Neighboring group effects on the stability of azaplatinacyclobutane rings in (2-aminoethyl)platinum(II) compounds

Green, Michael; Sarhan, Jamil K. K.; Al‐Najjar, Ibrahim M.

doi:10.1021/om00082a002

Cited by 19 publications

(17 citation statements)

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“…XLVII). Metallaazacyclobutadiene complexes of Pt II were indeed obtained by deprotonation of zwitterionic products resulting from the addition of basic amines to coordinated ethylene or other olefins (process A (or C) → F → D in Scheme 3), 84,88 some of them being crystallographically characterized. 86,89,90 Our study confirms the accessibility of these derivatives under appropriate experimental conditions, but shows that they are only off-loop species and not catalytic intermediates (none of these complexes leads to product liberation by a low-energy pathway), at least for the aniline addition to ethylene with this PtBr2/Brcatalytic system.…”

Section: Discussionmentioning

confidence: 99%

“…The N-H•••Pt bond (A) could generate a Pt IV hydride complex by proton transfer to the Pt atom (B), whereas the N-H•••Br bond (C) could promote HBr elimination as PhNH2 + Br -, leading to chelation of the CH2CH2NHPh ligand to generate a platinaazacyclobutane derivative (D), although the latter could also occur in two steps, promoted by an external base. Examples of this process were reported for derivatives of type cis-PtCl2(C2H4)(Y) (Y = PR3, py, NH3, am, DMSO),84,[86][87][88]…”

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confidence: 99%

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The Pt-Catalyzed Ethylene Hydroamination by Aniline: A Computational Investigation of the Catalytic Cycle

Dub

Poli

2010

J. Am. Chem. Soc.

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A full QM DFT study without system simplification and with the inclusion of solvation effects in aniline as solvent has addressed the addition of aniline to ethylene catalyzed by PtBr(2)/Br(-). The resting state of the catalytic cycle is the [PtBr(3)(C(2)H(4))](-) complex (II). A cycle involving aniline activation by N-H oxidative addition was found energetically prohibitive. The operating cycle involves ethylene activation followed by nucleophilic addition of aniline to the coordinated ethylene, intramolecular transfer of the ammonium proton to the metal center to generate a 5-coordinate (16-electron) Pt(IV)-H intermediate, and final reductive elimination of the PhNHEt product. Several low-energy ethylene complexes, namely trans- and cis-PtBr(2)(C(2)H(4))(PhNH(2)) (IV and V) and trans- and cis-PtBr(2)(C(2)H(4))(2) (VII and VIII) are susceptible to aniline nucleophilic addition to generate zwitterionic intermediates. However, only [PtBr(3)CH(2)CH(2)NH(2)Ph](-) (IX) derived from PhNH(2) addition to II is the productive intermediate. It easily transfers a proton to the Pt atom to yield [PtHBr(3)(CH(2)CH(2)NHPh)](-) (XX), which leads to rate-determining C-H reductive elimination through transition state TS(XX-L) with formation of the σ-complex [PtBr(3)(κ(2):C,H-HCH(2)CH(2)NHPh)](-) (L), from which the product can be liberated via ligand substitution by a new C(2)H(4) molecule to regenerate II. Saturated (18-electron) Pt(IV)-hydride complexes obtained by ligand addition or by chelation of the aminoalkyl ligand liberate the product through higher-energy pathways. Other pathways starting from the zwitterionic intermediates were also explored (intermolecular N deprotonation followed by C protonation or chelation to produce platina(II)azacyclobutane derivatives; intramolecular proton transfer from N to C, either direct or assisted by an external aniline molecule) but all gave higher-energy intermediates or led to the same rate-determining TS(XX-L).

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

The Pt-Catalyzed Ethylene Hydroamination by Aniline: A Computational Investigation of the Catalytic Cycle

Dub

Poli

2010

J. Am. Chem. Soc.

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“…The reactions of amines with platinum π-alkene complexes to form β-ammonioethanide, and in some cases azaplatinacyclobutane, complexes have been investigated for over 40 years, although never in the context of an intramolecular C–N bond forming event. − The reaction of a nitrogen nucleophile with a platinum(II) π-alkene complex to form a zwitterionic β-ammonioethanide complex was first reported in 1968 by Orchin, who demonstrated the reversible formation of PtCl 2 (Py) (CH 2 CH 2 Py) via reaction of pyridine with platinum ethylene complex PtCl 2 (pyridine)(π-H 2 CCH 2 ) . Panunzi and co-workers investigated the stoichiometric reactions of alkylamines with Pt(II) diene and monoolefin complexes and established the anti stereochemistry and outer-sphere nature of C–N bond formation .…”

