- Heteroleptic Chini-Type Platinum Clusters: Synthesis and Characterization of Bis-Phospine Derivatives of [Pt3n(CO)6n]2- (n = 2-4)
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The reactions of [Pt3n(CO)6n]2- (n = 2-4) homoleptic Chini-type clusters with stoichiometric amounts of Ph2PCH2CH2PPh2 (dppe) result in the heteroleptic Chini-type clusters [Pt6(CO)10(dppe)]2-, [Pt9(CO)16(dppe)]2-, and [Pt12(CO)20(dppe)2]2-. Their formation is accompanied by slight amounts of neutral species such as Pt4(CO)4(dppe)2, Pt6(CO)6(dppe)3, and Pt(dppe)2. A similar behavior was observed with the chiral ligand R-Ph2PCH(Me)CH2PPh2 (R-dppp), and two isomers of [Pt9(CO)16(R-dppp)]2- were identified. All the new species were spectroscopically characterized by means of IR and 31P NMR, and their structures were determined by single-crystal X-ray diffraction. The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh3, as well as more rigid bidentate ligands, that is, CH2C(PPh2)2 (P^P), CH2(PPh2)2 (dppm), and o-C6H4(PPh2)2 (dppb). From a structural point of view, functionalization of anionic platinum Chini clusters preserves their triangular Pt3 units, whereas the overall trigonal prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such transformations may be just local deformations, as found in [Pt9(CO)16(dppe)]2-, [Pt9(CO)16(R-dppp)]2-, [Pt12(CO)22(PPh3)2]2-, and [Pt9(CO)16(PPh3)2]2-; an inversion of the cage from trigonal prismatic to octahedral, as observed in [Pt6(CO)10(dppe)]2- and [Pt6(CO)10(PPh3)2]2-; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt-Pt contact as found in [Pt12(CO)20(dppe)2]2-.
- Cesari, Cristiana,Ciabatti, Iacopo,Femoni, Cristina,Iapalucci, Maria Carmela,Mancini, Federica,Zacchini, Stefano
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- Photoinduced net [2 + 2 + 2] cycloreversion of platinum(II) glycolate complexes: A new approach to the generation of reduced, coordinatively unsaturated metal species and the activation of carbohydrate carbon-carbon single bonds
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Photolysis of thermally stable (1,2-bis(diphenylphosphino)ethane)platinum(II) glycolate complexes causes a facile net [2 + 2 + 2] cycloreversion of the 2,5-dioxaplatinacyclopentane moiety to give two organic carbonyl compounds and a reactive (dppe)Pt0 intermediate, as shown by trapping with dppe, ethylene, or hydrogen. Photolysis under hydrogen in the presence of (PPh3)4RuH2 leads to hydrocracking of the glycol carbon-carbon single bond.
- Andrews, Mark A.,Gould, George L.
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- Transition metal chemistry of low valent group 13 organyls
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The coordination of low-valent group 13 organyls EIR [E = Al, Ga, In; R = Cp*, C(SiMe3)3] to transition metals has attracted increasing interest over the past decade. Complexes and cluster compounds of these new ligands with a number of transition metals have been isolated and characterised. The EIR moiety is formally isolobal with CO and PR3 (R = alkyl, Cp*) or carbenes (R = chelating group) with varying σ-donor and π-acceptor properties depending on the organic group R as well as the group 13 metal E. In this review, different ways of forming M-E bonds such as substitution reactions of labile ligands or insertion of EIR into transition metal halide bonds are described. Furthermore, the reactivity of homoleptic complexes Ma(EIR) b, is discussed, outlining the use of these new complex types in bond activation reactions. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Gemel, Christian,Steinke, Tobias,Cokoja, Mirza,Kempter, Andreas,Fischer, Roland A.
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- Chemistry of o-Xylidene-Metal Complexes. Part 1. o-Xylidene-magnesium Reagents as Metallocyclic Precursors and Synthesis of (cod = cyclo-octa-1,5-diene); the X-Ray Crystal Structure of the Macrometallocycle 3>
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A high yield sythesis of a tetrahydrofuran (thf) solution of the di-Grignard reagent (A) derived from o-bis(chloromethyl)benzene is described, as well as that of an analogue obtained from 1,2-bis(chloromethyl)-4,5-dimethylbenzene.Cooling (A) to ca. -40 deg C yields the colourless chloride-free Mg(CH2C6H4CH2-o)(thf) of unknown structure, whereas at ambient temperature a concentrated solution ( > ca. 0.1 mol dm-3) slowly (days) deposits colourless needles of 3>.A single-crystal X-ray structure determination of the latter (R=0.054 for 1117 'observed' reflections at 295 K) shows it to be trimer.Crystals are orthorhombic, space group F2dd, with a=24.706(8), b=8.948(3), c=44.315(9) Angstroem, and Z=8; the trimeric unit lies on a crystallographic two-fold axis.Each of the three magnesiums is bridged to the other two by a -CH2C6H4CH2-o ligand, the pseudo tetrahedral co-ordination about each magnesium atom being completed by a pair of thf molecules.The utility of the di-Grignard reagent as a general metallocycle precursor is illustrated by the synthesis of (cod=cyclo-octa-1,5-diene) from .In contrast with 2> (dppe=Ph2PCH2CH2PPh2, tmen=Me2NCH2CH2NMe2) affords .
