Ditertiary Phosphines as Monodentate Ligands in Transition Metal Carbonyl Complexes

Carbonyl complexes of chromium, molybdenum and tungsten have been synthesized in which two potentially chelating tetraphenyldiphosphinoethane molecules (Ph2PCH2CH2PPh2) are bound as monodentate ligands. The reaction of trans-(CO)4M(PPh2CH=CH2)2 (M = Cr, Mo, W) with diphenylphosphine (PPh2H) in the presence of potassium t-butoxide yields trans-(CO)4M(PPh2CH2CH2PPh2)2. The complexes, which represent the first of this type to be synthesized, have been characterized by 31P nmr. From the XAA\u27X\u27 phosphorus-31 spectra of the complexes, phosphorus-phosphorus coupling through the metal atom have been determined and have been found to be 26.0, 45.7 and 54.3 Hz respectively for chromium, molybdenum and tungsten. The phosphorus-phosphorus coupling constant for cis-(CO)4W(PPh2CH2CH2PPh2)2, obtained as a minor product, was determined to be 21.3. The reaction of trans-(CO)4W(PPh2CH=CH2)2 with PPh2H in the presence of the free radical catalyst, 2,2\u27-azobisisobutyronitrile (AIBN), resulted in isomerization and cyclization to give as a major product, a complex ·in which PPh2CH2CH2CH(PPh2)CH2PPh2 is present as a bidentate ligand. This complex, (CO)4W[PPh2CH2CH2CH(PPh2)CH2PPh2], and its oxide have been fully characterized by 31P nmr. The absence of a product in which PPh2H is coordinated or in which PPh2CH2CH2PPh2 is chelated suggests that the isomerization proceeds through an intramolecular mechanism. The reaction of cis-(CO)4W(PPh2H) 2 with PPh2 (CH=CH2) 2 in the presence of potassium t-butoxide gave (CO)4W(PPh2CH2CH2PPh2), a complex in which the phosphorus ligand is chelated. The reaction of cis-(CO)4W(PPh2H) 2 with PPh2H in the presence of AIBN yields the sterically favored trans-(CO)4W(PPh2CH2CH2PPh2)2. The reactions reported in this thesis represent an approach to controlling the number of metal sites to which a chelating phosphine is coordinated