Non-palindromic (C^C^D) gold(III) pincer complexes are not accessible by intramolecular oxidative addition of biphenylenes – an experimental and quantum chemical study

We herein report on the synthesis of biphenylenes substituted with a pyridine (N), a phosphine (P) and a carbene (C′) donor as well as a carbene donor with additional pyridine in the lateral position. We describe the synthesis and structures of derived gold(I) complexes, which we tried to use for the synthesis of non-palindromic [(C^C^D)AuIII] pincer complexes by means of an intramolecular oxidative addition of the strained biphenylene ring. However, the anticipated formation of gold(III) complexes failed due to kinetic and thermodynamic reasons, which we extensively investigated by quantum chemical calculations. Furthermore, we shed light on the oxidative addition of biphenylene to two different gold(I) systems reported in the literature. Our comprehensive quantum-chemical analysis is complemented by NMR experiments

Synthetic access to a phosphorescent non-palindromic pincer complex of palladium by a double oxidative addition-comproportionation sequence

A highly luminescent non-palindromic [(C^C^N)Pd] pincer complex forms upon reacting pyridine-substituted 2,2′-diiodo-biphenyl with [Pd(PPh$_{3}$)$_{4}$]. This case study establishes for the first time that the title compound is formed via a double oxidative addition – comproportionation sequence. DFT and TDDFT calculations complement mechanistic and photophysical characterizations

Synthesis and Characterization of Bis(pyridylimino)isoindolide Alkali Metal Complexes in Three Redox States

Non-innocent ligands (NILs) like bis(pyridylimino)isoindolide (BPI) play crucial roles in coordination chemistry, biosciences, catalysis and material sciences. Investigating the isolated redox states of NILs is inevitable for understanding their redox-activity and fine-tuning the properties of corresponding metal complexes. The limited number of fundamental studies on the coordination behavior and redox chemistry of reduced BPI species is suggested to hamper further applications of the title compounds. This work describes for the first time the isolation of alkali metal complexes of BPI and Me2BPI in three different oxidation states and their characterization by means of NMR or EPR spectroscopy, DFT calculations, and SC-XRD studies. The latter revealed the connection between bond orders in the ligand scaffold and its oxidation state. The paramagnetic compound Me2BPI-K2 was isolated as a coordination copolymer with 18-crown-6, which enabled the characterization of the dianionic BPI radical. Furthermore, the so-far unknown trianionic state of BPI was reported by the isolation of BPI-K3. This divulges an unprecedented bis(amidinato)isoindolide coordination mode

Quo Vadis CO2_2 Activation: Catalytic Reduction of CO2_2 to Methanol Using Aluminum and Gallium/Carbon‐based Ambiphiles

We report on so-called “hidden FLPs” (FLP: frustrated Lewis pair) consisting of a phosphorus ylide featuring a group 13 fragment in the ortho position of a phenyl ring scaffold to form five-membered ring structures. Although the formation of the Lewis acid/base adducts was observed in the solid state, most of the title compounds readily react with carbon dioxide to provide stable insertion products. Strikingly, 0.3–3.0 mol% of the reported aluminum and gallium/carbon-based ambiphiles catalyze the reduction of CO$_2$ to methanol with satisfactory high selectivity and yields using pinacol borane as stoichiometric reduction equivalent. Comprehensive computational studies provided valuable mechanistic insights and shed more light on activity differences

Reactivity of a Sterically Unencumbered α-Borylated Phosphorus Ylide towards Small Molecules

