Ylide Ligand Research Articles

N-Oxide Coordination to Mn(III) Chloride.

We report on the synthesis and characterization of Mn(III) chloride (MnIIICl3) complexes coordinated with N-oxide ylide ligands, namely trimethyl-N-oxide (Me3NO) and pyridine-N-oxide (PyNO). The compounds are reactive and, while isolable in the solid-state at room temperature, readily decompose into Mn(II). For example, "[MnIIICl3(ONMe3)n]" decomposes into the 2D polymeric network compound complex salt [MnII(µ-Cl)3MnII(µ-ONMe3)]n[MnII(µ-Cl)3]n·(Me3NO·HCl)3n (4). The reaction of MnIIICl3 with PyNO forms varied Mn(III) compounds with PyNO coordination and these react with hexamethylbenzene (HMB) to form the chlorinated organic product 1-cloromethyl-2,3,4,5,6-pentamethylbenzene (8). In contrast to N-oxide coordination to Mn(III), the reaction between [MnIIICl3(OPPh3)2] and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) resulted in electron transfer-forming d5 manganate of the [TEMPO] cation instead of TEMPO-Mn(III) adducts. The reactivity affected by N-oxide coordination is discussed through comparisons with other L-MnIIICl3 complexes within the context of reduction potential.

Synthesis and Reactivity of Amino(Ylide)Stannylenes

AbstractThe synthesis of two stable monoylide‐substituted stannylenes of type YCNSnR [R=Cl (1) or N(SiMe3)2 (2), and YCN=Ph3P(CN)C] starting from the cyanido‐substituted α‐metallated ylide YCN–K and SnCl2 or (SiMe3)2NSnCl is reported. Coordination of the cyano group to the tin center results in the dimerization of both stannylenes 1 and 2 in the solid state as well as in solution, where syn‐ and anti‐isomers are present. X‐ray diffraction analyses in combination with DFT calculations revealed that the π‐electron density of the ylide ligand is predominantly shifted into the cyano moiety rather than towards the tin center. This results in a strong preference of the dimers over the monomers, which is further emphasized by the reaction with 2,5‐di‐tert‐butylhydroquinone, which undergoes a [1+4] addition to the tin center to yield a spiro compound while preserving the cyclic core of the dimer. In contrast, phenyl isocyanate and dicyclohexylcarbodiimide insert into the Sn−Cylide bond, ultimately leading to the cleavage of the dimer and the formation of monomeric stannylenes with an ylide‐substituted thioamidato and amidinato ligand, respectively.

Design and synthesis of versatile ligand precursors based on phosphonium ylides for palladalactam formation and catalytic investigation.

A new series of ligand precursors designed for the synthesis of palladalactams has been developed. These precursors are easily accessible through a one-step reaction involving 2-chloro-N-phenylacetamide and a wide choice of various monophosphines, offering tunable electronic and steric properties within the ligand framework. The stability of both ligand precursors and resulting palladalactams in ambient air enhances their practical applicability. A newly synthesized palladalactam, featuring an electron-donating triethylphosphine moiety on the anionic phosphonium ylide ligand scaffold exhibited promising catalytic activities in the Mizoroki-Heck coupling reaction between aryl chlorides and alkenes. Theoretical calculations further affirmed that the ligand system in the complex is the most electron-donating, forming the strongest Pd-C bond compared to other complexes with alternative phosphine moieties.

Exploring the Coordination Properties of Phosphonium‐Functionalized N‐Heterocyclic Carbenes Towards Gold

AbstractGold(I) complexes with N‐heterocyclic carbene ligands functionalized with a pendant phosphonium moiety were synthesized by simple procedures. In particular, the simple addition of LiBr salt in the reaction media allows the formation of the NHC gold(I) mononuclear complexes, whilst in the absence of excess bromide ions the deprotonation of the methylene group in alpha position to the phosphonium group occurs, allowing the isolation of the dinuclear complexes with two C,C‐bridging NHC‐phosphonium ylide ligands. The complexes were characterized in solution with NMR spectroscopy and ESI‐MS spectrometry, as well as in the solid state by means of single crystal X‐ray diffraction analysis. Mononuclear gold(III) species were also isolated by Br2 oxidative addition to the mononuclear gold(I) species and fully characterized. Preliminary results of the biological effects on MCF7 cancer cells are also reported.

