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.

Abstract

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]+.