Alexander M. W. Cargill Thompson

The synthesis of 2,2′:6′,2″-terpyridine ligands — versatile building blocks for supramolecular chemistry

Abstract The tridentate ligand 2,2′:6′,2″-terpyridine is becoming increasingly widely used. Appended substituent groups may be utilized to tailor the properties of its complexes. 2,2′:6′,2″-Terpyridine ligands incorporating other metal binding functionalities and multinucleating ligands incorporating two or more terpyridine moieties may be used to assemble supramolecular coordination oligomers. The synthetic strategies used to prepare 2,2′:6′,2″-terpyridine ligands are reviewed comprehensively.

Multinucleating 2,2′ : 6′,2″-terpyridine ligands as building blocks for the assembly of co-ordination polymers and oligomers

The co-ordination properties of the tridentate ligand 2,2′ : 6′,2″-terpyridine (terpy) make it an ideal structural unit from which to assemble co-ordination oligomers and polymers with a linear connectivity about the metal centre. The dinucleating ‘back-to-back’ 2,2′ : 6′2″-terpyridine ligands 6′,6″-bis(2-pyridyl)-2,2′ : 4′,4″ : 2″,2‴-quaterpyridine L1 and 1,4-bis(2,2′ : 6′,2″-terpyridin-4′-yl)benzene L2 give rise to a linear connectivity at the ligand, whereas 1,3,5-tris(2,2′ : 6′,2″-terpyridin-4′-yl)benzene L3 is a trinucleating species which can give rise to arrays with a connectivity of three at the ligand. The co-ordination oligomers [(X-terpy)RuLRu(X-terpy)]4+(L = L1 or L2) and [{(X-terpy)Ru}3L3]6+(X-terpy = 4′-substituted 2,2′ : 6′,2″-terpyridine) have been prepared and characterised for a variety of electron-donating and -withdrawing substituent groups X.

Ligand reactivity in iron(II) complexes of 4′-(4‴-pyridyl)-2,2′ : 6′,2″-terpyridine

The ligand 4′-(4‴-pyridyl)-2,2′ : 6′,2″-terpyridine (pyterpy) acts as a tridentate ligand in which the 4-pyridyl ring is not co-ordinated in the complex cation [Fe(pyterpy)2]2+; the non-co-ordinated ring reacts with electrophiles to give species in which the charge perturbations are localised to a ‘4,4′-bipyridyl’ fragment.

Pendant-functionalised ligands for metallosupramolecular assemblies; ruthenium(II) and osmium(II) complexes of 4′-(4-pyridy1)-2,2′ : 6′,2″-terpyridine

The potentially tetradentate ligand 4′-(4-pyridyl)-2,2′ : 6′,2″-terpyridine (pyterpy) acts as a tridentate donor to iron(II), ruthenium(II) and osmium(II). The non-co-ordinated pyridyl group reacts with a range of electrophiles to give complexes containing the cationic ligands Hpyterpy and 4′-(4-methylpyridinio)-2,2′ : 6′,2″-terpyridine (mpyterpy) The electrochemical behaviour of these complexes has been studied and correlations between the redox potentials and Hammett σ+ parameters made.

Synthesis of the new tripodal ligand tris-[3-(2′-pyridyl)pyrazol-1-yl]hydroborate, and the crystal structure of its europium(III) complex

The new tripodal ligand tris-[3-(2′-pyridyl)pyrazol-1-yl]hydroborate (L–), comprising three N,N-bidentate chelating arms linked by the apical boron atom, has been synthesized; the crystal structure of [EuL(MeOH)2F][PF6] reveals the nine-coordinate metal lying within the hexadentate ligand cavity.

CYCLOMETALLATION REACTIONS OF 2-PHENYLPYRIDINE - CRYSTAL AND MOLECULAR-STRUCTURE OF (2-(2-PYRIDYL)PHENYL)PALLADIUM(II) TETRAMER AND (2-(2-PYRIDYL)PHENYL)MERCURY(II) TETRAMER

Abstract The reaction of 2-phenylpyridine (HL) with palladium(II) compounds has been investigated. Cyclometallated and non-cyclometallated complexes may be obtained, dependent upon the reaction conditions. Cyclometallated derivatives are obtained directly by the reaction of HL with {Pd(OAc)2}3, by thermal reactions of monodentate N-bonded HL complexes, or by a transmetallation reaction with [{HgLCl}4]. The crystal and molecular structure of (2-{2-pyridyl}phenyl)palladium chloride tetramer (monoclinic, a=9.342(2), b=19.582(6), c=10.897(2) A, β=104.56(2)°, P21/c) has been determined, and is reported, together with that of (2-{2-pyridyl}phenyl)mercury chloride tetramer (monoclinic, a=10.334(2), b=7.484(1), c=27.052(6) A, β=97.60(2)°, P2t/n).

