Ligand Metalation in Triisopropylphosphine−Platinum(II) Compounds

Thorn, David L.

doi:10.1021/om970759s

Cited by 28 publications

(25 citation statements)

References 8 publications

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“…However, the addition of THF rapidly traps the T-shaped complex forming the adduct 14 (Scheme 13). This species does undergo cyclometalation in the presence of trace amounts of acids to yield 16 [116]. The unsaturated agostic species 15 has been proposed as a reaction intermediate.…”

Section: Reviewmentioning

confidence: 99%

True and masked three-coordinate T-shaped platinum(II) intermediates

Ortuño¹,

Conejero²,

Lledós³

2013

Beilstein J. Org. Chem.

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SummaryAlthough four-coordinate square-planar geometries, with a formally 16-electron counting, are absolutely dominant in isolated Pt(II) complexes, three-coordinate, 14-electron Pt(II) complexes are believed to be key intermediates in a number of platinum-mediated organometallic transformations. Although very few authenticated three-coordinate Pt(II) complexes have been characterized, a much larger number of complexes can be described as operationally three-coordinate in a kinetic sense. In these compounds, which we have called masked T-shaped complexes, the fourth position is occupied by a very weak ligand (agostic bond, solvent molecule or counteranion), which can be easily displaced. This review summarizes the structural features of the true and masked T-shaped Pt(II) complexes reported so far and describes synthetic strategies employed for their formation. Moreover, recent experimental and theoretical reports are analyzed, which suggest the involvement of such intermediates in reaction mechanisms, particularly C–H bond-activation processes.

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Section: Reviewmentioning

confidence: 99%

True and masked three-coordinate T-shaped platinum(II) intermediates

Ortuño¹,

Conejero²,

Lledós³

2013

Beilstein J. Org. Chem.

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“…88 (2005) 517 ward as for the kinetics of ligand dissociation, because they cannot be assigned to a single step, and cannot discriminate between the two most-conceivable reaction mechanisms, electrophilic attack and oxidative addition. The electrophilic-attack mechanism is a very common pathway for cyclopalladation and has been proposed occasionally also for Pt II chemistry [18]. It does not require formation of a metal hydride, the central atom does not change oxidation number, and the H-atom dissociates as a free or a bound proton (Scheme 4).…”

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confidence: 99%

A Dissociative Route to CH Bond Activation: Ligand Cyclometalation in cis‐Dimethyl[(sulfinyl‐κS)bis[methane]][tris(2‐methylphenyl)phosphine]platinum(2+)

Romeo

Plutino

Romeo

2005

Helvetica Chimica Acta

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Dedicated to Prof. AndreÂ E. Merbach in recognition of his prominent contribution to the advancement of inorganic and organometallic reaction mechanismsThe dialkyl compound cis-dimethyl [(sulfinyl-kS)bis [methane]][tris(2-methylphenyl)phosphine]platinum(2 ) (cis-[Pt(Me) 2 (dmso)(P(o-tol) 3 ]; 1) has been isolated from the reaction of cis-dimethylbis[(sulfinylkS)bis [methane]]platinum(2 ) (cis-[Pt(Me) 2 (dmso) 2 ]) with tris(2-methylphenyl)phosphane (P(o-tol) 3 ). Restricted rotation around the PÀC ipso bonds of the phosphane ligand generates two different conformers, 1a and 1b, in rapid exchange in non-polar solvents at low temperature. Strong through-space contacts between the ortho-Me substituent groups on the ligand and the cis-Me groups in the coordination plane were determined, which proved useful for identifying the atropisomers formed. At room temperature, 1 H-NMR spectra of 1 maintain a static pattern upon onset of easy and rapid ortho-platination,, a new C,P-cyclometalated compound of platinum(II), with liberation of methane. The process has been studied by 1 H-and 31 P{ 1 H}-NMR in CDCl 3 , and kinetics experiments were performed by conventional spectrophotometric techniques. The first-order rate constants k c decrease with the addition of dimethyl sulfoxide until the process is blocked by the presence of a sufficient excess of sulfoxide. This behavior reveals a mechanism initiated by ligand dissociation and formation of a three-coordinate species. The value of the rate constant for dimethyl sulfoxide dissociation k 1 has been measured independently over a wide temperature range by both 1 H-NMR ligand exchange (isotopic labeling experiments) and ligand substitution (stopped-flow pyridine for dimethyl sulfoxide substitution). The rates of the two processes are in reasonable agreement at the same temperature, and a single Eyring plot can be constructed with the two sets of kinetics data. However, the value of the derived dissociation constant at 308 K (k 1 6.5 AE 0.3 s À1) is at least two orders of magnitude higher than that of cyclometalation (k c 0.0098 AE 0.0009 s À1 at 308 K). Clearly, the dissociation step is not rate-determining for cyclometalation. A multistep mechanism consistent with mass-law retardation is derived, which involves a pre-equilibrium that controls the concentration of an unsaturated three-coordinate, 14-electron T-shaped cis-[PtMe 2 {P(o-tol) 3 }] intermediate. Cyclometalation is initiated in this latter by an agostic interaction with the s(CÀH) orbital of a methyl group. Oxidative addition of the CÀH bond follows, yielding a cyclometalated-hydrido 16-electron Pt(IV) fivecoordinate intermediate. Finally, reductive elimination and re-entry of dimethyl sulfoxide with liberation of methane should yield the cyclometalated species 2.

