Amines from alkanes

The amido ligand is isoelectronic with the alkyl and alkoxo groups and has the possibility to exhibit N-M ir-interactions in order to stabilize the systems they form. Different synthetic reactions are used to prepare mono-Cp titanium derivatives containing amido ligands. These compounds are normally synthesized by (i) the action of the corresponding amide salt on Cp TiCl3, (ii) displacement of amine from a homoleptic amido titanium compound by a Cp reagent, (iii) dehalosilylation reactions, and (iv) elimination of alkane by reaction of an alkyltitanium compound with amine. 

Captodative alkenes 67 can be dialkylated, for example, by addition of iso-butyronitrile radical derived from thermal decomposition of AIBN under the same conditions as those which lead to polymerization of other acrylic alkenes. For example, a-morpholino-acrylonitrile (67, c = CN, d = N(CH2CH2)20) leads to 69, in 71% yield (Scheme 12) [4a]. With a-/-butylthio-acrylonitrile (67, c = CN, d = SC(CHj)3), the same process leads to 70 in 88% yield [7]. The adduct radical 68 is highly stabilized, and is in equilibrium with dimer 70. The reaction is quite general, and has been applied to other captodative alkenes (c = CN, COR, CO2R and d = NR2, OR, SR) together with various sorts of radical partners, derived from alkanes, alcohols, thiols, thioethers, amines, amides, ketones, aldehydes, acetals and thioacetals [44, 45]. 

This chapter vhll focus only on the most recent aspect of rhodium nitrene chemistry to perform C—H amination of alkanes, which has not been covered in previous reviews. The literature has been surveyed from 2001 to September 2008. 

In 2012, Du Bois and Zare published details of a novel method to observe intermediates in the CH amination reactions catalyzed by dirhodium carboxylate complexes [88]. In this study, desorption electrospray ionization (DESl) was coupled to mass spectroscopy to capture transient intermediates from solution having very short lifetimes (ca. nanoseconds to microseconds). Rh2(esp)2 is a catalyst for the amination of alkanes, such as adamantane, as shown in Scheme 24. 

Dimetallic elimination reactions leading to metal-metal bond formation are the amine or alkane eliminations that result from the condensation of a late transition metal hydrido complex with an early transition metal amido or alkyl complex, respectively. Examples of this method are Selegue s synthesis of the first Ti-Fe and Ti-Ru complexes 8a,b [8, 9] and the reaction of [Zr(CH2Ph)4) with [CoH(CO)4], although only spectroscopic evidence was provided for compound 18 (Scheme 4.3) [20]. 

An example of typieal H-atom abstraction from alkanes following the selectivity trends observed for radical reactions was discovered by Crabtree using photo-excited Hg atoms in the gas phase. The reaction applies not only to alkanes, but also to alcohols, ketones, amines, etc. 

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