Synthesis, structures, and emissive properties of platinum(II) complexes with a cyclometallating aryldiamine ligand

A new series of square planar Pt(II) complexes with the mer-coordinating tridentate ligand, pip(2)NCN(-) (pip(2)NCNH = 1,3-bis(piperdylmethyl)benzene), has been prepared: Pt(pip(2)NCN)Cl (2), Pt(pip(2)NCN)Br (3), Pt(pip(2)NCN)I (4), and [Pt(pip(2)NCN)(CH(3)N=C(CH(3))(2))][CF(3)SO(3)] (5). The complexes have been fully characterized by (1)H NMR spectroscopy, elemental analysis, and UV-vis spectroscopy. The X-ray crystal structures of pip(2)NCNBr (1), 2, and 5 are reported. Compound 1: triclinic, P, a = 10.081(1) A, b = 10.153(2) A, c = 10.390(1) A, alpha = 66.05(1) degrees, beta = 79.07(1) degrees, gamma = 64.51(1) degrees, V = 877.1(2) A(3), Z = 2. Complex 2: triclinic, P, a = 9.897(2) A, b = 10.191(2) A, c = 19.174(4) A, alpha = 75.09(3) degrees, beta = 76.14(3) degrees, gamma = 71.00(3) degrees, V = 1741.2(6) A(3), Z = 4. Complex 5: triclinic, P, a = 10.709(2) A, b = 11.2321(10) A, c = 12.447(2) A, alpha = 110.509(8) degrees, beta = 112.417(10) degrees, gamma = 91.066(9) degrees, V = 1276.1(3) A(3), Z = 2. In 77 K 3:1 EtOH/MeOH glassy solution, these colorless complexes exhibit weak red-orange to red emissions originating from a lowest spin-forbidden ligand field excited state.     

Luminescent platinum(II) dimers with a cyclometallating aryldiamine ligand

Triflate salts of three (Pt(pip2NCN))2(mu-L)2+ (pip2NCNH = 1,3-bis(piperidylmethyl)benzene) dimers bridged by a series of nitrogen-donor ligands (L = pyrazine (pyz), 1,2-bis(4-pyridyl)ethane (bpa), trans-1,2-bis(4-pyridyl)ethylene (bpe)) are reported. These complexes have been fully characterized by 1H NMR spectroscopy and elemental analysis. The X-ray crystal structures of [(Pt(pip2NCN))2(mu-pyz)](CF3SO3)2 and [(Pt(pip2NCN))2(mu-bpe)](CF3SO3)2 x 2CH2Cl2 are reported. [(Pt(pip2NCN))2(mu-pyz)](CF3SO3)2: triclinic, P, a = 12.5240(5) A, b = 14.1570(6) A, c = 14.2928(6) A, alpha = 106.458(1) degrees , beta = 92.527(1) degrees , gamma = 106.880(1) degrees , V = 2303.46(17) A(3), Z = 2. [(Pt(pip2NCN))2(mu-bpe)](CF3SO3)2 x 2CH2Cl2: monoclinic, P21/c, a = 10.1288(6) A, b = 16.3346(9) A, c = 17.4764(10) A, beta = 90.882(2) degrees , V = 2891.1(3) A3, Z = 2. These structures and solution measurements provide evidence for the strong trans-directing properties of the pip2NCN- ligand. The electronic structures of these complexes and those of the 4,4'-bipyridine (bpy) dimer, (Pt(pip2NCN))2(mu-bpy)2+, also have been investigated by UV-visible absorption and emission spectroscopies, as well as cyclic voltammetry. The accumulated data indicate that variations in the bridging ligands provide remarkable control over the electronic structures and photophysics of these complexes. Notably, the bpa dimer exhibits a broad, low-energy emission from a metal-centered 3LF excited state, whereas the bpe and bpy dimers exhibit structured emission from a lowest pyridyl-centered 3(pi-pi*) excited state. In contrast, the pyz dimer exhibits remarkably intense yellow emission tentatively assigned to a triplet metal-to-ligand charge-transfer excited state.     

