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1. Ligand-enforced intimacy between a gold cation and a carbenium ion: impact on stability and reactivity

   https://doi.org/10.1039/D0SC05777K  

   Litle, Elishua D.; Wilkins, Lewis C.; Gabbaï, François P. (March 2021, Chemical Science)

   null (Ed.)

   Controlling the reactivity of transition metal complexes by positioning non-innocent functionalities around the catalytic pocket is a concept that has led to significant advances in catalysis. Here we describe our efforts toward the synthesis of dicationic phosphine gold complexes of general formula [( o -Ph 2 P(C 6 H 4 )Carb)Au(tht)] 2+ decorated by a carbenium moiety (Carb) positioned in the immediate vicinity of the gold center. While the most acidic examples of such compounds have limited stability, the dicationic complexes with Carb + = 9- N -methylacridinium and Carb + = [C(Ar N ) 2 ] + (Ar N = p -(C 6 H 4 )NMe 2 ) are active as catalysts for the cycloisomerization of N -propargyl-4-fluorobenzamide, a substrate chosen to benchmark reactivity. The dicationic complex [( o -Ph 2 P(C 6 H 4 )C(Ar N ) 2 )Au(tht)] 2+ , which also promotes hydroarylation and enyne cyclization reactions, displays a higher catalytic activity than its acridinium analog, indicating that the electrophilic reactivity of these complexes scales with the Lewis acidity of the carbenium moiety. These results support the role of the carbenium unit as a non-innocent functionality which can readily enhance the activity of the adjacent metal center. Finally, we also describe our efforts toward the generation and isolation of free γ-cationic phosphines of general formula [( o -Ph 2 P(C 6 H 4 )Carb)] + . While cyclization into phosphonium species is observed for Carb + = [C(Ar N ) 2 ] + , [C(Ph)(Ar N )] + , and 9-xanthylium, [( o -Ph 2 P(C 6 H 4 )-9- N -methylacridinium)] + can be isolated as an air stable, biphilic derivative with uncompromised Lewis acidic and basic properties. 

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2. Cationic Complexes with Au→Ge Bonds – Synthesis and Carbophilic Reactivity

   https://doi.org/10.1002/ijch.202200036  

   Karimi, Mohammadjavad; Litle, Elishua; Gabbaï†, François P. (September 2022, Israel Journal of Chemistry)

   Abstract As part of our efforts to interface late transition metals with Lewis acidic main group fragments, we have decided to investigate gold complexes bearing halogermanes as Z‐type ligands. Toward this end, we have synthesized complexes of general formula [(o‐(Ph₂P)C₆H₄)₂(Ph)(X)GeAuCl] (X = F, Cl). Experimental and computational analyses indicate the presence of an Au→Ge interaction in both cases. Chloride abstraction reactions have also been investigated. In the case of X = Cl, double chloride abstraction with AgSbF₆affords a putative dication that gradually abstracts fluoride from its counterion. This putative dication is also significantly more active as a catalyst than its monocationic analog in alkyne hydroamination reactions. 

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3. Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear Pt ^II →Ge ^IV Complex

   https://doi.org/10.1002/anie.202107485  

   Karimi, Mohammadjavad; Tabei, Elham S.; Fayad, Remi; Saber, Mohamed R.; Danilov, Evgeny O.; Jones, Cameron; Castellano, Felix N.; Gabbaï, François P. (September 2021, Angewandte Chemie International Edition)

   Abstract 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‐(Ph₂P)C₆H₄)₂Ge^IVCl₂]Pt^IICl₂and [(o‐(Ph₂P)C₆H₄)₂ClGe^III]Pt^IIICl₃, 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‐(Ph₂P)C₆H₄)₂ClGe^III]Pt^ICl with quantum yields of 1.7 % and 3.2 % for the Ge^IV–Pt^IIand Ge^III–Pt^IIIisomers, respectively. Conversion of the Ge^IV–Pt^IIisomer 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^IIIisomer point to a ligand arene–Cl^.charge‐transfer complex as an intermediate. 

