Cu(I) Complexes of Multidentate N,C,N- and P,C,P-Carbodiphosphorane Ligands and Their Photoluminescence.

A series of dinuclear copper(I) N,C,N- and P,C,P-carbodiphosphorane (CDP) complexes using multidentate ligands CDP(Py)2 (1) and (CDP(CH2PPh2)2 (13) have been isolated and characterized. Detailed structural information was gained by single-crystal XRD analyses of nine representative examples. The common structural motive is the central double ylidic carbon atom with its characteristic two lone pairs involved in the binding of two geminal L-Cu(I) fragments at Cu-Cu distances in the range 2.55-2.67 Å. In order to enhance conformational rigidity within the characteristic Cu-C-Cu triangle, two types of chelating side arms were symmetrically attached to each phosphorus atom: two 2-pyridyl functions in ligand CDP(Py)2 (1) and its dinuclear copper complexes 2-9 and 11, as well as two diphenylphosphinomethylene functions in ligand CDP(CH2PPh2)2 (13) and its di- and mononuclear complexes 14-18. Neutral complexes were typically obtained via the reaction of 1 with Cu(I) species CuCl, CuI, and CuSPh or via the salt elimination reaction of [(CuCl)2(CDP(Py)2] (2) with sodium carbazolate. Cationic Cu(I) complexes were prepared upon treating 1 with two equivalents of [Cu(NCMe)4]PF6, followed by the addition of either two equivalents of an aryl phosphine (PPh3, P(C6H4OMe)3) or one equivalent of bisphosphine ligands bis[(2-diphenylphosphino)phenyl] ether (DPEPhos), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (XantPhos), or 1,1'-bis(diphenyl-phosphino) ferrocene (dppf). For the first time, carbodiphosphorane CDP(CH2PPh2)2 (13) could be isolated upon treating its precursor [CH(dppm)2]Cl (12) with NaNH2 in liquid NH3. A protonated and a deprotonated derivative of ligand 13 were prepared, and their coordination was compared to neutral CDP ligand 13. NMR analysis and DFT calculations reveal that the most stable tautomer of 13 does not show a CDP (or carbone) structure in its uncoordinated base form. For most of the prepared complexes, photoluminescence upon irradiation with UV light at room temperature was observed. Quantum yields (ΦPL) were determined to be 36% for dicationic [(CuPPh3)2(CDP(Py)2)](PF6)2 (4) and 60% for neutral [(CuSPh)2(CDP(CH2PPh2)2] (16).

Characterization of Phosphoranes Obtained by the Spontaneous Carbonyl-Catalyzed Phosphorylation of Monosaccharides and Polyols in Aqueous Media.

Phosphorylation is a very important biochemical process in metabolism and biochemical marking. The mechanism for the biophosphorylation of substrates and the hydrolysis/transesterification of RNA has been suggested to proceed through phosphorane intermediates. Although the phosphorane intermediate/transition state has long been a subject of many theoretical models and studies, it has neither been isolated nor characterized, with most information derived from the hydrolysis and radiolabeling of cyclic phosphotriesters. We herein present the first report of the spontaneous phosphorylation of sugars and polyols in the absence of enzymes. That is, aldehydes and ketones combine with inorganic phosphates to form activated phosphates that phosphorylate alcohols without the requirement of any enzyme or additional activating agent. This phosphorylation is particularly favored in polyhydroxycarbonyls that can form internal cyclic acetals to give rise to the corresponding acetal phosphoranes. We have further characterized these phosphoranes and demonstrated their dehydration to the corresponding phosphates by using high-resolution mass spectroscopy. The phosphorylation of adenosine and uridine to form the corresponding phosphoranes was also achieved.

Design, Isolation, and Spectroscopic Analysis of a Tetravalent Terbium Complex.

