Phosphine Adducts Research Articles

Cu(I) and Ag(I) complexes of two sterically demanding Xylyl-Substituted phosphine Ligands: Synthesis, Characterization, and structural examination

Two sterically demanding tertiary phosphines, PiPr2Xyl and PtBu2Xyl, (Xyl = 2,6-dimethylphenyl), the latter reported here for the first time, have been used to synthesize a series of dinuclear complexes of the general formula [M(μ-X)PR2Xyl]2, (R = iPr, tBu; M = Cu: X = Cl, Br, I, OTf; M = Ag: X = OTf, NTf2). All compounds have been characterized by multinuclear NMR spectroscopy in solution and, with the exception of AgNTf2(PtBu2Xyl), by X-ray diffraction analyses. The doubly halido-bridged compounds [Cu(μ-X)PR2Xyl]2 (R = iPr, tBu; X = Cl, Br, I) display Ci, C2-like, or C1 molecular symmetry, depending on the anion and the R group, and enclose planar or disphenoidal [CuX]2 cores with short, bonding Cu—Cu distances in case of X = I. On the other hand, centrosymmetric 8-membered rings with twist-chair conformations are found in the solid state structures of [M(μ-OTf)PR2Xyl]2 (R = iPr, tBu; M = Cu, Ag) and [Ag(μ-NTf2)PiPr2Xyl]2, with the anions in a κ2-μ2 coordination mode. Additionally, the cationic complex [Cu(PR2Xyl)2]+ has been obtained as a triflate or BArF salt (BArF- = B{3,5-(CF3)2C6H3}4-), and shows C2-like symmetry in the solid state, with PCuP angles of ca. 168-169° and synclinal dispositions of the Xyl groups with respect to the P∙∙∙P axis. Comparative discussion of relevant NMR data of Cu(I), Ag(I), and Au(I) adducts of the title phosphines is also provided.

Reactivity of Hg(II) ortho-cyano-aminothiophenolate coordination polymers [Hg{SC6H3XN(C≡N)}]n with cyclic aromatic amines, Ph3P = E (E = O, S) and [HgCl2(κ2-phen)

We report reactions of Hg(II) ortho-cyano-aminothiophenolate coordination polymers, [Hg{SC6H3XN(C≡N)}]n, with donor ligands. Addition of cyclic aromatic amines, such as pyridine (L), leads to breakdown of the polymeric structure to give mononuclear four-coordinate complexes, [Hg{κ2 -SC6H3XN(C≡N)}L2], while 2,2’-bipy and 1,10-phen (L2) similarly afford mononuclear chelate complexes [Hg{κ2 -SC6H3XN(C≡N)}(κ2-L2)]. In contrast, Ph3P = E (E = O, S) form 1:1 complexes which, on the basis of related phosphine adducts, are formulated as binuclear [Hg{µ-SC6H3XN(C≡N)}(κ1-E = PPh3)]2. Reaction of [Hg{SC6H4N(C≡N)}]n with [HgCl2(κ2 -phen)] affords an adduct tentatively formulated as [Hg{κ2-SC6H4N(C≡N)}(µ-Cl)2Hg(κ2-phen)] in which the two chlorides bridge the Hg.Hg vector.

Hydrolysis and oxidation products of phosphine adducts to beryllium chloride

Abstract The synthesis of bis(diphenylphosphino)ethane (dppe) and PMe3 mono-adducts [(dppe)BeCl2]n and [(PMe3)BeCl2]2 is described and their spectroscopic properties discussed. Hydrolysis of these two compounds and of the bis(diphenylphosphino)propane (dppp) adduct to BeCl2 gave [dppeH2][BeCl4], [Me3PH]n[Be4Cl9]n and [dpppH2][Be2Cl6], which have been isolated and structurally characterized by single crystal X-ray diffraction. The reactions of [(PMe3)BeCl2]2 with p-cresole gave [Me3PH]2[Be2Cl4(OC7H7)2]. This phenoxide together with [(Me3PO)2Be2Cl4], the oxidation product of [(PMe3)BeCl2]2, have also been structurally characterized.