Palladium(II) complexes with a chelating, monoanionic sulfur ylide

The insoluble, yellow dimeric palladium compound [PdI{κ2C-(CH2)2SO(Me)}]2 reacts with ammonia solutions to form the colourless ammine complex cis-[Pd(NH3)I{κ2C-(CH2)2SO(Me)}]. Although this material readily reconverts to the parent dimer, crystals for a structure determination could be obtained. The ammonia ligand in this compound can be displaced by Ph3P or it can function as a “built-in” base to deprotonate species with acidic protons. The latter reactivity has been observed with acylchalcogenoureas. Imidazolium salts however did not react with the ammine complex directly. They were accessible from the reaction of the parent dimer with the azolium salts in the presence of base. X-rax structures of several examples are reported and DFT calculations were used to elucidate the electronic structure of the ylide ligand and the bonding interactions with the palladium atom.

Thiophosphinoyl-Tethered Ylide-Substituted Heavier Carbenes: Synthesis, Structures and Stabilities.

The synthesis and structure analysis of a series of mono and diylide-substituted tetrylenes of type YEX and Y2 E (E=Ge, Sn, Pb; X=Cl or Br) using a thiophosphinoyl-tethered metallated ylide (Y=Ph2 P(S)-C-P(pip)Ph2 with pip=piperidyl) is reported, amongst the first ylide-substituted plumbylenes. The tetrylenes feature distinct trends in the spectroscopic and structural properties of the ylide ligand with increasing atomic number of the tetrel element. For instance, an increasingly high-field shifted signal for the thiophosphinoyl group is observed in the 31 P{1 H} NMR spectrum as a consequence of the increasing polarity of the element-carbon bond, which likewise results in a shortening of the ylidic C-P bond in the solid-state structure. The diylidyltetrylenes are unstable towards transylidation forming the mono(ylide)tetrylenes when treated with the tetrel dihalides according to the stability trend: Y2 Pb<Y2 Sn<Y2 Ge<YPbBr<YSnCl<YGeCl. Starting from the monoylide-substituted chlorotertrylenes the first unsymmetrical diylidyltetrylenes of type YEY' can be accessed, whose solid-state structures revealed that not the C-E but the S-E bond to the thiophosphinoyl group is most affected by the second ylide substituent.

Phosphonium Ylides vs Iminophosphoranes: The Role of the Coordinating Ylidic Atom in cis-[Phosphine-Ylide Rh(CO)2] Complexes.

The coordinating properties of two families of ylides, namely, phosphonium ylides and iminophosphoranes, differently substituted at the ylidic center (CH2- vs NiPr-), have been investigated in structurally related cationic phosphine-ylide Rh(CO)2 complexes obtained from readily available phosphine-phosphonium salt precursors derived from an ortho-phenylene bridge. However, while the Rh(CO)2 complex bearing the P+-CH2- donor moiety proved to be stable, the P═NiPr donor end appeared to induce lability to one of the CO groups. All of the RhI carbonyl complexes in both ylide series were fully characterized, including through X-ray diffraction analysis. Based on the experimental and calculated infrared (IR) CO stretching frequencies in Rh(CO)2 complexes, we evidenced that the phosphonium ylide ligand is a stronger donor than the iminophosphorane ligand. However, we also found that the difference in the intrinsic electronic properties can be largely compensated by the introduction of an iPr substituent on the N atom of the iminophosphorane, hence pointing to the noninnocent role of the peripheral substituent and opening novel possibilities to tune the properties of metal complexes containing ylide ligands.

Single-Site and Cooperative Bond Activation Reactions with Ylide-Functionalized Tetrylenes: A Computational Study.

