Pd^II- and Pt^II-mediated coupling of aryl isocyanides with N-heterocyclic thiones

Abstract

A PdII- and PtII-mediated reaction of aryl isocyanides with N-heterocyclic thiones results in a previously undescribed type of regioselectivity for ambident nucleophile addition to coordinated isocyanides.

Pyridine‐2(1H)‐thione as a Bifunctional Nucleophile in Reaction with PdII and PtII Aryl Isocyanide Complexes

“…The other one has a length of 1.242–1.271 Å, which is more consistent with the double C=N bond (1.260(1) Å) [27] . This situation was also observed earlier for complexes with azaheterocyclic thions in our previous work, [16] as well as for other deprotonated diaminocarbene complexes [28–30] . The distances between the sulfur and carbon atoms in the cyclometalated fragment are in the range 1.714(1)–1.717(1) Å and are greater than the values for the C=S double bond in the starting pyridinethione (1.692(2) Å) [31] .…”

“…The signals of the heterocyclic carbon atoms of the C=S bonds lie in the ranges 171.35–173.41 ppm being slightly downshifted in comparison to the chemical shift in initial pyridine‐2(1 H )‐thione (176.4 ppm) [20] . The 195Pt NMR spectra exhibit signals in the range from −3947 to −3938 ppm, which is close to the shifts for the other relevant Pt II deprotonated diaminocarbene complexes (−3850–(−3700) ppm) [16,21] . The assignments of the 13 C signals were performed by 1 H− 13 C HSQC and 1 H− 13 C HMBC NMR methods.…”

“…The 195Pt NMR spectra exhibit signals in the range from À 3947 to À 3938 ppm, which is close to the shifts for the other relevant Pt II deprotonated diaminocarbene complexes (À 3850-(À 3700) ppm). [16,21] The assignments of the 13 C signals were performed by 1 HÀ 13 C HSQC and 1 HÀ 13 C HMBC NMR methods.…”

“…Contrary, we found recently that the reaction of bis-(isocyanide) complexes of palladium(II) and platinum(II) with another type of nucleophiles -mercaptoazoles -proceeds in a completely different way. [16] This coupling leads to the formation of C,S-cyclometalated deprotonated diaminocarbene complexes (Route B, Scheme 1).…”

“…The choice of this compound as an object of study is due to the fact that pyridine is noticeably more aromatic than pyrrole and imidazole. [17,18] Earlier, we assumed that a similar reaction for 5-membered N-heterocyclic thiones [16] proceeds via the initial coordination of the thione sulfur atom to the metal center followed by the intramolecular nucleophilic addition of the heterocyclic nitrogen atom to the metal-ligated isocyanide carbon. In order to understand how this transformation is carried out for pyridine-2(1H)-thione and to know deeper the features of the reaction mechanism, we conducted the coupling reaction of pyridine-2(1H)-thione with a solution of complex 1 b in deuterochloroform in a 1 : 1 molar ratio in the absence of a base.…”