skip to main content

Title: Phosphorescent 2-, 3- and 4-coordinate cyclic (alkyl)(amino)carbene (CAAC) Cu( i ) complexes
The photophysical properties of several Cu( i ) complexes coordinated with cyclic (alkyl)(amino)carbene (CAAC) ligands were examined. All the compounds were found to be phosphorescent, regardless of whether they are 2-, 3- or 4-coordinated. Aggregate and excimer emission were observed from 2-coordinate CAAC–CuCl derivatives in methylcyclohexane solution. Emission from the complex 4-coordinated with a trispyrazolylborate ligand is red-shifted with respect to both the chloro-derivative and an analogous complex with an NHC ligand.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Chemical Communications
Page Range / eLocation ID:
9008 to 9011
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. A series of five ruthenium complexes containing triphenyl phosphine groups known to enhance both cellular penetration and photoinduced ligand exchange, cis -[Ru(bpy) 2 (P( p -R-Ph) 3 )(CH 3 CN)] 2+ , where bpy = 2,2′-bipyridine and P( p -R-Ph) 3 represent para -substituted triphenylphosphine ligands with R = –OCH 3 (1), –CH 3 (2) –H (3), –F (4), and –CF 3 (5), were synthesized and characterized. The photolysis of 1–5 in water with visible light ( λ irr ≥ 395 nm) results in the substitution of the coordinated acetonitrile with a solvent molecule, generating the corresponding aqua complex as the single photoproduct. A 3-fold variation in quantum yield was measured with 400 nm irradiation, Φ 400 , where 1 is the most efficient with a Φ 400 = 0.076(2), and 5 the least photoactive complex, with Φ 400 = 0.026(2). This trend is unexpected based on the red-shifted metal-to-ligand charge transfer (MLCT) absorption of 1 as compared to that of 5, but can be correlated to the substituent Hammett para parameters and p K a values of the ancillary phosphine ligands. Complexes 1–5 are not toxic towards the triple negative breast cancer cell line MDA-MB-231 in the dark, but 3 and 5 are >4.2 and >19-fold more cytotoxic upon irradiation with blue light, respectively. A number of experiments point to apoptosis, and not to necrosis or necroptosis, as the mechanism of cell death by 5 upon irradiation. These findings provide a foundation for understanding the role of phosphine ligands on photoinduced ligand substitution and show the enhancement afforded by –CF 3 groups on photochemotherapy, which will aid the future design of photocages for photochemotherapeutic drug delivery. 
    more » « less
  2. In a simple, one-step reaction, we have synthesized a pyridoxal-based chemosensor by reacting tris(hydroxymethyl)aminomethane (TRIS) together with pyridoxal hydrochloride to yield a Schiff-base ligand that is highly selective for the detection of Zn( ii ) ion. Both the ligand and the Zn( ii ) complex have been characterized by 1 H & 13 C NMR, ESI-MS, CHN analyses, and X-ray crystallography. The optical properties of the synthesized ligand were investigated in an aqueous buffer solution and found to be highly selective and sensitive toward Zn( ii ) ion through a fluorescence turn-on response. The competition studies reveal the response for zinc ion is unaffected by all alkali and alkaline earth metals; and suppressed by Cu( ii ) ion. The ligand itself shows a weak fluorescence intensity (quantum yield, Φ = 0.04), and the addition of zinc ion enhanced the fluorescence intensity 12-fold (quantum yield, Φ = 0.48). The detection limit for zinc ion was 2.77 × 10 −8 M, which is significantly lower than the WHO's guideline (76.5 μM). Addition of EDTA to a solution containing the ligand–Zn( ii ) complex quenched the fluorescence, indicating the reversibility of Zn( ii ) binding. Stoichiometric studies indicated the formation of a 2 : 1 L 2 Zn complex with a binding constant of 1.2 × 10 9 M −2 (±25%). The crystal structure of the zinc complex shows the same hydrated L 2 Zn complex, with Zn( ii ) ion binding with an octahedral coordination geometry. We also synthesized the copper( ii ) complex of the ligand, and the crystal structure showed the formation of a 1 : 1 adduct, revealing 1-dimensional polymeric networks with octahedral coordinated Cu( ii ). The ligand was employed as a sensor to detect zinc ion in HEK293 cell lines derived from human embryonic kidney cells grown in tissue culture which showed strong luminescence in the presence of Zn( ii ). We believe that the outstanding turn-on response, sensitivity, selectivity, lower detection limit, and reversibility toward zinc ion will find further application in chemical and biological science. 
    more » « less
  3. null (Ed.)
