Abstract
Ligand 2-diphenylphosphinothiophenol (Hsarp) reacted with Pt(PPh3)4 to yield trans-[PtH(sarp)(PPh3)], which undergoes fast exchange with free PPh3 on the NMR time scale and very slowly and reversibly formed some cis-[PtH(sarp)(PPh3)] over time in solution (11%, 24 h). Reaction of trans-[PtH(sarp)(PPh3)] with Hsarp in boiling toluene gave cis- and trans-[Pt(sarp)2]; the cis isomer being more stable. These complexes were characterized by (1)H and (31)P NMR and also analyzed by XRD in the case of trans-[PtH(sarp)(PPh3)], trans-[Pt(sarp)2], and cis-[Pt(sarp)2]. trans-[PtH(sarp)(PPh3)] was evaluated as a preformed, tin-free hydroformylation catalyst on styrene and found active at 100 °C, at pressures over 75 bar, yielding phenylpropanal (regioselectivities up to 83% in 2-phenylpropanal), with total conversions to aldehydes up to 100% at styrene/platinum ratios from 400/1 to 1000/1 and minimal hydrogenation products.
Highlights
Phosphinothiolato ligands behave as soft–soft chelates with very different donors in terms of size, electronic properties and Brønsted basicity
As part of a project on the synthesis of new amino- and phosphino-thiolates of group 10 metals, and on the analysis of the ligand-based stereoelectronic effects that are determinant in their properties and potential applications,2b,12 we report on platinum 2-diphenylphosphinothiophenolato complexes, their synthesis and structural features and the first tests as homogeneous, tin halide free hydroformylation catalysts.[13]
Ligands Hsarp and Hsarp′ readily reacted with Pt(PPh3)[4] to give hydride complexes trans-[PtH(sarp)(PPh3)]
Summary
Phosphinothiolato ligands behave as soft–soft chelates with very different donors in terms of size, electronic properties and Brønsted basicity. Upon heating Hsarp with Pt(PPh3)[4] or trans-1 in toluene at 110 °C, the platinum hydride was observed to decrease in concentration with time, until all the hydride turned into cis-[Pt(sarp)2] (cis-2). The reaction of Hsarp′ with Pt(PPh3)[4] in boiling toluene gave the bischelates 5, with the difference compared to 2, that a longer time (48 h) was needed for the bulkier ligand and the product was a mixture of cis and trans isomers, containing a slight excess of the latter (Scheme 3).
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