Ferida S. Esho

Dicopper(II) complexes of a macrocyclic ligand containing single hydroxo-, methoxo-, or 1,1-azido-bridges: synthesis, magnetic properties, electron spin resonance spectra, and the crystal and molecular structure of a µ-hydroxo-derivative

Reaction of 2,6-diacetylpyridine with 1,3-diaminopropane in methanol in the presence of M[ClO4]2(M = SrII or BaII) in 2:1:1 molar proportions yields the complexes [ML2(ClO4)2] of the new 20-membered macrocyclic tetraimine ligand L2 derived from the [2 + 2] condensation of 2 mol of diketone with 2 mol of diamine. The single Ba2+ in [BaL2(ClO4)2] may be replaced by two Cu2+ to afford, depending on the conditions, the complexes Cu2L2(OH)(ClO4)3·2H2O and Cu2L2(OMe)(ClO4)3˙2H2O formulated as containing two Cu2+ linked by, respectively, single hydroxo- and methoxo-bridges. Crystals of the µ-hydroxo-complex are tetragonal with a= 15.20(1), c= 14.50(1)A, Z= 4, and space group P42/n. 1 191 Reflections above background were measured by diffractometer and refined by Fourier methods to R 0.078. Each copper atom in the binuclear [Cu2L2(OH)(OH2)]3+ cation is bonded to the three nitrogen atoms of a trimethine group of the folded macrocycle [Cu–N 1.916(13)–2.066(12)A]. The approximate co-ordination square plane about each metal atom is completed by a shared oxygen atom, O(1)(presumed to be from OH–), at 1.916(9)A. The two Cu atoms are also linked in a shared axial position by a second oxygen atom, O(2)(presumed to be from H2O), at 2.519(12)A. The Cu–O(1)–Cu and Cu–O(2)–Cu angles are 110.3(7) and 77.3(4)°, respectively, and the Cu ⋯ Cu separation is 3.145(4)A. Magnetic susceptibility measurements in the temperature range 90–300 K establish that the two Cu2+ in each binuclear complex are antiferromagnetically coupled with J=–32 and –53 cm–1 for the µ-hydroxy- and µ-methoxo-derivatives, respectively, where 2J is the singlet–triplet separation. The appearance of a ‘ triplet ’ e.s.r. spectrum at g≈ 2 and a seven-line ΔM= 2 half-band spectrum at g≈ 4 for frozen methanol–dimethyl sulphoxide solutions of the µ-methoxo-complex indicate retention of the bridge in solution. Reaction of Cu2L2(OMe)(ClO4)3·2H2O with Na[N3] affords Cu2L2(N3)(ClO4)3 for which i.r. spectra suggest that the Cu2+ are intramolecularly linked by one nitrogen atom of the azide ion (µ-1,1-N3 bridging mode). E.s.r. spectra of frozen solutions of the monoazide show that the Cu2+ are weakly antiferromagnetically coupled. The structures and physical properties of the complexes are discussed in relation to the cavity size of the macrocycle L2.

Trihapto–hexahapto fluxional behaviour of a macrocyclic ligand: template synthesis, proton nuclear magnetic resonance spectra, and the crystal and molecular structure of an eleven-co-ordinate barium(II) complex

The alkaline-earth-metal ions Ca2+, Sr2+, and Ba2+, but not Mg2+, are templates for the high-yield synthesis of 1 : 1 complexes of the 20-membered macrocycle L1 derived from the cyclic condensation of 2 mol of 2,5-diformylfuran with 2 mol of 1,3-diaminopropane. Lead(II) is also effective as a template for the macrocycle synthesis. In the case of BaII only, complexes having a 2 : 1 ligand : metal stoicheiometry could also be prepared by anion exchange. Crystals of [BaL12(H2O)2][Co(NCS)4] are monoclinic with a= 11.57(1), b= 19.99(1), c= 23.18(1)A, β= 107.5(1)°, Z= 4, and space group P21/c. 4 329 Reflections above background were measured by diffractometer and refined by least-squares methods to R 0.062. The barium atom in the cation is bonded to all six heteroatoms of one macrocycle but only to three of the second macrocycle, this being severely folded so that one furan di-imine moiety is unco-ordinated. Two water molecules are also bonded to the barium atom giving an overall co-ordination number of 11. This structure is discussed in relation to those of other eleven-co-ordinate compounds. The hexahapto–trihapto co-ordination observed in the solid state is retained in solution as determined from the temperature-dependent 1H n.m.r. spectrum of the analogous complex [BaL12(MeCN)2][BPh4]2 in CD3CN. Below ca. 20 °C the resonances due to the imino-protons (HCN) and the methylene protons (CN–CH2) adjacent to the imine group each appear as pairs of well separated lines having a 3 : 1 intensity ratio. These are attributed to slowly exchanging co-ordinated and unco-ordinated furan di-imine moieties, respectively. Increase in temperature causes coalescence of the components of each doublet into a single line. The two sets of temperature-dependent spectra are described by the same free energy of activation (ΔG‡=ca. 62.5 kJ mol–1) indicating that they are associated with the same dynamic process, viz. interconversion of four equivalent configurations of the complex cation. The results are discussed in relation to the sizes of the metal cations and the flexibility and cavity dimensions of this and related macrocycles.

