White phosphorus first Grützmacher, Hansjörg
Nature chemistry,
04/2022, Letnik:
14, Številka:
4
Journal Article
Recenzirano
Many of the methods used to make phosphines proceed via phosphorus trichloride-based intermediates, leading to chloride waste that is difficult to recycle. It has now been shown that this ...disadvantage can be overcome by using a method that directly converts white phosphorus into value-added phosphorus compounds.
An industrially applicable catalytic methodology for dihydrogen formation from a proton source remains at the forefront of all efforts to replace the present fossil fuel economy by a hydrogen ...economy. This review tries to summarize the achievements which have been made with molecular organometallic complexes as catalysts for the dehydrogenation of alcohols. Biology uses NAD
+
as a metal-free hydrogen acceptor which converts with the help of enzymes (alcohol dehydrogenase, aldehyde dehydrogenase) alcohols in carbonyl compounds, NADH, and protons. In the regeneration of NADH to NAD
+
, electrons are stored in electron transfer enzymes (ferredoxines) which are subsequently used to reduce protons to hydrogen with the help of hydrogenases or nitrogenases which ensures a very low overpotential for the reduction. Man-made organometallic complexes are rather primitive with respect to this complex machinery but use some principles from biology as guide lines. Classical complexes like rhodium or ruthenium phosphane complexes achieve at best a few thousands of turn over frequencies (TOFs). Established reactions like oxidative addition of the hydroxyl group of the substrate to the metal centre, β-hydrogen elimination from the α-CH group of the coordinated alcohol, product dissociation, and reductive elimination of hydrogen are involved in the proposed catalytic cycles. Complexes which show metal–ligand cooperativity show a significantly better performance with respect to turn over frequencies (conversion rate = activity) and turn over numbers (number of product molecules per catalyst molecule = efficiency). In these catalytic systems, the alcohol substrate is converted with the help of active centres in the ligand backbone which participate directly and reversibly in the transformation of the substrate. Present results indicate that dehydrogenative coupling reactions of the type, R–CH
2
–OH + XH → RCOX + 2H
2
, proceed especially well and can be applied to a wide range of substrates including multiple dehydrogenative couplings leading to polyesters or polyamides. In photocatalytic conversions, alcohols can be deoxygenated to hydrocarbons, CO, and H
2
which should be further explored in the future. New developments consist of the construction of organometallic fuel cells (OMFCs) where the anode is composed of molecular catalysts embedded into a conducting support material. Here no free hydrogen is evolved but it is directly converted to electric current and protons according to H
2
→ 2H
+
+ 2e. The review focuses on the catalysis with organometallic complexes but lists some selected results obtained with heterogeneous catalytic systems for comparison.
The first 4π‐electron resonance‐stabilized 1,3‐digerma‐2,4‐diphosphacyclobutadiene LH2Ge2P2 4 (LH=CHCHNDipp2 Dipp=2,6‐iPr2C6H3) with four‐coordinate germanium supported by a β‐diketiminate ligand and ...two‐coordinate phosphorus atoms has been synthesized from the unprecedented phosphaketenyl‐functionalized N‐heterocyclic germylene LHGe‐P=C=O 2 a prepared by salt‐metathesis reaction of sodium phosphaethynolate (P≡C−ONa) with the corresponding chlorogermylene LHGeCl 1 a. Under UV/Vis light irradiation at ambient temperature, release of CO from the P=C=O group of 2 a leads to the elusive germanium–phosphorus triply bonded species LHGe≡P 3 a, which dimerizes spontaneously to yield black crystals of 4 as isolable product in 67 % yield. Notably, release of CO from the bulkier substituted LtBuGe‐P=C=O 2 b (LtBu=CHC(tBu)N‐Dipp2) furnishes, under concomitant extrusion of the diimine Dipp‐NC(tBu)2, the bis‐N,P‐heterocyclic germylene DippNC(tBu)C(H)PGe2 5.
Elusive Ge≡P: A 4π‐electron resonance‐stabilized 1,3‐digerma‐2,4‐diphosphacyclobutadiene derivative LH2Ge2P2 (3; LH=CHCHN(2,6‐iPr2C6H32), could be synthesized, isolated, and structurally characterized. This compound resulted from the phosphaketenyl‐functionalized germylene LHGe(P=C=O) (1) through photolytic release of CO and subsequent head‐to‐tail dimerization of the presumed phosphagermyne intermediate, LHGe≡P (2).
The production of phosphoryl species (PO, PO2, HOPO) is believed to be of great importance for efficient flame‐retardant action in the gas phase. We present a detailed investigation of the thermal ...decomposition of dimethyl methylphosphonate (DMMP) probed by vacuum ultraviolet (VUV) synchrotron radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. This technique provides a snapshot of the thermolysis process and direct evidence of how the reactive phosphoryl species are generated during heat exposure. One of the key findings of this work is that only PO is formed in high concentration upon DMMP decomposition, whereas PO2 is absent. It can be concluded that the formation of PO2 needs an oxidative environment, which is typically the case in a real flame. Based on the identification of products such as methanol, formaldehyde, and PO, as well as the intermediates OPCH3, H2CPOH, and H2CP(O)H, supported by quantum chemical calculations, we were able to describe the predominant pathways that lead to active phosphoryl species during the thermal decomposition of DMMP.
