Carbyne complex osmium

When the reaction was attempted with Cl2C=IrCl3(PPh3)2 a crystalline solid, which was a green color typical of osmium carbyne complexes, could be observed at -78°C, but attempts to characterize this solid at room temperature were unsuccessful (39). No well-defined carbyne complexes of iridium have been reported to date. 

Electrophilic attack at carbyne complexes may ultimately place the electrophile on either the metal or the (former) carbyne carbon, the two possibilities being related in principle by a-elimination/migratory insertion processes (Figure 5.39). The reactions of the osmium carbyne complex are suggestive of an analogy with alkynes. Each of these reactions (hydro-halogenation, chlorination, chalcogen addition, metal complexation see below) have parallels in the chemistry of alkynes. 

There are two principle methods for the synthesis of osmium carbyne complexes (1) modification of a halocarbene, or (2) reaction of a hydride with a terminal... 

The reaction of tellurium with osmium-carbyne complexes or with osmium-methylene complexes, or of sodium hydrogen telluride with iodomethyl(iodo)-osmium complexes produced tellurolato-osmium compounds. 

Roper and co-workers described the synthesis of the osmium carbyne complex 10 from the reaction of the dihalocarbene complex 9 with 2 equiv /7-tolyllithium [Eq. (16)] (56). 

The trigonal bipyramidal osmium carbyne complex 115 adds HCl across the metal-carbon triple bond to give the octahedral carbene complex 116 [Eq. (101)] (56). Protonation of 115 with aqueous HCIO4 gives the cationic... 

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)]. 

OsCl2(CO)(CTe)(PPh3)2]. The cationic osmium carbyne complex, [Os(CR)-(CO)a(PPh3)2]+ (R=p-tolyl), reacts with LijBtsBH] to form the unusual vinylidene complex (34). Iron, ruthenium, and osmium carbene complexes are also discussed in Section 2 (refs. 8, 34, and 38). 

Mononuclear Carbenes and Carbynes.—The osmium-carbyne complex (1) has been structurally characterized, and the Os=C distance found to be 1.77(2) A and the Os-C -C angle 164(2)°. The osmium-carbon triple bond in (1) interacts in an acetylene-like manner with AgCl to give the dimetallocyclopropene derivative (2), in which the Os-Q distance has increased to 1.839(5) A. 

Hydride addition in the cationic osmium carbyne complex [Os(CC6H4-pMe)-(CO)2(PPh3)2]+ unexpectedly occurs at the />ara-position of the aromatic ring of the carbyne ligand, giving the unusual vinylidene complex (3). ... 

The reactions of a neutral 10 as well as a cationic dihydrido(acetato)osmium complex 12 with acetylenic compounds were examined (Scheme 6-17) [11-13]. A vinyU-dene 99, an osmacyclopropene 100, or a carbyne complex 101 were obtained, depending on the starting hydrido(acetato) complexes or the kind of acetylene used. In any case, the reaction proceeded by insertion of a C C triple bond into one of the two Os-H bonds, but the acetato ligands do not take part in the reaction and act as stabilizing ligands. 

Carbene and Carbyne Complexes of Ruthenium, Osmium, and Iridium... 

It is interesting to note that the decrease in metal electron density that accompanies the change from five- to six-coordinate geometry does not have a detectable effect on the metal-carbene carbon bond length in these complexes. The metal-carbyne carbon bond in several osmium carbyne... 

Carbyne complex chemistry of osmium and ruthenium is discussed in this section. These studies demonstrate clearly the parallels that exist between the metal-carbon bonds in carbene and carbyne complexes and again emphasize the importance of metal basicity in determining complex reactivity. 

The a-osmiumdiazo compound 91 decomposes in a thermal reaction to yield the metallacyclic complex 93 (130). This resembles the electrophilic carbene insertion reaction forming OsCl(CO)2(PPh2C6H4CHCl) (PPh3) (77) (see Section V,D,2), and we suggest that a similar insertion reaction of an electrophilic, cationic osmium carbyne 92 is the key step in this transformation. An X-ray structure determination has confirmed the formulation of 93. 

The osmium-carbyne carbon bond lengths for the three complexes do not differ significantly, and reference to Table IV indicates that these distances are distinctly shorter than the characterized metal-carbon double bonds of osmium carbene and carbonyl complexes. In both osmium alkylidene and carbyne complexes, then, the metal-carbon multiple bond lengths are largely insensitive to changes in the metal electron density (cf. Section IV,B). 

The X-ray structure determination of 107 reveals that the osmium-carbon bond length is increased by 0.07 A on going from the parent carbyne complex 79 to the silver adduct 107. This may be contrasted with the weaker interaction between the metal-carbon bond and the Aul fragment in Os(CH2AuI)Cl(NO)(PPh3)2 (see Section IV,C,1). 

Scheme 8.20 Preparation of the five-coordinate osmium carbynes 75a,b and their reactions with chalcogens, HCI and chlorine to afford the six-coordinate carbene osmium(II) complexes 76a,b, 77a,b, and 78a,b (a R = Me, b R = Ph E = S, Se, Te)...

Osmium carbyne (see Carbyne Complexes) or aUcylidyne complexes have a triple bond between the metal and the carbon atom of the ligand. Carbyne complexes are related to singlet carbenes. They are analogous to linear nitrosyl (see Nitrosyl Complexes) complexes and the osmium is usually in a lower oxidation state. Alkylidyne complexes are related to triplet carbenes and the bonding between the osmium and the carbon atom is similar to the C-C bond in an alkyne. 

The chemistry of osmium carbene and carbyne complexes is rich owing to the high Os-C bond strength that stabilizes these species. Alkyl and vinyl complexes can convert to carbene and vinylidene complexes. They can interconvert... 

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