Alkyne complexes exchange reactions with alkynes

The formation of a bis(guanidinate)-supported titanium imido complex has been achieved in different ways, two of which are illustrated in Scheme 90. The product is an effective catalyst for the hydroamination of alkynes (cf. Section V.B). It also undergoes clean exchange reactions with other aromatic amines to afford new imide complexes such as [Me2NC(NPr )2]2Ti = NC6F5. ... 

An interesting new entry into metallocene-containing dithiolato and diselenolato complexes (see also Section 16.5.2.4.3) are the reactions of titanocene pentasulfide (57) or pentaselenide (58) with activated alkynes.83 Titanocene dithiolates (59) and diselenolates (60) with X = CF3 and C02Me were obtained. The authors also performed a number of exchange reactions with the Se compound (60 X = CQ2Me). 

A transmetalation of the styrylcarbene chromium complex 62 in the presence of stoichiometric amounts of [Ni(cod)2] to give the nickel carbene intermediate 63 was applied to the synthesis of Cr(CO)3-coordinated cycloheptatriene 64 upon reaction with terminal alkynes [57] (Scheme 37). The formation of pen-tacarbonyl(acetonitrile)chromium is expected to facilitate the metal exchange. 

Lactams Lactams represent a special type of C=N system due to the tautomerization between the lactam (keto amine) and lactim (hydroxyimine) forms. The lactim form is much more favored for cyclic than for non-cyclic amides of carbocyclic acids. In the reaction of complex 2b with N-methyl-e-caprolactam, a simple ligand exchange reaction occurs and complex 87 can be isolated. With P-propiolactam, the alkenyl-amido complex 88 is formed, which indicates an agostic interaction. The reaction of complex 1 with e-caprolactam gives, after elimination of the alkyne and of molecular hydrogen, complex 89 with a deproto-nated lactam in a r]2-amidate bonding fashion [47]. 

A route to alkylidynes containing metals with high oxidation states involves a metathesis exchange reaction that we have referred to briefly in earlier sections of Chapter 10. Scheme 10.10 shows the triply-bonded ditungsten complex 79 reacting with either alkynes or nitriles to give the corresponding metal carbyne (path a)90 or metal-carbyne plus nitride complex (path b).91 Scheme 10.10 also shows results of molecular orbital calculations at the DFT level.92 In the case... 

The remainder of this section will focus on true SBMs, which have been the subject of vigorous research. Despite the electron deficiency of early transition metal, lanthanide, and actinide complexes, several groups reported that some of these d f" complexes do react with the H-H bond from dihydrogen and C-H bonds from alkanes, alkenes, arenes, and alkynes in a type of exchange reaction shown in equation 11.32. So many examples of SBM involving early, middle, and late transition metal complexes have appeared in the chemical literature over the past 20 years that chemists now consider this reaction to be another fundamental type of organometallic transformation along with oxidative addition, reductive elimination, and others that we have already discussed. 

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