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.

Asymmetric synthesis of bis(tertiary arsines): highly stereoselective alkylations of diastereomers of a chiral phosphine-stabilized bis(arsenium triflate).

The addition of organolithium reagents to an equilibrating mixture of diastereomers of a phosphine-stabilized 1,2-ethanediylbis(phenylarsenium triflate) containing chiral arsenic stereocenters and an enantiomerically pure, atropisomeric tertiary phosphepine derived from lithiated (aR)-2,2'-dimethyl-1,1'-binaphthalene generates unequal mixtures of diastereomers and enantiomers of chelating 1,2-ethanediylbis(tertiary arsines), chiral at arsenic, with liberation of the (aR(P))-phosphepine. Thus, the addition of methyllithium in diethyl ether at -95 degrees C to a dichloromethane solution of the complex (R*(As),R*(As))-(+/-)/(R*(As),S*(As))-1,2-[(R(3)P)PhAsCH(2)CH(2)AsPh(PR(3))](OTf)(2), where R(3)P is (aR(P))-[2-(methoxymethyl)phenyl]phosphepine, generates (R*(As),R*(As))-(+/-)-1,2-ethanediylbis(methylphenylarsine) in 78% diastereoselectivity and 95% enantioselectivity in favor of the (R(As),R(As)) enantiomer. Under similar conditions, the addition of n-butyllithium in hexanes to a solution of the bis(phosphepine-stabilized)-diarsenium triflate at -95 degrees C gives the corresponding (R*(As),R*(As))-(+/-)-1,2-ethanediylbis[(n-butyl)phenylarsine) in 77% diastereoselectivity and 93% enantioselectivity in favor of the (R(As),R(As)) enantiomer.

Inorganic asymmetric synthesis: diastereoselective syntheses of mono- and dinuclear complexes containing octahedral, two-bladed propeller, bis(pyridine-2-aldehyde 2'-pyridylhydrazone)iron(II) stereocenters.

A C2 hexadentate diester derived from (5-hydroxymethyl)pyridine-2-aldehyde 2'-pyridylhydrazone (5-HOCH2PAPHY) and an enantiomerically pure (aS)-spirane dicarboxylic acid diastereoselectively reacts with iron(II) benzenesulfonate in methanol to furnish a 20% diastereomeric excess (de) of a two-bladed propeller, octahedral iron complex in which the P configuration of the newly created (+/-)-[Fe(PAPHY)2](2+) stereocenter predominates; when the reaction mixture is heated under reflux for 12 h, however, the excess of the diastereomer having the P configuration at iron increases to 80%, as determined by (1)H NMR spectroscopy. The configuration at iron in the major diastereomer of the complex was determined by comparison of the circular dichroism spectrum of the deprotonated complex with that of a related complex of known configuration. Repositioning of the hydroxymethyl group of the pyridine-2-aldehyde from the 5- to the 6-position produced a C2-spirane ligand that generates a double-stranded diiron(II) helicate in >99% de. Single crystal X-ray structure determinations of the racemates of the protonated and deprotonated helicates revealed that the complexes crystallize diastereoselectively, that is, two ligand strands of a S configuration generate two octahedral iron(II) stereocenters of P configuration to give a dinuclear metal helicate of P configuration and vice versa for the ligand of a R configuration.

Self-assembly of square-planar halide complexes of phosphine-stabilised stibenium salts.

Chloride and bromide ions direct the self-assembly of supramolecular square-planar halide complexes in which four trimethylphosphine-stabilised diphenylstibenium ions surround the central halide ion in discrete centrosymmetrical structures of C(4h) symmetry.

First Resolution of a Free Fluorophosphine Chiral at Phosphorus. Resolution and Reactions of Free and Coordinated (+/-)-Fluorophenylisopropylphosphine.