Synthetic strategies to yield molecular complexes of high-valent lanthanides, other than the ubiquitous Ce4+ ion, are exceptionally rare, and thorough, detailed characterization in these systems is limited by complex lifetime and reaction and isolation conditions. The synthesis of high-symmetry complexes in high purity with significant lifetimes in solution and the solid state is essential for determining the role of ligand-field splitting, multiconfigurational behavior, and covalency in governing the reactivity and physical properties of these potentially technologically transformative tetravalent ions. We report the synthesis and physical characterization of an S4 symmetric, four-coordinate tetravalent terbium complex, [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (where Et is ethyl and tBu is tert-butyl). The ligand field in this complex is weak and the metal-ligand bonds sufficiently covalent so that the tetravalent terbium ion is stable and accessible via a mild oxidant from the anionic, trivalent, terbium precursor, [(Et2O)K][Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4]. The significant stability of the tetravalent complex enables its thorough characterization. The stepwise development of the supporting ligand points to key ligand control elements for further extending the known tetravalent lanthanide ions in molecular complexes. Magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray absorption near-edge spectroscopy (XANES), and density functional theory studies indicate a 4f7 ground state for [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] with considerable zero-field splitting, demonstrating that magnetic, tetravalent lanthanide ions engage in covalent metal-ligand bonds. This result has significant implications for the use of tetravalent lanthanide ions in magnetic applications since the observed zero-field splitting is intermediate between that observed for the trivalent lanthanides and for the transition metals. The similarity of the multiconfigurational behavior in the ground state of [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (measured by Tb L3-edge XAS) to that observed in TbO2 implicates ligand control of multiconfigurational behavior as a key component of the stability of the complex.

Chiral Hypervalent, Pentacoordinated Phosphoranes.

This review presents synthetic procedures applied to the preparation of chiral (mainly optically active) pentacoordinated, hypervalent mono and bicyclic phosphoranes. The mechanisms of their stereoisomerization and their selected interconversions are also presented.

Ravynic acid, an antibiotic polyeneyne tetramic acid from Penicillium sp. elucidated through synthesis.

A new antibiotic natural product, ravynic acid, has been isolated from a Penicillium sp. of fungus, collected from Ravensbourne National Park. The 3-acylpolyenyne tetramic acid structure was definitively elucidated via synthesis. Highlights of the synthetic method include the heat induced formation of the 3-acylphosphorane tetramic acid and a selective Wittig cross-coupling to efficiently prepare the natural compounds carbon skeleton. The natural compound was shown to inhibit the growth of Staphylococcus aureus down to concentrations of 2.5 µg mL(-1).

First paraben substituted cyclotetraphosphazene compounds and DNA interaction analysis with a new automated biosensor.

Cancer, as one of the leading causes of death in the world, is caused by malignant cell division and growth that depends on rapid DNA replication. To develop anti-cancer drugs this feature of cancer could be exploited by utilizing DNA-damaging molecules. To achieve this, the paraben substituted cyclotetraphosphazene compounds have been synthesized for the first time and their effect on DNA (genotoxicity) has been investigated. The conventional genotoxicity testing methods are laborious, take time and are expensive. Biosensor based assays provide an alternative to investigate this drug/compound DNA interactions. Here for the first time, a new, easy and rapid screening method has been used to investigate the DNA damage, which is based on an automated biosensor device that relies on the real-time electrochemical profiling (REP™) technology. Using both the biosensor based screening method and the in vitro biological assay, the compounds 9 and 11 (propyl and benzyl substituted cyclotetraphosphazene compounds, respectively), have resulted in higher DNA damage than the others with 65% and 80% activity reduction, respectively.

Synthesis of a new class of fused cyclotetraphosphazene ring systems.

Octachlorocyclotetraphosphazene (1) was reacted with butylamines [n-butyl, i-butyl, sec-butyl, and t-butyl] in a 1:0.8 mol ratio in THF to obtain cyclotetraphosphazenes bearing a P-NH group, N4P4Cl7(NHR) [R = n-butyl (2a), i-butyl (2b), sec-butyl (2c), t-butyl (2d)](2a-d). The cyclotetraphosphazene derivatives 2a, 2b, and 2c were treated with sodium hydride giving rise to a new type of cyclophosphazene compounds (P8N8 ring) consisting of three fused tetramer rings (3a-c). Whereas reaction of sodium hydride with the t-butylaminocyclophosphazene derivative (2d) gave a P-O-P bridged compound (4) presumably as a result of hydrolysis reaction associated with moisture in the solvent. It is likely that the 16-membered cyclooctaphosphazene derivatives (3a-c) are formed by a proton abstraction/chloride ion elimination, intramolecular nucleophilic attack, ring opening and intermolecular condensation processes, respectively.

