Branched carbon-rich luminescent multinuclear platinum(II) and palladium(II) alkynyl complexes with phosphine ligands

In this review, the synthesis, electronic absorption and luminescent properties of a series of branched alkynylpalladium(II) and -platinum(II) phosphine complexes with different alkynyl backbones and some of their structurally related complexes in the literature will be discussed. With the growing research interest in the potential application of these complexes in the field of non-linear optics (NLO), the two-photon absorption (TPA) properties and the corresponding structure–property relationships of selected luminescent branched platinum(II) bis-alkynyl complexes will also be described.     

Synthesis and characterization of luminescent bis-cyclometalated platinum(IV) complexes

Presented is the synthesis and characterization of a series of luminescent heteroleptic bis-cyclometalated platinum(IV) complexes. An oxidation-facilitated cyclometalation is employed to convert platinum(II) pendant species into bis-cyclometalated platinum(IV) dichlorides, which are transformed into the tris-chelated diimine complexes through ligand substitution. The structure-property relationship is probed by judiciously varying substituents on both the C(∧)N and the N(∧)N ligands resulting in a family of complexes exhibiting blue emission, long excited-state lifetimes, and highly efficient oxygen quenching. Excited-state properties are corroborated by static and time-dependent density-functional theory calculations of both the singlet and the triplet state.     

A new family of platinum(II) complexes incorporating five‐ and six‐membered cyclic phosphine ligands

New platinum complexes of the type cis‐Pt(L)₂Cl₂ have been synthesized from five‐ and six‐membered cyclic phosphines, which were prepared after deoxygenating a series of phosphine oxides (3‐phospholene oxides, phospholane oxides, a 1,4‐dihydrophosphinine oxide, and a 1,2,3,6‐tetrahydrophosphinine oxide). The complexes were characterized by NMR and mass spectral data, and their stereostructures were elucidated by B3LYP/6‐31G(d)‐LANL2DZ ECP calculations. The phosphine intermediates were characterized as the corresponding phosphine‐boranes. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:63–70, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20579     

Syntheses and structural characterization of luminescent platinum(II) complexes containing di-tert-butylbipyridine and new 1,1-dithiolate ligands

Three new di-tert-butylbipyridine (dbbpy) complexes of platinum(II) (1-3) containing 1,1-dithiolate ligands have been synthesized and characterized. The 1,1-dithiolates are 2,2-diacetylethylene-1,1-dithiolate (S(2)C=C(C(O)Me)2) (1), 2-cyano-2-p-bromophenylethylene-1,1-dithiolate (S(2)C=C(CN)(p-C(6)H(4)Br)) (2), and p-bromophenyl-2-cyano-3,3-dithiolatoacrylate (S(2)C=C(CN)(COO-p-C(6)H(4)Br)) (3). Complex 1 exhibits a solvatochromic charge-transfer absorption in the 430-488 nm region of the spectrum and a luminescence around 635 nm in ambient temperature CH(2)Cl(2) solution. These observations are consistent with what has been seen previously in related Pt diimine 1,1-dithiolate complexes. The nature of the emissive state is assigned as a (3)(mixed metal/dithiolate-to-diimine) charge transfer, while the solvatochromic absorption band corresponds to the singlet transition of similar orbital character. The other complexes also exhibit a low-energy solvatochromic absorption. The crystal structures of two of the complexes have been determined, representing the first time that Pt(diimine)(1,1-dithiolate) complexes have been crystallographically studied. The structures confirm the expected square planar coordination geometry with distortions in bond angles dictated by the constraints of the chelating ligands. The Pt-S and Pt-N bond lengths and S-Pt-S and N-Pt-N bond angles for the two structures are identical within experimental error (2.283(2) and 2.278(2) A; 2.053(6) and 2.050(8) A; 75.01(8) degrees and 75.40(8) degrees; 79.2(2) degrees and 79.0(2) degrees, respectively). Crystal data for 1: monoclinic, space group P2(1)/n (No. 14), with a = 7.20480(10) A, b = 20.53880(10) A, c = 19.1072(2) A, beta = 93.83 degrees, V = A(3), Z = 4, R1 = 3.34% (I > 2sigma(I)), wR2 = 9.88% (I > 2sigma(I)) for 3922 unique reflections. Crystal data for 2: monoclinic, space group P2(1)/n (No. 14), with a = 15.0940(5) A, b = 9.5182(3) A, c = 20.4772(7) A, beta = 111.151(1) degrees, V = A(3), Z = 4, R1 = 4.07% (I > 2sigma(I)), wR2 = 8.64% (I > 2sigma(I)) for 3859 unique reflections.     