The trivalent fluorophosphine (+/-)-PFPh(i-Pr), (+/-)-1, has been prepared by halogen exchange of the corresponding chlorophosphine with sodium fluoride in hot sulfolane. The neat fluorophosphine rapidly decomposes by equilibrium redox disproportionation into PF(3)Ph(i-Pr) and (R,R)/(R,S)-Ph(i-Pr)PPPh(i-Pr), but in benzene, (+/-)-1 has considerable thermodynamic stability. The resolution of (+/-)-1 was achieved by a fractional crystallization of the diastereomers (R,R(P))- and (R,S(P))-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](fluorophenylisopropylphosphine)palladium(II), (R,R(P))- and (R,S(P))-5, whereby the less soluble (R,R(P)) diastereomer selectively crystallized in 64% yield in a typical second-order asymmetric transformation. Optically pure (S)-(-)-1, -210 (c 0.59, C(6)H(6)), was liberated from (R,R(P))-5 with (R,S)-1,2-phenylenebis(methylphenylphosphine). The optically active phosphine in benzene racemizes over 6 h without significant redox disproportionation. The methoxyphosphine (+/-)-P(OMe)Ph(i-Pr), (+/-)-9, was also resolved by the method of metal complexation. Thus, fractional crystallization of (R,R(P))- and (R,S(P))-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](methoxyphenylisopropylphosphine)palladium(II), (R,R(P))- and (R,S(P))-8, followed by liberation of the respective optically active methoxyphosphines from the separated diastereomers with 1,2-bis(diphenylphosphino)ethane, gave (R)-(+)- and (S)-(-)-9 of 92% and 96% ee, respectively. The barrier to unimolecular inversion for (+/-)-9 was determined to be >82.9 +/- 0.5 kJ mol(-)(1) by variable temperature (1)H NMR spectroscopy. The substitution of fluoride in (R,R(P))-5 by methoxide proceeds with predominant inversion of the configuration at phosphorus to give (R,R(P))- and (R,S(P))-8 with (R,S(P))/(R,R(P)) = (1)/(5). The crystal structures of (R,R(P))-5 and (R,R(P))-8 have been determined: (R,R(P))-5 (C(23)H(28)ClFNPPd) crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 9.967(2) Å, b = 10.998(4) Å, c = 21.324(3) Å, Z = 4, and R = 0.031; (R,R(P))-8 (C(24)H(31)ClNOPPd) crystallizes in the space group P2(1)2(1)2(1) with a = 10.444(3) Å, b = 12.146(3) Å, c = 19.047(2) Å, Z = 4, and R = 0.026.

A G2 Ab Initio Investigation of Ligand-Exchange Reactions Involving Mono- and Bis-Adducts of the Phosphenium Ion.

Ab initio calculations at the G2 level have been employed to investigate the ligand-exchange reactions between mono-adducts of the phosphenium ion (e.g., [H(3)N-PH(2)](+)) and simple first- or second-row Lewis bases (e.g., NH(3)). We have found virtually all the reactions to proceed without an intermediate barrier via a bis-adduct of the phosphenium ion with two Lewis bases (e.g., [H(3)N-PH(2)-NH(3)](+)). The ligand-exchange reactions are predicted to be experimentally feasible and the bis-adducts of the phosphenium ion to be experimentally observable in appropriate cases. The energetics of the ligand-exchange reactions may be rationalized using qualitative orbital interaction arguments in terms of the electronegativity of the ligand in the mono-adducts and the donor ability of the reacting Lewis base. Comparisons with previous investigations of corresponding ligand-exchange reactions involving pi-ligands reveal that the electronic characteristics of the bis-adduct resemble those of the transition structures for pi-ligand exchange.

First Resolution of a Free Secondary Phosphine Chiral at Phosphorus and Stereospecific Formation and Structural Characterization of a Homochiral Secondary Phosphine-Borane Complex.

The R(P) diastereomer of (-)-menthylmesitylphosphine, (R(P))-1, has been isolated with high configurational purity at phosphorus by fractional crystallization of an (R(P))-1/(S(P))-1 = 43/57 mixture from acetonitrile containing a trace of sodium acetylacetonate as a proton scavenger or by deboranation of the corresponding borane complex (S(P))-2 with diethylamine, thereby effecting the first resolution of a secondary phosphine chiral at phosphorus. The crystal and molecular structure of (S(P))-2 has been determined. The ready isolation of (S(P))-2 of 97% diastereomeric purity in 66% yield from an equilibrium (R(P))-2/(S(P))-2 = 28/72 mixture in n-hexane by second-order asymmetric transformation and its quantitative and stereospecific conversion under mild conditions into (R(P))-1 of similar purity augurs well for the future of the resolved secondary phosphines in stereoselective syntheses.

Self-Assembly of Homochiral Double Helix and Side-by-Side Helix Conformers of Double-Stranded Disilver(I)- and Digold(I)-Tetra(tertiary phosphine) Helicates.

