9 research outputs found
Oxidative Addition of MeI to a Rollover Complex of Platinum(II): Isolation of the Kinetic Product
A pair of new PtÂ(II)/PtÂ(IV) 2,2′-bipyridine
cyclometalated
rollover complexes have been synthesized and characterized. [PtÂ(bpy-H)Â(CH<sub>3</sub>)Â(PMe<sub>3</sub>)] (<b>1</b>), where bpy-H = Îş<sup>2</sup><i>N</i>,<i>C</i>-2,2′-bipyridine,
was
obtained from the electron-rich precursor <i>cis</i>-[PtÂ(CH<sub>3</sub>)<sub>2</sub>(DMSO)<sub>2</sub>] with a one-pot, two step
synthesis; its reactivity has been tested with CH<sub>3</sub>I, giving
the corresponding PtÂ(IV) complex <i>cis</i>-[PtÂ(bpy-H)Â(CH<sub>3</sub>)<sub>2</sub>(I)Â(PMe<sub>3</sub>)] (<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 CH<sub>3</sub>I, 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 PtÂ(II)/PtÂ(IV) 2,2′-bipyridine
cyclometalated
rollover complexes have been synthesized and characterized. [PtÂ(bpy-H)Â(CH<sub>3</sub>)Â(PMe<sub>3</sub>)] (<b>1</b>), where bpy-H = Îş<sup>2</sup><i>N</i>,<i>C</i>-2,2′-bipyridine,
was
obtained from the electron-rich precursor <i>cis</i>-[PtÂ(CH<sub>3</sub>)<sub>2</sub>(DMSO)<sub>2</sub>] with a one-pot, two step
synthesis; its reactivity has been tested with CH<sub>3</sub>I, giving
the corresponding PtÂ(IV) complex <i>cis</i>-[PtÂ(bpy-H)Â(CH<sub>3</sub>)<sub>2</sub>(I)Â(PMe<sub>3</sub>)] (<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 CH<sub>3</sub>I, usually thought of as the <i>kinetic</i> product
Mesoionic Complexes of Platinum(II) Derived from “Rollover” Cyclometalation: A Delicate Balance between Pt–C(sp<sup>3</sup>) and Pt–C(sp<sup>2</sup>) 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 [PtÂ(bipy-H)Â(Me)Â(L)] (L =
PPh<sub>3</sub>, PCy<sub>3</sub>, PÂ(OPh)<sub>3</sub>, PÂ(<i>p</i>-tolyl)<sub>3</sub>), whose protonation produces a series of stable
corresponding pyridylenes [PtÂ(bipy*)Â(Me)Â(L)]<sup>+</sup>. 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 [PtÂ(bipy)Â(Me)Â(L)]<sup>+</sup>, 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 (PCy<sub>3</sub>) providing the fastest reaction.
The mesoionic species [PtÂ(bipy*)Â(Me)Â(L)]<sup>+</sup> contain two Pt–C
bonds: the balance between the Pt–CÂ(sp<sup>2</sup>) and Pt–CÂ(sp<sup>3</sup>) 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
[PtÂ(bipy-H)Â(L)Â(L′)]<sup>+</sup>, whereas reaction of the neutral
[PtÂ(bipy-H)Â(Me)Â(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)Âquinoline, L, allowed the
synthesis of the family of complexes [PtÂ(L-H)Â(X)Â(L′)] and [PtÂ(L*)Â(X)Â(L′)]Â[BF<sub>4</sub>] (X = Me, Cl; L′ = neutral ligand), the former being
the first examples of PtÂ(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
[PtÂ(L-H)Â(Me)Â(L′)]/[PtÂ(L*)Â(Me)Â(L′)]<sup>+</sup> 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, PPh<sub>3</sub>). The crystal structures of [PtÂ(L-H)Â(Me)Â(PPh<sub>3</sub>)], [PtÂ(L-H)Â(Me)Â(CO)]
and [PtÂ(L*)Â(Me)Â(CO)]Â[BF<sub>4</sub>] were determined by X-ray powder
diffraction methods, the latter being the first structure of a PtÂ(II)-based,
protonated, rollover complex to be unraveled. The isomerization of
[PtÂ(L*)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup> in solution proceeds through
a retro-rollover process to give the corresponding adduct [PtÂ(L)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup>, 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–CÂ(heteroaryl) bond is cleaved
rather than a Pt–CÂ(alkyl) one
Rollover Cyclometalation with 2‑(2′-Pyridyl)quinoline
Rollover
cyclometalation of 2-(2′-pyridyl)Âquinoline, L, allowed the
synthesis of the family of complexes [PtÂ(L-H)Â(X)Â(L′)] and [PtÂ(L*)Â(X)Â(L′)]Â[BF<sub>4</sub>] (X = Me, Cl; L′ = neutral ligand), the former being
