Donald L. Jameson

An improved, two-step synthesis of 2,2′:6′,2″-terpyridine.

Abstract The important tridentate ligand 2,2′:6′,2″-terpyridine has been synthesized in two steps in an overall yield of 47%. The reaction can be scaled up to provide multigram quantitites of the ligand.

Structural considerations of terdentate ligands: crystal structures of 2,2′ : 6′,2″-terpyridine and 2,6-bis(pyrazol-1-yl)pyridine

The crystal structures of the terdentate ligands 2,2′ : 6′,2″-terpyridine (terpy) and 2,6-bis(pyrazol-1-yl)pyridine (bppy) were determined by single-crystal diffraction studies. The compound terpy crystallizes in the non-centrosymmetric orthorhombic space group P212121 with a= 3.947(1), b= 16.577(7) and c= 17.840(6)A; the structure was refined to R= 0.0745 for all 1087 independent data and R= 0.0470 for those 609 data with F > 6σ(F). The compound bppy crystallizes in the centrosymmetric orthorhombic space group Pnma with a= 11.929(3), b= 21.320(3) and c= 3.889(0)A; this structure was refined to R= 0.0409 for all 896 independent data and R= 0.0300 for those 723 reflections with F > 6σ(F). The structures of the free terpy and bppy ligands were compared directly with the structures of the co-ordinated terpy and bppy ligands in the [RuL(NO2)(PMe3)2][ClO4] complexes (L = terpy 1 or bppy 2) in order to determine if any ligand structural changes occur upon co-ordination to ruthenium. To act as terdentate ligands, it was observed that both terpy and bppy must adopt the cis,cis ligand configuration as opposed to the trans,trans configuration found in the solid state and as the equilibrium configuration in solution. Both terpy and bppy distort upon co-ordination to ruthenium. The greatest distortions for terpy occur primarily at the central pyridine ring. Large distortions were observed for bppy at both in the central pyridine ring and in the terminal pyrazole rings.

Redox and spin state control of Co(II) and Fe(II) N-heterocyclic complexes

Abstract Two series of complexes with the general formulas [Co(L) 2 ] 2+ and [Fe(L) 2 ] 2+ , where L represents the tridentating ligands 2,2′:6′;2′′-terpyridine (L 1 ), 6-( N -pyrazolyl)-2,2′-bipyridine (L 2 ); and 2,6-bis( N -pyrazolyl)pyridine (L 3 ), were prepared and characterized. The electronic properties of both series of compounds were investigated as a function of stepwise variation in coordinated pyridines relative to pyrazoles. In the cobalt series, the Co(III/II) redox potential measured an average anodic shift of 0.16 V for each pyridine coordination site replaced by pyrazole, while only a slight shift was observed for the Fe(III/II) couple. Solution magnetic susceptibility measurements showed a general shift toward a high-spin ground state as pyridine was replaced by coordinated pyrazoles. The cobalt series exhibited a μ eff of 3.2 B.M. for bis-terpy (L 1 ) which is close to the spin crossover, while the μ eff for [Co(L 2 ) 2 ] 2+ and [Co(L 3 ) 2 ] 2+ were measured at 4.5 and 4.6 B.M., respectively. For the iron series, [Fe(L 1 ) 2 ] 2+ and Fe(L 2 ) 2 ] 2+ exhibited a stable diamagnetic low-spin state; however, [Fe(L 3 ) 2 ] 2+ measured a μ eff of 4.6 B.M. which implies a spin equilibrium that is predominantly high-spin with possible low-spin contribution. The observed redox and spin state regulation correlate with the weaker σ-donor and π-acceptor properties of coordinated pyrazole relative to pyridine.

Tuning redox and spin state properties of Fe(II) N-heterocyclic complexes via electronic/steric influence on metal–ligand binding

A series of complexes with the general formula [Fe(L)2]2+, where L represents the tridentating 6-(N-3,5-dimethylpyrazolyl)2,2′-bipyridine (L4); 6-(N-pyrazolyl-1-ylmethyl)-2,2′-bipyridine (L5); and 6-(N-3,5-dimethylpyrazolyl-1-ylmethyl)-2,2′-bipyridine (L6), were prepared and characterized. The room temperature solution magnetic susceptibility and redox properties of these compounds were investigated as a function of stepwise variation in the ligand structure. The Fe(III/II) couple was characterized by way of cyclic voltammetry using aprotic solvent conditions (acetonitrile) where each complex was observed to have reversible behavior. NMR methodology was used for measuring the magnetic susceptibilities where both [Fe(L4)2]2+ and Fe(L5)2]2+ exhibited diamagnetic low spin behavior; however, [Fe(L6)2]2+ measured a μeff of 4.1 Bohr-magnetons indicating spin equilibrium predominantly in the high spin state.

