A Bis(thiophosphinoyl)methanediide Palladium Complex: Coordinated Dianion or Nucleophilic Carbene Complex?

A Silylene Stabilized by a σ‐Donating Nickel(0) Fragment

A donor‐stabilized silylene 4 featuring a Ni⁰‐based donating ligand was synthesized. Complex 4 exhibits a pyramidalized and nucleophilic Si^II center and shows a peculiar behavior due to the cooperative reactivity of Si and Ni centers. Calculations indicate that the orientation of Ni‐ligands with respect to the silylene moiety is crucial in determining the role of the Ni‐fragment (Lewis acid or Lewis base) towards silylene. Indeed, a simple 90° rotation of the Si−Ni bond, reverses the role of Ni, and transforms a classical silylene→Ni⁰ complex into an unprecedented Ni⁰→silylene complex.

Isolation and structure determination of a tetrameric sulfonyl dilithio methandiide in solution based on crystal structure analysis and 6Li/13C NMR spectroscopic data

Dilithio sulfonyl methandiides are a synthetically and structurally highly interesting group of functionalized geminal dianions. Although very desirable, knowledge of the structure of dilithio methandiides in solution was lacking up to now. Herein, we describe the isolation and determination of the structure of tetrameric dilithio (trimethylsilyl)(phenylsulfonyl) methandiide in solution and in the crystal. The elucidation of the structure of the tetramer is based on crystal structure analysis and ¹³C/⁶Li NMR spectroscopic data. A characteristic feature of the structure of the tetramer is the C₂ symmetric C–Li chain, composed of four doubly Li-coordinated dianionic carbon and five Li atoms. Three Li atoms are devoid of a contact to a dianionic C atom. The tetramer, the dianionic C atoms of which undergo fast exchange, is in THF solution in fast equilibrium with a further aggregate, which is stable only at low temperatures.

Geminal Dianions Stabilized by Main Group Elements

This review is dedicated to the chemistry of stable and isolable species that bear two lone pairs at the same C center, i.e., geminal dianions, stabilized by main group elements. Three cases can thus be considered: the geminal-dilithio derivative, for which the two substituents at C are neutral, the yldiide derivatives, for which one substituent is neutral while the other is charged, and finally the geminal bisylides, for which the two substituents are positively charged. In this review, the syntheses and electronic structures of the geminal dianions are presented, followed by the studies dedicated to their reactivity toward organic substrates and finally to their coordination chemistry and applications.

s-Block metal complexes of PC(H)P-bridged chalcogen-centred methanides: comparisons with isoelectronic PNP-bridged monoanions

This Perspective compares the chemistries of s-block metal complexes of isoelectronic PC(H)P- and PNP-bridged, chalcogen-centred monoanions with a focus on the unique behavior of the C(H)-bridged systems.

Cooperative bond activation reactions with carbene complexes

This review highlights the recent advances in the application of carbene complexes in bond activation reactions via metal–ligand cooperation.

Synthesis of a labile sulfur-centred ligand, [S(H)C(PPh2S)2](-): structural diversity in lithium(i), zinc(ii) and nickel(ii) complexes

A high-yield synthesis of [Li{S(H)C(PPh2S)2}]2 [Li2·(3)2] was developed and this reagent was used in metathesis with ZnCl2 and NiCl2 to produce homoleptic complexes 4 and 5b in 85 and 93% yields, respectively. The solid-state structure of the octahedral complex [Zn{S(H)C(PPh2S)2}2] (4) reveals notable inequivalence between the Zn-S(C) and Zn-S(P) contacts (2.274(1) Å vs. 2.842(1) and 2.884(1) Å, respectively). Two structural isomers of the homoleptic complex [Ni{S(H)C(PPh2S)2}2] were isolated after prolonged crystallization processes. The octahedral green Ni(ii) isomer 5a exhibits the two monoprotonated ligands bonded in a tridentate (S,S',S'') mode to the Ni(ii) centre with three distinctly different Ni-S bond lengths (2.3487(8), 2.4500(9) and 2.5953(10) Å). By contrast, in the red-brown square-planar complex 5b the two ligands are S,S'-chelated to Ni(ii) (d(Ni-S) = 2.165(2) and 2.195(2) Å) with one pendant PPh2S group. DFT calculations revealed that the energetic difference between singlet and triplet state octahedral and square-planar isomers of the Ni(ii) complex is essentially indistinguishable. Consistently, VT and (31)P CP/MAS NMR spectroscopic investigations indicated that a mixture of isomers exists in solution at room temperature, while the singlet state square-planar isomer 5b becomes favoured at -40 °C.

