31662-40-5Relevant academic research and scientific papers
Solid-liquid reactions of manganese and cobalt carbonyl anions with alkyl halides containing β-hydrogens or -halogens
Kovács, István,Ungváry, Ferenc,Garst, John F.
, p. 389 - 396 (2008/10/08)
Heterogeneous reactions afforded the first detection (by IR and NMR spectroscopy) of a secondary (η1-allyl)manganese carbonyl complex, CH3CH=CHCH(CH3)Mn(CO)5, which results from the reaction of solid NaMn(CO)5 with 4-bromo-2-pentene in benzene or in saturated hydrocarbons at temperatures up to 5°C. The analogous reaction of NaCo(CO)4 gives CH3-CH=CHCH(CH3)C(O)Co(CO)4, the product of CO insertion into CH3CH=CHCH(CH3)Co-(CO)4, which constitutes approximately 10% (by IR spectroscopy) of the equilibrium mixture with CH3CH=CHCH(CH3)C(O)Co(CO)4 under CO at 1 atm and 5°C. Addition of PPh3 to this mixture leads to the formation of isolable CH3CH=CHCH(CH3)C(O)Co(CO)3PPh3. Similar reactions of 4-bromo-2-pentene with NaMn(CO)4PPh3 and NaCo(CO)3PPh3 do not give metal-carbon-bonded species, nor do room-temperature reactions of 4-bromo-2-pentene with NaMn-(CO)5 and NaCo(CO)4. Instead, the products include 2-pentenes, 1,3-pentadienes, 4,5-dimethyl-2,6-octadiene isomers, BrMn(CO)5, Mn2(CO)10, Co2(CO)8, and η3-(CH3CHCHCHCH3)Co(CO)3. Reactions of dimethyl chlorosuccinate, ethyl 2-bromopropionate, methyl 3-bromopropionate, and dimethyl dibromosuccinate with NaMn(CO)5 and NaCo(CO)4 give varying amounts of alkylmetal carbonyl compounds and products of β-elimination. The characteristics of these transformations suggest radical mechanisms initiated by single electron transfer (SET). Radical pairs formed by SET are implicated as intermediates in both substitutions and eliminations.
Metal to ligand charge-transfer photochemistry of metal-metal-bonded complexes. 8. Photochemistry of (CO)5MnMn(CO)3(α-diimine) complexes. Coupling reactions of the radicals formed and X-ray structure of the photoproduct (CO)4Mn(σ-N,σ-N′,η 2-CN-iPr-pyca)Mn(CO)3
Van Der Graaf, Tim,Stufkens, Derk J.,Oskam, Ad,Goubitz, Kees
, p. 599 - 608 (2008/10/08)
This article describes the photochemistry between 133 and 298 K of five metal-metal-bonded carbonyls (CO)5MnMn(CO)3(α-diimine) (1a-e) (α-diimine = 4,4′-dimethyl-2,2′-bipyridine (bpy′ (1a)), pyridine-2-carbaldehyde N-isopropylimine (iPr-pyca (1b)), 1,4-diisopropyl-1,4-diaza-1,3-butadiene (iPr-DAB (1c)), 1,4-di-p-tolyl-1,4-diaza-1,3-butadiene (pTol-DAB (1d)), 1,4-di-p-anisyl-1,4-diaza-1,3-butadiene (pAn-DAB (1e))) by irradiation into their metal to α-diimine charge-transfer (MLCT) band. At room temperature these complexes undergo homolysis of the metal-metal bond and the radicals formed dimerize to give Mn2(CO)10 and Mn2(CO)6(α-diimine)2 (2a-e). Of these dimers, 2d,e were thermally unstable at room temperature. They decomposed into their radicals, which were characterized with ESR in the case of 2d. Complexes 1b-e showed a side reaction at room temperature, giving rise to the formation of (CO)4Mn(σ-N,σ-N′,η 2-CN-iPr-pyca)Mn(CO)3 (3b) and (CO)3Mn(σ-N,σ-N′,η2-CN,η 2-C′N′-R-DAB) (4c-e), respectively. The crystal structure of 3b was determined, and the data are as follows: monoclinic, P21/a, with a = 15.425 (1) A?, b = 9.867 (1) A?, c = 12.988 (1) A?, β = 111.310 (9)°, and Z = 4; R = 0.041. Both Mn atoms possess a distorted octahedral geometry, and the Mn-Mn distance is shorter than that in Mn2(CO)10. The formation of these complexes 3b, 4c-e was quenched by radical scavengers and favored in viscous solvents such as paraffin. At lower temperatures, the quantum yields for the photoproduction of 2-4 decreased, and in the case of 1c, a novel complex, 5c, was formed at T ? 180 K by reaction of the Mn(CO)3(iPr-DAB) radicals. 