Reaction of {LiC6H2−2,4,6‐Cyp3⋅Et2O}2(Cyp=cyclopentyl) (
Reaction of {LiC6H2−2,4,6‐Cyp3⋅Et2O}2(Cyp=cyclopentyl) (
- NSF-PAR ID:
- 10413042
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 135
- Issue:
- 22
- ISSN:
- 0044-8249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract 1 ) of the new dispersion energy donor (DED) ligand, 2,4,6‐triscyclopentylphenyl with SnCl2afforded a mixture of the distannene {Sn(C6H2−2,4,6‐Cyp3)2}2(2 ), and the cyclotristannane {Sn(C6H2−2,4,6‐Cyp3)2}3(3 ).2 is favored in solution at higher temperature (345 K or above) whereas3 is preferred near 298 K. Van't Hoff analysis revealed the3 to2 conversion has a ΔH =33.36 kcal mol−1and ΔS =0.102 kcal mol−1 K−1, which gives a ΔG 300 K=+2.86 kcal mol−1, showing that the conversion of3 to2 is an endergonic process. Computational studies show that DED stabilization in3 is −28.5 kcal mol−1per {Sn(C6H2−2,4,6‐Cyp3)2unit, which exceeds the DED energy in2 of −16.3 kcal mol−1per unit. The data clearly show that dispersion interactions are the main arbiter of the3 to2 equilibrium. Both2 and3 possess large dispersion stabilization energies which suppress monomer dissociation (supported by EDA results). -
more » « less
Abstract Binuclear alkyne manganese carbonyls of the type (RC≡CR')Mn2(CO)
n (R and R'=methyl or dimethylamino;n =8, 7, 6) and their isomers related to the experimentally known (MeC2NEt2)Mn2(CO)n (n =8, 7) structures have been investigated by density functional theory. The alkyne ligand remains intact in the only low energy (Me2N)2C2Mn2(CO)8isomer, which has a central Mn2C2tetrahedrane unit and is otherwise analogous to the well‐known (alkyne)Co2(CO)6derivatives except for one more CO group per metal atom. The low‐energy structures of the unsaturated (Me2N)2C2Mn2(CO)n (n =7, 6) systems include isomers in which the nitrogen atom of one of the dimethylamino groups as well as the C≡C triple bond of the alkyne is coordinated to the central Mn2unit. In other low‐energy (Me2N)2C2Mn2(CO)n (n =7, 6) isomers the alkyne C≡C triple bond has broken completely to form two separate bridging dimethylaminocarbyne Me2NC ligands analogous to the experimentally known iron carbonyl complex (Et2NC)2Fe2(CO)6. The (alkyne)Mn2(CO)n (n =8, 7, 6) systems of the alkynes MeC≡CMe and Me2NC≡CMe with methyl substituents have significantly more complicated potential surfaces. In these systems the lowest energy isomers have bridging ligands derived from the alkyne in which one or two hydrogen atoms have migrated from a methyl group to one or both of the alkyne carbon atoms. These bridging ligands include allene, manganallyl, and vinylcarbene ligands, the first two of which have been realized experimentally in research by Adams and coworkers. Theoretical studies suggest that the mechanism for the conversion of the simple alkyne octacarbonyl (MeC2NMe2)Mn2(CO)8to the dimethylaminomanganaallyl complex Mn2(CO)7[μ‐η4‐C3H3Me2] involves decarbonylation to the heptacarbonyl and the hexacarbonyl complexes. Subsequent hydrogen migrations then occur through intermediates with C−H−Mn agostic interactions to give the final product. Eight transition states for this mechanistic sequence have been identified with activation energies of ∼20 kcal/mol for the first hydrogen migration and ∼14 kcal/mol for the second hydrogen migration. -
more » « less
Abstract Reaction of (
P )AuOTf [P =P(t ‐Bu)2o ‐biphenyl] with indenyl‐ or 3‐methylindenyl lithium led to isolation of gold η1‐indenyl complexes (P )Au(η1‐inden‐1‐yl) (1 a ) and (P )Au(η1‐3‐methylinden‐1‐yl) (1 b ), respectively, in >65 % yield. Whereas complex1 b is static, complex1 a undergoes facile, degenerate 1,3‐migration of gold about the indenyl ligand (ΔG ≠153K=9.1±1.1 kcal/mol). Treatment of complexes1 a and1 b with (P )AuNTf2led to formation of the corresponding cationic bis(gold) indenyl complexestrans ‐[(P )Au]2(η1,η1‐inden‐1,3‐yl) (2 a ) andtrans ‐[(P )Au]2(η1,η2‐3‐methylinden‐1‐yl) (2 b ), respectively, which were characterized spectroscopically and modeled computationally. Despite the absence of aurophilic stabilization in complexes2 a and2 b , the binding affinity of mono(gold) complex1 a toward exogenous (P )Au+exceed that of free indene by ~350‐fold and similarly the binding affinity of1 b toward exogenous (P )Au+exceed that of 3‐methylindene by ~50‐fold. The energy barrier for protodeauration of bis(gold) indenyl complex2 a with HOAc was ≥8 kcal/mol higher than for protodeauration of mono(gold) complex1 a . -
more » « less
