Tridentate Nitrogen Donor Ligand Research Articles

Synthesis and Structural Studies of Ionic Monoorganopalladium(II) Complexes with Tridentate Nitrogen-Donor Ligands

Ionic palladium(I1) complexes of the types [PdCl(N-N-N)ICl and [PdR(N-N-N)IOTf', with R = Me or aryl, N N N = tridentate nitrogen donor ligand, and OTf = trifluoromethanesulfonate (triflate), have been prepared. The tridentate nitrogen-donor ligands used are 2,6-bis[( dimethy1amino)methyllpyridine (NN'N), NJVfl-trimethylN'(2-picoly1)ethylenediamine (pico), and NJVfl,NJV-pentamethyldiethylenetriamine (pmdeta). The chloro derivatives (3-5a) were obtained as yellow ionic complexes in excellent yields (81-93%). Crystals of 4a were obtained from methanovdiethyl ether and are monoclinic, space group P21/c (No. 141, a = 15.0760(7) A, b = 7.4468(8) A, c = 13.553(2) A, #? = 115.653(6), and 2 = 4. Refinement converged at R = 0.0325 (wR2 = 0.0663). The molecular structure shows a four-coordinate palladium center surrounded by the terdentate bound pic0 ligand and a chloride anion. There is no interaction of the palladium center with the second chloride anion (Pd-C12 L 4.2617 A). The Pd-NMe bond distance (2.023(3) A) is relatively short and is accompanied by a small trans N-Pd-N bond angle (168.03(12)). The methyl derivatives (3-5b) were also obtained in good yield (79-91%) via reaction of PdIMe(tmeda) (tmeda = NjVflfl-tetramethylethylenediamine) with silver trifluoromethanesulfonate and the ligand. An alternative route, starting from PdMez(tmeda1, is reported for the synthesis of [PdMe(NN)OTf (3b). Crystals of 3b were obtained from methanovdiethyl ether and are monoclinic, space group P21/a (No. 141, a = 7.738(1) A, b = 21.280(2) A, c = 11.399(1) A, ,8 = 92.05(1), and 2 = 4. Refinement converged a t R = 0.066 (R, = 0.065). The molecular structure of 3b shows a terdentate coordination of the NN'N ligand to the metal, with a relatively short Pd-N bond distance (1.996(8) A) and small N-Pd-N bond angle (161.7(3)). Yellow crystals of [PdMe(ON)(tmeda)lOTf (8), with O N = 24hydroxymethyl)6-[(dimethylamino)methyl]pyridine (71, were accidentally obtained from the reaction of [PdMe(MeCN)(tmeda)]OTf (I) with an impure sample of the NN'N ligand, containing the O N ligand. The molecular structure of 8 shows the O N ligand monodentate coordinated to the metal via its pyridyl nitrogen donor whereas the NMez and OH functionalities are free. The triflate anion is hydrogen bonded to the hydroxymethyl group with OH-O(S02CF3) = 2.759(3) A and-0-H-0 = 173(4). Crystals of [PdMe(ONN')(tmeda)lOTf (8) are triclinic, space group P1 (No. 21, a = 9.7902(14) A, b = 10.0555(15) A, c = 12.362(2) A, a = 75.828(12), p = 81.234(12), y = 84.836(11), and 2 = 2. Refinement converged at R = 0.032 ( R , = 0.040). The first examples of simple arylpalladium(I1) cations containing tridentate ligands were obtained in moderate to high yield (35-95%). The aryl groups studied differ in both steric and electronic properties. Conformational analysis by NMR of the NCCN moieties of the pic0 and pmdeta containing complexes showed the five-membered chelate rings in the complexes to occur selectively in one of the two possible conformations. The rotational-energy barriers of the aryl groups have been studied as a function of the ligand and were shown to increase in the order NNTJ < pic0 < pmdeta. This is explained in terms of the positioning and orientation of the pyridyl and NMe2 groups around the metal center. The aryl rotation is found to be blocked in ortho-substituted aryl complexes, leading to atropisomerism in the pmdeta complex.