Theoretical studies upon the electronic structures and spectroscopic properties for a series of luminescent terpyridyl platinum(II) phenylacetylide complexes

A comprehensive calculations were carried out to get a deep insight into the ground- and excited-state electronic structures and the spectroscopic properties for a series of [Pt(4-X–trpy)CCC₆H₄R]⁺ complexes (trpy = 2,2′,6′,2″-terpyridine; X = H, R = NO₂ (1), Cl (2), C₆H₅ (3) and CH₃ (4); R = Cl, X = CH₃ (5) and C₆H₅ (6)). MP2 (second-order Møller–Plesset perturbation) and CIS (single-excitation configuration interaction) methods were employed to optimize the structures of 1–6 in the ground and excited states, respectively. The investigation showed that substituted phenylacetylide and trpy ligands only give rise to a small variation in geometrical structures but lead to a sizable difference in the electronic structures for 1–6 in the ground and excited states. The introduction of electron-rich groups into the phenylacetylide and/or terpyridyl ligands produces two different low-lying absorptions for 1 and 2–6, i.e., Pt(5d) → π^*(trpy) metal-to-ligand charge transfer (MLCT) mixed with π → π^*(CCPh) intraligand charge transfer (ILCT) for 1 and Pt(5d)/π(CCPh) → π^*(trpy) charge transfer (MLCT and LLCT) for 2–6. Remarkable electronic resonance on the whole Pt–CCPh–NO₂ moiety for 1 may be responsible for the difference. Solvatochromism calculation revealed that only LLCT/MLCT transitions showed the solvent dependence, consistent with the experimental observations.     

Transition metalcarbon bonds XXXVII. platinum acetylide complexes formed from ethynyl alcohols or ethers

Several new platinum(II) acetylide complexes, trans-{Pt[CCCR₁R₂(OR₃)]₂-L₂} (R₁, R₂  H, Me, Et; CR₁R₂  cyclohexylidene; R₃  H, Me or Ph), trans-[Pt(CCCH₂CH₂OH)₂L₂], trans-[Pt(p-tolylacetylide)₂L₂] and trans-[PtX(p-tolylacetylide)L₂] (L  PMe₂Ph or in one case, AsMe₂Ph) have been prepared. Platinum(II) acetylide complexes with tertiary hydroxyl groups are easily dehydrated by acetic anhydride/pyridine to give platinum-enyne complexes. Analogous compounds with primary hydroxyl groups do not dehydrate but give acetates. ¹H and ¹³C NMR data are given and the shift reagent Eu(fod)₃ was used to analyse the ¹H NMR spectrum of trans-[Pt(CCCH₂CH₂OH)₂(PMe₂Ph)₂].     

Photophysical and anion sensing properties of platinum(II) terpyridyl complexes with phenolic ethynyl ligands

A series of platinum(ii) terpyridyl complexes with phenolic ethynyl ligands have been synthesized and characterized. Their photophysical and sensing properties towards anions such as fluoride, acetate and dihydrogenphosphate have been investigated. These complexes show a colorimetric response and fluorescence quenching in the presence of anions including fluoride, acetate and dihydrogenphosphate, and selective sensing towards fluoride in some cases. The sensing mechanism has been investigated by spectrophotometric and (1)H NMR titration.     

