Synthesis of fac-[Os(CO)3(L)Me2] (L = THF or MeCN) and some reactions with PPh3 and trityl salts

The reaction of cis-[Os(CO)4Me2] with Me3NO in the THF or MeCN yields the complexes fac-[Os(CO)3(L)Me2] (where L = THF or MeCN). Whereas the THF complex is unstable and only characterised spectroscopically, fac-[Os(CO)3(MeCN)Me2] has been isolated as a white solid and fully characterized by both analytical and spectroscopic methods. These complexes fac-[Os(CO)3(L)Me2] are shown to be useful intermediates. Thus, reaction with PPh3 gives fac-[Os(CO)3(PPh3)Me2] in good yield. Reactions of fac-[Os(CO)3(L)Me2] (L = CO or MeCN) with CPh3PF6 or B(C6F5)3 have been investigated. Whereas cis-[Os(CO)4Me2] showed no reaction with either CPh3PF6 or B(C6F5)3, the reaction of fac-[Os(CO)3(MeCN)Me2] with CPh3PF6 in CH2Cl2 occurred over 16 h at room temperature to give an unstable cationic product and CPh3Me. The reaction was monitored by both IR and NMR spectroscopies. When this reaction of fac-[Os(CO)3(MeCN)Me2] was carried out in the presence of a trapping ligand such as MeCN, the stable cationic product [Os(CO)3(MeCN)2Me]+ could be isolated and identified spectroscopically.