Sterically encumbered Lewis acid and Lewis base combinations do not undergo the ubiquitous neutralization reaction to form "classical" Lewis acid/Lewis base adducts. Rather, both the unquenched Lewis acidity and basicity of such sterically "frustrated Lewis pairs (FLPs)" is available to carry out unusual reactions. Typical examples of frustrated Lewis pairs are inter- or intramolecular combinations of bulky phosphines or amines with strongly electrophilic RB(C(6)F(5))(2) components. Many examples of such frustrated Lewis pairs are able to cleave dihydrogen heterolytically. The resulting H(+)/H(-) pairs (stabilized for example, in the form of the respective phosphonium cation/hydridoborate anion salts) serve as active metal-free catalysts for the hydrogenation of, for example, bulky imines, enamines, or enol ethers. Frustrated Lewis pairs also react with alkenes, aldehydes, and a variety of other small molecules, including carbon dioxide, in cooperative three-component reactions, offering new strategies for synthetic chemistry.

Frustrated Lewis pairs: metal-free hydrogen activation and more.

Thionation reactions of lawesson's reagents

Frustrated Lewis pairs comprising phosphine and borane react to reversibly bind and release CO2, offering a rare example of metal-free CO2 sequestration. The mechanism of formation of CO2 derivatives by almost simultaneous P-C and O-B bond formation was characterized by quantum chemical calculations.

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Reversible Metal-Free Carbon Dioxide Binding by Frustrated Lewis Pairs

Frustrierte Lewis‐Paare: metallfreie Wasserstoffaktivierung und mehr

The Transition Metal Coordination Chemistry of Hemilabile Ligands

A Cage Molecule with a Cubanoid P4B4 Framework: tBu4P4Ph4B4O12—A Structural Analogue of the Isovalence Electronic Organosilasesquioxanes R8Si8O12

A wide range of dithiophosphinic acids RR'P(S)SH with different organogroups was obtained in good yields by nucleophilic fission of perthiophosphonic anhydrids (RPS2)2 with Grignard reagents R'MgX. Some reactions, derivatives and metal complexes [RR'P(S)S] M/n of these acids, which are useful intermediates for the synthesis of chiral organophosphorus compounds, are reported. Eine Vielzahl von Dithiophosphinsauren RR'P(S)SH mit unterschiedlichen Organoresten konnte in guter Ausbeute durch nukleophile Spalung von Perthiophosphonsaureanhydriden (RPS2)2 mit Grignardverbindungen R'MgX dargestellt werden. Einige Reaktionen, Derivate und Metallkomplexe [RR'P(S)S] M/n dieser Sauren, die fur die Synthese chiraler Organophosphorverbindungen von Interesse sind, werden beschrieben.

ZUR KENNTNIS DER ORGANOPHOSPHORVERBINDUNGEN, XVII1 Dithiophosphinsäuren RR'P(S)SH, Ihre Synthese, Derivate und Metallkomplexe

Durch nucleophile Spaltung von Perthiophosphonsaureanhydriden (RPS2)2 mit Di-Grignard-reagentien XMgR′MgX konnen bequem bifunktionelle Dithiophosphinsauren XS(S)P(R)R′P(R)(S)SX (X = H, Na, NH4, (CH3)3NH; R = CH3, C6H5, 4-CH3OC6H4; R′ = 1,4-C6H4, [CH2]n mit n = 4–10) erhalten werden. Diese konnen leicht in die entsprechenden Ester, Saureamide und -chloride ubergefuhrt werden, wie an einigen Beispielen gezeigt wird. Bei der Oxidation von H4NS(S)P(R)R′P(R)(S)SNH4 (R = 4-CH3OC6H4; R′ = [CH2]6) mit Iod, Cu2+ oder Tl3+ entstand ein Gemisch oligometer Disulfane [(S)P(R)R′P(R)(S)SS]n (n = ca. 2–4), bei der Hydrolyse des Methylesters CH3S(S)P(R)R′P(R)(S)SCH3 (R = 4-CH3OC6H4; R = 1,4-C6H4) die bifunktionelle Monothiophosphinsaure HO(S)P(R)R′P(R)(S)OH.



On Organophosphorus Compounds, XVIII: Bifunctional Dithiophosphinic Acids HS(S)P(R)R′P(R)(S)SH and Some of Their Derivatives



Bifunctional dithiophosphinic acids are easily obtained by nucleophilic fission of perthiophosphonic anhydrides (RPS2)2 with di-Grignard reagents XMgR′MgX. By this method numercus compounds of the type XS(S)P(R)R′P(R)(S)SX (X = H, Na, NH4, (CH3)3NH; R = CH3, C6H5, 4-CH3OC6H4; R′ = 1,4′C6H4, [CH2]n with n = 4–10) were prepared. These could be easily converted into the corresponding esters, amides, and -chlorides as is shown by some examples. Oxidation of H4NS(S)P(R)R′P(R)(S)SNH4 (R = 4-CH3OC6H4; R′ = [CH2]6) with I2, CU2+, or Tl3+ gave a mixture of oligomeric disulfanes ((S)P(R)R′P(R)(S)SS)n (n = approx. 2–4), hydrolysis of the methyl ester CH3S(S)P(R)R′P(R)(S)SCH3 (R = 4-CH3OC6H4; R′ = 1,4-C6H4) gave the bifunctional monothiophosphinic acid HO(S)P(R)R′P(R)(S)OH.

