Structural and spectroscopic studies of rhodium-(I) and -(III) nitrato complexes

Refluxing Rh(NO3)3·2H2O with an excess of PPh3 in MeOH or EtOH for over 48 h gives trans-[Rh(CO)(ONO2)(PPh3)2]1 whereas the same reaction at room temperature gives predominantly [Rh(ONO2)(PPh3)3]2. X-Ray structure determinations of 1 and 2 show the nitrate groups to be monodentate in each case although disorder of the CO and NO3 groups in 1 precludes accurate determination of bond lengths and angles. There is no reaction of trans-[Rh(CO)X(PPh3)2](X = Cl, F or ONO2) with H2 at room temperature and 1 atm pressure, whereas there is an immediate reaction of [Rh(ONO2)(PPh3)3] under the same conditions to give [RhH2(ONO2)(PPh3)3]3, which has been characterised by multinuclear NMR spectroscopy. Compound 3 loses PPh3 to give [RhH2(O2NO)(PPh3)2]6a which has been characterised similarly and by X-ray crystallography; although the metal-bound hydrogens were not located the structure is clearly based on an octahedral geometry with trans phosphines and a bidentate nitrate.