Cobalt-catalyzed cross-electrophile coupling of alkynyl sulfides with unactivated chlorosilanes

Herein, we disclose a highly efficient cobalt-catalyzed cross-electrophile alkynylation of a broad range of unactivated chlorosilanes with alkynyl sulfides as a stable and practical alkynyl electrophiles. Strategically, employing easily synthesized alkynyl sulfides as alkynyl precursors allows access to various alkynylsilanes in good to excellent yields. Notably, this method avoids the utilization of strong bases, noble metal catalysts, high temperature and forcing reaction conditions, thus presenting apparent advantages, such as broad substrate scope (72 examples, up to 97% yield), high Csp-S chemo-selectivity and excellent functional group compatibility (Ar-X, X = Cl, Br, I, OTf, OTs). Moreover, the utilities of this method are also illustrated by downstream transformations and late-stage modification of structurally complex natural products and pharmaceuticals. Mechanistic studies elucidated that the cobalt catalyst initially reacted with alkynyl sulfides, and the activation of chlorosilanes occurred via an SN2 process instead of a radical pathway.

Nickel-Catalyzed Reductive [4 + 1] Sila-Cycloaddition of 1,3-Dienes with Dichlorosilanes

Transition-metal-catalyzed sila-cycloaddition has been a promising tool for accessing silacarbocycle derivatives, but the approach has been limited to a selection of well-defined sila-synthons. Herein, we demonstrate the potential of chlorosilanes, which are industrial feedstock chemicals, for this type of reaction under reductive nickel catalysis. This work extends the scope of reductive coupling from carbocycle to silacarbocycle synthesis and from single C-Si bond formation to sila-cycloaddition reactions. The reaction proceeds under mild conditions and shows good substrate scope and functionality tolerance, and it offers new access to silacyclopent-3-enes and spiro silacarbocycles. The optical properties of several spiro dithienosiloles as well as structural variations of the products are demonstrated.

Dipyrromethane‐Based PGeP Pincer Germyl Rhodium Complexes

A family of germyl rhodium complexes derived from the PGeP germylene 2,2’‐bis(di‐isopropylphosphanylmethyl)‐5,5’‐dimethyldipyrromethane‐1,1’‐diylgermanium(II), Ge(pyrmPⁱPr₂)₂CMe₂ (1), has been prepared. Germylene 1 reacted readily with [RhCl(PPh₃)₃] and [RhCl(cod)(PPh₃)] (cod=1,5‐cyclooctadiene) to give, in both cases, the PGeP‐pincer chloridogermyl rhodium(I) derivative [Rh{κ³P,Ge,P‐GeCl(pyrmPⁱPr₂)₂CMe₂}(PPh₃)] (2). Similarly, the reaction of 1 with [RhCl(cod)(MeCN)] afforded [Rh{κ³P,Ge,P‐GeCl(pyrmPⁱPr₂)₂CMe₂}(MeCN)] (3). The methoxidogermyl and methylgermyl rhodium(I) complexes [Rh{κ³P,Ge,P‐GeR(pyrmPⁱPr₂)₂CMe₂}(PPh₃)] (R=OMe, 4; Me, 5) were prepared by treating complex 2 with LiOMe and LiMe, respectively. Complex 5 readily reacted with CO to give the carbonyl rhodium(I) derivative [Rh{κ³P,Ge,P‐GeR(pyrmPⁱPr₂)₂CMe₂}(CO)] (6), with HCl, HSnPh₃ and Ph₂S₂ rendering the pentacoordinate methylgermyl rhodium(III) complexes [RhHX{κ³P,Ge,P‐GeMe(pyrmPⁱPr₂)₂CMe₂}] (X=Cl, 7; SnPh₃, 8) and [Rh(SPh)₂{κ³P,Ge,P‐GeMe(pyrmPⁱPr₂)₂CMe₂}] (9), respectively, and with H₂ to give the hexacoordinate derivative [RhH₂{κ³P,Ge,P‐GeMe(pyrmPⁱPr₂)₂CMe₂}(PPh₃)] (10). Complexes 3 and 5 are catalyst precursors for the hydroboration of styrene, 4‐vinyltoluene and 4‐vinylfluorobenzene with catecholborane under mild conditions.

Oxidative Addition of Silicon-Chloride Bonds to a Zerovalent Ruthenium Center and Direct Generation of an Ethylene Insertion Complex

The oxidative addition of a silicon-chloride (Si-Cl) bond to a metal center can be a key reaction step in coordinative silicon chemistry, but this reaction is seldom observed. Herein, we report direct oxidative addition of the Si-Cl bonds of dimethyldichlorosilane (Me₂SiCl₂) and cyclotrimethylenedichlorosilane [(CH₂)₃SiCl₂] to low-valent ruthenium complexes, yielding the 16e^- chloro(organosilyl)ruthenium complexes [N₃]Ru(Cl)(SiMe₂Cl) (4a) and [N₃]Ru(Cl)(SiCl(CH₂)₃) (4b) ([N₃] = 2,6-(MesN═CMe)₂C₅H₃N; Mes = 1,3,5-trimethylphenyl; Me = methyl). The reversible reaction of 4a with ethylene yields an 18e^- ethylene adduct, in which an ethylene is subsequently inserted into a ruthenium-silicon (Ru-Si) bond to produce the 16e^- complex [N₃]Ru(Cl)(CH₂CH₂SiMe₂Cl) (7). This study provides a good example of the direct generation of an ethylene insertion product, which is an important intermediate in the catalytic reduction of unsaturated molecules.