Crystal Structures of Gallium(III) Halides with Bulky Ligands

Three oxygen donor gallium(III) halide complexes, [GaX3(O=P(TMP)3] (TMP = trimethoxylphenyl and X = Cl− (1), Br− (2) and I− (3)), are prepared by oxidation in mixed solvents from their phosphine adducts of [GaX3(P(TMP)3]. Three crystalline compounds are obtained from the solutions and their crystal structures are determined in the solid state. It is rare to generate a crystalline phase for metal–adduct compounds of this bulky ligand; in this paper, three new crystal structures are presented.

A low-temperature thermal ALD process for nickel utilizing dichlorobis(triethylphosphine)nickel(II) and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine.

In this work, we developed a new ALD process for nickel metal from dichlorobis(triethylphosphine)nickel(II) (NiCl2(PEt3)2) and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine ((Me3Ge)2DHP). A series of phosphine adducts of nickel and cobalt halides were synthesized and characterized for their volatility and thermal stability. Also (Me3Ge)2DHP is a novel reducing agent in ALD. Smooth nickel films were deposited on different substrate materials at 110 °C, which is the lowest deposition temperature for Ni metal found in the literature. The growth rate is 0.2 Å per cycle when the film is not continuous and decreases to 0.1 Å per cycle after the film becomes pinhole-free. Besides a small amount (7 at%) of carbidic carbon, the films have only small amounts of impurities. Most notably, the chlorine content is below 0.2 at%, indicating efficient reduction. Furthermore, we think that (Me3Ge)2DHP can open new avenues for the ALD of other metals at low temperatures.

Ni(NHC)2 ] as a Scaffold for Structurally Characterized trans [H-Ni-PR2 ] and trans [R2 P-Ni-PR2 ] Complexes.

The addition of PPh2H, PPhMeH, PPhH2, P(para‐Tol)H2, PMesH2 and PH3 to the two‐coordinate Ni0 N‐heterocyclic carbene species [Ni(NHC)2] (NHC=IiPr2, IMe4, IEt2Me2) affords a series of mononuclear, terminal phosphido nickel complexes. Structural characterisation of nine of these compounds shows that they have unusual trans [H−Ni−PR2] or novel trans [R2P−Ni−PR2] geometries. The bis‐phosphido complexes are more accessible when smaller NHCs (IMe4>IEt2Me2>IiPr2) and phosphines are employed. P−P activation of the diphosphines R2P−PR2 (R2=Ph2, PhMe) provides an alternative route to some of the [Ni(NHC)2(PR2)2] complexes. DFT calculations capture these trends with P−H bond activation proceeding from unconventional phosphine adducts in which the H substituent bridges the Ni−P bond. P−P bond activation from [Ni(NHC)2(Ph2P−PPh2)] adducts proceeds with computed barriers below 10 kcal mol−1. The ability of the [Ni(NHC)2] moiety to afford isolable terminal phosphido products reflects the stability of the Ni−NHC bond that prevents ligand dissociation and onward reaction.

Simple, Axial Ligand-Mediated Route to Water-Soluble Iridium Corroles.

The synthesis and purification of water-soluble porphyrin-type compounds for photodynamic therapy and other medical applications is often a tedious exercise. Here, we have investigated the simple stratagem of adding a water-soluble axial ligand to the standard protocol for iridium insertion into simple meso-triarylcorroles. Early results showed that six-coordinate Ir[TpXPC](dna)2 derivatives, in which TpXPC = tris(para-X-phenyl)corrole (X = CF3, CN, H, and OMe) and dna = dinicotinic acid, are highly water-soluble. In the end, however, all axially nitrogen-ligated complexes proved unstable with respect to chromatographic purification and storage. Five-coordinate water-soluble phosphine adducts, fortunately, proved a great improvement. From the point of view of ease of purification and storage, the best products proved to be Ir[TpXPC](L), where X = CF3 and OMe and L = tris(2-carboxyethyl)phosphine (tcep) and trisodium tris(3-sulfonatophenyl)phosphine (tppts); carefully optimized synthetic protocols are presented for these four compounds.

The Reactivity of Isomeric Nitrenium Lewis Acids with Phosphines, Carbenes, and Phosphide.

