- Comparison of the electronic properties of diarylamido-based PNZ pincer ligands: Redox activity at the ligand and donor ability toward the metal
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This paper presents the synthesis and characterization of a series of pincer ligands and their Ni, Pd, Pt, and Rh complexes. The ligands under examination are based on a diarylamine which is modified either by two phosphino (-PR2) substituents in the ortho-positions (PNP ligands) or by a combination of a phosphino and an iminyl (?CH - NX) substituent (PNN ligands). The ligands can be broken down into three groups: (a) C2v-symmetric PNP ligands with identical side ?PR2 donors, (b) Cs-symmetric PNP? ligands with different ?PR2 side donors, and (c) PNN ligands containing a ?PiPr2 side donor. All of the ligands under study readily formed square-planar complexes of the types (PNZ)PdCl, (PNZ)Pd(OAc), and (PNZ)RhCO, where PNZ is the corresponding anionic tridentate pincer ligand. For select PNP ligands, (PNP)NiCl and (PNP)PtCl were also studied. The (PNZ)MCl complexes (M = Ni, Pd, Pt) underwent quasireversible oxidation in cyclic voltammetry experiments. Based on the close similarity of formal potentials for Ni, Pd, and Pt analogs, and based on the previous literature evidence, these oxidation events are ascribed primarily to the PNZ ligand, and the E1/2 values can be used to compare the ease of oxidation of different ligands. A (PNP)PdCl complex containing methoxy substituents para- to the central nitrogen underwent two quasireversible oxidations. Two mono-oxidized complexes were isolated and structurally characterized in comparison to their neutral analog, revealing minimal changes in the bond distances and angles. Several other neutral complexes were also structurally characterized. The carbonyl stretching frequency in (PNZ)RhCO complexes was used to gauge the donating ability of the various pincer ligands toward the metal. Comparison of E1/2 values for (PNZ)PdCl and ?CO values for (PNZ)RhCO revealed that the two are not consistently correlated across all the studied ligands and can be tuned to different degrees through judicious ligand alteration.
- Davidson, Jillian J.,Demott, Jessica C.,Douvris, Christos,Fafard, Claudia M.,Bhuvanesh, Nattamai,Chen, Chun-Hsing,Herbert, David E.,Lee, Chun-I,McCulloch, Billy J.,Foxman, Bruce M.,Ozerov, Oleg V.
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p. 2916 - 2935
(2015/03/30)
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- Homoleptic nickel(II) complexes of redox-tunable pincer-type ligands
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Different synthetic methods have been developed to prepare eight new redox-active pincer-type ligands, H(X,Y), that have pyrazol-1-yl flanking donors attached to an ortho-position of each ring of a diarylamine anchor and that have different groups, X and
- Hewage, Jeewantha S.,Wanniarachchi, Sarath,Morin, Tyler J.,Liddle, Brendan J.,Banaszynski, Megan,Lindeman, Sergey V.,Bennett, Brian,Gardinier, James R.
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supporting information
p. 10070 - 10084
(2015/01/09)
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- Preparation, properties, and reactivity of carbonylrhodium(I) complexes of di(2-pyrazolylaryl)amido-pincer ligands
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A series of six carbonylrhodium(I) complexes of three new and three previously reported di(2-3R-pyrazolyl)-p-Z/X-aryl)amido pincer ligands, ( RZX)Rh(CO), (R is the substituent at the 3-pyrazolyl position proximal to the metal; Z and X are the aryl substituents para- to the arylamido nitrogen) were prepared. The metal complexes were studied to assess how their properties and reactivities can be tuned by varying the groups along the ligand periphery and how they compared to other known carbonylrhodium(I) pincer derivatives. This study was facilitated by the discovery of a new CuI-catalyzed coupling reaction between 2-(pyrazolyl)-4-X-anilines (X = Me or CF3) and 2-bromoaryl-1H-pyrazoles that allow the fabrication of pincer ligands with two different aryl arms. The NNN-pincer scaffolds provide an electron-rich environment for the carbonylrhodium(I) fragment as indicated by carbonyl stretching frequencies that occur in the range of 1948-1968 cm-1. As such, the oxidative addition (OA) reactions with iodomethane proceed instantaneously to form trans-(NNN-pincer)Rh(Me)(CO)(I) in room temperature acetone solution. The OA reactions with iodoethane proceeded at a convenient rate in acetone near 45 °C which allowed detailed kinetic studies. The relative order of reactivity was found to be (CF3CF 3)Rh(CO) iPrMeMe)Rh(CO) MeMeMe) Rh(CO) ~ (CF3Me)Rh(CO) 2 = 8 × 10-3 M-1 s-1, being about three orders of magnitude greater than those reported for [Rh(CO)2I 2]- or CpRh(CO)(PPh3). After oxidative addition, the resultant rhodium(III) complexes were found to be unstable. Although a few trans-(RMeMe)Rh(E = Me, Et, or I)(CO)(I) could be isolated in pure form, all were found to slowly decompose in solution to give different products depending on the 3R-pyrazolyl substituents. Those with unsubstituted pyrazolyls (R = H) decompose with CO dissociation to give insoluble dimeric [(RMeMe)Rh(E)(μ-I)]2 while those with 3-alkylpyrazolyls (R = Me, iPr) decompose to give soluble, but unidentified products.
- Wanniarachchi, Sarath,Liddle, Brendan J.,Lindeman, Sergey V.,Gardinier, James R.
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scheme or table
p. 3623 - 3636
(2011/12/02)
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- Chemical switching behaviour of tricarbonylrhenium(i) complexes of a new redox active 'Pincer' ligand
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The structures and optoelectronic properties of tricarbonylrhenium(i) complexes of di(2-pyrazolyl-p-tolyl)amine in its neutral and deprotonated (uninegative amido) form were investigated. Reactions of the complexes with Bronsted acids or bases result in d
- Wanniarachchi, Sarath,Liddle, Brendan J.,Toussaint, John,Lindeman, Sergey V.,Bennett, Brian,Gardinier, James R.
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body text
p. 3167 - 3169
(2010/06/21)
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