Synthesis, structures and photophysical properties of luminescent copper(I) and platinum(II) complexes with a flexible naphthyridine-phosphine ligand

Condensation of Ph(2)PH and paraformaldehyde with 2-amino-7-methyl-1,8-naphthyridine gave the new flexible tridentate ligand 2-[N-(diphenylphosphino)methyl]amino-7-methyl-1,8-naphthyridine (L). Reaction of L with [Cu(CH(3)CN)(4)]BF(4) and/or different ancillary ligands in dichloromethane afforded N,P chelating or bridging luminescent complexes [(L)(2)Cu(2)](BF(4))(2), [(micro-L)(2)Cu(2)(PPh(3))(2)](BF(4))(2) and [(L)Cu(CNN)]BF(4) (CNN = 6-phenyl-2,2'-bipyridine), respectively. Complexes [(L)(2)Pt]Cl(2), [(L)(2)Pt](ClO(4))(2) and [(L)Pt(CNC)]Cl (CNC = 2,6-biphenylpyridine) were obtained from the reactions of Pt(SMe(2))(2)Cl(2) or (CNC)Pt(DMSO)Cl with L. The crystal structures and photophysical properties of the complexes are presented.     

Copper(II) complexes of a biphenyl-based ligand: Tuning the needs of the metal with those of the ligand

The novel pyrazole-containing tetradentate ligand 2,2′-bis[[(3,5-dimethylpyrazol-1-yl)methyl]amino]-1,1′-biphenyl (N₄-mpz), 1, was synthesized and three Cu(II) complexes, 2–4, were prepared from this compound. These complexes were characterized by a combination of elemental analysis, FAB-MS and electrochemistry and were shown to have the structure of [Cu(N₄-mpz)(Pz)]X₂ where X = BF₄ or ClO₄ or [Cu(N₄-mpz)(Cl)]Cl. The X-ray structure of [Cu(N₄-mpz)(Pz)] (ClO₄)₂ · CH₃OH, 2, was determined and it showed the Cu(II) coordinated by the four nitrogen donors from the ligand along with an exogenous pyrazole donor that had been extracted from another molecule of the ligand. Cyclic voltammetry studies indicated that the complexes undergo quasi-reversible one-electron reductions in acetonitrile at potentials between 396 and 422 mV versus Ag/AgCl.     

Synthesis and characterization of binuclear palladium(II) and platinum(II) complexes with a bridging hydroxypyridinate ligand

Summary Binuclear Pd^II and Pt^II complexes of the type [M₂Cl₂(-Opy)₂(PR₃)₂] [M = Pd or Pt; Opy = 2-OC₅H₄N (2-hydroxypyridinate ion); PR₃ = PEt₃, Pn-Bu₃, PMe₂Ph or PMePh₂] were synthesized and characterized by elemental analysis, ¹H- and ³¹P-n.m.r. spectroscopies. The Pd complexes exist in the sym trans form, whereas the corresponding Pt complexes were generated as different isomers.     

Lowest electronic excited states of platinum(II) diimine complexes

Absorption and emission spectra of Pt(diimine)L2 complexes (diimine = 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmbpy); L = pyrazolate (pz-), 3,5-dimethylpyrazolate (dmpz-), or 3,4,5-trimethylpyrazolate (tmpz-)) have been measured. Solvent-sensitive absorption bands (370-440 nm) are attributed to spin-allowed metal-to-ligand charge-transfer (1MLCT) transitions. As solids and in 77 K glassy solution, Pt(bpy)(pz)2 and Pt(dmbpy)(pz)2 exhibit highly structured emission systems (lambda max approximately 494 nm) similar to those of the diprotonated forms of these complexes. The highly structured bands (spacings 1000-1400 cm-1) indicate that the transition originates in a diimine-centered 3(pi-->pi*) (3LL) excited state. The intense solid-state and 77 K glassy solution emissions from 3MLCT[d(Pt)-->pi*(bpy)] excited states of complexes with dmpz- and tmpz- ligands occur at longer wavelengths (lambda max = 500-610 nm), with much broader vibronic structure. These findings are consistent with increasing electron donation of the pyrazolate ligands, leading to a distinct crossover from a lowest 3LL to a 3MLCT excited state.     

Synthesis and structural studies of binuclear platinum(II) complexes with a novel phosphorus-nitrogen-phosphorus ligand

The new pyridinediphosphinite ligand PONOP (1) was synthesized in one step from 2,6-pyridinedimethanol and diphenylchlorophosphane. Reaction of 1 with PtCl(2)(PhCN)(2) led to the neutral homobimetallic complex [Pt(2)Cl(4)(PONOP)(2)] (2), where the benzonitriles have been substituted by the phosphorus atoms of 1. The X-ray structure of 2 revealed a metallamacrocycle where the pyridines remained free. Addition of 2 equiv of [Cu(MeCN)(4)](BF(4)) to 2 led to CuCl and to the binuclear dicationic complex [Pt(2)Cl(2)(PONOP)(2)](BF(4))(2) (3), where chloro ligands have been substituted by pyridine groups. Conversely, reaction of 3 with chloride anions gave back complex 2. Solid-state (X-ray) and solution (NMR) studies indicated that after the transformation of 2 into 3, the platinum centers were brought much closer and the pyridinediphosphinite ligand was stiffened. The methylene NMR protons of 3 were strongly deshielded, and the corresponding proton-phosphorus coupling constants followed a Karplus-type relationship.     

