A Quest for Atropisomerism in Cojoined Square-Planar Metal Complexes: Synthesis and Structures of Sterically Congested Diplatinum Ethynediyl Adducts
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2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The reaction of trans-[(C6F5)(p-tol3P)2Pt(Cl)] and Me2PhP (4 equiv.) afforded trans-[(C6F5)(Me2PhP)(p-tol3P)Pt(Cl)] (2, 68 %), which is combined with HCCSiEt3in HNEt2in the presence of CuI (cat., 45 C) to yield trans-[(C6F5)(Me2PhP)(p-tol3P)Pt(CCSiEt3)] (3, 62 %). The reaction of 2 and 3 in HNEt2in the presence of nBu4NF/CuCl (cat., 45 C) gave a series of PtCCPt complexes in which the two phosphine ligands have scrambled over all four positions. Preparative TLC afforded the target complex trans,trans-[(C6F5)(p-tol3P)(Me2PhP)Pt(CC)Pt(PPhMe2)(Pp-tol3)(C6F5)] (4, 2.3 %) as well as trans,trans-[(C6F5)(Me2PhP)2Pt(CC)Pt(PPhMe2)(Pp-tol3)(C6F5)] (5, 5.6 %). The crystal structures of 2, 4, and 5 were determined. The last two show much congestion about the PtCCPt linkage, and various geometrical features have been analyzed. Low-temperature1H NMR spectra of 4 were recorded with the goal of observing separate signals for the Me2PhP groups. This would indicate a diastereotopic relationship and provide strong evidence for the first atropisomers based upon cojoined square-planar complexes. However, no decoalescence was observed (CD2Cl2/95 C, CDFCl2/100 C). Together with other data, this suggests that interconversion of the putative atropisomers remains rapid on the NMR timescale at temperatures below 95 C.
