Synthesis and structural study of (8-phenylsulfanylnaphth-1-yl)diphenylphosphine metal complexes

A series of three platinum(II) halide complexes 2–4 [Pt(X)₂{Nap(PPh₂)(SPh)}] (Nap = naphthalene-1,8-diyl; X = Cl, Br, I) and a ruthenium(II) p-cymene complex 5 [Ru(η⁶-MeC₆H₄ⁱPr)(Cl){Nap(PPh₂)(SPh)}]⁺Cl^? of the sterically crowded peri-substituted naphthalene phosphine 1 have been prepared. The compounds were fully characterised by multinuclear NMR, IR and MS and X-ray data for 1–5 are compared. Molecular structures are analysed by naphthalene ring torsions, peri-atom displacement, splay angle magnitude, P···S interactions, aromatic ring orientations and geometry around the metal centre. Platinum adopts a strictly square planar geometry which increases the distortion of the naphthalene skeleton in 2–4. Conversely, the classical-piano stool conformation of 5 results in a pseudo-octahedral conformation around the ruthenium atom which influences the naphthalene geometry to a much lesser extent with distortion of a similar magnitude to the free ligand 1.     

Synthesis and spectroscopy of cis-configured mononuclear palladium(II) and platinum(II) complexes of chalcogeno o-carboranes and structures of [Pt(SCboPh)2(dppm)], [Pt(SeCboPh)2(dppm)], [Pt(SCboS)(PMe2Ph)2] and [Pt(SCboS)(PMePh2)2]

The reactions of [MCl₂(P^∩P)] and [MCl₂(PR₃)₂)] with 1-mercapto-2-phenyl-o-carborane/NaSeCb^oPh and 1,2-dimercapto-o-carborane yield mononuclear complexes of composition, [M(SCb^oPh)₂(P^∩P)], [M(SeCb^oPh)₂(P^∩P)] (M = Pd or Pt; P^∩P = dppm (bis(diphenylphosphino)methane), dppe (1,2-bis(diphenylphosphino)ethane) or dppp (1,3-bis(diphenylphosphino)propane)) and [M(SCb^oS)(PR₃)₂] (2PR₃ = dppm, dppe, 2PEt₃, 2PMe₂Ph, 2PMePh₂ or 2PPh₃). These complexes have been characterized by elemental analysis and NMR (¹H, ³¹P, ⁷⁷Se and ¹⁹⁵Pt) spectroscopy. The ¹J(Pt–P) values and ¹⁹⁵Pt NMR chemical shifts are influenced by the nature of phosphine as well as thiolate ligand. Molecular structures of [Pt(SCb^oPh)₂(dppm)], [Pt(SeCb^oPh)₂(dppm)], [Pt(SCb^oS)(PMe₂Ph)₂] and [Pt(SCb^oS)(PMePh₂)₂] have been established by single crystal X-ray structural analyses. The platinum atom in all these complexes acquires a distorted square planar configuration defined by two cis-bound phosphine ligands and two chalcogenolate groups. The carborane rings are mutually anti in [Pt(SCb^oPh)₂(dppm)] and [Pt(SeCb^oPh)₂(dppm)].     

Synthesis and spectroscopy of cis-configured mononuclear palladium(II) and platinum(II) complexes of chalcogeno o-carboranes and structures of [Pt(SCboPh)2(dppm)], [Pt(SeCboPh)2(dppm)], [Pt(SCboS)(PMe2Ph)2] and [Pt(SCboS)(PMePh2)2]