- Lappert, Michael F.,Martin, Tony R.,Raston, Colin L.,Skelton, Brian W.,White, Allan H.
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- Homo- and heteroleptic complexes of four-membered group 13 metal(I) N-heterocyclic carbene analogues with group 10 metal(0) fragments
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A series of complexes between recently developed four-membered group 13 metal(I) heterocycles and group 10 metal(0) fragments have been prepared and structurally characterized. One prepared complex, [Pt{Ga[N(Ar)] 2CNCy2}3] (Ar = C6H 3Pri2-2,6; Cy = cyclohexyl), possesses the shortest Pt-Ga bonds yet reported, the covalent components of which are suggested by theoretical studies to have significant π character.
- Green, Shaun P.,Jones, Cameron,Stasch, Andreas
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- Thermolysis studies on platinacycloalkane complexes
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Thermal decomposition studies on platinacycloalkanes of the type Pt(CH 2)mL2 (where m = 6,7,8,10 and L2 = dppp {1,3-bis(diphenylphosphino)propane}, dppe {1,2-bis(diphenylphosphino) ethane} or L = PPh3, tBu3P) are described. The results reveal that the organic product distribution depends on various factors such as the nature of ligand, the metal system, the mode of decomposition, the ring size and the temperature. Possible mechanistic pathways for the formation of various products are discussed. These platinacycloalkanes can be used as models for metallacycloalkane intermediates in catalytic reactions.
- Zheng, Feng,Sivaramakrishna, Akella,Moss, John R.
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p. 2457 - 2465
(2011/06/26)
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- Syntheses of mono- and dinuclear silylplatinum complexes bearing a diphosphino ligand via stepwise bond activation of unsymmetric disilanes
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Zero-valence platinum complex [Pt(dppe)(η2-C 2H4)] (1, dppe = 1,2-bis(diphenylphosphino)ethane) treated with disilanes HR1R2SiSiMe3 (a, R1 = R2 = Me; b, R1 = R2 = Ph; c, R1 = H, R2 = Ph) afforded the corresponding disilanylplatinum hydrides [Pt(dppe)(H)(SiR1R2SiMe3)] (2a-c) by oxidative addition of the Si-H bond to the platinum center. The 1,2-silyl migration in 2a,b led to the formation of bis(silyl)platinum complexes [Pt(dppe)(SiHR 1R2)(SiMe3)] (3a,b) with a first-order rate constant of 7.2(2) × 10-4 s-1 at 25°C for 2a and 3.86(4) × 10-4 s-1 at 40°C for 2b, whereas 2c with R1 = H followed by the transient generation of 3c dimerized rapidly to give the bis(μ-silylene)diplatinum complex [Pt(dppe)(μ-SiHPh)] 2 (4c) in a mixture of cis/trans isomers. Heating of the toluene solution of 3b at 100°C resulted in a similar dimerization to 4b. In addition, a trinuclear platinum complex [Pt3(dppe) 3(μ3-SiPh)2] (5) with a trigonal bipyramidal Pt3Si2 core arose from the reaction of 4c with 1 at 60°C in toluene. Unsymmetric disilanes therefore accomplished the syntheses of various monomeric and dimeric platinum complexes via 1,2-hydrogen and silyl migration to the platinum center. The Royal Society of Chemistry.
