- Mechanistic insight into the protonolysis of the Pt-C bond as a model for C-H bond activation by platinum(II) complexes
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The kinetic and NMR features of the protonolysis reactions on platinum(II) alkyl complexes of the types cis-[PtMe2L2], [PtMe 2(L-L)], cis-[PtMeClL2], and [PtMeCl(L-L)] (L = PEt 3, P(Pri)3, PCy3, P(4-MePh) 3, L-L = dppm, dppe, dppp, dppb) in methanol suggest a rate-determining proton attack at the Pt - C bond. In contrast, a multistep oxidative-addition - reductive-elimination mechanism characterizes the methane loss on protonation of the corresponding trans-[PtMeClL2] species. Tools that were particularly diagnostic in suggesting different reaction pathways for the two systems were (i) the different results of kinetic deuterium isotope experiments, (ii) the detection or absence of Pt(IV) hydrido alkyl intermediate species by low-temperature 1H NMR experiments, and (iii) the detection or absence of isotope scrambling and incorporation of deuterium into Pt - CH3, combined with the loss of a range of CH nDn-4 isotopomers. For all systems, the rates of protonolysis are retarded by ligand steric congestion, accelerated by ligand electron donation, and almost unaffected by the chain length along the series of chelate complexes. A straight line correlates the rates of protonolysis of cis-dialkyl and cis-monoalkyl complexes, the difference in reactivity between the two systems being almost 5 orders of magnitude (slope of the line = 6 × 104). Factors controlling the dichotomy of behavior between complexes of different geometry have been taken into consideration. Application of the principle of microscopic reversibility suggests the reason why platinum complexes with nitrogen donor ligands appear to be far more efficient than platinum phosphane complexes in activating the C-H bond.
- Romeo, Raffaello,D'Amico, Giuseppina
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p. 3435 - 3446
(2008/10/09)
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- Intermolecular stacking of a tetranuclear cyclic Pt(II) complex: NMR characterization and X-ray crystal structure of cis-trans-cis-trans tetra[μ-2,6-diethynyl-4-nitroaniline-bis(tri(p-tolyl)phosphine)platinum(II)]
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The synthesis and characterization of a tetranuclear Pt complex, cis-trans-cis-trans tetra[μ-2,6-diethynyl-4-nitroaniline-bis(tri(p-tolyl)phosphine) platinum(II)], namely [L2Pt-DENA]4 with L = tri-p-tolylphosphine, is reported. The c
- Fratoddi, Ilaria,Delfini, Maurizio,Sciubba, Fabio,Hursthouse, Michael B.,Ogilvie, Helen R.,Russo, Maria V.
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p. 5920 - 5926
(2008/10/09)
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- Synthesis and characterisation of triselenocarbonate [CSe3] 2- complexes
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[Pt(CSe3)(PR3)2] (PR3 = PMe3, PMe2Ph, PPh3, P(p-tol)3, 1/2 dppp, 1/2 dppf) were all obtained by the reaction of the appropriate metal halide containing complex with carbon diselenide in liquid ammonia. Similar reaction with [Pt(Cl)2(dppe)] gave a mixture of triselenocarbonate and perselenocarbonate complexes. [{Pt(μ-CSe3)(PEt 3)}4] was formed when the analogous procedure was carried out using [Pt(Cl)2(PEt3)2]. Further reaction of [Pt(CSe3)(PMe2Ph)2] with [M(CO)6 (M = Cr, W, Mo) yielded bimetallic species of the type [Pt(PMe2Ph) 2(CSe3)M(CO)5] (M = Cr, W, Mo). The dimeric triselenocarbonate complexes [M{(CSe3)(η5-C 5Me5)}2] (M = Rh, Ir) and [{M(CSe 3)(η6-p-MeC6H4 iPr)}2] (M = Ru, Os) have been synthesised from the appropriate transition metal dimer starting material. The triselenocarbonate ligand is Se,Se' bidentate in the monomeric complexes. In the tetrameric structure the exocyclic selenium atoms link the four platinum centres together. The Soyal Society of Chemistry 2005.
