NCN-pincer Platinum Research Articles

Replacing the Z-phenyl Ring in Tamoxifen® with a para-Connected NCN Pincer-Pt-Cl Grouping by Post-Modification †.

Post-modification of a series of NCN-pincer platinum(II) complexes [PtX(NCN-R-4)] (NCN = [C6H2(CH2NMe2)2-2,6]–, R = C(O)H, C(O)Me and C(O)Et), X = Cl– or Br–) at the para-position using the McMurry reaction was studied. The synthetic route towards two new [PtCl(NCN-R-4)] (R = C(O)Me and C(O)Et) complexes used above is likewise described. The utility and limitations of the McMurry reaction involving these pincer complexes was systematically evaluated. The predicted “homo-coupling” reaction of [PtBr(NCN-C(O)H-4)] led to the unexpected formation of 3,3′,5,5′-tetra[(dimethylamino)methyl]-4,4′-bis(platinum halide)-benzophenone (halide = Br or Cl), referred to hereafter as the bispincer-benzophenone complex 13. This material was further characterized using X-ray crystal structure determination. The applicability of the pincer complexes in the McMurry reaction is shown to open a route towards the synthesis of tamoxifen-type derivatives of which one phenyl ring of Tamoxifen® itself is replaced by an NCN arylplatinum pincer fragment. The newly synthesized derivatives can be used as potential candidates in anti-cancer drug screening protocols. Two NCN-arylpincer platinum tamoxifen type derivatives, 5 and 6, were successfully synthesized and of 5 the separation of the diastereomeric E-/Z-forms was achieved. Compound 6, which is the pivaloyl protected NCN pincer platinum hydroxy-Tamoxifen® derivative, was obtained as a mixture of E-/Z-isomers. The new derivatives were further analyzed and characterized with 1H-, 13C{1H}- and 195Pt{1H}-NMR, IR, exact mass MS and elemental analysis.

Computational Analysis of Mesomerism in para-Substituted mer-NCN Pincer Platinum(II) Complexes, Including its Relationships with Hammett σp Substituent Parameters.

Density Functional Theory studies of square-planar PtII pincer structures, (4-Z-NCN)PtCl ([4-Z-NCN]- =[4-Z-2,6-(Me2 NCH2 )2 C6 H2 -N,C,N]- , Z=H, NO2 , CF3 , CO2 H, CHO, Cl, Br, I, F, SMe, SiMe3 , tBu, OH, NH2 , NMe2 ), enable characterisation of mesomerism for the pincer-Pt interaction. Relationships between Hammett σp substituent parameters of Z and DFT data obtained from NBO6 and AOMix computation are used to probe the interaction of the 5dyz orbital of platinum with π-orbitals of the arene ring. Analogous computation for 2,6-(Me2 CH2 )2 C6 H3 Z (Z=H, CF3 , CHO, Cl, Br, I, F, SMe, SiMe3 , tBu, OH, NH2 ) and (4-H-NCN)PtZ allows an estimation of the relative substituent effects of "(CH2 NMe2 )2 PtZ" on π-delocalisation in the pincer system.

Coordination Chemistry in Water of a Free and a Lipase-Embedded Cationic NCN-Pincer Platinum Center with Neutral and Ionic Triarylphosphines

The coordination chemistry in aqueous media was studied for the platinum center of low-molecular-weight cationic NCN-pincer platinum complexes [RC6H2(CH2NMe2)2-3,5-Pt(H2O)-4]+ (R = −(CH2)3P(═O)(OEt)(OC6H4NO2-4) (1(OH2)), H (2(OH2))) as well as of the platinum center of the NCN-pincer platinum cation embedded in the lipase cutinase (cut-1; molecular weight 20 619.3) with various anionic, neutral, and cationic triarylphosphines. A 31P NMR study of the coordination of triarylphosphines to the cationic NCN-pincer platinum center in low-molecular-weight [2(OH2)][OTf] in both D2O and Tris buffer (Tris = tris(hydroxylmethyl)aminomethane) showed that the phosphine–platinum coordination is strongly affected by Tris buffer molecules. Two crystal structures of a NCN-pincer platinum–phosphine and a NCN-pincer platinum–ethanolamine coordination complex with ethanolamine as a functional model of Tris with hydrogen bridges, provoking a dimeric supramolecular structure, confirmed that the coordination observed in solution occurred in the solid state as well. A 31P NMR and ESI-MS study of the lipase cut-1 showed that the coordination of various triarylphosphines to the enzyme-embedded platinum center is affected by the surrounding protein backbone, discriminating between phosphines on the basis of their size and charge. By using 31P NMR spectroscopy and ESI-MS spectrometry, study of the coordination of triarylphosphines to cut-1 was possible, thereby avoiding the need for the application of laborious biochemical procedures. To the best of our knowledge, this is the first example of a study involving the selective binding of organic ligands to the metal center of a semisynthetic metalloprotein, unequivocally demonstrating that the well-established coordination chemistry for small-molecule complexes can be transferred to biological molecules. This initial study allows future explorations in the field of selective protein targeting and identification, as in protein profiling or screening studies.