The reactions of [MCl₂(P^∩P)] and [MCl₂(PR₃)₂)] with 1-mercapto-2-phenyl-o-carborane/NaSeCb^oPh and 1,2-dimercapto-o-carborane yield mononuclear complexes of composition, [M(SCb^oPh)₂(P^∩P)], [M(SeCb^oPh)₂(P^∩P)] (M = Pd or Pt; P^∩P = dppm (bis(diphenylphosphino)methane), dppe (1,2-bis(diphenylphosphino)ethane) or dppp (1,3-bis(diphenylphosphino)propane)) and [M(SCb^oS)(PR₃)₂] (2PR₃ = dppm, dppe, 2PEt₃, 2PMe₂Ph, 2PMePh₂ or 2PPh₃). These complexes have been characterized by elemental analysis and NMR (¹H, ³¹P, ⁷⁷Se and ¹⁹⁵Pt) spectroscopy. The ¹J(Pt–P) values and ¹⁹⁵Pt NMR chemical shifts are influenced by the nature of phosphine as well as thiolate ligand. Molecular structures of [Pt(SCb^oPh)₂(dppm)], [Pt(SeCb^oPh)₂(dppm)], [Pt(SCb^oS)(PMe₂Ph)₂] and [Pt(SCb^oS)(PMePh₂)₂] have been established by single crystal X-ray structural analyses. The platinum atom in all these complexes acquires a distorted square planar configuration defined by two cis-bound phosphine ligands and two chalcogenolate groups. The carborane rings are mutually anti in [Pt(SCb^oPh)₂(dppm)] and [Pt(SeCb^oPh)₂(dppm)].     

NMR studies of dynamic behavior of dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) and related complexes in solution

The ¹H, ³¹P and ¹³C NMR spectra of cis-dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) complexes were obtained in several solvents. These complexes have an octahedral configuration with trans tertiary phosphine ligands. The coordinated tertiary phosphine ligands are partly dissociated in solution. One of the phosphine ligands in CoR₂(acac)(PR₃′)₂ can be readily displaced with pyridine bases to give pyridine-coordinated complexes. From observation of the ¹H and ³¹P NMR spectra several kinetic and thermodynamic data for exchange reactions and displacement reactions of tertiary phosphines were obtained.     

Mononuclear palladacycles of N,N′-diaryl-2-iminoisoindolines

Reaction of acetato-bridged dinuclear palladacycles, [Pd(iminoisoindoline)(μ-OAc)]₂, with stoichiometric amounts of PR₃ (where R = Ph or Cy) resulted in formation of the corresponding mononuclear phosphine-ligated, six-membered palladacycles with the general formula [Pd(iminoisoindoline)(OAc)PR₃]. The analogous chloride complexes were synthesized by reaction of [Pd(iminoisoindoline)(μ-OAc)]₂ with LiCl in acetone followed by addition of phosphine to afford the monomeric derivatives [Pd(iminoisoindoline)(Cl)PR₃]. Representative crystal structures of both types of mononuclear palladacycles confirmed the mononuclear nature of the complexes and showed a trans-arrangement of the phosphine ligand to the heterocyclic imine-nitrogen of the palladacycles.     

Synthesis and asymmetric catalytic application of chiral imidazolium–phosphines derived from (1R,2R)-trans-diaminocyclohexane

Reaction between a chiral imidazole–amine precursor derived from (1R,2R)-trans-diaminocyclohexane and P¹Cl (where P¹ = PPh₂, P(1,3,5-Me₃C₆H₃)₂, P(2,2′-O,O′-(1,1′-biphenyl), P((R)-(2,2′-O,O′-(1,1′-binaphthyl))) and P((S)-(2,2′-O,O′-(1,1′-binaphthyl)))) followed by RX (where R = ⁿPr, ⁱPr, CHPh₂, X = Br; R = ⁱPr, X = I), respectively, gives a selection of chiral imidazolium–phosphine compounds. Deprotonation of the imidazolium salt gives the corresponding NHC–P ligands that can be used in metal-mediated asymmetric catalytic applications. Catalytic reactions show that NHC–P ligands give a significantly greater rate of reaction for a palladium catalysed allylic substitution reaction in comparison to analogous di-NHC or NHC–imine ligands and that NHC–P hybrids are also effective for iridium catalysed transfer hydrogenation.     