Synthesis, crystal structure, and magnetic properties, of a Cu(II) solid state compound derived from the 3,4,9,10-perylenetetracarboxylate anion and diethylenetriammine (abstract)

Several strategies have been used to develop novel magnetic materials. One of these is the simultaneous use of at least two different ligands, one an oxygen donor and the other a nitrogen donor. With this approach, using the optically interesting oxygen donor, 3,4,9,10-perylenetetracarboxylate anion (petca), and the tridentate nitrogen donor ligand, diethylenetriamine (dien), we recently reported1 the synthesis of the solid state Cu(II) compound, [Cu5(dien)5(petca)2H2O4] (ClO4)2⋅2H2O (1). This compound contains three different copper species, a chain [Cu2 (dien)2(petca)n, a dimer [Cu2(dien)2(petca)(H2O)2] and a monomer [Cu(dien)(H2O)2] and several exchange pathways. We wish to report, that the dimeric units in 1 have been isolated. The structure of the compound [Cu2(dien)2(petca)H2O)2]⋅13H2O (2), has been determined by an x-ray single-crystal diffraction study. Two different dimers are present in the unit cell: isolated dimer units, surrounded by water molecules; and dimers connected through hydrogen bonds in a way that resembles the chains in 1. In both cases, the Cu(II) ion is coordinated to one oxygen from the petca anion, the three nitrogen atoms of the dien, and a water molecule, in a nearly square planar geometry. The magnetic properties of this compound relate to these structural features.

Synthesis of the first organopalladium(IV) cations, including the first X-ray study of isostructural organopalladium(IV) and platinum(IV) complexes, [fac-MMe3{tris(pyrazol-1-yl)methane-N,N′,N′}

Stable organopalladium(IV) complexes [fac-PdMe3(L)]I (L = tridentate nitrogen donor ligand) are formed on oxidative addition of iodomethane to PdMe2(L); the tris (Pyrazol-1-yl)methane complex is isostructural with the platinum(IV) analogue.

New iron(II) spin-crossover complexes with heterocyclic amine-derived ligands and STEPS experiments on photogenerated metastable high-spin states

Cationic complexes of the type [Fe(LNN)3]2+ and [Fe(LNNN)2]2+ have been isolated as Cl–, ClO4–, or BF4– salts, where LNN and LNNN represent bidentate and tridentate nitrogen-donor ligands respectively. The bidentate ligands were 2-(2′-pyridyl) benzimidazole (pybtim), 2-(2′-pyridyl)-N-methylbenzimidazole (mpybzim); 2-(2′-pyridyl) benzothiazole (pybzt), 2,2′-dipyridylamine (dpya), and the tridentates di(2-pyridylmethyl)amine (dpyma), 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy), 2,6-bis(N-methylbenzimidazol-2′-yl)pyridine (mbzimpy), and 2,6-bis(benzothiazol-2′-yl) pyridine (bztpy). Except for [Fe(dpya)3][ClO4]2, all these FeN6 chromophores exhibit strong absorption in the 550 nm region, which is assigned as a metal-to-ligand charge-transfer transition. Between 4 and 320 K, the iron(II) is in the low-spin form in the majority of these compounds; high-spin exceptions are [Fe(dpya)3][ClO4]2 and [Fe(mbzimpy)2]Cl2. Other complexes show evidence of the onset of a spin transition near 40 °C, while the salt [Fe(bztpy)2][ClO4]2·CHCl3 is a well defined spin-crossover system. The low-spin complex [Fe(bzimpy)2][ClO4]2 was excited by irradiation with visible light, and the generation and decay of the resulting high-spin form was observed under cryogenic conditions. In solution, [Fe(bzimpy)2]2+ acts as a weak diprotic acid and also exhibits quintet ⇌ singlet spin crossover (ΔH⊖=–42.7 kJ mol–1, ΔS⊖=–140.9 J K–1 mol–1). The complexes are all electrochemically oxidizable to their iron(III) forms in non-aqueous solution, but the dpyma, bztpy, pybtz, and dpya chelates thus formed are unstable. The iron(III) complex [Fe(H–2bzimpy)2]– containing the doubly deprotonated ligand was obtained as its low-spin triethylammonium salt. The high-spin chloro complexes [Fe(bzimpy)Cl3], [Fe(mbzimpy)Cl3], Fe(mbzimpy)Cl2, and the mixed-spin iron(II) complex salt [Fe(bzimpy)][FeCl4] were also isolated.