- Chiral platinum duphos terminal phosphido complexes: Synthesis, structure, phosphido transfer, and ligand behavior
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Treatment of Pt halide precursors with the secondary phosphine PHMe(Is) in the presence of the base NaOSiMe3 gave the terminal phosphido complexes Pt(Duphos)(Ph)(PMeIs) (Is = 2,4,6-(i-Pr)3C 6H2, Duphos = (R,R)-Me-Duphos (1), (R,R)-i-Pr-Duphos (2)), Pt((R,R)-Me-Duphos)(X)(PMeIs) (X = I (3), Cl (4)), and Pt((R,R)-Me-Duphos) (PMeIs)2 (5). Low-barrier pyramidal inversion in the phosphido complexes was investigated by 31P NMR spectroscopy. Protonation of 1-5 with HBF4 gave the secondary phosphine complexes [Pt(Duphos)(Ph)(PHMeIs)][BF4] (Duphos = (R,R)-Me-Duphos (6), (R,R)-i-Pr-Duphos) (7)), [Pt((R,R)-Me-Duphos)(X)(PHMeIs)][BF4] (X = I (8), Cl (9)), and [Pt((fl,/?)-Me-Duphos)(PHMeIs)2][BF 4]2 (10); cations 6, 9, and 10 were prepared independently from Pt chloride precursors using Ag(I) salts and PHMe(Is) and then deprotonated to yield phosphido complexes 1-5. Oxidation of the phosphido ligands in 4 and 5 with H2O2 gave Pt((R,R)-Me-Duphos)(Cl) (P(O)MeIs) (11) and Pt((R,R)-Me-Duphos)(P(O)-MeIs)2 (12), respectively. Complexes 1-6, 9, and 11 were structurally characterized by X-ray crystallography; structural and 31P NMR results suggest the trans influence order P(O)MeIs > PMeIs > PHMe(Is). Reaction of 1 with [Pd(allyl)Cl]2, followed by treatment with dppe, gave Pt((R,R)-Me-Duphos)-(Ph)(Cl), PMeIs(allyl) (13), and Pd(dppe)2. Treatment of 1 with Pd(P(o-Tol)3)2 gave an equilibrium mixture containing the two-coordinate palladium complex Pd(P(o-Tol) 3)(μ-PMeIs)Pt((R,R)-Me-Duphos)(Ph) (14), Pd(P(o-Tol) 3)2, P(o-Tol)3, and 1.
- Scriban, Corina,Glueck, David S.,DiPasquale, Antonio G.,Rheingold, Arnold L.
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- Electroanalytical and Spectrophotometric Investigations on the Metal(II)-1,2-Bis(diphenylphosphino)ethane-Acetylacetonate System (M = Ni, Pd, or Cu) in Acetonitrile
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The soft-hard mixed-ligand complexes + have been characterized by a combination of electroanalytical and spectrophotometric measurements.These species can easily be synthesized in acetonitrile both by a ligand conproportionation reaction upon starting from the corresponding acetylacetonate and diphosphine homoleptic species and from stoicheiometric amounts of 2+ and acac-.Upon reaction of equimolar amounts of and dppe, the same synthesis can be achieved in the case of M = Pd, while for M = Ni the ligand-exchange reaction is followed by the reduction of nickel(II) to nickel(I) and nickel(0) occuring at the expense of the displaced acac-.The mixed-ligand complex cannot ne obtained for Cu in that copper(II) is reduced to copper(I) when dppe is present.In this low oxidation state copper is unable to co-ordinate acac- and appears to be stable as + or +.
