Cr(III)-HMC (HMC = 5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane) Alkynyl Complexes: Preparation and Emission Properties

Geometric isomers of dichloridoiron(III) complexes of CTMC (5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradecane)

Di­chlorido­iron(III) com­plexes of two stereoisomers of a tetra­aza­macrocycle are examined. The stereoisomerism of the macrocycle is shown to determine the geometric isomerism of the resulting metal com­plex, and these results are com­pared to relevant previous reports.

Both trans and cis iron–CTMC com­plexes, namely, trans-di­chlorido­[(5SR,7RS,12RS,14SR)-5,7,12,14-tetra­methyl-1,4,8,11-tetra­aza­cyclo­tetra­deca­ne]iron(III) tetra­chlorido­ferrate, [Fe(C₁₄H₃₂N₄)Cl₂][FeCl₄] (1a), the analogous chloride methanol monosolvate, [Fe(C₁₄H₃₂N₄)Cl₂]Cl·CH₃OH (1b), and cis-di­chlo­rido­[(5SR,7RS,12SR,14RS)-5,7,12,14-tetra­methyl-1,4,8,11-tetra­aza­cyclo­tetra­dec­ane]iron(III) chloride, [Fe(C₁₄H₃₂N₄)Cl₂]Cl (2), were successfully synthesized and structurally characterized using X-ray diffraction. The coordination geometry of the macrocycle is dependent on the stereoisomerism of CTMC. The packing of these com­plexes appears to be strongly influenced by extensive hydro­gen-bonding inter­actions, which are in turn determined by the nature of the counter-anions (1aversus1b) and/or the coordination geometry of the macrocycle (1a/1bversus2). These observations are extended to related ferric cis- and trans-di­chloro macrocyclic com­plexes.

A unique series of chromium(iii) mono-alkynyl complexes supported by tetraazamacrocycles

Described herein is the synthesis and characterization of macrocyclic Cr^III mono-alkynyl complexes. By using the meso-form of the tetraazamacrocycle HMC (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane), trans-[Cr(HMC)(C₂Ph)Cl]OTf (1a), trans-[Cr(HMC)(C₂Np)Cl]OTf (2a), trans-[Cr(HMC)(C₂C₆H₄^tBu)Cl]OTf (3a), and trans-[Cr(HMC)(C₂(3,5-Cl₂C₆H₃))Cl]OTf (4a) complexes have been realized. These complexes were synthesized in high yield through the reaction of trans-[Cr(meso-HMC)(C₂Ar)₂]OTf (1b-4b) with stoichiometric amounts of methanolic HCl. Single crystal X-ray diffraction showed that the trans-stereochemistry and pseudo-octahedral geometry is retained in the desired mono-alkynyl complexes. The absorption spectra of complexes 1a-4a display d-d bands with distinct vibronic progressions that are slightly red shifted from trans-[Cr(HMC)(C₂Ar)₂]⁺ with approximately halved molar extinction coefficients. Time-delayed measurements of the emission spectra for complexes 1a-4a at 77 K revealed phosphorescence with lifetimes ranging between 343 μs (4a) and 397 μs (1a). The phosphorescence spectra of 1a-4a also exhibit more structuring than the bis-alkynyl complexes due to a strengthened vibronic coupling between the Cr^III metal center and alkynyl ligands.

Crystal structures of two (5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)iron(III) complexes

Reported in this contribution are the synthesis and crystal structures of two new Fe^III complexes of 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (HMC), namely, dichlorido(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)iron(III) chloride, [FeCl₂(C₁₆H₃₆N₄)]Cl or cis-[FeCl₂(rac-HMC)]Cl (1), and dichlorido(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)iron(III) tetrachloridoferrate, [FeCl₂(C₁₆H₃₆N₄)][FeCl₄] or trans-[FeCl₂(meso-HMC)][FeCl₄] (2). Single-crystal X-ray diffraction studies revealed that both 1 and 2 adopt a pseudo-octahedral geometry, where the macrocycles adopt folded and planar geometries, respectively. The chloride ligands in 1 are cis to each other, while those in 2 have a trans configuration. The relevant bond angles in 1 deviate substantially from an ideal octahedral coordination geometry, with the angles between the cis substituents varying from 81.55 (5) to 107.56 (4)°, and those between the trans-ligating atoms varying from 157.76 (8) to 170.88 (3)°. In contrast, 2 adopts a less strained configuration, in which the N-Fe-N angles vary from 84.61 (8) to 95.39 (8)° and the N-Fe-Cl angles vary from 86.02 (5) to 93.98 (5)°.

