Syntheses and reactivities of some ruthenium (VI) and osmium (VI) nitrido complexes containing schiff base ligands

Abstract

This thesis is divided into two parts. In Part I, two series of diamagnetic ruthenium(VI) nitrido complexes containing the Schiff base ligands, 5,5’-X2salchda or 5-Xsalpa (salchda and salpa = N,N’-bis(salicylidene)-o-cyclohexyldiamine and N-salicylidene-2-aminophenol dianions respectively, X = H, Me, MeO, Cl or Br) have been synthesized and characterized by IR, UV-Vis, 1H NMR, ESI-MS and CHN elemental analysis. The structures of [RuVI(N)(salchda)(CH3OH)](ClO4) and [RuVI(N)(salpa)(Cl)] have been determined by X-ray crystallography. The d(Ru≡N) are 1.592(4) and 1.593(3) Å respectively. They undergo N···N coupling reactions to afford ruthenium(III) complexes and dinitrogen gases are liberated. The ruthenium(VI) nitrido complexes are electrophilic, they react rapidly with triphenylphosphine to give ruthenium(III) phosphiniminato complexes. The crystal structure of [RuIII(N(H)PPh3)(5,5’-OMe2salchda)(NCCH3)](PF6) has been determined. The rate of the reaction of [RuVI(N)(salchda)(CH3OH)](ClO4) with PPh3 has been studied by stopped-flow spectrophotometric methods, the rate law is -d[RuVI]/dt = k2[RuVI][PPh3]. At 298 K, the rate constant, k2, is (5.16 ± 0.09) × 104 mol-1 dm3 s-1. Treatment of [RuVI(N)(salchda)(CH3OH)](PF6) with secondary amines in Et2O results in the formation of ruthenium(IV) hydrazido(1-) complexes, formulated as [RuIV(N(H)NR2)(salchda)(HNR2)](PF6) (HNR2 = pyrrolidine, morpholine or piperidine) or [RuIV(N(H)NR2)(salchda)X] (X = NCS or Br). The (RuIV-Nhydrazido) distances and (Ru-N-N) angles are 1.949(5) Å and 128.2(4)° in [RuIV(N(H)NC4H8)(salchda)(HNC4H8)](PF6) and 1.908(3) Å and 135.0(3)° in [RuIV(N(H)NC4H8O)(salchda)(NCS)] respectively. The kinetics of the reaction between [RuVI(N)(salchda)(CH3OH)](PF6) and morpholine reveals that the reaction is first order in RuVI and second order in morpholine with k3(CH3CN, 298K) = (2.08 ± 0.07) × 106 M-2 s-1. Ligand-induced aziridination is found to occur between [RuVI(N)(salchda)(CH3OH)](PF6) and alkenes in CH2Cl2 in the presence of neutral N-donor ligands. The crystal structure of [RuIII(Az1)(salchda)(py)](PF6), [RuIII(Az1)(5,5’-Br2salchda)(py)](PF6) and [RuIII(Az2)(salchda)(py)](PF6) (Az1 and Az2 = 2,2,3,3-tetramethylaziridine and trans-2-methyl-3-phenylaziridine respectively) have been determined by X-ray crystallography with d(Ru-Naziridine) = 2.1049(19), 2.107(4) and 2.102(7) Å respectively. In Part II, two series of osmium(VI) nitrido complexes with Schiff base ligands have been synthesized and characterized as in Part I. The Os≡N bond distances are 1.675(9) and 1.637(7) Å for [OsVI(N)(salchda)(OH2)](ClO4) and [OsVI(N)(salpa)(Cl)(OH2)] respectively. Treatment of [OsVI(N)(salchda)(OH2)](PF6) with N-donor ligands in CH3CN produces a number of novel μ-N2 diosmium complexes. The structure of [{OsII.5(salchda)(4-tBupy)}2(μ-N2)](PF6) has been determined by X-ray crystallography with N≡N bond distance of 1.16(3) Å. Similar to the corresponding ruthenium(VI) nitrido complex, [OsVI(N)(salchda)(OH2)](PF6) reacts with triphenylphosphine to produce the osmium(IV) phosphiniminato complex [OsIV(NPPh3)(salchda)Cl]. The rate constant for the reaction of [OsVI(N)(salchda)(OH2)](ClO4) with PPh3 is (4.24 ± 0.01) × 103 mol-1dm3s-1 at 298 K, which is an order of magnitude smaller than that of the reaction between [RuVI(N)(salchda)(CH3OH)](ClO4) and PPh3. Reaction between osmium(VI) nitrido complexes and Li2S in CH3OH at ambient temperature produces [OsII(NS)(L)(OCH3)] (L = salchda or salophen). The structure of [OsII(NS)(salophen)(OCH3)] has been determined by X-ray crystallography. The bond distances of d(Os-Nthionitrosyl) and d(N≡S) are 1.84(2) and 1.47(2) Å respectively.