25838-69-1Relevant academic research and scientific papers
Reactivity Patterns of the Unsaturated Tetrahedral Cluster . Easy Addition of Four MeCN Molecules and 'Ionic' or 'Neutral' Fragmentation Pathways of the Spiked-triangle Intermediate
Beringhelli, Tiziana,D'Alfonso, Giuseppe,Zarini, Marta
, p. 2407 - 2416 (1995)
The unsaturated (56 valence electrons, v.e.s) tetrahedral cluster 1 readily added four acetonitrile molecules, affording two isomers 2a and 2b of the 64 v.e.s derivative, containing a spiked-triangle metallic skeleton.These isomers at room temperature rapidly underwent an ionic fragmentation to the known unsaturated triangular cluster anion (1-) and to the cation (1+).The rate of decomposition significantly increased at low concentration.Treatment of compounds 2a and 2b with the ?-acidic ligand CO, in the absence of free acetonitrile, gave only neutral products.Monitoring by NMR spectroscopy has revealed the rapid stepwise substitution of the nitrile ligands, accompanied by fragmentation to the known saturated triangular clusters (n = 1-3) and to the mononuclear complexes (n = 0 or 1).The novel, unstable, mononuclear hydride has been obtained by treatment of with Me3NO in acetonitrile and by reaction of (1-) with CF3SO3H, in acetonitrile.In the presence of free acetonitrile, compounds 2a and 2b reacted with CO more slowly and gave both anionic and neutral triangular clusters.
Homogeneous CO hydrogenation: Ligand effects on the lewis acid-assisted reductive coupling of carbon monoxide
Miller, Alexander J. M.,Labinger, Jay A.,Bercaw, John E.
, p. 4499 - 4516 (2011/01/09)
Structure-function studies on the role of pendent Lewis acids in the reductive coupling of CO are reported. Cationic rhenium carbonyl complexes containing zero, one, or two phosphinoborane ligands (Ph2P(CH 2)nB(C8H14), n = 1-3) react with the nucleophilic hydride [HPt(dmpe)2]+ to reduce [M-CO] + to M-CHO; this step is relatively insensitive to the Lewis acid, as both pendent (internal) and external boranes of appropriate acid strength can be used. In contrast, whether a second hydride transfer and C-C bond forming steps occur depends strongly on the number of carbon atoms between P and B in the phosphinoborane ligands, as well as the number of pendent acids in the complex: shorter linker chain lengths favor such reductive coupling, whereas longer chains and external boranes are ineffective. A number of different species containing partially reduced CO groups, whose exact structures vary considerably with the nature and number of phosphinoborane ligands, have been crystallographically characterized. The reaction of [(Ph2P(CH 2)2B(C8H14))2Re(CO) 4]+ with [HPt(dmpe)2]+ takes place via a hydride shuttle mechanism, in which hydride is transferred from Pt to a pendent borane and thence to CO, rather than by direct hydride attack at CO. Addition of a second hydride in C6D5Cl at -40 °C affords an unusual anionic bis(carbene) complex, which converts to a C-C bonded product on warming. These results support a working model for Lewis acid-assisted reductive coupling of CO, in which B (pendent or external) shuttles hydride from Pt to coordinated CO, followed by formation of an intramolecular B-O bond, which facilitates reductive coupling.
Synthesis and Properties of IrRe2(μ-H)2(CO)9(η5-C 9H7)
Comstock, Matthew C.,Prussak-Wieckowska, Teresa,Wilson, Scott R.,Shapley, John R.
