Shedding Light on the Diverse Reactivity of NacNacAl with N‐Heterocycles

Abstract

The aluminum(I) compound NacNacAl (NacNac=[ArNC(Me)CHC(Me)NAr]−, Ar=2,6‐iPr2C6H3, 1) shows diverse and substrate‐controlled reactivity in reactions with N‐heterocycles. 4‐Dimethylaminopyridine (DMAP), a basic substrate in which the 4‐position is blocked, induces rearrangement of NacNacAl by shifting a hydrogen atom from the methyl group of the NacNac backbone to the aluminum center. In contrast, C−H activation of the methyl group of 4‐picoline takes place to produce a species with a reactive terminal methylene. Reaction of 1 with 3,5‐lutidine results in the first example of an uncatalyzed, room‐temperature cleavage of an sp2 C−H bond (in the 4‐position) by an AlI species. Another reactivity mode was observed for quinoline, which undergoes 2,2′‐coupling. Finally, the reaction of 1 with phthalazine produces the product of N−N bond cleavage.

Selective Cross‐Coupling of Unsaturated Substrates on AlI

“… [14] We have now established that reaction of the Al I compound 1 with a mixture of benzophenone and pyridine gives chemoselectively the analogous coupling product 5 (Scheme 2). This result is significant because 1 instantaneously reacts with both of these substrates independently: in the case of benzophenone it affords the adduct 3 or pinacolate NacNacAl(OCPh 2 ) 2 (if two equivalents of benzophenone are used), and with pyridine it gives a red gel of unknown composition [8b] . As expected, addition of pyridine to 3 also affords compound 5 , suggesting that the reagents are kinetically differentiated by 1 .…”

“…The Al atom is located within the O1N1O2 equatorial plane (deviation 0.089 Å). The Al1−N3 bond (2.154(3) Å) to the coordinated pyridine is longer than the Al−N bonds within the NacNaAl fragment (1.930(3) Å and 1.992(3) Å) and longer than the dative Al−N bond in NacNac'AlH(DMAP) (1.954(3) Å), [8b] likely because of the increased steric encumbrance around a five‐coordinate Al center. The former carbonyl C35 atom is in a tetrahedral environment, with an O1‐C35‐C34 angle of 109.9(3)°, typical for an sp 3 ‐hybridized carbon.…”

“…[16] The Al−N bonds within the NacNacAl moiety are normal, 1.883(3) and 1.893(3) Å, whereas the Al‐amide bond derived from the former pyridine molecule is much shorter at 1.823(4) Å. This situation is quite typical for aluminum amido compounds featuring a NacNac platform [8b] . The C34‐C35 connection formed as the result of the coupling is typical of a single covalent bond (1.577(5) Å).…”

“…Furthermore, with oxidizing bases, such as quinoline, reaction with 1 results in the C−C coupling of heterocycles [14] . But a less oxidizing and more basic heterocycle such as DMAP, leads to backbone deprotonation [8b] . It becomes, clear that for fenchone, which can be regarded as a weak but oxidizing base, the main mode of reactivity with Al I is charge transfer to the carbonyl moiety, likely creating a biradicaloid.…”

Seven-Membered Cyclic Diamidoalumanyls of Heavier Alkali Metals: Structures and C–H Activation of Arenes

“…Although Roesky’s monometallic β-diketiminate derivative, [HC­{C­(Me)­NDipp) 2 Al], has been widely employed as a highly reducing and hydrocarbon-soluble source of aluminum­(I), – unless promoted by palladium catalysis, it has been reported as inert toward arene solvents . This behavior contrasts significantly with many of the alkali metal alumanyl derivatives summarized in Figure .…”