Synthese,Struktur und einige Reaktionen [N-(N′,N′,N″,N″-tetramethyl)-guanidinyl]-substituierter Phosphorylverbindungen

Synthesis, Structure, and some Reactions of N-(N′,N′,N″,N″-tetramethyl)guanidinyl-substituted Phosphoryl Compounds The tetramethylguanidinyl-substituted phosphoryl compounds 1 – 10 were prepared in the reaction of the appropriate chlorophosphoryl compounds with either N′,N′,N″,N″-tetramethylguanidine (HTMG) or N-trimethylsilyl-(N′,N′,N″,N″-tetramethyl)guanidine (TMSTMG). With methyl iodide 1 reacted with N-alkylation to give the ammonium salt 11. 1 reacted with BF₃ · Et₂O at both imino nitrogen atoms with formation of the bis-BF₃-adduct 12 . The X-ray structure determination of phenylphosphonic acid-bis(N′,N′,N″,N″-tetramethylguanidinide) 3 shows shortened PN-bonds and widened PNC-angles, consistent with the partial double bond character of the PN-bond.     

Where organometallics and dendrimers merge: the incorporation of organometallic species into dendritic molecules

This review will describe the ongoing efforts being made to incorporate organometallic fragments into the framework of dendrimers. While purely dendritic organic molecules are well known and well studied, species incorporating organometallic moieties potentially offer many benefits that are not available to only organic containing dendrimers. For example, catalytic or redox active organometallic functions can be included in the dendritic framework and impart these characteristics onto the dendrimer. This report will give an overview of the latest developments in this field by highlighting selected examples that detail novel synthetic strategies or dendrimer construction methodologies, interesting practical applications or address specific problems associated with organometallic dendrimers.     

Reactions of Ru3(CO)12 with Diphosphenes — A New Route to 50‐Electron Ru3P2 nido‐Clusters

The reaction of the symmetric diphosphene 2, 4, 6‐(CF₃)₃‐C₆H₂‐P=P‐C₆H₂‐2, 4, 6‐(CF₃)₃ 4 with Ru₃(CO)₁₂ led to the 50‐electron Ru₃P₂ nido‐cluster Ru₃(CO)₉[μ‐P‐C₆H₂‐2, 4, 6‐(CF₃)₃]₂ 5 , which in solution at room temperature displays hindered rotation of the aromatic rings about the C(aryl)—P bonds. The structure of 5 was determined by X‐ray crystal structure analysis; its Ru₃P₂ centre forms a distorted square pyramid with one ruthenium atom at the apex. One of the two C₆H₂(CF₃)₃ groups is also appreciably distorted. Temperature‐dependent ¹⁹F NMR studies of the [A₃M₃X]₂ spin system (A = M = CF₃, X = ³¹P) of 5 indicated a rotational barrier ΔG^≠ of 82.3 kJ mol^‐1 at 141 °C. The same Ru₃P₂ core was obtained by the reaction of the unsymmetric diphosphene Mes*‐P=P‐Mes 11 with Ru₃(CO)₁₂; hindered rotation about the C(aryl)—P bonds was also observed, in this case.     

Novel nucleophilic substitution of alkyl bromo-2(1H)-pyridones

Nucleophilic substitution of certain alkyl bromo-2(1H)-pyridones gave some unexpected products where the alkyl group is substituted and the ring bromine is replaced by hydrogen. The expected ring substituted product is also formed, but only as the minor product in most cases. Many reactions are cited with various nucleophiles, and a plausible mechanism is also presented.     

A novel photoaddition of 2-phenylbenzimidazole

Irradiation of 2-phenylbenzimidazole ( 3 ) in the presence of methyl acrylate (20 equivalents) using a medium pressure mercury lamp gives methyl 2-(2-phenylbenzimidazol-1-yl)propionate ( 4 ) (75%) whose structure has been confirmed by an X-ray analysis. A similar reaction using acrylonitrile gave only a low yield (1%) of the corresponding propionitrile derivative 5 . A mechanism involving photoexcitation of 2-phenylbenzimidazole ( 3 ) followed by sequential single electron transfer, proton transfer and radical coupling is proposed to account for the formation of the novel photoadducts 4 and 5 .     

