Phosphane donor molecules

The theoretical section introduced divalent carbon(O) compounds as molecules CL2 where the ligand L is a ct donor. In principle this task can be fulfilled by various neutral group 15 compounds (N2, nitriles, amines, phosphanes, arsanes, etc.), neutral group 16 compounds (sulfides, selenides, etc.) as well as by divalent C(II) with a free pair of electrons at a carbon atom, such as isonitriles, NHCs, carbenes, CO, ylides, etc. The neutral and isolable compound C2PPh3 [14,15] may also serve as a donor L to stabilize a carbon atom. 

Complexes of type A with phosphane are determined by the tr-donor bond of the phosphorus atom. On the contrary, the (d-d)n back donation of the phosphorus is poor, due to much lower x-acceptor ability, and the balance of electrons cannot take place within the phosphorus metal bond. With respect to 31P NMR the phosphorus molecule is deshielded, exhibiting a low-field shift for the i 1-coordinated P atom of about 30-60 ppm compared to the uncoordinated phosphane phosphorus. 

In general, the solubility of solvent-free complexes is very low. However, coordination of Zr with donor solvents gives more soluble compounds. Depending on the extent of the steric effect of the pentahapto ligand, solvent mono or bis adducts are obtained. However stronger electron-donating molecules such as phosphanes do not form adducts, according to the Tewis acidity of the metal. 

The UV-cataiyzed reaction of Mc2PH with the vinyl-Ts silasesquioxane yields quantitatively the novel octakis(dimethylphosphinoethyl)octasilasesquioxane as the first reactive siloxane-based molecule with polydental o-donor properties emphasized by the easily performed conversion into the thio derivative or the formation of an octatungsten complex with W(CO)5-THF. Future work, therefore, has to focus on both the introduction of other phosphane ligands PR2 into the Si-O cage and the reaction with suitable transition metal fragments. 

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