Template synthesis of amidine- and amide-functionalised cobalt(III) hexaaza cage complexes

Abstract

The reaction of [Co(sen)]Cl 3 ؒH 2 O {sen = 4,4Ј,4Љ-ethylidynetris(3-azabutan-1-amine)} with methanal and ethyl cyanoacetate in aqueous base led to the synthesis of three functionalised cobalt() cage complexes: (1-cyano-8-methyl-2-oxo-3,6,10,13,16,19-hexaazabicyclo[6.6.6](2-amino-1-carboxy-8-methyl-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icos-2-ene)cobalt()]trichlorideethanol-water(1/0.5/3.5), [Co(Me,CO 2 H-2-aminosar-2-ene)]Cl 3 ؒ0.5C 2 H 5 OHؒ3.5H 2 O; and (2-amino-8-methyl-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icos-2-ene)cobalt() trichloride-water(1/3), [Co(Me-2-aminosar-2-ene)]Cl 3 ؒ 3H 2 O. The amidine-functionalised cages are the first hexaaza cages of that type. The structure of [Co(CN,Me-2-oxosar Ϫ H)][ClO 4 ] 3/2 Cl 1/2 ؒH 2 O has been established by X-ray crystallographic analysis. The syntheses, chemical reactions and spectroscopic and electrochemical properties of the cage complexes are described.

Computational Insights on the Geometrical Arrangements of Cu(II) with a Mixed-Donor N3S3 Macrobicyclic Ligand

“…Conversely, ligands from the sarcophagine family (sar, Chart ) are not prone to such behavior, − and generally only one molecular structure, which features the metal totally encapsulated by the hexadentate ligand, is found for a range of transition and d-block metal ions. Notably, expanded versions of these cage complexes, i.e., 1,5,5,9,13,13,20,20-octamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane (Me 8 tricosaneN 6 ), have been found to differ in this behavior and encapsulate transition metal atoms in a variety of geometries where the ligand acts as either hexadentate or pentadentate. , The chemistry of the first type of these species has shown unique physical properties, such as enhanced thermodynamic stability and extreme resistance to dissociation, which have, for instance, important applications in medicinal chemistry by complexation of 64 Cu(II) for diagnostic positron emission tomography (PET) imaging .…”

The Reactivity of Hexa(N‐methylideneimine)CoIII Complexes towards Nucleophiles: Structure and Mechanism

“…An additional CH 2 group with two diastereotopic hydrogen atoms was located and the 13 C spectrum also exhibited a strongly deshielded signal at δ = 176 ppm, indicative of the formation of an imino group. Formation of a C=N double bond was further confirmed by a strong, sharp band at 1647 cm –1 in the IR spectrum 26. However, the DEPT experiment together with the 1 H characteristics clearly show that, in contrast to the products obtained in the reaction with ammonia or aniline, the amidine‐C is not bonded to any hydrogen atoms.…”

“…The latter clearly contains the aniline component in the form of a coordinated formamidine moiety. The monosubstituted phenyl ring of this substituent could be readily recognised by its 1 H and 13 C NMR spectroscopic characteristics and the amidine functionality was identified by a strong C=N stretch vibration at 1658 cm –1 and corresponding NMR resonances at δ = 8.74 ppm and 162.6 ppm in the 1 H and 13 C spectra 6,26. Bridging of the two taci moieties was, however, not observed.…”

“…It is possible to control the reaction in such a way that one imino group reacts with OH – reforming the deprotonated, coordinated amine, whereas at the same time, an adjacent imino group reacts with CN – (Scheme ). The nitrile‐carbon atom can now react as an electrophilic centre,26,38 being able to accept the adjacent, negative nitrogen donor. In organic chemistry, the reaction of a nitrile RCN with an amine to give a corresponding amidine is only known for nitriles which are activated either by a strongly electron‐withdrawing substituent R or by coordination of a Lewis acid 39.…”

Untitled

“…59 Structures are reported for several octahedral azide complexes of Co III with tridentate amines, such as 60 Template syntheses of cobalt(III) hexaaza cage complexes have been reported. 61 Cobalt(III) complexes of a sarcophagine cage ligand bound to a polycyclic aromatic group intercalate into negatively supercoiled plasmid DNA; on irradiation single-strand DNA cleavage occurs. 62 This year there are welcome structural reports on simple nickel ammine complexes.…”