Expedient one-pot organometallics-free synthesis of tris(2-pyridyl)phosphine from 2-bromopyridine and elemental phosphorus

2-Bromopyridine reacts with elemental phosphorus (red or white) in a superbasic KOH/DMSO(H₂O) suspension at 100 °C (for red phosphorus) and 75 °C (for white phosphorus) over 3 h to afford tris(2-pyridyl)phosphine in a 62% yield (from red phosphorus) and a 50% yield (from white phosphorus). Under microwave assistance, the reaction with red phosphorus takes just 20 min to produce tris(2-pyridyl)phosphine in 53% yield. A hitherto unknown complex, [Pd(PPy₃)₂Cl₂]·CH₂Cl₂, synthesized from tris(2-pyridyl)phosphine and PdCl₂, has the cis-configuration; this is unusual for bis(phosphino)palladium dichloride complexes.     

Reactions of the unsaturated anion [Re3(μ-H)4(CO)10]− with phosphines. Synthesis of the anions [Re3(μ-H)2(CO)10(PR3)2]−, and crystal structure of [NEt4][Re3(μ-H)2(CO)10(PPh3)2]

The reaction of the unsaturated cluster anion [Re₃(μ-H)₄(CO)₁₀]⁻ with tertiary phosphines at room temperature results in the substitution of two hydride ligands (eliminated as H₂) by two PR₃ ligands, leading to saturated [Re₃(μ-H)₂(CO)₁₀-(PR₃)₂]⁻ compounds. A single crystal X-ray diffraction study of the PPh₃ derivative revealed that the two phosphines occupy non-equivalent equatorial coordination sites on the triangular cluster. The rate of the reaction greatly increases with increase of the basicity of the phosphine.     

Mixed-ligand complexes of copper(I) with diimines and phosphines: Effective catalysts for the coupling of phenylacetylene with halobenzene

New copper(I) mixed-ligand complexes 1–4 of the formula Cu(N–N)PR₃X, where N–N = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′dimbpy) and PR₃ = tricyclohexylphosphine, tris(2-cyanoethyl)phosphine and isopropyldiphenylphosphine, have been synthesized. The complexes were characterized by EA, IR, NMR and single crystal X-ray diffraction. The solution fluorescence emission spectra were measured. The single crystal X-ray analysis showed that the copper(I) ion is four-coordinate with a distorted tetrahedral geometry. The complexes catalyze the formation of diphenylacetylene from the coupling of halobenzene with phenylacetylene. The complex Cu(5,5′-dimethylbpy)P{(cyhexyl)₃}I showed the highest catalytic activity. At room temperature all four complexes exhibit, in dichloromethane, emission maxima in the 329–344 nm range, corresponding to intra-ligand excited states.     

NMR and theoretical study on interactions between diperoxovanadate complex and pyrazole-like ligands

To understand the effects of pyrazole substitution on reaction equilibrium, the interactions between a series of pyrazole-like ligands and [OV(O₂)₂(D₂O)]^?/[OV(O₂)₂(HOD)]^? were explored by using multinuclear (¹H, ¹³C, and ⁵¹V) magnetic resonance, HSQC, and variable temperature NMR in 0.15 mol/L NaCl ionic medium mimicking physiological conditions. These results show that the relative reactivities among the pyrazole-like ligands are 3-methyl-1H-pyrazole ≈ 4-methyl-1H-pyrazole ≈ 1H-pyrazole > 1-methyl-1H-pyrazole. As a result, the main factor which affects the reaction equilibrium is the steric effect instead of the electronic effect of the methyl group of these ligands. A pair of isomers has been formed resulting from the coordination of 3-methyl-1H-pyrazole and a vanadium complex, which is attributed to different types of coordination between the vanadium atom and the ligands. Thus, the competitive coordination leads to the formation of a series of six-coordinate peroxovanadate species [OV(O₂)₂L]^? (L, pyrazole-like ligands). Moreover, the results of density functional calculations provided a reasonable explanation on the relative reactivity of the pyrazole-like ligands as well as the important role of solvation in these reactions.     