Due to their transition metal‐like behavior divalent group 14 compounds bear huge potential for their application in bond activation reactions and catalysis. Here we report on detailed computational studies on the use of ylide‐substituted tetrylenes in the activation of dihydrogen and phenol. A series of acyclic and cyclic ylidyltetrylenes featuring various α‐substituents with different σ‐ and π‐donating capabilities have been investigated which demonstrate that particularly π‐accepting boryl groups lead to beneficial properties and low barriers for single‐site activation reactions, above all in the case of silylenes. In contrast, for the thermodynamically more stable germylenes and stannylenes an alternative mechanism involving the active participation of the ylide ligand in the E−H bond (E=H or PhO) activation process by addition across the element carbon linkage was found to be energetically favored. Furthermore, the boryl substituted tetrylenes allowed for a further activation pathway involving the active participation of the boron element bond. These cooperative mechanisms are especially attractive for the heavier cyclic ylidyltetrylenes in which the loss of the protonated ylide group is prevented due to the cyclic framework. Overall, the present studies suggest that cyclic ylide‐substituted germylenes and stannylenes bear huge potential for cooperative bond activations at mild conditions which should be experimentally addressed in the future.

Umicore acquires phosphine-bearing ylide ligands from Ruhr University Bochum

Sound transmission characteristics of panels have been extensively examined which is often quantified by transmission loss. Although acoustic materials are usually applied to passive noise solutions. In the present paper, the influence of sound-absorbing materials on the transmission loss of double-walled panels has been studied theoretically. An analytical method based on statistical energy analysis technique (SEA) is employed for predicting the transmission loss of double-wall steel and aluminum panels. Three commercially available acoustic materials, ie., polyurethane, glass wool, and melamine foam are chosen for investigation.

From carbones to carbenes and ylides in the coordination sphere of iridium.

The carbodiphosphorane-based iridium pincer complex (2) is demonstrated to rearrange in chlorinated organic solvents under cleavage of a P-C-bond to give a chelating phosphine ylide ligand. A detailed mechanistic investigation reveals that these types of donor groups are prone for P-C-bond cleavage in the coordination sphere of transition metal hydrido complexes. Finally, complex 2 is demonstrated to be an efficient hydrogen-borrowing catalyst.

Carbenes and phosphonium ylides: a fruitful association in coordination chemistry.

Among a plethora of σ-donor ligands available, carbon-centered ones have become essential, in particular with the emergence of N-heterocyclic carbenes (NHCs), positioning themselves as credible alternatives to traditional nitrogen- and phosphorus-based systems. Phosphonium ylides representing another class of neutral η1-bonded carbon ligands have also been shown to act as effective Lewis bases. Considering the intrinsic features of the carbene and phosphonium ylide ligands, similar in terms of electronic properties, but different in terms of bonding mode, the design of hybrid systems combining these two types of carbon functionalities appeared to be a natural and exciting challenge. This Perspective comprehensively covers the chemistry of such ligand architectures from synthesis and fundamental aspects to catalytic applications.

Synthesis, structure, magnetic property and selective dye absorption of a coordination polymer with intrinsic positive charged sites

A coordination polymer based on Co(II) cations and ylide ligands, i.e. CoL2 (H2L·Br = 3,5-dicarboxy-1-(naphthalen-2-ylmethyl) pyridin-1-ium bromide), has been synthesized by one-step method and characterized by powder X-ray diffractions (PXRD), single-crystal X-ray diffractions and thermogravimetric analyses (TGA). This complex possesses intrinsic positive charged sites distributed in its skeleton, and could selectively adsorb negative charged organic dyes rather than cationic organic dyes. Additionally, the magnetic property for CoL2 is also investigated.

