Synthesis and Electronic Structure of Carbene Complexes Based on a Sulfonyl-Substituted Dilithio Methandiide

The application of a sulfonyl-substituted dilithio methandiide in the synthesis of carbene complexes was examined. In all cases, the metal carbon interaction was found to be highly polar with only small π-contribution. Hence, the stability of these complexes was found to greatly rely on the coordination ability of the side-arms supporting the metal carbon interaction. As such, the sulfonyl moiety allowed the isolation of a carbene complex with the oxophilic zirconium, which is the first of its kind bearing no (bis)­phosphonium ligand framework. On the contrary, complexes with the late transition metals ruthenium and palladium were found to be more labile due to the facile decoordination of the sulfonyl moiety. This results in the opening of a reactive coordination site at the metal center and hence in further reactions such as cyclometalation or sulfur transfer from the thiophosphoryl moiety to the carbenic carbon atom

Selective Dehydrocoupling of Phosphines by Lithium Chloride Carbenoids

The development of a simple, transition-metal-free approach for the formation of phosphorus–phosphorus bonds through dehydrocoupling of phosphines is presented. The reaction is mediated by electronically stabilized lithium chloride carbenoids and affords a variety of different diphosphines under mild reaction conditions. The developed protocol is simple and highly efficient and allows the isolation of novel functionalized diphosphines in high yields

Structure, Bonding, and Reactivity of Room-Temperature-Stable Lithium Chloride Carbenoids

Electronic stabilization of the negative charge by a thiophosphinoyl and pyridyl/quinolyl substituent allows for the isolation of two lithium chloride carbenoids at room temperature. Molecular structure analysis by X-ray crystallography and multinuclear NMR spectroscopy reveal no direct lithium–carbon interaction in the solid state and in solution. This leads to remarkable thermal stability but also to a reduced ambiphilic character of the compounds. Thus, properties typically observed for nonstabilized Li/Cl carbenoids are less pronounced. Nevertheless, computational studies still show that despite the charge delocalization within the compound a high negative charge remains at the carbenoid carbon atom. Preliminary reactivity studies confirm this nucleophilic character and show that the carbenoids can still be used as a “carbene” source for the formation of carbene complexes

Structure, Bonding, and Reactivity of Room-Temperature-Stable Lithium Chloride Carbenoids

Electronic stabilization of the negative charge by a thiophosphinoyl and pyridyl/quinolyl substituent allows for the isolation of two lithium chloride carbenoids at room temperature. Molecular structure analysis by X-ray crystallography and multinuclear NMR spectroscopy reveal no direct lithium–carbon interaction in the solid state and in solution. This leads to remarkable thermal stability but also to a reduced ambiphilic character of the compounds. Thus, properties typically observed for nonstabilized Li/Cl carbenoids are less pronounced. Nevertheless, computational studies still show that despite the charge delocalization within the compound a high negative charge remains at the carbenoid carbon atom. Preliminary reactivity studies confirm this nucleophilic character and show that the carbenoids can still be used as a “carbene” source for the formation of carbene complexes

Structure, Bonding, and Reactivity of Room-Temperature-Stable Lithium Chloride Carbenoids

Electronic stabilization of the negative charge by a thiophosphinoyl and pyridyl/quinolyl substituent allows for the isolation of two lithium chloride carbenoids at room temperature. Molecular structure analysis by X-ray crystallography and multinuclear NMR spectroscopy reveal no direct lithium–carbon interaction in the solid state and in solution. This leads to remarkable thermal stability but also to a reduced ambiphilic character of the compounds. Thus, properties typically observed for nonstabilized Li/Cl carbenoids are less pronounced. Nevertheless, computational studies still show that despite the charge delocalization within the compound a high negative charge remains at the carbenoid carbon atom. Preliminary reactivity studies confirm this nucleophilic character and show that the carbenoids can still be used as a “carbene” source for the formation of carbene complexes

Structure, Bonding, and Reactivity of Room-Temperature-Stable Lithium Chloride Carbenoids

Electronic stabilization of the negative charge by a thiophosphinoyl and pyridyl/quinolyl substituent allows for the isolation of two lithium chloride carbenoids at room temperature. Molecular structure analysis by X-ray crystallography and multinuclear NMR spectroscopy reveal no direct lithium–carbon interaction in the solid state and in solution. This leads to remarkable thermal stability but also to a reduced ambiphilic character of the compounds. Thus, properties typically observed for nonstabilized Li/Cl carbenoids are less pronounced. Nevertheless, computational studies still show that despite the charge delocalization within the compound a high negative charge remains at the carbenoid carbon atom. Preliminary reactivity studies confirm this nucleophilic character and show that the carbenoids can still be used as a “carbene” source for the formation of carbene complexes