A Cationic NCN Pincer Platinum(II) Aquo Complex with a Bis(imidazolinyl)phenyl Ligand: Studies toward its Synthesis and Asymmetric Friedel–Crafts Alkylation of Indoles with Nitroalkenes

Studies toward the synthesis and characterization of a cationic NCN pincer platinum(II) aquo complex with a chiral bis(imidazolinyl)phenyl (Phebim) ligand are reported. During these studies, the new symmetrical Phebim-H ligands 1c,d and unsymmetrical hybrid oxazoline–imidazoline ligands 6a–c, as well as the related neutral symmetrical NCN pincer Pt(II) complexes 2b–d and 3a–d and unsymmetrical NCN′ pincers 7a,b and 8c have been isolated and characterized. Despite considerable attempts, only one of the expected cationic chiral NCN pincer Pt(II) complexes (4), which contains water as an exchangeable neutral ligand for the Pt(II) center, was obtained in pure form from the reaction of the neutral Pt–I complex 3a with AgOTf in wet CH2Cl2 at room temperature. In contrast, the cationic Pt(II) pyridine complexes 5a,c could be easily prepared in high yields from the reaction of the neutral Pt–Cl complexes 2a,c with AgOTf in the presence of pyridine in CH2Cl2 at room temperature. The molecular structures of the neu...

SO2-binding properties of cationic η6,η1-NCN-pincer arene ruthenium platinum complexes: spectroscopic and theoretical studies

The SO(2)-binding properties of a series of η(6),η(1)-NCN-pincer ruthenium platinum complexes (NCN = 2,6-bis[(dimethylamino)methyl]phenyl anion) have been studied by both UV-visible spectroscopy and theoretical calculations. When an electron-withdrawing [Ru(C(5)R(5))](+) fragment (R = H or Me) is η(6)-coordinated to the phenyl ring of the NCN-pincer platinum fragment (cf. [2](+) and [3](+), see Scheme 1), the characteristic orange coloration (pointing to η(1)- SO(2) binding to Pt) of a solution of the parent NCN-pincer platinum complex 1 in dichloromethane upon SO(2)-bubbling is not observed. However, when the ruthenium center is η(6)-coordinated to a phenyl substituent linked in para-position to the carbon-to-platinum bond, i.e. complex [4](+), the SO(2)-binding property of the NCN-platinum center seems to be retained, as bubbling SO(2) into a solution of the latter complex produces the characteristic orange color. We performed theoretical calculations at the MP2 level of approximation and TD-DFT studies, which enabled us to interpret the absence of color change in the case of [2](+) as an absence of coordination of SO(2) to platinum. We analyze this absence or weaker SO(2)-coordination in dichloromethane to be a consequence of the relative electron-poorness of the platinum center in the respective η(6)-ruthenium coordinated NCN-pincer platinum complexes, that leads to a lower binding energy and an elongated calculated Pt-S bond distance. We also discuss the effects of electrostatic interactions in these cationic systems, which also seems to play a destabilizing role for complex [2(SO(2))](+).

