Lewis-Acidity of Trimethylplatinum(IV) with Labile Oxygen-Donor Ligands

Abstract

Trimethylplatinum(IV) systems with labile ligands and weakly coordinating anions were investigated with respect to their Lewis-acidity and their ability to act as Lewis-acidic catalysts. The Lewis-acidity of tetrameric trimethylplatinum(IV) triflate (triflate = trifluoromethanesulfonate, OTf), [{Me3PtOTf}4], toward carbonyl compounds was quantified by NMR titration with crotonaldehyde (Childs' method) in CD2Cl2. The data show moderate but significant Lewis-acidity of the trimethyl platinum(IV) center (27% of the acidity of BBr3) and commensurate (moderate) intrinsic catalytic activity of the trimethylplatinum(IV) unit. Crystals of an aldehyde adduct were obtained. X-ray crystallography shows a binuclear metal complex, [{Me3Pt(crotonaldehyde)(μ-OTf)}2]. Despite the relatively low Lewis-acidity, in the absence of oxygen-donor ligands, the trimethylplatinum(IV) is capable of decomposing the [B(ArF)4]- anion (ArF = 3,5-(CF3)2C6H3) to yield B(ArF)3, apparently via aryl abstraction. Salt metathesis reactions of [{Me3PtOTf}4] with Na[B(ArF)4] in the presence of oxygen-donor ligands lead to mixtures that are highly catalytically active in the diastereoselective Mukaiyama-aldol reaction, likely via generation of very electrophilic silicon species.

Defected and Substitutionally Doped Nanotubes: Applications in Biosystems, Sensors, Nanoelectronics, and Catalysis

“…This suggests that although the LUMO energy of the dienophile (MA) was decreased by binding, the steric demand for the productive [4+2] cycloaddition made catalysis less likely. In agreement with the literature (Hsieh et al 2007), we determined that PtMe 3 + is a viable catalyst for the Diels-Alder reaction in addition to the other model Pt complexes. The Lewis acid catalyzed cycloaddition of MA and CPD varied inversely in efficiency with catalyst bulk.…”

“…This dichotomy in reactivity can be attributed to the steric bulk of the nanotube sidewall and a decreased electron density in the reactive d-orbital of the Pt dopant atom. PtMe 3 + is a known Lewis acid catalyst (Hsieh et al 2007;Procelewska et al 2005). Hence, we considered the use of Pt-doped SWCNTs as nanocatalysts (Yeung et al 2011).…”

Theoretical Studies of Substitutionally Doped Single-Walled Nanotubes

“…Although PtMe 3 + can be a catalyst for Diels-Alder reactions [237,238], the use of Pt-doped supramolecules including buckybowls, fullerenes, and nanotubes has not yet been realized. Our investigations provide a preliminary insight into this possibility [45].…”