Arylacetylide Complexes Research Articles

Platinum(II)-Substituted Phenylacetylide Complexes Supported by Acyclic Diaminocarbene Ligands.

We introduce phosphorescent platinum aryl acetylide complexes supported by tert-butyl-isocyanide and strongly σ-donating acyclic diaminocarbene (ADC) ligands. The precursor complexes cis-[Pt(CNtBu)2(C≡CAr)2] (4a-4f) are treated with diethylamine, which undergoes nucleophilic addition with one of the isocyanides to form the cis-[Pt(CNtBu)(ADC)(C≡CAr)2] complexes (5a-5f). The new compounds incorporate either electron-donating groups (4-OMe and 4-NMe2) or electron-withdrawing groups [3,5-(OMe)2, 3,5-(CF3)2, 4-CN, and 4-NO2] on the aryl acetylide. Experimental HOMO-LUMO gaps, estimated from cyclic voltammetry, span the range of 2.68-3.61 eV and are in most cases smaller than the unsubstituted parent complex, as corroborated by DFT. In the ADC complexes, peak photoluminescence wavelengths span the range of 428 nm (2a, unsubstituted phenylacetylide) to 525 nm (5f, 4-NO2-substituted), with the substituents inducing a red shift in all cases. The phosphorescence E0,0 values and electrochemical HOMO-LUMO gaps are loosely correlated, showing that both can be reduced by either electron-donating or electron-withdrawing substituents on the aryl acetylides. The photoluminescence quantum yields in the ADC complexes are between 0.044 and 0.31 and the lifetimes are between 4.8 and 14 μs, a factor of 1.8-10× higher (for ΦPL) and 1.2-3.6× longer (for τ) than the respective isocyanide precursor (ΦPL = 0.014-0.12, τ = 2.8-8.2 μs).

Helically chiral Pd(ii) complexes containing intramolecular PdPd metallophilicity as circularly polarized molecular phosphors.

Carbon-centred chirality of the pincer-type cyclometalated ligands is transferred to the helical chirality of dinuclear and tetranuclear Pd(ii) arylacetylide complexes, and hence phosphorescence with quantum yields up to 50% and dissymmetry factors in the 10-3 scale from the metal-metal-to-ligand charge-transfer excited states has been recorded in diluted solutions.

Cyclometallated tridentate platinum(ii) arylacetylide complexes: old wine in new bottles.

Square planar platinum(ii) complexes have been known for 150 years and pincer complexes, supported by a tridentate chelating ligand such as terpyridyl, have been known for more than 70 years. The development of cyclometallated platinum(ii) pincer complexes, in which the tridentate ligand forms one or more platinum-carbon bonds, has been much more recent. Particularly, in terms of their solution and solid-state luminescence these cyclometallated complexes show substantial advantages over their terpyridyl analogues. This tutorial review introduces the reader to the area of platinum(ii) cyclometallated pincer chemistry and shows the advantage of having an alkynyl group in the fourth coordination site on the metal. The basic design principles for the preparation of highly luminescent platinum(ii) cyclometallated pincer complexes are outlined and the strategy to improve the luminescence further by chemical manipulation of the pincer ligand and of the auxiliary ligand in the fourth coordination site are illustrated with recent examples from the literature. Recent applications of these cyclometallated pincer complexes in the area of opto-electronics is described, with emphasis on their use in OLEDs, OFETs and as NLO materials as well as demonstrating their potential use as triplet photosensitizers and as metal ion sensors. The aim of this review is to show the recent advances in this rapidly developing research field and to highlight the future promise of these materials.

