| 1. |
- Casey, Charles P., et al.
(author)
-
Quantitative Determination of the Regioselectivity of Nucleophilic Addition to η3-Propargyl Rhenium Complexes and Direct Observation of an Equilibrium between η3-Propargyl Rhenium Complexes and Rhenacyclobutenes.
- 2009
-
In: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 28:1, s. 123-131
-
Journal article (peer-reviewed)abstract
- PMe3 adds selectively to the central C of the η3-propargyl complex [C5Me5(CO)2Re(η3-CH2C≡CCMe3)][BF4] (1-t-Bu) to form the metallacyclobutene [C5Me5(CO)2Re(CH2C(PMe3):CCMe3)][BF4] (7). The rate of rearrangement of the metallacyclobutene 7 to η2-alkyne complex [C5Me5(CO)2Re(η2-Me3PCH2C≡CCMe3)][BF4] (8) is independent of phosphine concn., consistent with a dissociative mechanism proceeding via η3-propargyl complex 1-t-Bu. The rate of this rearrangement is 480 times slower than the rate of exchange of PMe3 with the labeled metallacyclobutene 7-d9. This rate ratio provides an indirect measurement of the regioselectivity for addn. of PMe3 to the central C of η3-propargyl complex 1-t-Bu to give 7 compared to addn. to a terminal C to give 8. The addn. of PPh3 to 1-t-Bu gives the metallacyclobutene [C5Me5(CO)2Re(CH2C(PPh3):CCMe3)][BF4] (11). Low-temp. 1H NMR spectra provide evidence for an equil. between metallacyclobutene 11 and η3-propargyl complex 1-t-Bu (Keq ≈ 44 M-1 at -46° and ΔG°(0°) = -1.2 ± 0.2 kcal mol-1). The crystal and mol. structures of [C5Me5(CO)2Re[η2-(Ar2PCH2CH2PPh2)CH2C≡CCMe3]][BF4]·2CH2Cl2 (Ar = 3,5-(CF3)2C6H3) and [C5Me5(CO)2Re(η2-Me3PCH2C≡CCMe3)]Cl·H2O were detd. by x-ray crystallog. [on SciFinder(R)]
|
|
| 2. |
- Ibrahem, Ismail, et al.
(author)
-
Enantioselective addition of aldehydes to amines via combined catalytic biomimetic oxidation and organocatalytic C-C bond formation.
- 2005
-
In: Tetrahedron Letters. - : Elsevier BV. - 0040-4039 .- 1359-8562. ; 46:23, s. 3965-3968
-
Journal article (peer-reviewed)abstract
- The biomimetic catalytic enantioselective addn. of aldehydes to amines is reported. This was accomplished by combining biomimetic coupled catalytic aerobic oxidn. of amines involving ruthenium-induced dehydrogenation and organocatalytic asym. Mannich reactions. The one-pot reactions furnished β-amino aldehyde and α-amino acid derivs. in high yields with excellent chemoselectivity and enantioselectivity. [on SciFinder(R)]
|
|
| 3. |
- Privalov, Timofei, et al.
(author)
-
DFT study of an inner-sphere mechanism in the hydrogen transfer from a hydroxycyclopentadienyl ruthenium hydride to imines
- 2007
-
In: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 26:11, s. 2840-2848
-
Journal article (peer-reviewed)abstract
- A combination of the DFT method with the computational description of environmental effects by solvent was applied to a theoretical study of the hydrogen transfer to imines by [2,3,4,5-Ph-4(eta(5)-C4COH)Ru(CO)(2)H] (2) within a molecular model that closely mimics the authentic reaction conditions. A consistent polarizable continuum solvent model (PCM) was instrumental and necessary in achieving stability of the computational model. Environmental effects by solvent were also considered in an extended model with an addition of explicit solvent molecules within the PCM. The study elucidates an inner-sphere mechanism in detail. Intermediate complexes and transition states are characterized. Three distinct energy barriers along the reaction coordinate are predicted when solvent effects are taken into account. The imine coordinates to ruthenium via ring slippage with an energy barrier of about 15 kcal/mol. Close in energy (12 kcal/mol) is the transition state of the hydride transfer, which gives an (eta(2)-cyclopentadienone)ruthenium amine intermediate. The presence of Ph groups on the Cp ring facilitates the ring slippage that occurs on imine coordination. This eta(2)-intermediate finally rearranges to the corresponding (eta(4)-cyclopentadienone)ruthenium amine complex via a transition state at 9 kcal/mol. The stable ruthenium amine complex was verified against an X-ray structure of the corresponding complex. Inclusion of the solvent (by PCM or explicit molecules) was required to stabilize low-hapticity intermediates and transition state structures.
|
|
| 4. |
|
|
| 5. |
- Samec, Joseph S. M., et al.
(author)
-
Bidentate N,O-prolinate ruthenium benzylidene catalyst highly active in RCM of disubstituted dienes.
- 2007
-
In: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :27, s. 2826-2828
-
Journal article (peer-reviewed)abstract
- Bidentate N,O-prolinate ruthenium benzylidene I was prepd. from com. available L-proline and Grubbs catalyst. The catalytic activity of I in ring-closing metathesis (RCM) of functionalized disubstituted dienes at 30° is disclosed. [on SciFinder(R)]
|
|
| 6. |
- Samec, Joseph S. M., et al.
(author)
-
Efficient ruthenium-catalyzed aerobic oxidation of amines by using a biomimetic coupled catalytic system.