Metallomicellanols: incorporation of ruthenium(II)–2,2′: 6′,2″-terpyridine triads into cascade polymers

Facile alkoxylation of 4′-chloro-2,2′ :6′,2″-terpyridine with the mono- and tri-hydroxylic cascade (dendritic) building blocks, 4-(3-hydroxypropyl)-4-(3-benzyloxypropyl)-1,7-bis(benzyloxy)heptane 4 and 4-amino-4-(3-hydroxypropyl)heptane-1,7-diol 3, has allowed the synthesis of a dodecaruthenium macromolecule 11 employing ligand–metal–ligand connectivity.

Complexes containing ferrocenyl groups as redox spectators; synthesis, molecular structure and co-ordination behaviour of 4′-ferrocenyl-2,2′:6′,2″-terpyridine

The new ligand 4′-ferrocenyl-2,2′:6′,2″-terpyridine L has been prepared in good yield from ferrocenecarbaldehyde by two different routes. The crystal and molecular structure of L has been determined [monoclinic, space group P21/c, a= 7.905(2), b= 22.045(4), c= 11.394(2)A, β= 107.10(3)°, Z= 4, R= 0.034 for 2486 independent reflections]. The co-ordination behaviour of L has been studied and the homoleptic complexes [ML2][PF6]2(M = Co, Fe or Ru) prepared and characterised. In addition, the heteroleptic complex [RuL(terpy)][PF6]2(terpy = 2,2′:6′,2″-terpyridine) has been prepared. All of these complexes are redox active.

Ligand substitution patterns control photophysical properties of ruthenium(II)=-2,2':6',2-terpyridine complexes : room temperature emission from [Ru(tpy)2]2+ analogues

Ruthenium(II) complexes of 2,2′:6′,2″-terpyridine have not been widely investigated as photocatalysts; the introduction of electron-withdrawing substituents into the 4′-position of the ligand results in complexes [Ru(Xtpy)2]2+ (Xtpy = Cltpy or MeSO2tpy), which luminesce in fluid solution at room temperature.

Metallosupramolecular complexes containing ferrocenyl groups as redox spectators; synthesis and co-ordination behaviour of the helicand 4′,4‴-bis(ferrocenyl)2,2′ : 6′,2″ : 6″,2‴ : 6‴,2â—-quinquepyridine

The compound 4′,4‴-bis(ferrocenyl)-2,2′ : 6′,2″ : 6″,2‴ : 6‴ : 2â�—-quinquepyridine (L) has been prepared in two steps from ferrocenecarbaldehyde and 2,6-diacetylpyridine and its co-ordination behaviour investigated. Reaction with cobalt(II) and iron(II) salts gives the seven-co-ordinate complexes [ML(H2O)2][PF6]2(M = Co or Fe). The presence of ferrocenyl groups in the ligand appears not to present a steric barrier to the formation of helicates, and the double-helical complexes [Ni2L2(H2O)2][PF6]4, and [Cu2L2][PF6]3 can be obtained by reaction with nickel(II) and copper(II) salts respectively. The compound L reacts with [RuCl3L′](L′= 2,2′ : 6′,2″-terpyridine or its 4′-dimethylamino, -methylsulfonyl or -ferrocenyl derivatives) to give the heteroleptic ruthenium(II) complexes [RuL(L′)][PF6]2. In these complexes L is acting as a tridentate hypodentate ligand leaving a non-co-ordinated didentate 2,2′-bipyridyl moiety. The latter may act as a didentate domain for an additional ruthenium centre, and the tetranuclear complexes [L′RuLRuCl(L′)][PF6]3 with two ruthenium(II) centres in two different, N6 and N5Cl, donor environments have been prepared.