Synthesis and Investigation of Macrocyclic Cr^III Bis(alkynyl) Complexes: Structural and Spectroscopic Properties

Abstract

The synthesis and characterization of four new CrIII–bis(alkynyl) complexes bearing the macrocyclic tetraaza ligand DMC (DMC = 5,12‐dimethyl‐1,4,8,11‐tetraazacyclotetradecane) are reported. Complexes trans‐[Cr(DMC)(C2R)2]X (R = Ph ([1]X), Fc ([2]X), X = Cl, ClO4. C2H ([3]X′); X′ = ClO4, BPh4) and cis‐[Cr(DMC)(C4TMS)2]Cl ([4]Cl) were studied using UV/Vis and FTIR spectroscopy, and their identities were verified with ESI‐MS and elemental analysis. The three trans complexes, [1]Cl, [2](ClO4), and [3](BPh4), were structurally characterized using single‐crystal X‐ray diffraction, which revealed a pseudo‐octahedral geometry around the Cr center with the nitrogen atoms occupying the equatorial plane and the alkynyl ligands residing in the apical positions. Spectroscopic analysis of [1]Cl, [3](BPh4) and [4]Cl shows highly structured d–d bands between 320 and 500 nm. All CrIII complexes reported herein are emissive, and detailed studies were performed for [1]Cl, [3](BPh4), and [4]Cl, yielding phosphorescence lifetimes (77 K) of 380, 358, and 160 µs, respectively, and room temperature quantum yields of 0.01 % for complex [1]Cl and 0.15 % for complex [4]Cl. Voltammetric studies of complex [2](ClO4) indicate a weak but discernible coupling between two ferrocenyl groups across the C2–Cr–C2 bridge.

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

“…The increased molar absorptivity of the d–d band compared to the trans / cis -[Cr­(HMC)­Cl 2 ]Cl starting material is evidential of this interaction, in addition to indicating intensity stealing from proximal charge transfer bands. This type of band intensification and mixing behavior is well-documented and supports the assertion that the acetylide ligand acts as a π-donating ligand. ,, …”

“…The averaged Cr1–C bond (2.077[5] Å) in complex [ 1 ]Cl is slightly shorter than but within the experimental errors of that observed for the related trans -[Cr­(HMC)­(C 2 Ph) 2 ]Cl complex (2.085[2] Å) . Both CC bonds in [ 1 ] + display a slight difference in length (1.206(7) Å and 1.22(2) Å for C1–C2 and C3–C4, respectively), and they are within experimental error of triple bond lengths observed for trans -[Cr­(HMC)­(C 2 Ph) 2 ]Cl (1.211[2] Å) and trans -[Cr­(DMC)­(C 2 Ph) 2 ]Cl (1.213(3) Å) . The C1–Cr1–C3 angle (176.5(6)°) shows only a slight deviation from linearity, though the appraisal of the Cr1–C1–C2 (165.3(9)°), Cr1–C3–C4 (164(1)°), and N–Cr–C (<95°) angles shows evidence that the −C 2 Np ligand tilts its bulk away from the ring, causing a minor distortion that can be observed in Figure .…”

“…During recent years, our laboratory, along with those of Berben, Shores, Nishijo, − and Wagenknecht, have developed alkynylation chemistry of M III (cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane) with M as Cr, Fe, − and Co. − In addition, we also investigated the synthesis and emission properties of Cr III (cyclam′) alkynyl complexes, where cyclam′ is the C- substituted cyclam HMC (5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) or DMC (5,12-dimethyl-1,4,8,11-tetraazacyclotetradecane) . While arylalkynyls with aryl as phenyl or its derivatives have been exploited frequently in these studies, alkynyls with expanded aromatic substituents were limited to the examples of Rh III /Cr III (cyclam) with Ar as naphthalene and phenanthrene .…”

“…assertion that the acetylide ligand acts as a π-donating ligand. 44,45,61 Absorption spectra of [1] + and [2] + display fine structures in the visible region because of the coupling of electronic states of the metal center to vibrational modes of the ligands. Analysis of the fine-structuring reveals irregularly spaced vibronic progressions between 1150 and 1700 cm −1 , a frequency range typically associated with aromatic ν(CC) stretching modes or phenyl ring deformations.…”

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

“…There has been recent interest in developing conjugated materials based on alkynyl complexes of 3d metals with cyclam (1,4,8,11-tetraazacyclotetradecane) or its C-functionalized derivatives as the supporting ligand (Ren, 2016). Noteworthy examples include magnetic coupling between Cr(cyclam) species mediated by ethynyltetrathiafulvalene ligands (Nishijo et al, 2011), the formation of [Co(cyclam)-Cl] 2 (-C 2m ) (m = 2-6) series (Cook et al, 2015(Cook et al, , 2016 and Cobased cross-conjugated gem-DEE complexes (gem-DEE is gem-diethynylethene; Natoli et al, 2015Natoli et al, , 2016Natoli et al, , 2019, and phosphorescence from [Cr(cyclam 0 )(C 2 R) 2 ]-type complexes, with cyclam 0 as either 5,5,7,12,12,14-hexamethyl-1,4,8,11tetraazacyclotetradecane (HMC;Tyler et al, 2016) or 5,12dimethyl-1,4,8,11-tetraazacyclotetradecane (DMC;Judkins et al, 2017). In particular, several trans-[Fe(cyclam)(C 2 R) 2 ]-type complexes were prepared by the reactions between LiC 2 R and [FeCl 2 (cyclam)]Cl (Cao et al, 2012(Cao et al, , 2013.…”