650598-01-9Relevant academic research and scientific papers
Remarkably stable Copper(I) α-carbonyl carbenes: synthesis, structure, and mechanistic studies of alkene cyclopropanation reactions
Shishkov, Igor V.,Rominger, Frank,Hofmann, Peter
, p. 1049 - 1059 (2009)
The reaction of [tBu2P(NSiMe3)2-k 2Cu(C2H4) (1) with various aryl diazo esters [p-X- C6H4]C(N2)[C(O)R] allowed us to synthesize the corresponding a-carbonyl copper(I) carbene complexes [tBu 2P(NSiMe3)2-/f2Ar|Cu=C[p-X-C6H4][C(O)R] (8), where X = OMe, NO,. The rotation barriers around the Cu-Ccarbene and C carbene -CAr bonds or their low limits were determined for some of these compounds by 1H-VT-NMR spectroscopy. Carbene 8g with X = OMe and R = OCH(p-Cl-CI-C6H4)2 was isolated in analytically pure, crystalline form as the first stable representative of this important class of compounds. Its solid-state molecular structure revealed an orthogonal position of the carbene fragment relative to both the ligand plane and the ester C=0 group and a remarkably short Cu-Ccarbene distance of 1.822(4) A. Compound 8g reacted with styrene stereoselectively to give the corresponding trans-cyclopropane derivative and [tBu2P(NSiMe 3)2-K2N]Cu(η2-CH 2=CHPh). The stoichiometric cyclopropanation of styrene with 8g and the previously described diarylcarbene [tBu2P(NSiMe 3)2-k2N]Cu=C[p-NO2-C6H 4]2 (6) in toluene-d8 revealed that the reactions are first order in both the copper carbenes and the alkene. The activation parameters for 8g (?H# = 51.5(9) kJ/mol and ?S# = -127.1(28) J/(mol K)] and for 6 (?H# = 53.4(8) kJ/mol and ?S# = -152.1(23) J/(mol K)) were derived from the kinetics of the cyclopropanation processes. Thermal decomposition of carbene 8g in toluene-d8 displayed first-order kinetics until 20-25% conversion with activation parameters ?H# = 85.5(24) kJ/mol and ?S# = -49.0(76) J/(mol K). Solutions of 6 in toluene-d8 also decompose in a first-order fashion with ?H# = 66.1(20) kJ/mol and ?S# =- 125.5(56) J/(mol K). A Hammett study employing 8g and para-substituted styrenes afforded p =- 1.06(19), demonstrating the electrophilic nature of a-carbonyl copper(I) carbene (Fischer-type) complexes. The electronic structure of 8 with X = R = OMe was investigated by DFT methods.
Mechanism of copper(I)-catalyzed cyclopropanation: A DFT study calibrated with copper(I) alkene complexes
Straub, Bernd F.,Gruber, Irene,Rominger, Frank,Hofmann, Peter
, p. 124 - 143 (2003)
The complete catalytic cycle of copper-catalyzed cyclopropanation is investigated by density functional model calculations. The study focuses on obtaining accurate relative stabilities of the ligand-metal cores of all catalytic intermediates and transition states. The copper iminophosphanamide [H2P(NH2) 2-κ2N]Cu serves as model fragment, since three copper catalyst key intermediates with an iminophosphanamide ligand have been isolated or detected. The electronic structure of the active intermediates, copper(I) carbenes of the d10-ML 3 type, and their reactivity towards ethene and vinyl alcohol is investigated. The reliability of the computed data is confirmed by their comparison with experimental data of [t-Bu2P(NSiMe 3)2-κ2N]Cu alkene and alkyne complexes, using relative ligand binding strengths and alkene ligand rotation barriers. The uncharged nature of the model complexes minimizes solvation artifacts and thus renders the evaluation of associative and dissociative ligand exchange pathways possible. The associative alkene ligand exchange with diazoalkane to a κN,κ O-diazoalkane complex, subsequent intramolecular rearrangement to a κ C-complex and N2 extrusion are identified on the most probable pathway to the electrophilic copper(I) carbene complexes of the Fischer type. They are predicted to react with alkenes to labile cupracyclobutanes with a planar N2CuIII C2 core, which undergo facile reductive elimination of a cyclopropane derivative.
Synthesis, molecular structures, and reactivity of mono- and binuclear neutral copper(I) carbenes
Hofmann, Peter,Shishkov, Igor V.,Rominger, Frank
, p. 11755 - 11762 (2009/05/08)
Mononuclear, neutral copper(I) carbenes [But 2P(NSiMe3)2-κ2N]Cu=CPh 2 and [But2P(NSiMe3) 2-κ2N]Cu=C(p-NO2C6H su
