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'Sn-2-1(5, R = R'= Me; 6, R = R' = Ph; 7, R = Ph, R' = Cl; 8, R = Ph, R' = Pr) 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) Angstrom), 9 (2.803(3) Angstrom), and 10 (2.793(2) Angstrom) but strong Sn-O coordinations for 7 (2.203(5)/2.278(6) Angstrom) and 11 (2.379(3)/ 2.412(3) Angstrom), 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.