Extending the Application Scope of Organophosphorus(V) Compounds in Pincer Chemistry

Organophosphorus compounds comprise indispensable ligands in organometallic and coordination chemistry. In particular, they are widely used in creation of the so-called pincer-type complexes which demonstrate unique physical... [ view full abstract ]

Organophosphorus compounds comprise indispensable ligands in organometallic and coordination chemistry. In particular, they are widely used in creation of the so-called pincer-type complexes which demonstrate unique physical and chemical properties owing to a specific monoanionic tridentate framework and find extensive use in catalysis and materials science. However, this concerns mainly various trivalent phosphorus derivatives, whereas the potential of their P(V)-counterparts is still underestimated. Recently we have shown that various m-functionalized thiophosphoryl-, thiophosphoryloxy- and thiophosphorylaminobenzenes can give rise to Pd(II) pincer complexes featuring high catalytic activity in cross-coupling reactions and prominent photophysical properties. In continuation of these studies, it seemed interesting to develop synthetic routes to pincer systems with another types of P(V)-ancillary donor groups. Thus, m-diphenylphosphinophenol was used as a convenient precursor for a series of pincer-type ligands combining thiocarbamate donor group with coordination-active phosphine oxide, phosphine sulfide, phosphine selenide, phosphinimine, and phosphonium ylide moieties. In most cases, cyclopalladation of the ligands smoothly proceeded under action of PdCl₂(PhCN)₂ in mild reactions conditions, affording κ³-X,N,S-pincer complexes with 5- and 6-membered fused metallacycles. The complexes obtained extend the panel of reported cyclopalladated complexes with the coordinated P=N and P=S moieties and serve as the first examples of pincer compounds with the P=Se and P=CHR moieties. To our surprise, even in the case of the P(O)-functionalized ligand bearing the hard oxygen coordination site, direct cyclopalladation afforded the desired pincer complex, although its yield did not exceed 5%. What is more important, some of the new pincer palladacycles can be efficiently synthesized under solvent-free conditions according to the new solid-phase methodology (know-how of our group), which arises as a cheap and green alternative for conventional synthesis of complex organometallic systems in solution.

This work was supported by the Grant of the President of the Russian Federation for young scientists (project no. MK-238.2017.3) and the Russian Foundation for Basic Research (project no. 16-03-00915).