- Arii, Hidekazu,Takahashi, Makiko,Nanjo, Masato,Mochida, Kunio
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p. 6434 - 6440
(2010/09/06)
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- On the reactivity of alkylthio bridged 44 CVE triangular platinum clusters: Reactions with bidentate phosphine ligands
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The 44 cve (cluster valence electrons) triangular platinum clusters [{Pt(PR3)}3(μ-SMe)3]Cl (PR3 = PPh3, 2a; P(4-FC6H4)3, 2b; P(n-Bu)3, 2c) were found to react with PPh2CH 2PPh2 (dppm) in a degradation reaction yielding dinuclear platinum(I) complexes [{Pt(PR3)}2(μ-SMe)(μ-dppm)]Cl (PR3 = PPh3, 3a; P(4-FC6H4) 3, 3b; P(n-Bu)3; 3e) and the platinum(II) complex [Pt(SMe)2(dppm)] (4), whereas the addition of PPh2CH 2CH2PPh2 (dppe) to cluster 2a afforded a mixture of degradation products, among others the complexes [Pt(dppe) 2] and [Pt(dppe)2]Cl2. On the other hand, the treatment of cluster 2a with PPh2CH2CH2CH 2PPh2 (dppp) ended up in the formation of the cationic complex [{Pt(dppp)}2(μ-SMe)2]Cl2 (5). Furthermore, the terminal PPh3 ligands in complex 3a proved to be subject to substitution by the stronger donating monodentate phosphine ligands PMePh2 and PMe2Ph yielding the analogous complexes [{Pt(PR3)}2(μ-SMe)(μ-dppm)]Cl (PR3 = PMePh2, 3c; PMe2Ph, 3d). NMR investigations on complexes 3 showed an inverse correlation of Tolmans electronic parameter ? with the coupling constants 1J(Pt,P) and 1J(Pt,Pt). All compounds were fully characterized by means of NMR and IR spectroscopy. X-ray diffraction analyses were performed for the complexes [{Pt{P(4-FC6H 4)3}}2(μ-SMe)(μ-dppm)]Cl (3b), [Pt(SMe)2(dppm)] (4), and [{Pt(dppp)}2(μ-SMe) 2]Cl2 (5).
- Albrecht, Christian,Bruhn, Clemens,Wagner, Christoph,Steinborn, Dirk
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p. 1301 - 1308
(2009/04/25)
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- P-C and C-C bond formation by Michael addition in platinum-catalyzed hydrophosphination and in the stoichiometric reactions of platinum phosphido complexes with activated alkenes
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We recently proposed a new mechanism for platinum-catalyzed hydrophosphination of activated alkenes, in which nucleophilic attack of a phosphido ligand in the intermediate hydride complex Pt(diphos)(PR 2)-(H) (1) on the alkene H2C=CH(X) (X = CN or CO 2R) gave the zwitterion Pt(diphos)(H)(PR2CH 2CHX) (2), containing a cationic Pt center and a phosphine ligand with a pendent stabilized carbanion. Subsequent C-H bond formation involving the Pt-H and the carbanion would yield the product R2PCH 2CH2X (3) and regenerate the catalyst, while attack of the carbanion on another alkene would yield byproducts derived from more than one alkene, such as R2P(CH2CH(X))nCH 2CH2X (7). Several tests of this mechanism and related pathways for product and byproduct formation were investigated. Attempts to trap the proposed carbanion with another electrophile led to the development of a Pt-catalyzed three-component coupling of secondary phosphines, tert-butyl acrylate, and benzaldehyde, yielding the functionalized phosphines R 2PCH2CH(CO2t-Bu)(CHPh(OH)) (R2P = Ph2P (10a); R2P = Me(Is)P (10b, Is = 2,4,6-(i-Pr) 3C6H2)). Reactions of the complexes Pt(diphos)(R′)(PR2) (diphos = (R,R)-Me-Duphos, R′ = Me, PR2 = PPh2 (11), PPh(i-Bu) (12); R′ = Ph, PR 2 = PMeIs (13); diphos = dppe, R' = Me, PR2 = PPh 2 (14), PPh(i-Bu) (15)), models for 1, with tert-butyl acrylate or acrylonitrile gave mixtures of products including Pt-(diphos)(R′)(CH(X) CH2PR2) (A, X = CO2t-Bu or CN), Pt(diphos)(R′)(CH(X)CH2CH(X)CH2PR2) (B), R2PCH2CH2X (3), R2P(CH 2CH(X))n(CH2CH2X) (7), and, in some cases, the dinuclear phosphido-bridged cations [(Pt(diphos)(Me)) 2(μ-PR2)]+ (17). When tert-butanol or water was added to these reactions, more of the phosphines 3 and 7, and less of the intermediates A and B, were formed. Decomposition of A and B gave unidentified platinum dialkyls (C), tentatively formulated as Pt(diphos)(R′)(CH(X) R″). The complex Pt(dppe)(Me)(CH(Me)CO2t-Bu) (21), a model for A, B, and C, was generated either from Pt(dppe)(Cl)-(CH(Me)CO2t-Bu) (20) and ZnMe2 or from Pt(dppe)(Me)(Cl) (19) and ZnBr(CH(Me)CO 2t-Bu)·THF; complexes 20 and 21 did not react with tert-butyl acrylate. These observations are consistent with the proposed nucleophilic mechanism for P-C and C-C bond formation.
