Eric N. Wilkes

METAL-DIRECTED MACROCYCLIZATION REACTIONS INVOLVING FORMALDEHYDE, AMINES AND MONO- OR BI-FUNCTIONAL METHYLENE COMPOUNDS

Reactions of transition metal complexes of ligands with predominantly amine donors with formaldehyde alone, or with formaldehyde and additional

Nickel(II) complexes of 15-membered tetraaza macrocycles with a primary amine or carboxylate pendant: structural characterization of a one-dimensional chain compound

Syntheses of nickel(II) complexes of the pendant arm polyamines 10-methyl-1,4,8,12-tetraazacyclopentadecane-10-amine (L3) and 7-methyl-1,5,9,13-tetraazabicyclo[1.1.2.2]heptadecane-7-amine (L5) as well as the pendant arm polyamino acids 1,4,8,12-tetraazacyclopentadecane-10-carboxylate (L4) and 1,5,9,13-tetraazabicyclo[1.1.2.2]heptadecane-7-carboxylate (L6) are described, as is the synthesis of the free ligand hydrochloride salts. All complexes form as purple octahedral paramagnetic species where coordination of the pendant arm is implied. The complex [Ni(L6H−1)](ClO4) crystallises in the monoclinic space group P2case1a, a = 10.807(8), b = 14.340(6), c = 11.789(3)A, β = 96.49(9)°. The nickel atom lies at the centre of a distorted octahedron of four secondary nitrogens and two carboxylate oxygens, one from the pendant of the macrocycle and the other bridging from the external oxygen of the carboxylate of an adjacent complex cation. The sharing of each carboxylate between its own and the next nickel centre persists throughout the lattice, leading to a one-dimensional chain compound where a C-pendant attached directly to the macrocyclic ring acts as the bridging group.

Comparative formation constants for metal ions with macrocyles based on 1, 4, 8, 11-tetraazacyclotetradecane and carrying diamine, dicar☐ylate or amine-car☐ylate pendants

Abstract Acid dissociation constants for the newly isolated dihydrogen anti -1, 4, 8, 11-tetraazacyclotetradecane-6, 13-dicar☐ylate (diacmac), as well as for hydrogen anti -6-methyl-1, 4, 8, 11-tetraazacyclotetradecane-6-amine-13-car☐ylate (acammac) and anti -6-13-dimethyl-1, 4, 8, 11-tetraazacyclotetradecane-6, 13-diamine (diammac) are reported. The ligands differ somewhat in their selection of metal ions, which is reflected in the formation constants for complexation (log K ML 25°C) which have been determined for the d 10 metal ions Zn 2+ (diammac, 14.9 ; acammac, 14.7 ; diammac, 26.3), Cd 2+ (diammac, 10.6; acammac, 16.7 ; diacmac, 15.9), Hg 2+ (diammac, 10.5 ; acammac, 17.3 ; diacmac, 21.8) and Pb 2+ (diammac, 10.8 ; acammac, 10.7 ; diacmac, 19.0) and the d 5 Mn 2+ ion (diammac, 6.2 ; acammac, 12.0 ; diacmac, 18.3). Differences arise in part from the increasing availability of potential O donors versus N donors in stepping from diammac to diacmac, and imply a clear role for the pendants in binding metal ions.

Isomers of 1,4,8,11-Tetraazacyclotetradecane-6,13-dicarboxylate Characterized as Cobalt(III) Complexes

The major trans (1) and minor cis (2) isomers of 1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate have been characterized as the complexes [Co(1)](ClO4) and [Co(H-2)(OH2)]Cl(ClO4).H2O. The former crystallized in the C-2/c space group and the latter in the P2(1)/c space group, with cell parameters a 16.258(7), b 9.050(3), c 15.413(6) Angstrom, beta133.29(3)degrees, and a 9.694(4), b 16.135(1), c 12.973(5) Angstrom, beta 93.00(2)degrees, respectively. Their characterization completes identification of the respective trans and cis isomers for the series of C-pendant macrocycles also including 1,4,8,11-tetraazacyclotetradecane-6-amine-13-carboxylate ((3), (4)) and 1,4,8,11-tetraazacyclotetradecane-6,13-diamine ((5), (6)). The complexes show limited distortion from octahedral geometry with the strain in the presence of the coordinated C-pendant carboxylate significantly reduced compared with that for the C-pendant amine in analogues, a consequence mainly of six-membered as opposed to five-membered chelate rings involving the pendant donor. A comparison of the physical properties for the trans isomers of the octahedral complexes of (1), (3), and (5), which reflect progressively increasing strain, is presented.

