Synthesis of trans bis-alkynyl complexes of Co(III) supported by a tetradentate macrocyclic amine: A spectroscopic, structural, and electrochemical analysis of π-interactions and electronic communication in the CCMCC structural unit

Synthetic and structural studies of mono-acetylide and unsymmetric bis-acetylide complexes based on CoIII-cyclam

“…It is clear from these CVs that the anodic peak is associated with reduction C and makes the couple quasireversible. This observation is consistent with the prior report of the CVs for [Co(cyclam)(C 2 R) 2 ] + , for which the reversibility of the Co(III/II) couple improves as R becoming more electron withdrawing[41]. Reduction of the nitro-group occurs at very negative potential and results in degradation of the Co compound, as evidenced by the broadening of the anodic peak below C and the appearance of a new anodic wave near 0 V when compared to the CVs in green and blue.…”

“…Based on the voltammetric results of 1b and 1c, a simple assignment to explain the observed couples is given in Scheme 2 below.Compound 2a exhibits an irreversible 1eoxidation and three 1ereductions. In contrast to 1a, it is the first 1ereduction B that is quasi-reversible, which is consistent with the prior report of [Co(cyclam)(C 2 R) 2 ] +[41]. As outlined in Scheme 2, the second 1ereduction is reversible because of the dissociation of the less electron deficient acetylide (-C 2 Ph).…”

“…is slightly longer than that of [Co(cyclam)(C 2 CF 3 ) 2 ] + , while the Co-C(phenylacetylene) bond length of 2a + is slightly shorter than that of [Co(cyclam)(C 2 Ph) 2 ] + . The shortness of Co-C in [Co(cyclam)(C 2 CF 3 ) 2 ] + was previously attributed to a weak -acidity of -C 2 CF 3 ligand[41]. However, our DFT calculations on related Co III acetylides generally place *(C≡C) significantly above Co d orbitals[37,45], which makes the former an unlikely acceptor.…”

“…In addition to the aforementioned study of Ru 2 -based acetylides, our laboratory has investigated a number of M III -cyclam (M = Cr, Fe and Co; cyclam = 1,4,8,11tetraazacyclotetradecane) based acetylide complexes, and elucidated their structural and voltammetric properties [34][35][36][37]. It should be noted that other laboratories have also explored the acetylide chemistry of M III -cyclam complexes [38][39][40][41][42][43]. [45].…”

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

“…43,50 More recently, the same protocol has been extended to prepare [Co(cyclam)(C 2 R) 2 ] + with R = CF 3 , Fc, Ph, C 6 H 4 -4-CH 3 , C 6 H 4 -4-CN and C 6 H 4 -4-CF 3 . 51 Although the [M(cyclam)(OTf) 2 ] + starting materials are often a mixture of cis (major) and trans isomers, the products of alkynylation reactions are predominantly the trans isomers (trans-[M(cyclam)(C 2 R) 2 ] + ). Careful examination of the synthesis of [Cr(cyclam)(C 2 R) 2 ] + by Wagenknecht et al revealed that the isomer distribution is sensitive to the solvent, and replacing THF with diethyl ether produced yields of the cis isomer as high as 66%.…”