5c was identified as Mn2(CO)4(σ-N,σ-N′,η 2-CN-iPr-DAB)2. Raising the temperature above 180 K caused a thermal conversion of 5c into Mn2(CO) 5(σ-N,σ-N′-iPr-DAB)(σ-N,σ-N′, η2-CN-iPr-DAB) (6c). A further increase of temperature above 200 K caused the formation of 2c out of 6c. At temperatures below 183 K, homolysis products were no longer formed, but instead the CO-loss complexes (CO)4Mn(μ-CO)Mn(CO)2(α-diimine) (7) were produced. The thermal and photochemical reactions of the CO-bridged complex 7a were studied. For both primary photoprocesses, homolysis and release of CO, the quantum yields were high and wavelength independent throughout the MLCT band. They are therefore proposed to occur from the same 3σbσ* state of the complex after intersystem crossing/internal conversion from the MLCT state(s). The relative quantum yields of homolysis and CO-loss reactions resemble the ones that were derived for Mn2(CO)10, which points to a similar mechanism for the photochemistry of both types of complexes.
Photochemical reactions between dinuclear metal carbonyl complexes and alkyl halides. Formal oxidative addition across a metal-metal single bond proceeding by a free radical chain mechanism
Biddulph, Michael A.,Davis, Reg,Wilson, Fiona I. C.
, p. 277 - 293 (2007/10/02)
Photochemical reactions between (L = CO, PBu3, PEt3, P(OMe)3, P(OPh)3, PPh3) and alkyl halides (RX) yield both alkyl and halo complexes, and , in equimolar quantities.Kinetic and quantum yield studies suggest that these reactions proceed by a radical chain pathway involving CO dissociation from the dinuclear complex and metal-metal bond homolysis of the coordinatively unsaturated dinuclear intermediate.
Photochemistry of organometallic halide complexes. Mechanisms for the formation of ionic products
Pan, Xiong,Philbin, Cecelia E.,Castellani, Michael P.,Tyler, David R.
, p. 671 - 676 (2008/10/08)
The photochemical reactions of the Mn(CO)5X (X = Cl, Br, I), CpMo(CO)3X (X = Cl, I), and CpFe(CO)2I complexes with various ligands were investigated with an emphasis on determining how ionic products form in these reactions. Two pathways account for the formation of ionic products: (1) M-X heterolysis and (2) metal-metal-bonded dimer formation followed by subsequent disproportionation. The metal-metal-bonded dimer may form via a secondary photolysis of a M-CO-loss photoproduct, via M-X heterolysis, or via a minor M-X homolysis pathway, followed by coupling of two metal radicals. CpMo(CO)3X reacts photochemically with a variety of ligands to give substitution products, but ionic products form only with pyridine and DMSO. With pyridine, the following sequence of reactions was found to yield ionic products: (1) CpMo(CO)3Cl →hν CpMo(CO)3 + Cl; (2) 2CpMo(CO)3 → Cp2Mo2(CO)6; (3) Cp2Mo2(CO)6 →hν CpMo(CO)3- + CpMo(CO)3py+. (Reaction 3 is the photochemical disproportionation of Cp2Mo2(CO)6 described previously by us.) The CpMo(CO)3X complexes are the only halides studied for which some M-X homolysis occurs; however, homolysis of the Mo-X bond is very inefficient: Φ = 9 × 10-4. For CpMo(CO)3X in DMSO, the only ionic product is CpMo(CO)2(DMSO)2+, formed by the following route: CpMo(CO)3Cl + DMSO →hν CpMo(CO)2(DMSO)Cl →hν CpMo(CO)2DMSO+ + Cl- → CpMo(CO)2(DMSO)2+. Ionic products form in the photochemical reactions of Mn(CO)5X complexes via the following route involving initial Mn-CO bond dissociation: Mn(CO)5X →hν Mn2(CO)8X2 →hν MnX2 + 3CO + 1/2 Mn2(CO)10. Photochemical disproportionation of the Mn2(CO)10 complex then occurs. Ionic products also form in the photochemical reactions of the CpFe(CO)2I complex via the intermediate formation of the metal-metal-bonded dimer, followed by disproportionation of this species. In this case, however, the dimer is formed by initial heterolysis of the Fe-I bond (CpFe(CO)2I →hν CpFe(CO)2+ + I-) followed by the sequence of reactions in Scheme II.