- Scriban, Corina,Glueck, David S.,Zakharov, Lev N.,Kassel, W. Scott,DiPasquale, Antonio G.,Golen, James A.,Rheingold, Arnold L.
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p. 5757 - 5767
(2008/10/09)
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- Water-promoted reaction of a platinum(II) oxo complex with ethylene
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Treatment of [(dppp)Pt(μ-O)]2(LiOTf)2 (dppp = Ph2P(CH2)3PPh2) with ethylene in the presence of trace amounts of water results in oxygen atom transfer to one arm of the bidentate phosphine ligand and formation of(dpppO)Pt(η2-CH2=CH2)2 (dpppO = Ph2P(CH2)3P(O)-Ph2). Further investigation reveals that the reaction of [L2Pt(μ-O)]2(LiOTf)2 with water forms (dppp)Pt(OH)2, which acts as a catalyst for the oxygen atom transfer reaction. The analogous oxo complex [(PPh3)2Pt(μ-O)]2-(LiBF4)2 does not react with ethylene under similar conditions. These results indicate that hydroxo complex intermediates should be considered in oxygen atom transfer reactions.
- Flint, Bruce,Li, Jian-Jun,Sharp, Paul R.
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p. 997 - 1000
(2008/10/08)
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- Coordination chemistry of P-rich phosphanes and silylphosphanes. XVIII. Syntheses and structures of [{η2-tBu2P-P=P-PtBu 2}Pt(PR3)2]
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tBu2P-P=P(Me)tBu2 reacts with [{η2-C2H4} -Pt(PR3)2] as well as with [{η2-tBu2P-P}Pt(PR3) 2] yielding [{η2-tBu2P-P=P-PtBu 2}Pt(PR3)2]; PR3 = PMe3 3a, PEtPh2 3b, 1/2dppe 3c, PPh3 3d, P(p-Tol)3 3e. All compounds are characterized by 1H and 31P NMR spectra, for 3b and 3d also crystal structure determinations were performed. 3b crystallizes in the triclinic space group P1 (No. 2) with a = 1212.58(7), b = 1430.74(8), c = 1629.34(11) pm, α = 77.321(6), β= 70.469(5), γ = 87.312(6)°. 3d crystallizes in the triclinic space group P1 (No. 2) with a = 1122.60(9), b = 1355.88(11), c = 2025.11(14) pm, α = 83.824(9), β = 82.498(9), γ = 67.214(8)°.
- Krautscheid,Matern,Fritz,Pikies
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p. 253 - 257
(2008/10/08)
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- Relative hydride, proton, and hydrogen atom transfer abilities of [HM(diphosphine)2]PF6 complexes (M = Pt, Ni)
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A series of [M(diphosphine)2]X2, [HM(diphosphine)2]X, and M(diphosphine)2 complexes have been prepared for the purpose of determining the relative thermodynamic hydricities of the [HM(diphosphine)2]X complexes (M = Ni, Pt; X = BF4, PF6; diphosphine = bis(diphenylphosphino)ethane (dppe), bis(diethylphosphino)ethane (depe), bis(dimethylphosphino)ethane (dmpe), bis(dimethylphosphino)propane (dmpp)). Measurements of the half-wave potentials (E1/2) for the M(II) and M(0) complexes and pKa measurements for the metal hydride complexes have been used in a thermochemical cycle to obtain quantitative thermodynamic information on the relative hydride donor abilities of the metal - hydride complexes. The hydride donor strengths vary by 23 kcal/mol and are influenced by the metal, the ligand substituents, and the size of the chelate bite of the diphosphine ligand. The best hydride donor of the complexes prepared is [HPt(dmpe)2](PF6), a third-row transition metal with basic substituents and a diphosphine ligand with a small chelate bite. The best hydride acceptors have the opposite characteristics. X-ray diffraction studies were carried out on eight complexes: [Ni(dmpe)2](BF4)2, [Ni(depe)2](BF4)2, [Ni(dmpp)2](BF4)2, [Pt(dmpp)2](PF6)2, [Ni(dmpe)2(CH3CN)](BF4)2, [Ni(dmpp)2(CH3CN)](BF4)2, Ni(dmpp)2, and Pt(dmpp)2. The cations [Ni(dmpp)2]2+ and [Pt(dmpp)2]2+ exhibit significant tetrahedral distortions from a square-planar geometry arising from the larger chelate bite of dmpp compared to that of dmpe. This tetrahedral distortion produces a decrease in the energy of the lowest unoccupied molecular orbital of the [M(dmpp)2]2+ complexes, stabilizes the +1 oxidation state, and makes the [HM(dmpp)2]+ complexes poorer hydride donors than their dmpe analogues. Another interesting structural feature is the shortening of the M-P bond upon reduction from M(II) to M(0).