, p. 4397 - 4404 (2008/10/09)
The slow addition of Re2(μ-H)2(CO)8 to a solution of Ir(CO)(η2C9H7) in hexane at reflux provides IrRe2(μ-H)2(CO)9(μ5-C 9H7) (1) in 80% yield. The molecular structure of 1 shows an IrRe2 triangle incorporating one Ir(CO)(η5-C9H7) and two Re(CO)4 fragments. The strongly different IT-Re distances suggest that one hydride ligand bridges one IT-Re edge and the other hydride bridges the Re-Re edge. Low-temperature 1H and 13C NMR spectra are consistent with this structure; at higher temperatures a dynamic process involving migration of one hydride ligand between the two Ir-Re edges is observed. Cluster 1 is readily deprotonated with KOH/ EtOH, and the resulting anion has been isolated as the PPN salt, [PPN][μ-H)(CO)9-C9H7)] (2). Both the 1H and low temperature 13C NMR spectra of 2 are consistent with a structure in which the remaining hydride ligand bridges the Re-Re edge. Variable-temperature 13C NMR spectra indicate that 2 undergoes CO scrambling localized on the Ir-Re edges. The reaction of 1 with PPh3 leads to IrRe2(μ-H)2(CO)8(PPh3)(η 5-C9H7) (3), which contains the phosphine on a rhenium atom, as well as to cluster fragmentation.
Transition-metal hydrides and carbonyl anions as ligands toward a Pt centre in rhenium-platinum triangular clusters: A qualitative order of 'thermodynamic nucleophilicity'
Bergamo, Mirka,Beringhelli, Tiziana,Ciani, Gianfranco,D'Alfonso, Giuseppe,Moret, Massimo,Sironi, Angelo
, p. 291 - 303 (2008/10/08)
Six novel mixed-metal spiked-triangle complexes [Re2Pt(μ-H)2(CO)9{X}] have been obtained. The metallo-ligands X bound to the Pt vertex are either transition-metal hydrides, such as HMn(CO)5, HRe(CO)4(PPh3), HRe(CO)3(PPh3)2, or carbonyl anions, such as [Mn(CO)5]-, [WCp(CO)3]- and [Co(CO)4]-. Two main synthetic routes have been used to prepare these complexes: (i) replacement of the labile ligand 1,5-cyclooctadiene (COD) of [Re2Pt(μ-H)2(CO)8(COD)] with CO and X; (ii) substitution of the labile 'ligand' HRe(CO)5 in [Re2Pt(μ-H)2(CO)9{HRe(CO)5}] by the ligands X. The neutral species [Re2PtMn(μ-H)3(CO)14] has been obtained by protonation of [Re2Pt(μ-H)2(CO)9{Mn(CO)5}] -. Variable temperature 1H NMR investigations showed that it exists in solution as two isomers a and b, likely differing in the location of one hydride, a having the structure [Re2Pt(μ-H)2(CO)9{HMn(CO)5}], and b the structure [Re2Pt(μ-H)3(CO)9{Mn(CO)5}]. The ligand HMn(CO)5 of a shows a high lability, being in fast exchange with free [HMn(CO)5] even at 193 K. At higher temperature interconversion between the two isomers and exchange between the hydrides bound to Pt in b is observed. The treatment of [Re2Pt(μ-H)2(CO)9{WCp(CO)3}] - with strong acids failed to give the protonated derivative. The strong nucleophile [FeCp(CO)2]- reacted with [Re2Pt(μ-H)2(CO)9{HRe(CO)5}] as a Broensted base rather than as a nucleophile, giving deprotonation instead of substitution of the labile HRe(CO)5 ligand bound to Pt. The complex [Re2Pt(μ-H)2(CO)9{HRe(CO) 4(PPh3)}] has been characterised by X-ray single crystal analysis. It crystallises in the monoclinic space group P21/c (No. 14) with a=9.229(3), b=30.700(8), c=12.915(3) A, β=98.05(2)°, V=3623(2) A3 and Z=4. A series of displacement reactions of the type [Re2Pt(μ-H)2(CO)9{X}]+X′ ? [Re2Pt(μ-H)2(CO)9(X′)] + X allowed the following qualitative order of affinity of the metallo-ligands X for the Pt atom (a scale of 'thermodynamic nucleophilicity') to be established: [Re(CO)5]- > [HRe2(CO)9]-≈[Mn(CO)5] ->[WCp(CO)3]->[Co(CO)4] -> [HRe(CO)4(PPh3)]>[HRe(CO)3(PPh 3)2]>[HRe(CO)5]>[HMn(CO) 5]>[HWCp(CO)3].