Heterobimetallic Pd-K carbene complexes via one-electron reductions of palladium radical carbenes

Heterobimetallic Pd-K carbenes featuring Pd-C_carbene-K moieties were synthesized via an unprecedented sequential substitution/reduction reaction from a radical precursor, [{PC˙(sp²)P} ^tBuPdI] ([PC(sp²)P] ^tBu = bis[2-(di-iso-propylphosphino)-4-tert-butylphenyl]methylene). Polymeric structures were observed in the solid state for the heterobimetallic compounds that can be interrupted in the presence of a donor solvent.

E–H (E = B, Si, Ge) bond activation of pinacolborane, silanes, and germanes by nucleophilic palladium carbene complexes

The polarity of the Pd–C bond can be tuned by the phosphine substituents of palladium carbene complexes as shown by the reactions of these compounds with silanes.

Redox-induced umpolung of transition metal carbenes

Metal carbene complexes have been at the forefront of organic and organometallic synthesis and are instrumental in guiding future sustainable chemistry efforts. While classical Fischer and Schrock type carbenes have been intensely studied, compounds that do not fall within one of these categories have attracted attention only recently. In addition, applications of carbene complexes rarely take advantage of redox processes, which could open up a new dimension for their use in practical processes. Herein, we report an umpolung of a nucleophilic palladium carbene complex, [{PC(sp²)P} ^tBuPd(PMe₃)] ({PC(sp²)P} ^tBu = bis[2-(di-iso-propylphosphino)-4-tert-butylphenyl]methylene), realized by successive one-electron oxidations that generated a cationic carbene complex, [{PC(sp²)P} ^tBuPdI]⁺, via a carbene radical, [{PC˙(sp²)P} ^tBuPdI]. An EPR spectroscopic study of [{PC˙(sp²)P} ^tBuPdI] indicated the presence of a ligand-centered radical, also supported by the results of reactions with 9,10-dihydroanthracene and PhSSPh. The cationic carbene complex shows electrophilic behavior toward nucleophiles such as NaH, ^p TolNHLi, PhONa, and PMe₃, resulting from an inversion of the electronic character of the Pd-C_carbene bond in [{PC(sp²)P} ^tBuPd(PMe₃)]. The redox induced umpolung is reversible and unprecedented.

Frustrated Lewis pair-like reactions of nucleophilic palladium carbenes with B(C6F5)3

Nucleophilic palladium carbenes react with the strong Lewis acid B(C₆F₅)₃via remote nucleophilic attack at the para-carbon of the supporting ligand or C–F activation of B(C₆F₅)₃; these reactions indicate frustrated Lewis pair-like behaviour given the steric inaccessibility of the nucleophilic carbene center.

Si–H activation by means of metal ligand cooperation in a methandiide derived carbene complex

Si–H bond activation of a series of silanes by means of metal ligand cooperation is reported.

Instability of metal 1,3-benzodi(thiophosphinoyl)methandiide complexes: formation of hafnium, tin and zirconium complexes of 1,3-benzodi(thiophosphinoyl)thioketone dianionic ligand [1,3-C6H4(PhPS)2CS]2−

The reaction illustrates that the metal centre and ligand substituents are crucial for the stabilization of a C_methandiideHf bond.

Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids

The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures.

A combined theoretical and experimental study for silver electroplating

A novel method combined theoretical and experimental study for environmental friendly silver electroplating was introduced. Quantum chemical calculations and molecular dynamic (MD) simulations were employed for predicting the behaviour and function of the complexing agents. Electronic properties, orbital information, and single point energies of the 5,5-dimethylhydantoin (DMH), nicotinic acid (NA), as well as their silver(I)-complexes were provided by quantum chemical calculations based on density functional theory (DFT). Adsorption behaviors of the agents on copper and silver surfaces were investigated using MD simulations. Basing on the data of quantum chemical calculations and MD simulations, we believed that DMH and NA could be the promising complexing agents for silver electroplating. The experimental results, including of electrochemical measurement and silver electroplating, further confirmed the above prediction. This efficient and versatile method thus opens a new window to study or design complexing agents for generalized metal electroplating and will vigorously promote the level of this research region.

Synthesis and bonding in carbene complexes of an unsymmetrical dilithio methandiide: a combined experimental and theoretical study

Herein, we report the preparation of a new unsymmetrical, bis(thiophosphinoyl)-substituted dilithio methandiide and its application for the synthesis of zirconium- and palladium-carbene complexes. These complexes were found to exhibit remarkably shielded (13)C NMR shifts, which are much more highfield-shifted than those of "normal" carbene complexes. DFT calculations were performed to determine the origin of these observations and to distinguish the electronic structure of these and related carbene complexes compared with the classical Fischer and Schrock-type complexes. Various methods show that these systems are best described as highly polarized Schrock-type complexes, in which the metal-carbon bond possesses more electrostatic contributions than in the prototype Schrock systems, or even as "masked" methandiides. As such, geminal dianions represent a kind of "extreme" Schrock-type ligands favoring the ionic resonance structure M(+)-CR2(-) as often used in textbooks to explain the nucleophilic nature of Schrock complexes.