Sulphur-bonded-only thiocyanate bridges: the synthesis and X-ray crystal structure of a di-µ-thiocyanato-(S)-di-copper (I) complex of a 20-membered macrocycle

In the di-copper (I) complex [Cu2L(SCN)2] of a 20-membered macrocyclic Schiff base ligand (L), the two tetrahedrally co-ordinated Cu1 ions are intramolecularly linked via the sulphur atoms only of the thiocyanate groups.

Complexation of alkali- and alkaline-earth-metal cations by a conjugated tetraimine macrocyclic ligand: synthesis, sodium-23 nuclear magnetic resonance spectra, and the X-ray structure of a twelve-co-ordinate barium(II)‘sandwich’ complex

Reaction of 2,5-diformylfuran with o-phenylenediamine in methanol in the presence of a salt of K+, Ca2+, Ba2+, or Pb2+ yields complexes of the 18-membered conjugated macrocyclic tetraimine L2 derived from the cyclic (2 + 2) condensation of 2 mol of dialdehyde with 2 mol of diamine. The complexes all have a 1 : 1 ligand : metal stoicheiometry except those of Ba2+ which contain two macrocyclic ligands per metal atom. Crystals of [BaL22][BPh4]2 are monoclinic with a= 23.25(1), b= 14.92(1), c= 23.69(1)A, β= 101.0(1)°, Z= 4, and space group A2/a(no.15). 1 468 Reflections above background were measured by diffractometer and refined to R 0.10. In the [BaL22]2+ cation the metal atom is sandwiched between two almost parallel ‘N4’ planes 2.6 A apart, the furan rings being tilted by 24.2 and 26.3° with respect to these planes. The barium atom is twelve-co-ordinate being bonded to the four nitrogen and two oxygen atoms of each ring [Ba–N 2.96(3)–3.08(3), Ba–O 2.91(2)–3.02(3)A]. The smaller ions Li+, Na+, and Mg2+ are ineffective as templates for the macrocycle synthesis but complexes of Na+(and of [NH4]+) could be prepared by neutralisation of the diacid salt [H2L2][ClO4]2 with aqueous NaOH (or aqueous NH3). The free macrocycle could not be isolated although ‘recrystallisation’ of the complexes of Na+ or [NH4]+ from hot alcohol afforded the metal-free alcohol addition products L2·2MeOH and L2·EtOH. The complexes have been characterised by i.r., u.v.–visible, mass, and 1H n.m.r, spectra. Sodium-23 n.m.r. spectra of equimolar solutions of NaL2(ClO4) and NaClO4·H2O in [2H6]dimethyl sulphoxide showed separate resonances at temperatures below about 30 °C indicating slow exchange of Na+ between macrocycle and solvent. The free energy of activation for exchange was estimated to be 59 kJ mol–1. The stoicheiometries and relative stabilities of the complexes are interpreted in terms of the sizes of the metal ions in relation to the fixed hole size of the macrocycle.