Section: Resultsmentioning

confidence: 99%

“…Although the reactions of alkylamines with platinum π-alkene complexes have been investigated, − the systems under investigation were not competent hydroamination catalysts. Rather, extant studies of platinum-catalyzed alkene hydroamination are restricted to transformations employing less basic nitrogen nucleophiles.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of the Platinum(II)-Catalyzed Hydroamination of 4-Pentenylamines

2016

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The mechanism of the platinum(II)-catalyzed intramolecular hydroamination of benzyl 4-pentenylamines has been evaluated under stoichiometric and catalytic conditions. Reaction of a benzyl 2,2-disubstituted 4-pentenylamine with [(PPh 3 )Pt(μ-Cl)Cl] 2 forms a thermally sensitive platinum amine complex that undergoes irreversible, intramolecular ligand exchange with the pendant CC bond to form a reactive platinum π-alkene complex. The π-alkene complex undergoes rapid, outer-sphere C−N bond formation, evidenced by the anti addition of Pt and N across the complexed CC bond, to form a thermally stable zwitterionic platinamethylpyrrolidinium complex. The zwitterionic complex is rapidly and exergonically deprotonated by free amine to form a neutral, bicyclic azaplatinacyclobutane complex that likely exists as a discrete 1:1 adduct with ammonium salt in the nonpolar reaction medium and that represents the resting state of the catalytic cycle. Turnover-limiting intramolecular protodemetalation of the azaplatinacyclobutane−ammonium adduct followed by ligand exchange releases the 2-methylpyrrolidine product.

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“…[16][17][18][19][20][21][22][23] In particular, amines (am) add to [PtCl2Y(C2H4)] (Y = Cl -, DMSO, amine, phosphine) to yield [Pt (-) Cl2Y(CH2CH2am (+) )] which then may evolve in different ways depending on the nature of the amine and Y. [24][25][26][27][28][29][30][31][32][33][34][35][36] For complexes of type trans-[PtCl2(C2H4)(am)], the observation of the zwitterionic product, which included an X-ray crystallographically characterized example, 26 was limited to amines of high basicity, in agreement with our observations for the bromide analogues.…”

Section: Introductionmentioning

confidence: 99%

Platinum-Catalyzed Hydroamination of Ethylene: Study of the Catalyst Decomposition Mechanism

2013

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A study of the addition of nucleophilic reagents that are also strong Brønsted bases (Et3N, pyridine, quinuclidine, MeO -) to nBu4P + [PtBr3(C2H4)] -(1) and trans-[PtBr2(NHEt2)(C2H4)] (7) has provided key information on the deactivation of the hydroamination PtBr2/Brcatalyst, leading to metallic platinum. The addition of NEt3 to 1 in CD2Cl2 is reversible and temperature dependent; the quantitative formation of the zwitterionic complex trans-[Pt (-) Br2( NEt3)-(CH2CH2N (+) Et3)] ( 9) is observed only at low temperature whereas slow deposition of metallic platinum occurs at room temperature. The addition of NEt3 to 7 in CD2Cl2 is also reversible and temperature dependent, yielding trans-[Pt (-) Br2(NHEt2)(CH2CH2N (+) Et3)] (10) quantitatively at low temperature. At room temperature, this reaction led to the deposition of metallic platinum and to the formation of a complex identified as trans-[PtBr2(NHEt2)(CH2CHNEt2)] (11). The carbyl ligand in 11 is shown by an X-ray structural study to be in-between the π-bonded enamine and the σ-bonded iminiumalkyl configurations. The addition of MeONa to 7 results in the formation of the same products 11 and Pt 0 . On the basis of these results, a mechanism for the base-induced decomposition of Pt II (C2H4) complexes that involves Wacker-type β-H elimination followed by intermolecular hydride transfer, ligand rearrangements and final deprotonation is proposed. Addition of more nucleophilic N-based ligands (pyridine, quinuclidine) to 7 ultimately leads to C2H4 and Et2NH substitution rather than to metal reduction, even though evidence for a kinetically controlled nucleophilic addition to the coordinated ethylene is given by the quinuclidine system. From the reaction with pyridine, complex cis-PtBr2(py)2 was isolated and structurally characterized.

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Neighboring group effects on the stability of azaplatinacyclobutane rings in (2-aminoethyl)platinum(II) compounds

Cited by 19 publications

References 0 publications

The Pt-Catalyzed Ethylene Hydroamination by Aniline: A Computational Investigation of the Catalytic Cycle

The Pt-Catalyzed Ethylene Hydroamination by Aniline: A Computational Investigation of the Catalytic Cycle

Mechanism of the Platinum(II)-Catalyzed Hydroamination of 4-Pentenylamines

Platinum-Catalyzed Hydroamination of Ethylene: Study of the Catalyst Decomposition Mechanism

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