The enantiomers of the (R,R)-(+/-) diastereomer of the chelating C(2)-tetra(tertiary phosphine) (R,R)-(+/-)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (R,R)-(+/-)/(R,S)-1, spontaneously self-assemble into homochiral double-stranded disilver(I) and digold(I) helicates of the type [M(2)(tetraphos)(2)]X(2) upon reaction with appropriate silver(I) and gold(I) salts. The corresponding copper(I) complex is mononuclear. Crystal and molecular structures of Delta-(-)-[Cu{(R,R)-1}]PF(6).EtOH, Lambda-(-)-[Ag(2){(R,R)-1}(2)](PF(6))(2), and Lambda-(-)-[Au(2){(R,R)-1}(2)](PF(6))(2).CH(2)Cl(2) are reported. The structure determinations on the silver and gold complexes are the first to be performed on enantiomerically pure dimetal helicates with chiral ligands. The dinuclear silver complex crystallizes with one molecule each of the left-handed (Lambda) D(2)-double helix and C(2)-side-by-side helix conformers of the cation and associated anions in each unit cell, whereas crystals of the analogous gold complex contain only the side-by-side helix and associated anions. The absolute configuration(s) of the metal stereocenter(s) in each complex is S. Conductance measurements in acetonitrile indicated considerable rearrangement of the mononuclear copper complex into the dinuclear helicate complex, whereas the silver and gold complexes conducted as di-univalent salts under similar conditions. Energy minimization calculations of the structures of the disilver complex cation with use of the program SPARTAN 3.0 predicted the structures observed with considerable accuracy, especially the conformations of the chiral central ten-membered ring in the complex and the relationship of the helicity of this ring to the stereoselective formation of the double helix and side-by-side helix structures. The resolution of (R,R)-(+/-)-1 is the first on a tetra(tertiary phosphine). The more-soluble (R,R)-(+/-) form of the ligand was separated in high yield from the less-soluble (R,S) form by selective extraction with tetrahydrofuran, whereupon it was resolved by the method of metal complexation with the readily prepared homochiral complex (+)-di(&mgr;-chloro)bis[(R)-1-[1-(dimethylamino)ethyl]-2-phenyl-C(2),N]dipalladium(II)-1-dichloromethane, (R)-2.CH(2)Cl(2). The enantiomers of the phosphine were obtained by liberation from the diastereomeric complexes (R(C)),(R(P),R(P))- and (R(C)),(S(P),S(P))-3 (X = PF(6)) and brought to optical purity by crystallization from acetone-ethanol, giving colorless needles having mp 88 degrees C and [alpha](21)(D) +20.5 (c 1.0, CH(2)Cl(2)) (S,S enantiomer) and [alpha](21)(D) -20.5 (c 1.0, CH(2)Cl(2)) (R,R enantiomer). The crystal and molecular structures of (R(C)),(R(P),R(P))-3 (X = PF(6)) have been determined. The complete optical purity of each enantiomer of the tetra(tertiary phosphine) was confirmed in each case by the quantitative repreparation of the diastereomeric palladium complex from which it was liberated.

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.

Phenylphosphonate transport by Helicobacter pylori.

BACKGROUND: Helicobacter pylori can utilize phenylphosphonate as a sole source of phosphorus, and it is able to transport the phosphonate N-phosphonoacetyl-L-aspartate. However, H. pylori does not have any genes homologous to those of the known pathways for phosphonate degradation in bacteria, indicating that it must have novel pathways for the transport and metabolism of phosphonates. METHODS: Phenylphosphonate transport by H. pylori was studied in strains LC20, J99 and N6 by the centrifugation through oil method using [(14)C]-labeled phenylphosphonate. RESULTS: The Michaelis constants of transport K(t) and V(max) for phenylphosphonate showed similar kinetics in the three strains. The Arrhenius plot for phenylphosphonate transport rates at permeant concentrations of 50 micromol/L was linear over the temperature range 10-40 degrees C with an activation energy of 3.5 kJ/mol, and a breakpoint between 5 and 10 degrees C. Transport rates increased with monovalent cation size. The effects of various inhibitors were investigated: iodoacetamide, amiloride, valinomycin, and nigericin reduced the rate of phenylphosphonate transport; sodium azide and sodium cyanide increased the transport rate; and monensin had no effect. CONCLUSIONS: The kinetics and properties of H. pylori phenylphosphonate transport were characterized, and the data suggested a carrier-mediated transport mechanism.

