Palladium(II)/(III) complexes of triaza macrocycles: synthesis and single crystal X-ray structures of [PdIII(tacn)2]3+and [PdII(tacn)(tacnH)]3+(tacn = 1,4,7-triazacyclononane)
Abstract:The complex cation [Pd(tacn),]2+ (tacn = 1,4,7-triazacyclononane) shows a one-electron oxidation at €+ = +0.07 V vs. Fc/Fc+ (ferrocene/ferrocinium) to afford the stable mononuclear Pd"1 species [Pd(tacn),]3+, which has a tetragonally-distorted octahedral structure with Pd-N(l) = 2.180(9), Pd-N(4) = 2.1 18(9), Pd-N(7) = 2.1 1 l(9) A.
“…Some minerals and zeolites doped with Pd III 23 as well as MCl-doped lattices (M = Na, K) are known. There are several molecular compounds having tridentate macrocyclic ligands such as 1,4,7-triazacyclononane, nido -borane, or other ligands. − Most of the reported EPR spectra for these compounds have relatively broad bands with little anisotropy and g values close to the free electron value. With few exceptions, the reported g values range from 2.123 to 2.005, and in most cases g ⊥ is very close to g || and often larger than g || in agreement with axially elongated octahedral geometry. , The only Pd III coordination compound in which the 105 Pd hyperfine structure is resolved in an EPR spectrum is [Pd(1,4,7-trithiacyclononane) 2 ] 3+ .…”
Reaction of Pd(2)(DAniF)(4), 1, (DAniF = di-p-anisylformamidinate) with 1 equiv of AgPF(6) in CH(2)Cl(2) at or below -10 degrees C produces the paramagnetic species [Pd(2)(DAniF)4]PF(6), 1-PF(6), that has been studied by X-ray crystallography, UV-vis spectroscopy, electrochemistry, and multifrequency (9.5, 34.5, 110, and 220 GHz) EPR spectroscopy. Upon oxidation of the precursor, the Pd-Pd distance decreases by 0.052 Angstrom from 2.6486(8) to 2.597(1) Angstrom. The EPR spectra show broad signals with line widths of about 1000 G. The spectra collected at high field show a large spread of g tensor components ( approximately 0.03), but these are masked at lower frequencies (9.5 and 34.5 GHz). A reinvestigation using high-field EPR of the p-tolyl analogue, which is the only other structurally characterized Pd(2)(5+) species (Cotton, F. A.; Matusz, M.; Poli, R.; Feng, X. J. Am. Chem. Soc. 1988, 110, 1144), shows that this species, which had been reported to give an isotropic 9.5 GHz EPR spectrum, also gives anisotropic 110 and 220 GHz EPR spectra with a similarly large spread of g tensor components consistent with the unpaired electron residing in a metal-based MO. The results of these studies and calculations using density functional theory are consistent with the oxidation being metal-based, resulting in an uncommon Pd(2)(5+) species with a Pd-Pd bond order of 1/2.
“…Some minerals and zeolites doped with Pd III 23 as well as MCl-doped lattices (M = Na, K) are known. There are several molecular compounds having tridentate macrocyclic ligands such as 1,4,7-triazacyclononane, nido -borane, or other ligands. − Most of the reported EPR spectra for these compounds have relatively broad bands with little anisotropy and g values close to the free electron value. With few exceptions, the reported g values range from 2.123 to 2.005, and in most cases g ⊥ is very close to g || and often larger than g || in agreement with axially elongated octahedral geometry. , The only Pd III coordination compound in which the 105 Pd hyperfine structure is resolved in an EPR spectrum is [Pd(1,4,7-trithiacyclononane) 2 ] 3+ .…”
Reaction of Pd(2)(DAniF)(4), 1, (DAniF = di-p-anisylformamidinate) with 1 equiv of AgPF(6) in CH(2)Cl(2) at or below -10 degrees C produces the paramagnetic species [Pd(2)(DAniF)4]PF(6), 1-PF(6), that has been studied by X-ray crystallography, UV-vis spectroscopy, electrochemistry, and multifrequency (9.5, 34.5, 110, and 220 GHz) EPR spectroscopy. Upon oxidation of the precursor, the Pd-Pd distance decreases by 0.052 Angstrom from 2.6486(8) to 2.597(1) Angstrom. The EPR spectra show broad signals with line widths of about 1000 G. The spectra collected at high field show a large spread of g tensor components ( approximately 0.03), but these are masked at lower frequencies (9.5 and 34.5 GHz). A reinvestigation using high-field EPR of the p-tolyl analogue, which is the only other structurally characterized Pd(2)(5+) species (Cotton, F. A.; Matusz, M.; Poli, R.; Feng, X. J. Am. Chem. Soc. 1988, 110, 1144), shows that this species, which had been reported to give an isotropic 9.5 GHz EPR spectrum, also gives anisotropic 110 and 220 GHz EPR spectra with a similarly large spread of g tensor components consistent with the unpaired electron residing in a metal-based MO. The results of these studies and calculations using density functional theory are consistent with the oxidation being metal-based, resulting in an uncommon Pd(2)(5+) species with a Pd-Pd bond order of 1/2.