- Burchell, Colin J.,Aucott, Stephen M.,Slawin, Alexandra M. Z.,Woollins, J. Derek
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p. 735 - 739
(2007/10/03)
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- Platinum(II) and mixed platinum(II)/gold(I) σ-alkynyl complexes. The first anionic σ-alkynyl metal polymers
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The alkynes C6Me4(C≡CH)2-1,4, C 6Me4(C≡CH)2-1,2, and C6Me 3(C≡CH)3-1,3,5 react with cis-[PtCl 2(PAr3)2] and NHEt2 and a catalytic amount of CuI to give complexes trans-[Pt-(C≡CC6Me 4C≡CH-4)2(PAr3)2] [Ar = Ph (1a), C6H4Me-4 (To) (1b)], trans-[Pt(C≡CC 6Me4-C≡CH-2)2(PAr3) 2] [Ar = Ph (2a), To (2b)], and trans-[Pt{C≡CC 6Me3(C≡CH)2-3,5}2(PAr 3)2] [Ar = Ph (3a), To (3b)], respectively. The reactions of [Au(acac)PAr3] (acac = acetylacetonato) with complex la or lb (2:1) or with 3b (4:1) give the neutral mixed PtIIAuI 2 or PtIIAuI4 σ-alkynyl complexes trans- [Pt(C≡CC6Me4C≡CAuPAr 3-4)2(PAr3)2] [Ar = Ph (4a), To (4b)] or trans-[Pt{C≡CC6Me3(C≡CAuPTo 3)2-3,5}2(PTo3)2] (5b), respectively. Additionally, the replacement of the triarylphosphine ligands present in 1a, 2a, 4b, or 5b with various trialkylphosphines produces the homologous derivatives with PMe3 (1c, 2c, 4c, 5c), PEt3 (1d), or P(nBu)3 (1e), respectively. PPN[Au(acac) 2] reacts with complex 1a, 1c, or 1e (1:1) to give (PPN) n[trans-Pt{(C≡CC6Me4C≡C-4) 2Au}(PR3)2]n [R = Ph (6a), Me (6c), nBu (6e)], while its reaction with 3b (2:1) produces (PPN) 2n[trans-Pt{C≡CC6Me3(C≡C) 2-3,5Au2(PTo3)2]n (7). Complexes 6a, 6c, 6e, and 7 are the first anionic σ-alkynyl metal polymers described so far. The crystal structures of 1a·CHCl3, 2b·2CHCl3, and 4b·5CH2Cl2 have been determined. Each complex displays crystallographic inversion symmetry.
- Vicente, Jose,Chicote, Maria-Teresa,Alvarez-Falcon, Miguel M.,Jones, Peter G.
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p. 2764 - 2772
(2008/10/09)
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- Coordination chemistry of P-rich phosphanes and silylphosphanes. XXI [1] the influence of the PR3 ligands on formation and properties of the phosphinophosphinidene complexes [{η2-tBu2P-P}Pt(PR3)
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(R3P)2PtCl2 and C2H4 yield the compounds [{η2-C2H4}Pt(PR3)2] (PR3 = PMe3, PEt3, PPhEt2, PPh2/su
- Matern, Eberhard,Pikies, Jerzy,Fritz, Gerhard
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p. 2136 - 2142
(2008/10/08)
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- Probing the bonding of phosphines and phosphites to platinum by NMR. Correlations of 1J(PtP) and Hammett substituent constants for phosphites and phosphines coordinated to platinum(II) and platinum(0)
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The values of 1J(PtP) have been measured for the platinum(II) complexes cis-[PtCl2L2] and cis-[PtMeClL2] and the platinum(0) complexes [PtL(norbornene)2] and [PtL2(norbornene)] where L = P(C6H4Z-4)3 and [PtL2(norbornene)], [PtL3] and [PtL4] where L = P(OC6H4Z-4)3 and Z = NMe2, OMe, Me, H, Cl, CF3. When 1J(PtP) is plotted against the Hammett substituent constant two distinct trends emerge: for platinum(II) the more electron-withdrawing the substituent the smaller the 1J(PtP), while for platinum(0) the more electron-withdrawing the substituent the larger the 1J(PtP). These observations are rationalised in terms of the σ and π-bonding components of the platinum-phosphorus bonds.
- Cobley, Christopher J.,Pringle, Paul G.
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p. 107 - 115
(2008/10/08)
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- Formation of platinum allyl and propargyl complexes from protonation of platinum enyne and diyne complexes
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Protonation of (Ph3P)2Pt[η2-HC=CC(CH3) =CH2] (2a) with excess HBF4·Et2O produced the π-allyl complex (Ph3P)2Pt[η3-H2C=CC(CH 3)=CH2] +BF4- (3a-BF4) instead of a π-propargyl complex. Reaction of excess CF3CO2H with 2a initially produced the analogous π-allyl complex 3a-CF3CO2 which then added CF3CO2H across the vinylidene unit of 3a-CF3CO2 to give the π-allyl complex (Ph3P)2Pt[η3-CH3C(CF 3CO2)C(CH3)CH2]+CF 3CO2- (5a). Protonation of the platinum diyne complex [(p-CH3-C6H4)3P] 2Pt(η2-CH3C≡CC≡CCH3) (7b) with HBF4·Et2O at -73°C initially produced the platinum hydride complex trans-[(p-CH3-C6H4)3P] 2-PtH(η2-CH3C ≡ CC ≡ CCH3) +BF4- (9), which rearranged to the platinum π-propargyl complex [(p-CH3-C6H4)3P] 2Pt[η3-(CH3CH=)-CC ≡ CCH3]+BF4- (11) at -28°C.
