Transmetalation of Methyl Groups Supported by Pt^II–Au^I Bonds in the Gas Phase, in Silico, and in Solution

Abstract

We report Pt(II)-to-Au(I) methyl transfer reactions that occur in the gas phase and in solution. The heterobimetallic Pt(II)/Au(I) complexes {[(dmpe)PtMe(2)][AuPR(3)]}(+) (R = Me (2a), Ph (2b), (t)Bu (2c)), observed in the gas phase by means of electrospray ionization, were subjected to collision induced dissociation (CID) from which we could observe Pt-to-Au transmetalation along two reaction pathways involving formation of a Au-Me bond, analogous to those observed for the Pt(II)/Cu(I) complex recently reported. In the first pathway, neutral AuMe is generated with concomitant migration of PR(3) from Au(I) to the Pt(II) center, forming cation [(dmpe)PtMe(PR(3))](+) (R = Me (5a) or Ph (5b)). In the second pathway, the monophosphine stays attached to the gold center, yielding cation [(dmpe)PtMe](+) (7) and R(3)PAuMe. Quantitative energy-resolved collision induced dissociation experiments as well as density functional theory (DFT) calculations were used to investigate the potential surface involved in the transmetalation processes. Energy barriers of 22.3 and 47.9 kcal mol(-1) for the two reaction processes of 2b and of 45.4 kcal mol(-1) for the single reaction process of 2c were obtained. Parallel reactivity is observed in THF solution, allowing for a comparison of the product distributions with those observed in the gas phase, and the postulation of simple steric control of the branching ratio between the two pathways. DFT calculations at the M06-2X//BP86/TZP level were in good agreement with the experiments.

Bimetallic Catalysis using Transition and Group 11 Metals: An Emerging Tool for CC Coupling and Other Reactions

“…Interestingly, the proposed transition state is supported by the existence of related compounds structurally characterized by X-ray diffraction. [60] This mechanism preceded the recent proposals of Chen for Pt/Cu and Pt/Au transmetalations, [37,38] and is also the first mechanistic precedent to the recent use of Pd/Cu and Pd/Au systems in catalysis.…”

“…More recently, similar behavior has been found with Au instead of Cu. [38] The remarkable feature in this transmetalation is the presence of Pt II ÀCu I or Pt II ÀAu I bonds supporting the transfer. The formation of TM À Au bonds had been proposed before for the Au-catalyzed isomerization of Pd complexes, discussed in the section on catalyzed isomerization involving transmetalation.…”

Unusual Metal–Metal Bonding in a Dinuclear Pt–Au Complex: Snapshot of a Transmetalation Process

“…[10] The energies associated with these two-electron interactions have been computed according to the following equation: The orbital interactions in the model complex 2 have been investigated with the EDA-NOCV method, [11] which combines the energy decomposition analysis (EDA) [12] with the natural orbitals for chemical valence (NOCV). [13] The EDA-NOCV method makes it possible to partition the total orbital interactions into pairwise contributions of the orbital interactions.…”

“…[8] The M-M interactions described above are of dative nature and are established between a basic donor metallic center and an acidic acceptor metal. A number of metals are known to fulfill this role but Pt II (d 8 ) is the donor center par excellence, [1,4,9,[14][15][16][17][18] while among the acceptors, Ag I (d 10 ) is by far the most representative example. [19,20] In contrast, very few examples of Pt II →Au I (d 10 ) have been fully characterized.…”

“…A number of metals are known to fulfill this role but Pt II (d 8 ) is the donor center par excellence, [1,4,9,[14][15][16][17][18] while among the acceptors, Ag I (d 10 ) is by far the most representative example. [19,20] In contrast, very few examples of Pt II →Au I (d 10 ) have been fully characterized. [21][22][23][24] From a structural point of view, several binding modes for the coordination of platinum (II) fragments to Lewis acidic metals are known.…”