Ka-Ho Choi

Synthesis, redox and optical properties of low-bandgap platinum(II) polyynes with 9-dicyanomethylene-substituted fluorene acceptors

In view of the strong electron-with-drawing nature of the cyano substituent, a blue donor/acceptor-type organometallic polymer (trans-[-Pt(PBu 3 ) 2 =C≡C-R-C≡C-] n (R = 9-dicyanomethylenefluorene-2,7-diyl)) was prepared in good yield by CuI-catalyzed polymerization involving the dehydrohalogenating coupling of trans-[-Pt(PBu 3 ) 2 Cl 2 ] and H-C≡C-R-C≡C-H. The thermal, redox and photoconducting properties of the polymer are reported. Electronic absorption studies indicate that it has a bandgap of 1.58 eV which is the lowest among any of the metal polyyne polymers reported in the literature. The derivatization of the polymer backbone with electron deficient dicyano-substituted electron acceptor in the side chain is found to be effective to tune the bandgap of this class of materials while maintaining their solubility and processability.

Synthesis, optical and photoconducting properties of platinum poly‐yne polymers functionalized with electron‐donating and electron‐withdrawing bithiazole units

By virtue of the electron-donating and electron-withdrawing properties of the thiazole ring, a new soluble rigid-rod organometallic polymer containing electron-donating and electron-withdrawing trans-[-Pt-(PBu3)2-C≡C—R—C≡C—]n (R = bithiazolediyl) groups is prepared by CuI-catalyzed dehydrohalogenation. The thermal properties and the optical absorption and photoluminescence spectra of the polymer are reported. The polymer is luminescent with a singlet emission peak at 539 nm and photoconducting in a single-layer sandwich structure photocell. The optical gap of the polymer is reduced compared to that for the oligothienyl analogue.

New ferrocenyl heterometallic complexes of 2,7-diethynylfluoren-9-one

A new series of rigid-rod alkynylferrocenyl precursors with central fluoren-9-one bridge, 2-bromo-7-(2-ferrocenylethynyl)fluoren-9-one ( 1b ), 2-trimethylsilylethynyl-7-(2-ferrocenylethynyl)fluoren-9-one ( 2 ) and 2-ethynyl-7-(2-ferrocenylethynyl)fluoren-9-one ( 3 ), have been prepared in moderate to good yields. The ferrocenylacetylene complex 3 can provide a direct access to novel heterometallic complexes, trans -[(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )CCRCCPt(PEt 3 ) 2 Ph] ( 4 ), trans -[(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )CCRCCPt(PBu 3 ) 2 CCRCC(η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 )] ( 5 ), [(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )CCRCCAu(PPh 3 )] ( 6 ) and [(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )CCRCCHgMe] ( 7 ) (Rfluoren-9-one-2,7-diyl), following the CuI-catalyzed dehydrohalogenation reactions with the appropriate metal chloride compounds. All the new complexes have been characterized by FTIR, 1 H-NMR and UV–vis spectroscopies and fast atom bombardment mass spectrometry. The solid state molecular structures of 3 , 5 , 6 and 7 have been established by X-ray crystallography. The redox chemistry of these mixed-metal species has been investigated by cyclic voltammetry and oxidation of the ferrocenyl moiety is facilitated by the presence of the heavy metal centre and increased conjugation in the chain through the ethynyl and fluorenone linkage units.

Synthesis, characterization and structural studies of new heterometallic alkynyl complexes of platinum and Group 11 metals with chelating bis(diphenylphosphino)ferrocene ligand

