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Prof. Javier A. Cabeza Dr. José M. Fernández-Colinas Dr. Joaquín García-Álvarez Dr. Pablo García-Álvarez Dr. Carlos J. Laglera-Gándara Marina Ramos-Martín 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(45):e202200847
A family of germyl rhodium complexes derived from the PGeP germylene 2,2’-bis(di-isopropylphosphanylmethyl)-5,5’-dimethyldipyrromethane-1,1’-diylgermanium(II), Ge(pyrmPiPr2)2CMe2 ( 1 ), has been prepared. Germylene 1 reacted readily with [RhCl(PPh3)3] and [RhCl(cod)(PPh3)] (cod=1,5-cyclooctadiene) to give, in both cases, the PGeP-pincer chloridogermyl rhodium(I) derivative [Rh{κ3P,Ge,P-GeCl(pyrmPiPr2)2CMe2}(PPh3)] ( 2 ). Similarly, the reaction of 1 with [RhCl(cod)(MeCN)] afforded [Rh{κ3P,Ge,P-GeCl(pyrmPiPr2)2CMe2}(MeCN)] ( 3 ). The methoxidogermyl and methylgermyl rhodium(I) complexes [Rh{κ3P,Ge,P-GeR(pyrmPiPr2)2CMe2}(PPh3)] (R=OMe, 4 ; Me, 5 ) were prepared by treating complex 2 with LiOMe and LiMe, respectively. Complex 5 readily reacted with CO to give the carbonyl rhodium(I) derivative [Rh{κ3P,Ge,P-GeR(pyrmPiPr2)2CMe2}(CO)] ( 6 ), with HCl, HSnPh3 and Ph2S2 rendering the pentacoordinate methylgermyl rhodium(III) complexes [RhHX{κ3P,Ge,P-GeMe(pyrmPiPr2)2CMe2}] (X=Cl, 7 ; SnPh3, 8 ) and [Rh(SPh)2{κ3P,Ge,P-GeMe(pyrmPiPr2)2CMe2}] ( 9 ), respectively, and with H2 to give the hexacoordinate derivative [RhH2{κ3P,Ge,P-GeMe(pyrmPiPr2)2CMe2}(PPh3)] ( 10 ). Complexes 3 and 5 are catalyst precursors for the hydroboration of styrene, 4-vinyltoluene and 4-vinylfluorobenzene with catecholborane under mild conditions. 相似文献
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Olivier Blacque Dr. Christian M. Frech Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1521-1531
Pincer‐type palladium complexes are among the most active Heck catalysts. Due to their exceptionally high thermal stability and the fact that they contain PdII centers, controversial PdII/PdIV cycles have been often proposed as potential catalytic mechanisms. However, pincer‐type PdIV intermediates have never been experimentally observed, and computational studies to support the proposed PdII/PdIV mechanisms with pincer‐type catalysts have never been carried out. In this computational study the feasibility of potential catalytic cycles involving PdIV intermediates was explored. Density functional calculations were performed on experimentally applied aminophosphine‐, phosphine‐, and phosphite‐based pincer‐type Heck catalysts with styrene and phenyl bromide as substrates and (E)‐stilbene as coupling product. The potential‐energy surfaces were calculated in dimethylformamide (DMF) as solvent and demonstrate that PdII/PdIV mechanisms are thermally accessible and thus a true alternative to formation of palladium nanoparticles. Initial reaction steps of the lowest energy path of the catalytic cycle of the Heck reaction include dissociation of the chloride ligands from the neutral pincer complexes [{2,6‐C6H3(XPR2)2}Pd(Cl)] [X=NH, R=piperidinyl ( 1 a ); X=O, R=piperidinyl ( 1 b ); X=O, R=iPr ( 1 c ); X=CH2, R=iPr ( 1 d )] to yield cationic, three‐coordinate, T‐shaped 14e? palladium intermediates of type [{2,6‐C6H3(XPR2)2}Pd]+ ( 2 ). An alternative reaction path to generate complexes of type 2 (relevant for electron‐poor pincer complexes) includes initial coordination of styrene to 1 to yield styrene adducts [{2,6‐C6H3(XPR2)2}Pd(Cl)(CH2?CHPh)] ( 4 ) and consecutive dissociation of the chloride ligand to yield cationic square‐planar styrene complexes [{2,6‐C6H3(XPR2)2}Pd(CH2?CHPh)]+ ( 6 ) and styrene. Cationic styrene adducts of type 6 were additionally found to be the resting states of the catalytic reaction. However, oxidative addition of phenyl bromide to 2 result in pentacoordinate PdIV complexes of type [{2,6‐C6H3(XPR2)2}Pd(Br)(C6H5)]+ ( 11 ), which subsequently coordinate styrene (in trans position relative to the phenyl unit of the pincer cores) to yield hexacoordinate phenyl styrene complexes [{2,6‐C6H3(XPR2)2}Pd(Br)(C6H5)(CH2?CHPh)]+ ( 12 ). Migration of the phenyl ligand to the olefinic bond gives cationic, pentacoordinate phenylethenyl complexes [{2,6‐C6H3(XPR2)2}Pd(Br)(CHPhCH2Ph)]+ ( 13 ). Subsequent β‐hydride elimination induces direct HBr liberation to yield cationic, square‐planar (E)‐stilbene complexes with general formula [{2,6‐C6H3(XPR2)2}Pd(CHPh?CHPh)]+ ( 14 ). Subsequent liberation of (E)‐stilbene closes the catalytic cycle. 相似文献
