Molybdenum , seven-coordinate complexes

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

C. Preparation of Six- and Seven-Coordinate Complexes of Molybdenum(ll) and Tungsten(ll) by Halogen Oxidation of Zero-Valent Carbonyl Complexes Containing at Least One Other Donor Ligand... 

Baker et al. have described the synthesis and reactions with donor ligands of the molybdenum complexes [MoClI(CO)3(NCMe)2])6° and [MoBrI(CO)3(NCMe)2],161 which are prepared by reaction offac-[Mo(CO)3 (NCMe)3]101 with C1I or BrI, respectively. Reaction of [M(CO)4(N N)J (M = Mo, W N N = bipy, phen) with ICN affords the seven-coordinate complexes [M](CN)(CO)3(N N)].162... 

The NMR characterisation of fBA adducts formed in the reaction of tungsten and molybdenum seven-coordinate compounds leaves little doubt concerning their formulation. However, we were unable to separate such compounds and to prepare a crystalline sample. To obtain a more stable terminal alkyne compound, we introduced two phosphine ligands into the coordination sphere of tungsten(II). In this way a cationic complex of tungsten(II), [WCl(CO)( BuC=CH)(NCMe)(PPh3)2]2[SnCl6], was prepared [45]. The crystal structure of this compound consists of two independent cations and a... 

To explore the influence of coordination environment on rates and mechanisms of electron transfer reactions at molybdenum centers, we have investigated [17-20] the electrochemical behavior of several families of oxomolybdenum (VI) complexes. The compounds are illustrated in Figure 4. The first three examples are seven-coordinate complexes and exhibit pentagonal bipyramidal geometry. These compounds contain a... 

Baker PK, Armstrong EM (1990) Mono- and dinuclear phosphine coordinated 1,4-bis (diphenylphosphino)ethyne seven-coordinate complexes of molybdenum(ll) and tungsten(II). Polyhedron 9 801-804... 

Triphosphamacrocycle complexes of molybdenum(II) and tungsten(II) 22 have been prepared by oxidative addition of halogens (CI2, Br2,12) to molybdenum and tungsten tricarbonyl complexes 19 (Scheme 12.8). The metal(O) precursors give rise initially to seven-coordinate salts 21 with a halide anion which may be exchanged for other counter ions. The seven-coordinate complexes 21 are all fluxional in solution. The salts all convert slowly into the neutral seven-coordinate dicarbonyldihalogeno complexes 22 in solution [38]. 

In seven-coordinate molybdenum peroxo complexes of the type Mo(0)(02)2L2, there is the problem of dissociation of the complex in the case of monodentate ligands like pyridine, HMPA, DMF or H2O. Bidentate hgands like 2,2 -bipyridine, on the other hand, tend to give insoluble complexes. A solution to this problem was presented by Thiel in 1997 and 1998 . His group utilized the Mo-diperoxo complex 160 bearing a pyrazolylpyridine ligand. 

The first step of the mechanism leading The electrochemical study of the seven-to the formation of 8 and free nitrite coordinate complex [Mo(N2RR )(dtc)3]+ from the reaction of 7 with O2 probably 9+ (R, R = alkyl or aryl, dtc = 5 2CNMe2) involved a single electron transfer. Sub- provided an example of electrode-induced sequent radical-radical coupling of the activation of a hydrazido(2—) ligand. Corn-products, to afford a molybdenum-bound plex 9+ was shown to reduce in two nitrate, followed by N—O bond cleavage separate diffusion-controlled one-electron would eventually lead to the observed steps, with the first one reversible on the products (Sch. 8) [27]. CV timescale at room temperature and... 

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