Stanley Wild

Tertiary arsine-stabilised arsenium salts: syntheses and comparisons with phosphine analogues

The first tertiary arsine-stabilised arsenium salts, [(L)AsMePh]OTf (L = Ph3As, Me2PhAs, [2-(MeOCH2)C6H4]Ph2As, [2-(MeOCH2)C6H4]Me2As), have been prepared by chloride abstraction from chloromethylphenylarsine with trimethylsilyl triflate in the presence of the arsine. The complexes have been characterised by crystallography and 1H NMR spectroscopy. The chiral cations in the complexes have structures based on the trigonal pyramid in which the arsine is coordinated orthogonally to the prochiral, six-electron MePhAs+ ion that forms the base of the pyramid. The NMR data for the complexes in dichloromethane-d2 are consistent with rapid exchange of the arsine on the arsenium ion, even at 183 K. The corresponding phosphine-stabilised complexes are considerably more stable than their arsine counterparts in dichloromethane-d2 with the free energy of activation DeltaG = ca. 60 kJ mol(-1) being calculated for phosphine exchange in [(Me2PhP)AsMePh]OTf at 281 K; for [(Me2[2-(MeOCH2)C6H4]P)AsMePh]OTf in the same solvent, DeltaG = ca. 70 kJ mol(-1) at 323 K.

Cationic η5-cyclopentadienylpalladium(II) complexes. Compounds of type [Pd(η5-C5H5)L2]PF6 containing tertiary phosphines, arsines, and stibines. Crystal and molecular structure of [Pd(η5-C5H5)(SbPh3)2]PF6·CH2Cl2

The complexes [Pd(η5-C5H5)L2]PF6[where L = PMe2Ph, PPh3, AsMe2Ph, AsPh3, or SbPh3 and L2=(SS)-, (RR,SS)-, (RS)-C6H4(PMePh)2-o or (SS)-, (RR,SS)-, (RS)-C6H4(AsMePh)2-o] have been prepared in high yield from the appropriate complexes [PdCl2L2] and cyclopentadiene in Me2CO in the presence of AgPFe6, or with AgNO3 followed by metathesis with NH4PF6. The brightly coloured compounds conduct as uni-univalent electrolytes in Me2CO and CH2Cl2 and have spectroscopic properties consistent with η5 co-ordination of the cyclopentadienyl moiety in solution. The molecular structure of [Pd(η5-C5H5)(SbPh3)2]PF6·CH2Cl2 has been determined by a single-crystal X-ray analysis. The crystals are monoclinic, space group P21/c with a= 12.506(6), b= 19.002(7), c= 18.575(5)A, β= 106.53(3)°, and Z= 4. The structure was solved by heavy-atom methods at 295(1) K and refined by least-squares methods to R= 0.051 for 4 384 observed reflections. The arrangement of the two antimony atoms and the centre of the cyclopentadienyl ring about the palladium atom is approximately trigonal. The co-ordinated cyclopentadienyl moiety shows no significant deviations from planarity.

Origin of the Unusual Ultraviolet Absorption of Arsenicin A

This paper presents a combined experimental and theoretical study of the electronic spectrum of the natural adamantane-type polyarsenical Arsenicin A. Experiments reveal that this molecule strongly absorbs UV light in the absence of an obvious chromophore. The observed absorbance is supported by the time-dependent density functional (TD-DFT) calculations with B3LYP, M06-L, and M06-2X functionals combined with the 6-311+G(3df,2pd) basis set, as well as by symmetry-adapted cluster/configuration interaction (SAC-CI) theory. The theoretical investigations reveal that the absorption is facilitated by through-space and through-bond interactions, between the lone pairs on the arsenic and oxygen atoms and the σ-bonding framework of the molecule, that destabilize occupied and stabilize unoccupied molecular orbitals.

SYNTHESIS OF β-TRIMETHYLARSONIUMLACTATE

Abstract The biochemistry of arsenic is of considerable interest owing to the widespread presence of the element in marine organisms.1 The substance arsenobetaine (Me3-As+CH2CO2 −) has been isolated from the tail muscle of the western rock lobster (Panulirus longipes cygnus) and from the flesh of the dusky shark (Carcharhinus obscurus) and subsequently characterized by independent synthesis and X-ray crystal structure analysis.2 In addition, two arsenic-containing ribose derivatives have been isolated from the brown kelp Ecklonia radiata, which is part of the coastal ecosystem to which the rock lobster belongs.3 Assimilation, reduction, and methylation of arsenate also occurs in photosynthetic marine organisms,4,5 particularly in phosphate-depleted tropical waters, and in molluscs and ascidians, where arsenic accumulation was found to be greatest in organisms bearing symbiotic algae.5 Marine algae cultured in [74As] arsenate synthesize an arsenic-containing phospholipid.6 Base-catalysed deacylation of the...

Crystal structure of dicarbonyl-η-cyclopentadienyl[(3-dimethylarsino)propyl]molybdenum

The crystal structure of the title compound has been determined from X-ray diffractometer data by the heavy-atom method and refined by least squares to R 0.060 for 2 013 observed reflections. Crystals are orthorhombic, space group Pcab, a= 15.903(5), b= 13.297(2), c= 12.925(2)A, Z= 8. Mo–As is 2.533(2), and the Mo–C(alkyl) 2.35(1)A. The η5-cyclopentadienyl group occupies an apical position in the pseudo-square-pyramidal complex.

