Oxidative Addition of MeI to a Rollover Complex of Platinum(II): Isolation of the Kinetic Product

A pair of new Pt­(II)/Pt­(IV) 2,2′-bipyridine cyclometalated rollover complexes have been synthesized and characterized. [Pt­(bpy-H)­(CH₃)­(PMe₃)] (<b>1</b>), where bpy-H = κ²<i>N</i>,<i>C</i>-2,2′-bipyridine, was obtained from the electron-rich precursor <i>cis</i>-[Pt­(CH₃)₂(DMSO)₂] with a one-pot, two step synthesis; its reactivity has been tested with CH₃I, giving the corresponding Pt­(IV) complex <i>cis</i>-[Pt­(bpy-H)­(CH₃)₂(I)­(PMe₃)] (<b>2</b>), which was fully characterized. Crystals suitable for X-ray analysis were obtained and allowed the determination of the structure of isomer <b>2A</b> which is the product of the <i>trans</i> addition of CH₃I, usually thought of as the <i>kinetic</i> product

Oxidative Addition of MeI to a Rollover Complex of Platinum(II): Isolation of the Kinetic Product

A pair of new Pt­(II)/Pt­(IV) 2,2′-bipyridine cyclometalated rollover complexes have been synthesized and characterized. [Pt­(bpy-H)­(CH₃)­(PMe₃)] (<b>1</b>), where bpy-H = κ²<i>N</i>,<i>C</i>-2,2′-bipyridine, was obtained from the electron-rich precursor <i>cis</i>-[Pt­(CH₃)₂(DMSO)₂] with a one-pot, two step synthesis; its reactivity has been tested with CH₃I, giving the corresponding Pt­(IV) complex <i>cis</i>-[Pt­(bpy-H)­(CH₃)₂(I)­(PMe₃)] (<b>2</b>), which was fully characterized. Crystals suitable for X-ray analysis were obtained and allowed the determination of the structure of isomer <b>2A</b> which is the product of the <i>trans</i> addition of CH₃I, usually thought of as the <i>kinetic</i> product

Mesoionic Complexes of Platinum(II) Derived from “Rollover” Cyclometalation: A Delicate Balance between Pt–C(sp³) and Pt–C(sp²) Bond Cleavage as a Result of Different Reaction Conditions

“Rollover” cyclometalation is a particular case of metal-mediated C–H bond activation, and the resulting complexes constitute an emerging class of cyclometalated compounds. In the case of 2,2′-bipyridine “rollover cyclometalation” has been used to synthesize the complexes [Pt­(bipy-H)­(Me)­(L)] (L = PPh₃, PCy₃, P­(OPh)₃, P­(<i>p</i>-tolyl)₃), whose protonation produces a series of stable corresponding pyridylenes [Pt­(bipy*)­(Me)­(L)]⁺. The unusual bipy* ligand may be described as an abnormal-remote heterocyclic chelated carbene or simply as a mesoionic cyclometalated ligand. These cationic species spontaneously convert in solution, through a retro-rollover reaction, to the corresponding isomers [Pt­(bipy)­(Me)­(L)]⁺, where the 2,2′-bipyridine is coordinated in the classical N,N bidentate mode. Isomerization is achieved at different rates (ranging over three orders of magnitude), depending on the nature of the phosphane ligand, the most basic (PCy₃) providing the fastest reaction. The mesoionic species [Pt­(bipy*)­(Me)­(L)]⁺ contain two Pt–C bonds: the balance between the Pt–C­(sp²) and Pt–C­(sp³) bond rupture is subtle, and competition is observed according to the reaction conditions. In the presence of an external neutral ligand L′ methane is released to give the cationic derivatives [Pt­(bipy-H)­(L)­(L′)]⁺, whereas reaction of the neutral [Pt­(bipy-H)­(Me)­(L)] with HCl may follow different routes depending on the nature of the neutral ligand L. Assuming all reactions take place through the formation of a hydride intermediate, quantum chemical calculations show that computed energy barriers are qualitatively consistent with observed reaction rates

