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Thermally Stable Ln(II) and Ca(II) Bis(benzhydryl) Complexes: Excellent Precatalysts for Intermolecular Hydrophosphination of C–C Multiple Bonds

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journal contribution
posted on 01.04.2019, 00:00 by Alexander N. Selikhov, Gleb S. Plankin, Anton V. Cherkasov, Andrey S. Shavyrin, Elisa Louyriac, Laurent Maron, Alexander A. Trifonov
A series of Ln­(II) and Ca­(II) bis­(alkyl) complexes with bulky benzhydryl ligands, [(p-tBu-C6H4)2­CH]2­M­(Ln) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI2­(THF)n (n = 0–2) and [(p-tBu-C6H4)2CH]­Na+. In complex 1, the benzhydryl ligands are bound to the metal center in η2-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in η3-fashion. In complex 2, one ligand is η3-coordinated while the second one is η4-coordinated to the Sm­(II) ion. Complexes 24 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C6D6 at 100 °C during 72 h. Complex 1 behaves differently: thermolysis in C6D6 solution at 75 °C results in total decomposition in 8 h. Addition of DME promotes decomposition of 24 and makes it feasible at 40 °C. Complexes 14 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C–C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH2 toward the internal CC bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph2PH and PhPH2 was realized due to the application of Yb­(II) complex as a catalyst.