The First Rigid O,C,O-Pincer Ligand and Its Application for the Synthesis of Penta- and Hexacoordinate Organotin(IV) Compounds

The synthesis of the aryldiphosphonic ester C6H2[P(O)(OEt)2]2-1,3-t-Bu-5 (2) and of its organotin derivatives C6H2[P(O)(OEt)2]2-2,6-t-Bu-4-RR‘2Sn-1 (5, R = R‘ = Me; 6, R = R‘ = Ph; 7, R = Ph, R‘ = Cl; 8, R = Ph, R‘ = Br) is reported. Also reported is the preparation of the organosilicon and organotin compounds C6H2[P(O)(OEt)2]2-2,4-Me3Si-1 (3), C6H2[P(O)(OEt)2]2-2,4-(Me3Si)2-1,5 (4), C6H3[P(O)(OEt)2]2-2,4-Ph2RSn-1 (9, R = Ph; 12, R = Br), and C6H3[P(O)(OEt)2]2-2,4-(Ph2RSn)2-1,5 (10, R = Ph; 11, R = Br). X-ray investigations reveal weak intramolecular Sn−O interactions for 6 (2.865(3)−3.063(4) Å), 9 (2.803(3) Å), and 10 (2.793(2) Å) but strong Sn−O coordinations for 7 (2.203(5)/2.278(6) Å) and 11 (2.379(3)/2.412(3) Å), indicating the high donor capacity of the new rigid O,C,O- and O,C-chelating ligands in these compounds. NMR studies confirm that the basic coordination geometry found in the solid state is maintained in solution.