Controlling the Thermal Stability and Volatility of Organogold(I) Compounds for Vapor Deposition with Complementary Ligand Design

Atomic layer deposition (ALD) of gold is being studied by multiple research groups, but to date no process using non‐energetic co‐reactants has been demonstrated. In order to access milder co‐reactants, precursors with higher thermal stability are required. We set out to uncover how structure and bonding affect the stability and volatility of a family of twelve organogold(I) compounds using a combination of techniques: X‐ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and density functional theory (DFT). Small, unsubstituted phosphonium ylide ligands bind more strongly to Au(I) than their silyl‐substituted analogues, but the utility of both these ligands suffers due to their poor volatility and substantial thermal decomposition. Pentafluorophenyl (C6F5) is introduced as a new, very electronegative ligand for gold vapor deposition precursors, and it was found that the disadvantage to volatility due to π‐stacking and other intermolecular interactions in the solid state was overshadowed by dramatic improvements to kinetic and thermodynamic stability. We introduce a new figure of merit to compare and rank the suitability of these and other complexes as precursors for vapor deposition. Finally, DFT calculations on four compounds that have high figures of merit show a linear correlation between the gold‐coordinative ligand bond dissociation energies and the observed decomposition temperatures, highlighting and justifying this design strategy.

From Ylides to Doubly Yldiide-Bridged Iron(II) High Spin Dimers via Self-Protolysis.

A synthetic strategy for the preparation of novel doubly yldiide bridged iron(II) high spin dimers ([(μ2-C)FeL]2, L = N(SiMe3)2, Mesityl) has been developed. This includes the synthesis of ylide-iron(II) monomers [(Ylide)FeL2] via adduct formation. Subsequent self-protolysis at elevated temperatures by in situ deprotonation of the ylide ligands results in a dimerization reaction forming the desired bridging μ2-C yldiide ligands in [(μ2-C)FeL]2. The comprehensive structural and electronic analysis of dimers [(μ2-C)FeL]2, including NMR, Mössbauer, and X-ray spectroscopy, as well as X-ray crystallography, SQUID, and DFT calculations, confirm their high-spin FeII configurations. Interestingly, the Fe2C2 cores display very acute Fe–C–Fe angles (averaged: 78.6(2)°) resulting in short Fe···Fe distances (averaged: 2.588(2) Å). A remarkably strong antiferromagnetic coupling between the Fe centers has been identified. Strongly polarized Fe–C bonds are observed where the negative charge is mostly centered at the μ2-C yldiide ligands.

Synthesis, characterization, theoretical and cytotoxicity studies of Pd(II) and Pt(II) complexes with new bidentate carbon donor ligand

The new phosphonium salt, the C,C-chelating phosphorus ylide ligand, (MeOC6H5C(O)CHPPh2(CH2)2PPh2CHC(O)C6H5OMe), and its Pd(II) and Pt(II) complexes have been synthesized and the cytotoxic activity of the synthesized complexes against three human cancer cell lines, including HeLa (Human cervix cancer cell line), KB (human oral cancer cell line) and U87 MG (human glioblastoma cell line) were evaluated using an MTT assay. The new compounds were identified and characterized using multinuclear (1H, 13C and 31P) NMR, infrared (IR) spectroscopy, elemental analysis, and through UV absorption and fluorescence emission spectra. Also, the crystal structure of the phosphorus ylide ligand was determined by single-crystal X-ray diffraction analysis. According to the obtained results from the MTT assay, the Pd(II) and Pt(II) complexes demonstrated a higher cytotoxic activity against KB human oral cancer cells in comparison with other cell lines, rendering these compounds into suitable candidates for further anti-oral cancer studies. Furthermore, a theoretical study on structure and nature of the MC bonding between the Y ligand (ylide) and MCl2 fragment in the [YMCl2] (M = Pd, Pt and Y = (MeOC6H5C(O)CHPPh2(CH2)2PPh2CHC(O)C6H5OMe)) complexes have been reported via NBO and energy-decomposition analysis (EDA).

Crystal structures of the [IrIII{C(C4H6O2)(dppm)-κ3 P,C,O}(dppm)H](CF3O3S)2 and [IrIII{C(C4H6O2)(dppm)-κ2 P,C}(CO)(dppm)H](CF3O3S)2 phosphorus ylide complexes, generated by a Wittig-type carbon-carbon coupling reaction of a carbodiphospho-rane PCP ligand system.