Synthesis, structure, and electrochemistry of di- and zerovalent nickel, palladium, and platinum monomers and dimers derived from an enantiopure (S,S)-tetra(tertiary phosphine).

The ligand (S,S)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (S,S)-tetraphos, reacts with hexa(aqua)nickel(II) chloride in the presence of trimethylsilyl triflate (TMSOTf) in dichloromethane to give the yellow square-planar complex [Ni{(R,R)-tetraphos}](OTf)2, which has been crystallographically characterized as the square-pyramidal, acetonitrile adduct [Ni(NCMe){(R,R)-tetraphos}]OTf. Cyclic voltammograms of the nickel(II) complex in dichloromethane and acetonitrile at 20 degrees C showed two reduction processes at negative potentials with oxidative (E(p)(ox)) and reductive (E(p)(red)) peak separations similar to those observed for ferrocene/ferrocenium under identical conditions, suggesting two one-electron steps. The cyclic voltammetric data for the divalent nickel complex in acetonitrile at temperatures below -20 degrees C were interpreted according to reversible coordination of acetonitrile to the nickel(I) and nickel(0) complexes. The divalent palladium and platinum complexes [M{(R,R)-tetraphos}](PF6)2 and [M2{(R,R)-tetraphos}2](OTf)4 have been prepared. The reduction potentials for the complexes [M{(R,R)-tetraphos}](PF6)2 increase in the order nickel(II) < palladium(II) < platinum(II). The reaction of (S,S)-tetraphos with bis(cycloocta-1,5-diene)nickel(0) in benzene affords orange [Ni{(R,R)-tetraphos}], which slowly rearranges into the thermodynamically more stable, yellow, double-stranded helicate [Ni2{(R,R)-tetraphos}2]; the crystal structures of both complexes have been determined. The reactions of (S,S)-tetraphos with [M(PPh3)4] in toluene (M = Pd) or benzene (M = Pt) furnish the double-stranded helicates [M2{(R,R)-tetraphos}2]; the palladium complex crystallizes from hot benzene as the 2-benzene solvate and was structurally characterized by X-ray crystallography. In each of the three zerovalent complexes, the coordinated (R,R)-tetraphos stereospecifically generates tetrahedral M(PP)2 stereocenters of M configuration.

Inorganic asymmetric synthesis: asymmetric synthesis of a two-bladed propeller, octahedral metal complex.

A C2 hexadentate, in which two pyridine-2-aldehyde 2'-pyridylhydrazone (PAPHY) groups are linked to a chiral auxiliary derived from (R,R)-tartaric acid, (R,R)-1, reacts with iron(II) benzenesulfonate to give the two-bladed propeller, octahedral complex (P(Fe))-[Fe{(R,R)-1}](PhSO3)2 with complete diastereoselectivity, as determined by 1H NMR spectroscopy and X-ray crystallography. Saponification of the ester linkages and deprotonation of the hydrazone-NH groups in the configurationally pure diastereomer affords the complex (P(Fe))-[Fe(5-HOCH2PAPY)2] with 85% retention of configuration at the iron stereocenter, as determined by reprotonation of the neutral complex with enantiomerically pure (aR)-binaphthyl phosphoric acid and analysis of the 1H NMR spectrum of the mixture of diastereomeric salts produced. This is the first asymmetric synthesis of a two-bladed propeller, octahedral metal complex by the classical organic methodology of chiral auxiliary-directed, asymmetric synthesis.

Reactivity of cyclooligophosphanes: synthesis and structural characterisation of cyclo-1,4-(BH3)2(P4Ph4CH2) and cyclo-1,2-(BH3)2(P5Ph5).

The borane complexes cyclo-1,4-(BH3)2(P4Ph4CH2) (3) and cyclo-1,2-(BH3)2(P5Ph5) (4) were prepared by reaction of cyclo-(P4Ph4CH2) and cyclo-(P5Ph5) with BH3(SMe2). Only the 2:1 complexes 3 and 4 were isolated, even when an excess of the borane source was used. In solution, 3 exists as a mixture of the two diastereomers (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-)-3 and (R(P)*,R(P)*,R(P)*,R(P)*)-(+/-)-3. However, in the solid state the (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-) diastereomer is the major stereoisomer. Similarly, while only one isomer of 4 is observed in its X-ray structure, NMR spectroscopic investigations reveal that it forms a complex mixture of isomers in solution. 3 may be deprotonated with tBuLi to give the lithium salt cyclo-1,4-(BH3)2(P4Ph4CHLi) (3 x Li), though this could not be isolated in pure form.

