Mixed-ligand complexes of copper(ii) with thienoyltrifluoroacetonate and nitrogen containing ligands: synthesis, structures, antimicrobial activity, cytotoxicity, Hirshfeld surface analysis and DFT studies.

Mixed-ligand complexes of copper(ii) with thienoyltrifluoroacetonate (TTA-H), 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), and tetramethylethylenediamine (tmen), associated with counter ions such as Cl-, and NO3 - have been synthesized and characterized by molar conductance measurements, elemental analysis, mass spectrometry, IR and UV-Vis spectroscopy, antimicrobial activity, cytotoxicity assay studies, and single-crystal X-ray diffraction. The UV-Vis spectra and crystal structures are consistent with the adoption of square pyramidal geometry for all of the complexes except [Cu(TTA)tmen]NO3 and [Cu(TTA)2tmen] which have square planar and octahedral geometries, respectively. Conductance measurements of the mixed-ligand complexes indicated that they were all non-electrolytes, with the ligands and anions being coordinated to Cu except [Cu(TTA)tmen]NO3 which is a 1 : 1 electrolyte. All of the complexes were moderately active on all the fungi tested (Candida albicans, Aspergillus niger, Penicillium notatum, Rhizopus stolonifer) except [Cu(TTA)bipyCl] which showed increased activity in Candida albicans and Aspergillus niger. All of the compounds tested showed LC50 values greater than 100 with [Cu(TTA)(phen)NO3] being the least toxic of the compounds. Molecular geometries of the complexes were optimized at the PBE1PBE/def2SVP and PBE1PBE/6-311g(d,p) level of theory and the results were compared with the single-crystal X-ray diffraction data. Electronic properties such as HOMO, LUMO, HOMO-LUMO gaps and global reactivity descriptors are reported at the PBE1PBE/6-311g(d,p) level of theory. Hirshfeld surface analysis was carried out to investigate the cooperative non-covalent supramolecular interactions within the various complexes.

Synthesis and Structure of an o-Carboranyl-Substituted Three-Coordinate Borane Radical Anion.

Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC6 H4 )-closo-1,2-C2 B10 H10 -2-)2 (4-MeC6 H4 )B] (1), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr2 . Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1.- was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1, 1.- , their calculated geometries, and the S1 excited state of 1. Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals.

Optimization of Aqueous Stability versus π-Conjugation in Tetracationic Bis(triarylborane) Chromophores: Applications in Live-Cell Fluorescence Imaging.

The stability of tetracationic triarylboranes in dilute aqueous solution was investigated by tuning the steric demand of the linker in a (para-(N,N,N-trimethylammonio)xylyl)2 B-(linker)-B(para-(N,N,N-trimethylammonio)xylyl)2 structure. With increasing steric bulk of the linker, namely 1,4-phenylene, 2,2'''-(3,3'''-dimethyl)-5,2':5',2'':5'',5'''-quaterthiophene, 9,10-anthracenylene, and 4,4'''-(5'-(3,5-dimethylphenyl))(5''-(3''',5'''-dimethylphenyl))-2',2''-bithiophene, the stability of the compounds increased. The anthracene-based chromophore, compound 3M is water-stable for at least 48 h, is nontoxic to cells and exhibits an exceedingly high fluorescence quantum yield of 0.86 in water making it an ideal candidate for confocal live-cell imaging of lysosomes.

Synthesis, Photophysical, and Electrochemical Properties of Pyrenes Substituted with Donors or Acceptors at the 4- or 4,9-Positions.