Low-Temperature Photochemistry of (η5-C5R5)Fe(CO)2Mn(CO)5 (R = H, Me): Substitution by P-Donor Ligands and Kinaetics of Thermal Fe-Mn Bond Homolysis
Pope, Keith R.,Wrighton, Mark S.
, p. 4545 - 4552 (2007/10/02)
Low-temperature irradiation of (η5 C5R5)Fe(CO)2Mn(CO)5 (R = H, Me) results in loss of CO as the only detectable photoprocess (Φapp for CO = 10-3 at 313 nm, and Φ313/Φ366 = 20 at 93 K) and yields a coordinatively unsaturated dinuclear photoproduct, (η5C5R5)FeMn(CO)6.It should be appreciated that CO loss and Mn-Fe bond cleavage are competitive processes with CO loss far more dominant at low temperature in a rigid glass.Warming of a glass containing (η5-C5R5)FeMn(CO)6 in the presence of PR3 (R = Ph, OPh) results in formation of (η5-C5R5)Fe(CO)2Mn(CO)4PR3.The substitution product could be generated by an independent route from irradiation of a room temperature solution of 5-C5R5)Fe(CO)2>2 and 2.Spectroscopic evidence, including IR, UV-vis, NMR, and MS, supports the conclusion that substitution of CO by PR3 in (η5-C5R5)Fe(CO)2Mn(CO)5 occurs exclusively on the Mn atom.It was further determined that Φdiss for (η5-C5H5)Fe(CO)2Mn(CO)5 at room temperature in the presence of P(OPh)3 in CCl4 is 0.89 +/- 0.08 and 0.89 +/- 0.1 at 313 and 366 nm, respectively, and Φapp for (η5-C5H5)Fe(CO)2Mn(CO)4P(OPh)3 is 0.26 +/- 0.03 and 0.29 +/- 0.04 at 313 and 366 nm, respectively, in the same solution.The products (η5-C5R5)Fe(CO)2Mn(CO)4PPh3 are labile with respect to Fe-Mn bond cleavage and a kinetic analysis yielded activation parameters for this thermal reaction ΔH = 106 +/- 6 and 84.3 +/- 4 kJ mol-1 for R = H, Me, respectively, and ΔS = 41.5 +/- 40 and -21.4 +/- 23 J mol-1 K-1 for R = H, Me, respectively.
Spontaneous and Induced Homolysis of Bis(triphenylphosphine)octacarbonyldimanganese (Mn-Mn)
Poee, Anthony,Sekhar, Chandra V.
, p. 4874 - 4883 (2007/10/02)
Kinetic studies show that the complex Mn2(CO)8(PPh3)2 reacts thermally by two paths with C2H2Cl4, C16H33I, O2, NO, P(OEt)3, and P-n-Bu3 in decalin or cylcohexane.Reactions with CO or P(OPh)3 proceed only by one of these paths.The two paths are approximately equal importance and both show a very close fit to the same, rather complex, form of rate equation.The equation is quite inconsistent with any form of rate-determining dissociation, but it is consistent with two forms of reversible homolysis, one spontaneous and one induced.The latter involves initial, reversible formation of a reactive isomer of Mn2(CO)8(PPh3)2 which undergoes homolysis when attacked by a sufficiently reactive reagent.Both paths are therefore operative in reactions with the more reactive reagents, but reactions with CO and P(OPh)3 proceed only via spontaneous homolysis because these reagents are evidently unable to induce homolysis of the reactive isomer of the complex.A possible structure for the reactive isomer is one formed by metal migration, i.e., it can be formulated as (Ph3P)(OC)4Mn(μ-CO)Mn(CO)3(PPh3) which contains a bridging CO ligand, no Mn-Mn bond, and a vacant coordination site on one Mn atom.Attack at this site by suitably active reagents is postulated to lead to fragmentation.These results show that behavior previously thought to be uniquely indicative of spontaneous homolysis could also be explained by reversible homolysis induced by the reactant after isomerization of the complex.Rate constants are derived for halogen transfer from C2H2Cl4 or C16H33I to .Mn(CO)4(PPh3) and for nucleophilic displacement of PPh3 from .Mn(CO)4(PPh3) by P(OPh)3, P(OEt)3, and CO.