The influence of substituents on α‐borylated phosphorus ylides (α‐BCPs) has been investigated in a combined experimental and quantum chemical approach. The synthesis and characterization of Me$_{3}$PC(H)B(iBu)$_{2}$ (1), consisting of small Me substituents on phosphorous and iBu residues on boron, is reported. Compound 1 is accessible through a novel synthetic approach, which has been further elucidated through DFT studies. The reactivity of 1 towards various small molecules was probed and compared with that of a previously published derivative, Ph$_{3}$PC(Me)BEt$_{2}$ (2). Both α‐BCPs react with NH$_{3}$ to undergo heterolytic N−H bond cleavage. Different di‐ and trimeric ring structures were observed in the reaction products of 1 with CO and CO$_{2}$. With PhNCO and PHNCS, the expected insertion products [Me$_{3}$PC(H)(PhNCO)B(iBu)$_{2}$] and [Me$_{3}$PC(H)(PhNCS)B(iBu)$_{2}$], respectively, were isolated

A neutral, acyclic, borataalkene-like ligand for group 11 metals: L- and Z-type ligands side by side

The overall neutral α-borylated phosphorus ylide Ph$_{3}$PC(Me)BEt$_{2}$ behaves like a polar borataalkene and can act as acyclic, ambiphilic π-type ligand with L- and Z-type functionalities side by side. In the complexes [MX{η$^{2}$-Ph$_{3}$PC(Me)BEt$_{2}$}] (M = Cu, (Ag), Au; X = Cl, NTf$_{2}$), the bonding is dominated by the highly nucleophilic ylidic carbon atom (L-type ligand). The Lewis acidic boron atom furnishes nonetheless a small but significant bonding contribution (Z-type ligand)

Heterobimetallic Gold/Ruthenium Complexes Synthesized via Post‐functionalization and Applied in Dual Photoredox Gold Catalysis

The synthesis of heterobimetallic AuI/RuII complexes of the general formula syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$ is reported. The ditopic bridging ligand L1∩L2 refers to a P,N hybrid ligand composed of phosphine and bipyridine substructures, which was obtained via a post-functionalization strategy based on Diels-Alder reaction between a phosphole and a maleimide moiety. It was found that the stereochemistry at the phosphorus atom of the resulting 7-phosphanorbornene backbone can be controlled by executing the metal coordination and the cycloaddition reaction in a different order. All precursors, as well as the mono- and multimetallic complexes, were isolated and fully characterized by various spectroscopic methods such as NMR, IR, and UV-vis spectroscopy as well as cyclic voltammetry. Photophysical measurements show efficient phosphorescence for the investigated monometallic complex anti-[(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$ and the bimetallic analogue syn-[{AuCl}(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$, thus indicating a small influence of the {AuCl} fragment on the photoluminescence properties. The heterobimetallic Au$^{I}$/Ru$^{II}$ complexes syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$ are both active catalysts in the P-arylation of aryldiazonium salts promoted by visible light with H-phosphonate affording arylphosphonates in yields of up to 91 %. Both dinuclear complexes outperform their monometallic counterparts

NON‐Ligated N‐Heterocyclic Tetrylenes

We report on the synthesis of N-heterocyclic tetrylenes ligated by the NON-donor framework 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene. The molecular structures of the germylene (3), stannylene (4) and plumbylene (5) where determined by X-ray diffraction studies. Furthermore, we present quantum chemical studies on the sigma-donor and pi-acceptor properties of 3-5. Additionally, we report on the reactivity of the tetrylenes towards the transition metal carbonyls [Rh(CO)(2)Cl](2), [W(CO)(6)] and [Ni(CO)(4)]. The isolated complexes (6 and 7) show the differing reactivity of NHTs compared to NHCs. Instead of just forming the anticipated complex [(NON)Sn-Rh(CO)(2)Cl], 4 inserts into the Rh-Cl bond to afford [(NON)Sn(Cl)Rh(CO)(C6H6)] (6, additional CO/C6H6 exchange) and [(NON)Sn(Cl)Rh-2(CO)(4)Cl] (7). By avoiding halogenated transition metal precursors in order to prevent insertion reactions, germylene 3 shows "classical" coordination chemistry towards {Ni(CO)(3)} forming the complex [(NON)Ge-Ni(CO)(3)] (8)