Rhenium 2-oxoalkyl (enolate) complexes. Synthesis and carbon-carbon bond-forming reactions with nitriles
Stack,Doney,Bergman,Heathcock
, p. 453 - 466 (2008/10/08)
Several carbon-bound rhenium enolates, based on (C-O)5Re and (Ph3P)(CO)4Re, can be prepared by alkylation of the corresponding carbonylmetalate anions with α-chloro carbonyl or α-sulfonyloxy carbonyl compounds. These materials can be isolated by standard chromatographic methods and are air-stable in solution and the solid state. Irradiation of the (CO)5Re derivatives led to decomposition. Thermal activation of these compounds required elevated temperatures, which in the presence of Ph3P and a nitrile resulted in the formation of carbon-carbon bond between the enolate and nitrile carbon atoms. The mechanism of the nitrile/enolate condensation has been examined and is proposed to proceed through a Ph3P-substituted nitrile complex. This complex was synthesized independently, and its efficacy as an intermediate was demonstrated. Labile derivatives of the Ph3P-substituted enolates were prepared by reaction of the enolates with Me3NO in CH3CN. Acetonitrile complexes are obtained for the ester and nitrile enolates.
Carbon-carbon bond forming reactions of rhenium enolates with terminal alkynes. Evidence for an alkyne C-H oxidative addition mechanism and observation of highly stereoselective base-catalyzed proton transfer reactions in rhenium metallacycles
Stack, Jeffrey G.,Simpson, Robert D.,Hollander, Frederick J.,Bergman, Robert G.,Heathcock, Clayton H.
, p. 2716 - 2729 (2007/10/02)
The acetonitrile-substituted complexes fac-(MeCN)(OC)3(PPh3)ReCH(R2)CO(R1) (4, R1 = OEt R2 = H; 5, R1 = OEt R2 = Me) and the chelating amide complex 6 react with terminal alkynes (R3 C≡CH) to afford five-membered metallacycles 7-9 The metallacycles possess an exocyclic double bond which exists in the less thermodynamically stable Z stereochemistry, in which the alkyl group R3 is oriented proximate to the metal center. These complexes rearrange in the presence of a Lewis base to form the endocyclic isomers 10-12. The structure of the metallacycle 10g was determined by a single-crystal X-ray diffraction study. Labeling studies demonstrated that the 1,3-hydrogen shift involved in this rearrangement is intramolecular and stereospecific with respect to the rhenium center, even though it is mediated by an external reagent. Deuterium incorporation into the 7-position of the endo metallacycles can also be induced by base and once again occurs stereospecifically (anti to the phosphine ligand). Treatment of the metallacycles with acid results in removal of the metal and yields the unsaturated esters as a mixture of stereo- and regioisomers. Kinetic studies demonstrated that the reaction of 4 with terminal alkynes involves reversible dissociation of the coordinated acetonitrile to form an unsaturated intermediate 29 (R1 = CO2Et) This intermediate reacts faster with more electron-rich alkynes (HC≡CCMe3) than electron-deficient alkynes (HC≡CCO2Me) and displays a R3C≡CH/R3C≡CD kinetic isotope effect kH/kD of 2.0. On the basis of these results and information about reactions of related rhenium complexes, we suggest that formation of the metallacycles is best accommodated by the mechanism shown in Scheme VIII: insertion of 29 into the alkyne C-H bond leading to a 7-coordmate rhenium acetylide hydride 31, 1,3-migration of the hydride to the acetylide β-carbon, providing vinylidene complex 32, and then migration of the enolate ligand to the a-carbon of the vinylidene group, giving the exo metallacycle.
A Radical-Chain Mechanism for Dinuclear C-H Bond Formation
Edidin, Robin T.,Norton, Jack R.
