Fischer carbyne metal complexes

Transition metal carbyne complexes are still relatively uncommon as only a few synthetic approaches to these compounds has proved generally applicable. In addition to making the initial characterization (723), the Fischer group has made the largest contribution to carbyne complex chemistry, with some 200 mononuclear complexes of Group 6 and 7 metals having been prepared. 

The reversible [2+2] cycloaddition of metal alkylidyne or Fischer-type metal carbyne complexes remains the only general methodology for the synthesis of metallacyclobutadiene complexes. Recent literature revolves principally around the heavier group 6 metals and the investigation of intermediates in catalytic alkyne metathesis (Scheme 25 Equation 45) <1996CHEC-II(lb)887> (W <2005OM4684>, Mo <2003JOM56>). 

The first transition metal carbyne complexes, [M(CR)X(CO)4], were synthesized in Fischer s laboratory by treatment of alkoxycarbene penta-... 

Transition metal carbyne complexes are described by the general formula L M=CR where the carbyne ligand (=CR) is bonded to the metal by a metal-carbon triple bond. Transition metal carbene complexes have found numerous applications in synthetic organic chemistry through a variety of carbene transfer and cycloaddition reactions [17]. In contrast, carbyne (L M=CR) and vinylidene (L M=C=CRR ) complexes have far fewer applications, in part because their overall chemistry is significantly less developed [18]. Addition reactions to transition metal vinylidene complexes will be discussed in Chapter 21. The first successful synthesis of a carbyne complex was reported by Fischer and co-workers in 1973 [Eq. (8) 19]. Subsequently, many other carbyne complexes have been synthesized by the classic route of Fischer or by new synthetic methods [20]. 

Weiss, K. (1988) Catalytic Reactions of Carbyne Complexes in H. Fischer, Transition Metal Carbyne Complexes, VCH Publisher Weinheim. 

S, F. Vyboishchikov and G, Frenking,/. Am. Chem. Soc., submitted for publication. Structure and Bonding of Low-Valent (Fischer-Type) and High-Valent (Schrock-Type) Transition Metal Carbyne Complexes,... 

G. Huttner, A. Frank, and E. O. Fischer, Israel J. Chem., IS, 133 (1976/77). Transition Metal Carbyne Complexes. XXIX. Metal Carbon Triple Bonds X-Ray Studies on Group Via Metal Carbyne Complexes. 

Metal carbyne complexes MsCR also have Fischer and Schrock extreme bonding formulations, although the distinction i less marked than for carbenes. In one bonding model, the free carbyne can be considered as doublet for Fischer and quartet for Schrock forms (Fig. A doublet carbene is a 2e donor via its... 

During this same year, 1971, E.O. Fischer synthesized the first metal-carbyne complex and the Monsanto Company developed the rhodium-catalyzed carbonylation of methanol to acetic acid. In 1975, the DuPont de Nemours Company produced adiponitrile using the Ni°-catalyzed hydrocyanation of butadiene. 

Metal-carbyne complexes M CR are less known than metal carbenes. The carbyne can also be nucleophilic (Schrock type) or electrophilic (Fischer type). Fischer-type metal-carbynes are obtained by reaction of BF3 on a neutral Fischer-type metal-carbene complex, whereas Sehroek earbynes are often obtained by deshydrohalogenation of a Schrock-type metal-carbene eomplex. They catalyze alkyne metathesis and, in particular, give heterocycles with unsaturated substrates. 

E. O. Fischer, F. J. Gammel, J. O. Besenhard, and A. Frank, and D. Neugebauer, J. Organomet. Chem., 1980, 191, 261. Transition-metal carbyne complexes LIV. New metallocene-carbene and carbyne complexes of Group VI, preparation and electrochemical characteristics. 

Several stable Group 6 metal-ketene complexes are known [14], and photo-driven insertion of CO into a tungsten-carbyne-carbon triple bond has been demonstrated [15]. In addition, thermal decomposition of the nonheteroatom-stabilized carbene complexes (CO)5M=CPh2 (M=Cr, W) produces diphenylke-tene [16]. Thus, the intermediacy of transient metal-ketene complexes in the photodriven reactions of Group 6 Fischer carbenes seems at least possible. 

The same dichotomy of bonding models is also found for carbyne complexes that have a formal triple bond M=CR. There are metal-carbyne bonds that belong to the donor-acceptor type (the Fischer car-... 

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... 

P. Kim and R. J. Angelici, Transition Metal Complexes with Terminal Carbyne Ligands, in Adv. Organomet. Chem., 1987, 27, 51 H. Fischer, P. Hoffmann, F. R. Kreissl, R. R. Schrock, U. Schubert, and K. Weiss, Carbyne Complexes, VCH, Weinheim, Germany, 1988. 

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)... 

The mechanism of ligand substitution reactions in the carbyne complexes /rar7.v-M(CR)X(CO)4 (M = Cr, W R = Me, Ph, NEtj X = Cl, Br, 1, SePh) was investigated by H, Fischer and co-workers (JOO). The influence of the metal center, the trans ligand, and the carbyne substituent on the M—CO dissociation step was determined. The reactions with PPhj in 1,1,2-trichloroethane [Eq. (62)] all follow first-order kinetics, with activa-... 

Carbyne ligands can also be grouped into two classes Fischer and Schrock carbynes. The metal-carbyne carbon triple bond (Fig. 3) for a Fischer carbyne complex is formed... 

The reactions of Fischer and Schrock carbyne complexes are of interest because they may act as intermediates in chemical synthesis. Typical reactivity of carbyne complexes with nucleophiles (i.e., alkyl lithium reagents and metal(I) alkoxides) are consistent with the electronics and molecular orbital calculations for these types of complexes [Eq. (9) 22]. The nucleophile adds to the carbyne-carbon, resulting in the formation of a carbene complex. The reaction of a Grignard reagent with a carbyne complex is expected to demonstrate similar reactivity. 

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. 

Nine years after Fischer s report of the first stable transition metal-carbene complex, the first report was made of the synthesis of complexes containing a transition metal-carbon triple bond fittingly this report was also made by the Fischer group.15 Carbyne complexes have metal-carbon triple bonds, and they are formally analogous to alkynes.16 Many carbyne complexes are now known examples of carbyne ligands include the following. 

Complexes containing metal-carbon triple bonds in which the metal is in a relatively high formal oxidation state are frequently designated alkylidynes. Carbyne complexes are also sometimes classified as Fischer-type or Schrock-type, as in the case of carbene complexes. The distinction between these is discussed in Chapter 10. 

Since Fischer s breakthrough, numerous new carbyne complexes involving mainly Group 5, 6, 7, 8, and 9 metals have been prepared, their structures determined, and their chemistry explored. Some examples of metal carbynes appear as structures 65, 66, and 67. 

There are several parallels between the chemistries of the carbene and carbyne ligands. The classification of carbyne complexes into two major structural types—Fischer and Schrock—is perhaps the most obvious of these parallels. Complex 64 represents the prototypical Fischer carbyne complex Ccarbyne bonded to a low-valent metal with Ji-accepting CO ligands attached. Structure 65, on the other hand, is a classic example of a Schrock carbyne complex because a high-valent metal is present with electron-donating ligands attached. Atoms attached to Ccaibyne helpful in distinguishing between Fischer and Schrock carbene complexes (i.e., heteroatoms for the former and H and C for the latter), are less important in the case of carbyne complexes. It is convenient to classify carbyne complexes... 

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