Nitrosyl complexes of ruthenium and osmium

Abstract

This study concerns the synthesis, structure and reactivity of nitrosyl complexes of ruthenium and osmium. Attempts have been made to prepare coordinatively saturated and unsaturated complexes and a study of their oxidative addition reactions bears considerable resemblance to the more familiar carbonyl complexes M(CO)3(PPh3)2. A number of interesting atom transfer reactions, generally involving oxygen, have been observed. The d8 complex RuCl(CO)(NO)(PPh3)2 results from the interaction of RuHCl(CO)(PPh3)3 with N-methyl-N-nitrosotoluene-p-sulphonamide. The labile halide ligand is readily displaced by a large range of anions and it is believed that both linear and bent nitrosyl linkages may exist for different members of this series. The structures of these complexes are discussed in the light of recent X-ray crystal structure data. Halogens and hydrogen halides add to give the familiar RuX3(NO)(PPh3)2; RuCl3(NO)(PPh2Me)2 is prepared in a direct reaction and also by phosphine exchange and 1H n.m.r. data confirm that the phosphine ligands are trans. The complexes RuX(CO)(NO)(PPh3)2 react readily with O2 to form the dioxygen complexes Ru(O2)X(NO)(PPh3)2. Halogens and hydrogen halides produce RuX3(NO)(PPh3)2. The dioxygen complexes react with SO2 and N2O4 to give sulphato and dinitrato complexes respectively. The reaction with CO results in the intramolecular oxidation of the nitrosyl group to coordinated nitrate accompanied by the incorporation of two moles of CO, i.e. RuX(NO3)(CO)2(PPh3)2 is formed. The dioxygen complexes catalytically oxidise triphenylphosphine or triphenylarsine to the respective oxides and RuX(NO)(PPh3)2 can be isolated from this cycle. Reactions of these four-coordinated complexes with O2, CO, Cl2 and NOBF4 are recorded. The dinitrosyl complex Ru(NO)2(PPh3)2 is reported from a number of syntheses, the most successful being via a ligand reaction when RuCl2(CO)2(PPh3)2 is heated with NaNO2 and Ph3P in dimethyl formamide. The P-tolyldiphenylphosphine analogue is also reported and the mono-substituted product Ru(NO)2(PPh3)[P(OPh)3] is produced in an exchange reaction between Ru(NO)2(PPh3)2 and excess triphenylphosphite. This phosphite complex reacts with Ph3P and O2 to produce Ru(O2)(NO2)(NO)PPh3)2 by an atom transfer process. Ru(NO)2(PPh3)2 reacts with the acids HY (Y = BF4, PF6, ClO4) and O2 to give the dinitrosyl cations [Ru(OH)(NO)2(PPh3)2]+Y- in which the two nitrosyl groups are structurally and electronically inequivalent. [RuCl(NO)2(PPh3)2]BF4 is reported and reactions of these dinitrosyl cations with halide ions to give RuX2(NO3)(NO)(PPh3)2, with intramolecular oxidation of the NO group, are also described. OsCl2(OH)(NO)(PPh3)2 reacts irreversibly with alcohols to form OsCl2(OR)(NO)(PPh3)2 (R = CH3, C2H5, n-C3H7, (CH3O)CH2CH2) which readily undergo hydride abstraction to form OsHCl2(NO)(PPh3)2. Sodium borohydride converts this complex to the trihydrido species OsH3(NO)(PPh3)2 and if the reaction is performed in the presence of Ph3P, OsH(NO)(PPh3)3 results. The coordinated perchlorate complex OsHCl(OClO3)(NO)(PPh3)2 results form the reaction of OsHCl2(NO)(PPh3)2 with silver perchlorate; this is readily reversed by chloride ions or the solvents CH2Cl2 and CHCl3. This perchlorato complex also arises from the reaction of OsH(CO)(NO)(PPh3)2 with HClO4 and a related tetrafluoroborato complex, OsH(OC2H5)(FBF3)(NO)(PPh3)2 by substituting HBF4. This complex reacts with Ph3P to give [OsH(OH)(NO)(PPh3)3]BF4, CO to give [Os(CO)2(NO)(PPh3)2]BF4 and LiX (X = Br, I) to give OsHX2(NO)(PPh3)2. OsHCl(OClO3)(NO)(PPh3)2 reacts with NaOH in methanol, in the presence of O2 to produce Os(O2)Cl(NO)(PPh3)2. This dioxygen complex is far less stable than the ruthenium analogue but it undergoes similar reactions. Ph3P is oxidised, SO2 and CO give sulphato and a nitratodicarbonyl complex respectively. Infra-red, 1H n.m.r., conductivity, molecular weight data and elemental analysis have been used in formulation and structural assignment.