Asymmetric transformation of a double-stranded, dicopper(I) helicate containing achiral bis(bidentate) Schiff bases.

Reactions of the bis(bidentate) Schiff-bases N,N'-bis(6-alkyl-2-pyridylmethylene)ethane-1,2-diamine (where alkyl = H, Me, iPr) (L) with tetrakis(acetonitrile)copper(I) hexafluorophosphate and silver(I) hexafluorophosphate afforded, respectively, the double-stranded, dinuclear metal helicates [T-4-(R,R)]-(+/-)-[M2L2](PF6)2 (M = Cu, Ag). The helicates were characterized by 1H and 13C NMR spectroscopy, conductivity, microanalysis, and single-crystal X-ray structure determinations on selected compounds. Intermolecular ligand exchange and intramolecular inversion rates for the complexes were investigated by 1H NMR spectroscopy. Reversible intermolecular ligand exchange between two differently substituted helicates followed first-order kinetics. The rate constants (k) and corresponding half-lives (t(1/2)) for ligand exchange for the dicopper(I) helicates were k = (1.6-1.8) x 10(-6) s(-1) (t(1/2) = 110-120 h) in acetone-d6, k = 4.9 x 10(-6) s(-1) (t(1/2) = 40 h) in dichloromethane-d2, and k > 2 x 10(-3) s(-1) (t(1/2) < 5 min) in acetonitrile-d3. Ligand exchange for the disilver(I) helicates occurred with k > 2 x 10(-3) s(-1) (t(1/2) < 5 min). Racemization of the dicopper(I) helicate by an intramolecular mechanism was investigated by determination of the coalescence temperature for the diastereotopic isopropyl-Me groups in the appropriate complex, and DeltaG() >> 76 kJ mol(-1) was calculated for the process in acetone-d6, nitromethane-d3, and dichloromethane-d2 with DeltaG() = 75 kJ mol(-1) in acetonitrile-d3. Complete anion exchange of the hexafluorophosphate salt of a dicopper(I) helicate with the enantiomerically pure Delta-(-)-tris(catecholato)arsenate(V) ([As(cat)3]-) in the presence of Dabco gave the two diastereomers (R,R)-[Cu2L2][Delta-(-)-[As(cat)3]]2 and (S,S)-[Cu2L2][Delta-(-)-[As(cat)3]]2 in up to 54% diastereomeric excess, as determined by (1)H NMR spectroscopy. The diastereomerically and enantiomerically pure salt (R,R)-[Cu(2)L2][Delta-(-)-[As(cat)3]]2 crystallized from the solution in a typical second-order asymmetric transformation. The asymmetric transformation of the dicopper(I) helicate is the first synthesis of a diastereomerically and enantiomerically pure dicopper(I) helicate containing achiral ligands.

Phosphine-stabilized arsenium salts: water-stable, labile, coordination complexes.

A series of air- and water-stable tertiary phosphine-stabilized arsenium salts of the type R(3)P-->AsR(2)(+)PF(6)(-) has been isolated. In the crystal structures of two chiral triarylphosphine complexes of prochiral methylphenylarsenium hexafluorophosphate, the stereochemistry around arsenic is trigonal pyramidal with the phosphorus atom occupying the apical position, the As-P bond being orthogonal to the plane of the trigonal (lone-pair included) arsenium ion: Ph(3)P-->AsMePh(+) PF(6)(-), P2(1)/c, a = 10.7775(2) A, b = 17.7987(3) A, c = 13.3797(2) A, beta = 109.066(1) degrees, V = 2425.78(7) A(3), T = 200 K, Z = 4; Ph(2)(2-MeOC(6)H(4))P-->AsMePh(+) PF(6)(-), P1, a = 10.8077(2) A, b = 10.9741(2) A, c = 13.5648(2) A, alpha = 99.0162(9) degrees, beta = 105.2121(9) degrees, gamma = 116.4717(9) degrees, V = 1318.11(5) A(3), T = 200 K, Z = 2. The arsenium ion in each case appears to be further stabilized by conjugation of the lone pair with the phenyl group, with which the arsenic and methyl-carbon atoms are almost coplanar. In the crystal structure of the 2-(methoxymethylphenyl)diphenylphosphine adduct of methylphenylarsenium hexafluorophosphate, there operates a counteractive chelate effect in which anchimeric oxygen coordination to arsenic destabilizes the arsenic-phosphorus bond in the six-membered chelate ring. Although they are stable, phosphine-stabilized arsenium salts undergo rapid phosphine exchange and attack at arsenic by anionic carbon and oxygen nucleophiles to give tertiary arsines and arsinous acid esters, respectively, with liberation of the phosphine.