We report herein an efficient and direct functionalization of the 4,9-positions of pyrene by Ir-catalyzed borylation. Three pinacol boronates (-Bpin), including 4-(Bpin)-2,7-di( tert-butyl)pyrene (5), 4,9- bis(Bpin)-2,7-di( tert-butyl)pyrene (6), and 4,10- bis(Bpin)-2,7-di( tert-butyl)pyrene (7), were synthesized. The structures of 6 and 7 have been confirmed by single-crystal X-ray diffraction. To demonstrate the utility of these compounds, donor (NPh2)-substituted compounds 4-diphenylamino-2,7-di( tert-butyl)pyrene (1) and 4,9- bis(diphenylamino)-2,7-di( tert-butyl)pyrene (2) have been synthesized on a gram scale. Acceptor (BMes2)-substituted compounds 4,9- bis(BMes2)pyrene (3) and 4,9- bis(BMes2)-1,2,3,6,7,8-hexahydropyrene (4) were synthesized for comparison. The photophysical and electrochemical properties of compounds 1-4 have been studied both experimentally and theoretically. The S0 → S1 transitions of the 4- or 4,9-disubstituted pyrenes, 1-3, are allowed, with moderate fluorescence quantum yields and radiative decay rates. The photophysical and electrochemical properties of 1-3 were compared with the 2,6-naphthalenylene-cored compound 4 as well as the previously reported 2,7- and 1,6- pyrenylene-cored compounds.

Pyrene Molecular Orbital Shuffle-Controlling Excited State and Redox Properties by Changing the Nature of the Frontier Orbitals.

We show that by judicious choice of substituents at the 2- and 7-positions of pyrene, the frontier orbital order of pyrene can be modified, giving enhanced control over the nature and properties of the photoexcited states and the redox potentials. Specifically, we introduced a julolidine-like moiety and Bmes2 (mes=2,4,6-Me3 C6 H2 ) as very strong donor (D) and acceptor (A), respectively, giving 2,7-D-π-D- and unsymmetric 2,7-D-π-A-pyrene derivatives, in which the donor destabilizes the HOMO-1 and the acceptor stabilizes the LUMO+1 of the pyrene core. Consequently, for 2,7-substituted pyrene derivatives, unusual properties are obtained. For example, very large bathochromic shifts were observed for all of our compounds, and unprecedented green light emission occurs for the D/D system. In addition, very high radiative rate constants in solution and in the solid state were recorded for the D-π-D- and D-π-A-substituted compounds. All compounds show reversible one-electron oxidations, and Jul2 Pyr exhibits a second oxidation, with the largest potential splitting (ΔE=440 mV) thus far reported for 2,7-substituted pyrenes. Spectroelectrochemical measurements confirm an unexpectedly strong coupling between the 2,7-substituents in our pyrene derivatives.

A Cyclic Alkyl(amino)carbene as Two-Atom π-Chromophore Leading to the First Phosphorescent Linear CuI Complexes.

The members of a series of linear and trigonal copper(I) complexes bearing a cyclic alkyl(amino)carbene (CAAC) ligand show surprising photophysical properties compared to those of the corresponding N-heterocyclic carbene (NHC) complexes. Whereas the linear NHC complexes [CuX(NHC)] are almost non-emissive, [CuX(CAAC)] (X=Cl, Br, I) and [Cu(CAAC)2 ]PF6 show very bright emissions from their triplet excited states in the blue to green region, displaying quantum yields of up to 65 % in the solid state, even though the π-acceptor comprises only the carbene C and N atoms with no other π conjugation. [Cu(CAAC)2 ]PF6 is the fastest CuI -based triplet state emitter characterized to date, not displaying thermally activated delayed fluorescence (TADF), with an intrinsic lifetime of only 10.6 µs, that is, kr =9.4×104  s-1 , competitive with many PtII - and IrIII -based emitters. In order to test the stability of such linear copper CAAC complexes in devices, some of our compounds have been applied in proof-of-principle organic light-emitting diodes (OLEDs). This case study thus demonstrates for the first time the use of CAACs as suitable π-chromophores for CuI -based phosphorescent emitters, and their implementation in OLEDs underlines the general applicability of this class of ligands in materials science.