Metal-ion controlled reactions of 2,6-diacetylpyridine with 1,2-di-aminoethane and 2,6-diformylpyridine with o-phenylenediamine and the crystal and molecular structure of a pentagonal pyramidal cadmium(II) complex containing unidentate o-phenylenediamine

Reaction of 2,6-diacetylpyridine (dap) with an excess of 1,2-diaminoethane (en) in the presence of Ba[ClO4]2 in MeOH or EtOH at room temperature yields the complex [BaL2(ClO4)2]·H2O where the ligand L2 is the open-chain condensate of two molecules of dap with three molecules of en. The i.r. spectrum of the solid complex indicates that L2 exists in the di-imine form containing two imidazolidine rings derived from the nucleophilic addition of the two primary amine groups of the tetra-imine form across adjacent CN linkages. The use of higher reaction temperatures affords the complex [BaL1(ClO4)2] of the 18-membered macrocycle L1 derived from the [2 + 2] condensation of two molecules of dap with two molecules of en. The intermediacy of the co-ordinated open-chain ligand L2 in the L1 macrocycle formation is evidenced by the subsequent ring closure of [BaL2(ClO4)2]·H2O in the absence of added diketone; a transamination mechanism is proposed. Corresponding reactions of 2,6-diformylpyridine (dfp) with o-phenylenediamine (opd) in the presence of Ba2+ give complexes of the 18-membered macrocycle with the isolation of any intermediate. The single Ba2+ in [BaL2(ClO4)2]·H2O may be replaced by two Cu2+ with isomerization of L2 to the tetra-imine form, L3. The isomerization is reversed on treatment of Cu2L3(ClO4)4·2H2O with NCS–. The Ba2+in the macrocyclic complex [BaL1(ClO4)2] may also be replaced by two Cu2+ to yield Cu2L1(OH)(ClO4)3·H2O in which the two Cu2+ ions are intramolecularly bridged, and antiferromagnetically coupled, via the hydroxide ion. The use of Cd[ClO4]2·6H2O as template affords the complexes [CdL5(en)][ClO4]2 and [CdL6(opd)][ClO4]2 where L5 is the open-chain ligand derived from the condensation of one molecule of dap with two molecules of en, and L6 is the corresponding ligand derived from dfp and opd. Crystals of [CdL6(opd)][ClO4]2 are triclinic with a= 9.117(9), b= 10.797(8), c= 16.084(11)A, α= 97.89(8), β= 81.43(9), γ= 70.70(10)°, Z= 2, and space group P. 2 560 Reflections above background were measured by a diffractometer and refined by full-matrix least-squares to R 0.065. The co-ordination geometry of the Cd atom is approximately pentagonal pyramidal, being bonded to the five nitrogen atoms (Cd–N 2.35–2.46 A) of L6 in the pentagonal plane and to one NH2 group [Cd–N 2.341(9)A] of the opd molecule in one axial position, the metal lying 0.42 A above the equatorial N5 plane. The other NH2 group of opd is not co-ordinated. An incomplete X-ray analysis of [CdL5(en)][ClO4]2 indicates a seven-co-ordinate polymeric structure in which the en molecules bridge adjacent Cd2+ ions. Treatment of CdL6(opd)(ClO4)2·6H2O with Ni2+ in the presence of O2 yields the complex[Ni(L8)2][ClO4]2·H2O the properties of which suggest that the terminal NH2 groups of L6 have added across the adjacent CN bonds, this being followed by oxidative dehydrogenation to generate 2,6-di(2-benzimidazolyl) pyridine.

Dicopper(II) complexes of a binucleating N4 macrocycle containing mono- and di-atomic bridges; magnetic interactions mediated by alkoxo- and diaza-bridging ligands. Crystal structures of [Cu2(L1)(pz)2][ClO4]2, [Cu2(L1)(OEt)2(NCS)2], and [Cu2(L1)(OMe)2(MeCN)2][BPh4]2

Dicopper(II) complexes of 20-membered N4 binucleating macrocycles L1–L3 derived by a cyclic [2 + 2] condensation of diformylthiophene or diformylfuran with the appropriate diamine have been synthesised and characterised by analytical, spectroscopic, magnetic, and X-ray diffraction methods. A pair of bridging ligands, either alkoxo, OR–(R = H, Me, or Et), or diaza (pyrazolate or 1,2,4-triazolate), links the CuII ions. The crystal structure of three compounds [Cu2(L1)(pz)2][ClO4]2(1), [Cu2(L1)(OEt)2(NCS)2](6), and [Cu2(L1)(OMe)2(MeCN)2][BPh4]2(7) have been determined by X-ray diffraction (Hpz = pyrazole). In structures (6) and (7) the copper(II) ions have a trigonal-bipyramidal environment, with ethoxy [(6)] or methoxy [(7)] bridges in a position axial to one CuII and equatorial to the other. Despite the parallel disposition of the dz2 magnetic orbitals, strong antiferromagnetic superexchange is observed for this and the other parallel-planar alkoxobridged dimer described. In structure (1), the copper co-ordination environment is square planar, with cis disposed pyrazolate bridges. Moderate antiferromagnetic exchange is present in (1) and the other diaza compounds, and well defined triplet e.s.r. spectra are observed.

