Molybdenum cyano complexes

Experimental Procedure 3.1.4. Preparation of a Molybdenum Vinylidene Complex from a Carbyne Complex Tetrabutylanunoniuih Cyano(ethoxycarbonyl) vinylidene (dicarbonyl) hydro-tris(3,5-dimethyl-1 -pyrazblyl)borato molybdenum [526] [37] pp 151 and 188... 

By way of example, we can focus on the cyano complexes. Palladium and platinum can form homoleptic complexes with two, four, or six cyanides, depending on the metal oxidation state zero, two, and four, respectively. Rhenium forms heptacyano complexes in its - -3 and -t-4 oxidation states but forms an octacyano complex in its -t-5 state. Molybdenum and tungsten also appear commonly in octacyano complexes for +4 and - -5 oxidation states, and heptacyano analogs for the - -2 and - -3 cases, with only one occurrence of [Mo(CN)6]" anions in two oxidation states (n = 3, 4). Similar situations can be found with phosphine or carbonyl complexes. For instance, the group... 

Apart from the lanthanide and actinide exchange reactions described in Sections 7 and 8, the photochemical investigations of the cyano-complexes of molybdenum(iv) mentioned in Section 4,i <-i and the n.m.r. investigations outlined above, no further kinetic studies of metal ions with high co-ordination numbers have appeared. 

A more complex reaction is involved in the cooligomerization of acetylenes and tert-butyl isocyanide using nickel acetate as the catalyst (Scheme 20)43 the nature of intermediate complexes leading to the formation of 2-cyano-5-terf-butylaminopyrroles has not been established. Cocyclization of tert-butyl isocyanide with coordinated hexafluoro-2-butyne gives rise to coordinated cyclopentadienone anils for molybdenum systems,44 hence the nature of acetylene substitutents and of the organometallic catalyst play crucial roles in these processes. The pyrrole products from the former reaction can be decomposed by sulfuric acid and the overall sequence provides a simple synthesis of 5-amino-2-cyanopyrroles (Scheme 20). 

Propynylnaphthalene 15 furnishes dinaphthylacetylene 20 in near quantitative yield. On the other hand, the Mori system performs somewhat less well if heteroatoms are present in the substrates, suggesting that the catalytic system is poisoned by the presence of the heteroatom through complexation and/or chelation of the active molybdenum center. Cyano groups and bromides/iodides inhibit the reactivity of the catalyst system. However, both propynylated phenols (16) and esters (17) give satisfactory dimerization results (21, 22). 

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