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A chiral C2-symmetric NCN ligand, (5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)benzene has been synthesized. A direct cyclometalation of this ligand with K2MCl4 (M = Pt, Pd) in dry acetic acid offered the corresponding pincer complexes, [(5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)phenyl]platinum(II) chloride 5a and its palladium(II) analogue 5b. The Pt(II) and Pd(II) complexes 5 were characterized by NMR spectroscopy, and X-ray crystal structure analysis was done for the Pt(II) complex. The NMR data for both the complexes and X-ray crystal structural data for the chloro-Pt(II) complex indicate the existence of intramolecular C-H?Cl hydrogen bonding both in solution and in solid states. Chloride abstraction from 5a by treatment with silver triflate resulted in the corresponding triflate complex 6a, which generates the corresponding cationic aqua complex 7a in the presence of water molecules. The Pt(II) complex 6a/7a was used as asymmetric catalyst in the aldol reaction between methyl isocyanoacetate and aldehydes and also in the silylcyanation of aldehydes. 相似文献
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The unsymmetrical, achiral and chiral NCN pincer ligand precursors (3a-3d) with oxazoline and pyrazole as N donors as well as (3e) which has oxazolinyl and amino group have been synthesized in a facile manner in four steps starting from commercially available isophthalaldehyde. Direct C2 metallation of the precursors (3a-3e) with Pd(OAc)2 in refluxing HOAc, followed by treatment with LiCl at room temperature provided convenient access to the corresponding pincer palladium(II) complexes (4a-4e). The molecular structure of complex 4e has been determined by X-ray single-crystal diffraction. The obtained Pd complexes exhibited good activities in the Suzuki reactions of aryl bromides and activated aryl chlorides with phenylboronic acid. 相似文献
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《Mendeleev Communications》2020,30(3):276-278
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Daniel M. Beagan Dr. Nicholas A. Maciulis Dr. Maren Pink Dr. Veronica Carta I. J. Huerfano Dr. Chun-Hsing Chen Dr. Kenneth G. Caulton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(45):11676-11681
The reaction chemistry of the bis-tetrazinyl pyridine ligand (btzp) towards nitrogen oxyanions coordinated to zinc is studied in order to explore the reduction of the NOx− substrates with a redox-active ligand in the absence of redox activity at the metal. Following syntheses and characterization of (btzp)ZnX2 for X=Cl, NO3 and NO2, featuring O−Zn linkage of both nitrogen oxyanions, it is shown that a silylating agent selectively delivers silyl substituents to tetrazine nitrogens, without reductive deoxygenation of NOx−1. A new synthesis of the highly hydrogenated H4btzp, containing two dihydrotetrazine reductants is described as is the synthesis and characterization of (H4btzp)ZnX2 for X=Cl and NO3, both of which show considerable hydrogen bonding potential of the dihydrotetrazine ring NH groups. The (H4btzp)ZnCl2 complex does not bind zinc in the pincer pocket, but instead H4btzp becomes a bridge between neighboring atoms through tetrazine nitrogen atoms, forming a polymeric chain. The reaction of AgNO2 with (H4btzp)ZnCl2 is shown to proceed with fast nitrite deoxygenation, yielding water and free NO. Half of the H4btzp reducing equivalents form Ag0 and thus the chloride ligand remains coordinated to the zinc metal center to yield (btzp)ZnCl2. To compare with AgNO2, experiments of (H4btzp)ZnCl2 with NaNO2 result in salt metathesis between chloride and nitrite, highlighting the importance of a redox-active cation in the reduction of nitrite to NO. 相似文献