Search

Isomeric bis(phosphanyl) carbenium ions have been investigated by theoretical [MP2/6-31G(d,p) level of theory] and experimental means. On the potential energy surface (PES) of phosphorus cations of the formula [P2CH5]+, five stable isomers are found. Their structures follow the stability order (ΔErel/kcal mol−1): P-protonated diphosphiranium, [(H2P)(HP)CH2]+ 1a (0.0) > C-phosphonio phosphaalkene, [H3P–HCPH]+ 2a (4.5) ≫ bis(phosphanyl) carbenium, [CH(PH2)2]+ 3a (18.5) > C-phosphanyl methylenephosphonium, [H2P–CHPH2]+ 4a (22.6) ≫ diphosphirenium, 5a (47.1). The stability order is very different for the family of the four related stable [P2CH(NH2)4]+ ions 1b, 2b, 4b, 5b in which the phosphorus-bound hydrogens (and one carbon-bound hydrogen in the case of 1b) have been replaced by NH2 groups: 2b (−39.6) ≫ 1b (0.0) > 5b (2.2) ≥ 4b (3.7). None of these ions has a structure comparable to the classical amidinium ion [HC(NH2)2]+. While all amino carbenium ions have a positively charged carbon atom, all phosphorus analogues carry a negative charge on carbon. In some, even the p(π)-population exceeds unity suggesting that these should be considered as cationic methanides. Experimentally, a derivative of the diphosphiranium ion 1a could be prepared by methylation of 1,2-bis-(2,4,6-tri-tert-butylphenyl)diphosphirane with MeO3SCF3, and this new compound 8 was characterized by NMR methods. Although the most stable member in this family, it could only be observed under stable ion conditions (T

A synthesis of the new ligand 5-diphenylphosphanyl-10-methyl-5H-dibenzo[a,d]cycloheptene (metroppph) was developed in order to prepare highly distorted tetra-co-ordinated rhodium(+I) complexes. The ligand metroppph contains a cycloheptatriene ring in a rigid boat conformation such that a Ph2P and an olefinic binding site are perfectly arranged for transition metal complexation. Four equivalents of metroppph react with [Rh2(μ-Cl)2(cod)2] in the presence of KPF6 to yield almost quantitatively [Rh(+I)(metroppph)2]PF6, which was isolated in the form of dark red-violet crystals. A crystal structure analysis reveals that the co-ordination sphere of the rhodium centre in [Rh(+I)(metroppph)2]+ deviates strongly from a square planar arrangement (φ = 42°). One methyl group in [Rh(+I)(metroppph)2]+ can be deprotonated by KOBut to give the allyl complex [Rh(allyltroppph)(metroppph)]. This complex has a structure that may be best described as a distorted trigonal bipyramid. The boron hydride [BEt3H]− and organolithium reagents, LiR, react with [Rh(allyltroppph)(metroppph)] in allylic alkylation reactions to yield anionic rhodate complexes [Rh(RCH2troppph)(metroppph)]− (R = H, Me, n-Bu, Ph) that formally have a d10 valence electron configuration. The rhodate [Rh(metroppph)2]− can be obtained directly by reduction of cation [Rh(metroppph)2]+ with alkali metals. In a sym-proportionation reaction [Rh(metroppph)2]+ and [Rh(metroppph)2]− give the neutral d9-[Rh(metroppph)2] radical (K = 1.1 × 107), which is not stable but decomposes with loss of H2 to give the allyl complex [Rh(allyltroppph)(metroppph)]. The structures in solution of [Rh(metroppph)2]+, [Rh(allyltroppph)(metroppph)], and [Rh(nBuCH2troppph)(metroppph)]− were determined by NMR techniques, which reveal that (i) they match the solid state structures and (ii) are rather similar to each other. This fact may explain the remarkable electronic flexibility of the rhodium centre, which changes reversibly its formal oxidation state from + I to 0 to − I at rather low negative potentials (ΔE01 = − 0.882 V; ΔE02 = − 1.298 V).

The stability of phosphiranes can be enhanced by inclusion of the PC2 ring into a polycyclic framework. BABAR-Phos type phosphiranes are easily prepared in high yield, they are thermally stable and allow the synthesis of various platinum(0) complexes. In contrast to other platinum(0) phosphine complexes, these are active hydrosilylation catalyst precursors. The reversible insertion of an electron rich metal centre into one P–C bond of the phosphirane ring was demonstrated for the first time.

The oxidation of the methylenediphosphanes 3a,b with hexafluoroacetone does not lead to the expected dioxaphospholane heterocycles, but yields quantitatively the carbodiphosphoranes 5a,b. Compounds 5a,b easily add HCl, HF or Cl2 to the ylidic bonds. The chloro derivative 14b, and its analogue 17 were used for the synthesis of phosphonium substituted carbenes.

Many catalytic active transition metal complexes contain phosphines as ligands which control decisively the activity and selectivity of the catalyst. Therefore synthetic methods which allow the preparation of highly functionalized phosphines are needed to match the increasing demands for higher activity and selectivity in catalytic processes. In this report we introduce a simple general new method for the synthesis of phosphines, arsines, and stibines. This allowed for example the preparations of phosphines based on serine and thymine derivatives (SerPhos and ThymPhos, respectively).

