Gold(III)-Olefin-Komplexe

Synthesis of New Donor-Substituted Biphenyls: Pre-ligands for Highly Luminescent (C^C^D) Gold(III) Pincer Complexes

We herein report on new synthetic strategies for the preparation of pyridine and imidazole substituted 2,2'-dihalo biphenyls. These structures are pre-ligands suitable for the preparation of respective stannoles. The latter can successfully be transmetalated to K[AuCl4 ] forming non-palindromic [(C^C^D)AuIII ] pincer complexes featuring a lateral pyridine (D=N) or N-heterocyclic carbene (NHC, D=C') donor. The latter is the first report on a pincer complex with two formally anionic sp2 and one carbenic carbon donor. The [(C^C^D)AuIII ] complexes show intense phosphorescence in solution at room temperature. We discuss the developed multistep strategy and touch upon synthetic challenges. The prepared complexes have been fully characterized including X-ray diffraction analysis. The gold(III) complexes' photophysical properties have been investigated by absorption and emission spectroscopy as well as quantum chemical calculations on the quasi-relativistic two-component TD-DFT and GW/Bethe-Salpeter level including spin-orbit coupling. Thus, we shed light on the electronic influence of the non-palindromic pincer ligand and reveal non-radiative relaxation pathways of the different ligands employed.

Do Gold(III) Complexes Form Hydrogen Bonds? An Exploration of AuIII Dicarboranyl Chemistry

The reaction of 1,1'-Li₂ [(2,2'-C₂ B₁₀ H₁₀ )₂ ] with the cyclometallated gold(III) complex (C^N)AuCl₂ afforded the first examples of gold(III) dicarboranyl complexes. The reactivity of these complexes is subject to the trans-influence exerted by the dicarboranyl ligand, which is substantially weaker than that of non-carboranyl anionic C-ligands. In line with this, displacement of coordinated pyridine by chloride is only possible under forcing conditions. While treatment of (C^N)Au{(2,2'-C₂ B₁₀ H₁₀ )₂ } (2) with triflic acid leads to Au-C rather than Au-N bond protonolysis, aqueous HBr cleaves the Au-N bond to give the pyridinium bromo complex 7. The trans-influence of a series of ligands including dicarboranyl and bis(dicarboranyl) was assessed by means of DFT calculations. The analysis demonstrated that it was not sufficient to rely exclusively on geometric descriptors (calculated or experimental) when attempting to rank ligands for their trans influence. Complex (C^N)Au(C₂ B₁₀ H₁₁ )₂ containing two non-chelating dicarboranyl ligands was prepared similar to 2. Its reaction with trifluoroacetic acid also leads to Au-N cleavage to give trans-(Hpy^C)Au(OAc^F )(C₂ B₁₀ H₁₁ )₂ (8). In crystals of 8 the pyridinium N-H bond points towards the metal centre, while in 7 it is bent away. The possible contribution of gold(III)⋅⋅⋅H-N hydrogen bonding in these complexes was investigated by DFT calculations. The results show that, unlike the situation for platinum(II), there is no evidence for an energetically significant contribution by hydrogen bonding in the case of gold(III).

Chiral AuI - and AuIII -Isothiourea Complexes: Synthesis, Characterization and Application

During an investigation into the potential union of Lewis basic isothiourea organocatalysis and gold catalysis, the formation of gold-isothiourea complexes was observed. These novel gold complexes were formed in high yield and were found to be air- and moisture stable. A series of neutral and cationic chiral gold(I) and gold(III) complexes bearing enantiopure isothiourea ligands was therefore synthesized and fully characterized. The steric and electronic properties of the isothiourea ligands was assessed through calculation of their percent buried volume and the synthesis and analysis of novel iridium(I)-isothiourea carbonyl complexes. The novel gold(I)- and gold(III)-isothiourea complexes have been applied in preliminary catalytic and biological studies, and display promising preliminary levels of catalytic activity and potency towards cancerous cell lines and clinically relevant enzymes.