    Two NNN pincer complexes of Cu( ii ) and Ni( ii ) with BPI Me − [BPI Me − = 1,3-bis((6-methylpyridin-2-yl)imino)isoindolin-2-ide] have been prepared and characterized structurally, spectroscopically, and electrochemically. The single crystal structures of the two complexes confirmed their distorted trigonal bipyramidal geometry attained by three equatorial N-atoms from the ligand and two axially positioned water molecules to give [Cu(BPI Me )(H 2 O) 2 ]ClO 4 and [Ni(BPI Me )(H 2 O) 2 ]ClO 4 . Electrochemical studies of Cu( ii ) and Ni( ii ) complexes have been performed in acetonitrile to identify metal-based and ligand-based redox activity. When subjected to a saturated CO 2 atmosphere, both complexes displayed catalytic activity for the reduction of CO 2 with the Cu( ii ) complex displaying higher activity than the Ni( ii ) analogue. However, both complexes were shown to decompose into catalytically active heterogeneous materials on the electrode surface over extended reductive electrolysis periods. Surface analysis of these materials using energy dispersive spectroscopy as well as their physical appearance suggests the reductive deposition of copper and nickel metal on the electrode surface. Electrocatalysis and decomposition are proposed to be triggered by ligand reduction, where complex stability is believed to be tied to fluxional ligand coordination in the reduced state. 
    more » « less
  4. Four macrocyclic hybrid salts with different numbers of benzimidazolium and amine units, [H 2 L][PF 6 ] 2 (L = L 1 , L 2 , L 3 ) and [H 4 L 4 ][PF 6 ] 4 , have been employed as the heterocyclic carbene (NHC) precursors toward new Ag( i )– and Au( i )–NHC complexes. Three trinuclear and one tetranuclear Ag( i ) complexes 1–4 have been obtained from the reactions of the NHC precursors and Ag 2 O in acetonitrile. Four dinuclear Au( i )–NHC complexes 5–8 have been prepared by reacting the NHC precursors and AuCl(SMe 2 ) in the presence of NaOAc in DMF. The molecular structures of all the complexes are established by single-crystal X-ray diffraction studies. The metal ions in the Ag( i ) complexes 1–3 and the Au( i ) complexes 5–7 are coordinated with two macrocyclic NHC ligands to form a sandwiched structure. In contrast, a trinuclear Ag 3 core is located in the cavity of one macrocyclic ligand in [Ag 3 (L 4 )][PF 6 ] 3 ( 4 ). The photoluminescence properties of Au( i ) complexes 5–8 have also been investigated. 
    more » « less
  5. Interest in O 2 -dependent aliphatic carbon–carbon (C–C) bond cleavage reactions of first row divalent metal diketonate complexes stems from the desire to further understand the reaction pathways of enzymes such as DKE1 and to extract information to develop applications in organic synthesis. A recent report of O 2 -dependent aliphatic C–C bond cleavage at ambient temperature in Ni( ii ) diketonate complexes supported by a tridentate nitrogen donor ligand [(MBBP)Ni(PhC(O)CHC(O)Ph)]Cl ( 7-Cl ; MBBP = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine) in the presence of NEt 3 spurred our interest in further examining the chemistry of such complexes. A series of new TERPY-ligated Ni( ii ) diketonate complexes of the general formula [(TERPY)Ni(R 2 -1,3-diketonate)]ClO 4 ( 1 : R = CH 3 ; 2 : R = C(CH 3 ) 3 ; 3 : R = Ph) was prepared under air and characterized using single crystal X-ray crystallography, elemental analysis, 1 H NMR, ESI-MS, FTIR, and UV-vis. Analysis of the reaction mixtures in which these complexes were generated using 1 H NMR and ESI-MS revealed the presence of both the desired diketonate complex and the bis-TERPY derivative [(TERPY) 2 Ni](ClO 4 ) 2 ( 4 ). Through selective crystallization 1–3 were isolated in analytically pure form. Analysis of reaction mixtures leading to the formation of the MBBP analogs [(MBBP)Ni(R 2 -1,3-diketonate)]X (X = ClO 4 : 5 : R = CH 3 ; 6 : R = C(CH 3 ) 3 ; 7-ClO4 : R = Ph; X = Cl: 7-Cl : R = Ph) using 1 H NMR and ESI-MS revealed the presence of [(MBBP) 2 Ni](ClO 4 ) 2 ( 8 ). Analysis of aerobic acetonitrile solutions of analytically pure 1–3 , 5 and 6 containing NEt 3 and in some cases H 2 O using 1 H NMR and UV-vis revealed evidence for the formation of additional bis-ligand complexes ( 4 and 8 ) but suggested no oxidative diketonate cleavage reactivity. Analysis of the organic products generated from 3 , 7-ClO4 and 7-Cl revealed unaltered dibenzoylmethane. Our results therefore indicate that N 3 -ligated Ni( ii ) complexes of unsubstituted diketonate ligands do not exhibit O 2 -dependent aliphatic C–C bond clevage at room temperature, including in the presence of NEt 3 and/or H 2 O. 
    more » « less