- Casey, Charles P.,Chung, Steven,Ha, Yunkyoung,Powell, Douglas R.
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p. 127 - 138
(2008/10/08)
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- Hydrosilylation with platinum complexes. Preparation, low-temperature NMR spectra, and X-ray crystal structure of the novel bis-olefin catalyst cis-PtCl2(PhCH=CH2)2
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The bis-olefin complex cis-PtCl2(PhCH=CH2)2 (1) has been prepared and shown to exist in several isomeric forms by 1H and 195Pt NMR spectroscopy. Complex 1 is a synthetically useful form of soluble PtCl2 and also catalyzes the hydrosilylation of styrene with Et3SiH. This latter reaction has been carried out with a variety of known complexes of platinum(II), and the results have been compared with those found for some trichlorostannate complexes of platinum. One isomer of 1 has been crystallized and its structure determined by X-ray diffraction. Crystal data for this isomer: space group P21/c, a = 13.805 (7) ?, b = 10.235 (2) ?, c = 10.985 (7) ?, β = 106.51 (4)°; Z = 4; V = 1489.1 ?3.
- Albinati, Alberto,Caseri, Walter R.,Pregosin, Paul S.
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p. 788 - 793
(2008/10/08)
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- Preparation and characterization of some mixed ligand complexes of platinum(II)
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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 PtII 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 CC 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.
- Clark, Howard C.,Goel, Anil B.,Jain, Vimal K.,Tyers, Kenneth G.,Wong, Chun S.
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p. 123 - 134
(2007/10/02)
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- Substitution and Isomerisation Reactions at Platinum(II) involving Halide, Tertiary Phosphine, Carbonyl, and Isonitrile Ligands
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Carbon monoxide catalyses trans to cis isomerisations of (L = tertiary phosphine) in chloroform solution.The process involves formation of five-co-ordinate intermediates from which halide or tertiary phosphine can be eliminated, giving trans-(1+) or cis- respectively.Structure changes appear to be by pseudo-rotations rather than by consecutive displacements.A number of isonitrile complexes undergo similar reactions.Halide-bridged cations (2+) formed by halide extraction from cis- by Ag(1+) enter rapid (n.m.r. time-scale) exchange processes with the latter complexes at ambient temperatures.Halide elimination from cis- by solvent chloroform appears to initiate the process.The trans isomers do not participate in the exchange.
- Cross, Ronald J.,Phillips, Ian G.
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p. 2261 - 2264
(2007/10/02)
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- Study of PtX2(PR3)2 in the presence of PR3 in CH2Cl2 solution and the cis-trans isomerization reaction as studied by 31P NMR. Crystal structure of [PtCl(PMe3)3]Cl
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The identity of the species present in dichloromethane solutions of PtX2L2 and L (L = PMe3, PEt3, P-n-Bu3, P(tol)3 where tol = p-tolyl; Pt:L ratios from 1:0.05 to 1:5) are cis- and trans-PtX2L2, [PtXL3]+ (X = Cl, Br), and [PtXL4]+ (X = Cl, Br, I; L = PMe3). The only species with three coordinated phosphines which is five-coordinate in solution is PtI2(PMe3)3, whose IR and NMR parameters are consistent with a square-pyramidal geometry having one phosphine in the apical position. All other tris complexes [PtXL3]+ are four-coordinate in solution as shown by UV and 31P NMR spectroscopy, and this geometry is also found in the solid state ([PtCl(PMe3)3]Cl X-ray crystal structure). The complexes [PtX(PMe3)4]+ have a square-pyramidal geometry with X in the apical position. In the case of L = PMe3,31P NMR studies show that intermolecular phosphine exchange occurs between [PtClL3]+, [PtClL4]+, PtI2L3, and free L, whose activation parameters, estimated from line-shape analysis, are reported. Contrary to previous reports, chloride ion is found to displace one phosphine from [PtClL3]+ ion, giving the cis-PtCl2L2 isomer in a fast step prior to cis-trans equilibration. The results indicate that the cis-trans isomerization of PtX2L2 catalyzed by L proceeds by rapid displacement of X- by L followed by slow displacement of L by X- and not by pseudorotation of a five-coordinate intermediate. A similar mechanism was established for the isomerization of the alkyl complex PtCl(CH2CN)(PPh3)2.
- Favez, Roland,Roulet, Raymond,Pinkerton, Alan A.,Schwarzenbach, Dieter
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p. 1356 - 1365
(2008/10/08)
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