Thermally Stable Gold(III) Alkene and Alkyne Complexes: Synthesis, Structures, and Assessment of the trans-Influence on Gold-Ligand Bond Enthalpies

The reaction of [C^C)Au(OEt₂ )₂ ]⁺ with 1,5-cyclooctadiene or norbornadiene affords the corresponding olefin complexes [(C^C)Au(COD)]SbF₆ and [(C^C)Au(NBD)]SbF₆ , which are thermally stable in solution and the solid state (C^C=4,4'-di-tert-butylbiphenyl-2,2'-diyl). The crystal structures of these complexes have been determined. By contrast, dienones such as dibenzylideneacetone are O- rather than C=C-bonded. The reactions of (C^C)Au(OAc^F )(L) (L=PMe₃ or CNxyl) with B(C₆ F₅ )₃ in the presence of bis(1-adamantyl)acetylene give the mixed-ligand alkyne complexes [(C^C)Au(AdC≡CAd)(L)]⁺ , the first complexes of their type in gold chemistry. In the presence of an excess of acetylene these compounds are thermally stable in solution and as solids. The bonding of n- and π-donor ligands to Au^III fragments and the effect of the trans influence exerted by N- and C-donors was explored with the aid of DFT calculations. Results show that the Au-L bond enthalpies trans to anionic C are 35-60 % of the enthalpies trans to N, with strong π-acceptors being particularly affected. In comparison with [Me₂ Au]⁺ , the [(C^C)Au]⁺ fragment is more polar and in bond enthalpy terms resembles Me₂ Pt.

Gold(III) Alkyne Complexes: Bonding and Reaction Pathways

The synthesis and characterization of hitherto hypothetical AuIII π-alkyne complexes is reported. Bonding and stability depend strongly on the trans effect and steric factors. Bonding characteristics shed light on the reasons for the very different stabilities between the classical alkyne complexes of PtII and their drastically more reactive AuIII congeners. Lack of back-bonding facilitates alkyne slippage, which is energetically less costly for gold than for platinum and explains the propensity of gold to facilitate C-C bond formation. Cycloaddition followed by aryl migration and reductive deprotonation is presented as a new reaction sequence in gold chemistry.

Methyl-, Ethenyl-, and Ethynyl-Bridged Cationic Digold Complexes Stabilized by Coordination to a Bulky Terphenylphosphine Ligand

Reactions of the gold(I) triflimide complex [Au(NTf2 )(PMe2 Ar${{^{{\rm Dipp}{_{2}}}}}$)] (1) with the gold(I) hydrocarbyl species [AuR(PMe2 Ar${{^{{\rm Dipp}{_{2}}}}}$)] (2 a-2 c) enable the isolation of hydrocarbyl-bridged cationic digold complexes with the general composition [Au2 (μ-R)(PMe2 Ar${{^{{\rm Dipp}{_{2}}}}}$)2 ][NTf2 ], where Ar${{^{{\rm Dipp}{_{2}}}}}$=C6 H3 -2,6-(C6 H3 -2,6-iPr2 )2 and R=Me (3), CHCH2 (4), or CCH (5). Compound 3 is the first alkyl-bridged digold complex to be reported and features a symmetric [Au(μ-CH3 )Au](+) core. Complexes 4 and 5 are the first species of their kind that contain simple, unsubstituted vinyl and acetylide units, respectively. In the series of complexes 3-5, the bridging carbon atom systematically changes its hybridization from sp(3) to sp(2) and sp. Concomitant with this change, and owing to variations in the nature of the bonding within the [Au(μ-R)Au](+) unit, there is a gradual decrease in aurophilicity, that is, the strength of the Au⋅⋅⋅Au bonding interaction decreases. This change is illustrated by a monotonic increase in the Au-Au distance by approximately 0.3 Å from R=CH3 (2.71 Å) to CHCH2 (3.07 Å) and CCH (3.31 Å).

Enhanced π-backdonation from gold(I): isolation of original carbonyl and carbene complexes

The specific electronic properties of bent o-carborane diphosphine gold(I) fragments were exploited to obtain the first classical carbonyl complex of gold [(DPCb)AuCO](+) (ν(CO)=2143 cm(-1) ) and the diphenylcarbene complex [(DPCb)Au(CPh2 )](+) , which is stabilized by the gold fragment rather than the carbene substituents. These two complexes were characterized by spectroscopic and crystallographic means. The [(DPCb)Au](+) fragment plays a major role in their stability, as substantiated by DFT calculations. The bending induced by the diphosphine ligand substantially enhances π-backdonation and thereby allows the isolation of carbonyl and carbene complexes featuring significant π-bond character.