Water-Soluble Triarylborane Chromophores for One- and Two-Photon Excited Fluorescence Imaging of Mitochondria in Cells.

Three water-soluble tetracationic quadrupolar chromophores comprising two three-coordinate boron π-acceptor groups bridged by thiophene-containing moieties were synthesised for biological imaging applications. Compound 3 containing the bulkier 5-(3,5-Me2 C6 H2 )-2,2'-(C4 H2 S)2 -5'-(3,5-Me2 C6 H2 ) bridge is stable over a long period of time, exhibits a high fluorescence quantum yield and strong one- and two-photon absorption (TPA), and has a TPA cross section of 268 GM at 800 nm in water. Confocal laser scanning fluorescence microscopy studies in live cells indicated localisation of the chromophore at the mitochondria; moreover, cytotoxicity measurements proved biocompatibility. Thus, chromophore 3 has excellent potential for one- and two-photon-excited fluorescence imaging of mitochondrial function in cells.

Synthesis and fluxional behaviour of novel chloroborole dimers.

The (B-Cl)-chloroboroles 2-chloro-1,3-di(4-R-phenyl)-2,4,5,6-tetra-hydrocyclopenta[c]borole (R = H, Br) undergo a novel dimerisation process in CH2Cl2 solution. The resulting unsymmetric dimers are highly fluxional in solution via reversible enantiomerisation through an intermediate with mirror symmetry. DFT calculations suggest an unusual dimerisation mechanism and provide insight into the dynamics of the dimers.

Cyclic (Alkyl)(Amino)Carbene Complexes of Rhodium and Nickel and Their Steric and Electronic Parameters.

N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) are of great interest, as their electronic and steric properties provide a unique class of ligands and organocatalysts. Herein, substitution reactions involving novel carbonyl complexes of rhodium and nickel were studied to provide a deeper understanding of the fundamental electronic factors characterizing CAAC(methyl) , which were compared with the large array of data available for NHC and sterically more demanding CAAC ligands.

The Radical Anion and Dianion of Tetraazapentacene.

The mono- and bis-reduction of 6,13-bis((triisopropylsilyl)ethynyl)quinoxalino[2,3-b]phenazine (1) with potassium anthracenide in THF is reported. Both the radical anion 1(.-) and the dianion 1(2-) were isolated and characterized by optical and structural (single-crystal X-ray diffraction) methods. Solutions of the radical anion 1(.-) were stable in air for several hours and characterized by EPR spectroscopy. Dianion 1(2-) is highly fluorescent and photostable.

Reductive Coupling of Diynes at Rhodium Gives Fluorescent Rhodacyclopentadienes or Phosphorescent Rhodium 2,2'-Biphenyl Complexes.

Reactions of [Rh(κ(2) -O,O-acac)(PMe3 )2 ] (acac=acetylacetonato) and α,ω-bis(arylbutadiynyl)alkanes afford two isomeric types of MC4 metallacycles with very different photophysical properties. As a result of a [2+2] reductive coupling at Rh, 2,5-bis(arylethynyl)rhodacyclopentadienes (A) are formed, which display intense fluorescence (Φ=0.07-0.54, τ=0.2-2.5 ns) despite the presence of the heavy metal atom. Rhodium biphenyl complexes (B), which show exceptionally long-lived (hundreds of µs) phosphorescence (Φ=0.01-0.33) at room temperature in solution, have been isolated as a second isomer originating from an unusual [4+2] cycloaddition reaction and a subsequent ß-H-shift. We attribute the different photophysical properties of isomers A and B to a higher excited state density and a less stabilized T1 state in the biphenyl complexes B, allowing for more efficient intersystem crossing S1 →Tn and T1 →S0 . Control of the isomer distribution is achieved by modification of the bis- (diyne) linker length, providing a fundamentally new route to access photoactive metal biphenyl compounds.

Correlations and Contrasts in Homo- and Heteroleptic Cyclic (Alkyl)(amino)carbene-Containing Pt(0) Complexes.