Synthesis and resolution of (R,R)-(+/-)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane: new ligand for the stereoselective self-assembly of dicopper(I), disilver(I), and digold(I) helicates.

Diphenylvinylarsine oxide reacts with 1,2-bis(phenylphosphino)ethane in the presence of potassium tert-butoxide to give the anti-Markovnikov product (R,R)-(+/-)/(R,S)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane dioxide-1AsO,10AsO, which, upon reduction with HSiCl(3)/NEt(3) in boiling acetonitrile, affords in 84% overall yield the di(tertiary arsine)-di(tertiary phosphine) (R,R)-(+/-)/(R,S)-diphars. After separation of the diastereomers by fractional crystallization, the (R,R)-(+/-) form of the ligand was resolved by metal complexation with (+)-di(mu-chloro)bis[(R)-1-[1-(dimethylamino)ethyl]-2-phenyl-C(2),N]dipalladium(II): (R,R)-diphars, mp 87-88 degrees C, has [alpha](D)(21) = -18.6 (c 1.0, CH(2)Cl(2)); (S,S)-diphars has [alpha](D)(21) = +18.4 (c 1.0, CH(2)Cl(2)). The crystal and molecular structures of the complexes (M)-[M(2)[(R,R)-diphars](2)](PF(6))(2) (M = Cu, Ag, Au) have been determined: [M-(S(Cu),S(Cu))]-(-)-[Cu(2)[(R,R)-diphars](2)](PF(6))(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.084(3) A, b = 18.376(3) A, c = 29.149(6) A, Z = 4; [M-(S(Ag),S(Ag))]-(+)-[Ag(2)[(R,R)-diphars](2)](PF(6))(2), triclinic, P1, a = 12.487(2) A, b = 12.695(4) A, c = 27.243(4) A, alpha = 92.06 degrees, beta = 95.19 degrees, gamma = 98.23 degrees, Z = 2; [M-(S(Au),S(Au))]-(-)-[Au(2)[(R,R)-diphars](2)](PF(6))(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.199(4) A, b = 18.373(4) A, c = 29.347(2) A, Z = 4. In the copper(I) and gold(I) helicates, each ligand strand completes 1.5 turns of an M helix in a parallel arrangement about the two chiral MAs(2)P(2) stereocenters of S configuration. The unit cell of the silver(I) complex contains one molecule each of the parallel helicate of M configuration and the conformationally related double alpha-helix of M configuration in which each ligand strand completes 0.5 turns of an M helix about two metal stereocenters of S configuration. Energy minimization calculations of the three structures with use of the program SPARTAN 5.0 gave results that were in close agreement with the core structures observed.

Photoluminescence properties of four-coordinate gold(I)-phosphine complexes of the types [Au(diphos)2]PF6 and [Au2(tetraphos)2](PF6)2.