the first examples of PtÂ(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
[PtÂ(L-H)Â(Me)Â(L′)]/[PtÂ(L*)Â(Me)Â(L′)]<sup>+</sup> 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, PPh<sub>3</sub>). The crystal structures of [PtÂ(L-H)Â(Me)Â(PPh<sub>3</sub>)], [PtÂ(L-H)Â(Me)Â(CO)]
and [PtÂ(L*)Â(Me)Â(CO)]Â[BF<sub>4</sub>] were determined by X-ray powder
diffraction methods, the latter being the first structure of a PtÂ(II)-based,
protonated, rollover complex to be unraveled. The isomerization of
[PtÂ(L*)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup> in solution proceeds through
a retro-rollover process to give the corresponding adduct [PtÂ(L)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup>, 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–CÂ(heteroaryl) bond is cleaved
rather than a Pt–CÂ(alkyl) one
Rollover Cyclometalation with 2‑(2′-Pyridyl)quinoline
Rollover
cyclometalation of 2-(2′-pyridyl)Âquinoline, L, allowed the
synthesis of the family of complexes [PtÂ(L-H)Â(X)Â(L′)] and [PtÂ(L*)Â(X)Â(L′)]Â[BF<sub>4</sub>] (X = Me, Cl; L′ = neutral ligand), the former being
the first examples of PtÂ(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
[PtÂ(L-H)Â(Me)Â(L′)]/[PtÂ(L*)Â(Me)Â(L′)]<sup>+</sup> 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, PPh<sub>3</sub>). The crystal structures of [PtÂ(L-H)Â(Me)Â(PPh<sub>3</sub>)], [PtÂ(L-H)Â(Me)Â(CO)]
and [PtÂ(L*)Â(Me)Â(CO)]Â[BF<sub>4</sub>] were determined by X-ray powder
diffraction methods, the latter being the first structure of a PtÂ(II)-based,
protonated, rollover complex to be unraveled. The isomerization of
[PtÂ(L*)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup> in solution proceeds through
a retro-rollover process to give the corresponding adduct [PtÂ(L)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup>, 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–CÂ(heteroaryl) bond is cleaved
rather than a Pt–CÂ(alkyl) one
Rollover Cyclometalation with 2‑(2′-Pyridyl)quinoline
Rollover
cyclometalation of 2-(2′-pyridyl)Âquinoline, L, allowed the
synthesis of the family of complexes [PtÂ(L-H)Â(X)Â(L′)] and [PtÂ(L*)Â(X)Â(L′)]Â[BF<sub>4</sub>] (X = Me, Cl; L′ = neutral ligand), the former being
the first examples of PtÂ(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
[PtÂ(L-H)Â(Me)Â(L′)]/[PtÂ(L*)Â(Me)Â(L′)]<sup>+</sup> 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, PPh<sub>3</sub>). The crystal structures of [PtÂ(L-H)Â(Me)Â(PPh<sub>3</sub>)], [PtÂ(L-H)Â(Me)Â(CO)]
and [PtÂ(L*)Â(Me)Â(CO)]Â[BF<sub>4</sub>] were determined by X-ray powder
diffraction methods, the latter being the first structure of a PtÂ(II)-based,
protonated, rollover complex to be unraveled. The isomerization of
[PtÂ(L*)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup> in solution proceeds through
a retro-rollover process to give the corresponding adduct [PtÂ(L)Â(Me)Â(PPh<sub>3</sub>)]<sup>+</sup>, 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–CÂ(heteroaryl) bond is cleaved
rather than a Pt–CÂ(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 platinumÂ(II) rollover
complexes [PtÂ(bipy-H)Â(L)ÂCl] (bipy-H = 2,2′-bipyridine C(3′)-N
cyclometalated, L= DMSO, PPh<sub>3</sub>) a second rollover cyclometalation
may produce a series of PtÂ(II)/PdÂ(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 platinumÂ(II) rollover
complexes [PtÂ(bipy-H)Â(L)ÂCl] (bipy-H = 2,2′-bipyridine C(3′)-N
cyclometalated, L= DMSO, PPh<sub>3</sub>) a second rollover cyclometalation
may produce a series of PtÂ(II)/PdÂ(II) heterobimetallic complexes where
the two metals are linked by the planar, highly delocalized, doubly
deprotonated 2,2′-bipyridine