Multinuclear NMR and theoretical investigation on interactions between diperoxovanadate complex and 4-picoline-like ligands

To understand the 4-substituting group effects of organic ligands in pyridine ring on the reaction equilibrium, the interactions between a series of 4-picoline-like ligands and [OV(O₂)₂(D₂O)]^?/[OV(O₂)₂(HOD)]^? in solution were explored by the combined use of multinuclear (¹H, ¹³C, and ⁵¹V) magnetic resonance, DOSY, and variable-temperature NMR in 0.15 mol/L NaCl ionic medium for mimicking the physiological condition. Some direct NMR data are given for the first time. The reactivity among the 4-picoline-like ligands is 4-picoline > isonicotinate > isonicotinamide > ethyl isonicotinate. The competitive coordination results in the formation of a series of new six-coordinated peroxovanadate species [OV(O₂)₂L]^n? (L = 4-picoline-like ligands, n = 1 or 2). The results of density functional calculations provide a reasonable explanation on the relative reactivity of the 4-picoline-like ligands. Solvation effects play an important role in these reactions.     

Density functional study of the complete pathway for the Heck reaction with palladium diphosphines

The reaction mechanism for the complete catalytic cycle of the Heck reaction (between phenyl bromide, C₆H₅Br, and ethylene, C₂H₄, in the presence of the base, NEt₃ to form the product styrene, C₆H₅–C₂H₃), catalyzed by diphosphinopalladium complexes, Pd(PR₃)₂ {R = H, Me, Ph}, was investigated by using density functional theory (DFT). The relative free energies of the fully-optimized species in gas phase at 298.15 K and 1 atm were corrected for solvation in DMSO at 1 mol/L by using conductor-like polarizable continuum model (CPCM). The calculations indicate a four-step mechanism for the catalysis, including oxidative addition of C₆H₅Br, migratory insertion of C₆H₅ to C₂H₄, β-hydride transfer/olefin elimination of product, and catalyst regeneration by removal of HBr. Our calculations demonstrate that Pd π-complexes can be formed with phenyl bromide and ethylene before the oxidative addition occurs. Subsequently, various reaction paths were studied for the oxidative addition of phenyl bromide to palladium complexes, coordinated by phosphine(s) and/or ethylene. Interestingly, all pathways lead to palladium monophosphine as the active catalyst. Careful exploration was made on two possible pathways for the migratory insertion and β-hydride-transfer/olefin elimination: (1) the neutral path with bromide bound to Pd and (2) the cationic path with prior bromide ion dissociation. The neutral path is preferred to the cationic path, especially when the more bulky phosphines such as triphenylphosphine are involved.     

Hydrocarbon (π- and σ-) complexes of nickel,palladium and platinum: Synthesis,reactivity and applications

With the exception of metallocenes, transition metal complexes with hydrocarbon ligands only are rare. However, complexes of this type containing Group 10 metals are known and have been shown to be quite stable. These complexes are versatile precursors for many organometallic compounds. In addition, such compounds can play an important role in many reactions including C–H or C–C activation reactions and have useful applications in the thermal and photochemical production of metal films by chemical vapour deposition (CVD). The present review summarizes the synthesis, properties and chemistry of hydrocarbon complexes of Group 10 metals of the type L_nM or L_nMR₁R₂ (where L_n = σ- or π-hydrocarbon ligands; M = Ni, Pd and Pt; R₁, R₂ = σ-hydrocarbon ligands) without the involvement of any hetero donor ligands such as N, P, O and S in the metal coordination spheres.     

Preparation of (2,2-difluoroethenylidene)bis(tributylstannane) and arylation reaction: efficient approach to 1,1-diaryl-2,2-difluoroethenes

Reaction of 2,2-difluoro-1-tributylstannylethenyl p-toluenesulfonate (1) with bis(tributyltin) in the presence of 5 mol % Pd(PPh₃)₄ and 30 equiv LiBr in THF at reflux temperature for 7 h afforded (2,2-difluoroethenylidene)bis(tributylstannane) (2) in a 70% yield. Coupling reaction of 2 with aryl iodides in the presence of 5 mol % Pd(PPh₃)₄ and 5 mol % CuI in DMF at 80 °C for 3–4 h provided the coupled products 3 in 59–85% yields.     