The reaction of [IrIII{C(dppm)2-κ3 P,C,P'}ClH(NH3C2)]Cl with ethyl diazo-acetate, a well known C=C coupling reagent, leads to the formation of a C=C unit, accompanied by N2 abstraction, reorganization of a dppm subunit and, considered as a whole, to the transformation of the PCP pincer carbodi-phospho-rane system to a phospho-rus ylide ligand. After removal of the halogenides, the iridium center is stabilized by the carbonyl O atom through the formation of a five-membered chelate ring. A PCO pincer ligand system is thereby generated, which coordinates the iridium(III) atom threefold in a facial manner. The phospho-rus electron-donor atoms and the ylide carbon atom of the resulting [IrIII{C(C4H6O2)(dppm)-κ3 P,C,O}(dppm)H](CF3O3S)2 complex, also termed as [bis-(di-phenyl-phosphan-yl)methane]({[(di-phenyl-phosphan-yl)meth-yl]di-phenyl-phosphanyl-idene}(eth-oxy-oxoethanyl-idene)methanyl-idene-κ3 P,C,O)hydridoiridium(III) bis-(tri-fluoro-methane-sulfonate), are in plane and the hydrido ligand and the carbonyl O atom are located trans to each other, perpendicular to the meridional plane. The addition of carbon monoxide causes a replacement of the carbonyl O atom of the acetate subunit by a carbonyl ligand, thereby creating [bis-(di-phenyl-phosphan-yl)methane]-carbon-yl({[(di-phenyl-phosphan-yl)meth-yl]di-phenyl-phosphanyl-idene}(eth-oxy-oxoethanyl-idene)methanyl-idene-κ2 P,C}hydridoiridium(III) bis-(tri-fluoro-methane-sulfonate)-di-chloro-methane-ethyl acetate (6/2/3) or, more simply, [IrIII{C(C4H6O2)(dppm)-κ2 P,C}(CO)(dppm)H](CF3O3S)2·0.33CH2Cl2·0.5C4H8O2. One tri-fluoro-meth-ane-sulfonate counter-ion of 3 shows positional disorder in a 2:1 ratio. Complex 4 shows pseudo-merohedral twinning (matrix: 0 0 0 0 1 0 1). The di-chloro-methane solvent is disordered over two orientations with occupation factors of 0.5 and 0.166.

A comparison of donor–acceptor interactions of N-heterocyclic carbenes and sulfonium ylides in coordination with coinage metal ions

This study seeks to characterize the structure and nature of metal–ligand bonds in sulfonium ylide complexes [{S(R)2CHCOC10H7}2 → M]+ and N-heterocyclic carbene complexes [{NHC(R)2}2 → M]+ {M = Cu(I), Ag (I), Au(I) and R = F, Cl, Br, H, Me, Si(CH3)3} at PBE/def2-SVP level of theory which is nominated among eight scrutinized DFT methods. Compared to sulfonium ylides, NHC(R)’s form stronger bonds with coinage metal ions not only in the presence of electron-donating substituents (R = H, Me, Si(CH3)3) but also in the presence of electron-withdrawing substituents (R = F, Cl, Br). Besides, the nature of C → M bonds in the complexes is analyzed through the charge and energy decomposition analysis EDA-NOCV. In both studied complexes, the electrostatic nature of C → M bond is a dominant term in the interaction energy. The comparison of EDA-NOCV results for C → M bonds in both [{S(R)2CHCOC10H7}2 → M]+ and [{NHC(R)2}2 → M]+ complexes indicates that sulfonium ylide ligands S(R)2CHCOC10H7 are slightly better σ-donors and weaker π-acceptors than their corresponding NHC(R) ligands.

Ylide Ligands as Building Blocks for Bioactive Group 11 Metal Complexes.