- Berning, Douglas E.,Noll, Bruce C.,DuBois, Daniel L.
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p. 11432 - 11447
(2007/10/03)
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- Reactions of organotin(IV) compounds with platinum complexes. Part II. Oxidative addition of SnRxCl4-x to [Pt(COD)2] and subsequent reactions with tertiary phosphines
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Organotin(IV) compounds SnRxCl4-x (R=Me, Ph; x=4-0) add oxidatively to [Pt(COD)2] (COD=cycloocta-1,5-diene) to yield platinum(II) complexes in which Pt has inserted into the Sn-Cl or Sn-R bonds, displacing one COD entity. The new com
- Al-Allaf, Talal A. K.
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- Coordination chemistry of P-rich phosphanes and silylphosphanes. XV. Influence of the chelate compounds dppe and dppp on formation and properties of the Pt complexes of tBu2P-P
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The chelating ligands dppe and dppp replace the PPh3 groups in [η2-{tBu2P-P}Pt(PPh3) 2] 1 yielding [η2-{tBu2P-P}Pt(dppe)] 2 and [η2-{t
- Krautscheid,Matern,Fritz,Pikies
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p. 501 - 505
(2008/10/09)
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- Unexpected substitution reactions of bis(phosphine)platinum ethene complexes
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Reaction of [Pt(C2H4)(PR3)2] (R = Ph or C6H4Me-4) with moderately bulky phosphines at low temperatures did not give the expected tris- or tetrakis-phosphine complexes. Instead, mixed-phosph
- Chaloner, Penny A.,Broadwood-Strong, Gillian T. L.
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p. 1039 - 1043
(2007/10/03)
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- Fluoride-induced reduction of palladium(II) and platinum(II) phosphine complexes
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A novel redox reaction involving fluoride and phosphine complexes of palladium(II) is reported. The scope of this reaction has been investigated using the ligands PPh3, Ph2P(CH2)nPPh2 (n = 1-4), Ph2PCH2C(CH3)2CH2PPh 2, Ph2PCH3, and P(CH2CH2CN)3; several solvents including DMSO, pyridine, acetonitrile, and THF; and either n-Bu4NF·3H2O or KF/18-crown-6 as the fluoride source. The reduction products are palladium(0) phosphine complexes for which this reaction offers a convenient synthetic route. 31P and 19F NMR spectra permitted identification of the initial oxidation products as difluorophosphoranes (R3PF2), which subsequently hydrolyzed, forming phosphine oxides if a hydrated fluoride source is used. Results implicating a fluoride-induced redox reaction in the thermal decomposition of [(Ph3P)3PdCl]BF4 to yield [Pd3Cl(PPh2)2(PPh3) 3]BF4 are also presented. Preliminary results indicate that platinum complexes also undergo this reaction, but nickel complexes yield NiF2. The X-ray parameters for Pd(dppp)2 (dppp = 1,3-bis(diphenyphosphino)propane) are: monoclinic, space group C2/c (No. 15), a = 18.396 (2) A?, b = 13.290 (1) A?, c = 20.186 (2) A?, β = 109.383 (5)°, and Z = 4.
- Mason,Verkade
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p. 2212 - 2220
(2008/10/08)
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- Mechanistic studies of the thermolytic and photolytic rearrangement of [bis(diphenylphosphino)ethane]bis(neophyl)platinum(II)
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Comparative mechanistic studies are presented of the thermolytic and photolytic behavior of the bis-(neophyl)platinum(II) derivative Pt(CH2CMe2Ph)2(dppe) (neophyl = 2-methyl-2-phenylpropyl; dppe = 1,2-bis(diphenylphoephino)ethane). Thermolytic rearrangement is less facile than for monodentate P-donor analogues and affords the platinaindan Pt(2-C6H4CMe2CH2)(dppe) by intramolecular aromatic C-H activation and H-transfer to eliminated tert-butylbenzene. The kinetic isotope effect on metallacyclization (kobsH/kobsD = 2.40) and the negative activation entropy (ΔS≠obs = -13 (±4) J·K-1·mol-1) suggest a pathway in which scission of one Pt-P is mechanistically significant but C-H addition to Pt has the most energetic transition state. Photolytic rearrangement in toluene-d0 proceeds by two major paths, both of which involve primary Pt-C homolysis. The resultant neophyl radical may then provide a destination for migrating hydrogen in a cyclometalation of the residual 17-electron organoplatinum species, leading to Pt(2-C6H4CMe2CH2)(dppe). Alternatively, H-abstraction by the neophyl fragment within the solvent cage produces a benzyl radical which recombines with the metal moiety to give Pt(CH2Ph)(CH2Me2Ph)(dppe). This benzylplatinum complex is also photolabile, giving ultimately platinaindan via benzyl radical expulsion. This indirect solvent metalation is not evident during photolysis in toluene-d8 and in benzene.
