Reactivity of [Pt(P t Bu3)2] with Zinc(I/II) Compounds: Bimetallic Adducts, Zn-Zn Bond Cleavage, and Cooperative Reactivity.

Nereida Hidalgo,Israel Fernández,Carlos Romero-Pérez,Celia Maya,Jesús Campos

doi:10.1021/acs.organomet.1c00088

Nereida Hidalgo, Israel Fernández + Show 3 more

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https://doi.org/10.1021/acs.organomet.1c00088

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Abstract

Metal-only Lewis pairs (MOLPs) based on zinc electrophiles are particularly interesting due to their relevance to Negishi cross-coupling reactions. Zinc-based ligands in bimetallic complexes also render unique reactivity to the transition metals at which they are bound. Here we explore the use of sterically hindered [Pt(PtBu3)2] (1) to access Pt/Zn bimetallic complexes. Compounds [(PtBu3)2Pt → Zn(C6F5)2] (2) and [Pt(ZnCp*)6] (3) (Cp* = pentamethylcyclopentadienyl) were isolated by reactions with Zn(C6F5)2 and [Zn2Cp*2], respectively. We also disclose the cooperative reactivity of 1/ZnX2 pairs (X = Cl, Br, I, and OTf) toward water and dihydrogen, which can be understood in terms of bimetallic frustration.

Highlights

The unique features of bimetallic complexes are behind the rapid development that has recently taken place in the field.[1]
metal-only Lewis pairs (MOLPs) constructed around Lewis acidic zinc(II) fragments are appealing due to their relevance to Negishi cross-coupling catalysis
Pt(II) compounds is accelerated upon Zn(C6F5)[2] coordination,[6] while Whittlesey and Macgregor have explored a heterobimetallic Ru/Zn compound and demonstrated that the unsaturated “ZnMe” terminus promotes C−H reductive elimination and dihydrogen activation at the Ru(II) site.[7]

Summary

■ INTRODUCTION

The unique features of bimetallic complexes are behind the rapid development that has recently taken place in the field.[1]. We determined the kinetic isotopic effect (KIE) for H2 versus D2 splitting, which has a strong inverse value of 0.59 ± 0.1 (see the Supporting Information for details) This is an uncommon finding[25] that compares well with our previously reported Pt(0)/Au(I) bimetallic FLP (KIE = 0.46 ± 0.04), where a genuine frustrated mechanism was ascertained.19b We postulated that the origin for such a strong inverse KIE derived from an FLP productlike transition state whose bimetallic structure offered an assortment of H-containing bending modes that contribute to the zero-point energy (ZPE). Compound [PtH(PtBu3)2]+, which would be an intermediate during FLP-type H2 activation, promotes H/D scrambling at a rate comparable to the bimetallic pair This agrees with its existence as a transient intermediate during the hydrogenation of 1, supporting the idea of a bimetallic FLP mechanism (through B in Scheme 5).

■ ACKNOWLEDGMENTS

■ REFERENCES