George A. Gott

Preparation, properties, and reactions with sulphur dioxide of triphenylphosphine oxide complexes of manganese(II) thiocyanate. Crystal structures of [{Mn(OPPh3)2(NCS)(µ-NCS)}2], [Mn(OPPh3)4(NCS)2], and (PPh3O)(PPh3OH)(HSO4), a derivative of sulphuric acid formed under ambient air oxidation of sulphur dioxide

Manganese(II) thiocyanate reacts with triphenylphosphine oxide to yield the complexes [Mn(OPPh3)n(NCS)2](n= 1,2,3, or 4) which have been characterised by elemental analyses, i.r. and e.s.r. spectroscopy, and magnetic susceptibility measurements. These complexes are non-electrolytes in nitromethane solution. The crystal structures of the bis, [{Mn(OPPh3)2(NCS)(µ-NCS)}2], and tetrakis, [Mn(OPPh3)4(NCS)2], complexes are reported. The former is centrosymmetric comprising two Mn(OPPh3)2(NCS)2 units bridged by two NCS ligands, the geometry around each manganese atom being square pyramidal with an OPPh3 ligand in the axial position; the latter is a trans-pseudo-octahedral monomer with inversion symmetry about the central manganese atom. The reactions of the complexes with sulphur dioxide in both the solid state and in toluene suspensions have been investigated. The tris and tetrakis complexes react reversibly to give 1:1 adducts, [Mn(OPPh3)n{NCS)2(SO2)], whereas the mono and bis complexes are inactive towards sulphur dioxide. Dilute solutions of [Mn(OPPh3)4(NCS)2(SO2)] in the presence of air result in the oxidation of sulphur dioxide to sulphuric acid, as evidenced by the isolation and X-ray crystallographic characterisation of (PPh3O)(PPh3OH)(HSO4). This derivative of sulphuric acid is characterised by extremely strong hydrogen bonds, 2.351 and 2.492 A.

Thermodynamic and kinetic studies on the reaction of sulphur dioxide with manganese(II) phosphine oxide complexes

Abstract The bonding of sulphur dioxide to Mn(OPPh 3 ) 4 X 2 (X = NCS or I) in the solid state has been studied using a gas burette; thermodynamic data obtained indicate that the binding of sulphur dioxide is weak, and kinetic data for the reaction of sulphur dioxide with Mn(OPPh 3 ) 4 (NCS) 2 indicate a two stage reaction, both of which obey pseudo first order kinetics.

The co-ordination of small molecules by manganese(II) phosphine complexes. Part 14. Some novel mixed tertiary phosphine–t-butyl isocyanide complexes of manganese(II): [MnBr2(CNBut)(PPhMe2)] and [Mn(CNBut)4(PR3)2]2+(PR3= PPhMe2, PPh2Me, PPhEt2, or PPrn3), and the X-ray crystal structure of bis(dimethylphenylphosphine)tetrakis(t-butyl isocyanide)manganese(II) bis[tribromo(dimethylphenylphosphine oxide)manganate(II)], [Mn(CNBut)4(PPhMe2)2][MnBr3(OPPhMe2)]2

The complex [MnBr2(CNBut)(PPhMe2)] has been prepared by reaction of [MnBr2(PPhMe2)] with CNBut. In ethanol solution rearrangement occurs to give the complex [Mn(CNBut)4(PPhMe2)2][MnBr4] and this reacts with other phosphines to yield [Mn(CNBut)4(PR3)2]2+(PR3= PPrn3, PPhEt2, or PPh2Me). Air oxidation of an ethanol solution of [Mn(CNBut)4(PPhMe2)2]2+ produces red crystals of [Mn(CNBut)4(PPhMe2)2][MnBr3(OPPhMe2)]2 the structure of which is reported. In the cation MnII is octahedrally co-ordinated and lies on a crystallographic inversion centre. The latter also relates each pair of anions which have MnII in tetrahedral co-ordination. The Mn–P bonds of the cation are rather short at 2.344(3)A whereas all other cation and anion dimensions are unremarkable.

The coordination of small molecules by manganese(II) phosphine complexes. Part 12. The synthesis of some tetrahydrofuran/long chain tertiary phosphine complexes of manganese(II) halides, MnX2(phosphine)(THF), and their reaction with molecular oxygen

Abstract Manganese(II) complexes of long chain phosphines, MnX 2 (phosphine)(THF) XCl, Br, I; phosphine=P(C 12 H 25 ) 3 , P(C 14 H 29 ) 3 , P(C 16 H 33 ) 3 , PPh(C 12 H 25 ) 2 , PPh(C 14 H 29 ) 2 , PPh(C 16 H 33 ) 2 ; THF=tetrahydrofuran have been prepared and characterised. These complexes react reversibly with molecular oxygen both in the solid state and in THF and toluene solution forming 1:1 Mn:O 2 adducts. These adducts are monomeric in toluene and THF and molecular weight measurements confirm that the THF ligand remains coordinated in toluene solution leading to the formation of MnX 2 (phosphine)(THF)(O 2 ) species. All the O 2 -adducts are highly coloured and binding curves have been constructed and K o 2 values calculated. Based on these K o 2 values the affinity for dioxygen is in the order XCl>Br>I in toluene solution, with Hill coefficient, n , indicating cooperativity (1-1.5). In THF dioxygen binding does not appear to be cooperative.