Alkylation of spiro[fluorene‐9,3’‐indazole] at N(1) and N(2) with tBuCl affords the nitrenium cations [C6H4N2(tBu)C(C12H8)][BF4], 1 and 2, respectively. Compound 1 converts to 2 over the temperature range 303–323 K with a free energy barrier of 28±5 kcal mol−1. Reaction of 1 with PMe3 afforded the N‐bound phosphine adduct [C6H4N(tBu)N(PMe3)C(C12H8)]BF4] 3. However, phosphines attack 2 at the para‐carbon atom of the aryl group with concurrent cleavage of N(2)−C(1) bond and proton migration to C(1) affording [(R3P)C6H3NN(tBu)CH(C12H8)][BF4] (R=Me 4, nBu 5). Analogous reactions of 1 and 2 with the carbene SIMes prompt attack at the para‐carbon with concurrent loss of H. affording the radical cation salts [(SIMes)C6H3N(tBu)NC(C12H8).][BF4] 6 and [(SIMes)C6H3NN(tBu)C(C12H8).][BF4] 7, whereas reaction of 2 with BAC gives the Lewis acid‐base adduct, [C6H4N(BAC)N(tBu)C(C12H8)][BF4] 8. Finally, reactions of 1 and 2 with KPPh2 result in electron transfer affording (PPh2)2 and the persistent radicals C6H4N(tBu)NC(C12H8). and C6H4NN(tBu)C(C12H8).. The detailed reaction mechanisms are also explored by extensive DFT calculations.

DFT Study on the Mechanism of Iron-Catalyzed Diazocarbonylation.

The mechanism of the carbonylation of diazomethane in the presence of iron–carbonyl–phosphine catalysts has been investigated by means of DFT calculations at the M06/def-TZVP//B97D3/def2-TZVP level of theory, in combination with the SMD solvation method. The reaction rate is determined by the formation of the coordinatively unsaturated doublet-state Fe(CO)3(P) precursor followed by the diazoalkane coordination and the N2 extrusion. The free energy of activation is predicted to be 18.5 and 28.2 kcal/mol for the PF3 and PPh3 containing systems, respectively. Thus, in the presence of less basic P-donor ligands with stronger -acceptor properties, a significant increase in the reaction rate can be expected. According to energy decomposition analysis combined with natural orbitals of chemical valence (EDA–NOCV) calculations, diazomethane in the Fe(CO)3(phosphine)(η1-CH2N2) adduct reveals a -donor–-acceptor type of coordination.

Stabilization of Linear C3 by Two Donor Ligands: A Theoretical Study of L-C3 -L (L=PPh3 , NHCMe , cAACMe )*.

Quantum chemical studies using density functional theory and ab initio methods have been carried out for the molecules L‐C3‐L with L=PPh3 (1), NHCMe (2, NHC=N‐heterocyclic carbene), and cAACMe (3, cAAC=cyclic (alkyl)(amino) carbene). The calculations predict that 1 and 2 have equilibrium geometries where the ligands are bonded with rather acute bonding angles at the linear C3 moiety. The phosphine adduct 1 has a synclinal (gauche) conformation whereas 2 exhibits a trans conformation of the ligands. In contrast, the compound 3 possesses a nearly linear arrangement of the carbene ligands at the C3 fragment. The bond dissociation energies of the ligands have the order 1<2<3. The bonding analysis using charge and energy decomposition methods suggests that 3 is best described as a cumulene with electron‐sharing double bonds between neutral fragments (cAACMe)2 and C3 in the respective electronic quintet state yielding (cAACMe)=C3=(cAACMe). In contrast, 1 and 2 possess electron‐sharing and dative bonds between positively charged ligands [(PPh3)2]+ or [(NHCMe)2]+ and negatively charged [C3]− fragments in the respective doublet state.

