Metal-carbyne complexes Bridging

In this review, well-defined metal-containing PAEs are described whose primary structure is represented by one of the schematic drawings A-C and E shown in Fig. 2. In contrast to the structures shown in the A-C systems, E has a conjugated phenyleneethynylene with metal chelates as end groups. PAEs containing metal complex as side groups (D) have, up to now, not been described in the literature. The classes of compounds such as metal-bridged alkynes, the poly(metallayne)s, and polymer carbyne complexes (structures G and H) do not in fact represent PAEs. 

An impressive series of carbene- and carbyne-bridged complexes of platinum have been formed by reaction of metal carbene complexes with a platinum complex (equation 141). These complexes have been verified by X-ray crystallography, and the synthetic method appears to be one of some generality. Among the complexes of this type formed from carbenes are ones having metal frameworks with Pt—W,409-413 Pt—Mn414-418 and Pt—Cr413,417 bonds. 

Extension to trimetallic complexes has led to the preparation of similar bridging carbene and carbyne complexes with Pt3,421 Pt2W422 and PtWFe423 metal frameworks. 

In addition to complexes containing carbenes bonded to a single metal atom (M=CRR ), complexes are also known where the carbene ligand bridges two metal atoms (M-CRR -M, p-methylenes) similarly there is an extensive chemistry of metal-carbynes (M=CR, with a formal triple bond between the metal and the ligand) and p-methylidynes where the ligand is again... 

In addition to complexes of terminal alkylidenes, many complexes containing alkylidenes bridging two metal atoms have been made these are commonly known as p-methylene complexes. A wide range of complexes containing other metal-carbon bonds are known such as the carbyne complexes (for example, Cr = CPh(CO)5) which contain metal-carbon triple bonds. While such species may well be involved in some catalytic reactions, their importance in industrially catalyzed processes still has to be evaluated. 

The osmium carbyne complex 115 reacts with elemental sulfur, selenium, and tellurium to afford the complexes 135 in which the element atoms "bridge the metal-carbon triple bond [Eq. (123)] (56). Complex 115 also reacts with transition metal Lewis acids such as AgCl or Cul to give dinuclear compounds with bridging carbyne ligands. Reaction with elemental chlorine results in addition across the metal-carbon triple bond to generate the chlorocarbene osmium complex 136 [Eq. (124)]. 

Utilization of the electron-rich metal-carbyne bond to function as a ir-ligand toward coordinatively unsaturated metal complexes has widely been employed by Stone and co-workers (226,227) and represents a versatile route for the synthesis of bimetallic and trimetallic complexes with metal-metal bonds. Bimetallic carbido-bridged complexes [M]=C=[M]... 

Metal Carbenes and Metal Carbynes as Precursors for a Rational Synthesis of Carbido and Hydrocarbon Bridged Complexes... 

METAL CARBENES AND METAL CARBYNES AS PRECURSORS FOR A RATIONAL SYNTHESIS OF CARBIDO AND HYDROCARBON BRIDGED COMPLEXES... 

The complexes with a double bond M=0 and M=NR, i.e. metal-oxo and metal-imido are isoelectronic to metal-carbene complexes and show, as the latter, a rich chemistry, all the more so as the binary complexes M(=0)n and M(=NR)n are well known. - - The phosphinidenes M=PR and the nitrido complexes M=N, isoelectronic to metal carbynes, are also known. All these ligands can bridge two or three metals, in which case there is no multiple bond. 

Byers, P.K, Carr, N. and Stone, F.G.A. (1990) Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M ( CR)(CO)2 (C6F5)AuC(pz)3 j (M = W or Mo, R — alkyl or aryl, pz — pyrazol-l-yl) crystal structure of pjC PtAu(C6F5)( l3-CMe)(CO)2(PMe2Ph)2 (C6F5)AuC(pz)3 ]. Journal of the Chemical Society, Dalton Transactions, (12), 3701—3708. 

The rapid development of the chemistry of transition metal complexes containing terminal carbene (A) or carbyne (B) ligands (7) has been followed more recently by much research centered on bridged methylene compounds (C) (2). The importance of /t-methylidyne complexes, whether in recently established binuclear examples (D), the well-known trinuclear derivatives (E), or the unusual complexes (F), has also become apparent. All are based on one-carbon (C,) fragments, and considerable interest is centered on their possible significance as models for intermediates in surface-catalyzed reactions between carbon monoxide and hydrogen (Fischer -Tropsch reactions) and related processes. These topics have been extensively ... 

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