Chromium complexes carbyne

Lithium ben/cnetellurolate converted a carbonyl chromium carbyne complex to a phenyltellurocarbene complex4. 

As has been demonstrated in Section 3.1.2.4, complexation of amino groups offers a quite different concept for reversible protection. Making use of this principle, the coordination of chromium carbyne complexes with amino acids was described as a new amino protection. Similarly, bis(ethylene-diamine)cobalt(III) complexes of amino acids constitute a new interesting method for protection which recently was extended to the development of a new type of anchoring in solid-phase synthesis (Scheme 69). First, a t-BOC amino acid is condensed with the aquabis(ethylenediamine)cobalt(lII) complex of p-aminomethylbenzoic acid. The handle obtained in this way is then linked to aminomethyl polystyrene to give the anchored amino acid (69). Due to the sufficient stability of the complex toward... 

G. A. McDermott, A. M. Domes, and A. Mayr, Synthesis of Carbyne Complexes of Chromium, Molybdenum, and Tungsten by Formal Oxide Abstraction from Acyl Ligands, Organometallics 6, 925-931 (1987). 

The synthesis of cyclopropyl carbyne complexes follows the general Fischer synthesis of carbyne complexes from alkoxycarbene complexes typical of transition metals of group 6 (Cr, Mo, W). Thus, addition of cyclopropyllithium to chromium and tungsten hexacar-bonyl followed by alkylation of the acylmetallate intermediate with triethyloxonium fluo-roborate gave cyclopropyl ethoxycarbene complexes which, upon subsequent reaction with boron tribromide at -25 °C, afforded the corresponding /ra 5 -bromotetracarbonyl cyclopropylcarbyne complexes (equation 91). However, whereas the monotungsten... 

When hydroxycarbene complexes of tungsten are reacted with dicyclohexylcarbodi-imide (DCCD), a novel carbyne complex is formed, having a metal acylate moiety ligated trans to the carbyne ligand . Reaction of the corresponding complexes of chromium with DCCD yields different (noncarbyne) products. 

The reactions of Fischer carbene complexes with alkynes can under certain conditions lead to products that result from the incorporation of two alkynes, the carbene ligand and a carbon monoxide. In inter-molecular reactions, this is most commonly observed for acetylene itself or for sterically unhindered al-kynes. °2 As can be anticipated by the mechanism in Scheme 36, two-alkyne incorporated products of the type (258) are also favored for high alkyne concentration. Synthetically, the two-alkyne reactions are most useful in intramolecular reactions, two of which have been reported and are exemplified by the reactions in Scheme 43. The typical product from the reaction of a Fischer carbene complex with a diyne, such as (308), is a bicyclic phenol of the type (309). ° These products are apparently the result of the assembly of pieces indicated by (311). Under some conditions, dienones of the type (310) and (314) can be isolated, and it is thought they are the immediate precursors of the phenol products via an in situ reduction by a chromium(O) species. This reaction is completely regioselective with diyne (308) and the phenol (309) results from incorporation of the terminal alkyne of (308) before the disubstituted alkyne. Phenols of the type (309) have also been observed from the reaction of diynes with carbyne complexes. ... 

Finally, the octahedral molybdenum-carbyne complex ( j -C5H5)Fe[ 7 -C5H4-C = Mo(CO)4Br] undergoes a one-electron oxidation at E° = -F 0.79 V in DME [34], which is very near to that of the corresponding chromium complex illustrated in Scheme 7-4 and Table 7-5. 

Ernst Otto Fischer (bom 1918) was a student of Walter Hieber at Technische Hochschule Miinchen where he received his Ph.D. degree in 1948. He elucidated the molecular stmcture of ferrocene shortly after this compound was discovered. Further highlights in his life s work were the synthesis of dibenzene-chromium (C6H5)2Cr in 1955, the discoveries of the first metal carbene (1967), and the first me-tal-carbyne complex (1971). In 1964 he succeeded Walter Hieber to the chair of inorganic chemistry at Technische Hochschule Miinchen from which he retired in 1985. He received the Nobel prize for chemistry jointly with Geoffrey Wilkinson (Imperial College London) in 1973. 

By reaction with the Fischer type carbyne complexes loose the surface chromium(II) atoms of the reduced Phillips their polymerisations activity for 1-alkenes (16). The surface chromium(II) atoms enhance the metathesis activity of the bimetallic catalysts (Table 1). In contrast to the original Fischer type carbyne complexes are the bimetallic catalysts stable at room temperature. They can be stored for a year at 25°C without changing their metathesis activity (14). 

Fischer first prepared carbyne complexes by the action of boron halides on carbene compounds of chromium, molybdenum, and tungsten. 

These reactions occur quite readily [reaction (5.143)]. The carbonyl groups much more easily undergo substitution reactions in 18e carbyne complexes of chromium group metals than in M(CO)6 ... 

The products of thermal decomposition of the chromium carbene adduct [(OC)5Cr=C(Cl)NEta] depend on whether the material is heated in solution or as a solid. In solution the carbyne complex [Cl(OC)4Cr=CNEtg] results, but the solid affords a mixture containing the isonitrile adduct [(OC)5Cr(C3 Et)]. The... 

Alkylidene and alkylidyne complexes are also referred to as carbene and carbyne complexes. Alkylidene complexes are of two types. The ones in which the metal is in a low oxidation state, like the chromium complex 2.37, are called Fischer carbenes. In contrast, complex 2.38, wha e the metal ion is in a high oxidation state, is referred to as a Schrock carbene. 

The syntheses of many Co3(CO)9X compounds from dicobalt octacarbonyl and XCCI3 have been optimized 347), and further reactions starting from 0(60)4 and XCCI3 360), or RCF —Co(CO)4 46) have been investigated in order to determine the mechanism of formation of the clusters. Methinyltricobalt enneacarbonyls are also formed from Co2(CO)g and such apical carbon precursors as acetylenes 140), dimethyl ketene 408), or carbyne chromium complexes (7 73). In several cases (7 72,... 

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). 

Katz and co-workers reported the reactions of the chromium and tungsten ethylidyne complexes 249 and 250 with l-alkynyl-l -vinylbiphenyl (193.194). For both metals the reactions lead to the incorporation of the carbyne ligand into the organic substrate, but in slightly different ways as shown by formation of the products 251-253 [Eq. (187)]. The product of... 

Heterogeneous, bimetallic metathesis catalysts are formed by reactions of Fischer type carbyne tungsten or molybdenum complexes with the reduced Phillips catalyst, a suface chromium(II) compound on silica (14).(scheme 5). The bimetallic surface compounds can result from 2+1 cycloaddition reactions. Similar reactions are well known by the work of Stone (15). 

---