Reaction of the platinum bis(alkynyl) complex [Pt(dppf)(CCPh) 2 ] ( 1 ) (dppf=bis(diphenylphosphino)ferrocene) with an equimolar amount of Group 11 metal salts [Cu(NCMe) 4 ]BF 4 and AgBF 4 initially gives 1:1 mixed-metal complexes [Pt(dppf)(CCPh) 2 Cu(NCMe)]BF 4 ( 2 ) and [Pt(dppf)(CCPh) 2 Ag]BF 4 ( 3 ) in good yields. Upon standing in solution at room temperature, compounds 2 and 3 rearrange and aggregate to the corresponding diplatinum complexes [{Pt(dppf)(CCPh) 2 } 2 M]BF 4 (M=Cu ( 4 ), Ag ( 5 )) which exhibit an intense molecular ion envelope for the respective cation in their electrospray mass spectra. Compounds 4 and 5 can also be formed when the reaction is performed using a 2:1 molar ratio of 1 and the Group 11 salts. The X-ray crystal structures of 1 , 4 and 5 have been determined. Structures of 4 and 5 reveal that the two square-planar platinum coordination planes in the cation are approximately orthogonal and the Group 11 metal ion is bonded in an η 2 -fashion to four carboncarbon triple bonds to afford heterometallic pentanuclear Fe 2 Pt 2 M complexes (M=Cu, Ag) in which each platinum center is stabilized by a dppf ligand. Each of the new complexes displays a reversible oxidation couple corresponding to the ferrocenyl unit of dppf and there is less stabilization of the silver in the mixed-metal complex than in the copper congeners.

Synthesis, structures and electrochemistry of bis(alkynylferrocene) complexes with fluorene spacers

Abstract New bis(alkynylferrocene) complexes with fluorenyl-based spacers [(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )CCRCC(η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 )] (R=fluoren-9-one-2,7-diyl, 1 ; fluorene-2,7-diyl, 2 ; 9-ferrocenylmethylenefluorene-2,7-diyl, 3 ) have been prepared in excellent yields by the Sonogashira coupling reactions of ethynylferrocene with half an equivalent of the corresponding dibromofluorene derivatives BrRBr. All the compounds have been characterized by FTIR, 1 H-NMR and UV–vis spectroscopies and fast atom bombardment mass spectrometry (FABMS). The molecular structures of 1 and 2 have been elucidated by single-crystal X-ray analyses. The redox chemistry of these fluorene-linked biferrocenes has been investigated by cyclic voltammetry and the interaction between the ferrocene units is rather weak in each case. The half-wave potential of the terminal ferrocenyl moieties increases progressively in the order 3 2 1 when the substituent at the 9-position of the central spacer changes from an electron-donating ferrocenyl group (as in 3 ) to an electron-deficient oxo group (as in 1 ). This is consistent with the loss of electron density from the ferrocenyl unit to the net electron-accepting fluorenone through the ethynyl bridge in 1 .

Syntheses, Structures and Photophysical Properties of Metal Carbonyl Clusters with Dansyl and Acridone Luminophores

A series of fluorescent transition metal complexes bearing the 5-(dimethylamino)naphthalene-1-sulfonyl (R1) and acridone (R2) frameworks have been prepared. Reactions of the fluorescent-labeled alkyne ligands R1CH2C≡CH and R2CH2C≡CH with various metal carbonyl compounds [Co2(CO)8], [Et3NH][Fe2(CO)6(μ-CO)(μ-StBu)] and [M3(CO)10(NCMe)2] (M = Ru, Os) readily afforded new cluster complexes of the stoichiometry [Co2(CO)6(μ-η2-RCH2CCH)] (1: R = R1, 2: R2), [Fe2(CO)6(μ-StBu)(μ-η2-RCH2C=CH2)] (3: R = R1, 4: R2), [Ru3(CO)9(μ-CO)(μ3-η2-RCH2CCH)] (5: R = R1, 6: R2) and [Os3(CO)9(μ-CO)(μ3-η2-RCH2CCH)] (7: R = R1, 8: R2) in moderate to good yields. All of these new complexes have been fully characterized by FTIR, 1H NMR spectroscopy, UV/Vis spectroscopy and fast atom bombardment mass spectrometry (FABMS). The single-crystal X-ray structural analyses and molecular orbital calculations on 1, 2, 4 and 8 have been performed. It was found that all of these compounds are fluorescent in solutions at room temperature and a luminescence band characteristic of the inherent fluorophore is observed in these metal structures. However, a strong quenching of the fluorescence intensity of the chromophoric groups was observed upon coordination of metal cluster moieties. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Metal?metal and ligand?ligand interactions in gold poly-yne systemsBased on the presentation given at CrystEngComm Discussion, 29th June?1st July 2002, Bristol, UK.