Crystal structures of 5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-decane cobalt(III) mono-phenyl-acetyl-ide and bis-phenyl-acetyl-ide

Reported in this contribution are the synthesis and crystal structures of new mono- and bis-phenyl-acetyl-ides based on CoIII(DMC) (DMC is 5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne). Chlorido-(5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)(phenyl-ethyn-yl)cobalt(III) chloride-aceto-nitrile-methanol (1/1/1), [Co(C8H5)Cl(C12H28N4)]Cl·CH3CN·CH3OH, 1, and (5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)bis-(phenyl-ethyn-yl)cobalt(III) tri-fluoro-methane-sulfonate-di-chloro-methane (2/1), [Co(C8H5)2(C12H28N4)]2(CF3SO3)2·CH2Cl2, 2, were prepared under weak-base conditions in satisfactory yields. Single-crystal X-ray diffraction studies revealed that both 1 and 2 adopt a pseudo-octa-hedral symmetry in which the Cl-Co-C angles of 1 and C-Co-C of 2 range from 177.7 (2) to 178.0 (2)° and from 177.67 (9) to 179.67 (9)°, respectively. In both structures, the CoIII metal center is coordinated in the equatorial plane by four N atoms, in which the N-Co-N angles range from 85.6 (3) to 94.4 (3)°. The structure of 1 features two crystallographically independent mol-ecules in its triclinic cell (Z' = 2), which are related to each other by pseudo-monoclinic symmetry. The crystal investigated was twinned by a symmetry operator of the approximate double-volume C-centered cell (180° rotation around [201] of the actual triclinic cell), with a refined twin ratio of 0.798 (3) to 0.202 (3). Both methanol solvent mol-ecules in 1 are disordered, the major occupancy rates refined to 0.643 (16) and 0.357 (16). Compound 2 also contains two mol-ecules in the asymmetric unit, together with two tri-fluoro-methane-sulfonate anions [of which one is disordered; occupancy values of 0.503 (16) and 0.497 (16)] and a disordered di-chloro-methane [occupancy values of 0.545 (12) and 0.455 (12)].

Chromium(III) Bis-Arylterpyridyl Complexes with Enhanced Visible Absorption via Incorporation of Intraligand Charge-Transfer Transitions

A series of chromium(III) bis-arylterpyridyl complexes containing intraligand charge-transfer (ILCT) excited states were prepared and characterized. These complexes show significant absorption in the visible region due to the ILCT bands. The ILCT bands are tunable across the UV and visible spectrum via incorporation of electron-withdrawing and electron-donating groups on the aryl ring. The absorption of Cr(4'-(4-methoxyphenyl)-2,2':6',2″-terpyridine)₂³⁺ (4) in particular is much stronger in the visible region (ε = 11 900 M^-1 cm^-1 at 450 nm and ε = 5090 M^-1 cm^-1 at 500 nm) than that of the parent complex Cr(tpy)₂³⁺ (tpy = 2,2':6',2″-terpyridine; ε = 2160 M^-1 cm^-1 at 450 nm, and ε = 170 M^-1 cm^-1 at 500 nm). Emission experiments on this series reveal Cr(III)-based phosphorescence with lifetimes from 140 to 600 ns upon excitation into the ILCT bands, which indicates funneling of the excitation energy from ligand-localized excited states to Cr(III)-based excited states. Cyclic voltammograms exhibit at least three reversible ligand-based reductions. The first reduction shows shifts of up to -160 mV compared to Cr(tpy)₂³⁺. The excited-state reduction potential of these complexes ranges from +0.95 to +1.04 V vs the ferrocene/ferrocenium couple, making them potent photooxidants.

A trans-bidentate bis-pyridinyl ligand with a transition metal hinge

A titanocene based metalloligand, Cp*₂Ti(C₂2-py)₂, was synthesized and ligated to either Cu(i) or Pd(ii), binding Cu(i) between its alkynes and Pd(ii) between its pyridinyl rings.

Sustainable metal alkynyl chemistry: 3d metals and polyaza macrocyclic ligands

This article describes the recent development of sustainable metal-alkynyl chemistry based on the combination of 3d metals and polyaza macrocycles.