An improved synthetic route to homoleptic complex [Pt(CAAC(Me))2] (CAAC = cyclic (alkyl)(amino)carbenes) and convenient routes to new heteroleptic complexes of the form [Pt(CAAC(Me))(PR3)] are presented. Although the homoleptic complex was found to be inert to many reagents, oxidative addition and metal-only Lewis pair (MOLP) formation was observed from one of the heteroleptic complexes. The spectroscopic, structural, and electrochemical properties of the zero-valent complexes were explored in concert with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The homoleptic [Pt(CAAC)2] and heteroleptic [Pt(CAAC)(PR3)] complexes were found to be similar in their spectroscopic and structural properties, but their electrochemical behavior and reactivity differ greatly. The unusually strong color of the CAAC-containing Pt(0) complexes was investigated by TD-DFT calculations and attributed to excitations into the LUMOs of the complexes, which are predominantly composed of bonding π interactions between Pt and the CAAC carbon atoms.

Reactions of group 4 metallocenes with monosubstituted acetonitriles: keteniminate formation versus C-C coupling.

The reactions of the Group 4 metallocene dichlorides [Cp'2 MCl2 ] (1 a: M=Ti, Cp'=Cp*=η(5) -pentamethylcyclopentadienyl, 1 b: M=Zr, Cp'=Cp=η(5) -cyclopentadienyl) with lithiated MesCH2-C≡N gave [Cp*2 TiCl(N=C=C(HMes))] (3; Mes=mesityl) in the case of 1 a. For compound 1 b, a nitrile-nitrile coupling resulted in a five-membered bridge in 4. The reaction of the metallocene alkyne complex [Cp*2 Zr(η(2) -Me3 SiC2 SiMe3 )] (2) with PhCH2 C≡N led in the first step to the unstable product [Cp*2 Zr(η(2) -Me3 SiC2 SiMe3 )(NC=CH2 Ph)] (5). After the elimination of the alkyne, a mixture of products was formed. By variation of the solvent and the reaction temperature, three compounds were isolated: a diazadiene complex 6, a bis(keteniminate) complex 7, and 8 with a keteniminate ligand and a five-membered metallacycle. Subsequent variation of the Cp ligand and the metal center by using [Cp2 Zr] and [Cp*2 Ti] with Me3 SiC2 SiMe3 in the reactions with PhCH2-C≡N gave complex mixtures.

Taming the beast: fluoromesityl groups induce a dramatic stability enhancement in boroles.

The electron-deficient pentaarylborole 1-(2',4',6'-tris(trifluoromethyl)phenyl)-2,3,4,5-tetraphenylborole (1) has been synthesised with the long-term aim of developing borole-based optoelectronic materials. The bulky 2,4,6-tris(trifluoromethyl)phenyl (FMes) group on the boron atom of 1 significantly improves (>600 times) its air stability relative to its mesityl analogue. Moreover, 1 shows good thermal stability without undergoing the dimerisation or isomerisation reactions reported for some other boroles. A triarylborole analogue (2), belonging to a new class of borole with the 3- and 4-positions of the BC4 ring linked by a -(CH2)3- group, has also been synthesised to elucidate the influence of carbon-bonded substituents on the stability of boroles. Both boroles were prepared through the reaction of Li[FMesBF3] and divinyldilithium reagents, a new and general method for borole syntheses. Compound 2 was found to isomerise through a [1,3]-H shift and double-bond rearrangement to an s-trans-butadienylborane species under highly basic (NaOH) conditions. The increased steric crowding at the boron centre through incorporation of the FMes group does not preclude binding of Lewis bases to either 1 or 2, as demonstrated by their fully reversible binding of pyridine. Interestingly, 1 exhibits a blue-shifted absorption spectrum, as compared with its mesityl analogue, a result contrary to previous understanding of the influence of substituent electronics on the absorption spectra of boroles. Most importantly, these boroles exhibit much greater air-stability than previously reported analogues without sacrificing the strong electron-accepting ability that makes boroles so attractive; indeed, 1 and 2 have very low reduction potentials of -1.52 and -1.69 eV vs. Fc/Fc+, respectively.

