Tetracarbonyl complexes, molybdenum

E. O. Fischer, G. Kreis, C. G. Kreiter, J. Muller, G. Huttner, and H. Lorenz, trans-Halo[alkyl(aryl)carbyne]tetracarbonyl Complexes of Chromium, Molybdenum and Tungsten. A New Complex Type with Transition Metal-Carbon Triple Bond, Angew. Chem. Int. Ed. Engl. 12, 564-565 (1973). 

An efficient method for the formal abstraction of oxide from acyl ligands was developed in our laboratory 44). Oxalyl halides react directly with the pentacarbonylmetal acyl complexes of chromium, molybdenum, and tungsten to form the fra ,s-alkylidyne(halo)tetracarbonyl complexes [Eq. (5)]. Other suitable Lewis acids are COCI2, CI3COCI, CI3COCOCI, and... 

Metal alkylidyne complexes undergo a variety of oxidation and reduction reactions as well as redox-induced transformations of the alkylidyne ligands. A method for the direct transformation of Fischer-type carbyne complexes into Schrock-type alkylidyne complexes was developed in our laboratory. Bromine oxidation of the /ra/7, -carbyne bromo tetracarbonyl complexes 49 of molybdenum and tungsten in the presence of dimethox-yethane affords the dme-stabilized alkylidyne tribromo metal complexes 50 [Eq. (42)] (81). For alkyl-substituted complexes (R = Me, CH2CMe3)... 

Competition experiments again feature prominently in another discussion of the possible role of transient five-coordinate [Co(NH3)5] in induced and in spontaneous aquation of pentaaminecobalt(III) derivatives. " The operation or nonoperation of the D mechanism at various cobalt(III) centers and at penta-cyanoferrate(II) still requires a few experiments providing unambiguous results. Its operation at molybdenum(O)- and tungsten(0)-penta or tetracarbonyl complexes seems more firmly based. The question of its operation at pentacyanoferrates(III) does not seem to have caused much concern. The only recent paper which mentions kinetics of such a reaction, replacement of 2-methyl imidazolate in [Fe "(CN)5(2-Meimid)] ", reports that the limiting first-order rate constant is 2.3 x 10 s at 298 K, but is more preoccupied with redox catalysis by traces of iron(II) than with simple substitution. 

In a similar manner, Jt-allyl complexes of manganese, iron, and molybdenum carbonyls have been obtained from the corresponding metal carbonyl halides [5], In the case of the reaction of dicarbonyl(r 5-cyclopentadienyl)molybdenum bromide with allyl bromide, the c-allyl derivative is obtained in 75% yield in dichloromethane, but the Jt-allyl complex is the sole product (95%), when the reaction is conducted in a watenbenzene two-phase system. Similar solvent effects are observed in the corresponding reaction of the iron compound. As with the cobalt tetracarbonyl anion, it is... 

Upon UV irradiation in hydrocarbon solution, the hexacarbonyls of chromium, molybdenum, and tungsten react differently with conjugated dienes like 1,3-butadiene (la), ( )-l,3-pentadiene (lb), 2-methyl-1,3-butadiene (lc), ( , )-2,4-hexadiene (Id), ( )-2-methyl-l,3-pentadiene (le), 2-ethyl-1,3-butadiene (If), or 1,3-cyclohexadiene (Ig). Chromium hexacarbonyl (2) yields, with the acyclic dienes la-lf, tetracarbonyl-r/2-dienechromium(0) complexes (3a-3f) in a smooth reaction (8-10). With 1,3-cyclohexadiene, in addition to 3g, dicarbonylbis(>/4-l,3-cyclohexadiene)chromium(0) (4g) is obtained [Eqs. (7) and (8)j. During chromatography on silica gel, the 1,3-cyclohexadiene complex 3g dismutates readily to [Cr(CO)6] and 4g [Eq. (9)]. Under the same conditions with 2 1,3-cyclopentadiene (lh) yields, in a hydrogen-transfer reaction, the stable dicarbonyl- / 5-cyclopentadienyl-r/ 3-cyclopent-enylchromium (5) (11-13) [Eq. (10)]. 

Richard followed the course of the reactions of Cr(CO)6 and Mo(CO)6 with hexamethylborazine by UV-vis spectroscopy but although he observed that the intensity of the absorption maximum of the hexacarbonyls at around 290 nm decreased and a new band at around 350 nm appeared, he was unable to identify the new product. Experiments with other starting materials such as norborna-diene chromium and molybdenum tetracarbonyl or tris(aniline) molybdenum tricarbonyl which readily react with arenes by ligand exchange, also failed. The key to success was to use tris(acetonitrile) chromium tricarbonyl as the precursor, which in dioxan under reduced pressure afforded the desired hexamethylborazine chromium tricarbonyl as a stable crystalline solid in 90% yield. This was the breakthrough and, after we had communicated the synthesis and spectroscopic data of the complex in the January issue 1967 of Angewandte Chemie, Richard finished his work and defended his Ph.D. thesis in June 1967. Six months before, in December 1966,1 defended my Habilitation thesis in front of the faculty and became Privatdozent (lecturer) on the 1st of January 1967. 

Only one example of a chelated tetracarbonyl chromium-containing complex has been reported during the period under review <1997T17297>. Molybdenum- and tungsten-containing complexes have also been studied. 

O4M02PC23H29, Molybdenum, tetracarbonyl-bis(Ti -cyclopentadienyl)(p,-di-tert-butyl-phosphido)- jL-hydrido-di, 25 168 Oghl4CioFIi23 Xanthosine palladium(II) complexes, 23 54... 

Br2MoC4, Molybdenum(ll), dibromo-tetracarbonyl-, 28 145 04CgH4, Phthalic acid, rhodium complex, 27 291... 

The use of liquid ammonia well above its normal boiling point as a solvent and reactant has been fruitful. The metal hexacarbonyls themselves have afforded the complexes [M(CO)3(NH3)3] (M = Cr, Mo, W) and [Cr(CO)s NH3] 81). The tetracarbonyl(dipyridyl)metal complexes of chromium, molybdenum, and tungsten and their (o-phen) analogs react with liquid ammonia to give very air-sensitive compounds, such as [M(CO)3(dipy) (NH3)], which finally yield mainly [M(CO)3(NH3)3] 81). The [M(CO)4... 

Similarly, iodination of tetracarbonyl(2,5-dithiahexane)metal (Cr, Mo, W) complexes gives isolable seven-coordinate products [Ml2(CO)3(2,5-dithia-hexane)] only for molybdenum and tungsten. Reduction of these iodo compounds with lithium aluminum hydride forms unisolable materials with M—H bonds 45). 

The molybdenum compound readily adds carbon monoxide at room temperature and atmospheric pressure forming the tetracarbonyl C8HsMo(CO)4 in which the C8Hs ring is thought to have the boat form [39]. Treatment of C8H8Mo(CO)3 or C8H8Mo(CO)4 with adds causes protonation and the homotropylium molybdenum tricarbonyl cation, 6.15, is formed [40]. In this complex the hydrocarbon is a 7-electron... 

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