Synthesis and characterisation of new platinum ethynyl dimers and polymers with pendant ferrocenyl groups

The square-planar platinum(II) complex trans-[(Ph₂FcP)₂PtCl₂] (1) (Fc=ferrocenyl), that is a metal-containing polymer precursor, has been synthesised and its single crystal structure determined. Using 1, new ferrocene-containing platinum ethynyl dimers trans-[(Ph₂FcP)₂Pt(CCR)₂] {R=SiMe₃ (2), C₆H₅ (3) and C₆H₄-p-NO₂ (4)} and a polymer [(Ph₂FcP)₂Pt(CCC₆H₂-p-(OC₈H₁₇)₂CC)]_n (5) have been formed by the reaction of the metal precursor with the appropriate mono- and bis-ethynyl ligands. Single crystal X-ray studies of 4 have shown it to exist as two different polymorphic forms, both having trans-geometry with respect to the ferrocenyl phosphines and ethynyl ligands. GPC measurements on the polymer show a high degree of polymerisation with an average molecular weight of ca. 88?000.     

Strongly luminescent palladium(0) and platinum(0) diphosphine complexes

The synthesis, structure, and photoluminescence of palladium(0) and platinum(0) complexes containing biarydiphosphines, biphep (biphep = 2,2'-bis(diphenylphosphino)-1,1'-biphenyl) and binap (binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) have been studied. X-ray structure analysis of [Pt(biphep)(2)] revealed the distorted-tetrahedral geometry of the complex. The photophysical properties of the three complexes [Pd(biphep)(2)], [Pt(biphep)(2)], and [Pd(binap)(2)] were investigated and compared with that of the previously reported [Pt(binap)(2)] complex. The [Pd(biphep)(2)] complex shows the strongest luminescence with a high quantum yield (38%) and a long lifetime (3.2 micros) in a toluene solution at room temperature. The luminescence should be due to metal-to-ligand charge transfer excited states. At room temperature, radiative rate constants of the four complexes show similar values. The difference in the luminescent properties should reflect the different nonradiative rate constants of the complexes. The temperature-dependence of the luminescence spectra and lifetime of the complexes were also discussed.     

Synthesis and luminescent properties of cis bis-N-heterocyclic carbene platinum(II) bis-arylacetylide complexes

A series of luminescent N-heterocyclic carbene platinum(II) complexes, [(pmim)Pt(C≡C-R)(2)] (R = C(6)H(5) (2), C(6)H(4)OMe (3), C(6)H(2)(OMe)(3) (4), C(6)H(4)NMe(2) (5), C(4)H(3)S (6), C(6)H(4)C≡CC(6)H(5) (7), 1-pyrenyl (8), and C(6)H(4)F (9)), were successfully synthesized using the precursor (pmim)PtI(2), 1 (pmim = 1,1'-dipentyl-3,3'-methylene-diimidazoline-2,2'-diylidene). The X-ray crystal structures of 1, 4, 5, and 7 have been determined. These complexes showed long-lived emission in solution at room temperature. The emission origin of the complexes is tentatively assigned to be from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) character. TD-DFT and DFT calculations have been performed on most of the complexes to ascertain the nature of the excited state. Changes in the alkynyl ligands lead to a change in the absorption and emission maxima seen for these complexes in a potentially predictable way.     

Hydrolysis of platinum(II) phosphine complexes in aqueous 1.0 M NaNO3 medium

Hydrolysis of [Pt(PR₃)₂]²⁺ (R=Me, Et) have been investigated at 25.0°C in 1.000 M NaNO₃ by the combined emf–NMR method. Quantitative analysis of the emf and ³¹P NMR data revealed the formation of [{Pt(PR₃)₂(μ-OH)}₂]²⁺ as the only hydrolysis product in the range 1.5<−log h<5.7. Least-squares calculation gave log β_Me=−4.19±0.04 and log β_Et=−3.58±0.04, where β_Me and β_Et stand for the formation constants of the dimeric cations of methyl and ethyl derivatives, respectively. The ¹⁹⁵Pt NMR data were also consistent with this model.     