In vitro and in vivo evaluation of water-soluble iminophosphorane ruthenium(II) compounds. A potential chemotherapeutic agent for triple negative breast cancer.

A series of organometallic ruthenium(II) complexes containing iminophosphorane ligands have been synthesized and characterized. Cationic compounds with chloride as counterion are soluble in water (70-100 mg/mL). Most compounds (especially highly water-soluble 2) are more cytotoxic to a number of human cancer cell lines than cisplatin. Initial mechanistic studies indicate that the cell death type for these compounds is mainly through canonical or caspase-dependent apoptosis, nondependent on p53, and that the compounds do not interact with DNA or inhibit protease cathepsin B. In vivo experiments of 2 on MDA-MB-231 xenografts in NOD.CB17-Prkdc SCID/J mice showed an impressive tumor reduction (shrinkage) of 56% after 28 days of treatment (14 doses of 5 mg/kg every other day) with low systemic toxicity. Pharmacokinetic studies showed a quick absorption of 2 in plasma with preferential accumulation in the breast tumor tissues when compared to kidney and liver, which may explain its high efficacy in vivo.

Chemoselective Wittig and Michael ligations of unprotected peptidyl phosphoranes in water furnish potent inhibitors of caspase-3.

Unprotected peptidyl phosphoranes 1 with sequence Ac-L-aspartyl-L-glutamyl-L-valinyl-L-aspartyl are released from polymer support and react with aliphatic and aromatic aldehydes in aqueous medium in a Wittig ligation. Obtained vinyl ketones 6-12 are potent inhibitors of caspase-3. Vinyl ketone 6, derived from formaldehyde, undergoes Michael ligations with thiol nucleophiles furnishing products 14-16, also in aqueous medium. The demonstrated ligation reactions enable the modification of complex functionalized peptides in water providing bioactive protein ligands without side-chain protection.

Characterization of the transient oxaphosphetane BChE inhibitor formed from spontaneously activated ethephon.

The major plant growth regulator ethephon degrades to ethylene and phosphate in aqueous solutions and plants and is spontaneously activated to a butyrylcholinesterase (BChE) inhibitor in alkaline solutions and animal tissues. In the present (31)P NMR kinetic study of the reactions of ethephon in pH 7.4 carbonate buffer, we observed a transient peak at 28.11 ppm. The time course for the appearance and disappearance of this peak matches the activation/degradation kinetic profile of the BChE inhibitor, and the chemical shift supports the proposed 2-oxo-2-hydroxy-1,2-oxaphosphetane structure.

Soluble peptidyl phosphoranes for metal-free, stereoselective ligations in organic and aqueous solution.

Protocols for solid-phase syntheses of soluble peptidyl phosphoranes are presented. Various supported phosphoranylidene acetates were prepared on Rink amide or via alkylation of trialkyl- and triarylphosphines with bromoacetyl Wang ester. C-Acylation was conducted racemization-free with activated Fmoc-amino acids, followed by SPPS (solid-phase peptide synthesis). Acidic conditions released decarboxylated peptidyl phosphoranes into solution. The protocol allowed for the electronic variation of peptidyl phosphoranes which were investigated in ligation reactions with azides in organic and aqueous solvents.

Liquid chromatography/electrospray time-of-flight mass spectrometry for the characterisation of cyclic phosphazenes.

Cyclic phosphazenes with different substituents were synthesised and investigated by liquid chromatography (LC) and electrospray ionisation mass spectrometry (ESI-MS). Hexachlorocyclotriphosphazene was functionalised with aliphatic substituents as alcohols and amines, leading to product mixtures, which were subsequently analysed. In contrast to classical methods of structural analysis such as nuclear magnetic resonance (NMR) spectroscopy or X-ray crystallography, which are restricted to pure compounds, these complex mixtures can favourably be analysed by means of LC/ESI-MS. The main products could be separated from by-products and, moreover, all the components of the unknown mixture were unambiguously identified by accurate mass measurements. For all compounds with different side-chain ratios, remaining chlorine atoms or hydroxyl groups and even for spiro or ansa products, molecular structures could be suggested.