Synthesis of Tungsten Oxo Alkylidene Biphenolate Complexes and Ring-Opening Metathesis Polymerization of Norbornenes and Norbornadienes

We have synthesized and characterized tungsten oxo alkylidene biphenolate complexes with the formulas W(O)(CHR)(rac-biphenolate)(PPhMe2) and (R,S)-[W(μ-O)(CHR)(biphenolate)]2 (R = CMe2Ph; biphenolate = L1 or L2 in the text). They behave as initiators for the stereoselective (cis,isotactic) polymerization of 2,3-dicarbomethoxy-5-norbornadiene and eight enantiomerically pure 5-substituted norbornenes with a cis,isotactic precision of 95–98% in most cases. The active initiators are 14e W(O)(CHR)(biphenolate) complexes, which are formed through either dissociation of PPhMe2 from the phosphine adducts or scission of the heterochiral dimer. Addition of B(C6F5)3 (one per W) to (R,S)-[W(μ-O)(CHR)(L1)]2 led to formation of what we propose to be monomeric W[OB(C6F5)3](CHR)(L1) in equilibrium with B(C6F5)3 and (R,S)-[W(μ-O)(CHR)(L1)]2. This mixture decomposed over a period of 1–2 h, was much slower to initiate polymerization than (R,S)-[W(μ-O)(CHR)(L1)]2, and was much less stereoselective. Polymerization of five of the monomers with the imido alkyidene initiator, W(N-2,6-Me2C6H3)(CHCMe2Ph)(rac-L1), gave virtually identical results compared to the results obtained with oxo complexes.

Phosphine-Stabilized Digermavinylidene

An intramolecular germylene-phosphine Lewis pair (1) was reacted with germanium dichloride to give in 92% yield a phosphine adduct of a chloro substituted germyl-germylene (2). After reduction of this dichloride with strong reductants like the Mg(I) reagent {(MesNacnac)Mg}2 (72% yield) or Na (52% yield) a phosphine stabilized digermavinylidene (3) was isolated as crystalline material [MesNacnac = {[(Mes)NC(Me)]2CH}-, Mes = 2,4,6-Me3C6H2]. The electronic structure of the digermavinylidene was investigated by density functional theory calculations. In reaction with adamantylphosphaalkyne the product of a [2+2] cycloaddition was characterized (4). Adamantylazide abstracts at room temperature a germanium atom from the digermavinylidene and a tetrameric organogermanium nitride (5) was isolated as colorless crystals.

Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes

The synthesis and the characterization of a series of phosphine adducts of (imido)vanadium(IV) dichloride complexes of the type V(═NR)Cl2(PMe2Ph)2 [R = 2,6-Cl2-Ph (1), 2,6-iPr2-Ph (2), and tBu (3)] and V(═NtBu)Cl2(PMe3)2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N–V–C bond. Complexes 1–3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et2AlCl (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1–3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly(ethylene)s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform c...

Facile Access to Unprecedented Electron-Precise Monohydrodiboranes(4), cis-1,2-Dihydrodiboranes(4), and a 1,1-Dihydrodiborane(5).

2,3-Bis(dimethylamino)-substituted B2 N2 C2 heterocycles underwent selective dimethylamino/hydride exchange with either one or two equivalents of BH3 ⋅SMe2 to give the corresponding cyclic monohydrido- or (cis)1,2-dihydridodiboranes(4), respectively. Upon either heating or irradiation in solution, the latter underwent ring contraction to the corresponding five-membered BN2 C2 heterocycles, whereas irradiation of the 1,2-dimethylaminoethene-supported 1,2-dihydridodiborane(4) in the presence of PEt3 gave an unprecedented unsymmetrical 1,1-dihydrodiborane(5) phosphine adduct.

The Myeloablative Drug Busulfan Converts Cysteine to Dehydroalanine and Lanthionine in Redoxins.