Rollover Cyclometalation with 2‑(2′-Pyridyl)quinoline

Rollover cyclometalation of 2-(2′-pyridyl)­quinoline, L, allowed the synthesis of the family of complexes [Pt­(L-H)­(X)­(L′)] and [Pt­(L*)­(X)­(L′)]­[BF₄] (X = Me, Cl; L′ = neutral ligand), the former being the first examples of Pt­(II) rollover complexes derived from the ligand L. The ligand L* is a C,N cyclometalated, N-protonated isomer of L, and can also be described as an abnormal-remote pyridylene. The corresponding [Pt­(L-H)­(Me)­(L′)]/[Pt­(L*)­(Me)­(L′)]⁺ complexes constitute an uncommon Brønsted–Lowry acid–base conjugated couple. The species obtained were investigated in depth through NMR and UV–vis spectroscopy, cyclic voltammetry, and density functional theory (DFT) methods to correlate different chemico-physical properties with the nature of the cyclometalated ligand (e.g., L vs bipy or L* vs L) and of the neutral ligand (DMSO, CO, PPh₃). The crystal structures of [Pt­(L-H)­(Me)­(PPh₃)], [Pt­(L-H)­(Me)­(CO)] and [Pt­(L*)­(Me)­(CO)]­[BF₄] were determined by X-ray powder diffraction methods, the latter being the first structure of a Pt­(II)-based, protonated, rollover complex to be unraveled. The isomerization of [Pt­(L*)­(Me)­(PPh₃)]⁺ in solution proceeds through a retro-rollover process to give the corresponding adduct [Pt­(L)­(Me)­(PPh₃)]⁺, where L acts as a classical N,N chelating ligand. Notably, the retro-rollover reaction is the first process, among the plethora of Pt–C bond protonolysis reactions reported in the literature, where a Pt–C­(heteroaryl) bond is cleaved rather than a Pt–C­(alkyl) one

Rollover Cyclometalation with 2‑(2′-Pyridyl)quinoline

Rollover cyclometalation of 2-(2′-pyridyl)­quinoline, L, allowed the synthesis of the family of complexes [Pt­(L-H)­(X)­(L′)] and [Pt­(L*)­(X)­(L′)]­[BF₄] (X = Me, Cl; L′ = neutral ligand), the former being the first examples of Pt­(II) rollover complexes derived from the ligand L. The ligand L* is a C,N cyclometalated, N-protonated isomer of L, and can also be described as an abnormal-remote pyridylene. The corresponding [Pt­(L-H)­(Me)­(L′)]/[Pt­(L*)­(Me)­(L′)]⁺ complexes constitute an uncommon Brønsted–Lowry acid–base conjugated couple. The species obtained were investigated in depth through NMR and UV–vis spectroscopy, cyclic voltammetry, and density functional theory (DFT) methods to correlate different chemico-physical properties with the nature of the cyclometalated ligand (e.g., L vs bipy or L* vs L) and of the neutral ligand (DMSO, CO, PPh₃). The crystal structures of [Pt­(L-H)­(Me)­(PPh₃)], [Pt­(L-H)­(Me)­(CO)] and [Pt­(L*)­(Me)­(CO)]­[BF₄] were determined by X-ray powder diffraction methods, the latter being the first structure of a Pt­(II)-based, protonated, rollover complex to be unraveled. The isomerization of [Pt­(L*)­(Me)­(PPh₃)]⁺ in solution proceeds through a retro-rollover process to give the corresponding adduct [Pt­(L)­(Me)­(PPh₃)]⁺, where L acts as a classical N,N chelating ligand. Notably, the retro-rollover reaction is the first process, among the plethora of Pt–C bond protonolysis reactions reported in the literature, where a Pt–C­(heteroaryl) bond is cleaved rather than a Pt–C­(alkyl) one