Application of crystallization-induced asymmetric transformation to a general, scalable method for the resolution of 2,8-disubstituted Tröger's base derivatives.

A general method for the gram scale resolution of 2-substituted and 2,8-disubstituted Trögers base (TB) derivatives in 63-91% yield has been achieved through the application of crystallization-induced asymmetric transformation (CIAT). Enantiomeric ratios of the resolved TB derivatives range from 99.1:0.9 to >99.5:0.5. Among the Trögers base compounds resolved are four synthetically valuable bromo and iodo derivatives.

Design and synthesis of a series of facially coordinating tridentate ligands containing an N2O donor atom set

Abstract The preparation of a series of facially coordinating tridentate ligands is described. The N2O ligands contain a phenol and either two imidazole, two pyridine or two pyrazole donor atoms.

Synthesis, characterization and crystal structure of trans-[2,6-bis(3-phenylpyrazol-1-yl-κN2)pyridine-κN]chloro-bis(trimethylphosphine)ruthenium(II) perchlorate: evidence for meridional steric crowding

The synthesis, characterization, and crystal structure of trans-[RuL(Cl)(PMe3)2]ClO4[L = 2,6-bis(3-phenylpyrazol-1-yl)pyridine] are reported. The complex crystallizes in the non-centrosymmetric trigonal space group P3121 (no. 152) with a= 14.158(2), c= 14.493(3)A, and Z= 3. Both the RuII-containing cation and the perchlorate anion (which is disordered) lie on a crystallographic two-fold axis. This represents the first structural characterization of a transition-metal complex which utilizes a member of the family of bis(pyrazolyl)pyridine ligands. In addition, the crystal structure yields evidence that the ligand L may be sterically more suitable for co-ordination to a ruthenium(II) centre than the analogous diphenyl-substituted terpyridine ligand, dpt (6,6″-diphenyl-2,2′ : 6′2″-terpyridine). For both tridentate ligands, the donor nitrogen atoms take up three meridional sites and the phenyl substituents are directed toward the fourth equatorial co-ordination site; however, due to the large distance between the two phenyl arms of L (relative to the dpt), the former ligand can be utilized in synthesising the present ruthenium(II) complex whereas the analogous dpt complex cannot readily be prepared.

Crystal and molecular structure of the bidentate ligand 2,2-di(1-pyrazolyl)propane, CH3C(C3N2H3)2CH3

The title compound lies on a site of C2 symmetry, with the two planar pyrazolyl moieties oriented at 86.1° to one another. The hydrogen atoms were located and refined.

Crystal and molecular structure of di(1-pyrazolyl)methane, CH2(C3N2H3)2

The title compound consists of two planar pyrazolyl fragments oriented at 73.0° to each other and linked to a common carbon atom. All hydrogen atoms were located unambiguously and their positions were refined.

Synthesis and characterization of ruthenium complexes which utilize a new family of terdentate ligands based upon 2,6-bis(pyrazol-1-yl)pyridine

To demonstrate the synthetic utility of a new family of terdentate ligands based on 2,6-bis(pyrazol-1-yl)pyridine (bpp), reaction conditions were developed to generate a variety of [RuL(NO2)(PMe3)2]+ complexes [L = bpp, 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine(bdmpp), 2,6-bis(3-phenylpyrazol-1-yl)pyridine (bppp) or 2,6-bis(3-p-chlorophenylpyrazol-1-yl)pyridine (bcppp)]. These complexes were characterized by elemental analysis, 1H and 13C NMR, infrared and UV/VIS spectroscopies, cyclic voltammetry, and single-crystal X-ray diffraction studies. The substituents of the terdentate bpp ligands sterically affected the Ru–N(pyrazole) bond lengths, the displacement of the nitrogen atoms of the nitro ligands from the RuL plane, and the twisting of the N–O vectors of the nitro ligand from that plane. Also the substituents affected the potentials and peak-current ratios of the RuIII–RuII couples. The log (ipc/ipa) values (ipc= cathodic peak current, ipa= anodic peak current) are linearly correlated with the steric size of the substituents as estimated by Tolmans cone angles and with the distance of the nitro ligand out of the RuL plane. A linear correlation was also found between the differences in infrared absorbances due to the N–O symmetric and asymmetric stretches and the ratio of the N–O bond distances observed from the four crystal structures.