G. Jeffery Leigh

The Chemistry of Nitrogen Fixation and Models for The Reactions of Nitrogenase

Publisher Summary This chapter discusses the chemistry of nitrogen fixation and models for the reactions of nitrogenase. The interest in nitrogen fixation for the inorganic chemist is to try to understand, using simple compounds, what nature does so comparatively effortlessly within the enzyme, nitrogenase. This is of particular value considering the increasing demand for nitrogenous fertilizers, and the vast industrial expenditure of energy in producing ammonia. The literature of chemical nitrogen fixation, even excluding that related to the Haber process, is now considerable. The mechanisms of reaction of coordinated dinitrogen are a matter of dispute. There are several proposals extant, chemical and biological, and these are espoused by their progenitors with varying degrees of fervor. However, there is now sufficient chemistry available for us to make preliminary judgments concerning the validity of the various proposals.

A convenient synthesis of 1,2-bis(dichlorophosphino)ethane, 1,2-bis(dimethylphosphino)ethane and 1,2-bis(diethylphosphino)ethane

Abstract A simple synthesis of 1,2-bis(dimethylphosphino)ethane, 1,2-bis(diethyl-phosphino)ethane, and 1,2-bis(dicyclohexylphosphino)ethane is reported. The method involves the synthesis of 1,2-bis(dichlorophosphino)ethane using a procedure patented by Toy and Uhing; the halide is allowed to react with the appropriate Grignard reagent to give the required tetraalkyldiphosphine. The phosphines produced in this way are moderately sensitive to air but not spontaneously inflammable as previously reported.

Diazoalkane complexes of tungsten from the condensation of hydrazido Complexes with Ketones

Abstract Hydrazido(2−) and hydrazido(1−) complexes of tungsten condense with ketones, R 1 R 2 CO, in the presence of catalytic amounts of acid to yield complexes containing the groups W = NN = CR 1 R 2 and WNHN =CR 1 R 2 respectively. The other ligands are halide ions and monotertiary phosphines. These new complexes yield secondary amines and ammonia on reduction with LiAlH 4 ; acids produce nitrogen-free tungsten materials, hydrazine and azines.

Rhodium(I), rhodium(III), palladium(II), and platinum(II) complexes containing ligands of the type PRnQ3–n(n= 0,1, or 2; R = Me, Et, But, or Ph; Q = CH2OCOMe or CH2OH)

We report the characterisation of the phosphines PRnQ3–n(n= 0,1, or 2; R = Me, Et, But, Or Ph; Q = CH2OCOMe or CH2OH) and of their complexes with halides of PtII, PdII, RhI, and RhIII. The methylene protons of the acetoxymethyl- and hydroxymethyl-groups show no 31P–1H coupling in the complexes, and this is attributed to |2J(PH)+4J(PH)| being accidentally nearly zero. Although the phosphines render the complexes more soluble in hydroxylic solvents than complexes of more conventional phosphines, and complexes derived from phosphines containing two or more hydroxymethyl groups are water soluble, the new complexes were not found to possess exceptional or unusual catalytic properties for the hydrogenation or isomerisation of olefins.

Non-planar co-ordination of the Schiff-base dianion N,N′-2,2-dimethyltrimethylenebis[salicylideneiminate(2–)] to vanadium

The Schiff-base dianion N,N′-2,2-dimethyltrimethylenebis[salicylideneiminate(2–)](salnptn) coordinates to vanadium(IV) to form [VO(salnptn)] whose crystal structure has been determined. The compound is polymeric in the solid state with ⋯ VO → VO → VO ⋯ chains, the salnptn donor atoms being coplanar and the salnptn framework umbrella-shaped. In the derivative [VO(OMe)(salnptn)], the crystal structure of which has also been determined, the OMe and the vanadyl oxygen are co-ordinated cis to each other, and the salnptn now occupies three equatorial and one axial co-ordination positions. Even N,N′-ethylenebis(salicylideneiminate) seems to behave analogously, though it is normally planar.