Nickel-Catalyzed Reductive C(sp2 )-Si Coupling of Chlorohydrosilanes via Si-Cl Cleavage

We report here a new method for the synthesis of organohydrosilanes from phenols and ketones. This method is established through reductive C-Si coupling of chlorohydrosilanes via unconventional Si-Cl cleavage. The reaction offers access to aryl- and alkenylhydrosilanes with a scope that is complementary to those of the established methods. Electron-rich, electron-poor, and ortho-/meta-/para-substituted (hetero)aryl electrophiles, as well as cyclic and acyclic alkenyl electrophiles, were coupled successfully. Functionalities, including Grignard-sensitive groups (e.g., primary amine, amide, phenol, ketone, ester, and free indole), acid-sensitive groups (e.g., ketal and THP protection), alkyl-Cl, pyridine, furan, thiophene, Ar-Bpin, and Ar-SiMe₃ , were tolerated. Gram-scale reaction, incorporation of -Si(H)R₂ into complex biologically active molecules, and derivatization of formed organohydrosilanes are demonstrated.

Nickel-Catalyzed Reductive Csp3-Ge Coupling of Alkyl Bromides with Chlorogermanes

Reductive cross-coupling provides facile access to organogermanes, but it remains largely unexplored. Herein we report a nickel-catalyzed reductive Csp³-Ge coupling of alkyl bromides with chlorogermanes. This work has established a new method for producing alkylgermanes. The reaction proceeds under very mild conditions and tolerates various functionalities including ether, alcohol, alkene, nitrile, amine, ester, phosphonates, amides, ketone, and aldehyde. The application of this method to the modification of bioactive molecules is demonstrated.

Nickel-Catalyzed Reductive C-Ge Coupling of Aryl/Alkenyl Electrophiles with Chlorogermanes

Cross-electrophile coupling has emerged as a promising tool for molecular synthesis; however, current studies have focused mainly on forging C-C bonds. We report a cross-electrophile C-Ge coupling reaction and thereby demonstrate the possibility of constructing organogermanes from carbon electrophiles and chlorogermanes. The reaction proceeds under mild conditions and offers access to both aryl and alkenyl germanes. Electron-rich, electron-poor, and ortho-/meta-/para-substituted (hetero)aryl electrophiles, as well as cyclic and acyclic alkenyl electrophiles, were coupled. Gram-scale reaction, incorporation of the -GeR₃ moiety into complex biologically active molecules, and derivatization of formed organogermanes are demonstrated.

Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear PtII →GeIV Complex

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph₂ P)C₆ H₄ )₂ Ge^IV Cl₂ ]Pt^II Cl₂ and [(o-(Ph₂ P)C₆ H₄ )₂ ClGe^III ]Pt^III Cl₃ , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph₂ P)C₆ H₄ )₂ ClGe^III ]Pt^I Cl with quantum yields of 1.7 % and 3.2 % for the Ge^IV -Pt^II and Ge^III -Pt^III isomers, respectively. Conversion of the Ge^IV -Pt^II isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Finally, transient-absorption-spectroscopy studies carried out on the Ge^III -Pt^III isomer point to a ligand arene-Cl^. charge-transfer complex as an intermediate.

Cross-Coupling of Heteroatomic Electrophiles

At the advent of cross-coupling chemistry, carbon electrophiles based on halides or pseudohalides were the only suitable electrophilic coupling partners. Almost two decades passed before the first cross-coupling reaction of heteroatom-based electrophiles was reported. Early work by Murai and Tanaka initiated investigations into silicon electrophiles. Narasaka and Johnson pioneered the way in the use of nitrogen electrophiles, while Suginome began the exploration of boron electrophiles. The chemistry reviewed within provides perspective on the use of heteroatomic electrophiles, specifically silicon-, nitrogen-, boron-, oxygen-, and phosphorus-based electrophiles in transition-metal catalyzed cross-coupling. For the purposes of this review, a loose definition of cross-coupling is utilized; all reactions minimally proceed via an oxidative addition event. Although not cross-coupling in a traditional sense, we have also included catalyzed reactions that join a heteroatomic electrophile with an in situ generated nucleophile. However, for brevity, those involving hydroamination or C-H activation as a key step are largely excluded. This work includes primary references published up to and including October 2018.

Germylene stabilized group 12 metal complexes and their reactivity with chalcogens

This manuscript reports the first examples of germylene stabilized cadmium complexes 3, 6, and 7, and novel germylene zinc complexes 2 and 5.

A dipyrromethane-based diphosphane–germylene as precursor to tetrahedral copper(i) and T-shaped silver(i) and gold(i) PGeP pincer complexes

A dipyrromethane-based PGeP germylene has allowed the synthesis of unusual tetrahedral copper(i) and T-shaped silver(i) and gold(i) germyl complexes.

Synthesis and initial transition metal chemistry of the first PGeP pincer-type germylene

The first PGeP pincer-type germylene has been synthesized. Its divalent Ge atom easily inserts into M–M and M–Cl bonds, giving rise to products that contain a PGeP bridging germylene or a PGeP pincer chlorogermyl ligand.