- 2005
-
In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 11:8, s. 2327-2334
-
Journal article (peer-reviewed)abstract
- Efficient aerobic oxidn. of amines was developed using a biomimetic coupled catalytic system involving a Ru-induced dehydrogenation. The principle for this aerobic oxidn. is that the electron transfer from the amine to O2 occurs stepwise via coupled redox systems and this leads to a low-energy electron transfer. A substrate-selective Ru catalyst dehydrogenates the amine and the H atoms abstracted are transported to an electron-rich quinone (2a; 2,6-dimethoxy-p-benzoquinone). The hydroquinone thus formed is subsequently reoxidized by air with the aid of an oxygen-activating [Co(salen)]-type complex (27; [Co(MeN(CH2CH2CH2N:CHC6H4O-2)2)]). The reaction can be used for the prepn. of ketimines and aldimines in good to high yields from the appropriate corresponding amines. The reaction proceeds with high selectivity, and the catalytic system tolerates air without being deactivated. The rate of the dehydrogenation was studied by using quinone 2a as the terminal oxidant. A catalytic cycle in which the amine promotes the dissocn. of the dimeric catalyst (OC)2(η5-Ph4C5OH)Ru(Ό-H)Ru(η5-OC5Ph4)(CO)2 is presented. [on SciFinder(R)]
|
|
| 7. |
|
|
| 8. |
- Samec, Joseph S. M., et al.
(author)
-
Efficient Ruthenium-Catalyzed Transfer Hydrogenation of Functionalized Imines by Isopropanol under Controlled Microwave Heating
- 2005
-
In: Canadian journal of chemistry (Print). - 0008-4042 .- 1480-3291. ; 83:6, s. 909-916
-
Journal article (peer-reviewed)abstract
- Transfer hydrogenation of various functionalized imines by isopropanol catalyzed by [Ru(CO)(2)(Ph4C4CO)](2) (3) has been studied. The use of either an oil bath or controlled microwave heating in toluene led to an efficient procedure with high turnover frequencies and the product amines were obtained in high yields. An advantage with catalyst 3 over the conventional [Ru-2(CO)(4)(mu-H)(Ph4C4COHOCC4Ph4)] (1) is the absence of an initiation period, which results in a faster reaction with 3 as compared to 1.
|
|
| 9. |
- Samec, Joseph S. M., et al.
(author)
-
Mechanistic aspects of transition metal-catalyzed hydrogen transfer reactions.
- 2006
-
In: Chemical Society Reviews. - : Royal Society of Chemistry (RSC). - 0306-0012 .- 1460-4744. ; 35:3, s. 237-248
-
Journal article (peer-reviewed)abstract
- A review. In this tutorial review recent mechanistic studies on transition metal-catalyzed hydrogen transfer reactions are discussed. A common feature of these reactions is that they involve metal hydrides, which may be monohydrides or dihydrides. An important question is whether the substrate coordinates to the metal (inner-sphere hydrogen transfer) or if there is a direct concerted transfer of hydrogen from the metal to substrate (outer-sphere hydrogen transfer). Both exptl. and theor. studies are reviewed. [on SciFinder(R)]
|
|
| 10. |
- Samec, Joseph S. M., et al.
(author)
-
Mechanistic study of hydrogen transfer to imines from a hydroxycyclopentadienyl ruthenium hydride. Experimental support for a mechanism involving coordination of imine to ruthenium prior to hydrogen transfer
- 2006
-
In: Journal of the American Chemical Society. - Washington, DC : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 128:44, s. 14293-14305
-
Journal article (peer-reviewed)abstract
- Reaction of [2,3,4,5-Ph-4(eta(5)-C4COH) Ru(CO)(2)H] (2) with different imines afforded ruthenium amine complexes at low temperatures. At higher temperatures in the presence of 2, the complexes decomposed to give [Ru-2(CO)(4)(mu-H)(C4Ph4COHOCC4Ph4)] (1) and free amine. Electron-rich imines gave ruthenium amine complexes with 2 at a lower temperature than did electron-deficient imines. The negligible deuterium isotope effect (k(RuHOH)/k(RuDOD) = 1.05) observed in the reaction of 2 with N-phenyl[1-(4-methoxyphenyl) ethylidene]amine (12) shows that neither hydride (RuH) nor proton (OH) is transferred to the imine in the rate-determining step. In the dehydrogenation of N-phenyl-1-phenylethylamine (4) to the corresponding imine 8 by [2,3,4,5-Ph-4(eta(4)-C4CO) Ru(CO)(2)] (A), the kinetic isotope effects observed support a stepwise hydrogen transfer where the isotope effect for C-H cleavage (k(CHNH)/k(CDNH) = 3.24) is equal to the combined (C-H, N-H) isotope effect (k(CHNH)/k(CDND) = 3.26). Hydrogenation of N-methyl(1-phenylethylidene) amine (14) by 2 in the presence of the external amine trap N-methyl-1-(4-methoxyphenyl) ethylamine (16) afforded 90-100% of complex [2,3,4,5-Ph-4(eta(4)-C4CO)] Ru(CO)(2)NH(CH3)(CHPhCH3) (15), which is the complex between ruthenium and the amine newly generated from the imine. At -80 degrees C the reaction of hydride 2 with 4-BnNHsC(6)H(9)=NPh (18), with an internal amine trap, only afforded [2,3,4,5-Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Ph)(C6H10-4-NHBn) (19), where the ruthenium binds to the amine originating from the imine, showing that neither complex A nor the diamine is formed. Above -8 degrees C complex 19 rearranged to the thermodynamically more stable [Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Bn)(C6H10-4-NHPh) (20). These results are consistent with an inner sphere mechanism in which the substrate coordinates to ruthenium prior to hydrogen transfer and are difficult to explain with the outer sphere pathway previously proposed.
|
|
