Synthesis, Structure, and Electronic Properties of Monomeric and Dimeric Trispyrazolylborate Platinum(II) Hydride Complexes

Reinartz, Stefan; Baik, Mu‐Hyun; White, Peter S.; Brookhart, Maurice; Templeton, Joseph L.

doi:10.1021/ic010099q

Cited by 41 publications

(46 citation statements)

References 92 publications

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“…Moreover, the nitrogen atom of the pendant pyrazolyl ring is well situated to activate a water molecule for concerted attack on the CO ligand, as shown in A. The structure of B is supported by related reports [31,32] and by our previous observation that 1 is quantitatively converted into 6 under acidic conditions. [20] Possible reaction pathways: Scheme 2 presents three possible pathways for the formation of a s-CH 4 intermediate from B.…”

Section: Resultssupporting

confidence: 66%

Proton Walk in the Aqueous Platinum Complex [TpPtMeCO] via a Sticky σ‐Methane Ligand

Lo¹,

Iron²,

Martin³

et al. 2007

Chemistry A European J

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Both experimental and theoretical evidence suggest that the proton exchange between water and the methyl group in [TpPt(CO)CH(3)] (1, Tp=hydridotripyrazolylborate) involves the formation and deprotonation of a "sticky" sigma-methane ligand. The efficiency of this nontrivial process has been attributed to the spatial orientation of functional groups that operate in concert to activate a water molecule and then achieve a multistep proton walk from water to an uncoordinated pyrazolyl nitrogen atom, to the methyl ligand, and then back to the nitrogen atom and water. The overall proton-exchange process has been proposed to involve an initial attack of water at the CO ligand in 1 with concerted deprotonation by the uncoordinated pyrazolyl nitrogen atom. The pyrazolium proton is then transferred to the Pt--CH(3) bond, leading to a sigma-methane intermediate. Subsequent rotation and deprotonation of the sigma-methane ligand, followed by reformation of 1 and water, result in scrambling of the methyl protons with the hydrogen atoms of water. An alternative two-step process that involves oxidative addition and reductive elimination has also been considered. The two competing mechanistic routes from 1 into [D(3)]-1, as well as the conversion of 1 into [TpPt(CH(3))H(2)] (2), have been examined by density functional theory (DFT) using a variety of exchange-correlation methods, primarily PW6B95, which was recently shown to be highly accurate for evaluating reactions of late-transition-metal complexes. The key role played by the free pyrazolyl nitrogen atom, acting as a proton carrier that abstracts a proton from water and transfers the proton to the Pt--CH(3) bond, is reminiscent of the dual functionality of histidine in the catalytic triad of natural serine proteases.

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Section: Resultssupporting

confidence: 66%

Proton Walk in the Aqueous Platinum Complex [TpPtMeCO] via a Sticky σ‐Methane Ligand

Lo¹,

Iron²,

Martin³

et al. 2007

Chemistry A European J

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“…21 Note that some of the known platinum olefin hydride complexes may be better described as β-agostic alkyl complexes. [22][23][24][25] Many of the platinum olefin hydride complexes are stabilized by attachment of the olefin to an ancillary ligand, 26,27 are cationic, 22,23,[28][29][30][31] or adopt a pseudosix-coordinate Pt(II) environment. 32,33 Only one type of neutral, four-coordinate platinum olefin hydride complex supported by a chelating nitrogen-based ligand has been isolated.…”

Section: Resultsmentioning

confidence: 99%

“…Complex 5 may result from β-hydrogen elimination from an azaplatinacyclobutane (following dissociation of the amino group to generate an open coordination site) and is of interest in that few platinum olefin hydride complexes have been isolated, due to the ease with which they undergo migratory insertion . Note that some of the known platinum olefin hydride complexes may be better described as β-agostic alkyl complexes. − Many of the platinum olefin hydride complexes are stabilized by attachment of the olefin to an ancillary ligand, , are cationic, ,,− or adopt a pseudo-six-coordinate Pt(II) environment. , Only one type of neutral, four-coordinate platinum olefin hydride complex supported by a chelating nitrogen-based ligand has been isolated. − For example, the diiminate complex [{( o -Me 2 - p - t Bu-C 6 H 2 )NC(Me)} 2 CH]Pt(H)(CH 2 CH t Bu) possesses a 1 H NMR resonance for the hydride ligand at −21.5 ppm ( J PtH = 1185 Hz), which is comparable to the value associated with 5 (−20.68 ppm) …”