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4. Coinage Metal Complexes of a Sterically Encumbered Anionic Pyridylborate

   https://doi.org/10.1002/chem.202401204  

   Vanga, Mukundam; Muñoz‐Castro, Alvaro; Dias, H_V_Rasika (June 2024, Chemistry – A European Journal)

   Abstract Sterically loaded, anionic pyridine has been synthesized and utilized successfully in the stabilization of a isoleptic series of coinage metal complexes. The treatment of [4‐(Ph₃B)‐2,6‐Trip₂Py]K (Trip=2,4,6‐ⁱPr₃C₆H₂) with CuBr(PPh₃), AgCl(PPh₃) or AuCl(PPh₃) (Py=pyridine) afforded the corresponding [4‐(Ph₃B)‐2,6‐Trip₂Py]M(PPh₃) (M=Au, Ag, Cu) complexes, via salt metathesis, as isolable, crystalline solids. Notably, these reactions avoid the facile single electron transfer chemistry reported with the less bulky ligand systems. The X‐ray structures revealed that they are two‐coordinate metal adducts. The M−N and M−P bond distances are longest in the silver and shortest in the copper adduct among the three group 11 family members. Computational analysis revealed an interesting stability dependence on steric bulk of the anionic pyridine (i. e., pyridyl borate) ligand. A comparison of structures and bonding of [4‐(Ph₃B)‐2,6‐Trip₂Py]Au(PPh₃) to pyridine andm‐terphenyl complexes, {[2,6‐Trip₂Py]Au(PPh₃)}[SbF₆] and [2,6‐Trip₂Ph]Au(PPh₃) are also provided. The Au(I) isocyanide complex, [4‐(Ph₃B)‐2,6‐Trip₂Py]Au(CNBu^t) has been stabilized using the same anionic pyridylborate illustrating that it can support other gold‐ligand moieties as well. 

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5. Ionization of gold (γ-methoxy)vinyl complexes generates reactive gold vinyl carbene complexes

   https://doi.org/10.1039/c9sc01574d  

   Kim, Nana; Widenhoefer, Ross A. (June 2019, Chemical Science)

   Cationic gold vinyl carbene/allylic cation complexes of the form ( E )-[(L)AuC(H)C(H)CAr 2 ] + OTf − {L = IPr, Ar = Ph [( E )- 5a ], L = IPr, Ar = 4-C 6 H 4 OMe [( E )- 5b ], L = P( t -Bu) 2 o -biphenyl, Ar = 4-C 6 H 4 OMe [( E )- 5c ]} were generated in solution via Lewis acid-mediated ionization of the corresponding gold (γ-methoxy)vinyl complexes ( E )-(L)AuC(H)C(H)C(OMe)Ar 2 at or below −95 °C. Complexes ( E )- 5b and ( E )- 5c were fully characterized in solution employing multinuclear NMR spectroscopy, which established the predominant contribution of the aurated allylic cation resonance structure and the significant distribution of positive charge into the γ-anisyl rings. Complex ( E )- 5b reacted rapidly at −95 °C with neutral two-electron, hydride, and oxygen atom donors exclusively at the C1 position of the vinyl carbene moiety and with p -methoxystyrene to form the corresponding vinylcyclopropane. In the absence of nucleophile ( E )- 5a decomposed predominantly via intermolecular carbene dimerization whereas formation of 1-aryl-5-methoxy indene upon ionization of ( Z )-(IPr)AuC(H)C(H)C(OMe)(4-C 6 H 4 OMe) 2 [( Z )- 6b ] implicated an intramolecular Friedel–Crafts or electrocyclic Nazarov pathway for the decomposition of the unobserved vinyl carbene complex ( Z )-[(IPr)AuC(H)C(H)C(4-C 6 H 4 OMe) 2 ] + OTf − [( Z )- 5b ]. 

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