- Ankianiec, Bernardeta C.,Hardy, David T.,Thomson, S. Katherine,Watkins, W. Niall,Young, G. Brent
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p. 2591 - 2598
(2008/10/08)
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- Synthesis, structural properties, and reaction chemistry of hydrido alkyl diaminocarbene complexes of platinum(II). Cleavage of the metal-carbene and metal-alkyl bonds and synthesis of formamidines and cis hydrido carbene derivatives
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Hydrido alkyl carbene complexes of the type PtH(RX)[C(N(CH2)nCH2)NHR](PPh 3) (n = 2, RX = CF3 (1), CH2CN (2), CH2CF3 (3); n = 4, RX = CF3 (4); R = p-MeOC6H4) have been prepared by reaction of the parent isocyanide precursors PtH(RX)(CNR)(PPh3) with azetidine or piperidine. Complexes 1-4 have cis Pt-H and Pt-RX bonds with the carbene ligand trans to hydride. They have been characterized by analytical data and their IR and 1H, 19F, 31P, and 13C NMR spectra. Compound 2 was also structurally characterized by X-ray analysis. The triclinic crystal, space group P1, has lattice parameters a = 12.998 (3) ?, b = 11.833 (2) ?, c = 10.257 (2) ?, α = 100.83 (4)°, β = 80.72 (3)°, γ = 114.20 (4)°, and Z = 2. The structure was refined to R = 0.022 and Rw = 0.022. The coordination geometry around the Pt atom in 2 is distorted square planar. The geometry of the carbene ligand is essentially planar. The plane of the carbene intersects the platinum square plane at an angle of 73.7 (2)°. The molecules of 2 are associated in the solid state to give dimers through intermolecular interactions between the nitrogen atom of CH2CN and the aminocarbene proton of an adjacent molecule. Important bond lengths are Pt-C(carbene) = 2.069 (4) ?, Pt-H = 1.61 (4) ?, Pt-CH2CN = 2.116 (7) ?, and Pt-P = 2.252 (2) ?. The isocyanide complex PtH(CF3)(CNR)(PPh3) reacts with excess HNEt2 in refluxing THF for 3 days to give a mixture of isomers with the carbene ligand trans to hydride (5a), PPh3 (5b), or trifluoromethyl (5c). Complexes 1-5 are stable in the solid state and in solution, and no reductive elimination of HRX is observed in refluxing THF for several hours even in the presence of diphenylacetylene. However, complexes 2 and 3, but not 1 and 4, react with equivalent amounts of PPh3 to give trans-(PPh3)2PtH[C(NCH2CH2CH 2)NR] (6) and formation of CH3CN and CH3CF3, respectively. Isotopic experiments with N-D and Pt-D derivatives indicate that this reaction proceeds through the protonolysis of the metal-alkyl bond by the aminocarbene proton, promoted by PPh3. Complex 6 reacts with HBF4 to give the hydrido carbene derivative trans-{(PPh3)2PtH[C(NCH2CH2CH 2)NHR]}BF4 (7). Similarly the reactions of 2 with equimolar amounts of diphosphines yield (P-P)PtH[C(NCH2CH2CH2)NR] (P-P = Ph2PCH2CH2PPh2 (8), Ph2PCH=CHPPh2 (9)) and CH3CN. Complexes 8 and 9 react with HBF4 to produce the cis hydrido carbene derivatives {(P-P)PtH[C(NCH2CH2CH2)NHR]}BF4 (10 and 11, respectively). On the other hand, complexes 1 and 4 react with diphosphines to give metal-carbene bond cleavage and formation of (P-P)PtH(CF3) and the formamidines HC(NCH2CH2CH2)=N(R) and HC[N(CH2)4CH2]=N(R), respectively.