Synthesis and characterization of bioorganometallic conjugates composed of NCN-pincer platinum(II) complexes and uracil derivatives

The conjugation of the NCN-pincer platinum(II) complexes as an oraganometallic compound and the uracil derivatives as a nucleobase was demonstrated to give the corresponding bioorganometallics. The NCN-pincer ligands bearing the 6-ethynyl-1-octyluracil, 5-ethynyl-1-octyluracil, and the furanopyrimidine moiety were synthesized. In a crystal state, the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil moiety was found to form a hydrogen-bonded dimer through intermolecular hydrogen bonds between the uracil moieties, which was connected through π–π interaction between the uracil and benzene moieties of the NCN-pincer ligand. The reaction of the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil moiety with [Pt(tolyl-4) 2(SEt 2)] 2 led to the formation of the NCN-pincer platinum(II) complex bearing the 6-ethynyl-1-octyluracil moiety. The NCN-pincer platinum(II) complex bearing the furanopyrimidine moiety was obtained by the reaction of the NCN-pincer ligand bearing the furanopyrimidine moiety with [Pt(tolyl-4) 2(SEt 2)] 2. The single-crystal X-ray structure determination of the NCN-pincer platinum(II) complex bearing the furanopyrimidine moiety revealed the formation of the furanopyrimidine ring and the π stack dimer between the furanopyrimidine and benzene moieties of the NCN-pincer ligand in the crystal packing. The NCN-pincer platinum(II) complexes bearing the 6-ethynyl-1-octyluracil moiety or the furanopyrimidine moiety exhibited emission in both solution and solid states.

Selective detection of SO2 at room temperature based on organoplatinum functionalized single-walled carbon nanotube field effect transistors

We report a field effect transistor (FET) based on a network of single-walled carbon nanotubes (SWCNTs) that for the first time can selectively detect a single gaseous molecule in air by chemically functionalizing the SWCNTs with a selective molecular receptor. As a target model we used SO2. The molecular synthetic receptor is a square-planar NCN-pincer platinum (II) complex (NCN is the N,C,N′-terdentate-coordinating monoanionic [C6H3(CH2NMe2)3-2,6]− ligand) to which SO2 selectively binds. Because of the strong electronwithdrawing character of SO2, it withdraws negative charge from the synthetic receptor thus affecting the electronic properties of the functionalized SWCNTs. The minimum concentration detected is 0.05% SO2 in air at room temperature. Interferences like CH4 and CO2 need to be present in a higher concentration than SO2 to give a significant response.

Substituted 4,4′-Stilbenoid NCN-Pincer Platinum(II) Complexes. Luminescence and Tuning of the Electronic and NLO Properties and the Application in an OLED

A series of 4,4′-disubstituted organic−organometallic stilbenes, i.e., the 4′-substituted stilbenoid-NCN-pincer platinum(II) complexes [PtCl(NCN-R-4)] (NCN-R-4 = [C6H2(CH2NMe2)2-2,6-R-4]− in which R = C2H2C6H4-R′-4′ with R′ = NPh2, NMe2, OMe, SiMe3 H, I, CN, NO2) (1−8), were studied for their electronic, electrochemical, and NLO properties. Complex 7 was also chemically oxidized using Cu(II)Cl2, yielding the [Pt(IV)Cl3(NCN(C2H2C6H4-CN-4′)-4)] complex 11. In contrast to 1 and 7, 11 did not show luminescent properties in solution at room temperature. In the solid state (X-ray crystallography) 11 has an overall bent structure, with the pincer moiety and the cyano group beneath the plane of the central double bond. Stilbenoid pincer complex 1 (R′ = NPh2) was also studied with UV/vis spectroscopy in a series of different solvents. The compound shows an intense low-energy transition band, appearing at a lower energy (λmax = 374–379 nm) than 2 (R′ = NMe2), which contains a stronger donor group. The UV/vis absorp...

A Tin(IV) Porphyrin with Two Axial Organometallic NCN-Pincer Platinum Units

A tin(IV) porphyrin was combined with two axial NCN-pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN-pincer platinum derived benzoic acid. The solid-state structure determined by X-ray crystallography revealed some close contacts between the pincer complexes and the meso-p-tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures.

Preparation and Characterization of Luminescent SCS and NCN Pincer Platinum Complexes Derived from 3,5-Bis(anilinothiocarbonyl)toluene

Starting from 5-methyl-1,3-bis(anilinothiocarbonyl)benzene (1), two types of luminescent pincer platinum complexes with κ3S,C,S and κ3N,C,N coordination modes were obtained. Reaction of 1 with K2PtCl4 afforded a pincer Pt(II) complex (3) with the κ3S,C,S coordination mode, whereas oxidative cyclization of 1 yielded 5-methyl-1,3-bis(benzothiazol-2-yl)benzene (2), which provided a pincer Pt(II) complex (4) with the κ3N,C,N coordination mode. Molecular structures and photochemical properties of the complexes have been examined. The decay lifetimes of the emission from the complexes were in the range 10-5−10-6 s, which were indicative of phosphorescent emission.