, p. 948 - 953 (2007/10/02)
Both the formation of (Ph3PAu)2Os(CO)4 from Ph3PAuCH3 and H2Os(CO)4 and the formation of (Ph3PAu)Mn(CO)5 from Ph3PAuCH3 and HMn(CO)5 occur by radical-chain mechanisms.The chain carriers are .Mn(CO)5 and .Os(H)(CO)4, respectively, arising from hydrogen atom abstraction from the initial hydrides.Photolysis of a small amount of the appropriate dimer (Mn2(CO)10 or H2Os2(CO)8) generates the chain carrier and thus initiates the reaction.No such reaction occurs between Ph3PAuCH3 and HRe(CO)5, even in the presence of substantial amounts of .Re(CO)5.The formation of H2Os(CO)3PPh3 from Ph3P and H2Os(CO)4 also occurs by a radical-chain mechanism with .Os(H)(CO)4 as the chain carrier, and the reactions of Ph3PAuCH3 and Ph3P with H2Os(CO)4 can be simultaneously initiated.
NOVEL, DINUCLEAR MECHANISM FOR CATALYTIC OLEFIN DIMERIZATION. PHOTOCHEMICAL REACTIVITY OF ( mu -HYDRIDO)( mu -ALKENYL)DIRHENIUM OCTACARBONYL COMPOUNDS.
Nubel,Brown
, p. 3474 - 3484 (2007/10/02)
UV photolysis of ( mu -hydrido)( mu -ethenyl)dirhenium octacarbonyl, ( mu -H)( mu CH equals CH//2)Re//2(CO)//8(I), in the presence of ethylene affords ( mu -hydrido)( mu -butenyl)dirhenium octacarbonyl complexes. A mechanism is proposed in which the initial step is photodissociation of CO from I, as photolysis of I in the presence of **1**3CO or PPh//3 results in CO substitution. Subsequent steps in the formation of the mu -hydrido mu -butenyl species are coordination of ethylene, insertion of ethylene into the Re-H or Re-ethenyl sigma bond, recoordination of CO, C-C or C-H reductive elimination to yield Re//2(CO)//8(1-butene), and oxidative addition of a vinylic C-H bond of coordinated butene.
The Reactivity of the Unsaturated Dimeric Rhenium Complexes > and : X-Ray Crystal Structure of >
Prest, David W.,Mays, Martin J.,Raithby, Paul R.
, p. 2021 - 2028 (2007/10/02)
The complexes react with P(OMe)3 giving 1 : 1 adducts which exist in solution in two isomeric forms, both containing a terminal H and a (μ-H) ligand.Both (1) and (2) react with RNC (R = But, Bun, p-MeOC6H4, or p-MeC6H4SO2CH2) to give the complexes (5) containing an NC-bonded formimidoyl ligand.With CH3CN (1) and (2) react to give a major product formulated as > and containing an N-bonded ethylideneimino group; for the product with L-L = dppm this formulation has been confirmed by an X-ray diffraction study.The complex crystallises in the monoclinic space group P21/n with a = 9.765(3), b = 29.940(8), c = 11.813(4) Angstroem, β = 104.69(2) deg, and Z = 4.The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by full-matrix least squares to R = 0.071 for 2614 unique, observed diffractometer data.The minor product obtained in the reaction of (2) with CH3CN is suggested on the basis of spectroscopic evidence to be (7b) containing an NC-bonded acetimidoyl ligand.Both (1) and (2) form an unstable adduct with CO but do not react with HCCH, H2C=CH2, or MeO2CCCCO2Me.
FREE RADICAL INTERMEDIATES IN THE REACTION BETWEEN DECACARBONYLDIRHENIUM AND TRIPHENYLPHOSPHANE
Cox, David J.,Davis, Reg
, p. 339 - 345 (2007/10/02)
The reaction between Re2(CO)10 and PPh3 in refluxing xylene has been re-examined.The main products are 1,2-diaxial Re2(CO)8(PPh3)2 and mer-trans-HRe(CO)(PPh3)2.A range of other products have been isolated by chromatographic procedures and their production rationalised.The previously reported isolable paramagnetic products have not been confirmed, but evidence is presented for their formation as unstable intermediates.