DFT and TD-DFT calculations on the electronic structures and spectroscopic properties of cyclometalated platinum(II) complexes

The electronic structures and spectroscopic properties of the three tridentate cyclometalated Pt(II) complexes Pt(N/\N/\C)C(triple bond)CPh (N/\N/\CH = 6-phenyl-2,2'-bipyridine) (1), Pt(N/\N/\S)C(triple bond)CPh (N/\N/\SH = 6-thienyl-2,2'-bipyridine) (2), and Pt(N/\N/\O)C(triple bond)CPh (N/\N/\OH = 6-furyl-2,2'-bipyridine) (3) were investigated theoretically using the density functional theory (DFT) method. The geometric structures of the complexes in the ground and excited states were explored at the B3LYP and UB3LYP levels, respectively. The absorption and emission spectra of the complexes in CH2Cl2 and CH3CN solutions were calculated by time-dependent density functional theory (TD-DFT) with the PCM solvent model. The calculated energies of the lowest singlet state and lowest triplet state in the three complexes are in good agreement with the results of experimental absorption and luminescence studies. All of the lowest-lying transitions were categorized as LLCT combined with MLCT transitions. The 623-nm emission of 1 from the 3A' --> 1A' transition was assigned as 3LLCT and 3MLCT transitions, whereas the 657- and 681-nm emissions of 2 and 3, respectively, were attributed to 3ILCT perturbed by 3MLCT transitions. NLO response calculations revealed that the nonzero values of the static first hyperpolarizability (beta0) for 1-3 are greatly enhanced through the introduction of the metal Pt(II) into the cyclometalated ligands, an effect that is determined by MLCT and LLCT transitions.     

Mixed ligand complexes of palladium(II) and platinum(II) with methionine and 2,4-disubstituted pyrimidines

Summary Mixed ligand complexes ofcis-[M(MetH)Cl₂] (M=Pd²⁺ and Pt²⁺; MetH=methionine) with 2,4-disubstituted pyrimidines were prepared and characterised. Thecis-[Pd(MetH)Cl₂] complex reacted with cytosine (2-hydroxy-4-aminopyrimidine), isocytosine (2-amino-4-hydroxypyrimidine) and thiocytosine (2-thio-4-amino-pyrimidine) to form ternary complexes.cis-[Pt(MetH)Cl₂] however reacted with cytosine, uracil (2,4-pyrimidine dione or 2,4-dihydroxypyrimidine) to yield the corresponding mixed ligand complexes. The primary ligand, methionine, binds to the metal ion through sulphur and amino nitrogenvia a six membered chelate ring. The secondary ligands (substituted pyrimidines) bind to the Pd²⁺ or Pt²⁺ metal ion through the ring nitrogen (N₃), as monodentate ligand. Thiocytosine however acts as a bidentate ligand, coordinating to the metal ion through-SH and ring nitrogen (N₃). All complexes are 11 electrolytes, except the thiocytosine complex, which is a 12 electrolyte.     

Gold(I) and platinum(II) complexes with a new diphosphine ligand based on the cyclotriphosphazene platform

A new diphosphine ligand assembled on the cyclotriphosphazene platform forms linear chelate and dimetallic bridged complexes with Au(I) and a cis-chelate complex with Pt(II).     

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.     

Cationic palladium(II), platinum(II) and ruthenium(II) complexes containing a chelating difluoro-substituted thiourea ligand

The fluorine substituted thiourea 2,6-F₂C₆H₃C(O)NHC(S)NEt₂ was prepared in good yield from the reaction of 2,6-F₂C₆H₃C(O)Cl with KSCN and Et₂NH in acetone. Using this compound several heteroleptic, monocationic Pd(II), Pt(II) and Ru(II) complexes of the type cis-[M{κ²S,O-2,6-F₂C₆H₃C(O)NC(S)NEt₂}(L)]PF₆ [M = Pt, Pd; L = (Ph₃P)₂, ^tBu₂bipy, 1,10-phen] as well as [Ru(η⁶-p-cym){κ²S,O-2,6-F₂C₆H₃C(O)NC(S)NEt₂}(PPh₃)]PF₆ were prepared in high yields. The compounds were characterised by spectroscopic methods and, in one case, by single crystal X-ray diffraction.     