- Daniele, Salvatore,Basato, Marino,Corain, Benedetto,Favero, Giancarlo,Bontempelli, Gino
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Read Online
- 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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p. 4161 - 4176
(2007/10/03)
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- Palladium-catalyzed asymmetric phosphination. Enantioselective synthesis of PAMP-BH3, ligand effects on catalysis, and direct observation of the stereochemistry of transmetalation and reductive elimination
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The complexes Pd(diphos)(o-An)(I) (o-An = o-MeOC6H4; diphos = dppe (3), (S,S)-Chiraphos (4), (R,R)-Me-Duphos (5), (R,S) -t-Bu-Josiphos (6), (R)-Tol-Binap (7)) were prepared. Complex 6 catalyzed the coupling of PH(Me)(Ph)(BH3) (2) with o-AnI in the presence of base to yield PAMP-BH3 (P(Me)(Ph)(o-An)(BH3) (1)) in low enantiomeric excess. The course of stoichiometric reactions of 3-7 with 2 and NaOSiMe3 depended on the diphosphine ligand. Complexes 6 and 7 gave PAMP-BH3 (1) and Pd(0) species; no intermediates were observed. With 3, the intermediate Pd(dppe)(o-An)(P(Me)(Ph)(BH3)) (10) was observed by 31P NMR, while 4 gave the isolable diastereomeric palladium complexes (Sp)-Pd((S,S)-Chiraphos)(o-An)(P(Me)(Ph)(BH3)) (11a) and (RP)-Pd((S,S)-Chiraphos)(o-An)(P(Me)(Ph)(BH3)) (11b), whose absolute configurations were determined by X-ray crystallography after separation. The analogous Pd((R,R)-Me-Duphos)(o-An)(P(Me)(Ph)(BH3)) diastereomers (12a,b) were also separated and isolated. Treatment of 4 with highly enantioenriched 2 (R or S) gave 11a or 11b in high diastereomeric excess with retention of configuration at phosphorus. P-C reductive elimination from either isomer of highly diastereoenriched 11 in the presence of excess diphenylacetylene yielded Pd((S,S)-Chiraphos)(PhC≡CPh) (14) and highly enantioenriched PAMP-BH3 (1), with retention of configuration.
- Moncarz, Julian R.,Brunker, Tim J.,Jewett, John C.,Orchowski, Michael,Glueck, David S.,Sommer, Roger D.,Lam, Kin-Chung,Incarvito, Christopher D.,Concolino, Thomas E.,Ceccarelli, Christopher,Zakharov, Lev N.,Rheingold, Arnold L.
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p. 3205 - 3221
(2008/10/08)
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- Taking too many precautions in making a catalyst is never a loss of time: A lesson we learned at our own expense
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The reaction in MeOH between the bis-chelate complex [Pd(dppe)2](OAc)2 and Pd(OAc)2 to give the monochelate product Pd(OAc)2(dppe) is assisted by free acetate ion, and its rate is proportional to the concentrations of both reagents (dppe = 1,2-bis(diphenylphosphino)-ethane). The aggregation of Pd(OAc)2 in CH2Cl2 and the low dielectric constant of this solvent are proposed to be important factors in accelerating the formation of Pd(OAc)2(dppe) in CH2Cl2.
- Bianchini, Claudio,Meli, Andrea,Oberhauser, Werner
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p. 4281 - 4285
(2008/10/08)
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- Synthesis and reactivity of a novel palladium germylene system
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The synthesis of three novel Pd germylene complexes is reported. (Ph3P)2PdGe[N(SiMe3)2]2 (1) was synthesized by ligand substitution of (Ph3P)4Pd, whereas (Et3P)PdGe[N(SiMe3)2]2 (2) and {appePdGe[N(SiMe3)2]2}2 (3b) (dppe = (diphenylphosphino)ethane) were synthesized by photolytic reduction of their corresponding phosphine oxalato complexes followed by addition of the germylene ligand. In solution, 3b exists in equilibrium with the monomeric dppePdGe[N(SiMe3)2]2 (3a). The germylene ligand of 2 was found to be 1 order of magnitude more labile than the analogous Pt system and 2 orders of magnitude less labile than the analogous Ni system. The reactivity of these new palladium germylenes toward O2 is described.
- Cygan, Zuzanna T.,Bender IV, John E.,Litz, Kyle E.,Kampf, Jeff W.,Banaszak Holl, Mark M.