The myeloablative agent busulfan (1,4-butanediol dimethanesulfonate) is an old drug that is used routinely to eliminate cancerous bone marrow prior to hematopoietic stem cell transplant. The myeloablative activity and systemic toxicity of busulfan have been ascribed to its ability to cross-link DNA. In contrast, here we demonstrate that incubation of busulfan with the thiol redox proteins glutaredoxin or thioredoxin at pH 7.4 and 37 °C results in the formation of putative S-tetrahydrothiophenium adducts at their catalytic Cys residues, followed by β-elimination to yield dehydroalanine. Both proteins contain a second Cys, in their catalytic C-X-X-C motif, which reacts with the dehydroalanine, the initial Cys adduct with busulfan, or the S-tetrahydrothiophenium, to form novel intramolecular cross-links. The reactivity of the dehydroalanine (DHA) formed is further demonstrated by adduction with glutathione to yield a lanthionine and by a novel reaction with the reducing agent tris(2-carboxyethyl)phosphine (TCEP), which yields a phosphine adduct via Michael addition to the DHA. Formation of a second quaternary organophosphonium salt via nucleophilic substitution with TCEP on the initial busulfan-protein adduct or on the THT(+)-Redoxin species is also observed. These results reveal a rich potential for reactions of busulfan with proteins in vitro, and likely in vivo. It is striking that several of the chemically altered protein products retain none of the atoms of busulfan, in contrast to typical drug-protein adducts or traditional protein modification reagents. In particular, the ability of a clinically used drug to convert Cys to dehydrolanine in intact proteins, and its subsequent reaction with biological thiols, is unprecedented.

Basic Reactivity Pattern of a Cyclic Disilylated Germylene.

In order to estimate the reactivity of disilylated germylene phosphine adducts, a cyclic version of this compound class was reacted with a number of different reagents. Reactions with the chalcogens sulfur, selenium, and tellurium led to dimers of the heavy ketone analogues. Reactions with water and ethyl bromide proceeded to give the respective oxidized germanol and germyl bromide. Two different reactions with alkynes were observed which led either to a germacyclopropene, by addition of tolane to the germylene, or to a silagermacyclobutene, likely formed by addition of the alkyne across a silagermene. Reaction via the silagermene was also observed in the reaction with benzophenone. Reaction of a germylene phosphine adduct with GeCl2·(dioxane) provided insertion of the silylated germylene into a Ge–Cl bond, leading to a germylated chlorogermylene phosphine adduct.

Investigation of Functional Group Effects on Palladium Catalysed Asymmetric P–H Addition

The pincer catalysed asymmetric P–H addition of diphenylphosphine to 3-benzylidene-2,4-pentadione is herein reported. Albeit successful in catalysing a series of similar substrates, unexpected chelation of the dione substrate to a CP and CN palladacycle catalyst resulted in inactivation of the catalyst with adjacent coordination sites. Protected phosphine adducts were isolated and characterised, providing critical insights to the choice of catalyst for structurally distinct functional groups borne by the substrate.

Silylated Group 14 Ylenes: An Emerging Class of Reactive Compounds

AbstractSilyl‐substituted heavy‐element tetrylenes are very reactive entities and therefore prefer variously to dimerize to heavy olefin analogues, to oligomerize to cyclic products, or to undergo some type of rearrangement reaction. Our work on the synthesis of oligosilanyl‐substituted plumbylenes, stannylenes, and germylenes has shown that trapping such tetrylenes as phosphine adducts is a good method for preventing dimerization or rearrangement and allows the chemistry of the free tetrylene to be studied either through phosphane abstraction or even through thermally induced dissociation. In addition to a number of typical reactions with these tetrylenes, which occur in such a way that the divalent element becomes tetravalent, it was found in the case of germylenes that addition of monosubstituted alkynes proceeds by insertion into a Ge–Si bond with preservation of the divalent state of the germylene. The obtained tetrylene phosphane adducts could also be used as precursors for the generation of transition‐metal complexes with tetrylene ligands.

ChemInform Abstract: Palladacycle Catalyzed Asymmetric P—H Addition of Diarylphosphines to N‐Enoyl Phthalimides.

AbstractThe facile phospha‐Michael addition provides highly enantioenriched tertiary phosphine adducts.

Palladacycle promoted base controlled regio- and enantioselective hydrophosphination of 2-pyridylacrylate/amide and the cytotoxicity of their gold complexes

The regioselective asymmetric hydrophosphination of pyridine-functionalized alkenes can be achieved in the presence of stoichiometric amounts of the chiral palladium complex (R)-1. The presence or absence of base affords the respective β- and α-adducts with excellent regiocontrol. Chiral gold-phosphine complexes incorporating the adducts exhibited good in vitro anticancer activity against the breast cancer cell line MDA-MB-231. Selectivity between the cancer cell line and normal cells was also observed.