| dc.description.abstract | The use of Z-ligands to modulate the electronic property of transition metal centers is a powerful strategy in catalyst design. Our group has shown that antimony-based ambiphilic ligand, accept electron density from adjacent metal centers by the σ* orbital of the antimony (V) center and thus increasing the electrophilic reactivity of the trancition metal center. In this thesis, we were eager to determine if the charge of the Ztype ligand can be used to further enhance this effect. To this end, we synthesized a dicationic gold complex [46]^2+ ([(o‐(Phv2P)Cv6Hv4)v2(o‐Phv2PO)Cv6vHV4)SbAuCl]^2^+) featuring a dicationic antimony (V) ligand with a phosphine oxide arm coordinating to the antimony center. Both experimental and computational results show that the gold complex possess a strong Au→Sb interaction reinforced by the dicationic character of the antimony center. The gold‐bound chloride anion of this complex is rather inert and necessitates the addition of excess AgNTfv2 to undergo activation. The activated complex, referred to as [47]^2+ ([((o‐(Phv2P)Cv6Hv4)v2(o‐Phv2PO)Cv6Hv4)SbAuNTfv2]^2+) readily catalyzes both the polymerization and the hydroamination of styrene. This atypical reactivity underscores the strong σ‐accepting properties of the dicationic antimony ligand and its activating impact on the gold center. Building on these original results, we have chosen to investigate antimonysubstituted 2,2′-bipyridine (bipy) ligands in order to determine if the redox activity of the peripheral antimony center could be used to influence the reactivity of a transition metal coordinated to the bipy ligand. To this end, we synthesized 4-diphenylstibino-2,2′-bipyridine (54), which could be obtained by reaction of 4-lithio-2,2′-bipyridine with Phv2SbCl. The ligand 54 was treated with Pt(CHv3CN)v2Clv2 to afford the platinum complex 55. Interestingly, the latter reacts with PhIClv2 to afford 56, a complex in which the peripheral stibine moiety has been converted into a dichlorostiborane. Complexes 55 and 56 have both been fully characterized. Computational, UV–vis, and cyclic voltammetry studies show that oxidation of the antimony atom leads to a lowering of the bipy-centered LUMO, indicating that 56 is more electron deficient than 55. A congruent picture emerges from reactivity studies, which show that 56 is a more active catalyst for the hydroarylation of ethyl propiolate by mesitylene.
A similar concept was also applied to cyclometalated iridium(III) complexes. Reaction of 4-(diphenylstibino)-2,2′-bipyridine (54) with [(ppy)v2Ir(-Cl)]v2 afforded the corresponding tris-chelate iridium complex [(ppy)v2Ir(54) ] + ([64] + ) which was isolated as a hexafluorophosphate salt ([64][PF^6]). Reaction of [64][PF^6] with excess PhIClv2 in DMSO induced the conversion of the diphenylantimony moiety of [65] + into an anionic diphenyltrichloroantimonate leading to a zwitterionic complex referred to as 65-Cl. Complexes [64][PF^6] and 65-Cl have been characterized by NMR and the structure of 65- Cl confirmed using X-ray diffraction. DFT calculations and electrochemical measurments show that the electron-rich diphenyltrichloroantimonate moiety in 65-Cl cathodically shifts the Ir(III/IV) redox couple. Luminescence measurements also show that 65-Cl is less emissive than [64] + . | en |
