Robert S. Vagg

Studies on the metal-amide bond. I. Metal complexes of the bis-amide tetradentate ligand N,N′-bis(2′-pyridinecarboxamide)-1,2-benzene

Abstract Complexes of general formula M(bpbH2)Cl2· nH2O, where bpbH2 = N,N′-bis(2′-pyridinecarboxamide)-1,2-benzene and M = Mn (n = 0), Co (n = 1), Co and Ni (n = 2) and Cu (n = 1.5) have been prepared. As well, the complexes Ag(bpbH2)(NO3) and Co(bpbH2)(NCS)2·2.5H2O were isolated. The copper and nickel complexes exhibit clear evidence of neutral amide-N coordination. Several of the metal ions used promote amide deprotonation on coordination, and a series of complexes of formula M(bpb)·H2O (M = Co, Ni, Cu, Zn and Pd) are reported. A planar MIIN4 system is proposed for these complexes. Stereochemistries for the complexes have been proposed utilising microanalyses, magnetic susceptibilities, thermogravimetric analyses and infrared and visible spectral data.

Studies on the metalamide bond. VII. Metal complexes of the flexible N4 ligand N,N′-bis(2′-pyridinecarboxamide)1,2-ethane

Abstract The isolation and characterization of a series of transition metal complexes is described with the ligand bpenH 2 in both neutral and deprotonated forms. The ligand acts as a planar N 4 tetradentate in the monomeric deprotonated complexes of general forms M(bpen)nH 2 O (M = Cu II , Ni II , Pd II or Pt II . Metal chloride and perchlorate salts of the neutral ligand, of general formulae M(bpenH 2 )Cl 2 nH 2 O and M 2 (bpenH 2 ) 3 (ClO 4 ) 4 nH 2 O, are reported (M = Mn II , Fe II , Co II , Ni II , Cu II or Zn 11 ) with the ligand bonding through pyridine-N and amine-O atoms in a bridging bis-bidentate function. In the chloride complexes high-spin six-coordinate geometries are indicated for the polymeric solid products. The perchlorate complexes are dimeric and high-spin, with each metal atom exhibiting N 3 O 3 six-coordination. Proton NMR studies on the ligand show coupling of the amide protons with those of the central ethylene group. Deprotonation is confirmed by loss of this coupling for the Ni 11 , Pd 11 and Pt 11 chelates, 1 H 195 Pt coupling being observed in the latter compound The neutral and deprotonated chelate forms also are readily differentiated by thier IR absorption. Deuterium isotopic substitution of amide protons has been used to assist IR assignments.

Studies on the metalamide bond. II. The crystal structure of the deprotonated copper(II) complex of N,N′-bis-(2′-pyridinecarboxamide)-1,2-benzene

Abstract Aqua [N,N′bis(2′-pyridinecarboxamido)-1,2-benzene]copper(II), C 18 H 14 N 4 O 3 Cu, is triclinic, space group P 1 , with a = 7.443(3), b = 9.560(2), c = 11.197(4), A , α = 92.63(2), β = 100.02(2), γ = 84.50(2)°, Z = 2. The structure was refined to R = 0.038 for 2813 diffractometer data using least-squares methods. The copper atom is five-coordinate, the ligand acting as a planar N 4 tetradentated in encompassing the base of a distorted square-based pyramid [CuN(amide) 1.933(2) A , average CuN (pyridine) 2.023(2) A , N(amide)CuN(amide) 82.8°, N(pyridine)CuN(pyridine) 110.7°] and with the Cu atom raised 0.19 A above the N 4 plane towards the apical water molecule (CuO 2.286(2) A ). The water molecule hydrogen bonds carbonyl oxygen atoms of adjacent chelate molecules, which are packed in layers parallel to (21 2 . An intra-molecular steric interaction between the two H atoms in the 6-positions of the pyridine rings (H H 1.98 A ) is evident.

