G.J. Leigh

Improved preparation of tertiary phosphine and related substitution products of group VI metal carbonyls

Abstract The substitution of carbon monoxide in the Group VI metal carbonyls by tertiary phosphines, arsines, stibines or certain tertiary amines in boiling ethanol is strongly catalysed by sodium borohydride. This catalysis has been used to prepare a wide range of known and new substituted carbonyls of chromium, molybdenum and tungsten.

New synthetic routes to mono-, di- and tri-carbonyl halido complexes of rhenium(I) and rhenium(III) with tertiary phosphine

Abstract Carbonylation of tertiary phosphine complexes under reducing conditions is shown to be a reliable and direct route to rhemium mono- and poly-carbonyl complexes.

The alkylation of ligating dinitrogen to form alkylazo and related complexes

Abstract The dinitrogen complexes [M(N2)2(Ph2PCH2CH2PPh2)2] (M = Mo or W) react with alkyl halides in benzene to form alkylazo complexes and with 1,4-dibromobutane to form complexes derived from the heterocyclic hydrazine H2NNC4H8.

The organometallic chemistry of nitrogenases

Abstract Nitrogenases mediate the reduction of many substrates other than dinitrogen and a summary is given. Several chemical systems that mimic aspects of nitrogenase reactivity, including transition metal complexes of alkynes and olefins, are outlined. Their protonation has been studied and their relevance to reduction of alkynes and olefins by nitrogenase is assessed. Cyclopropene is reduced by molybdenum nitrogenase to propene and cyclopropane. The reactions of cyclopropene with different transition metal complexes are discussed and a study of interactions of cyclopropenes with models for the active site of the nitrogenase enzyme are described. These models include transition metal hydrides, such as [FeH(H 2 )(dmpe) 2 ][BPh 4 ] and [MoH 4 (dppe) 2 ] reducing 3,3-dimethylcyclopropene and cyclopropene. Products observed upon protonation and deuteration of several platinum-cyclopropene complexes are presented and a mechanism for their formation is proposed.

The search for a coordinated dialkyl disulphide: The crystal and molecular structure of (μ-ethanedithiolato)bis(tricarbonyliron)(FeFe)

Despite considerable effort, no compounds containing an alkyl disulphide linked to a single metalion have been isolated. The complex [{fFe(SCH 2 CH 2 - S) 2 } 2 ] 2− is a strong reducing agent. [Fe 3 (CO) 12 ] with 1,2,5,6-tetrathiacyclooctane yields [(SCH 2 CH 2 S){Fe- (CO) 3 } 2 ], the structure of which has been determined by X-ray analysis.

The preparation of mono(η5 -cyclopentadienyl) complexes of niobium and tantalum

Abstract Treatment of NbX 5 or TaX 5 (X  Br or Cl) with Mg(C 5 H 5 ) 2 or Sn(CH 3 ) 3 (C 5 H 5 ) produces the complexes (M(C 5 H 5 )X 4 ] (X  Cl, M  Nb or Ta; X  Br, M  Ta) and [Nb(C 5 H 5 )Br 3 ].

The conversion of ligating dinitrogen into amines

Abstract Treatment of organohydrazido(2−)-complexes of molybdenum and tungsten with lithium aluminum hydride gives good yields of amines. Simple acid treatment gives essentially none, and base distillation yields around 40%.

A convenient route to complexes of the type [MoO(SR)4]–(R = aryl) and [MoO{S(CH2)nS}2]–(n= 2 or 3) preparation and crystal structure of [PPh4][Mo(NNMe2)O(SC6H5)3]·(C2H5)2O

The complexes [MoO(SR)4]–(R = aryl) and [MoO{S(CH2)nS}2]–(n= 2 or 3) can be prepared by reaction of an MoVI butanediolato-complex with thiolate anion in methanol. The complexes [MoO(SPh)4]– react with R′2NNH2[R′2= Me2 or (CH2)5] in refluxing CH3CN to give [Mo(NNR′2)O(SPh)3]–. Crystal Data for [PPh4][Mo(NNMe2)O(SC6H5)3]·(C2H5)2O : space group Pbca, a= 12.789(4), b= 19.375(3), c= 36.941(3)A, Z= 8.3 225 Independent reflections with I > 3σ(I) gave R= 0.076. The geometry is essentially square-pyramidal with an apical oxo-group and the NNMe2 group in the basal plane. Although the MO–N and N–N distances of 1.821(9) and 1.292(14)A respectively are analogous to other hydrazido(2–) complexes, the Mo–N–NMe2 system is anomalously bent with MO–N–N = 152.5(10)°.

Heterobimetallic complexes containing both iron(II) and cobalt(II)

Attempts to use the uncomplexed central nitrogen atom in [CoCl 2 (η 2 -Me 2 NCH 2 NMeCH 2 NMe 2 )] as a donor to a second (iron) atom failed. The complexes isolated were [{M 5 Cl 10 (thf) 6 } n ] (M=Fe or Co) and (H 2 NMe 2 )(Me 2 NCH 2 )[CoCl 4 ]. It was not possible to assign the cobalt and iron atoms in the structure of the first complex. Subsequently, we isolated and completely characterised two more iron/cobalt complexes, [Cl 2 Co(μ-Cl) 2 Fe(thf) 4 ] and [{Cl 2 Co(μ-Cl) 2 Fe(C 2 H 5 OH) 4 } n ].

Complexes of osmium with metal-nitrogen multiple bonds

New arylimido-complexes of osmium [OsCl2(NC6H4X)(PPh3)2] (X = H, Cl, or OMe) were prepared from [OsCl3O(PPh3)2] and Ph3P=NCOC6H4X. The preparations of [Os(N3)2(PMe2Ph)4] and [OsCl2(N3)(PR2Ph)3] (R = Me, Et, Prn, or Bun) were also achieved. Attempts to obtain nitrido-complexes by decomposition of these azides were not successful.