- Michelin, Rino A.,Bertani, Roberta,Mozzon, Mirto,Zanotto, Livio,Benetollo, Franco,Bombieri, Gabriella
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p. 1449 - 1459
(2008/10/08)
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- Studies of CO labilization and intramolecular hydride transfer reactions in group VI (Cr, Mo, W) metal-platinum heterobimetallic μ-phosphido hydrido carbonyl complexes
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Oxidative addition of the P-H bond of the secondary phosphine complexes M(CO)5(PR2H) (M = Cr, Mo, W; R = Ph, nPr) to Pt(C2H4)(PPh3)2 gives (OC)5M(μ-PR2)PtH(PPh3)2, which rapidly loses CO (a reversible process) to give (OC)4M(μ-PR2)(μ-H)Pt(PPh3)2 via a "platinum-assisted mechanism" involving PPh3 dissociation, formation of a μ-carbonyl intermediate (OC)4M-(μ-PR2)(μ-CO)PtH(PPh3), subsequent rearrangement to (OC)4M(μ-PR2)(μ-H)Pt(CO)(PPh3), and substitutional loss of CO from Pt (by PPh3). The complexes (OC)4M(μ-PPh2)(μ-H)Pt(PR3)2 (PR3 = PEt3, PMe2Ph) can be obtained from the reaction of M(CO)5(PPh2Li) and trans-PtHCl(PR3)2. Reaction of M(CO)5(PPh2H) with Pt(1,5-COD)2 in the presence of ethylene gives (OC)5M(μ-PPh2)PtH(COD), which rapidly rearranges, via β-H transfer, to the complex (OC)4M(μ-PPh2)(μ-CO)Pt(η 3-cyclooctenyl). Addition of M(CO)5(PPh2H) to Pt(C2H4)2(PCy3) gives the complexes (OC)4M(μ-PPh2)(μ-H)Pt(CO)(PCy3) while reaction of cis-(OC)4M(PEt3)(PPh2H) (M = Mo, W) with Pt(C2H4)2(PCy3) gives mer-(OC)3(PEt3)M(μ-PPh 2)(μ-CO)PtH(PCy3). For M = Mo this μ-carbonyl terminal-hydrido complex equilibrates with a small amount of the μ-hydrido terminal-carbonyl isomer fac-(OC)3(PEt3)Mo(μ-PPh 2)(μ-H)Pt(CO)(PCy3). The molecular structure of the complexes (OC)4Cr(μ-PPh2)(μ-H)Pt(PEt3)2 and (OC)4Cr(μ-PPh2)(μ-CO)Pt(η 3-cyclooctenyl) (contains a semibridging carbonyl ligand) have been determined by single-crystal X-ray diffraction methods. The complex (OC)4Cr(μ-PPh2)(μ-H)Pt(PEt3)2 crystallizes in the space group Cc with a = 16.719 (9) A?, b = 11.468 (3) A?, c = 18.275 (6) A?, β = 113.68 (3)°, V = 3209 A?3, and Z = 4. The structure was refined to R = 0.0346 and Rw = 0.0401 for the 3801 reflections with I > 3σ(I). Corresponding data for (OC)4Cr(μ-PPh2)(μ-CO)Pt(η 3-cyclooctenyl) are space group P21/a, a = 25.212 (3) A?, b = 10.172 (2) A?, c = 9.577 (2) A?, β = 90.53 (1)°, V = 2456 A?3, and Z = 4. R = 0.0329, Rw = 0.0382 for 3384 reflections with I > 3σ(I).
- Powell, John,Gregg, Michael R.,Sawyer, Jeffery F.
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p. 4451 - 4460
(2008/10/08)
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- NMR and kinetic studies on phosphine-induced coupling of (η3-methallyl) (acetylacetonato) palladium and -platinum: Uniquely facile C-C bond formation with an (η3-allyl) platinum complex
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Low-temperature 1H NMR measurements on a mixture of M(η3-CH2CMeCH2) (acac) (1, M = Pt; 2 M = Pd) and 2 equiv of PPh3 or 1 equiv of (Z)-Ph2PCH=CHPPh2 in dichloromethane gave unambiguous evidence for the formation of the ion pair [M(η3-CH2CMeCH2)(PR3) 2]+[CH(COMe)2]-. On warming these solutions to room temperature, the formation of moderate to good yields of the C-C coupling product CH2-CMeCH2CH(COMe)2 and zerovalent metal-phosphine complexes occurred. The kinetics of this process were examined by means of UV-visible spectroscopy to give evidence for almost exclusive participation of [M(η3-CH2CMeCH2)(PR3) 2]+[CH(COMe)2]- (M = Pt, PR3 = PPh3; M = Pd, PR3 = 1/2Ph2PCH2CH2PPh2) in the rate-determining step. The collapse of these ion pairs to the product was estimated to be faster in benzene than that in dichloromethane, the latter in turn having been found to be faster than that in acetonitrile/THF. The platinum analogue 1 reacted more slowly than the palladium analogue 2, but the rate difference was not so remarkable as was the case in the reductive elimination of dialkylmetal complexes of these two metals. The origin of this unique metal effect found in the reaction of 1 and 2 is discussed in terms of the nature of the η3-allyl-metal bonding.