Studies on the metalamide bond. IX. Metal complexes of some sterically hindered bis-picolinamide tetradentate ligands☆

Abstract The synthesis is described of some bis-picollinamide ligands in which N 4 tetradentate function on coordination would enfore severe intramolecular steric interactions. These ligands are N,N′-bis(6′-methylpyridine-2′-carboxamide)-1-ethane (6-mebpenH 2 ), N,N′-bis(6′-mehtylpyridine-2′-carboxamide)-1,2-benzene (6-mebpbH 2 ) and N,N′N-bis(2′-quinolylcarboxamine)-1,2-ethane (bqenH 2 ). Their complexing abilities with bivalent Cu, Ni and Pd have been studies, and comparison are made with analogous unhindered ligands reported previously. The complexes isolated each have characterized by microanalysis, magnetic susceptibility, thermogravimetrinc analysis, and by visible, i.r. and n.m.r. spectral data. In the compound Pd(6-mebpenH 2 )Cl 2 the ligand displays an apparent unique trans -bidentate function. The deprotonated complexes isolated with the three ligands have N 4 tetradentate coordination, with resultant steric strain. Deuterium isotopic substitution has been used to assist with i.r. assignments.

Design of chiral picen-based metal complexes for molecular recognition of α-aminoacids and nucleic acids

Abstract Molecular design features which determine the enantio- and stereoselective behaviour of metal complexes derived from chiral linear N 4 -tctradentate ligands with terminal α-pyridyl groups arc described. Examples are provided of the ability of these complexes to recognise the molecular structures of biologically interesting molecules (α-aminoacids and nucleic acids). Noncovalent binding and sterie factors which influence these molecular recognition processes are analysed and assessed. These include discriminatory interactions which occur at the intra ligand. inter ligand ( intra molecular) and inter molecular levels.

Development of DNA-immobilised chromatographic stationary phases for optical resolution and DNA-affinity comparison of metal complexes

Abstract Two chiral stationary phases which exploit DNA as a chiral discriminator have been developed. A covalently-bound DNA stationary phase for HPLC applications was used to optically resolve [Ru(dipyrido[6,7-d:2′,3′-f]-quinoxaline) 3 ] 2+ and [Ru(1,10-phenanthroline) 3 ] 2+ complex ions. This shows that the column retention times are influenced both by pH and by the size of the aromatic ligands. DNA-immobilised on cellulose paper proved effective for simultaneously comparing the relative retention of a number of metal complexes and R F data correlate well with the degree of aromatic area in the complexes available for intercalation into DNA.

Studies on the metalamide bond. XII. The crystal structure of [N,N′-bis(2′-pyridinecarboxamido)-1,2-ethane]nickel(II) monohydrate ☆

Abstract [N,N′-Bis(2′-pyridinecarboxamido)-1,2-ethane]nickel(II) monohydrate, C 14 H 14 N 4 O 3 Ni, is monoclinic, space group I 2/ a , with a = 7.241(3), b = 17.141(6), c = 11.132(3) A , β = 102.2(1)°, Z = 4. The structure was refined to R = 0.071 for 949 photographic reflexions by least-squares calculations. The molecules have space group imposed C2(2) symmetry. The nickel atom is four coordinate with the ligand acting, as a planar N 4 -tetradentae [NiN(amide) 1.839(6), NiN(pyridine) 1.952(6) A, N(amide)NiN(amide) 82.9(3)°, N(pyridine)NiN(pyridine) 108.4(3)°]. The amide nitrogen atom is almost trigonally planar, and that the ligand can adopt a nearly planar arrangement about the nickel atom is due to the flexible ethylene link. The chelate molecules stack with their molecular planes parallel to (10 1 . The water molecule hydrogen bonds the carboxyl oxygen atoms of two chelate molecules which are related by the two-fold axis contained by it.

