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 Cr(HMC) and Co(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 (CNp) complexes, trans-[Cr(HMC)(CNp)]Cl ([1]Cl) and cis-[Cr(HMC)(CNp)]Cl ([2]Cl), were prepared from the reactions between trans/cis-[Cr(HMC)Cl]Cl and lithium 1-ethynylnaphthalene (LiCNp) in yields of 73 and 66%, respectively. Also investigated are Co(cyclam) complexes bearing both CNp and CANT (ANT = 9-anthryl), namely [Co(cyclam)(CAr)Cl]Cl (Ar = ANT ([3]Cl), Np ([4]Cl)), [Co(cyclam)(CNp)(NCCH)](OTf) ([5](OTf)), and [Co(cyclam)(CNp)]OTf ([6]OTf). Complexes [3]Cl (72%) and [4]Cl (67%) were prepared from the reaction between [Co(cyclam)Cl]Cl and MeSiCANT or MeSiCNp, respectively, in the presence of triethylamine. The reaction of [4]Cl with excess silver triflate in CHCN yielded complex [5](OTf) (78%), which was reacted with HCNp 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].

New Synthetic Route for Cobalt(III) Dissymmetric Bisalkynyl Complexes Based on Cobalt(III)(cyclam)(C2NAPMes)

“…Consistent with previous studies, the Co-C1 bond length is significantly longer in the bis-NAP Mes species, 3b [1.933(4) Å], compared to the mono-NAP Mes , 1a [1.859(3) Å], which can be attributed to the trans-influence as the increased donor strength provided by the alkynyl compared to the Cl in the axial position results in a weaker bond. [19,21,22,[31][32][33] The influence of the electron withdrawing/donating character of the alkynyl ligand on the Co-C1 bond length can be observed across the literature with [Co(cyclam)(C 2 CF 3 ) 2 ] + (1.917) [34] < [Co(cyclam)(C 2 C 6 F 5 ) 2 ] + (1.926) [22] < 3b (1.933) < [Co(cyclam)(C 2 C 6 H 4 -4-NMe 2 ) 2 ] + (1.942) [21] < [Co(cyclam)(C 2 Ph) 2 ] + (2.001). [35] The electron withdrawing species (-CF 3 , C 6 F 5 , and -NAP Mes ) have notably shortened bond lengths (Co-C) compared to the electron donating groups [-NMe 2 and -N(Ph-4-OMe) 2 ] due to reduced antibonding contribution from the π(C≡C) to the Co dπ.…”

“…[8] Generally, Co III (cyclam) acetylides display a d-d transition around 450-500 nm, with higher energy transitions occurring for the bis-acetylide complexes and the lower energy for the mono-acetylides. [19,21,22,31,32,36,37] However, only compound 1a has a discernible d-d transition at 480 nm, suggesting the broad π-π*(NAP Mes ) transition obscures the d-d peaks for 3a-c (Figure 5). Based on previous work on [Co(cyclam)-(C 2 NAPiPr)(C 2 C 6 H 4 -4-NMe 2 )]Cl, [20] the sharp peak at 287 nm observed for compound 3a was assigned to the π-π* transition localized on the donor ligand (-C 6 H 4 -4-NMe 2 ).…”

Investigation of nitro–nitrito photoisomerization: crystal structure oftrans-chloridonitro(1,4,8,11-tetraazacyclotetradecane-κ4N,N′,N′′,N′′′)cobalt(III) chloride

“…(Oba & Mochida, 2015), the conformation of cyclam in these crystals being trans-III according to Tobe's classification (Bosnich et al, 1965). The (cyclam)chlorocobalt(III) alkynyl complexes such as trans-[Co(cyclam)Cl(1-ethynylnaphthalene)]CF 3 SO 3 ÁOEt 2 (Judkins et al, 2018) have been studied for their structural and spectroscopic properties.…”

Heterometal Grafted Metalla-ynes and Poly(metalla-ynes): A Review on Structure–Property Relationships and Applications

“…It is to be noted that the high conductivity, preservation of conjugation through the metal fragment, high triplet yield, etc. make "d" fragment a matter of choice for the metalla-ynes and poly(metalla-ynes) [21]. The heterometallic complexes bearing conjugated metalla-yne fragments often display modulated properties due to the synergistic effect of the two different metal ions [2,3,[22][23][24][25].…”