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p. 5373 - 5381
(2008/10/08)
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- (Phenylalkyl)palladium complexes containing β-hydrogen atoms: Synthesis and characterization of [PdR2(dppe)], [PdR(SPh)(dppe)] (R = CH2CH2Ph, CH2CH2CH2Ph, CH2CHMePh), and [Pd(CH2CH2CH2Ph)X(dppe)] (X = I, Br, Cl)
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Reactions of HgR2 (R = CH2CH2Ph, 1a; CH2CH2CH2Ph, 1b; CH2CHMePh, 1c) (prepared from HgCl2 and the requisite Grignard compounds) with lithium in toluene afforded (phenylalkyl)lithium compounds LiR (2a-c) in yields of between 64 and 81%. At -30 °C, they react with [PdCl2(dppe)] [dppe = 1,2-bis(diphenylphosphanyl)ethane] yielding bis(phenylalkyl)palladium(II) complexes [PdR2(dppe)] (3a-c) which were isolated (Tdec = 159 °C, 3a; 80 °C, 3b; 145 °C, 3c) and fully characterized by 1H, 13C, and 31P NMR spectroscopy. Single-crystal X-ray diffraction of [Pd(CH2CH2Ph)2(dppe)] (3a) showed that the palladium atom is square-planar coordinated by two 2-phenylethyl ligands and the dppe ligand. The two CH2CH2Ph ligands exhibite nearly a fully staggered conformation. Overall, a good approximation for the complex is that it has C2 symmetry with the C2 axis defined by the Pd atom and the midpoint of the central C-C bond of the dppe ligand. Bis(phenylalkyl)palladium complexes 3a and 3b reacted with PhSH in a 1:1 ratio yielding [PdR(SPh)(dppe)] (R = CH2CH2Ph, 5a; CH2CH2CH2Ph, 5b), whereas in the case of complex 3c, besides [Pd(CH2CHMePh)(SPh)(dppe)] (5c), a considerable amount of [Pd(SPh)2(dppe)] (6a) was formed. Reactions of 3b with the less acidic alkanethiols iPrSH and tBuSH resulted in the formation of [Pd(CH2CH2CH2Ph)(SR′)(dppe)] (R′ = iPr, 5d; tBu, 5e) along with smaller amounts of [Pd(SR′)2(dppe)] (6) and [Pd(dppe)2] (7). Furthermore, complex 3b was found to react in THF with disulfides R′SSR′ (R· = Ph, Bz, Me), yielding [Pd(CH2CH2CH2Ph)(SR′)(dppe)] (R′ = Ph, 5b; Bz, 5f, Me, 5g) with small amounts (3-13%) of [Pd(SR′)2(dppe)] (6) as side products. The corresponding reaction with MeSe-SeMe afforded [Pd(CH2CH2CH2Ph)(SeMe)(dppe)] (8a) and 3% of [Pd(SeMe)2(dppe)] (9a) and [Pd(dppe)2] (7). Reactions of complex 5b with MeI and H2C=CHCH2Br in tetrahydrofuran and with neat H2C=CHCH2Cl readily proceeded at -30 °C to give halo(3-phenylpropyl)palladium complexes [Pd(CH2CH2CH2Ph)X(dppe)] (X = I, 10a; Br, 10b; Cl, 10c). They were isolated as pale yellow powdery/microcrystalline substances and fully characterized by 13C and 31P NMR spectroscopy. Solutions of complexes 10 in THF decompose rapidly above -30 °C. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Spaniel, Thomas,Schmidt, Harry,Wagner, Christoph,Merzweiler, Kurt,Steinborn, Dirk
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p. 2868 - 2877
(2007/10/03)
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- Synthesis, characterization, and reactivity of cationic hydride [HPd(diphosphine)2]+CF3 SO3-, the missing member of the family [HM(dppe)2]+X- (M = Ni, Pd, Pt). DFT QM/MM structural predictions for the [HPd(dppe)2]+ moiety
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The synthesis, characterization, and properties of the cationic hydride [HPd(dppe)2]+CF3SO3 -·1/8THF, the missing member of the family [HM(dppe)2]+X- (M = Ni, Pd, Pt), are described. The Pd hydride is not stable in solution and may react as either a proton or a hydride donor. DFT QM/MM calculations of the [HPd(dppe)2]+ moiety have allowed us to predict its structure and reactivity.
- Aresta, Michele,Dibenedetto, Angela,Amodio, Eliana,Papai, Imre,Schubert, Gabor
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p. 6550 - 6552
(2008/10/08)
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- Full picture of the catalytic cycle underlying palladium-catalyzed metal-carbon bond formation
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A catalytic cycle of reaction between [η 5-1-(diphenylphosphino)-2,4-diphenylcyclopentadienyl]tricarbonylmetal iodides, [η5-1-Ph2P-2,4-Ph2C5H 2]M(CO)3I (1a, M = Mo; 1b, M = W), with zerovalent palladium and tributyltin acetylides affords the final acetylide products [η5-1-Ph2P-2,4-Ph2C5H 2]M(CO)3C=CPh (5a, M = Mo; 56, M = W). This communication describes the main processes and intermediates involved in this palladium-catalyzed metal-carbon bond formation.