Studies on the metalamide bond. XIX. A comparison of molecular distortions in the crystal structures of [N,N′-bis(2′-pyridinecarboxamido)-1,2-benzene] nickel(II) with its 6′-methyl-substituted Analogue

Abstract [ N,N ′-Bis(pyridine-2′-carboxamide)-1,2-benzene]nickel(II) monohydrate, C 18 H 14 N 4 O 3 Ni, crystallizes in the monoclinic space group C 2/ c with a = 14.240(4), b = 20.071(3), c = 16.275(2) A,β = 97.25(2) o , Z = 12 and its crystal structure has been refined to R = 0.033 for 3597 diffractometer data. [ N,N ′-Bis(6′-methylpyridine-2′-carboxamide)-1,2- benzene]nickel(II) monohydrate, C 20 H 18 N 4 O 3 Ni, crystallizes in the orthorhombic space group Pbca with a = 10.14(2) b = 17.12(2), c = 21.11(5) A, Z = 8 and its crystal structure has been refined to R = 0.088 for 1979 photographic data. In both structures the nickel atoms are four coordinate with the ligands acting as N 4 tetradentates. For the first mentioned complex the structure consists of two independent molecules one of which is constrained, by space group requirements, to have C 2 (2) symmetry. These two molecules are closely similar and both exhibit nearly planar molecular arrangements with a small tetrahedral twist of up to 4 o at the nickel atoms. In the second complex the methyl substitution at the 6′-pyridyl positions causes severe steric strain in the molecule which gives rise to a 14.9 o tetrahedral twist at the nickel atom and approximately 25% pyramidal distortion at both amide nitrogen atoms. The resulting methyl-methyl separation of 3.26(1) A is considerably less than the sum of the van der Waals radii for two such groups. This close separation leads to carbon-acid character for the methyl group protons which are shown to exchange for deuterons in NMR studies. A full analysis of the out-of-plane distortions and torsion angles of the two structures and a comparison with the previously reported analogous copper structures are made.

Chiral metal complexes. 23. Stereoselective synthesis of α-aminoacidates

Abstract A series of ternary complexes of cobalt(III) containing a chiral linear N4 tetradentate and either an optically active α-aminoacid or a substituted aminomalonic acid has been synthesised and characterised. A high degree of stereoselectivity is observed for these complexes. The crystal structure of one of these species, Λ-β1-[Co(R,R-picchxn)(R-ABMA)]ClO4·1.5H2O, where R,R-picchxn is N,N′-di(2-picolyl) -1R,2R-diaminocyclohexane and ABMAH2 is 2-amino-2-benzylpropanedicarboxylic acid, has been determined. Crystal data: C28H36N5ClO9.5Co is orthorhombic, space group P212121, with a=12.659(4), b= 14.560(4), c=34.049(8) A and Z=8: The structure was refined by block-matrix least-squares methods to R=0.071 for 3024 non-zero reflexions. The complex crystallises with two complex cations in the asymmetric unit. Each cation has a Λ-β1 geometry, and the benzylaminomalonic acid ligand coordinates with an R (pro-S) absolute configuration. An intramolecular hydrogen bond between a tetradentate secondary amine group and the carboxyl group of the aminoacid is obvious in each cation, and this appears to confer thermodynamic stability on this diastereoisomer. Decarboxylation of the complexes containing coordinated aminomalonic acids gives corresponding diastereoisomers of aminoacids in high optical yield. The nature of the precursor and final complexes casts some light on the origins of the chiral discriminations important in these species and their reactivity.

Studies on the metalamide bond. VIII. The crystal structure of [N,N′-bis(2′-pyridinecarboxamido)-trans-1,2,-cyclohexane] nickel(II) ☆

Abstract [N,N′-bis(2′-pyridinecarboxamido )- trans -1,2-cyclohexane] nickel(II) C 18 H 18 N 4 Ni, is monoclinic, space group I2/a, with a = 13.652(8), b = 12.127(6), c = 10.739(5) A , β = 106.0(1)°, Z = 4. The structure was refined to R = 0.088 for 811 photographic reflexions using least-squares calculations. The molecule has space group imposed C 2(2) symmetry and the nickel atom is four-coordinate with the ligand acting as distored square-planar N 4 -tetradentate [NiN(amide) 1.868(7), NiN(pyridine) 1.944(8) A , N(amide)Ni;N(amide) 86.2(4)°, N(pyridine)Ni;N(pyridine) 107.0(4)°]. The amide nitrogen atom is best described as having a flattened pyramidal geometry. Steric interactions are further alleviated by rotations with the non-planar amide chelate ring. The cyclohexane ring adopts a skew-chair conformation in which the methine hydrogens are in transconfiguration. The molecules are packed in the lattice in layers parallel to (101).