Synthesis, structure, and reactivity of N-benzoyl iminophosphoranes ortho lithiated at the benzoyl group.

Ortho lithiation of N-benzamido-P,P,P-triaryliminophosphoranes through deprotonation with alkyllithium bases was achieved with ortho-C═O and ortho-P═N chemoselectivity. However, the synthetic scope of these processes was rather limited. Ortho-lithiated N-benzamido-P,P,P-triphenyliminophosphorane 8 was efficiently prepared via lithium/halogen exchange of the corresponding ortho-brominated precursor with s-BuLi in THF at -90 °C. The reaction of 8 with a variety of electrophiles provides an easy and mild method for the regioselective synthesis of ortho-modified iminophosphoranes via C-C (alkylation and hydroxyalkylation) and C-X (X = I, Si, P, Sn, and Hg) bond-forming reactions. NMR characterization of 8 in THF solution showed that 8 exists as an equilibrium mixture of one monomer and two dimers. The Li atoms of these species become members of five-membered rings through chelation by the ortho-metalated carbon and the carbonyl oxygen. The dimers differ in the relative orientation of the two chelates with respect to the plane defined by the C(2)Li(2) core. The equilibrium between all species is established by splitting the dimers into monomers and subsequent recombination with formation of a different dimer.

The diverse behaviour of the P-Cl bonds in the spiro-cis-ansa spermidine derivative cyclotriphosphazene towards mono-functional nucleophilic reagents.

A number of new spiro-ansa spermidine derivative cyclotriphosphazenes (2-10) is synthesized in order to provide insight into the reaction mechanism for nucleophilic substitution. The structures of the compounds were determined by elemental analysis, mass (MS), (1)H, (19)F (for 9) and (31)P NMR spectroscopies. Compounds (2-8) and 9, 10 can be formed by a proton abstraction-chloride elimination and both the S(N)(1) and S(N)(2) reaction mechanisms, respectively.

Generation of nitrene by the photolysis of N-substituted iminodibenzothiophene.

To evaluate the ability of dibenzothiophene N-substituted sulfilimines as photochemical nitrene sources, their photolyses in the presence of several trapping reagents, such as sulfides, olefins, and phosphorus compounds, were performed. In the reactions, the corresponding imino-transfer compounds, namely sulfilimines, aziridines, and iminophosphoranes, were formed in good yields, indicating dibenzothiophene N-tosyl and N-acylsulfilimines have a potent nature as nitrogen sources.

Synthesis, structure and isomerization of arylphosphoranes with anti-apicophilic bonding modes using a novel bidentate ligand with two C(2)F(5) groups.

A series of anti-apicophilic pentacoordinate phosphoranes (with one chelating substituent in an O-equatorial, C-apical bonding mode at pentacoordinated phosphorus atom) bearing a para-substituted aryl group (-C(6)H(4)(p-X); X = H, CF(3), F, OMe) or a mesityl (2,4,6-trimethylphenyl) group were isolated using a novel bulky bidentate ligand with two C(2)F(5) groups. These phosphoranes were stable to isomerization at room temperature, and quantitatively converted into the corresponding more stable isomers (O-apical) at elevated temperatures in solution. On the basis of a kinetic study, the free energy of activation (DeltaG(double dagger)) of the stereomutation of the O-equatorial mesitylphosphorane to its O-apical isomer was higher than that of the CF(3) derivative by 2.6 kcal mol(-1), giving rise to a further example of the steric effect of the C(2)F(5) group to freeze the isomerization of the pentacoordinate phosphorus compounds. Kinetic measurements of the isomerization of the O-equatorial ortho-unsubstituted derivatives (-C(6)H(4)(p-X)) to the corresponding O-apical isomers suggested that the O-equatorial isomers were stabilized by the pi --> sigma*(P-O) interaction in the ground state.

Synthesis of oxime phosphoranes from reaction between triphenylphosphine and acetylenic esters in the presence of oxime derivatives.