Novel antitumor dinuclear platinum (II) complexes with a new chiral tetradentate ligand as the carrier group

Seven dinuclear platinum(II) complexes with a novel chiral tetradentate ligand, (1R,1′R,2R,2′R)‐N¹,N^1′‐(1,4‐phenylenebis(methylene))dicyclohexane‐1,2‐diamine, were designed, synthesized and spectrally characterized. All the complexes were evaluated for their in vitro cytotoxicity against human HepG‐2, A549, HCT‐116 and MCF‐7 cancer cell lines. The results indicated that all compounds showed positive biological activity against HepG‐2, A549 and HCT‐116 cancer cell lines. In particular, compounds D7 and D2 showed better activity than carboplatin against HepG‐2 and A549 and compound D7 also showed an activity close to that of oxaliplatin. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and characterization of some mixed ligand complexes of platinum(II)

The mixed ligand complexes PtX₂(ER₃)L and PtXY(ER₃)L (where ER₃ = PR₃ or AsMe₃; L = phosphine, arsine; X = Cl; Y = Cl, H or Me) have been prepared and characterized. Reaction of PtMe₂(ER₃)L with HCl yields PtMeCl(ER₃)L, in exclusively one of three possible isomeric forms. Excess tetramethyltin reacts with Pt₂Cl₂(μ-Cl)₂(PMe₂Ph)₂ giving both cis and trans Pt₂(μ-Cl)₂(PMe₂Ph)₂, as identified from the NMR spectra. Cleavage of Pt₂(μ-Cl)₂Me₂(PMe₂Ph)₂ with donor ligands such as AsPh₃, PMe₂ or pyridine, was useful as a synthetic route to the unsymmetrical methylchloro Pt^II derivatives. The reaction of cis-[PtMe₂(PPh₃)(AsPh₃)] with excess dimethylacetylenedicarboxylate (DMA) yielded only one product, which was of the formula trans-[Pt{C(COOCH₃)C(COOCH₃)CH₃}₂(PPh₃)(AsPh₃)], with the alkenyl groups having the same geometry about the CC bond. The use of diethylacetylene-dicarboxylate (DEA) rather than DMA gave a similar product. However, when cis-[PtMe₂(PEt₃)(AsPh₃)] was allowed to react with DMA, two products of the formula trans-[Pt{C(COOCH₃)C(COOCH₃)CH₃}₂(PEt₃)(AsPh₃)] were obtained, with the stereochemistry of both alkenyl groups being either cis or trans.     

Participation of co-ligands in electronic transitions of platinum(II) diazabutadiene complexes

The low-lying electronic transitions and photochemical reactions of a series of [((i)Pr-DAB)Pt(R)(2)] (where the co-ligand R = CH(3), CD(3), adme, neop, neoSi, C(triple bond)C(t)Bu, C(triple bond)CPh, Ph, Mes) compounds were studied using both experimental (electronic absorption and resonance Raman spectroscopy) and theoretical (density functional theory, DFT) techniques. The high-lying filled orbitals were revealed to have a significant co-ligand contribution in the case of alkyl complexes, while this contribution is predominant for the complexes with unsaturated co-ligands. Because the electronic transition removes electron density from the sigma(Pt-C) bond in the former complexes, it is best described as a metal-to-ligand charge transfer transition (MLCT) with partial sigma-bond-to-ligand charge transfer (SBLCT) character. Because the sigma(Pt-C) orbital is not involved in the HOMOs of the latter complexes, the low-lying transitions were characterized as mixed MLCT/L'LCT, where L'LCT stands for ligand-to-ligand charge transfer from the pi system of the unsaturated co-ligand to the pi((i)Pr-DAB) orbital. The alkyl complexes are photoreactive on visible light irradiation with Pt-C bond homolysis as the primary step. The efficiency of the photoreaction increases with increasing sigma donor strength of the alkyl ligand. The absolute quantum yield is quite low. The other complexes are virtually photostable, except when irradiated at relatively high energies.     

