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Synthesis and structure of the first phosphine oxide complex of copper(I): evidence for a marked "borderline" character of the metal centre.
No full textThe remarkable stability of [Cu(dppf)(odppf)]BF4 [dppf = 1,1'-bis(diphenylphosphino)ferrocene, odppf = 1,1'-bis(oxodiphenylphosphoranyl)ferrocene], characterized in the solid state by X-ray analysis and in solution by P-31 NMR spectroscopy, reveals a marked borderline character of copper(I)
cis-Bis(phosphine)platinum(II) complexes with pyrimidyl nucleobases. Synthesis, characterization, and crystal structures of cis-(1-methylthyminato-N3)(N,N-dimethylformamide-O)(1,1'-bis(diphenylphosphino)ferrocene)platinum(II) tetrafluoroborate-dichloromethane, [(dppf)Pt(1-MeTy(-H))(DMF)]BF4.cntdot.CH2Cl2, and cis-(1-methylthyminato-N3)(1-methylcytosine-N3)(1,1'-bis(diphenylphosphino)ferrocene)platinum(II) tetrafluoroborate, [(dppf)Pt(1-MeTy(-H))(1-MeCy)]BF4
No full textThe dinuclear complex [(dppf)Pt(mu-OH)]2(BF4)2, where dppf is 1,1'-bis(diphenylphosphino)ferrocene, reacts with 1-methylthymine (1-MeTy), in dimethylformamide, dimethyl sulfoxide, or acetonitrile, to give the mononuclear complex [(dppf)Pt(1-MeTy(-H))(S)]+. The dimethylformamide adduct (S = DMF), [(dppf)Pt(1-MeTy(-H))(DMF)]BF4.CH2Cl2 (1), has been characterized by single-crystal X-ray analysis. The complex crystallizes in the orthorhombic system, space group P2(1)2(1)2(1), with a = 13.492 (3) angstrom, b = 14.063 (3) angstrom, c = 23.906 (4) angstrom, and Z = 4. The structure was solved by heavy-atom methods and refined by least-squares techniques to R = 0.078 for 2949 unique data (I > 3-sigma(I)). In the cationic unit, the ligand geometry around Pt is distorted square planar, the chelating bis(phosphine) dppf, the N(3)-bonded 1-methylthyminate and the O-bonded DMF ligands defining the coordination sphere of the metal ion. The 1-MeTy(-H) ring forms an angle of 104.8-degrees with the ligand square plane, while the DMF mean plane is at 73.0-degrees to the same plane. Addition of 1-methylcytosine (1-MeCy) to 1 affords the corresponding adduca [(dppf)Pt(1-MeTy(-H))(1-MeCy)]+ (2) as a mixture of two isomeric forms (2a,b). In solution at room temperature 2a extensively converts in 2b (90% in DMF) in several hours. Crystals of 2 are obtained from a chloroform solution of the two isomers and have been characterized by single-crystal X-ray analysis. They crystallize in the monoclinic system, space group C2/c, with a = 17.821 (5) angstrom, b = 21.718 (7) angstrom, c = 13.814 (3) angstrom, beta = 113.6 (2)-degrees, and Z = 4. The structure was solved by heavy-atom methods and refined by least-squares techniques to R = 0.060 for 2657 unique data (I > 3-sigma(I)). In the cationic complex [(dppf)Pt(1-MeTy(-H))(1-MeCy)]+ the platinum atom is coordinated by the chelated bis(phosphine), by the deprotonated 1-MeTy, and by the neutral 1-MeCy ligands. In 2 both the nucleobases are platinated at the N(3) site with their rings being perpendicular to the PtP2 plane. The structures in solution of the two isomers 2a and 2b are discussed on the basis of their H-1 and P-31 NMR spectra. Isomer 2b contains the neutral cytosine ligand coordinated to the platinum through the monodeprotonated exocyclic amino group, with the proton switched to the N(3) position. The conversion of 2a into 2b is consistent with the migration of the platinum from the N(3) to N(4) site of 1-MeCy indicating that the thermodynamically favored adduct of this neutral ligand is its imino oxo tautomeric form. In addition, the characterization of the species [(dppf)Pt(1-MeCy(-H))]+, obtained from [(dppf)Pt(mu-OH)]2(BF4)2 and 1-MeCy in acetonitrile, is described. On the basis of H-1 and P-31 NMR spectra, the complex appears to contain the deprotonated 1-MeCy chelated to the (dppf)Pt2+ moiety through its N(3) and N(4) donor atoms