A 35-fold excess of methyl triflate (2) is required to quantitively prepare 3, the first phosphanyl phosphenium ion, from diphosphene 1. Experimental data and calculations indicate that the P=P bond becomes stronger upon alkylation.

In prokaryotic transcription regulation several host factors form a complex with RNA polymerase and the nascent mRNA. As part of a process known as antitermination, two of these host factors, NusB and NusE, bind to form a heterodimer, which interacts with a specific boxA site on the RNA. The NusB/NusE/boxA RNA ternary complex interacts with the RNA polymerase transcription complex, stabilizing it and allowing transcription past premature termination points. The NusB protein also binds boxA RNA individually and retains all specificity for boxA. However, NusE increases the affinity of RNA to NusB in the ternary complex which contributes to efficient antitermination. To understand the molecular mechanism of the process, we have determined the structure of NusB from the thermophilic bacterium Aquifex aeolicus and studied the interaction of NusB and NusE. We characterize this binding interaction using NMR, isothermal titration calorimetry, gel-filtration and analytical ultracentrifugation. The binding site of NusE on NusB was determined using NMR chemical shift perturbation studies. We have also determined the NusE binding site in the ternary E. coli NusB/NusE/boxA RNA complex and show it is very similar to that in the NusB/NusE complex. There is one loop of residues, from 113−118 in NusB that are affected by NusE binding in the ternary complex, but not in the binary complex. This difference may be correlated to an increase in binding affinity of RNA for the NusB/NusE complex. Funded in part by NCI Contract N01-CO-12400.

Copper phosphide or arsenide complexes, [Cu(EPh(2))(neo)] (E = P, As, neo = 2,9-dimethyl-1,10-phenanthroline; trivial name: neocuprine) react selectively with the N-protected brominated serine derivatives, 2-(S)-(alkoxycarbonylamino)-3-bromomethylpropionates ((ROCO)SerBr, : R = PhCH(2), : tBu, : Me) to give the corresponding phosphanylated or arsanylated amino acids, (ROCO)SerPhos (: Phos = PPh(2)) and (Z)SerArs (Ars = AsPh(2), Z = PhCH(2)OCO). The dipeptide (Z)AlaSerPhos was likewise prepared. The phosphanes , and the arsane reacted cleanly with [Rh(2)(micro-Cl)(2)(cod)(2)] to give the rhodium(I) complexes [RhCl(cod)((Z)SerPhos)] , [RhCl(cod)((Boc)SerPhos)] (Boc = tBuOCO), [RhCl(cod)((Z)AlaSerPhos)] , and [RhCl(cod)((Z)SerArs)] which were characterized by X-ray diffraction studies. A common structural feature is an intramolecular (N)H[dot dot dot]Cl(Rh)-hydrogen bridge which according to NMR investigations remains intact in solution. The abstraction of chloride from the coordination sphere of Rh(I) in or has a profound structural impact. While in and , the ligands bind in a monodentate fashion, via the phosphorus atom only, they serve as bidentate ligands via the phosphorus centre and the peptidic C=O group in [Rh(cod)(kappa(2)-(Z)SerPhos)]PF(6) and [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6). This causes also the amino acid residue structures to change from alpha-helix type in and to a beta-sheet type in both. Addition of chloride to and fully re-establishes the structures of both. The complexes [RhCl(cod)((Z)SerPhos)] and [RhCl(cod)((Boc)SerPhos)] show good activities in homogeneously catalyzed hydrogenations of olefins while the dipeptide complex is less active. Phosphane addition to greatly diminishes the catalytic activity. The cationic complex [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6) shows low activity which, however, is greatly increased by addition of one equivalent of phosphane.

Contains fulltext : 49036.pdf (Publisher’s version ) (Closed access) (1)H-NMR spectroscopy at 500 MHz was used to confirm that a previously unidentified singlet resonance at 3.14 ppm in the spectra of cerebrospinal fluid and plasma samples corresponds to dimethyl sulfone (DMSO(2)). A triple resonance inverse cryogenic NMR probe, with pre-amplifier and the RF-coils cooled to low temperature, was used to obtain an (1)H-(13)C HSQC spectrum of CSF containing 8 microM (753 ng/ml) DMSO(2). The (1)H-(13)C correlation signal for DMSO(2) was assigned by comparison with the spectrum from an authentic reference sample. In plasma and CSF from healthy controls, the concentration of DMSO(2) ranged between 0 and 25 micromol/l. The concentration of DMSO(2) in plasma from three of four patients with severe methionine adenosyltransferase I/III (MAT I/III) deficiency was about twice the maximum observed for controls. Thus, DMSO(2) occurs as a regular metabolite at low micromolar concentrations in cerebrospinal fluid and plasma. It derives from dietary sources, from intestinal bacterial metabolism and from human endogenous methanethiol metabolism.

Using the tropp(Ph) ligand 1, stable monomeric d(8)-Ir+I, d(9)-Ir-0 and d(10)-Ir-I complexes could be isolated and structurally characterized; in all complexes, the metal centre lies within a coordination sphere intermediate between a square plane and a tetrahedron.