Aromatic PCN pincer palladium complexes: forming and breaking C[sbnd]C bonds

Through a salt metathesis reaction, (t−BuPCN)Pd-ONO2 (2) was prepared and used as a precursor for producing (t−BuPCN)Pd-OH (3) and (t−BuPCN)Pd-aryl acetylide complexes 4 (phenyl acetylide) and 5 (p-tolyl acetylide). The aryl acetylide complexes could also be prepared through another synthetic route: by condensation of 3 with the corresponding aryl acetylene. The reactivity of complexes 3 and 4 toward carbon dioxide was studied and it was found that both reactions give the hydrogen carbonate complex (6). The low reactivity of the Pd-acetylide bond was further confirmed by the fact that the propiolate complex undergoes decarboxylation to give 4. PCN palladium complexes are good catalysts for the decarboxylative cross coupling reactions between acetylene carboxylic acids and aryl halides. The yield of the cross coupling product was improved by adding a catalytic amount of CuI.

Induced Circular Dichroism in Phosphine Gold(I) Aryl Acetylide Urea Complexes through Hydrogen-Bonded Chiral Co-Assemblies.

Phosphine gold(I) aryl acetylide complexes equipped with a central bis(urea) moiety form 1D hydrogen-bonded polymeric assemblies in solution that do not display any optical activity. Chiral co-assemblies are formed by simple addition of an enantiopure (metal-free) complementary monomer. Although exhibiting an intrinsically achiral linear geometry, the gold(I) aryl acetylide fragment is located in the chiral environment displayed by the hydrogen-bonded co-assemblies, as demonstrated by induced circular dichroism (ICD).

Theoretical studies on the photophysical properties of luminescent pincer gold(iii) arylacetylide complexes: the role of π-conjugation at the C-deprotonated [C^N^C] ligand.

We have performed theoretical analyses of the photophysical properties of a series of cyclometalated gold(iii) arylacetylide complexes, [(C^N^C)AuIIIC[triple bond, length as m-dash]CPh-4-OMe], with different extents of π-conjugation at the doubly C-deprotonated [C^N^C] ligand via replacement of one of the phenyl moieties in the non-conjugated CH^N^C ligand (1) by a naphthalenyl (2) or a fluorenyl moiety (3-exo and 3-endo; HCH^N^CH = 2,6-diphenylpyridine). Conforming to the conventional wisdom that extended π-conjugation imposes rigidity on the structure of the 3IL(ππ*(C^N^C)) excited state (IL = intraligand), the calculated Huang-Rhys factors for the 3IL → S0 transition follow the order: 1 > 2 > 3-exo ∼ 3-endo, which corroborates qualitatively the experimental non-radiative decay rate constants, k nr: 1 ≫ 2 > 3-exo, but not 3-endo. Density Functional Theory (DFT) calculations revealed that there is an additional triplet excited state minimum of 3LLCT character (LLCT = ligand-to-ligand charge transfer; 3[π(C[triple bond, length as m-dash]CPh-4-OMe) → π*(C^N^C)]) for complexes 1 and 3-endo. This 3LLCT excited state, possessing a large out-of-plane torsional motion between the planes of the C^N^C and arylacetylide ligands, has a double minimum anharmonic potential energy surface along this torsional coordinate which leads to enhanced Franck-Condon overlap between the 3LLCT excited state and the ground state. Together with the larger spin-orbit coupling (SOC) and solvent reorganization energy for the 3LLCT → S0 transition compared with those for the 3IL → S0 transition, the calculated k nr values for the 3LLCT → S0 transition are more than 690- and 1500-fold greater than the corresponding 3IL → S0 transition for complexes 1 and 3-endo respectively. Importantly, when this 3LLCT → S0 decay channel is taken into consideration, the non-radiative decay rate constant k nr could be reproduced quantitatively and in the order of: 1 ≫ 3-endo, 2 > 3-exo. This challenges the common view that the facile non-radiative decay rate of transition metal complexes is due to the presence of a low-lying metal-centred 3dd or 3LMCT excited state (LMCT = ligand-to-metal charge transfer). By analysis of the relative order of MOs of the chromophoric [C^N^C] cyclometalated and arylacetylide ligands, one may discern why complexes 1 and 3-endo have a low-lying 3LLCT excited state while 3-exo does not.