Triangulo-pentahalotrimetal complexes of nickel(II) and cobalt(II) with N,N,N′,N′,N-tetramethylethane-1,2-diamine and related compounds

Abstract Nickel(II) and cobalt(II) form complexes [M3Cl5(neutral didentate ligand)3]+ containing the triangulo-trihalotrimetal moieties with considerable ease, and they are very similar in structure to the known titanium, vanadium, and iron homologues. However, chromium and copper are not. The supporting neutral ligand is almost invariably N,N,N′,N′-tetramethylethane-1,2-diamine. These compounds show a great affinity for water and react to lose one apical chloride to be replaced by hydroxide. The analogous bromide derivatives have also been prepared and characterised. For the first time, a triangulo-trihalotrimetal compound containing fluoride has also been prepared.

Complexes of tertiary phosphines with iron(II) and dinitrogen, dihydrogen, and other small molecules

The treatment of [FeCl2(diphosphine)2] with sodium borohydride in ethanol produces the hydrides [FeH3(diphosphine)2]+ in high yield. These complexes react with a variety of small molecules including N2 to give further complexes. CO2 and CS2 insert into the iron hydride bond to yield formato- and dithioformato-complexes, respectively, and carboxymethyl acetylene and phenyl acetylene yield a cyclic alkenyl complex and an acetylide, respectively.

Complexes of metal(II) halides of the first transition series with N,N,N′,N′-tetramethylmethane-diamine, -ethane-1,2-diamine and -propane-1,3-diamine

Complexes of metal(II) halides of the first transition series with three diamines Me 2 N(CH 2 ) n NMe 2 have been studied. For n =1 (tmmn), only dinuclear species [{MX 2 (tmmn)} 2 ] have been isolated, whereas for n =3 (tmpn) only tetrahedral mononuclear species [MX 2 (tmpn)] have been characterised. For n =2 (tmen), structures of both kinds have been prepared, and also of a third kind, octahedral trans -[MX 2 (tmen) 2 ]. These different structures are often interconvertible. The structural types are rationalised in terms of the dimensions of the diamines rather than of the properties of the metal(II) ions.

Mössbauer and preparative studies of some iron(II) complexes of diphosphines

Analytical and Mossbauer spectral data show that Ph2PCH2CH2PPh2(dppe) forms adducts [FeCl2(dppe)] and [FeI2(dppe)], and that [FeCl2(dppe)2] does not exist. The phosphine 1,2-C6H4(PPh2)2(opdp) forms adducts FeX2(opdp)2, which exists in one form (high-spin, trans octahedral) for X = Cl, and in two isomeric forms for X = Br or I. One isomer for X = I is high-spin, trans octahedral, and the other is ionic low-spin, and five-co-ordinate. A comparison is made of these structures and of their Mossbauer spectra with those of derivatives of Me2PCH2CH2PMe2, Et2PCH2CH2PEt2, Pri2PCH2CH2Pri2, and Ph2PCH2PPh2.

Redox potential–structure relationships in metal complexes. Part 2. The influence of trans-substituents upon the redox properties of certain dinitrogen complexes of molybdenum and tungsten and some carbonyl analogues: inner-sphere versus outer-sphere electron transfer in the alkylation of co-ordinated dinitrogen

The preparation of some new anionic dinitrogen complexes of the type trans-[M(N2)X(dppe)2]– is described (M = Mo or W; X = SCN, CN, or N3; dppe = Ph2PCH2CH2PPh2) together with their monocarbonyl analogues(M = Mo). Relationships between E½ox, ν(N2), and ν(CO) of these complexes and those of [M(N2)(NCR)(dppe)2] and the standard series [Cr(CO)5(L or X–)] have allowed us to identify the formation of a labile ammine complex [Mo(N2)(NH3)(dppe)2] in tetrahydrofuran and to predict E½ox and ν(N2) for as yet unsynthesised complexes related to those described. Furthermore, aspects of the reactivity of the co-ordinated dinitrogen ligand have been correlated with the ‘electron-richness’ of the complex (as measured by E½ox) with particular reference to (a) inner-sphere versus outer-sphere electron-transfer alkylation of co-ordinated dinitrogen to give organodiazenido-complexes and (b) the protonation of [M(N2)(NCR)(dppe)2] complexes which give the new hydrazido(2–)-salts, [M(N2H2)(NCR)(dppe)2][HSO4]2, with retention of the trans-RCN ligand.