Metal ligand triple bonds

In Reaction 6 the metal-metal triple bond is cleaved and replaced by a metal-ligand triple bond. 

Many anionic nucleophiles add to the carbyne carbon in cationic Fischer complexes, and these reactions can be used to synthesize carbene ligands unavailable by other routes. The stepwise reduction of a metal-carbon triple bond has been demonstrated (32) ... 

Reactions of carbyne complexes that maintain the integrity of the metal-carbon triple bond form the third route to new carbynes. Substituent modification, ligand exchange, oxidation, and reduction reactions have all been reported (see, e.g., Ref. 126). 

In the first structurally characterized complexes of type A the metal-phosphorus triple bonds are kinetically stabilized by bulky substituents at the amido ligands. Therefore, these compounds reveal exclusively end-on reactivity via the phosphorus lone pair. This reactivity pattern seems also valid for the solution stable alkoxide derivative [(C/0)3Mo=P], for which the reaction potential is under investigation [13]. In contrast, due to their lesser degree of kinetic stabilization by bulky substituents the short-lived alkoxide containing complexes [(R 0)3W=Pj (R =t-Bu (3c), Ph (3d)), generated by the metathesis reaction between the alkoxide-dimer and the phosphaalkyne (cf. Eq. 8), show additionally a high side-on reactivity towards the phos-phaalkynes of the reaction mixture. Thus, there occurs a formal cycloaddition reaction with the phosphaalkynes, and a subsequent 1,3-OR shift yields the formation of four-membered diphospha-metallo-cyclobutane derivatives 6(Eq. 8) [15,31, 37]. 

The synthesis of stable complexes with transition metal-phosphorus triple bonds is of fundamental importance and opens a novel chapter of a special field of coordination chemistry. The synthesis of analogous complexes with ligands of the heavier homologues like arsenic has partially been carried out [6], while for antimony and bismuth, the elusive M=Sb and M=Bi systems have now moved within reach. Moreover, the experimental and theoretical... 

The lowest oxidation state, -3, having a ns np electron configuration, is found in transition metal complexes of ligand-free Pn anions. When a single Pn ion is attached to a metal, they are collectively referred to as pnictido ligands and form terminal metal-pnictogen triple bonds, which are known for all group 15 elements except bismuth. ... 

Carbyne complexes have metal-carbon triple bonds they are formally analogous to alkynes. Many carbyne complexes are now known examples of carbyne ligands include the following ... 

Nucleophilic displacement at a terminal methylidyne ligand, with regeneration of a metal - carbon triple bond in 199 (E = S or Se, R = Me, Ph, or P-NO2QH4) to form a new methylidyne ligand, occurs in the reaction of 198 [L = HB(3,5-Mc2—C3HN2)3] with thiolate or selenolate anions under phase-transfer conditions 149). 

Substitution of the ligand trans to the metal-carbon triple bond, usually a halide, was observed in several situations. Substitution of halide in the tetracarbonyl systems is rare because most nucleophiles will substitute carbon monoxide. It was found that the halide is substituted by the carbonyl metallate anions [Mo( / -CjH5)(CO)3]" and [Co(CO)4] [Eq. (74)]... 

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)]. 

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]. 

Titanium amido and imido complexes are of increasing interest as reagents in organic transformations and catalysis.1 1 For ease of representation, the terminal titanium-imido or titanium-oxo linkages are generally drawn as Ti=X (X = NR, O). Nevertheless, the formal metal-ligand multiple bonds in these complexes are better described as a2-tt4 triple bonds. 

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. 

It has been noted that metal-carbon triple bonds behave in a similar way as alkynes with respect to jr-complex formation13,15. Various heterometallic gold complexes with bridging carbyne ligands reflect this analogy. Alkylidyne complexes like [W(=CR)(CO)2( 5-C5H5)], [W(=CR)(CO)2( 75-C2B9H9R )] (R = alkyl, aryl, amino R = H, Me) readily... 

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