In search of new platforms that support redox-controlled catalysis, we have investigated the noninnocent behavior of chlorostibine ligands coordinated to gold. The gold chlorostibine complex ((o-(Ph2P)C6H4)2SbCl)AuCl (1-Cl) undergoes a clean oxidation reaction on treatment with PhICl2. This oxidation reaction affords the corresponding trichlorostiborane complex ((o-(Ph2P)C6H4)2SbCl3)AuCl (2-Cl), which can be converted into the more tractable trifluoride analogue ((o-(Ph2P)C6H4)2SbF3)AuCl (3-Cl) by treatment with a fluoride source. As supported by experimental and computational results, these complexes possess a Au→Sb donor-acceptor interaction which is distinctly stronger in the oxidized complexes 2-Cl and 3-Cl. Both 1-Cl and 3-Cl undergo a clean chloride abstraction reaction to afford the corresponding cationic gold species [((o-(Ph2P)C6H4)2SbCl)Au](+) ([1](+)) and [((o-(Ph2P)C6H4)2SbF3)Au](+) ([3](+)), which have been isolated as SbF6(-) salts. As a result of a stronger Au→Sb interaction, cation [3](+) features a more Lewis acidic gold center. It forms an isolable water adduct and also activates terminal alkynes toward hydroamination with arylamines. These results demonstrate that the redox state of noninnocent Z-ligands can be used to control the catalytic activity of the adjoining metal center.

In our search for novel main-group-based redox-active platforms for solar fuel production, we have synthesized Cl2Sb(IV)Pt(III)Cl3(o-dppp)2 (2, o-dppp = o-(Ph2P)C6H4)), a complex featuring a highly oxidized [PtSb](VII) core. This thermally stable complex quickly evolves chlorine upon irradiation with a Xe lamp, leading to [Cl2Sb(IV)Pt(I)Cl(o-dppp)2] (1) as the photoproduct. This photoreduction is very efficient, with a maximum quantum yield of 13.8% when carried out in a 4.4 M solution of 2,3-dimethyl-1,3-butadiene in CH2Cl2. Remarkably, 2 also evolves chlorine when irradiated in the solid state under ambient conditions in the absence of a trap.

The synthesis and spectroscopic characterization of a family of Ni–X (X = Cl, Br, I, H) complexes supported by the bulky α-diimine chelate N,N′-bis­(1R,2R,3R,5S)-(−)-isopinocampheyl-2,3-butanediimine (ipcADI) are described. Diimine-supported, three-coordinate nickel­(I)–X complexes have been proposed as key intermediates in a host of catalytic transformations such as C–C and C–heteroatom cross-coupling and C–H functionalization but have until now remained synthetically elusive. A combination of structural, spectroscopic, electrochemical, and computational studies were used to establish the electronic structure of each monomeric [(ipcADI)­NiX] (X = Cl, Br, I) complex as a nickel­(I) derivative supported by a redox-neutral α-diimine chelate. The dimeric nickel hydride, [(ipcADI)­Ni­(μ2-H)]2, was prepared and characterized by X-ray diffraction; however, magnetic measurements and 1H NMR spectroscopy support monomer formation at ambient temperature in THF solution. This nickel hydride was used as a precatalyst for the hydrogen isotope exchange (HIE) of C–H bonds in arenes and pharmaceuticals. By virtue of the multisite reactivity and high efficiency, the new nickel precatalyst provided unprecedented high specific activities (50–99 Ci/mmol) in radiolabeling, meeting the threshold required for radioligand binding assays. Use of air-stable and readily synthesized nickel precursor, [(ipcADI)­NiBr2], broad functional group tolerance, and compatibility with polar protic solvents are additional assets of the nickel-catalyzed HIE method.

An operationally simple protocol for a palladium-catalyzed 13CO and 14CO exchange with activated aliphatic and benzoic carbonyls is presented. Several 13C and 14C building blocks, natural product derivatives, and pharmaceuticals have been prepared to showcase the method for late-stage carbon isotope incorporation and its functional group compatibility.

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