Four-membered heterometallacyclic d° and d¹ complexes of Group†4 metallocenes with amidato ligands.

A study of the coordination chemistry of different amidato ligands [(R)N-C(Ph)O] (R=Ph, 2,6-diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp2M(Cl){κ(2)-N,O-(R)N-C(Ph)O}] M=Zr, R=Dipp (1 a), Ph (1 b); M=Hf, R=Ph (2)) were synthesized by reaction of [Cp2MCl2] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp2Zr(H)Cl]. Salt metathesis reaction of [Cp2Zr(H)Cl] with deprotonated amide [(Dipp)N-C(Ph)O] gave the zirconocene hydrido complex [Cp2M(H){κ(2)-N,O-(Dipp)N-C(Ph)O}] (3). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)3Mg(Cl) {κ(2)-N,O-(Dipp)N-C(Ph)O}] (4; py=pyridine). The paramagnetic complexes [Cp'2Ti{κ(2)-N,O-(R)N-C(Ph)O}] (Cp'=Cp, R=Ph (7 a); Cp'=Cp, R=Dipp (7 b); Cp'=Cp*, R=Ph (8)) were prepared by the reaction of the known titanocene alkyne complexes [Cp2'Ti(η(2)-Me3SiC2SiMe3)] (Cp'=Cp (5), Cp'=Cp* (6)) with the corresponding amides. Complexes 1 a, 2, 3, 4, 7 a, 7 b, and 8 were characterized by X-ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy.

Bis(µ2-iso-propyl-imido-κ(2) N:N)bis-[(η(5)-cyclo-penta-dien-yl)(ethenolato-κO)titanium(IV)].

The title dinuclear half-sandwich complex, [CpTi(OCH=CH2)(µ2-N-iPr)]2 (Cp = cyclo-penta-dien-yl; iPr = isopropyl), was ob-tained from the reaction of Cp2TiCl2, n-butyl-lithium and iso-propyl-amine in tetra-hydro-furan. Each Ti(IV) atom is coordinated by one Cp ligand, one vin-yloxy unit and two bridging imido groups in a strongly distorted tetra-hedral geometry. There are two half mol-ecules in the asymmetric unit, such that whole mol-ecules being generated by inversion symmetry.

Synthesis, characterization and reactivity of group 4 metallocene bis(diphenylphosphino)acetylene complexes-a reactivity and bonding study.

A study of the coordination chemistry of bis(diphenylphosphino)acetylene, Ph2P-C≡C-PPh2, with selected group 4 metallocenes is presented. By substitution of the alkyne in complexes of the type Cp'2M(L)(η(2)-Me3SiC2SiMe3) (M = Ti, no L; M = Zr, L = pyridine; Cp' = substituted or unsubstituted bridged or unbridged η(5)-cyclopentadienyl), the expected mononuclear complexes Cp*2Ti(η(2)-Ph2PC2PPh2) (4Ti), (rac-ebthi)Ti(η(2)-Ph2PC2PPh2) (5Ti), and (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) [ebthi = ethylenebis(tetrahydroindenyl)] were obtained. When [Cp2Zr] was used in the reaction of Cp2Zr(py)(η(2)-Me3SiC2SiMe3) with Ph2P-C≡C-PPh2, the dinuclear complex [Cp2Zr(η(2)-Ph2PC2PPh2)]2 (6) was formed and isolated in the solid state. In solution, this complex is in equilibrium with the very spectacular structure of complex 7b as the first example of such a highly strained four-membered heterometallacycle of a group 4 metal, involving the rare R2PCCR' fragment in the cyclic unit. Both the stability and reactivity of heterodisubstituted alkynes X-C≡C-X (X = NR2, PR2, SR, SiR3, etc.) themselves and also of their complexes are of general interest. Complex 6 did not react with a second [Cp2Zr] fragment to form a homobimetallic complex. In contrast, for (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) this reaction occurs. In the reaction of complex 4Ti with the Ni(0) complex (Cy3P)2Ni(η(2)-C2H4) (Cy = cyclohexyl), C-P bond cleavage of the alkyne ligand resulted in the formation of the isolated complex [(Cy3P)Ni(µ-PPh2)]2 (11). The structure and bonding of the complexes were investigated by DFT analysis to compare the different possible coordination modes of the R2P-C≡C-PR2 ligand. For compound 7b, a flip-flop coordination of the phosphorus atoms was proposed. Complexes 4Ti, 5Ti, 5Zr, 6, and 11 were characterized by X-ray crystallography.

