Co(cyclam) Complexes of Triarylamine-acetylide: Structural and Spectroscopic Properties and DFT Analysis

Abstract

Reported herein are the syntheses of mono-and bis-C 2 TPA (HC 2 TPA = 4-ethynyl-N,N-bis(4-methoxyphenyl)aniline) complexes of Co III (cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane) complexes, and the formation of η 2 -adducts of Cu(I)/Ag(I) to the acetylenic bond of TPAC 2 ligand. The reaction between trans-[Co(cyclam)Cl 2 ]Cl and HC 2 TPA in the presence of Et 2 NH yielded trans-[Co(cyclam)(C 2 TPA)Cl]Cl ([1]Cl) and subsequent treatment of [1]Cl with CuCl or AgNO 3 afforded trans-[Co(cyclam)(C 2 TPAη 2 -CuCl 2 )Cl] (2a) or trans-[Co(cyclam)(C 2 TPA-η 2 -Ag(NO 3 ) 2 )(NO 3 )] (2b), respectively. The reaction between [Co(cyclam)Cl 2 ]Cl and 3 equiv of LiC 2 TPA afforded trans-[Co(cyclam)(C 2 TPA) 2 ]Cl ([3]Cl). X-ray diffraction studies of compounds [1]Cl, 2a/b, and [3]Cl established their molecular structures. All four compounds display redox couples that are characteristic of TPA (reversible oxidation) and Co III (irreversible reduction) center. The reversible TPA oxidation in compounds [1]Cl and [3]Cl enables further UV−vis/near-IR spectroelectrochemical studies to elucidate the change of electronic structures upon oxidation. The electronic spectra of both compounds [1]Cl and [3]Cl and their oxidized derivatives have been rationalized based on DFT and TD-DFT analysis.

A Series of Mono- and Bis-Alkynyl Co(III) Complexes Supported by a Tetra-imine Macrocyclic Ligand (TIM)

“…The addition of a second alkynyl ligand in the trans position results in a stark shift in ν­(CC) to lower frequency as evidenced in complexes 3a , 3b , and 3c which have (CC) stretches at 2111, 2107, and 2125 cm –1 , respectively. As previously noted, , the trend observed is a result of the changing antibonding interactions between Co d π and filled π­(CC) orbitals in which the replacement of the chloro ligand (weak π donor) in 1 with the acetonitrile molecule (weak π acceptor) in 2 alleviates the d π-π­(CC) antibonding interaction, resulting in stronger CC bonds. The addition of the second alkynyl in 3 results in greater antibonding d π-π­(CC), yielding weaker CC bonds .…”

“…The bulk of the trans -bis-alkynyl Co complexes are based on Co III (cyclam) (type IB in Chart ), which was first reported by Shores and co-workers . A number of symmetric analogues have been prepared by the laboratories of Wagenknecht , and Ren. , Building on the success of Shores and co-workers in realizing selective mono-alkynylation, our laboratory has generated a variety of unsymmetric trans -bis-alkynyl Co complexes. − Most importantly, the donor-bridge-acceptor (D-B-A) type complex trans -[Co­(cyclam)­(C 2 NAP iPr )­(C 2 C 6 H 4 -4-NR 2 )] + (-C 2 NAP iPr = 4-ethynyl- N -isopropyl-1,8-naphthalimide) was prepared and a charge separated state (CSS, D + -B-A – ) was detected using both fs-transient absorption spectroscopy and time-resolved IR techniques . Nonetheless, the lifetimes of the CSS were relatively short (<10 ps) due to the quenching by a low-lying Co­(III)-centered triplet state.…”