New macrocyclic ligands: XIV. synthesis and X-ray structures of potentially pentadentate ligands incorporating non-symmetrically arranged N4S-, N3OS-, N2O2S- and N2S2O-heteroatoms

The synthesis and characterization of new mixed-donor macrocyclic ligands incorporating nitrogen, sulfur and/or oxygen heteroatoms are described. The new 17- or 18-membered macrocyclic rings contain unsymmetrical arrangements of their heteroatoms in contrast to related, previously reported rings in which the donor sets are arranged symmetrically. The X-ray structures of the 17-membered rings incorporating N4O- and N4S-donor sets are presented.

Notes. Complexes containing mercury–molybdenum bonds: new compounds of the type [HgX{trans-Mo(CO)2L(η5-C5H5)}](L = arsine or phosphine). Crystal and molecular structure of the complex [Hg(CN){trans-Mo(CO)2(AsMe2Ph)(η5-C5H5)}]

The series of Hg–Mo bonded complexes [Hg(CN){trans-Mo(CO)2L(η5-C5H5)}](where L = AsMe2Ph, PMe2Ph, PMePh2, or PPh3) have been prepared from Hg(CN)2 and the salts Na[Mo(CO)2L(η5-C5H5)] or dimers [Hg{trans-Mo(CO)2L(η5-C5H5)}2]. The cyanomercury complexes are extremely useful intermediates for the facile synthesis of the derivatives [HgX{trans-Mo(CO)2L(η5-C5H5)}](where X = Cl, Br, I, NO3, O2CMe, OCN, SCN, or S2CNEt2). The molecular structure of the complex [Hg(CN){trans-Mo(CO)2(AsMe2Ph)(η5-C5H5)}] has been determined by single-crystal X-ray analysis. The crystals are monoclinic, space group P21/c, with a= 14.570(4), b= 12.457(3), c= 10.783(3)A, β= 114.04(2)°, and Z= 4. The structure was solved by heavy-atom methods and refined by least squares to a residual of 0.037 for 2 218 reflections with |I0| > 3σ(I). The Hg–Mo bond length [2.654(1)A] is the shortest hitherto observed.

Resolutions using metal complexes. Resolution of (RR,SS)-ortho-phenylenebis(methylphenylarsine) using internally diastereoisomeric palladium complexes

The dissymmetric chelating agent (RR,SS)-ortho-phenylenebis(methylphenylarsine) has been resolved into its enantiomers by fractionally crystallising internally diastereoisomeric palladium complexes containing the ditertiary arsine and optically active ortho-metallated dimethyl(α-methylbenzyl)amine. The full procedure is described and constitutes the first satisfactory route to optically active ditertiary arsines containing asymmetric arsenic atoms. The optically active ditertiary arsines, α(589 nm, CH2Cl2)± 95°, are air-stable crystalline solids, m.p. 75–76 °C, and the absolute configuration of the enantiomer with a positive rotation at the sodium D line (589 nm) has been established as RR by a single-crystal X-ray determination of the structure of the internally diastereoisomeric palladium complex containing (S)(–)-dimethyl(α-methylbenzyl)amine. The meso diastereoisomer undergoes a halide-ion assisted epimerisation in acidic methanol solution and may be converted, under suitable conditions, into the less soluble racemic diastereoisomer thereby effecting a second-order asymmetric transformation between the diastereoisomeric ditertiary arsines.

Temperature-Dependent Cooperative Coiling of Helical Conformers of Enantiopure Oligo(Tertiary Phosphines)

The specific optical rotation of an enantiopure, syndiotactic hexa(tertiary phosphine) displays a marked temperature dependence that is consistent with the cooperative formation of helically coiled conformers in solution.

Macro- and spiro-heterocycles

Publisher Summary This chapter provides a description of phosphorus in seven-membered rings. It refers to the publication of a comprehensive review by Caminade and Majoral of phosphorus-containing macrocycles and cryptands. It also mentions two important earlier reviews by Gallagher and Quin concerning the stereochemical aspects of heterocyclic phosphorus compounds. Parent rings with one phosphorus atom involving seven, eight, and nine membered rings are included in the chapter. Among seven membered rings, monocyclic phosphepanes, monocyclic phosphepins, fused benzo and dibenzo derivatives, and bicyclic systems are discussed. In eight membered rings, the first authenticated synthesis of a phosphocane, the phosphocane oxide was reported in 1972 by Markls method of cleavage of the appropriate tetraphenylalkyldiphosphonium salt. Rings with two or more heteroatoms are elucidated in the chapter. These include cyclic quarternizations at phosphorus, cyclizations involving organophosphides and other nucleophiles, metal template syntheses, cyclic phosphonites, cyclic oxphosphoranes, cyclic phosphazene derivatives, and polyazaphosphorus macrocycles. Bicyclic systems with bridgehead phosphorus include information on bridgehead tertiary phosphines, calixarene phosphites, and phosphatrenes.