A new one-pot, simple and effective procedure is presented for the preparation of O-containing phosphorus ylides by the Michael addition reaction of N-methylpyrrole-2-carbaldehydoxime, pyridin-2-carbaldehydoxime or acetophenonoxime with acetylenic esters.

Synthesis and application of a bidentate ligand based on decafluoro-3-phenyl-3-pentanol: steric effect of pentafluoroethyl groups on the stereomutation of O-equatorial C-apical spirophosphoranes.

1,1,1,2,2,4,4,5,5,5-Decafluoro-3-phenyl-3-pentanol was prepared by a Cannizzaro-type disproportionation reaction, and the dimetallated compound was used as a bidentate ligand, which is bulkier than the Martin ligand (1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol). A P-H spirophosphorane was synthesized by utilizing the new bidentate ligand, and the structure of the product was essentially the same as that of the P-H phosphorane with Martin ligands. Phosphoranes that exhibit reversed apicophilicity (O-equatorial) were also synthesized and could be converted into the corresponding stable stereoisomers (O-apical). The crystal structures of O-equatorial phosphoranes and the O-apical isomers were slightly affected by the steric repulsion of pentafluoroethyl groups. Kinetic measurements revealed that the stereomutation of O-equatorial methylphosphorane to the O-apical isomer was slowed. The activation enthalpy for the stereomutation of the former to the latter was higher than that of the phosphorane with Martin ligands by 5.1 kcal mol(-1).

The first structural study on a cyclic tricoordinate phosphorochloridite and a pentacoordinate phosphorane based on 1,2,3,5-protected myo-inositol--a new conformation of 1,3,2-dioxaphosphorinane ring.

Treatment of the phosphoramidite [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(O(2)P-NH-i-Pr)] with o-chloranil affords the first example of inositol-based pentacoordinate phosphorane [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(O(2)P-NH-i-Pr)(1,2-O(2)C(6)Cl(4))] (9) (X-ray structure) with a trigonal bipyramidal geometry at phosphorus. The six-membered 1,3,2-dioxaphosphorinane ring with the inositol residue has an unusual boat conformation in 9 which is quite different from that found in unrestrained rings investigated before, but is similar to that of its P(III) chloro precursor [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(O(2)PCl)] (X-ray structure). Also, a convenient and chromatography-free procedure for the protected myo-inositol derivative [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(OH)(2)] is reported.

Experimental determination of the nN --> sigma*P-O interaction energy of O-equatorial C-apical phosphoranes bearing a primary amino group.

The reaction of a chlorophosphorane (9-Cl) with primary amines produced anti-apicophilic spirophosphoranes (5, O-equatorial phosphoranes), which violate the apicophilicity concept, having an apical carbon-equatorial oxygen configuration, along with the ordinarily expected O-apical stereoisomers (6) with the apical oxygen-equatorial carbon configuration. Although the amino group is electronegative in nature, the O-equatorial phosphoranes were found to be stable at room temperature and could still be converted to their more stable O-apical pseudorotamers (6) when they were heated in solution. X-ray analysis implied that this remarkable stability of the O-equatorial isomers could be attributed to the orbital interaction between the lone-pair electrons of the nitrogen atom (n(N)) and the antibonding sigma(P-O) orbital in the equatorial plane. A kinetic study of the isomerization of 5 to 6 and that between diastereomeric O-apical phosphoranes 13b-exo and 13b-endo revealed that 5b bearing an n-propylamino substituent at the central phosphorus atom was found to be less stable than the corresponding isomeric 6b by ca. 7.5 kcal mol(-1). This value was smaller than the difference in energy (11.9 kcal mol(-1)) between the O-equatorial (1b) and the O-apical n-butylphosphorane (2b) by 4.4 kcal mol(-1). This value of 4.4 kcal mol(-1) can be regarded as the stabilization energy induced by the n(N) --> sigma(P-O) interaction. The experimentally determined value was in excellent agreement with that derived from density functional theory (DFT) calculations at the B3PW91 level (4.0 kcal mol(-1)) between the nonsubstituted aminophosphoranes (5g is less stable than 6g by 10.1 kcal mol(-1)) and their P-methyl-substituted counterparts (1a is less stable than 2a by 14.1 kcal mol(-1)).