Covalent Immobilization of Redox-Active Fe(κ2-dppe)(η5-C5Me5)-Based π-Conjugated Wires on Oxide-Free Hydrogen-Terminated Silicon Surfaces

Several redox-active Fe(κ2-dppe)(η5-C5Me5) arylacetylide complexes (dppe = 1,2-bis(diphenylphosphino)ethane) featuring a pendant ethynyl (1b–d and 2) or ethenyl (3) group have been grafted on oxide-free hydrogen-terminated silicon (Si–H) surfaces through a covalent interfacial Si–C bond. They form densely packed redox-active monolayers. The charge-transfer process between the terminal redox center and the underlying silicon interface was subsequently studied by cyclic voltammetry. The latter turned out to be strongly dependent on the nature of the spacer linking the organometallic end groups to the silicon surface, the highest charge-transfer rates being obtained for monolayers anchored through conjugated and unsaturated spacers. Although the rates measured were among the highest values obtained for redox-active systems grafted to Si–H surfaces, this study nevertheless suggests that the electron tunnelling is not entirely controlling the interfacial charge-transfer process for the shorter linkers tested. In this respect, strategies to improve further the charge-transfer kinetics of the produced redox-active films are briefly discussed.

Synthesis and Characterization of Redox-Active Mononuclear Fe(κ2-dppe)(η5-C5Me5)-Terminated π-Conjugated Wires

Several new redox-active Fe(κ2-dppe)(η5-C5Me5) arylacetylide complexes featuring pendant ethynyl (Fe(κ2-dppe)(η5-C5Me5)[{C≡C(1,4-C6H4)}nC≡CH] (1b–d; n = 1–3), Fe(κ2-dppe)(η5-C5Me5)[C≡C(1,3-C6H4)C≡CH] (2)) or ethenyl (Fe(κ2-dppe)(η5-C5Me5)[C≡C(1,4-C6H4)CH═CH2] (3)) groups have been synthesized and characterized under their Fe(II) and Fe(III) states. In contrast to the known ethynyl Fe(III) complex [Fe(κ2-dppe)(η5-C5Me5)(C≡CH)][PF6] (1a[PF6]), most of the new Fe(III) derivatives turned out to be kinetically stable in solution. A consistent picture of the electronic structure of the latter complexes in both redox states emerged from experimental data and DFT calculations. This study revealed that beyond the first 1,4-phenylene ring, modification or extension of the carbon-rich linker using (4-phenylene)ethynylene spacers will have only a minor influence on their electronic properties in their ground state, while still maintaining some (weak) electronic interaction along the carbon-rich backbone.

Highly Efficient Solution‐Processable Organic Light‐Emitting Devices with Pincer‐Type Cyclometalated Platinum(II) Arylacetylide Complexes

Let your light shine: By using pincer-type cyclometalated PtII arylacetylide complexes as dopants, a maximum current efficiency of 26.57 cd A−1 (22.12 cd A−1 at 1000 cd m−2) has been achieved with solution-processable phosphorescent OLEDs, the highest ever reported for this type of devices based on phosphorescent PtII emitters.

Experimental Evidence for Magnetic Exchange in Di- and Trinuclear Uranium(IV) Ethynylbenzene Complexes