Spectrophotometric detection of sulfur dioxide: a study of the solution equilibria of the reaction of sulfur dioxide with manganese(II) complexes

Abstract Spectrophotometric detection of sulfur dioxide binding by certain manganese(II) complexes in tetrahydrofuran solutions can be followed by monitoring changes in the electronic spectra. Solution isotherms have been constructed and from these the affinity of these complexes towards sulfur dioxide follows the order: Mn(Ph 3 PO) 2 I 2 >Mn(Ph 3 PS) 2 I 2 > Mn(Ph 3 AsO) 2 I 2 ; Mn(Ph 3 PS) 4 I 2 >Mn(Ph 3 PO) 4 I 2 >Mn(Ph 3 AsO) 4 I 2 ; Mn(dpeO 2 ) 2 I 2 >Mn(dpeS 2 ) 2 I 2 [Ph 2 P(Y)CH 2 CH 2 P(Y)Ph 2 ; Y = O, dpeO 2 ; Y = S, dpeS 2 ]; and MnL 4 I 2 >MnL 2 I 2 for the monodentate ligands.

Notes. Reaction of manganese(II) arsine oxide complexes with sulphur dioxide: some unexpected products. The X-ray crystal structure of [(Ph3AsO)2H]I3

The reaction of [Mn(OAsPh3)4I2] with sulphur dioxide in toluene yields [Mn(OAsPh3)3(O2SI)2)]. Two unexpected products, [(Ph3AsO)2H]I3 and [AsPh3I]I3, have been isolated from the reaction filtrate. The molecular structure of [(Ph3AsO)2H]I3 has been determined by single-crystal X-ray diffraction techniques.

The co-ordination of small molecules by manganese(II) phosphine complexes. Part 11. The co-ordination of dioxygen by manganese(II) complexes containing long-chain phosphine ligands

Manganese(II) complexes of long-chain phosphines, [MnX2(phosphine)][X = Cl, Br, or I; phosphine = P(C12H25)3, P(C14H29)3, P(C16H33)3, PPh(C12H25)2, PPh(C14H29)2, or PPh(C16H33)2], have been prepared. They form highly coloured 1 : 1 adducts with dioxygen, [MnX2(phosphine)(O2)], in both toluene and tetrahydrofuran (thf) solution. Infrared and e.s.r. spectra strongly suggest that these [MnX2(phosphine)] complexes are pseudotetrahedral dimers in the solid state and in toluene, contrasting vividly with the previously reported structure of [Mnl2(PPhMe2)]. Some molecular weight data indicate the product of dioxygenation in toluene to be the monomeric [MnX2(phosphine)(O2)] species. Dioxygen-binding curves for toluene and thf solutions have been obtained and equilibrium constants, KO1, for the dioxygenation reaction have been deduced. The general observation that KO2 increases and P50, the partial pressure when 50% of sites are deoxygenated, decreases for changes in halide ligand from Cl to Br to I in both solvents mirrors earlier observations with complexes of short-chain phosphines. The affinity of the complexes for O2 in thf is in the order phenyldialkylphosphines < trialkylphosphines. Hill coefficients, n, are approximately 1 for thf solutions of the chloride and bromide complexes, but for the iodides in thf and all of the complexes in toluene n lies in the range 1.10–1.64 indicating co-operativity for O2 binding, which may be related to the dimeric structure proposed for the complexes in toluene.

Notes. The co-ordination of small molecules by manganese(II) phosphine complexes. The reaction of some [MnX2L](X = Cl, Br, or I; L = PPrn3, PMe2Ph, or PPh3) complexes with tetracyanoethylene

When [MnX2L](X = Cl, Br, or I; L = PPrn3, PMe2Ph, or PPh3) complexes react with tetracyanoethylene (tcne) in toluene slurries the 1 : 1 adducts [MnX2L(tcne)] are formed. The magnetic moments of the adducts at room temperature, µeff.= 4.6–4.9, are consistent with a d4 manganese(III) species, and i.r., visible, and e.s.r. spectroscopic data are also consistent with the transfer of an electron from manganese(II) to tcne on adduct formation resulting in a manganese(III)–tcne˙– species. The tcne co-ordinates via a nitrile nitrogen.

The co-ordination of small molecules by manganese(II) phosphine complexes. Part 9. The reaction of ethylene with [MnX2L](X = Cl, Br, or I; L = PPrn3, PBun3, PPhMe2, PPhEt2, or PPh3) in tetrahydrofuran solution

The reaction of the [MnX2L] complexes (X = Cl, Br, or I; L = PPrn3, PBun3, PPhMe2, PPhEt2, or PPh3) with ethylene has been studied in tetrahydrofuran solution. The complexes with X = Cl, L = PPrn3, PBun3, PPhMe2, or PPhEt2 and X = Br, L = PBun3 were found to react in a 1 : 1 ratio, whereas the other complexes were found to be inactive towards ethylene. This order of binding ability, i.e. Cl > Br I, contrasts markedly with the ability of the [MnX2L] complexes to bind sulphur dioxide, for which the order is I > Br Cl.

The X-ray crystal structure of trans-bis(sulphur dioxide)tetrakis(triphenylphosphineoxide)manganese(II) di-iodide, a compound which undergoes demi-reversible binding of sulphur dioxide: the first crystallographically characterised example of O-bonded sulphur dioxide in a transition metal complex

The X-ray crystal structure of the complex trans-[Mn(OPPh3)4(SO2)2]I2 shows it to contain O-bonded Sulphur dioxide groups; one of these can be lost to form Mn(OPPh3)4(SO2)I2, and the reaction is reversible.