- Tollis, Simona,Narducci, Valentina,Cianfriglia, Paola,Lo Sterzo, Claudio,Viola, Egidio
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p. 2388 - 2390
(2008/10/08)
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- Carbon-sulfur bond-forming reductive elimination involving sp-, sp2-, and sp3-hybridized carbon. Mechanism, steric effects, and electronic effects on sulfide formation
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Palladium thiolato complexes [(L)Pd(R)(SR')], within which L is a chelating ligand such as DPPE, DPPP, DPPBz, DPPF, or TRANSPHOS, R is a methyl, alkenyl, aryl, or alkynyl ligand, and R' is an aryl or alkyl group, were synthesized by substitution or proton-transfer reactions. All of these thiolato complexes were found to undergo carbon-sulfur bond-forming inductive elimination in high yields to form dialkyl sulfides, diaryl sulfides, alkyl aryl sulfides, alkyl alkenyl sulfides, and alkyl alkynyl sulfides. Reductive eliminations forming alkenyl alkyl sulfides and aryl alkyl sulfides were the fastest. Eliminations of alkynyl alkyl sulfides were slower, and elimination of dialkyl sulfide was the slowest. Thus the relative rates for sulfide elimination as a function of the hybridization of the palladium-bound carbon follow the trend sp2 > sp >> sp3. Rates of reductive elimination were faster for cis-chelating phosphine ligands with larger bite angles. Kinetic studies, along with results from radical trapping reactions, analysis of solvent effects; and analysis of complexes with chelating phosphines of varying rigidity, were conducted with [Pd(L)(S-tert-butyl)(Ar)] and [Pd(L)(S- tert-butyl)(Me)]. Carbon-sulfur bond-forming reductive eliminations involving both saturated and unsaturated hydrocarbyl groups proceed by an intramolecular, concerted mechanism. Systematic changes in the electronic properties of the thiolate and aryl groups showed that reductive elimination is the fastest for electron deficient aryl groups and electron rich arenethiolates, suggesting that the reaction follows a mechanism in which the thiolate acts as a nucleophile and the aryl group an electrophile. Studies with thiolate ligands and hydrocarbyl ligands of varying steric demands favor a migration mechanism involving coordination of the hydrocarbyl ligand in the transition state.
- Mann, Grace,Baranano, David,Hartwig, John F.,Rheingold, Arnold L.,Guzei, Ilia A.
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p. 9205 - 9219
(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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- Isomerization of (πr-allyl)palladium complexes via nucleophilic displacement by palladium(0). A common mechanism in palladium(0)-catalyzed allylic substitution
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Treatment of (π-allyl)palladium complexes such as 6 and 9 with Pd(PPh3)4 leads to rapid isomerization at -15 °C in tetrahydrofuran and other solvents. At 0°C and in the presence of more than 2 equiv of triphenylphosphine per palladium, the phosphine attacks the T-allyl group to give allylic phosphonium salts 7 with concomitant formation of a palladium(0)-phosphine complex, and isomerization of 6 is observed. Attack by PPh3 on 6 was shown to be stereospecific and to proceed with inversion. Studies of the Pd(0)-catalyzed substitution of le (X = OAc) with several different nucleophiles support the hypothesis that Pd(0) acts as a nucleophile on (π-allyl)palladium complexes, in a reaction that leads to loss of stereospecificity in these systems.
- Granberg, Kenneth L.,B?ckvall, Jan-E.
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p. 6858 - 6863
(2007/10/02)
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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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- Palladium-assisted macrocyclization approach to cytochalasins: A synthesis of antibiotic A26771B
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A synthetic strategy to macrocycles possessing a gamma -oxo delta -hydroxy-, gamma , delta -dihydroxy- and gamma -hydroxy- alpha , beta -unsaturated carbonyl system derives from a palladium-catalyzed C-C bond-forming reaction. In this approach, the macrocyclization employs a beta -keto sulfone as an electrofugal group and a 2-ethoxyallyl acetate as a nucleofugal group mediated by a phosphine-palladium (0) complex. In addition to facilitating anion formation and nucleophilic attack on the ( pi -allyl) palladium intermediate, the benzenesulfonyl group serves as a stereochemical control element which permits relay of stereochemical information between remote centers. The total synthesis of antibiotic A26771B is completed in 12 steps from 10-undecenal to illustrate the applicability of this methodology. Refs.
- Trost,Brickner
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p. 568 - 575
(2007/10/22)
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