We report the preparation and magnetic property investigations of a structurally related family of mono-, di-, and trinuclear U(IV) aryl acetylide complexes. The reaction between [(NN'(3))UCl] and lithiated aryl acetylides leads to the formation of the hexacoordinate complexes [(NN'(3))U(CCPh)(2)(Li.THF)] (1) and [(NN'(3))(2)U(2)(p-DEB)(THF)] (2) as red-brown and yellow-green crystalline solids, respectively. In contrast, combining the uranacycle [(bit-NN'(3))U] (bit-NN'(3) = [N(CH(2)CH(2)NSi(t)BuMe(2))(2)(CH(2)CH(2)Si(t)BuMeCH(2)]) with stoichiometric amounts of mono-, bis-, and tris(ethynyl) benzenes affords the yellow-green pentacoordinate arylacetylide complexes [(NN'(3))U(CCPh)] (3), [(NN'(3))(2)U(2)(m-DEB)] (4), [(NN'(3))(2)U(2)(p-DEB)] (5), and [(NN'(3))(3)U(3)(TEB)] (6), where NN'(3) = [N(CH(2)CH(2)NSi(t)BuMe(2))(3)]. The measured magnetic susceptibilities for 1-6 trend toward non-magnetic ground states at low temperatures. Nevertheless, the di- and trinuclear pentacoordinate compounds 4-6 appear to display weak magnetic communication between the uranium centers. This communication is modeled by fitting of the direct current (DC) magnetic susceptibility data, using the spin Hamiltonian H = -2J(S(i) x S(j)). These results are consistent with weak ferromagnetic coupling for complexes 4-6 (J = 4.76, 2.75, and 1.11 cm(-1), respectively), while the fit for 2 is consistent with a near-negligible exchange interaction (J = -0.05 cm(-1)). Geometry-optimized Stuttgart/6-31 g* B3LYP hybrid DFT calculations were carried out (spin-orbit coupling omitted) on model complexes of 3-5. The mononuclear complex shows a triplet ground state with singly occupied degenerate f orbitals. The meta- and para-bridged species are computed to show very weak ferro- and antiferromagnetic coupling, respectively. All three complexes show only small net spin density on the acetylide-containing ligands. The monomeric phenylacetylide complex 3 undergoes a reversible redox couple at -1.02 V versus [Cp(2)Fe](+/0), assignable to an oxidation of U(IV) to U(V).

Synthesis, Structures, and Excited‐State Geometries of Alkynylgold(I) Complexes

AbstractA series of phosphane‐ and (N‐heterocyclic carbene)gold(I) complexes were prepared by deprotonation of terminal alkyne precursors and reaction with the corresponding gold(I) chlorides. Some ten new compounds are reported; these are characterized by multinuclear NMR, optical spectroscopy, and elemental analysis. Crystallographic characterization is reported for five complexes. Organogold species bearing conjugated aryl substituents on the alkynyl ligand are luminescent. Density‐functional theory calculations on a model complex suggest that emission and the first several absorption transitions result from excited states dominated by the arylacetylide ligand. Excited‐state geometry optimization finds that the lowest‐energy triplet state bears linear, two‐coordinate gold(I) with a miniscule lengthening of the alkynyl carbon–carbon bond. An unusual triplet excited state having a bent geometry at gold lies at higher energy in arylacetylide complexes. For the model terminal acetylideMe3PAuC≡CH, the calculations find this bent state to be the lowest‐energy triplet.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Spin Delocalization in Electron-Rich Iron(III) Piano-Stool σ-Acetylides. An Experimental (NMR) and Theoretical (DFT) Investigation

Several paramagnetic electron-rich Fe(III) mononuclear arylacetylide complexes of formula [(η2-dppe)(η5-C5Me5)Fe(C⋮C−Ar)]+ in which Ar represents a functional aryl group were studied by means of multinuclear NMR. All signals detected for the various nuclei were assigned. Hyperfine coupling constants for selected nuclei of the arylacetylide ligand were derived from 1H or 19F NMR contact shifts. These NMR data are diagnostic of a metal-centered unpaired electron partly residing in a π molecular orbital on the arylacetylide ligand, in line with DFT computations. We show here that the 1H NMR paramagnetic shifts of the ortho (H1) and meta (H2) arylacetylide protons convey decisive information on the charge distribution in the aryl ring. Estimates of the relaxation rates of the unpaired electron were also derived from half-widths of the 1H NMR signals. Finally, line-broadening studies of Fe(II)/Fe(III) mixtures allowed extracting the self-exchange rates for several redox couples among these complexes. The self-...