Methyl- and phenyl-bis(tertiary phosphine) N-bonded carboxamido complexes of platinum(II)

Methyl- or phenylN-carboxamido-complexes of platinum(II) Pt(NHCOR')RL₂ (L = PEt₃, R = Me, R′ = Me, CH = CH₂; L = PEt₃, R = Ph, R′ = Me; L = PMe₂Ph, R = Ph, R′ = Me, Ph; L = PMePh₂, R = Ph, R′ =₃, R = Ph, R′ = Me) have been prepared by the reaction of KOH with cationic nitrile complexes [PtR(NCR′)L₂]BF₄. Thermally unstable hydrido-N-carboxamido-complexes could be detected spectroscopically. IR and NMR (¹H, ³¹P) spectra of some of the complexes indicate the existence of a solvent- and temperature-dependent equilibrium between syn-and anti-isomers arising from restricted rotation about the NC bond of the carboxamido-group. The anti-isomer is favoured by nonpolar solvents and by increasing bulk of L. In the complex [PtH(NCCH CH₂)(PEt₃)₂]BF₄, IR and NMR spectra show acrlonitrile to be bound through nitrogen, not through the olefinic CC bond.     

Electrochemical and chemical synthesis of new luminescent schiff base complexes

Bis-chelate complexes of zinc, cadmium, lead, and mercury with o-N-tosylbenzylidene imines containing the C₇H₁₅ and C₁₈H₃₇ substituents at the C=N group nitrogen atom were prepared by the methods of electrochemical and chemical syntheses. The structure of the azomethines and their complexes was established by the methods of heteronuclear ¹H, ¹³C NMR spectroscopy (multidimensional and multinuclear COSY, HETCOR and HETCOR_LONG techniques). The complexes, as demonstrated by the X-ray analysis for the zinc chelate, have strongly distorted octahedral structure formed by the four azomethine nitrogen atoms and two oxygen atoms of the tosyl fragments. The coordination compounds show fluorescence in the blue part of the spectrum in high quantum yields for the zinc chelates.     

cis-Dicyanoosmium(II) diimine complexes bearing phosphine or sulfoxide ligands: spectroscopic and luminescent studies

A series of cis-dicyanoosmium(II) complexes [Os(PPh3)2(CN)2(N intersectionN)] (N intersectionN = Ph2phen (2a), bpy (2b), phen (2c), Ph2bpy (2d), tBu2bpy (2e)) and [Os(DMSO)2(CN)2(N intersectionN)] (3a-3e, N intersectionN = Br2phen (3f), Clphen (3g)), were synthesized and their spectroscopic and photophysical properties were examined, and [Os(PMe3)2(CN)2(phen)] (4) with axial PMe3 ligands was similarly prepared. The molecular structures of 2a, 2c, [2c.Zn(NO3)2]infinity, 2d, 2e, 3b, 3d, 3e, and 4 were determined by X-ray crystallographic analyses. The two CN ligands are cis to each other with mean Os-C bond distance of 2.0 A. The two PR3 (R = Ph, Me) or DMSO ligands are trans to each other with P/S-Os-P/S angles of approximately 177 degrees . The UV-vis absorption spectra of 2a-2e display an intense absorption band at 268-315 nm (epsilon = approximately (1.54-4.82) x 104 M-1 cm-1) that are attributed to pi --> pi*(N intersection N) and/or pi --> pi*(PPh3) transitions. The moderately intense absorption bands with lambdamax at 387-460 nm (epsilon = approximately (2.4-11.3) x 103 M(-1) cm(-1)) are attributed to a 1MLCT transition. A weak, broad absorption at 487-600 nm (epsilon = approximately 390-1900 M(-1) cm(-1)) is assigned to a 3MLCT transition. Excitation of 2a-2e in dichloromethane at 420 nm gives an emission with peak maximum at 654-703 nm and lifetime of 0.16-0.67 micros. The emission energies, lifetimes, and quantum yields show solvatochromic responses, and plots of numax, tau, and Phi, respectively, versus ET (solvent polarity parameter) show linear correlations, indicating that the emission is sensitive to the local environment. The broad structureless solid-state emission of 2a-2e at 298 (lambdamax 622-707 nm) and 77 (lambdamax 602-675 nm) K are assigned to 3MLCT excited states. The 77 K MeOH/EtOH (1:4) glassy solutions of 2a-2e also exhibit 3MLCT emissions with lambdamax = 560-585 nm. The 1MLCT absorption and 3MLCT emission of 3a-3g occur at lambdamax = 332-390 nm and 553-644 nm, respectively. In the presence of Zn(NO3)2, both the 1MLCT absorption and 3MLCT emission of 2c in acetonitrile blue-shift from 397 to 341 nm and 651 to 531 nm, respectively. The enhancement of emission intensity (I/Io) of 2e at 531 nm reached a maximum of approximately 810 upon the addition of two equivs of Zn(NO3)2. The crystallographic and spectroscopic evidence suggests that 2c undergoes binding of Zn2+ ions via the cyano moieties.     

