22180-53-6Relevant articles and documents
Efficient oxidative carbonylation of iPrOH to oxalate catalyzed by Pd(II)-PPh3 complexes using benzoquinone as a stoichiometric oxidant
Amadio,Toniolo
, p. 72 - 77 (2014)
The catalytic system trans-[PdBr2(PPh3) 2]/NEt3/PPh3/LiBr is highly active and selective in the oxidative carbonylation of iPrOH to the corresponding oxalate using benzoquinone (BQ) as a stoichiometric oxidant. The oxalate is formed together with minor amounts of carbonate and acetone. The influence of each component in the catalytic system is discussed together with the influence of the concentration of BQ, reaction time, temperature and CO pressure. NEt3 neutralizes the acid released in the catalytic cycle, thus favouring the formation of a dicarboalkoxy intermediate. Added PPh 3 reacts with benzoquinone giving betaine, which is a base that contributes to a further enhancement of the catalytic activity. The Br - anion might coordinate the Pd(0) which is formed in the product forming step thus stabilizing it against decomposition and making its reoxidation easier and reentering into the catalytic cycle. The catalytic activity depends slightly only on the concentration of BQ, suggesting that either uncoordinated BQ is not involved in the slow step of the catalytic cycle or that BQ is strongly coordinated in these species. The catalytic activity toward oxalate increases upon increasing the concentrations of NEt3 and PPh3, whereas the selectivity toward carbonate and the formation of acetone remains practically constant. The increase of the pressure of CO has a similar effect, except that the formation of acetone is suppressed. It is suggested that at relatively high pressure of CO, a pentacoordinated species may be formed so that there is no place for any interaction between palladium and the C-H bond before the β-H elimination. Instead there is a nucleophilic intrasphere attack of the alkoxy ligand onto a CO ligand. After catalysis the precursor trans-[PdBr2(PPh3)2] has been detected, together with trans-[PdBr(COOiPr)(PPh3) 2] and [Pd(BQ)(PPh3)2]. PPh3 remains coordinated to the palladium centre during catalysis. A BQ- and halides-assisted catalytic cycle is proposed. In this cycle, the reoxidation occurs through the release of a proton from an ammonium salt or a phosphonium salt, which are formed during the catalysis, with reformation of the catalyst precursor.
Atomic contributions from spin-orbit coupling to 29Si NMR chemical shifts in metallasilatrane complexes
Autschbach, Jochen,Sutter, Kiplangat,Truflandier, Lionel A.,Brendler, Erica,Wagler, Joerg
, p. 12803 - 12813 (2012)
New members of a novel class of metallasilatrane complexes [X-Si-(μ-mt)4-M-Y], with M=Ni, Pd, Pt, X=F, Cl, Y=Cl, Br, I, and mt=2-mercapto-1-methylimidazolide, have been synthesized and characterized structurally by X-ray diffraction and by 29Si solid-state NMR. Spin-orbit (SO) effects on the 29Si chemical shifts induced by the metal, by the sulfur atoms in the ligand, and by heavy halide ligands Y=Cl, Br, I were investigated with the help of relativistic density functional calculations. Operators used in the calculations were constructed such that SO coupling can selectively be switched off for certain atoms. The unexpectedly large SO effects on the 29Si shielding in the Ni complex with X=Y=Cl reported recently originate directly from the Ni atom, not from other moderately heavy atoms in the complex. With respect to Pd, SO effects are amplified for Ni owing to its smaller ligand-field splitting, despite the smaller nuclear charge. In the X=Cl, Y=Cl, Br, I series of complexes the Y ligand strongly modulates the 29Si shift by amplifying or suppressing the metal SO effects. The pronounced delocalization of the partially covalent M←Y bond plays an important role in modulating the 29Si shielding. We also demonstrate an influence from the X ligand on the 29Si SO shielding contributions originating at Y. The NMR spectra for [X-Si-(μ-mt) 4-M-Y] must be interpreted mainly based on electronic and relativistic effects, rather than structural differences between the complexes. The results highlight the sometimes unintuitive role of SO coupling in NMR spectra of complexes containing heavy atoms. All in a spin! The class of metallasilatrane complexes [X-Si-(μ-mt)4-M-Y] with M=Ni, Pd, and Pt, previously reported for X=Y=Cl (shown here), has been extended by new members with X=F and Y=Br and I. New synthetic routes, structural characterizations by X-ray diffraction, and 29Si solid-state NMR data are reported. Spin-orbit effects on the 29Si chemical shifts were investigated with the help of relativistic density functional calculations. Copyright
Oxidative Mechanochemistry: Direct, Room-Temperature, Solvent-Free Conversion of Palladium and Gold Metals into Soluble Salts and Coordination Complexes
Do, Jean-Louis,Tan, Davin,Fri??i?, Tomislav
supporting information, p. 2667 - 2671 (2018/02/06)
Noble metals are valued, critical elements whose chemical activation or recycling is challenging, and traditionally requires high temperatures, strong acids or bases, or aggressive complexation agents. By using elementary palladium and gold, demonstrated here is the use of mechanochemistry for noble-metal activation and recycling by mild, clean, solvent-free, and room-temperature chemistry. The process leads to direct, efficient, one-pot conversion of the metals, including spent catalysts, into either simple water-soluble salts or metal–organic catalysts.
A Combined Experimental/Computational Study of the Mechanism of a Palladium-Catalyzed Bora-Negishi Reaction
Campos, Jesús,Nova, Ainara,Kolychev, Eugene L.,Aldridge, Simon
, p. 12655 - 12667 (2017/09/18)
Experimental and computational efforts are reported which illuminate the mechanism of a novel boron version of the widespread Negishi coupling reaction that offers a new protocol for the formation of aryl/acyl C?B bonds using a bulky boryl fragment. The role of nucleophilic borylzinc reagents in the reduction of the PdII pre-catalysts to Pd0 active species has been demonstrated. The non-innocent behavior of the PPh3 ligands of the [Pd(PPh3)2Cl2] pre-catalyst under activation conditions has been probed both experimentally and computationally, revealing the formation of a trimetallic Pd species bearing bridging phosphide (PPh2?) ligands. Our studies also reveal the monoligated formulation of the Pd0 active species, which led us to synthesize related (η3-indenyl)Pd-monophosphine catalysts which show improved catalytic performances under mild conditions. A complete mechanistic proposal to aid future catalyst developments is provided.