Oxidative coupling of phenylacetylene by a di-copper(II) complex of a macrocyclic ligand and the X-ray structure of a tetra-copper(I) phenylacetylide complex

Reaction of phenylacetylene with a di-µ-hydroxo-di-copper(II) complex of a macrocyclic ligand affords diphenyldiacetylene together with a tetranuclear copper(I) complex containing a Cu4-phenylacetylide core in which the terminal carbon atom is five-co-ordinate.

Dicobalt(II) complexes of a macrocyclic ligand containing hydroxo-, alkoxo-, phenoxo-, thiolato-, halogeno-, and pseudohalogeno-bridges: structures and magnetic exchange interactions

Two families of dicobalt(II) complex of a binucleating macrocyclic ligand (L), C18H20N4O2, derived from a cyclic [2 + 2] condensation of 2,5-diformylfuran with 1,3-diaminopropane, have been synthesised and characterised by analytical, spectroscopic, magnetic, and X-ray diffraction methods. They differ in the co-ordination geometry of the cobalt(II) ions (tetrahedral or trigonal bipyramidal) but are alike in that the metal ions are intramolecularly linked via two bridging ligands which may be the same or different. The co-ordination number of the metal ions is determined by the nature of the bridging groups which include OH–, OMe–, OEt–, OPrn–, OPri–, OBut–, OPh–, SEt–, SPh–, Cl–, Br–, 1,1-N3–, and nitrogen atom-only NCS– and NCSe–. Crystals of [CO2L(OEt)(NCS)3](1) are monoclinic with a= 9.03(1), b= 10.73(1), c= 14.64(1)A, β= 99.0(1)°, Z= 2, and space group P21/c. Crystals of [CO2L(OMe)(N3)3](2) are monoclinic with a= 8.381 (7), b= 10,09(1), c= 14.185(11)A, β= 96.1(1)°, Z= 2, and space group P21/n. For (1) and (2), 692 and 700 reflections above background were measured by diffractometer and refined by Fourier methods to R 0.099 and 0.115, respectively. In both structures each cobalt(II) ion has a distorted trigonal-bipyramidal environment, being bonded to two nitrogen atoms of the macrocycle and a disordered N/O bridge atom in the equatorial plane. The two axial sites are occupied by a nitrogen atom of a terminal anion [NCS– in (1), N3– in (2)] and the other disordered N/O bridge atom. The Co ⋯ Co separations are 3.119(6) and 3.195(6)A, respectively. The structures are compared to those of other metal complexes of the same macrocycle. The magnetic moments of the five-co-ordinate complexes show little dependence on temperature although a small ferromagnetic interaction is apparent for the µ-azido-µ-methoxo-complex. All the tetrahedral complexes exhibit antiferromagnetic superexchange, the coupling constants J(in H=–2JS1S2) ranging from –5.5 cm–1 for the di-µ-bromo-complex to –90.5 cm–1 for the di-µ-thiophenolato-complex.

Alkaline earth, lead(II), and cadmium(II) complexes of a nitrogen analogue of [18]annulene; X-ray crystal structure of the lead and cadmium complexes

CaII, SrII, BaII, and PbII are effective templates for the synthesis of a conjugated, 18-membered, hexadentate ‘N6’ macrocycle; the crystal and molecular structures of a PbII complex, and of a CdII complex prepared by metal exchange, have been determined.

Metal-induced ring contraction in a macrocyclic ligand; X-ray crystal structure of a cobalt complex

Replacement of alkaline earth metal ions from a conjugated hexadentate nitrogen analogue of [18]-annulene by some first row transition metal ions significantly smaller than the macrocycle cavity is accompanied by an intramolecular ring contraction yielding a 15-membered quinquedentate macrocycle of improved fit; the X-ray crystal structure of the cobalt complex has been determined.