Solubility of novel open-chain crown ether bridged diphosphates in supercritical carbon dioxide

The solubility of newly synthesized chelating agents, i.e., tetraethylene glycol bis (2-ethylhexyl) dimethyl diphosphate (EG4EH), tetraethylene glycol bis (n-octyl) dimethyl diphosphate (EG4Oct), and tetraethylene glycol bis (2-butoxyethyl) dimethyl diphosphate (EG4BOE) in supercritical carbon dioxide (scCO₂) were determined at temperatures ranging from (318.15 to 333.15) K and pressures ranging from (12 to 21) MPa. Solubility increases in the order of EG4Oct (MW = 606.33) < EG4BOE (MW = 582.26) < EG4EH (MW = 606.33), indicating that branched side chains of the ligands play an important part in increasing solubility in scCO₂. Semi empirical density-based models proposed by Bartle and Chrastil were used to correlate the experimental data, and AARD values were calculated to be (1.2 to 2.9)% and (0.40 to 0.93)% for Bartle and Chrastil model, respectively. Additionally, the partial molar volumes of those compounds were estimated following the theory developed by Kumar and Johnston.     

Reactions of trans-[RuCl2(CO)2(PEt3)2] with 1,1-dithiolates: Stepwise formation of cis-[Ru(CO)(PEt3)(S2X)] (X = CNMe2, CNEt2, COEt,P(OEt)2, PPh2)

Trans-[RuCl₂(CO)₂(PEt₃)₂] reacts with two equivalents of a series of 1,1-dithiolate ligands to form the bis(dithiolate) complexes, cis-[Ru(CO)(PEt₃)(S₂X)₂] (X = CNMe₂, CNEt₂, COEt, P(OEt)₂, PPh₂). Two intermediates have been isolated; trans-[Ru(PEt₃)₂Cl(CO){S₂P(OEt)₂}] and trans-[Ru(PEt₃)₂(CO)(η¹-S₂COEt)(η²-S₂COEt)], allowing a simple reaction scheme to be postulated involving three steps; (i) initial replacement of cis carbonyl and chloride ligands, (ii) substitution of the second chloride, (iii) loss of a phosphine. Thermolysis of cis-[Ru(CO)(PEt₃)(S₂CNMe₂)₂] with Ru₃(CO)₁₂ in xylene affords trinuclear [Ru₃(μ₃-S)₂(PEt₃)(CO)₈] as a result of dithiocarbamate degradation. Crystal structures of cis-[Ru(CO)(PEt₃)(S₂X)₂] (X = NMe₂, COEt), trans-[Ru(PEt₃)₂Cl(CO){S₂P(OEt)₂}], trans-[Ru(PEt₃)₂(CO)(η¹-S₂COEt)(η²-S₂COEt)] and [Ru₃(μ₃-S)₂(PEt₃)(CO)₈] are reported.     

Kinetic resolution of P-stereogenic phosphine boranes via deprotonation using s-butyllithium/(−)-sparteine

The attempted kinetic resolution of racemic secondary phosphine boranes [t-BuPhP(BH₃)H and t-BuMeP(BH₃)H] by P–H deprotonation using 0.5 equiv of s-BuLi and (?)-sparteine was unsuccessful and generated racemic benzyl bromide-trapped adducts in 42–49% yield. In contrast, an efficient kinetic resolution was observed with racemic tertiary phosphine boranes [t-BuPhP(BH₃)Me and t-BuEtP(BH₃)Me] by C–H deprotonation on the P–Me group using 0.5 or 0.6 equiv of s-BuLi and (?)-sparteine. For example, the use of 0.6 equiv of s-BuLi/(?)-sparteine with t-BuEtP(BH₃)Me and trapping with DMF gave the (R)-aldehyde adduct in 37% yield and 83:17 er together with recovered (R)-t-BuEtP(BH₃)Me in 44% yield and 74:26 er. These are the first examples of kinetic resolution of P-stereogenic phosphine boranes via deprotonation using s-BuLi/(?)-sparteine.     