Reactions of dimethyldivinylsilane,dimethyldivinyltin and allyltrimethyltin with diethylene (tertiary) phosphine)platinum complexes

The compounds [Pt(C₂H₄)₂(PR₃)] [PR₃ = P-tBu₂Me, P(C₆H₁₁)₃, PPh₃] react dimethyldivinylsilane or dimethyldivinyltin to give chelate complexes [Pt{(CH₂CH)₂MMe₂} (PR₃)] (M = Si or Sn). allyltrimethyltin reacts with various diethylene (tertiary phosphine)platinum compounds with cleavage of the allyl group to afford complexes [Pt(SnMe₃)(η³-C₃H₅)(PR₂)]. The NMR spectra (¹³C, ¹H and ³¹P) of the new compounds have been recorded, and the data are discussed in terms of the structures proposed.     

Gold-heterometal complexes. Evolution of a new class of luminescent materials

A very promising area of research in which metallophilic attraction has become the dominating factor determining the structural patterns that give rise to luminescent materials is discussed. In addition to the intrinsic conditions that a gold complex requires to show luminescence, we show how the type and number of the ligands, the coordination environments around the metal centres, the temperature, the heterometal, the metal-metal distances, etc., increase the possibilities of electronic transitions and, hence, multiply the factors that affect the energy and number of emissions. We think that far from being a hindrance or a problem these findings actually give rise to a fascinating area of research with promising future applications, for instance, in imaging technology, vapour sensors, light emitting devices or even medicine, where the demand for optoelectronic devices is increasing every day.     

A new family of luminescent compounds: platinum(II) imidoylamidinates exhibiting pH-dependent room temperature luminescence

The imidoylamidinate platinum(II) compounds [Pt{NH=C(R)NC(Ph)NPh}2] (R = CH2Ph 2, p-ClC6H43, Ph 4) were prepared by the reaction of the appropriate trans-[PtCl2(RCN)2] with 4 equiv of the amidine PhC(NH)NHPh giving 2-4 and 2 equivs of the salt PhC(=NH)NHPh.HCl. We also synthesized, by the double alkylation of 4 with MeOSO2CF3, complex [Pt{NH=C(Ph)N(Me)C(Ph)=NPh}2][CF3SO3]2 (5) which models the bis-protonated form of 4. The complexes were characterized by 1H, 13C NMR, and IR spectroscopies, FAB-MS and by C, H, N elemental analysis. The X-ray crystallography of 4.2CH2Cl2 enables the confirmation of the square planar coordination geometry of the metal center with almost planar imidoylamidine ligands, while in 5.2CHCl3 the planarity of the metallacycles is lost and and the central N atom is sp3-hybridized. The imidoylamidinate complexes represent a new family of Pt(II)-based luminescent complexes and they are emissive at room temperature both in solution and in the solid state, with an emission quantum yield ranging from 3.7 x 10(-4) to 6.2 x 10(-2) in methanol solution; the emission intensity is pH-dependent, being quenched at low pH. UV-visible and luminescence spectroscopies indicate that the lowest excited state of these compounds is 3MLCT or 3IL with significant MLCT character, with emission lifetimes of a few micros. A blue shift of both the absorption and emission with increasing solvent polarity and with decreasing pi-electron withdrawing properties of the ligand substituent was observed.     

Amido phosphine complexes of zinc

The first examples of amido phosphine complexes of zinc have been prepared. Addition of N-(2-diphenylphosphinophenyl)-2,6-diisopropylaniline (H[NP]) to ZnMe(2) or ZnEt(2) in diethyl ether at -35 degrees C generated the monomeric, three-coordinate [NP]ZnR (R = Me, Et), while the metathesis reaction of ZnCl(2) with [NP]Li(THF)(2) in diethyl ether at -35 degrees C produced homoleptic [NP](2)Zn.