Characterization of the Minor cis Isomer of a Dipendant Polyamino Acid Macrocycle as a Dimeric Nickel(II) Complex

The dipendant-arm polyamino acid macrocycle 13-amino-13-methyl-1,4,8,11-tetraazacyclotetradecane-6-carboxylate (acammac), characterized earlier as the major trans isomer (3), has been isolated as the minor cis isomer (4) by crystallization as the [Ni(4)](ClO4) complex. The complex has been examined by an X-ray crystal structure analysis, and the cation exists as a dimer with each carboxylate group bound both to its ‘parent’ nickel atom and bridging to the adjacent nickel atom. The macrocycle adopts a folded geometry, each nickel atom appearing as a cis-NiN4O2 chromophore. The pendant primary amine group and three of the four secondary amine groups are also coordinated, whereas the fourth secondary amine group is not coordinated but stabilized by a proton bridging within a superbase between the uncoordinated amine and one of the coordinated amines.

Comparative stability constants for metal ions with tetraazamacrocycles of various ring sizes carrying a single amine or carboxylate pendant group

Acid dissociation constants for a series of tetraazamonocycloalkanes of {13}–{15} membered ring sizes, as well as for a related ‘reinforced’ {15R} tetraazabicycloalkane, each with one primary amine or carboxylate C-pendant, are reported. Further, formation constants with the metal ions ZnII, CdII, PbII, HgII, MnII and CoII have been determined. The ligands differ in their selection of metal ions, reflected in the formation constants for 1:1 complexation (KML). Differences arise in part from the increasing ring size or rigidity and also from the availability of potential pendant O-donors versus N-donors in stepping from amine to carboxylate pendant ligands, implying a role for the pendants in binding the metal ions.

Synthesis of a new potentially sexidentate pendant-arm macrocyclic polyamino acid and co-ordination to cobalt(III)

From reaction of bis(ethane-1,2-diamine)copper(II) with formaldehyde and diethyl malonate then formaldehyde and nitroethane in turn the pendant-arm macrocyclic complex ion (hydrogen 13-methyl-13-nitro-1,4,8,11-tetraazacyclotetradecane-6-carboxylate)copper(II) was prepared. Reduction with zinc in aqueous acid yields the free pendant-arm β-polyamino acid macrocycle hydrogen 13-amino-13-methyl-1,4,8,11-tetraazacyclotetradecane-6-carboxylate (L3) as the hydrochloride salt. Co-ordination to cobalt(III) was achieved following reaction with cobalt(II) ion and air, yielding the chloro(hydrogen 13-amino-13-methyl-1,4,8,11-tetraazacyclotetradecane-6-carboxylate)cobalt(III) ion, as well as its aqua analogue. The chlorocobalt(III) complex crystallized as the perchlorate salt in the space group Pbca, a= 10.256(4), b= 12.689(5), c= 33.08(2)A, Z= 8, with the co-ordinated chloride in a cis disposition relative to the pendant amine, the four secondary amines co-ordinated in a folded geometry with uncommon RRRR stereochemistry, and the pendant carboxylic acid group not co-ordinated. Equilibration of the reaction mixture from this synthesis at pH 8 over activated carbon yielded almost exclusively the complex with the ligand bound as a sexidentate ligand where the pendant amine and carboxylate groups occupy trans sites. This complex crystallized as the perchlorate salt in the space group P21/n with a= 10.939(2), b= 13.355(2), c= 14.596(2)A, β= 102.17(1)° and Z= 4. Metal–donor distances [Co-O 1.899(2), Co–N(pendant) 1.956(2), average Co–N(secondary) 1.951A] are at the short end of the range for saturated polydentate amino acid ligands, presumably influenced by the sterically efficient ligand.