Synthesis, Photophysics, and Optical Limiting of Platinum(II) 4‘-Tolylterpyridyl Arylacetylide Complexes

A series of 4'-tolylterpyridyl platinum(II) complexes with different arylacetylide ligands, namely, phenylacetylide, 4-bromophenylacetylide, 4-nitrophenylacetylide, 4-methoxyphenylacetylide, 4-dimethylaminophenylacetylide, 1-naphthylacetylide, and 3-quinolinylacetylide, were synthesized. Their photophysical properties, such as electronic absorption spectra, emission characteristics at room temperature and 77 K, and transient difference absorption spectra, have been investigated. All of these complexes exhibit a metal-to-ligand charge-transfer (1MLCT) transition at ca. 420-430 nm in their electronic absorption spectra. For ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, an additional solvatochromic charge-transfer band appears at ca. 460-540 nm. This band is sensitive to the para substituents on the phenylacetylide ligand and is tentatively assigned to a metal- or/and acetylide-to-terpyridyl charge-transfer transition (i.e., a 1MLCT or/and 1LLCT transition). All of the complexes exhibit room-temperature phosphorescence. The emission can be attributed to a 3MLCT state except for ttpy-C6H4NO2-4, for which the emission likely originates from an intraligand 3pi,pi* state involving the nitrophenylacetylide ligand. For ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, there probably is more than one low-energy state in close energy proximity, resulting in multiple exponential decays. In addition, the triplet transient absorption difference spectra of ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4NO2-4, and ttpy-Quin exhibit moderately intense, broad absorption bands in the visible region and extending into the near-IR region, which likely originate from the same excited state that emits or from a state that is in equilibrium with the emitting state. It appears that the electron-rich arylacetylide ligands, especially 4-methoxyphenylacetylide and 4-dimethylaminophenylacetylide, cause a decrease of the emission efficiency and disappearance of the transient absorption. In contrast, the complexes that exhibit positive absorption bands in the visible spectral region of the triplet transient difference absorption spectra show substantial optical limiting for nanosecond laser pulses at 532 nm.

Water soluble luminescent platinum terpyridine complexes with glycosylated acetylide and arylacetylide ligands: photoluminescent properties and cytotoxicities

Platinum(II) terpyridine complexes with glycosylated acetylide and arylacetylide ligands bind to DNA with binding constants approximately 10(5) mol(-1) dm(3); the glycosylated arylacetylide complexes exhibit emission at lambda(max) approximately 620 nm in water and are up to approximately 100-times higher in potency than the clinical cisplatin drug in killing cancer cells.

Polymorphic forms of a gold(I) arylacetylide complex with contrasting phosphorescent characteristics.

The spectroscopic properties and crystal structures of the gold(I) arylacetylide complexes [(R(3)P)Au(Ctbd1;CAr)] (R = Cy, Ar = 4-nitrophenyl, 1; 4-trifluoromethylphenyl, 2; pentafluorophenyl, 3; R = Ph, Ar = 4-nitrophenyl, 4) have been examined. The dipole-allowed and -forbidden transitions of 1 (4 in parentheses) at lambda(max) 340 (336) and ca. 485 (470) nm in CH(2)Cl(2) solution at 298 K are assigned to the singlet and triplet intraligand charge transfer (ILCT) transitions of the 4-nitrophenylacetylide moiety, whereas 2 (3 in parentheses) shows localized singlet and triplet acetylenic pipi transitions at lambda(max) 287 (276) and 426 nm, respectively. Two polymorphs of 1 with contrasting phosphorescent characteristics have been identified. At 298 K, the emissive form of 1, as well as 2-4, are highly phosphorescent with peak maximum at 504, 425, 521, and 495 nm, respectively; the other polymorph of 1 is nonemissive at 298 K but emission is detected at 77 K with peak maximum at 486 nm. Crystallographic studies reveal that the major differences between the emissive and nonemissive forms of 1 are the orientations of the molecular dipoles and the dihedral angles between neighboring 4-nitrophenyl moieties. Crystal 2 is isostructural to the nonemissive form of 1, but does not display polymorphism. The molecular planes of two neighboring lumophores are coplanar in the emissive form of 1, parallel in 4, and nearly perpendicular (78.6 degrees ) to each other in the nonemissive form of 1. Both the nature of the excited state and the dihedral angle between adjacent [Au(Ctbd1;CAr)] moieties determine the phosphorescent properties of these molecular crystals.