Search results for "COORDINATION CHEMISTRY"
showing 10 items of 231 documents
Measuring the Relative Reactivity of the Carbon-Hydrogen Bonds of Alkanes as Nucleophiles
2018
We report quantitative measurements of the relative reactivities of a series of C-H bonds of gaseous or liquid CnH2n+2 alkanes (n = 1-8, 29 different C-H bonds) towards insitu generated electrophiles (copper, silver, and rhodium carbenes), with methane as the reference. This strategy surpasses the drawback of previous model reactions of alkanes with strong electrophiles suffering from C-C cleavage processes, which precluded direct comparison of the relative reactivities of alkane C-H bonds.
Comparative chemistry of 18-electron Mo(II) and 17-electron Mo(III) compounds containing only carbon-based ligands
1998
International audience; The chemical reactivity of various kinetically stable isomers of compound CpMo(η3-C3H5)(η4-C4H6), 1, and its oxidation product [1]+, as well as the bis-allyl Mo(III) complex CpMo(η3-C3H5)2, 2, and the bis-diene Mo(II) complex [CpMo(η4-C4H6)2]+, 3, is reviewed. The inertness toward isomerization processes of the allyl and butadiene ligands in the Mo(II) complexes has allowed a study of the relative reactivity toward both electrophilic and nucleophilic addition processes as a function of coordination mode. The dependence of various reaction pathways on the metal oxidation state has also been investigated. Of particular interest is the discovery that the electronically …
Efficient palladium–ferrocenylphosphine catalytic systems for allylic amination of monoterpene derivatives
2006
Ferrocenylphosphines added to [Pd(µ-Cl)(η3-C3H5)]2 dimeric precursor produce efficient catalysts to effect the allylic amination of terpenic allylacetates. Particularly convenient are tetrakis(diphenylphosphino)ferrocene and 1,1′-bis(diphenylphosphino)ferrocene, which allow the amination of allylacetates with good to excellent selectivity, and have turnover numbers as high as 80 000, for instance, for the formation of allylaniline. Herein, we report on reactions that selectively transform geranylacetate, nerylacetate, linalylacetate and perillylacetate into the corresponding allylic amines. These preparative methods give facile access to various products of great potential industrial intere…
Cyclopentadienylmolybdenum(II) and -(III) complexes containing diene and allyl ligands. Part 4. Reactivity studies of the bisallyl complex CpMo(supin…
1998
Abstract Compound CpMo( η 3 -C 3 H 5 ) 2 , 3, has been synthesized from CpMoCl 4 and four equivalents of allylmagnesium bromide. While the compound is stable in donor solvents at room temperature, warming in refluxing MeCN induces the formation of 1,5-hexadiene by a metal-mediated allyl-allyl coupling process. Treatment of 3 with Bu t NC at room temperature affords CpMo( η 3 -C 3 H 5 )(Bu t NC) 2 , 4. A similar reduction with presumed allyl radical loss occurs for [CpMo( η 3 -C 3 H 5 )( η 4 -C 4 H 6 )] + , [1c] + , to afford [CpMo( η 4 -C 4 H 6 )(Bu t NC) 2 ] + , 5. Treatment of [1c] + with methyllithium affords two products, the major one (1c) corresponding to the one-electron reduction pa…
Amino-phosphanes in RhI-Catalyzed Hydroformylation: Hemilabile Behavior of P,N Ligands under High CO Pressure and Catalytic Properties
2005
International audience; The catalytic properties of rhodium complexes containing the α-, β-, or γ-amino-phosphane ligands Ph2PCH2NEt2 (α-P,N-1), Ph2PCH(Ar)NHPh [α-P,N-2; Ar = η6(o-C6H4Cl)Cr(CO)3], Ph2PCH2NPh2 (α-P,N-3), Ph2PCH2CH(Ph)NHPh (β-P,N), Ph2PCH2(o-C6H4–NMe2) (γ-P,N-1), Ph2PCH(o-C6H4–CH2NHPh) (γ-P,N-2), and the α,β-diamino-phosphane ligand Et2NCH2P(Ph)CH2CH(Ph)NHPh (α,β-N,P,N), in styrene hydroformylation have been examined. The results show that the activity increases when the number of backbone carbon atoms linking P and N decreases from 3 to 1. IR and 31P HPNMR studies in solution show that all P,N ligands adopt exclusively a κ1-P coordination mode in rhodium chloride carbonyl co…
Amino-phosphanes in Rh(I)-catalyzed hydroformylation: new mechanistic insights using D2O as deuterium-labeling agent