Facile access to tuneable Schwartz's reagents: oxidative addition products from the reaction of amide N-H bonds with reduced zirconocene complexes.

On the tracks of Schwartz's reagent: Two zirconocene hydrido amidate complexes are synthesized by formal oxidative addition of amide NH bonds to reduced zirconocene fragments. Insertion reactions with alkenes show a different behavior than Schwartz's reagent by forming branched insertion products. The insertion product and the hydrido complex are characterized by X-ray analysis.

{N,N-Bis[bis-(2,2,2-tri-fluoro-eth-oxy)phosphan-yl]methyl-amine-κ(2) P,P'}bis-(η(5)-cyclo-penta-dien-yl)titanium(II).

The title compound, [Ti(C5H5)2(C9H11F12NO4P2)], is a four-membered titanacycle obtained from the reaction of Cp2Ti(η(2)-Me3SiC2SiMe3) and CH3N[P(OCH2CF3)2]2 {N,N-bis-[bis-(tri-fluoro-eth-oxy)phosphan-yl]methyl-amine, tfepma}. The Ti(II) atom is coordinated by two cyclo-penta-dienyl (Cp) ligands and the chelating tfepma ligand in a strongly distorted tetra-hedral geometry. The mol-ecule is located on a mirror plane.

Highly strained heterometallacycles of Group†4 metallocenes with bis(diphenylphosphino)methanide ligands.

A study of the coordination chemistry of different bis(diphenylphosphino)methanide ligands [Ph2PC(X)PPh2] (X = H, SiMe3) with Group 4 metallocenes is presented. The paramagnetic complexes [Cp2Ti{κ(2)-P,P-Ph2PC(X)PPh2}] (X = H (3 a), X = SiMe3 (3 b)) have been prepared by the reactions of [(Cp2TiCl)2] with [Li{C(X)PPh2}2(thf)3]. Complex 3 b could also be synthesized by reaction of the known titanocene alkyne complex [Cp2Ti(η(2)-Me3SiC2SiMe3)] with Ph2PC(H)(SiMe3)PPh2 (2 b). The heterometallacyclic complex [Cp2Zr(H){κ(2)-P,P-Ph2PC(H)PPh2}] (4 aH) has been prepared by reaction of the Schwartz reagent with [Li{C(H)PPh2}2(thf)3]. Reactions of [Cp2HfCl2] with [Li{C(X)PPh2}2(thf)3] gave the highly strained corresponding metallacycles [Cp2M(Cl){κ(2)-P,P-Ph2PC(X)PPh2}] (5 aCl and 5 bCl) in very good yields. Complexes 3 a, 4 aH, and 5 aCl have been characterized by X-ray crystallography. Complex 3 a has also been characterized by EPR spectroscopy. The structure and bonding of the complexes has been investigated by DFT analysis. Reactions of complexes 4 aH, 5 aCl, and 5 bCl did not give the corresponding more unsaturated heterometallacyclobuta-2,3-dienes.