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

Described herein is the synthesis and characterization of macrocyclic CrIII 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)(C2C6H4tBu)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 CrIII metal center and alkynyl ligands.

Synthesis and Characterizations of Macrocyclic Cr(III) and Co(III) 1-Ethynyl Naphthalene and 9-Ethynyl Anthracene Complexes: An Investigation of Structural and Spectroscopic Properties.

Reported herein are the syntheses and structural and emission spectroscopic characterizations of new CrIII(HMC) and CoIII(cyclam) complexes bearing fluorophore alkynyl ligands, where HMC and cyclam are 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane and 1,4,8,11-tetraazacyclotetradecane, respectively. Two Cr(III) bis-1-ethynylnaphthalene (C2Np) complexes, trans-[Cr(HMC)(C2Np)2]Cl ([1]Cl) and cis-[Cr(HMC)(C2Np)2]Cl ([2]Cl), were prepared from the reactions between trans/cis-[Cr(HMC)Cl2]Cl and lithium 1-ethynylnaphthalene (LiC2Np) in yields of 73 and 66%, respectively. Also investigated are CoIII(cyclam) complexes bearing both C2Np and C2ANT (ANT = 9-anthryl), namely [Co(cyclam)(C2Ar)Cl]Cl (Ar = ANT ([3]Cl), Np ([4]Cl)), [Co(cyclam)(C2Np)(NCCH3)](OTf)2 ([5](OTf)2), and [Co(cyclam)(C2Np)2]OTf ([6]OTf). Complexes [3]Cl (72%) and [4]Cl (67%) were prepared from the reaction between [Co(cyclam)Cl2]Cl and Me3SiC2ANT or Me3SiC2Np, respectively, in the presence of triethylamine. The reaction of [4]Cl with excess silver triflate in CH3CN yielded complex [5](OTf)2 (78%), which was reacted with HC2Np in the presence of triethylamine to form complex [6]OTf in 39% yield. Single crystal X-ray diffraction studies of [1]+, [3]+, [4]+, and [6]+ revealed a pseudo-octahedral geometry around the Cr(III) or Co(III) center with the tetraaza-macrocyclic ligand occupying the equatorial plane and the alkynyl- and/or chloro-ligand occupying the apical positions. The absorption spectra of complexes [1]+ and [2]+ display structured d-d bands between 400 and 550 nm, a feature that is absent in the d-d absorption of the Co(III) complexes [3]+-[6]+. Contrasting emission behaviors were observed: the Cr(III) complexes display metal-centered phosphorescence, while the Co(III) species exhibit ligand-based fluorescence. Time-delayed phosphorescence measurements revealed lifetimes of 447 and 97 µs for [1]+ and [2]+ at 77 K, respectively, and a room temperature lifetime of 218 µs for [1]+.

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

Presented here is the chemistry of Cr(III) alkynyl complexes based on the rac-HMC and meso-HMC ligands (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Thus far, two pairs of cis/trans-[Cr(rac/meso-HMC)(C2R)2]Cl (R = Ph, C2H/C2SiMe3) complexes have been synthesized from reactions between cis/trans-[Cr(rac/meso-HMC)Cl2]Cl and LiC2R. These complexes were characterized using single crystal X-ray diffraction, UV-vis spectroscopy, FT-IR spectroscopy, and fluorimetry. Single crystal X-ray diffraction studies revealed that these complexes adopt a pseudo-octahedral geometry. The electronic spectra of both the cis- and trans-[Cr(rac/meso-HMC)(C4R')2]Cl (R' = H or SiMe3) complexes exhibit d-d bands with pronounced vibronic progression associated with the asymmetric stretch of the Cr-bound C≡C bonds. All of these complexes are phosphorescent and show structured emissions originating from the ligand field excited states.