Numerous reports describe the photoluminescence of two- and three-coordinate gold(I)-phosphine complexes, but emission in their analogous four-coordinate complexes is almost unknown. This work examines the luminescence of tetrahedral gold(I) complexes of the types [Au(diphos)(2)]PF(6) (diphos = 1,2-bis(diphenylphosphino)ethane, 1) and [Au(2)(tetraphos)(2)](PF(6))(2) (tetraphos = (R,R)-(+/-)/(R,S)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (R,R)-(+/-)/(R,S)-2). Although nonemitting in solution, these complexes luminesce with an intense yellow color (lambda(max) 580-620 nm) at 293 K in the solid state or when immobilized as molecular dispersions within solid matrixes. The excited-state lifetimes of the emissions (tau 4.1-9.4 micros) are markedly dependent on the inter- and intramolecular phenyl-phenyl pairing interactions present. At 77 K in an ethanol glass, two transitions are observed: a minor emission at lambda(max) 415-450 nm and a major emission at lambda(max) 520-595 nm. For [Au(1)(2)]PF(6), lifetimes of tau 251.0 +/- 20.5 micros were determined for the former transition and tau 14.9 +/- 4.6 micros for the latter. Density functional theory (DFT) calculations and comparative studies indicate that the former of these emissions involves triplet LMCT pi(Ph) --> Au(d)-P(p) transitions associated with individual P-phenyl groups. The latter emissions, which are the only ones observed at 293 K, are assigned to LMCT pi(Ph-Ph) --> Au(d)-P(p) transitions associated with excited P-phenyl dimers. Other tetrahedral gold(I)-phosphine complexes containing paired P-Ph substituents display similar emissions. The corresponding phosphine ligands, whether free, protonated, or bound to Ag(I), do not exhibit comparable emissions. Far from being rare, luminescence in four-coordinate Au(I)-phosphine complexes appears to be general when stacked P-phenyl groups are present.

Diastereoselectivity and molecular recognition in the self-assembly of double-stranded dinuclear metal complexes of the type [M2[(R,S)-tetraphos]2](PF6)2 (M = Ag and Au).

The ligand (R,S)-Ph(2)PCH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)PPh(2), (R,S)-tetraphos, combines with silver(I) and gold(I) ions in the presence of hexafluorophosphate to diastereoselectively self-assemble the head-to-head (H,H) diastereomers of the double-stranded, dinuclear metal complexes [M(2)[(R,S)-tetraphos](2)](PF(6))(2) in which the two chiral metal centers in the complexes have M (R end of phosphine) and P (S end of phosphine) configurations. The crystal and molecular structures of the compounds have been determined: (H,H)-(M,P) -[Ag(2)[(R,S)-tetraphos](2)](PF(6))(2), monoclinic, P2(1)/c, a = 10.3784(2), b = 47.320(1), c = 17.3385(4) A, beta = 103.8963(5) degrees, Z = 4; (H,H)-(M,P)-[Au(2)[(R,S)-tetraphos](2)](PF(6))(2), monoclinic, P.2(1) (No. 4, c unique axis), a = 24.385(4), b = 46.175(3), c = 14.820(4) A, Z = 8. The complexes crystallize as racemic compounds in which the unit cell in each case contains equal numbers of enantiomorphic molecules of the cation and associated anions. The cations in both structures have similar side-by-side structures of idealized C(2) symmetry, the bulk helicity of each molecule in the solid state being due solely to the twist of the central ten-membered ring containing the two metal ions of opposite configuration, which has the chiral twist-boat-chair-boat conformation. When 1 equiv each of (R,S)-tetraphos, (R,R)-(+/-)-tetraphos, (S,S)-(+)-tetraphos, 2 equiv of Ph(2)PCH(2)CH(2)PPh(2) (dppe), and 7 equiv of [AuCl(SMe(2))] in dichloromethane are allowed to react for several minutes in the presence of an excess of ammonium hexafluorophosphate in water (two phases), the products are the double-stranded digold(I) complexes in which each ligand strand has recognized itself by stereoselective self-assembly, together with [Au(dppe)(2)]PF(6).

Configurationally homogeneous diastereomers of a linear hexa(tertiary phosphine): enantioselective self-assembly of a double-stranded parallel helicate of the type (P)-[Cu(3)(hexaphos)(2)](PF(6))(3).

Three configurationally homogeneous diastereomers of the linear hexa(tertiary phosphine) Ph(2)PCH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)PPh(2) (hexaphos) have been isolated in enantiomerically pure form, namely (R,S,S,R)-, (R,S,S,S)-, and (S,S,S,S)-hexaphos. The strongly helicating (R,S,S,R)-(-) form of the ligand combines with copper(I) ions to generate by stereoselective self-assembly the P enantiomer of a parallel helicate of the type [Cu(3)(hexaphos)(2)](PF(6))(3), which has been characterized by x-ray crystallography. Theoretical modeling of the cation indicates that it is the relationship between the helicities of the two 10-membered rings containing the three copper ions, each of which has the twist-boat-chair-boat conformation, and the configurations of the three chiral, tetrahedral copper stereocenters of P configuration that determines the stereochemistry of the parallel and double alpha-helix conformers of the double-stranded trinuclear metal helicate.