Molecular fire extinguishers: The production of phosphoryl species is believed to be of great importance for efficient flame‐retardant action in the gas phase. A detailed investigation on the pathways to the PO radical from thermally cracked dimethyl methylphosphonate is presented.
Metal-catalyzed asymmetric processes offer one of the most straightforward ways to introduce stereogenic centers. Hence, the development of novel chiral ligands that can effectively induce asymmetry ...in reactions is crucial in modern organic synthesis. While many established chiral ligands bind to a metal through heteroatoms, structures that coordinate to metals through carbon atoms have received little attention so far. Here, we highlight the increasing number of such chiral chelating olefin ligands as well as their application in a variety of metal-catalyzed transformations.
Carbon dioxide and two equivalents of Na(OCP) form, in an equilibrium reaction, a CO2 adduct of the composition Na2(P2C3O4). The anion of this salt, O2C-P(CO)2P(2-), is built up by a four-membered ...1,3-diphosphetane-2,4-dione ring and a carboxylate unit attached to one of the phosphorus atoms. A remarkable π-delocalization was observed within the OCPCO moiety. The stepwise reaction mechanism leading to Na2(P2C3O4) was investigated with quantum chemical calculations. Accompanied by the release of CO2, Na2(P2C3O4) reacts with both 2-iodopropane and 4,4',4''-trimethoxytriphenylmethyl chloride to form four-membered cyclic anions. For comparison the analogous reactions were performed with Na(OCP) instead of Na2(P2C3O4) and the results are discussed in detail.
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•Phosphinines with different coordination modes.•Phosphinines in metal–ligand cooperativity.•Phosphinines in the activation of small molecules.•Phosphinines in catalysis.•Phosphinines ...in material science.•Phosphinines in light-induced transformations.
This review covers the progress that has been made during the last 10 years in the coordination chemistry of 1-phosphinines, 1,4-diphosphinines and 1,3,5-triphosphinines and related ligands. There is particular emphasis on the reactivity and application of phosphinine-containing transition metal complexes in relation to the electronic, structural and coordination properties of the corresponding phosphorus heterocycle.
The development of an efficient catalytic process that mimics the enzymatic function of alcohol dehydrogenase is critical for using biomass alcohols for both the production of H2 as a chemical energy ...carrier and fine chemicals under waste-free conditions. Dehydrogenation of alcohol-water mixtures into their corresponding acids with molecular hydrogen as the sole by-product from the reaction can be catalysed by a ruthenium complex with a chelating bis(olefin) diazadiene ligand. This complex, K(dme)2Ru(H)(trop2dad), stores up to two equivalents of hydrogen intramolecularly, and catalyses the production of H2 from alcohols in the presence of water and a base under homogeneous conditions. The conversion of a MeOH-H2O mixture proceeds selectively to CO2/H2 gas formation under neutral conditions, thereby allowing the use of the entire hydrogen content (12% by weight). Isolation and characterization of the ruthenium complexes from these reactions suggested a mechanistic scenario in which the trop2dad ligand behaves as a chemically 'non-innocent' co-operative ligand.
Stable Aminyl Radical Metal Complex Bůttner, Torsten; Geier, Jens; Frison, Gilles ...
Science (American Association for the Advancement of Science),
01/2005, Letnik:
307, Številka:
5707
Journal Article
Recenzirano
Metal-stabilized phenoxyl radicals appear to be important intermediates in a variety of enzymatic oxidations. We report that transition metal coordination also supports an aminyl radical, resulting ...in a stable crystalline complex: Rh(I)(trop₂Nsuperscript .)(bipy)⁺OTf⁻ (where trop is 5-H-dibenzoa,dcycloheptene-5-yl, bipy is 2,2'-bipyridyl, OTf⁻ is trifluorosulfonate). It is accessible under mild conditions by one-electron oxidation of the amide complex Rh(I)(trop₂N)(bipy), at a potential of -0.55 volt versus ferrocene/ferrocenium. Both electron paramagnetic resonance spectroscopy and density functional theory support 57% localization of the unpaired spin at N. In reactions with H-atom donors, the Rh-coordinated aminyl behaves as a nucleophilic radical.
The reactivity of Na(OCP) was investigated towards triorganyl compounds of the heavier group 14 elements (R3EX R = Ph or (i)Pr; E = Si, Ge, Sn, Pb; X = Cl, OTf). In the case of E = Si two ...constitutional isomers were formed and characterised in situ: R3Si-O-Ctriple bond, length as m-dashP is the kinetic and R3Si-Pdouble bond, length as m-dashCdouble bond, length as m-dashO is the thermodynamic product, representing experimental evidence of the ambident character of the (OCP)(-) anion. Applying theoretical calculations and spectroscopic methods, the compound previously reported as (i)Pr3Si-O-Ctriple bond, length as m-dashP can now unambiguously be identified as (i)Pr3Si-Pdouble bond, length as m-dashCdouble bond, length as m-dashO. The heavier analogues form exclusively the phosphaketene isomer R3E-Pdouble bond, length as m-dashCdouble bond, length as m-dashO (E = Ge, Sn, Pb). DFT calculations were performed to gain deeper insight into the bonding and thermodynamic stability of these compounds.