Polysulfonylamine. CLX [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 10 [2] Die dreidimensionalen Koordinationspolymere M[(CH3SO2)2N] mit M = Kalium,Rubidium, Caesium (isotype Strukturen für M = K,Rb)

Polysulfonylamines. CLX. Crystal Structures of Metal Di(methanesulfonyl)amides. 10. The Three‐Dimensional Coordination Polymers M[(CH₃SO₂)₂N], where M is Potassium, Rubidium, Cesium (Isotypic Structures for M = K, Rb) Low‐temperature X‐ray crystal structures are reported for KA (monoclinic, space group P2₁/c, Z′ = 1), RbA (isotypic and isostructural with KA), and CsA (monoclinic, P2₁/n, Z′ = 1), where A^— denotes the anion obtained by deprotonation of the strong nitrogen acid (MeSO₂)₂NH. In KA and RbA, the anion is distorted into a rare C₁ conformation, whereas the standard C₂ conformation is retained in the cesium complex. The structures consist of three‐dimensional coordination networks, in which each cation adopts an irregular (O₆N)‐heptacoordination by forming close contacts to one (O, N)‐chelating, one (O, O)‐chelating and three κ¹O‐bonding ligands; however, the coordination number for Cs⁺ is effectively increased to 8 by a very short Cs···Cs contact distance of 422.5 pm. The crystal packings of the isotypic compounds KA and RbA display lamellar layer substructures that involve six independent ligand‐metal bonds and comprise an internal cation lamella and peripheral regions built up from anion monolayers; the 3D framework is completed by one independent M—O bond cross‐linking the layer substructures. In contrast, CsA features anion monolayers that intercalate planar zigzag chains of cations (Cs···Cs alternatingly 422.5 and 487.5 pm, Cs···Cs···Cs 135.7°), whereby each chain is surrounded and coordinated by four anion stacks and each anion stack connects two cation chains. All structures exhibit close C—H···A interanion contacts consistent with weak hydrogen bonding.     

Swelling and network parameters of crosslinked thermoreversible hydrogels of poly(N-ethylacrylamide)

Samples of Poly(N-ethylacrylamide) (PEA) have been synthesized by free radical polymerization in water using N,N′-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels obtained by swelling them in water, 15 wt% KCl and 1 wt% sodium dodecyl sulphate (SDS) were examined by gravimetric, dimensional and compression-strain measurements to afford values of swelling ratio, polymer-solvent interaction parameters, elastic moduli and effective crosslinking density ν_e. Crosslinking inefficiency is evidenced by the low value (0.23) of ν_e relative to the theoretical crosslinking density ν_t based on the content of BIS in the synthesis. A small but finite extrapolated value of ν_e at ν_t = 0 is indicative of hydrophobic physical interactions. In water at 298 K increasing the content of BIS leads to a decrease in swelling and increases in values of elastic moduli and polymer-water interaction parameter. At a fixed content of BIS the values of ν_e and the elastic moduli exhibit an unusual increase with temperature, the crosslinking thus being thermally reversible. It is proposed that this results from a balance between hydrophobic interaction and breakage of hydrophilic hydrogen bonding. Although KCl in the medium decreases the swelling compared with that in water, the opposite effect occurs on incorporation of SDS, which is assumed to confer some polyelectrolyte character to the PEA chains. The finding, that these two swelling media reduce the values of ν_e and elastic moduli cf the value in water, has not been resolved satisfactorily.     

Chemically modified "polar patch" mutants of subtilisin in peptide synthesis with remarkably broad substrate acceptance: designing combinatorial biocatalysts

A significant enhancement of the applicability of the serine protease subtilisin Bacillus lentus (SBL) in peptide synthesis was achieved by using the strategy of combined site-directed mutagenesis and chemical modification to create chemically modified mutant (CMM) enzymes. The introduction of polar and/or homochiral auxiliary substituents, such as X=oxazolidinones, alkylammonium groups, and carbohydrates at position 166 at the base of the primary specificity S(1) pocket created SBL CMMs S166C-S-X with strikingly broad structural substrate specificities. These CMMs are capable of catalyzing the coupling reactions of not only L-amino acid esters but also D-amino acid esters as acyl donors with glycinamide to give the corresponding dipeptides in good yields. These powerful enzymes are also applicable to the coupling of L-amino acid acyl donors with alpha-branched acyl acceptor, L-alaninamide. Typical increases in isolated yields of dipeptides of 60-80 % over SBL-WT (e.g. 0 % yield of Z-D-Glu-GlyNH(2) using SBL-WT-->74 % using S166C-S-(CH(2))(2) NMe(3) (+)) demonstrate the remarkable synthetic utility of this "polar patch" strategy. Such wide-ranging systems displaying broadened and therefore similarly high, balanced yields of products (e.g. 91 % Z-L-Ala-GlyNH(2) and 86 % yield of Z-D-Ala-GlyNH(2) using S166C-S-(3R,4S)-indenooxazolidinone) may now allow the use of biocatalysts in parallel library synthesis.