Homoleptic complexes of cobalt(0) and nickel(0, I) with 1,1 '-bis(diphenylphosphino)ferrocene (dppf): Synthesis and characterization
No full textReduction of Co(dppf)Cl-2 with 2 equiv of sodium naphthalenide in THF, in the presence of dppf, affords the homoleptic complex Co(dppf)(2), 1, isolated in 65% yield as a brick red solid, extremely air sensitive. In solution, under inert atmosphere, 1 slowly decomposes into Co and dppf, following a first-order kinetic law (t(1/2) = 21 h at 22 degrees C). Similarly to the Rh and Ir congeners, 1 undergoes a one-electron reversible reduction to [Co(dppf)(2)](-). Attempts to obtain this d(10) species by chemical as well as electrochemical reduction of 1 lead to the hydride HCo(dppf)(2), 2, as the only product that can be isolated. Reduction of Ni(dppf)Cl-2 with sodium in the presence of dppf and catalytic amounts of naphthalene affords Ni(dppf)(2), 3, isolated in 60% yield as a yellow air stable solid. The stoichiometric oxidation of 3 with [FeCp2]PF6 forms the d(9) complex [Ni(dppf)(2)]PF6, 4, which represents the second example of a structurally characterized Ni(I) complex stabilized by phosphines. A single-crystal X-ray analysis shows for the metal a distorted tetrahedral environment with a dihedral angle defined by the planes containing the atoms P(1), Ni, P(2) and P(3), Ni, P(4) of 78.2 and remarkably long Ni-P bond distances (2.342(3) - 2.394(3) angstrom). The EPR spectroscopic properties of 1 (at 106 K in THF) and 4 (at 7 K in 2-methyl-THF) have been examined and g tensor values measured (1, g(x) = 2.008, g(y) = 2.182, g(z) = 2.326; 4, g(x) = 2.098, g(y) = 2.113, g(z) = 2.332). A linear dependence between the hyperfine constants and the Ni-P bond distances has been evidenced. Finally, the change with time of the EPR spectrum of 4 indicates that it very slowly releases dppf
Structural Characterization of a Trinuclear Complex of Platinum(II) Containing Bridging 1-Methylcytosine Ligands. A Combined X-ray and Multinuclear NMR Study
No full textThe dinuclear complexes cis-[(PMe3)2Pt(1-MeCy(-H))]2X2 (X = NO3- (1A), ClO4- (1B)), containing NH2-deprotonated 1-methylcytosine (1-MeCy(-H)) ligands, in aqueous or DMSO solution, at 80-degrees-C convert quantitatively into the corresponding trinuclear derivatives cis-[(PMe3)2Pt(1-MeCy(-H))]3X3(2A,B) which have been characterized in the solid state by single-crystal X-ray analysis and in solution by multinuclear (H-1, P-31, Pt-195, C-13, and N-15) NMR spectroscopy. The nitrate salt (2A) crystallizes from ethanol in the triclinic system, space group Pl. The crystals, stable only in the presence of the solvent, have the following cell dimensions: a = 13.542(5) angstrom, b = 17.352(5) angstrom, c = 20.721(6) angstrom, alpha = 113.13(2)degrees, beta = 104.30(3)degrees, gamma = 95.77(3)degrees, Z = 2. The structure, formulated as cis-[(PMe3)2Pt(1-MeCy(-H))]3(NO3)3.EtOH.H2O, was refined to R = 6.3 and R(w) = 6.3. Better structural data were obtained with the perchlorate derivative (2B), cis-[(PMe3)2Pt(1-MeCy(-H))]3(ClO4)3.2H2O, whose structure was refined to R = 4.4 and R(w) =4.9. The colorless prisms formed from aqueous solutions have the following crystallographic data: triclinic system, space group P1BAR, a = 14.634(7) angstrom, b = 14.791(9) angstrom, c = 14.980(9) angstrom, alpha = 101.93(5)degrees, beta = 103.46(5)degrees, gamma = 90.50(4)degrees, Z = 2. In both salts, the molecular structure of the cationic complex contains three cis-(PMe3)2Pt units linked to three 1-methylcytosine anions through the N(3) and N(4) atoms. The resulting 12-membered ring contains the pyrimidinic rings almost perpendicular to the plane defined by the metal atoms. Each platinum has a square-planar coordination with a Pt...Pt distance of 5.2A. The H-1, P-31, and C-13 NMR spectra indicate that the approximate S3 symmetry of the cation is maintained in solution. The compounds 1A and 2A were also characterized by N-15 NMR spectroscopy, at natural abundance. The spectroscopic data, obtained in DMSO-d6 solution, are compared with those of the derivative cis-[(PMe3)2Pt(1-MeCY)2](NO3)2 containing as ligands the neutral N(3)-bonded nucleobase. The dinuclear and trinuclear complexes exhibit very similar N-15 chemical shifts and 2J(PN) coupling constants but remarkably different from those of the mononuclear complex
9-METHYLADENINE COMPLEXES OF PLATINUM(II) WITH PHOSPHINES. STABILITY OF THE CYCLIC TRIMER cis-[(PMePh2)2Pt(9-MeAd(-H))]3(NO3)3 in solution
No full textHydroxo and oxo complexes of platinum(II) stabilized by phosphanes: Synthesis and characterization - X-ray structures of cis-[L2Pt(mu-OH)](2)(NO3)(2) (L = PMe2Ph, PMePh2) and [{cis-(PMe2Ph)(2)Pt}(3)(mu-O)(2)]Cl-2
No full textThe dinuclear hydroxo complexes cis- [L2Pt(mu-OH)](2)(NO3)(2) (L = PMe2Ph and PMePh2) have been characterized by single-crystal X-ray analysis, and their reactivity towards chloride ions has been investigated. Reaction of cis-[L2Pt(mu-OH)](2)X-2 (L = PMe3, PMe2Ph; X = NO3-, CIO4-) with (NEt4)CI.H2O or (AsPh4)CI, in a 1:2 molar ratio, afforded a mixture of cis-[L2PtCl2] and [{cis-L(2)pt}(3)(mu-O)(2)](2+) in ca. equimolar amounts. The trinuclear oxo compounds, separated by fractional crystallization of the reaction mixtures, were fully characterized by spectroscopic techniques, and the derivative [(cis-(PMe2Ph)(2)Pt)(3)(mu-O)(2)]CI2 was also characterized by X-ray diffraction methods. Under the same experimental conditions, the structurally analogous hydroxo complex, stabilized by the less basic and more hindered PMePh2 ligand, reacted with Cl- to give cis-[(PMePh2)(2)PtCl2] as the only isolable species. The P-31 NMR spectroscopic analysis of the reaction mixtures allowed the detection of a moderately stable product, which is most likely to be the neutral hydroxo complex cis-[L2PtCl(OH)]
Synthesis, characterization and cytotoxic properties of platinum(II) complexes containing the nucleosides adenosine and cytidine
Full text linkCytidine (cyt) and adenosine (ado) react with cis-[L(2)Pt(μ-OH)](2)(NO(3))(2) (L=PMe(3), PPh(3)) in various solvents to give the nucleoside complexes cis-[L(2)Pt{cyt(-H),N(3)N(4)}](3)(NO(3))(3) (L=PMe(3), 1),cis-[L(2)Pt{cyt(-H),N(4)}(cyt,N(3))]NO(3) (L=PPh(3), 2), cis-[L(2)Pt{ado(-H),N(1)N(6)}](2)(NO(3))(2) (L=PMe(3), 3) and cis-[L(2)Pt{ado(-H),N(6)N(7)}]NO(3) (L=PPh(3), 4). When the condensation reaction is carried out in solution of nitriles (RCN, R=Me, Ph) the amidine derivatives