Orthogonal Nanoparticle Catalysis with Organogermanes

Abstract

Although nanoparticles are widely used as catalysts, little is knownabout their potential ability to trigger privileged transformations as compared to homogeneous molecular or bulk heterogeneous catalysts.W eh erein demonstrate (and rationalize) that nanoparticles displayorthogonal reactivity to molecular catalysts in the cross-coupling of aryl halides with aryl germanes.W hile the aryl germanes are unreactive in L n Pd 0 /L n Pd II catalysis and allowselective functionalization of established coupling partners in their presence,t hey display superior reactivity under Pd nanoparticle conditions,o utcompeting established coupling partners (such as ArBPin and ArBMIDA) and allowing air-tolerant, base-free,a nd orthogonal access to valuable and challenging biaryl motifs.A s opposed to the notoriously unstable polyfluoroaryl-and 2-pyridylboronic acids,the corresponding germanes are highly stable and readily coupled. Our mechanistic and computational studies provideu nambiguous support of nanoparticle catalysis and suggest that owingtothe electron richness of aryl germanes,t hey preferentially react by electrophilic aromatic substitution, and in turn are preferentially activated by the more electrophilic nanoparticles.

Co-Catalyzed E-(β)-Selective Hydrogermylation of Terminal Alkynes

“…Despite enormous success in this area, the need for more rapid, selective, advanced synthetic methodologies drives search for new coupling partners. Recently, organogermanes [1][2][3][4][5] have emerged as perspective coupling partners to circumvent limitations of traditional organozinc and organomagnesium reagents 6,7 (low functional group tolerance); organosilanes 8 (low reactivity), organostannanes [9][10][11] (acute toxicity: endocrine disruptors, immunotoxicants, carcinogens and obesogens); and organoboronic acids 12,13 (acid/base sensitivity). In this regard, vinylgermanes are of particular interest as versatile synthetic building blocks due to their low toxicity, 14 resistance to protonolysis, 15 and benchtop stability.…”

Synthesis and Application of Heterocyclic Germatranes via Rhodium‐Catalyzed Directed C−H Activation/Annulation with Alkynyl Germatranes and Palladium‐Catalyzed Cross‐Coupling

“…However, compared with other metal-or metalloid-containing heterocyclic nucleophilic reagents, rather less attention has been paid to Ge-containing heterocyclic nucleophiles, since Ge-related cross-coupling reactions were scarcely reported. [6] Our group has been focusing on developing a series of facilely synthesized, air-and moisture-stable and environmental-friendly germatranes (abbreviated as Ge in following text) as nucleophiles for Pd-catalyzed crosscoupling reaction. [7] Our previous studies have revealed that germatranization of heterocyclic halides could furnish various Ge-containing heterocyclic nucleophiles (Scheme 1a), [7a] which were also proved to be competent for construction of complex heterocycles under Pd-catalyzed cross-coupling reaction conditions.…”

Modular and Selective Arylation of Aryl Germanes (C−GeEt3) over C−Bpin, C−SiR3 and Halogens Enabled by Light‐Activated Gold Catalysis

“…Recently, our group added organogermanes (-GeR 3 ) [5] to the selectivity toolbox, which are robust, non-toxic, easily installable, [6] and unreactive in standard Pd 0 /Pd II -catalyzed couplings, while privileged coupling partners with aryl iodides under nanoparticle catalysis that outcompete for example, ArBPin or ArBMIDA. [7] However, the currently available sequential or iterative coupling repertoire with Pd is far from complete, and the increasing demands towards a rapid and automated exploration of chemical space will greatly benefit from new and orthogonal disconnections. [8] For example, none of these methods allow to assemble richly decorated small molecules in the presence of CÀiodine bonds, which owing to their pronounced halogen bonding [9] are receiving increasing interest in medicinal and materials chemistry.…”

“…We subsequently explored the scope of the couplings and investigated especially those aryl germanes that would, as the corresponding aryl boronic acids, be unstable and sluggishly reactive or incompatible in the widely employed Pd-catalyzed Suzuki cross coupling, [21] that is, highly fluorinated, heterocyclic, sterically hindered as well as halogenated aryl germanes. [7] The presence of fluorine in ortho-or para-positions of the germane (1-3, see Table 1) as well as electron-rich heterocycles, such as the sterically demanding isoxazole (16), 2-and 3-substituted thiophenes (15,17), and a 1,3-benzodioxole (18) were well tolerated. Notably, analogous couplings of the latter previously needed metal and base additives to proceed.…”

“…Notably, analogous couplings of the latter previously needed metal and base additives to proceed. [16c] Similarly, the halogens Cl, Br, and I were fully tolerated in the couplings (5)(6)(7)(8)(9)(10)(11)(12)(13)(14), offering powerful handles for follow-up functionalizations by established Pd catalysis. A frequent challenge in gold-catalyzed coupling processes is ortho-substitution.…”