Section: Resultsmentioning

confidence: 99%

Nucleophilic Attack of Amides onto Coordinated Ethylene in Platinum Complexes Supported by a Chelating Pyridyl−Pyrrolide Ligand: Azaplatinacyclobutane and Vinylamine Complexes

McBee

Tilley

2009

Organometallics

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The platinum ethylene complexes (PyPyr)Pt(C 2 H 4 )Cl (1) and (PyPyr)Pt(C 2 H 4 )OTf (4) (PyPyr = 3,5-diphenyl-2-(2-pyridyl)pyrrolide) were treated with 1 equiv of LiN(SiMe 3 ) 2 , LiN i Pr 2 , and LiNH-(o-xylyl) to produce the platinum complexes (PyPyr)PtH[η 2 -CH 2 dCHN(SiMe 3 ) 2 ] (5), (PyPyr)Pt[κ 2 C,N-(CH 2 CH 2 N i Pr 2 )] (6), and (PyPyr)Pt{κ 2 C,N-[CH 2 CH 2 NH(o-xylyl)]} (7), respectively. X-ray crystallography reveals that 7 adopts a square-planar geometry at the platinum center and the azaplatinacyclobutane ring displays a puckering of the β-carbon out of planarity by 0.270 Å . Thermolysis of 5 and 7 at 60°C for 16 h releases the vinylamines (CH 2 dCH)N(SiMe 3 ) 2 and (CH 2 dCH)NH(o-xylyl), respectively. Heating 5 and 7 under 1 atm of H 2 at 60°C releases the ethylamines EtN(SiMe 3 ) 2 and EtNH(o-xylyl), respectively. Addition of P i Pr 3 to 7 produces (PyPyr)Pt(P i Pr 3 )[CH 2 CH 2 NH(o-xylyl)] (8) in 95% yield, while additions of 1 equiv of a Lewis base (L) to 1 result in displacement of ethylene to give (PyPyr)Pt(L)Cl (L = NEt 3 (9), NH 2 Ph (10), P i Pr 3 (11)). The amido complex (PyPyr)Pt(P i Pr 3 )[NH(o-xylyl)] (12) results from treament of 11 with LiNH(o-xylyl), and 12 does not undergo ethylene insertion into the Pt-N bond under 1 atm of C 2 H 4 at 120°C over 3 days. Addition of 1 equiv of LiNH(o-xylyl) to (PyPyr)Pt(SMe 2 )Cl (2) produces the μ-amido-bridged dimer [(PyPyr)Pt(μ-NH(o-xylyl))] 2 (13), and treatment of 13 with 2 equiv of i Pr 3 P produces 12. These reactivity studies are consistent with a mechanism for the formation of 5-7 involving nucleophilic attack of an amide onto coordinated olefin.

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“…Although some of these compounds have been prepared by halogen [58] or methide [74] abstraction as described above, the vast majority of the Pt(II) derivatives stabilized by solvent molecules have been obtained by protonation of neutral alkyl, aryl or hydride Pt(II), as shown in Scheme 8 (see for example: [55,59–60 63,67,69,72,77–81]), or Pt(IV) complexes [96–98]. Nonetheless, this method has not yet been exploited for the preparation of true 14-electron species or agostic stabilized derivatives.…”

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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Synthesis, Structure, and Electronic Properties of Monomeric and Dimeric Trispyrazolylborate Platinum(II) Hydride Complexes

Cited by 41 publications

References 92 publications

Proton Walk in the Aqueous Platinum Complex [TpPtMeCO] via a Sticky σ‐Methane Ligand

Proton Walk in the Aqueous Platinum Complex [TpPtMeCO] via a Sticky σ‐Methane Ligand

Nucleophilic Attack of Amides onto Coordinated Ethylene in Platinum Complexes Supported by a Chelating Pyridyl−Pyrrolide Ligand: Azaplatinacyclobutane and Vinylamine Complexes

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

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