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“…Isolated sigma or agostic CH interactions such as that observed in 8 b (and further confirmed in 9 ), which then undergo CH activation are relatively rare, especially for late transition metals 22. 27b, 29, 39, 40, 51 This coupled with the Rh III oxidation state in the starting material that would disfavour an oxidative addition route prompted us to investigate the mechanism of this CH activation process by using computational methods.…”

Section: Resultsmentioning

confidence: 93%

“…The downfield shift of these compared with the free ligand is consistent with a cyclometallated alkyl group. [22,27] Although we have not been able to unambiguously assign these resonances to specific CH 2 groups, it is most likely that they belong to the diastereotopic protons on either C1 or C3 ( Figure 3) because they are absent in the spectra of 4, 5 and 6. Two isomeric species in an approximate 1:2 ratio are also observed in the 31 P{ 1 H} NMR spectrum as a set of doublet of doublets showing cis 31 P-31 P coupling, as well as coupling to the Rh III centre (J- Hz).…”

Section: Resultsmentioning

confidence: 93%

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Reactivity of the Latent 12‐Electron Fragment [Rh(PiBu₃)₂]⁺ with Aryl Bromides: ArylBr and Phosphine Ligand CH Activation

Townsend

Chaplin

Naser

et al. 2010

Chemistry A European J

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Oxidative addition of aryl bromides to 12-electron [Rh(PiBu(3))(2)][BAr(F)(4)] (Ar(F)=3,5-(CF(3))(2)C(6)H(3)) forms a variety of products. With p-tolyl bromides, Rh(III) dimeric complexes result [Rh(PiBu(3))(2)(o/p-MeC(6)H(4))(mu-Br)](2)[BAr(F)(4)](2). Similarly, reaction with p-ClC(6)H(4)Br gives [Rh(PiBu(3))(2)(p-ClC(6)H(4))(mu-Br)](2)[BAr(F)(4)](2). In contrast, the use of o-BrC(6)H(4)Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C-H activation: [Rh{PiBu(2)(CH(2)CHCH(3)CH(2))}(PiBu(3))(mu-Br)](2)[BAr(F)(4)](2). Trapping experiments with ortho-bromo anisole or ortho-bromo thioanisole indicate that a possible intermediate for this process is a low-coordinate Rh(III) complex that then undergoes C-H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rh(PiBu(3))(2)(C(6)H(4)OMe)Br][BAr(F)(4)] (the solid-state structure of the 5-methyl substituted analogue is reported) and [Rh(PiBu(3))(2)(C(6)H(4)SMe)Br][BAr(F)(4)]. The anisole-derived complex proceeds to give [Rh{PiBu(2)(CH(2)CHCH(3)CH(2))}(PiBu(3))(mu-Br)](2)[BAr(F)(4)](2), whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu(3))(2)(C(6)H(4)OMe)Br][BAr(F)(4)] and its onward reactivity to give the products of C-H activation and aryl elimination suggest that it is implicated on the pathway of a sigma-bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C-H bond cleavage through phosphine-assisted deprotonation of a non-agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C-H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid-state by X-ray crystallography.

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Ligand Metalation in Triisopropylphosphine−Platinum(II) Compounds

Cited by 28 publications

References 8 publications

True and masked three-coordinate T-shaped platinum(II) intermediates

True and masked three-coordinate T-shaped platinum(II) intermediates

A Dissociative Route to CH Bond Activation: Ligand Cyclometalation in cis‐Dimethyl[(sulfinyl‐κS)bis[methane]][tris(2‐methylphenyl)phosphine]platinum(2+)

Reactivity of the Latent 12‐Electron Fragment [Rh(PiBu₃)₂]⁺ with Aryl Bromides: ArylBr and Phosphine Ligand CH Activation

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Ligand Metalation in Triisopropylphosphine−Platinum(II) Compounds

Cited by 28 publications

References 8 publications

True and masked three-coordinate T-shaped platinum(II) intermediates

True and masked three-coordinate T-shaped platinum(II) intermediates

A Dissociative Route to CH Bond Activation: Ligand Cyclometalation in cis‐Dimethyl[(sulfinyl‐κS)bis[methane]][tris(2‐methylphenyl)phosphine]platinum(2+)

Reactivity of the Latent 12‐Electron Fragment [Rh(PiBu3)2]+ with Aryl Bromides: ArylBr and Phosphine Ligand CH Activation

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Reactivity of the Latent 12‐Electron Fragment [Rh(PiBu₃)₂]⁺ with Aryl Bromides: ArylBr and Phosphine Ligand CH Activation