The reactivity of the phosphonium salt (cyanomethyl)triphenylphosphonium chloride and the ylide (triphenylphosphonio)cyanomethanide towards Group 11 metal complexes is described. Mononuclear neutral gold(I) and gold(III) complexes of the type [AuX{CH(CN)PPh3 }] or [AuX3 {CH(CN)PPh3 }] and cationic derivatives such as [AuL{CH(CN)PPh3 }]X have been prepared. Surprisingly, the cationic gold species could only be prepared with ligands with a large steric hindrance, such as bulky NHCs or the JohnPhos phosphine, in contrast to silver and copper derivatives, which have dimeric structures through the coordination of the metal to the cyano group of the ylide of a second complex. Bis(ylide) metal complexes have also been synthesised in which a different structure is observed for the gold complexes compared with the copper and silver complexes. Although gold forms mononuclear species, the silver complex presents a two-dimensional polymeric structure as a result of further coordination of the silver centre to the nitrogen atoms of cyano groups of further silver complexes. These complexes possess two chiral centres; the gold compound was obtained as a mixture of diastereoisomers, whereas the copper and silver derivatives afford only one diastereoisomer. These compounds were screened for their in vitro cytotoxic activity against the human lung carcinoma cell line (A549). The IC50 values reveal an excellent cytotoxic activity for these metal complexes compared with cisplatin.

Synthesis and reactivity of [M(η3-allyl)(η2-amidinato)(CO)2(phosphonium ylide)] (M = Mo, W): Investigation of the ligand properties of phosphonium ylides

Abstract Phosphonium ylide complexes of Mo and W formulated as [M(η3-allyl){η2-(NPh)2CH}(CO)2(CH2PR3)] (M = Mo, R = Me: 2a-Mo; M = Mo, R = Ph: 2b-Mo, and M = W, R = Me: 2a-W) were prepared by the reaction of amidinato(pyridine) complex, [M(η3-allyl){η2-(NPh)2CH}(CO)2(NC5H5)] (M = Mo: 1-Mo and M = W: 1-W), with a phosphonium ylide, CH2PR3 (R = Me, Ph), which was generated in situ by the reaction of the corresponding phosphonium salt with nBuLi. These complexes were characterized spectroscopically, as well as by the X-ray diffraction. The phosphonium ylide ligand shows stronger electron donating ability toward the metal than N-heterocyclic carbene or phosphine ligands. This trend is supported by the comparison of the spectroscopic data and the DFT calculations. We also investigated the reactivity of the phosphonium ylide complexes 2-Mo with two-electron donors such as PEt3 and NHC. In the case of the PPh3 ylide complex (2b-Mo), the substitution reaction of the ylide ligand for the two-electron donors took place cleanly to yield the corresponding complexes. On the other hand, in the PMe3 ylide complex (2a-Mo), the substituted complexes formed but the unreacted ylide complex 2a-Mo was also present in the reaction mixture. These results show that the bond strength of the M-C(phosphonium ylide) bond is affected by the substituents on the phosphorus atom.

Using Ylide Functionalization to Stabilize Boron Cations

AbstractThe metalated ylide YNa [Y=(Ph3PCSO2Tol)−] was employed as X,L‐donor ligand for the preparation of a series of boron cations. Treatment of the bis‐ylide functionalized borane Y2BH with different trityl salts or B(C6F5)3 for hydride abstraction readily results in the formation of the bis‐ylide functionalized boron cation [Y−B−Y]+ (2). The high donor capacity of the ylide ligands allowed the isolation of the cationic species and its characterization in solution as well as in solid state. DFT calculations demonstrate that the cation is efficiently stabilized through electrostatic effects as well as π‐donation from the ylide ligands, which results in its high stability. Despite the high stability of 2 [Y−B−Y]+ serves as viable source for the preparation of further borenium cations of type Y2B+←LB by addition of Lewis bases such as amines and amides. Primary and secondary amines react to tris(amino)boranes via N−H activation across the B−C bond.