2005
International audience; In previous work, we have demonstrated that the dangling amino group in amino-phosphane ligands increases the rate of Rh-catalyzed styrene hydroformylation as a function of the amino group basicity and of the distance between the P and N functions. We now report additional stereochemical and mechanistic insights resulting from new catalytic experiments performed with Rh-α-P,N catalytic systems in the presence of D2O. In addition to the expected D0 product, the formation of the β-D1 aldehyde, PhCH(CH2D)CHO was observed in all cases by 1H and 13C NMR spectroscopy, indicating that H/D exchange occurs for the rhodium-hydride complex. Minor amounts of a β-D2 product, PhCH…
New chiral α-aminophosphine oxides and sulfides: an unprecedented rhodium-catalyzed ligand epimerization
2001
International audience; New chiral α-aminophosphine oxide N,P(O) and sulfide N,P(S) ligands have been prepared in one-pot syntheses by addition of Ph2PH to (S)-PhCH[double bond, length half m-dash]NCH(Ph)CH3, followed by oxidation with O2 or S8. Crystallization from cold methanol leads to the isolation of an enantiomerically pure single N,P(O) diastereomer and to a 1 : 1 mixture of the two N,P(S) diastereomers. The coordination chemistry of these ligands with [RhCl(COD)]2 and [RhCl(CO)2]2 has been investigated under argon and syngas. At high temperatures, a P–C oxidative addition of the N,P(O) ligand followed by imine elimination leads to several hydrido rhodium species. The complexes conta…
Investigation into the reaction of (t-BuC5H4)2Nb(η2-Te2)H with CH3Li: Hydride abstraction versus telluride methylation
2007
Abstract The reaction of [ Cp 2 ′ Nb ( Te 2 ) H ] ( 1 ) (Cp′ = t -BuC 5 H 4 ) with CH 3 Li in THF was examined by variable temperature 1 H NMR, ESR and mass spectroscopic means. From these methods it is evident that the diamagnetic compounds [ Cp 2 ′ NbH 2 ( TeCH 3 ) ] ( 2 ) and [ Cp 2 ′ Nb ( Te ) CH 3 ] ( 3 ) as well as the paramagnetic compound [ Cp 2 ′ Nb ( TeCH 3 ) 2 ] ( 4 ) form simultaneously. In the subsequent reaction of the intermediate solution with [Co 2 (CO) 8 ] compound 4 was consumed and the compound [ Cp 2 ′ Nb ( μ - TeCH 3 ) 2 Co(CO) 2 ] ( 5 ) formed in good yield. Complex 5 was characterized by IR and variable temperature 1 H NMR spectroscopies. Electrochemical two-electro…
The Radical Trap in Atom Transfer Radical Polymerization Need Not Be Thermodynamically Stable. A Study of the MoX3(PMe3)3 Catalysts
2005
The molybdenum(III) coordination complexes MoX(3)(PMe(3))(3) (X = Cl, Br, and I) are capable of controlling styrene polymerization under typical atom transfer radical polymerization (ATRP) conditions, in conjunction with 2-bromoethylbenzene (BEB) as an initiator. The process is accelerated by the presence of Al(OPr(i))(3) as a cocatalyst. Electrochemical and synthetic studies aimed at identifying the nature of the spin trap have been carried out. The cyclic voltammogram of MoX(3)(PMe(3))(3) (X = Cl, Br, I) shows partial reversibility (increasing in the order ClBrI) for the one-electron oxidation wave. Addition of X(-) changes the voltammogram, indicating the formation of MoX(4)(PMe(3))(3) f…
Experimental and Theoretical Studies of Nonclassical d 0 Cyclopentadienyl Polyhydride Complexes of Molybdenum and Tungsten
1998
Low-temperature protonation of compounds Cp{sup *}MH{sub 5}(PMe{sub 3}) (M = Mo, 1; W, 2) by HBF{sub 4}{center_dot}Et{sub 2}O in CD{sub 2}Cl{sub 2} or CDFCl{sub 2} affords the thermally unstable hexahydride derivatives [Cp{sup *}MH{sub 6}(PMe{sub 3})]{sup +} (M = Mo, 3; W, 4). The corresponding protonation of 1- and 2-d{sup 5} affords 3- and 4-d{sup 5}, respectively. The {Delta}{delta} on going from H{sub 6} to HD{sub 5} is small for both compounds, but positive for 3 and negative for 4, and no isotopic perturbation of resonance (IPR) is observed. The T{sub 1min} at 400 MHz for [Cp{sup *}MH{sub 6}(PMe{sub 3})]{sup +} apparently doubles on going from Mo to W (52 ms for 3 and approximately 10…