cis-[(PPh(3))(2)PtNH=C(R){cyt(-2H)}]NO(3) (R=Me, 5a; R=Ph, 5b) and cis-[(PPh(3))(2)PtNH=C(R){ado(-2H)}]NO(3) (R=Me, 6a: R=Ph, 6b) are quantitatively formed. The coordination mode of these nucleosides, characterized in solution by multinuclear NMR spectroscopy and mass spectrometry, is similar to that previously observed for the nucleobases 1-methylcytosine (1-MeCy) and 9-methyladenine (9-MeAd). The cytotoxic properties of the new complexes, and those of the nucleobase analogs, cis-[(PPh(3))(2)PtNH=C(R){1-MeCy(-2H)}]NO(3) (R=Me, 7a: R=Ph, 7b), cis-[(PPh(3))(2)PtNH=C(R){9-MeAd(-2H)}]NO(3) (R=Me, 8a: R=Ph, 8b) have been investigated in a wide panel of human cancer cells. Interestingly, whereas the Pt(II) nucleoside complexes (1-4) did not show appreciable cytotoxicity, the corresponding amidine derivatives (7a, 7b, 8a, 8b, 5b, and 6b) exhibited a significant in vitro antitumor activity
Synthesis and characterization of rhodium(0) and rhodium(-I) complexes stabilized by 1,1'-bis(diphenylphosphino)ferrocene (dppf). Crystal structure of Rh(dppf)2 and [Na(THF)5][Rh(dppf)2].THF
No full textThe rhodium(I) complex stabilised by the organometallic ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf), [Rh(dppf)(2)](+)(1) can be electrochemically reduced to the Rh(0) and Rh(-1) species, [Rh(dppf)(2)] (2) and [Rh(dppf)(2)](-) (3), respectively, in two reversible single-electron processes. These low-valent complexes have been obtained by the chemical reduction of 1 with sodium naphtalenide in tetrahydrofuran solution and their crystal and molecular structures determined by single-crystal X-ray analyses. The anionic complex [Rh(dppf)(2)](-) crystallises as sodium-solvated salt, [Na(THF)(5)][Rh(dppf)(2)]. THF (3) in the monoclinic system. The coordination geometry around the metal in the d(10) configuration is a slightly distorted tetrahedral in which the bite angles of the chelated diphosphines is 103 degrees (average) and the Rh-P bond distances is in the range of 2.230(5)-2.251(5) Angstrom. The sodium cation is surrounded by five molecules of THF in a slightly distorted trigonal-bipyramidal environment. Complex 2 is conveniently prepared by reacting equimolar amount of I and 3 in THF and crystallises in the triclinic system. The dihedral angle defined by the planes containing the atoms P(1)-Rh-P(2) and P(3)-Rh-P(4) is 75.2 degrees, indicating a geometry of the rhodium in the d(9) configuration intermediately between the highly distorted square-planar (dihedral angle 49.7 degrees), found earlier in the cationic d(8) species 1, and in the anionic d(10) complex (dihedral angle 95.0 degrees). Reduction of the metal centre causes a decrease in the Rh-P bond length of 0.034 Angstrom (average) from Rh(I) to Rh(0) and 0.071 Angstrom from Rh(0) to Rh(-1), respectively, with a concomitant increase of the bite angle of the diphosphine which ranges from 93.4 degrees (average) in [Rh(dppf)(2)](+) to 102.6 degrees in [Rh(dppf)(2)](-). The EPR spectroscopic properties of 2 and the analogue iridium derivative, [Ir(dppf)2], have been examined at 20 K in 2-methyltetrahydrofuran matrix. A linear dependence between the hyperfine constants and the M-P (M = Rh, Ir) bond distances has been evidenced. This fact suggests the possibility to use the phosphorus coupling as an indication of the metal-phosphorus bond length in similar complexes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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