Versatile binding properties of di-pyridyl ligands with Cu(II) complexes: The syntheses,structural characterization and thermal analysis of six new species

A novel series of 4,4′-bipyridine- and 1,2-bis(4-pyridyl)ethane-Cu(II) complexes were synthesized using a variety of amine ligands (DPA = di(2-pyridylmethyl)amine, Medpt = 3,3′-diamino-N-methyldipropylamine, Hbpca = bis(2-pyridylcarbonyl)amine, TPA = tris(2-pyridylmethyl)amine) and cyclen = 1,4,7,10-tetraazacyclododecane). Different complexes were obtained including mononuclear [Cu(cyclen)(4,4′-bipy)](ClO₄)₂ (1), dinuclear {[Cu(μ₂-bpca)(4,4′-bipy)(H₂O)]ClO₄}₂ (2), [Cu₂(DPA)₂(μ₂-4,4′-bipy)(ClO₄)₄)]·H₂O (3), [Cu₂(cyclen)₂(μ₂-bpe)](ClO₄)₄ (4) and [Cu₂(TPA)₂(μ₂-bpe)](ClO₄)₄ (5) and the 1-D polymer, {[Cu(Medpt)(μ₂-4,4′-bipy)](ClO₄)₂}_n (6). In the 1–6 samples, cooling up to 100 K produces only the expected, minor, changes in cell constants given no space group changes. Therefore, data for the 100 K structures are reported only. Single-crystal X-ray crystallography reveals the monodentate coordination of the 4,4′-bipy in 1 and 2, and the bridged nature of the di-pyridyl ligands in the dinuclear complexes 2–5 and in the polymeric complex 6. In this series, structures 3–6 consist of the 4,4′-bipy or bpe bridging the two Cu(II) centers, the coordination by the tri- or the tetra-N donors of the amine, and the ClO₄^? groups as counter ions in 4–6 complexes. In the complexes 3–6, the Cu···Cu distances across the bridged di-pyridyl ligands were found to be greater than 11 Å. The magnetic properties of complex 3 reveal no evidence for magnetic coupling between the two Cu(II) centers (J = ?0.58 cm^?1).     

THEORETICAL INVESTIGATION OF KETENE BONDING MODES IN BIS(PHOSPHINE) PALLADIUM KETENE COMPLEXES

Abstract

Theoretical studies were carried out on a series of bis(phosphine) palladium ketene complexes (PR₃)₂Pd(CH₂=C=O), and on the related CH₂=C=O and Pd(PR₃)₂ molecular fragments in order to investigate the electronic structure and the bonding of the ketene ligand to the metal fragment in these complexes. An analysis of the frontier MOs has been performed in order to understand the interactions between the ketene and the metal fragments. The calculated results have shown that the η²-(C,C) mode is preferred over the η²-(C,O) mode by 10–15 kcal/mol in bis(phosphine) palladium ketene complexes. The basicity and bulkiness of the phosphine ligands PR₃ have little effect on the bonding mode in (PR₃)₂Pd(CH₂=C=O) complexes. The most stable structure was calculated to be the η²-(C,C) square planar geometry with the CH₂ group of ketene out of the molecular plane. Comparison and discussion between the two bonding modes were also presented in this paper.     

Synthesis,characterization, and catalytic activity of a ruthenium carbene complex coordinated with bidentate 2-pyridine-carboxylato ligands

The halide and phosphine free complex [(sIMes)(C₅H₄N-2-CO₂)₂RuCHPh] (7) (sIMes = 1,3-dimesitylimidazolidin-2-ylidene) bearing two bidentate 2-pyridinecarboxylato ligands was synthesized from the carbene complex [(sIMes)(PCy₃)(Cl)₂RuCHPh] (4) and the silver 2-pyridine-carboxylate (8). The molecular structure of the octahedral complex 7 reveals that the two carboxylato functions are coordinated in cis geometry to the ruthenium center. Catalyst 7 exhibits activity in ring-closing metathesis (RCM) reactions after addition of a cocatalyst (HCl) in dichloromethane as well as in methanol solution.