Zur Kenntnis der Organophosphorverbindungen, XVIII: Bifunktionelle Dithiophosphinsäuren HS(S)P(R)R′P(R)(S)SH und einige ihrer Derivate

By reaction of RP(O)Cl2 with RP(O)(OSiMe3)2, phosphonic anhydrides (RPO2)3 (R = tBu, 2-methylphenyl, 2,4,6-trimethylphenyl) 1a−c are conveniently obtained. In contrast to 1b and 1c, compound 1a is remarkably stable against protolysis. Intermediates of hydrolysis of 1a, namely tris(tert-butyl)triphosphonic acid (2) and bis(tert-butyl)diphosphonic acid (3), can also be isolated in good yield. The structures of 1−3 were determined mainly by NMR spectroscopy (1 H, 13C, 31P). Assuming an energetic preference for the chair conformations in solution, and considering the steric requirements of the bulky substituents R, configurations Ia (point group Cs, two R in equatorial positions) for 1a and b, and IIa (point group C3v, all R equatorial) for 1c are suggested. − Reaction of 1a with N-benzyloxycarbonylglycine (4) in methanol affords strong evidence that in the first step of peptide synthesis with (RPO2)3, a mixed anhydride of triphosphonic acid and the N-protected amino acid is formed. − The crystal structure of 1a (monoclinic, space group P21/n) widely corresponds to the suggested configuration Ia, but reveals an envelope conformation for the six-membered ring with a P3O2 plane in the crystal. In the crystal structure of the octahydrate of the disodium salt of 2 (monoclinic, space group P21/c), it can be seen that the polar end groups of the anions [tBu3P3O7]2− together with the water molecules and the Na+ cations, form hydrogen-bonded double-layers, strictly separated from each other by the non-polar tert-butyl groups of the anions.

A Convenient Synthesis of Phosphonic Anhydrides − Trimers [RPO2]3 (R = tert-Butyl, 2-Methylphenyl, 2,4,6-Trimethylphenyl): Their Structures and Reaction Products

Bifunktionelle Organobromphosphane Br2P[CH2]nPBr2 (n = 1–10) 1 und BrP(R′)RP-(R′)Br (R = [CH2]n, p-C6H4; R′ = Alkyl, Ph) 4 bzw. 8a wurden in Abhangigkeit von n, R und R′ nach verschiedenen Verfahren synthetisiert. Einige ihrer Reaktionen werden beschrieben und ihre 31P-NMR-Spektren diskutiert. 1,2-Diphosphacycloalkane 13 wurden in stereospezifischer Reaktion durch Dehalogenierung von 4 mit Metallen erhalten.



On Organophosphorus Compounds, XIX. Synthesis and Properties of Bifunctional Organobromophosphanes



Bifunctional organobromophosphanes Br2P[CH2]nPBr2 (n = 1–10) 1 and BrP(R′)RP-(R′)Br (R = [CH2]n, p-C6H4, R′ = Alkyl, Ph) 4 and 8a, respectively, were synthesized by different methods depending on n, R and R′. Some of their reactions are reported and their 31P NMR spectra discussed. 1,2-Diphosphacycloalkanes 13 were obtained in a stereospecific reaction by dehalogenation of 4 with metals.

Klaus Diemert

Papers

A Cage Molecule with a Cubanoid P4B4 Framework: tBu4P4Ph4B4O12—A Structural Analogue of the Isovalence Electronic Organosilasesquioxanes R8Si8O12

ZUR KENNTNIS DER ORGANOPHOSPHORVERBINDUNGEN, XVII1 Dithiophosphinsäuren RR'P(S)SH, Ihre Synthese, Derivate und Metallkomplexe

Zur Kenntnis der Organophosphorverbindungen, XVIII: Bifunktionelle Dithiophosphinsäuren HS(S)P(R)R′P(R)(S)SH und einige ihrer Derivate

A Convenient Synthesis of Phosphonic Anhydrides − Trimers [RPO2]3 (R = tert-Butyl, 2-Methylphenyl, 2,4,6-Trimethylphenyl): Their Structures and Reaction Products

Zur Kenntnis der Organophosphorverbindungen, XIX. Synthese und Eigenschaften bifunktioneller Organobromphosphane