- Kurosawa, Hideo,Ishii, Koichiro,Kawasaki, Yoshikane,Murai, Shinji
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p. 1756 - 1760
(2008/10/08)
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- HYDROSILYLATION CHEMISTRY AND CATALYSIS WITH cis-PtCl2(PhCH equals CH2)2.
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The precursor cis-PtCl//2(PhCH equals CH//2)//2 is shown to catalyze (i) the hydrosilylation of various terminal olefins and acetylenes, (ii) the reduction of carbonyl functions with silanes in the presence of pyridine or aniline as cocatalyst, and (iii) the formation of R//3**1SiOR**2 from R//3**1SiH and R**2OH. The hydrosilylation of styrene is shown to proceed via reduction of PtCl//2(PhCH equals CH//2)//2 to Pt(PhCH equals CH//2)//3 with concomitant formation of 2 equiv of R//3SiCl and 1 equiv of PhCH//2CH//3. Extensive **1**9**5Pt measurements together with **1**3C studies on complexed styrene selectively enriched at the beta -carbon support the formationof the Pt(0) complex. The precursor cis-PtCl//2(PhCH equals CH//2)//2 is suggested to arise from the trans isomer which is identified by **1**9**5Pt NMR and its reaction chemistry.
- Caseri,Pregosin
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p. 1373 - 1380
(2008/10/08)
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- A convenient and novel route to bis(η-alkyne)platinum(0) and other platinum(0) complexes from Speier's hydrosilylation catalyst H2[PtCl6]·xH2O. X-ray structure of [Pt{(η-CH2=CHSiMe2)2O}(P-t-Bu3)]
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Evidence that the hydrosilylation catalyst, obtained by refluxing H2[PtCl6]·xH2O in (Me2ViSi)2O (solution A), is a Pt(0) species comprises (i) the isolation and X-ray characterization of [Rt{(η-CH2CHMe2Si)2O}(P-t-Bu3)], after addition of P-t-Bu3 to A, (ii) the convenient high-yield synthesis of various other Pt(0) complexes from A, and (iii) CV, GC/MS, and 195Pt NMR data.
- Chandra, Grish,Lo, Peter Y.,Hitchcock, Peter B.,Lappert, Michael F.
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p. 191 - 192
(2008/10/08)
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- β-Hydride Elimination from Methoxo vs. Ethyl Ligands: Thermolysis of (DPPE)Pt(OCH3)2, (DPPE)Pt(CH2CH3)(OCH3) and (DPPE)Pt(CH2CH3)2
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Thermolysis of (DPPE)Pt(OCH3)2 (1) (DPPE=1,2-bis(diphenylphosphino)ethane, (C6H5)2PCH2CH2P(C6H5)2) at 25 deg C leads to a mixture of methanol, formaldehyde oligomers, and small amounts of carbon monoxide (CO).Kinetics experiments, labeling studies, and solvent effects suggest this decomposition proceeds by initial preequilibrium β-hydride migration to the metal followed by rate-limiting release of organic products.While 1 decomposes at 25 deg C and (DPPE)Pt(CH2CH3)2 only slowly releases ethylene and ethane at 160 deg C, (DPPE)Pt(CH2CH3)(OCH3) (3) decomposes to a mixture of ethylene, ethane, methanol, and formaldehyde oligomers at 100 deg C.The predominance of ethylene over ethane suggests thermolysis proceeding by β-elimination from the ethyl ligand is energetically easier than the comparable process from the methoxo ligand by 0.3 kcal/mol.Labeling studies confirm the preequilibrium nature of this β-elimination.The relative M-C vs.M-O bond strengths are discussed in light of this information.
- Bryndza, Henry E.,Calabrese, Joseph C.,Marsi, Marianne,Roe, D. Christopher,Tam, Wilson,Bercaw, John E.
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p. 4805 - 4813
(2007/10/02)
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- MIXED LIGAND COMPLEXES OF PLATINUM(0) CONTAINING DIPHOSPHINES
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The reaction of PtCl2L (L = diphosphine) with the appropriate diphosphine L' in ethanol followed by reduction with aqueous sodium borohydride leads to either disproportionation to give mixtures of the bis(diphosphine) complexes PtL2 and PtL'2 or to the fo
- Clark, Howard C.,Kapoor, Pramesh N.,McMahon, Ian J.
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p. 107 - 116
(2007/10/02)
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