Structure, Bonding, and Reactivity of Room-Temperature-Stable Lithium Chloride Carbenoids

Electronic stabilization of the negative charge by a thiophosphinoyl and pyridyl/quinolyl substituent allows for the isolation of two lithium chloride carbenoids at room temperature. Molecular structure analysis by X-ray crystallography and multinuclear NMR spectroscopy reveal no direct lithium–carbon interaction in the solid state and in solution. This leads to remarkable thermal stability but also to a reduced ambiphilic character of the compounds. Thus, properties typically observed for nonstabilized Li/Cl carbenoids are less pronounced. Nevertheless, computational studies still show that despite the charge delocalization within the compound a high negative charge remains at the carbenoid carbon atom. Preliminary reactivity studies confirm this nucleophilic character and show that the carbenoids can still be used as a “carbene” source for the formation of carbene complexes

Mono- and Bis-Cyclometalated Palladium Complexes: Synthesis, Characterization, and Catalytic Activity

Cyclometalated palladium complexes have found a variety of applications, above all in homogeneous catalysis. Most complexes include mono-cyclometalated ligands, particularly systems with P- or N-donors. Herein, we report the preparation of a series of mono- and bis-cyclometalated palladium complexes with a silyl-substituted thiophosphinoyl ligand. The complexes have been synthesized via oxidative addition and dehydrohalogenation reactions. Thereby, dehydrohalogenation selectively results in the second cyclometalation and not in the formation of a carbene species. In the formed square-planar palladacycles the ligands exhibit <i>S,C</i>- and <i>S,C,C-</i>coordination modes, respectively. Depending on the silyl moiety, cyclometalation occurs via an aryl or even a methyl group, thus also giving way to unusual silapalladacyclobutanes with an open-book geometry. The complexes have been characterized in solution as well as in the solid state. Preliminary catalytic studies show that both the mono- and bis-cyclometalated complexes can be applied as catalysts in C–C coupling reactions

Cooperative Bond Activation Reactions with Ruthenium Carbene Complex PhSO₂(Ph₂PNSiMe₃)CRu(<i>p</i>‑cymene): RuC and N–Si Bond Reactivity

The synthesis of ruthenium carbene complex PhSO₂(Ph₂PNSiMe₃)­CRu­(<i>p</i>-cymene) (<b>3</b>) and its application in cooperative bond activation reactions were studied. Compound <b>3</b> is accessible via salt metathesis using the dilithium methandiide ligand or alternatively via dehydrohalogenation of the corresponding chlorido complex <b>2</b>. The carbene complex was studied by X-ray crystallography, multielement NMR spectroscopy, and DFT studies, all of which confirm the presence of a RuC double bond. The polarization of the RuC bond is less pronounced than in an analogous carbene complex with a thiophosphoryl instead of the iminophosphoryl moiety. This should be beneficial for realizing reversible activation processes by the addition of element-hydrogen bonds across the RuC double bond. Accordingly, <b>3</b> is more stable and the RuC linkage less reactive in the activation of aromatic alcohols and elemental dihydrogen, showing reversible processes and longer reaction times. Despite the selective addition of dihydrogen across the Ru–C bond, the activation of O–H bonds was accompanied by hydrolysis of the N–Si linkage. The reaction of <b>3</b> with water led to the hydrolysis of the N–Si bond as well as protonative cleavage of the central P–C bond in the ligand backbone, thus resulting in the formation of an unusual dinuclear ruthenium–imido complex

Cooperative P–H Bond Activation with Ruthenium and Iridium Carbene Complexes

The reactivity of nucleophilic ruthenium and iridium carbene complexes toward the P–H bond in secondary phosphines and phosphine oxides was studied. While the reactions of the free phosphines resulted in the formation of product mixtures, the oxidized congeners gave way to fast and selective P–H bond activation reactions by means of metal–ligand cooperation and net addition of the P–H bond across the metal–carbon double bond. The formed phosphoryl complexes were characterized in the solid state and in solution, indicating C–H···O hydrogen bonding as a structural motif. Computational studies to provide insights into the reaction mechanism revealed thatin contrast to other E–H bond activation reactions with carbene complexesno concerted 1,2-addition across the MC bond is operative. Instead, the P–H bond activation of the phosphine oxides preferably proceeds via coordination of the phosphinous acid tautomer to the metal, followed by hydrogen transfer to the carbenic carbon atom