A silsesquioxane-based diphosphinite ligand : synthesis, DFT study, and coordination chemistry

The incompletely condensed silsesquioxane disilanol (c-C5H9)7Si7O9(OH)2OSiMePh2 was used as a backbone for the synthesis of the diphosphinite ligand (c-C5H9)7Si7O9(OPPh2)2OSiMePh2 (1), based on a silsesquioxane framework. By reaction with black selenium, the corresponding selenide (2) was obtained, showing a JSe-P value of 815 Hz in the 31P NMR spectrum. DFT calcns. established a good insight into the electron d. of the P atoms present in the two model compds. CH3OPPh2 (3) and Ph2P(HSiOH)2OPH2 (4). The Mulliken charge distributions show a clear electron-withdrawing effect of the siloxy group, which is also present in diphosphinite ligand 1. By reaction of compd. 1 with PdCl2(C6H5CN)2, the palladium complex [PdCl2R(OPPh2)2] (5) was obtained (R = (c-C5H9)7Si7O9OSiMePh2). From a similar reaction of 1 with PtCl2(cod), the platinum analog [PtCl2R(OPPh2)2] (6) could be isolated. The equimolar reaction of Mo(CO)4(pip)2 (pip = piperidine) with 1 yielded the molybdenum complex [Mo(CO)4R(OPPh2)2] (7). Ligand 1 showed a clear tendency to coordinate in a cis fashion for all complexes 5-7, as was detd. by NMR spectroscopy and x-ray crystallog. However, the analogous reaction of 1 with RhCl(CO)2 dimer yielded the mononuclear trans-[RhCl(CO)(1)] (8). Complexes 5-8 were structurally characterized as the 1st examples of transition-metal complexes with a silsesquioxane-based bidentate phosphinite ligand. [on SciFinder (R)