Reactions between Dinuclear Metal Carbonyl Complexes and Alkyl Halides: Formal Oxidative Addition across a Metal-Metal Single Bond
Biddulph, Michael A.,Davis, Reg,Wells, Clifford H. J.,Wilson, Fiona I. C.
, p. 1287 - 1288 (2007/10/02)
Photochemical reactions between 2> (R=Et, Bun, OEt) and alkyl halides (R'X) proceed to completion in 2 to 4 h yielding equimolar quantities of and , by a route involving reaction of R'X with mononuclear intermediates.
Kinetics and Mechanism of Substitution Reactions of Some (η3-Allyl)manganese Tetracarbonyl Compounds
Palmer, G. Todd,Basolo, Fred
, p. 3122 - 3129 (2007/10/02)
Kinetic data are reported for CO substitution of (η3-C3H4X)Mn(CO)4, where X is a substituent in the 1- or the 2-position of the allyl ligand and where X1 = H, Me, Ph, t-Bu, and Cl.Also the anti- and the syn-(η3-C3H3(1,2-Ph2))Mn(CO)4 isomers were prepared for the fist time and their rates of substitution determined.In all cases the rates of reaction are first order in substrate concentration and zero order in entering nucleophile concentrations.Studies on decarbonylation reactions of (η1-C3H5)Mn(CO)4L rule out an η3 --> η1 --> η3 mechanism.It appears that CO substitution takes place by a dissociation (SN1 process, and the kinetic parameters for (η3-C3H5)Mn(CO)4 are k(45 deg C) = 2.8 X 10-4 s-1, ΔH(excit.) = 26.8 kcal/mol, and ΔS(excit.) = 9.6 eu.Substituents on the 1-position of the allyl group have a small retardation effect on the rates of CO substitution.Substituents on the 2-position enhance the rates of reaction; furthermore, this rate enhancement increases with increasing bulkiness of the substituent.Still, the maximum rate observed was only 500 times greater than that for the parent comopound, and this is for the 2-tert-butylallyl compound.Unfortunately, all attempts to prepare the desired compounds with strong electron-donating and -withdrawing substituents on the allyl ligand failed.
Substitution of Mn(CO)5 Is Associative
Herrinton, Thomas R.,Brown, Theodore L.
, p. 5700 - 5703 (2007/10/02)
The substitution of Mn(CO)5 radicals by triphenylphosphine (PPh3) or triphenylarsine (AsPh3) in hexane has been studied by observing the manner in which the competition between CCl4 and PPh3 or between CH2Br2 and AsPh3 is affected by changes in concentrations of the reactants.In both cases the substitution process shows kinetics behavior indicative of an associative process.The second-order rate constants are 1.7 (+/- 0.2) E7 and 6.5 (+/-0.8) E4 M-1 s-1 for PPh3 and AsPh3, respectively, in hexane at 24 deg C.Less extensive measurements provide analogous bimolecular rate constants for substitution by P(n-Bu)3, P(i-Pr)3, and P(O-i-Pr)3 of 1.0 (+/-0.1) E9, 6.7 (+/-0.7) E7, and 3.1 (+/-0.3) E7 M-1 s-1, respectively.There is no evidence in the results for a concurrent dissociative loss of CO from Mn(CO)5.On the basis of the data for AsPh3, which exhibits the smallest associative rate constant, the first-order dissociative rate constant must be less than about 90 s-1.
