Bent Bis Research Articles

Oxidation and reduction chemistry of bis(η-arene)niobium compounds; the X-ray crystal structure of bis(η-toluene)(trimethylphosphine)niobium tetrafluoroborate

Cyclic voltammetry shows that [Nb(η-C6H5Me)2] undergoes both one-electron reversible reduction and oxidation; chemical oxidation with AgBF4 in the presence of PR3(R = Me, R3= Me2Ph) yields [Nb(η-C6H5Me)2(PR3)]BF4. The X-ray crystal structure of [Nb(η-C6H5Me)2(PMe3)]BF4 has been determined and shows the molecule to have the bent bis(η-arene) structure. Reduction of [Nb(η-C6H3Me3-2,4,6)2] with potassium and treatment with carbon monoxide yields [Nb(CO)6]–; reduction in the presence of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclo-octadecane,L) gives [KL][Nb(η-C6H3Me3-2,4,6)2].

Synthesis of zerovalent bis(η-arene) compounds of zirconium, hafnium, niobium, tantalum, and tungsten using the metal vapours

Co-condensation of the vapours of the metals niobium, tantalum, and tungsten, derived from a positive hearth electron-gun furnace, with an excess of arenes gives the bis(η-arene) compounds [M(η-arene)2](M = Nb, Ta, or W). Similarly, zirconium and hafnium vapours with a mixture of arenes and trimethylphosphine give the bent bis(η-arene) compounds [M(η-arene)2(PMe3)](M = Zr and Hf). The bis(η-arene)tungsten compounds protonate readily in dilute aqueous acids to form the bent bis(η-arene)hydrido-cations [W(η-arene)2H][PF6]. Spectroscopic properties and other characterising data are presented for the new compounds.

Photoelectron studies of some bent bis(η-cyclopentadienyl)metal complexes. Part I. Some eighteen-electron systems with hydride, alkyl, olefin, allyl, and carbonyl ligands

Photoelectron spectra of some bent bis(η-cyclopentadienyl)metal complexes, namely [(cp)2ReH], [(cp)2MH2](M = Mo and W). [(cp)2TaH3], [(cp)2MMe2](M = Mo and W), [(cp)2MoL](L = CO and η-C2H4), [(cp)2WL](L =η-C2H4 and η-C3H6), and [(cp)2Nb(η-C3H5)] have been measured. A unified bonding model is proposed which accounts for the observed spectra.

Some organic chemistry of molybdenum and related topics

General features of molybdenum chemistry are briefly surveyed and then three areas of molybdenum chemistry are presented in more detail. Evidence concerning the structure and bonding in bent bis it-cyclopentadienyl metal compounds is discussed. New reactions of bis It-cyclopentadienyl molybdenum (and tungsten) complexes are described: in particular the reactions of the dihydride (ic-C5H5)2MoH2 leading to molybdenum aryl derivatives. Arene molybdenum chemistry has been explored and the arene—metal bond has been found to survive in a wide variety of chemical environments. INTRODUCTION The organometallic chemistry of molybdenum started in the mid-1950s and most of the early compounds were carbonyl derivatives. This was largely due to the availability of molybdenum hexacarbonyl together with its ease of handling. These carbonyl derivatives were usually prepared by thermal substitution: nL + Mo(CO)6 -* LMo(CO)6 By this route molybdenum was bonded to arenes, azulenes, t-cyclopentadienyl and to many olefm ligands such as cycloheptatriene and bicycloheptadiene. Many of these compounds were important since they often provided the first examples of a particular organometal system at a time when it was by no means clear what were the limits of stability of organometal bonds. Two other early compounds of interest were the his t-cyclopentadienylmolybdenum dihydride and bis t-benzene molybdenum. Much of this early work was done in the laboratories of Fischer and Wilkinson1. The second phase of organomolybdenum chemistry largely concerned the development and study of arene molybdenum carbonyls, and, especially, of it-cyclopentadienyl molybdenum carbonyl chemistry. The ic-C5H5Mo(CO)3X system has been shown to provide a wide range of derivatives where for example, X = aIkyl2, acyl3, aryl4, perfluoroalkyl5, sulphinato6, silyl7, stannyl8, germyl9 and other metal ligands with aluminium10, magnesium1 1, palladium and platinum'2. Also, the substitution properties of itC5H5Mo(CO)3X by ligands such as nitrosyls'3, polypyrazolylborates'4, phosphines and phosphites have been studied1 5• Several molybdenum compounds containing 2 x le 'carbene' ligands have been described16, and ligands which contribute three electrons to the molybdenum have been found in the compounds it-C5H5Mo(CO)2D, D = 7r-allyl'7. benzyP8. 373