Abstract We have been interested in the development of rubisco‐based biomimetic systems for reversible CO2capture from air. Our design of the chemical CO2capture and release (CCR) system is informed by the understanding of the binding of the activator CO2(ACO2) in rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase). The active site consists of the tetrapeptide sequence Lys‐Asp‐Asp‐Glu (or KDDE) and the Lys sidechain amine is responsible for the CO2capture reaction. We are studying the structural chemistry and the thermodynamics of CO2capture based on the tetrapeptide CH3CO−KDDE−NH2(“KDDE”) in aqueous solution to develop rubisco mimetic CCR systems. Here, we report the results of1H NMR and13C NMR analyses of CO2capture by butylamine and by KDDE. The carbamylation of butylamine was studied to develop the NMR method and with the protocol established, we were able to quantify the oligopeptide carbamylation at much lower concentration. We performed a pH profile in the multi equilibrium system and measured amine species and carbamic acid/carbamate species by the integration of1H NMR signals as a function of pH in the range 8≤pH≤11. The determination of Δ
G 1(R) for the reaction R−NH2+CO2R−NH−COOH requires the solution of a multi‐equilibrium equation system, which accounts for the dissociation constants K 2andK 3controlling carbonate and bicarbonate concentrations, the acid dissociation constantK 4of the conjugated acid of the amine, and the acid dissociation constantK 5of the alkylcarbamic acid. We show how the multi‐equilibrium equation system can be solved with the measurements of the daughter/parent ratioX , the knowledge of the pH values, and the initial concentrations [HCO3−]0and [R‐NH2]0. For the reaction energies of the carbamylations of butylamine and KDDE, our best values are ΔG 1(Bu)=−1.57 kcal/mol and ΔG 1(KDDE)=−1.17 kcal/mol. Both CO2capture reactions are modestly exergonic and thereby ensure reversibility in an energy‐efficient manner. These results validate the hypothesis that KDDE‐type oligopeptides may serve as reversible CCR systems in aqueous solution and guide designs for their improvement. -
more » « less
Abstract Aluminyl anions are low‐valent, anionic, and carbenoid aluminum species commonly found stabilized with potassium cations from the reaction of Al‐halogen precursors and alkali compounds. These systems are very reactive toward the activation of
σ ‐bonds and in reactions with electrophiles. Various research groups have detected that the potassium atoms play a stabilization role via electrostatic and cationinteractions with nearby (aromatic)‐carbocyclic rings from both the ligand and from the reaction with unsaturated substrates. Since stabilizing K⋯H bonds are witnessed in the activation of this class of molecules, we aim to unveil the role of these metals in the activation of the smaller and less polarizable H2molecule, together with a comprehensive characterization of the reaction mechanism. In this work, the activation of H2utilizing a NON‐xanthene‐Al dimer, [K{Al(NON)}]2( D ) and monomeric, [Al(NON)]−(M ) complexes are studied using density functional theory and high‐level coupled‐cluster theory to reveal the potential role of K+atoms during the activation of this gas. Furthermore, we aim to reveal whetherD is more reactive thanM (or vice versa), or if complicity between the two monomer units exits within theD complex toward the activation of H2. The results suggest that activation energies using the dimeric and monomeric complexes were found to be very close (around 33 kcal mol−1). However, a partition of activation energies unveiled that the nature of the energy barriers for the monomeric and dimeric complexes are inherently different. The former is dominated by a more substantial distortion of the reactants (and increased interaction energies between them). Interestingly, during the oxidative addition, the distortion of the Al complex is minimal, while H2distorts the most, usually over 0.77. Overall, it is found here that electrostatic and induction energies between the complexes and H2are the main stabilizing components up to the respective transition states. The results suggest that the K+atoms act as stabilizers of the dimeric structure, and their cooperative role on the reaction mechanism may be negligible, acting as mere spectators in the activation of H2. Cooperation between the two monomers in D is lacking, and therefore the subsequent activation of H2is wholly disengaged.
