Rhenium chemistry of pyridyldiazoles : oxygen atom transfer, oxidation, substitution and twin isomerization involving oxo, phosphine oxide and phosphine coordination

Abstract

The pyridyldiazoles (L) used are 2,5-bis(2-pyridyl)-1,3,4-oxadiazole and 2,5-bis(2-pyridyl)-1,3,4-thiadiazole. The oxygen atom transfer reaction of [ReOCl₃(L)] with PPh₂R (R = Ph, Me) and Ph₂P(CH₂)_xPPh₂ (PxP, x = 1-4) has afforded meridional [Re(OPPh₂R)Cl₃(L)] and [Re(OPxP)Cl₃(L)] respectively. These (R = Ph, x = 1) are oxidised by HNO₃ yielding [Re(OPPh₃)Cl₃(L)]Re0₄ and [Re(OPlP)Cl₃(L)]Re0₄. Treatment of [Re(OPPh₂R)Cl₃(L)] with PPh₂R has furnished facial [Re(PPh₂R)Cl₃(L)]. The [Re(OPxP)Cl₃(L)] species undergo spontaneous twin isomerization in solution leading to [Re(PxPO)Cl₃(L)]. All compounds have been characterized with the help of spectral and electrochemical data. The X-ray structure of a [Re(OPPh₃)Cl₃(L)]ReO₄ complex is reported. The rates and activation parameters of oxygen atom transfer and twin isomerization reactions have been determined and reaction models proposed.