position of a square-based pyramid. These results are discussed in terms of the reactivity of these metal complexes in ring-opening polymerizations and copolymerizations with PO and CO2, respectively.
Probing 'spin-forbidden' oxygen-atom transfer: Gas-phase reactions of chromium-porphyrin complexes
Crestoni, Maria Elisa,Fornarini, Simonetta,Lanucara, Francesco,Warren, Jeffrey J.,Mayer, James M.
, p. 4336 - 4343 (2010/05/14)
Oxygen-atom transfer reactions of metalloporphyrin species play an important role in biochemical and synthetic oxidation reactions. An emerging theme in this chemistry is that spin-state changes can play important roles, and a 'two-state' reactivity model