The acetylide-functionalised thiophene gold(I) complexes [(PPh3)Au(CC(C4H2S)(C4H3S))] 1, [(PPh3)Au(CC(C4H2S)CC)Au(PPh3)] 2, [(PR3)Au(CC(C4H2S)2CC)Au(PR3)] (R = Ph 3, Cy 4) and [(PPh3)Au(CC(C4H2S)3CC)Au(PPh3)] 5 have been prepared by the reaction of the trimethylsilylethynyl oligothiophene with KOH/MeOH, followed by the addition of a stoichiometric amount of the gold(I) phosphine chloride and NaOMe in MeOH. The products have been characterised spectroscopically and their single crystal X-ray structures determined. In the molecular structures of all the complexes the Au(I) centres adopt the expected linear, two-coordinate geometry, except that in 2 the material forms a polymer through additional Au⋯Au interactions [Au⋯Au 3.2915(10) and 3.2347(9) A] between the molecular units. With the longer acetylene-functionalised spacer groups no Au⋯Au interactions are present, but hydrogen bonding and π⋯π interactions are of significance. The solution absorption and emission spectra of these complexes have been recorded and the maxima are increasingly red-shifted as the length and planarity of the functionalised spacer groups increases which is consistent with the absorptions and emissions being dominated by ligand-centred π–π* transitions.

Synthesis, structures and properties of platinum(II) complexes of oligothiophene-functionalized ferrocenylacetylene

A series of rigid-rod alkynylferrocenyl precursors with oligothiophene (from thiophene to terthiophene) linkage units in the backbone, [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mBr] 2a–2c, [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCSiMe3] 3a–3c and [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCH] 4a–4c (m = 1–3), have been prepared in moderate to good yields. The ferrocenylacetylene complexes 4a–4c can be used to form a range of stable platinum(II) alkynyl and bis(alkynyl) compounds trans-[(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCPt(PEt3)2Ph] 5a–5c and trans-[(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCPt(PBu3)2CC(C4H2S)mCC(η5-C5H4)Fe(η5-C5H5)] 6a–6c (m = 1–3). All these new compounds have been fully characterized by analytical and spectroscopic methods and the molecular structures of the bithienyl-linked complexes [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)2CC(η5-C5H4)Fe(η5-C5H5)], 2b, 4b, 5b and 6b have been established by X-ray crystallography. Structural analysis of 6b confirms its rigid-rod structural motif, featuring coplanar bithienyl rings and a trans arrangement of the two bithiophene groups. An iron–iron through-space distance of ca. 32 A is observed in 6b. Although there is no significant metallocene–metallocene interaction through the alkynyl–platinum–oligothiophene bridge, a slight negative shift of the ferrocene–ferrocenium redox potential in the platinum-containing species indicates some degree of electron delocalization into the platinum segment, in line with the results from theoretical studies. Oxidation of the thiophene units is facilitated by the presence of the platinum centre and increased conjugation in the chain.

Antimicrobial and toxicological evaluations of binuclear mercury(II)bis(alkynyl) complexes containing oligothiophenes and bithiazoles

Metals and metal complexes are promising antimicrobials due to their powerful inhibitory activity against microbes. However, the potential for metal toxicity to life remains unsolved. Mercury is a toxic element with no known positive biological functions, and its toxicity to humans is well known. With the known toxicity of Hg and its complexes, their usefulness for antimicrobial therapy should not be neglected. In this work, we investigated the antimicrobial activity of bis-(alkynyl)mercury(II) complexes with oligothiophene and bithiazole linking units against MRSA and C. albicans (pathogens commonly co-inhabit infected sites), and their cytotoxicity was tested on NIH 3T3 cells. Among the Hg(II) complexes, complex 2 showed potent microcidal activity against MRSA (MIC and MBC values = 0.2 μg mL−1) and C. albicans (MIC and MBC values = 0.4 μg mL−1). Complex 2 displayed a highly distinguished zone of clearance with comparably sharp zone edges on microbial agar plates. Time–kill kinetic studies showed that MRSA colonies were reduced by approximately 5 logs during the initial 3 h exposure to complex 2 at an 8× MIC level. The possible antimicrobial mechanism might be due to the intracellular ROS generation by complex 2 that caused the loss in MRSA viability. Complex 2 exhibited a higher IC50 value (0.8 μg mL−1) towards NIH 3T3 cells that was greater than its corresponding MIC values against tested microbes. Hg(II) complexes would be potent antimicrobials, but a challenge is to fully utilize their potential inhibitory effects on microbes while lowering their toxic levels on human health.