Synthesis and supramolecular association of immobilized NCN-pincer platinum(II) complexes on hyperbranched polyglycerol supports.

Pertosylation of hyperbranched polyglycerol (M(n)=2000; M(w)/M(n)=1.3) followed by partial displacement of the tosyl groups with carboxylic acid functionalized NCN-pincer platinum(II) complexes [PtI-2,6-(NMe(2)CH(2))(2)C(6)H(2)-4-COOH], resulted in covalent attachment of the NCN-pincer complexes to the polyglycerol. These functionalized hyperbranched macromolecules have been characterized by (1)H, (13)C, and (195)Pt NMR, UV-visible, and IR spectroscopy. The presence of Pt and I atoms renders them directly visible by transmission electron microscopy (TEM) without staining procedures, which offers images of associated hyperbranched macromolecules. TEM micrographs show disk-shaped structures with a small size-distribution (15-20 nm), and characteristic core-shell ring structures. The thickness of the corona observed in TEM could be correlated with the substitution degree with pincer platinum moieties.

Optically Active Hyperbranched Polyglycerol as Scaffold for Covalent and Noncovalent Immobilization of Platinum(II) NCN-Pincer Complexes. Catalytic Application and Recovery

New optically active hyperbranched polymers have been used as microenvironments as well as scaffolds for noncovalent and covalent immobilization of pincer platinum(II) complexes, respectively. The catalytic activity/selectivity of the incorporated platinum(II) complexes in these polymeric chiral supports was investigated. Chiral amphiphilic hyperbranched polyglycerols with core−shell “nanocapsules” structure, namely (−)-P(G40C160.5) (1) and (+)-P(G73C160.5) (2), have been prepared in two straightforward steps by ring-opening multibranching polymerization (ROMBP) of either (−)- or (+)-glycidol, resulting in (−)-PG40 (Mn = 3000, Mw/Mn = 1.3) or (+)-PG73 (Mn = 5500, Mw/Mn = 1.6), respectively. Polymerization was followed by partial esterification of a certain fraction of OH groups with palmitoyl chloride. Multifunctional hydrophilic NCN-pincer platinum(II) complexes with sulfonate groups, [PtCl(NCN-SO3H)] (3; NCN = 2,6-bis[(dimethylamino)methyl]phenyl anion), were encapsulated in 1 and 2. The NCN-pincer platinum(II) species encapsulated in the chiral nanocapsules 1 + 3 and 2 + 3 show only slight CD activity with intensity bands of opposite sign, +0.4 mdeg and −0.5 mdeg, respectively, at 320 nm. Pertosylation of the chiral polyglycerols (−)-PG40 and (+)-PG73 afforded the fully tosylated hyperbranched polymers (−)-PG40Tos1.0 (4) and (+)-PG73Tos1.0 (5). Partial displacement of the tosyl groups of 4 with potassium carboxylate functionalized NCN-pincer platinum(II) complexes [PtI(NCN-COOK)] (7) resulted in covalent attachment of the NCN-pincer complexes to the polyglycerol (8). CD spectra of the tosylated compounds 4 and 5 were recorded, showing opposite signals at 256 nm of −1.8 and +2.0 mdeg, respectively, which confirm retention of the chirality during the pertosylation. The decrease in CD intensity of 8 compared to 4 might be attributed to either partial inversion of chirality or racemization during functionalization. The noncovalent encapsulated Pt(II) complexes 1 + 3 and 2 + 3 as well as the covalently attached polymers 8 showed catalytic activity in Michael additions between methyl vinyl ketone and ethyl α-cyanopropionate, although no enantiomeric excess was observed. Quantitative recuperation of these catalysts from catalytic reactions was achieved by dialysis. The combination of the nanosize of the hyperbranched polymer with the catalytic activity of pincer platinum complexes renders these materials promising with respect to application in membrane reactors.