“…However, there is a shift from the pendant methyl being equatorial in I to axial in diammac. The Pd−N distances are slightly shorter than in the Pd(II) complex of cyclam [2.044(7), 2.057(7) Å] and shorter still than in complexes of cyclic amines such as 1,4,7-triazacyclononane where the amine acts as a simple chelate [average 2.056(6) Å] . 1 ORTEP drawing of the cation of I showing the crystallographic numbering (50% probability ellipsoids shown; hydrogen atoms omitted).…”
The bis(diamine)palladium(II) cations (diamine = ethane-1,2-diamine, propane-1,3-diamine, or butane-1,4-diamine) all undergo condensation reactions with formaldehyde and nitroethane to produce macromonocycles where each pair of cis-disposed primary amines has been converted to a -NH-CH(2)-C(CH(3))(NO(2))-CH(2)-NH- strap. The 14-membered-ring macrocycle has been previously prepared by condensation around copper(II) and nickel(II), but this does not permit synthesis of the larger ring macrocycles. The macrocyclic complex (6,13-dimethyl-6, 13-dinitro-1,4,8,11-tetraazacyclotetradecane)palladium(II) perchlorate crystallizes in the triclinic space group P&onemacr;, a = 8.105(3) Å, b = 8.370(2) Å, c = 9.437(4) Å, alpha = 69.04(3) degrees, beta = 68.60(3), gamma = 71.53(3) degrees. Complexes of the 16- and 18-membered macrocycles (3,11-dimethyl-3,11-dinitro-1,5,9,13-tetraazacyclohexadecane)palladium(II) perchlorate and (3,12-dimethyl-3,12-dinitro-1,5,10,14-tetraaazacyclooctadecane)palladium(II) perchlorate crystallize in the monoclinic space group P2(1)/c, with a = 8.391(2) Å, b = 12.816(3) Å, c = 23.925(9) Å, and beta = 93.18(2) degrees, and the triclinic space group P&onemacr;, with a = 7.746(5) Å, b = 9.912(5) Å, c = 18.96(2) Å, alpha = 91.76(6) degrees, beta = 101.73(7) degrees, and gamma = 112.83(5) degrees respectively. The larger macrocycles are "swollen" by incorporating longer methylene chains, "swelling" leading to an increase in Pd-N distance and in tetrahedral distortion, with the dominant geometric isomer apparently changing with macrocycle size from anti-disposed nitro pendants (14-membered) to the syn isomer (16-, 18-membered). An irreversible Pd(II/IV) oxidation occurs at ca +1 V (vs Ag/AgCl), varying slightly with ring size, with a multi-electron nitro group reduction observed near -0.8 V in each case. Electronic spectra also vary slightly with ring size.
In this article we present the rational synthesis and full characterization of molecular Pd 3 clusters sandwiched by imidazolium-and pyridinium-functionalized cycloheptatrienide ligands, of general formula [Pd 3 Br 3 (C 7 H 6 R) 2 ] + . From functionalized η 3 -cycloheptatrienide Pd complexes as starting materials, PdBr 2 (η 3 -C 7 H 6 R), a number of synthetic routes were tested and a generally applicable strategy was developed on the basis of the formation of dimeric "preclusters", [{PdBr(η 3 -C 7 H 6 R)} 2 (μ-Br)] + , which exhibit a Pd−Pd interaction. Spectroscopic and electrochemical results indicate a noninteger, common oxidation state of Pd in the trinuclear clusters, and crystallographic analysis reveals distinct differences in the binding properties of the Pd atoms in the solid state, suggesting that in certain environments there are even two discernible oxidation states, which is supported by computational analysis of the charge distribution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