Rollover Cyclometalation with 2‑(2′-Pyridyl)quinoline

Rollover cyclometalation of 2-(2′-pyridyl)­quinoline, L, allowed the synthesis of the family of complexes [Pt­(L-H)­(X)­(L′)] and [Pt­(L*)­(X)­(L′)]­[BF₄] (X = Me, Cl; L′ = neutral ligand), the former being the first examples of Pt­(II) rollover complexes derived from the ligand L. The ligand L* is a C,N cyclometalated, N-protonated isomer of L, and can also be described as an abnormal-remote pyridylene. The corresponding [Pt­(L-H)­(Me)­(L′)]/[Pt­(L*)­(Me)­(L′)]⁺ complexes constitute an uncommon Brønsted–Lowry acid–base conjugated couple. The species obtained were investigated in depth through NMR and UV–vis spectroscopy, cyclic voltammetry, and density functional theory (DFT) methods to correlate different chemico-physical properties with the nature of the cyclometalated ligand (e.g., L vs bipy or L* vs L) and of the neutral ligand (DMSO, CO, PPh₃). The crystal structures of [Pt­(L-H)­(Me)­(PPh₃)], [Pt­(L-H)­(Me)­(CO)] and [Pt­(L*)­(Me)­(CO)]­[BF₄] were determined by X-ray powder diffraction methods, the latter being the first structure of a Pt­(II)-based, protonated, rollover complex to be unraveled. The isomerization of [Pt­(L*)­(Me)­(PPh₃)]⁺ in solution proceeds through a retro-rollover process to give the corresponding adduct [Pt­(L)­(Me)­(PPh₃)]⁺, where L acts as a classical N,N chelating ligand. Notably, the retro-rollover reaction is the first process, among the plethora of Pt–C bond protonolysis reactions reported in the literature, where a Pt–C­(heteroaryl) bond is cleaved rather than a Pt–C­(alkyl) one

Rollover Cyclometalation with 2‑(2′-Pyridyl)quinoline

Rollover cyclometalation of 2-(2′-pyridyl)­quinoline, L, allowed the synthesis of the family of complexes [Pt­(L-H)­(X)­(L′)] and [Pt­(L*)­(X)­(L′)]­[BF₄] (X = Me, Cl; L′ = neutral ligand), the former being the first examples of Pt­(II) rollover complexes derived from the ligand L. The ligand L* is a C,N cyclometalated, N-protonated isomer of L, and can also be described as an abnormal-remote pyridylene. The corresponding [Pt­(L-H)­(Me)­(L′)]/[Pt­(L*)­(Me)­(L′)]⁺ complexes constitute an uncommon Brønsted–Lowry acid–base conjugated couple. The species obtained were investigated in depth through NMR and UV–vis spectroscopy, cyclic voltammetry, and density functional theory (DFT) methods to correlate different chemico-physical properties with the nature of the cyclometalated ligand (e.g., L vs bipy or L* vs L) and of the neutral ligand (DMSO, CO, PPh₃). The crystal structures of [Pt­(L-H)­(Me)­(PPh₃)], [Pt­(L-H)­(Me)­(CO)] and [Pt­(L*)­(Me)­(CO)]­[BF₄] were determined by X-ray powder diffraction methods, the latter being the first structure of a Pt­(II)-based, protonated, rollover complex to be unraveled. The isomerization of [Pt­(L*)­(Me)­(PPh₃)]⁺ in solution proceeds through a retro-rollover process to give the corresponding adduct [Pt­(L)­(Me)­(PPh₃)]⁺, where L acts as a classical N,N chelating ligand. Notably, the retro-rollover reaction is the first process, among the plethora of Pt–C bond protonolysis reactions reported in the literature, where a Pt–C­(heteroaryl) bond is cleaved rather than a Pt–C­(alkyl) one

Heterobimetallic Rollover Derivatives

Heterobimetallic complexes with metal centers connected by a small delocalized ligand constitute an interesting class of compounds. Here we report that starting from the mononuclear platinum­(II) rollover complexes [Pt­(bipy-H)­(L)­Cl] (bipy-H = 2,2′-bipyridine C(3′)-N cyclometalated, L= DMSO, PPh₃) a second rollover cyclometalation may produce a series of Pt­(II)/Pd­(II) heterobimetallic complexes where the two metals are linked by the planar, highly delocalized, doubly deprotonated 2,2′-bipyridine

Heterobimetallic Rollover Derivatives

Heterobimetallic complexes with metal centers connected by a small delocalized ligand constitute an interesting class of compounds. Here we report that starting from the mononuclear platinum­(II) rollover complexes [Pt­(bipy-H)­(L)­Cl] (bipy-H = 2,2′-bipyridine C(3′)-N cyclometalated, L= DMSO, PPh₃) a second rollover cyclometalation may produce a series of Pt­(II)/Pd­(II) heterobimetallic complexes where the two metals are linked by the planar, highly delocalized, doubly deprotonated 2,2′-bipyridine