Alkynes cyclometallation

Ortho C-H Bond Activation Regioselective Oxidative Cycloaddition of Aromatic Amides to Alkynes. Cyclometalation reactions with nickel phosphine COD complexes used an amido nitrogen atom as the coordinating atom. The insertion and cyclization with alkynes is then proposed to proceed via the cyclometalation nickel intermediate as an active center to give the six-membered isoquinolone derivatives shown in Eq. (6.6). In 2013, Chatani et al. [22] also reported on these chelation-assisted transformations in details as the review articles. 

A wide variety of five-membered zirconacydes 8 may be formed by the formal co-cycliza-tion of two 7i-components (3 and 6 alkene, alkyne, allene, imine, carbonyl, nitrile) on zir-conocene ( Cp2Zr ) (Scheme 3.2) [2,3,8]. The co-cydization takes place via the r 2-complex 5 of one of the components, which is usually formed by complexation of 3 with a zircono-cene equivalent (path a) ( Cp2Zr itself is probably too unstable to be a true intermediate) or by oxidation on the metal (cyclometallation/p-hydrogen elimination) (path b). Two additional routes to zirconocene r 2-complexes are by the reverse of the co-cyclization reaction (i. e. 8 reverting to 5 or 9 via 7), and by rearrangement of iminoacyl complexes (see Section... 

Crabtree and coworkers used the cyclometallated lr(lll)-hydride complex 19 for the intramolecular hydroalkoxylahon and hydroaminahon of aromatic alkynes (Equahon 6.10) [25], while Liu and coworkers used the neutral lr(lll)-hydride complex 20 in combinahon with cocatalytic amounts of NaB[3,5-C6H3(CF3)2]4 for the synthesis of a range of indoles (Table 6.4) [26]. 

Cyclohexyldienyl complexes, with Ti(IV), 4, 327 Cyclohexylisocyanides, with gold(I) halides, 2, 281 Cyclohexylphosphine, for semiconductor growth, 12, 9 Cyclohexyl selenides, preparation, 9, 480 Cyclohydrocarbonylation alkenes, 11, 515 alkynes, 11, 522 dienes, 11, 522 overview, 11, 511-555 for ring expansion, 11, 527 Cycloisomerizations, via silver catalysts, 9, 558 Cyclomanganation, product types, 5, 777-778 Cyclometallated azobenzenes, liquid crystals, 12, 251 Cyclometallated complexes for OLEDs... 

Cyclometallation (also called oxidative coupling) is a rather special case of oxidative addition. In this reaction, two unsaturated molecules, X=Y and X =Y, add to the same metal atom M. One of the X—Y bonds and one of the X —Y bonds are broken, and new M X and M -Y bonds form. However, a new Y—Y bond also forms, and the overall result is a cyclometaUated compound (Figure 3.7a). As in oxidative addition, the oxidation state of the metal center increases by 2. Cyclometallation is common with alkynes (Figure 3.7b), as well as with alkenes activated by electron-withdrawing groups [21]. 

Attempts to prepare titanaindanes and titanaindenes from thermolysis of 28a or 28b in the presence of alkenes and alkynes failed only the cyclometalated complexes 30a and 30b from intramolecular C-H activation in 29 were observed [Eq. (7)].42 A similar reaction has been observed for substituted Cp2Zr-benzyne complexes.2... 

The activation of intramolecular carbon-hydrogen bonds by metal ions in the gas phase first involves tt-coordination, followed by remote functionalization of C—H or C—C several carbons distant from the initial coordination site. Schwarz has reviewed his prolithic work in this area. High-resolution translational energy loss measurements on the remote functionalization of internal alkynes by Cr" have been made. These indicate that the ions involved are in the ground state and that no added collisional energy transfer is needed for cyclometallation to proceed. The reactions of Fe", Co", and/or Ni" have been studied with alkyl-substituted amines, " alcohols, ketones, nitriles, " ... 

Scheme 7.3 One-pot synthesis of heterocyclic compounds through two types of insertions of an alkyne and two alkynes into the metal-carbon bond of activated cyclometalated benzyl methyl sulfide [67]...

Alkynylations (reactions with alkynes) have already been shown in Sect. 7.3 as reactions of cyclometalation reaction products with alkynes. 

For example, a benzamide as an arylamide reacts with an alkyne in the presence of a rhodium compound to give the cychzation product isoquinolone 7.93 via a cyclometalation intermediate 7.92 coordinated by an alkyne, as shown in Eq. (7.81) [157]. 

Other examples of arylimines and arylketones as substrates in cyclometalation reactions are shown in Eqs. (7.82) and (7.83), respectively. These products are also prepared via cyclometalation intermediates 7.94 and 7.95, followed by insertion of an alkyne moiety between the metal and y-carbon atom, that is, at the ortho-caibm [161,164]. 

Cyclometallated complexes incorporating transition metals other than palladium react with alkynes and act as synthetic precursors to hetero-... 

Reaction of the cyclometallated derivative of phenyl-2-pyridylketone 73 leads to indenol-chelated, palladium-containing derivatives 74. Here, incorporating an electrophilic (CO) function in the starting palladacycle signifies that, following alkyne insertion in the Pd-C bond, an intramolecular attack of the vinyl palladated unit on the metal-bound, activated CO function occurs. This is in sharp contrast to the reaction described in Scheme 9 whereby incorporating a nucleophilic, masked, secondary amine function leads to indole derivatives 40 and to the azepinium synthesis from the metallated benzylpyridine complex 34. Therefore, these reactions are rather sensitive to the nature of other potentially reactive functions within the metallacyclic framework. 

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