Effect of amine ligand bulk on the interaction of methionine with platinum(II) diamine complexes

Molecular mechanics and dynamics calculations have been used in conjunction with experimental data to study the effects of amine ligand bulk on the formation of both guanine and methionine complexes with platinum diamine compounds. The AMBER force field has been supplemented with previous modifications [Yao; et al. Inorg. Chem. 1994, 33, 6061-6077. Cerasino; et al. Inorg. Chem. 1997, 36, 6070-6079] and has been further modified to include parameters for platinum bound to the sulfur atom of methionine. Molecular mechanics calculations with this modified AMBER force field have suggested that a platinum complex with two sulfur-bound methionine ligands and a bulky diamine ligand (N,N,N',N'-tetramethylethylenediamine, Me(4)en) would have severe interligand clashes; such interligand clashes are less pronounced in bis(9-ethylguanine) complexes. Consistent with these observations, NMR studies with [Pt(Me(4)en)(D(2)O)(2)](2+) have indicated that guanine 5'-monophosphate reacts in a 2:1 guanine:platinum ratio while both methionine and N-acetylmethionine react with only a 1:1 stoichiometry. Methionine forms a chelate via the sulfur and nitrogen atoms whereas N-acetylmethionine forms a chelate via the sulfur and oxygen atoms. The oxygen of the latter chelate can be displaced by the addition of guanosine 5'-monophosphate, although complete displacement of the N-acetylmethionine was not observed.     

Capped-tetrahedrally coordinated Fe(II) and Co(II) complexes using a "Click"-derived tripodal ligand: geometric and electronic structures

The 'Click'-derived tripodal ligand tris[(1-benzyl-1H-1,2,3-triazole-4-yl)methyl]amine, tbta, was used to synthesize the complexes [Fe(tbta)Cl]BF(4), 1, and [Co(tbta)Cl]BF(4), 2. Both complexes were characterized by (1)H NMR spectroscopy and elemental analysis. Single-crystal X-ray structural determination of 2 shows a 4 + 1 coordination around the cobalt(II) center with a rather long bond between Co(II) and the central amine nitrogen atom of tbta. Such a coordination geometry is best described as capped tetrahedral. 1 and 2 are thus the first examples of pseudotetrahedral coordinated Fe(II) and Co(II) complexes with tbta. A combination of SQUID susceptometry, EPR spectroscopy, M?ssbauer spectroscopy, and DFT calculations was used to elucidate the electronic structures of these complexes and determine the spin state of the metal center. Comparisons are made between the complexes presented here with related complexes of other ligands such as tris(2-pyridylmethyl)amine, tmpa, hydrotris(pyrazolyl) borate, Tp, and tris(2-(1-pyrazolyl)methyl)amine, amtp. 1 and 2 were tested as precatalysts for the homopolymerization of ethylene, and both complexes delivered distinctly different products in this reaction. Blind catalyst runs were carried out with the metal salts to prove the importance of the tripodal ligand for product formation.     

Copper(II) complexes with a flexible oxamato ligand

We report on a convenient synthesis of the ligand precursor, diethylethylene-1,2-bis(oxamate), (Et₂H₂oeo, 1), and show how a partial and preferential hydrolysis of the ester group can give rise to the dianionic ligand, (H₂oeo)²⁻. Reaction of this ligand with Cu(II) affords the neutral dimeric species, [Cu₂(H₂oeo)₂], which has a low aqueous solubility. We describe the crystal structure of the hydrate Cu₂(H₂oeo)₂(H₂O)₄ (2) and report magnetic studies that show a weak exchange interaction in the solid. Under more basic conditions and in the presence of Cu(II) ions, we are able to avoid amide cleavage and yet deprotonate the amide group, resulting in the formation of the highly soluble [Cu(Hoeo)₂]⁴⁻ complex anion. The structure of (NBu₄)₄[Cu(Hoeo)₂](H₂O)₄ (3) is described and compared with the recently reported anhydrous phase.     

Synthesis and structures of cis- and trans-bis(alkyneselenolato)platinum(II) complexes

The reaction of 2 equiv of LiSeCC-n-C(5)H(11) (1) with cis-PtCl(2)(Ph(3)P)(2) (2) gives a mixture of the cis and trans isomers of Pt(Ph(3)P)(2)(SeCC-n-C(5)H(11))(2) (3), which slowly isomerizes in CH(2)Cl(2) to the preferred trans form trans-3. The closely related cis-[Pt(dppf)(2)(SeCC-n-C(5)H(11))(2)] (4) (dppf = bis(diphenylphosphino)ferrocene) was prepared by a similar metathetical reaction using the platinum chloride complex of the chelating dppf to impose the cis geometry. The structures of the cis and trans complexes have been investigated in solution by heteronuclear NMR ((31)P, (77)Se, and (195)Pt) and, in the cases of trans-3 and 4, characterized in the solid state by single-crystal X-ray diffraction. Changing the coordination geometry from cis to trans induces significant changes in the structural and spectroscopic parameters, which do not comply with the previously anticipated donor-acceptor properties of selenolate ligands.