Reactivity of Tris(allyl)aluminum toward Pyridine: Coordination versus Carbometalation

Abstract

Tris(allyl)aluminum as its THF adduct, [Al(η 1 -C 3 H 5 ) 3 (THF)] (1), reacted with pyridine either under substitution to give [Al(η 1 -C 3 H 5 ) 3 (py)] (7) (py = pyridine) or under carbometalation to give N-metalated 2-allyldihydropyridine depending on the solvent. The substituent pattern of the pyridine substrate and the aluminum center's electrophilicity in [Al(η 1 -C 3 H 5 ) 3 (L)] (L = neutral ligand) influenced the outcome of the reaction. Reactions of one N-metalated dihydropyridine with electrophiles have been studied. A crystalline derivative of tris(allyl)aluminum, [Al(η 1 -C 3 H 5 ) 3 (OPPh 3 )] (2), and tetrakis(allyl)aluminate in the ion pair [K(15-crown-5) 2 ][Al(η 1 -C 3 H 5 ) 4 ] (4) were characterized by single-crystal X-ray diffraction and shown to contain four-coordinate aluminum centers.

Cationic Bismuth Amides: Accessibility, Structure, and Reactivity

“…Resonances for THF were also detected. A 13 C resonance for the ipso ‐Ph atom could not be detected . 11 B NMR (160 MHz, [D 8 ]THF): δ =−6.5 ppm (s, B(C 6 H 3 (CF 3 ) 2 ) 4 ); 31 P NMR (162 MHz, [D 8 ]THF): δ =32.4 ppm (s); 15 N NMR (41 MHz, [D 8 ]THF): δ =−171.8 ppm (s, N i Pr 2 ).…”

“…Yield:2 3mg, 15 mmol, 75 %. J HH = 6.4 Hz, (MeMeCHN) 2 C(NiPr 2 )), 1.23 (d, 6H, 3 J HH = 6.4 Hz, (MeM-eCHN) 2 C(NiPr 2 )), 1.36 (d, 12 H, 3 J HH = 6.8 Hz, (iPrN) 2 C(N(CHMe 2 ) 2 )), 1.39 (d, 12 H, 3 J HH = 6.6 Hz, N(CHMe 2 ) 2 ), 3.74 (sept, 2H, 3 J HH = 6.8 Hz, (iPrN) 2 C(N(CHMe 2 ) 2 )), 5.36 (sept, 2H, 3 J HH = 6.4 Hz, (Me 2 CHN) 2 C(NiPr 2 )), 5.98 (sept, 2H, 3 J HH = 6.6 Hz, N(CHMe 2 ) 2 ), 7.57 (s, 4H, p-(3,5-C 6 H 3 (CF 3 ) 2 ), 7.79 ppm (s, 8H, o-(3,5-C 6 H 3 (CF 3 ) 2 ); 13 CNMR (126 MHz, [D 8 ]THF): d = 23.36 (s, (iPrN) 2 C(N(CHMe 2 ) 2 )), 25.16 (s, (MeMeCHN) 2 C(NiPr 2 )), 26.79 (s, (MeMeCHN) 2 C(NiPr 2 )), 29.35 (s, N(CHMe 2 ) 2 ), 48.00 (s, (Me 2 CHN) 2 C(NiPr 2 )), 51.99 (s,…”

Structurally Defined Allyl Compounds of Main Group Metals: Coordination and Reactivity

“…Adduct formation or ligand‐exchange reactions between pyridine and allyl compounds of main group metals without subsequent carbometalation have been reported for [Zn(C 3 H 5 ) 2 ],144 [B(C 3 H 5 ) 3 ],82 and [Ga(C 3 H 5 ) 3 (thf)]76 (Scheme ). In the case of [Al(C 3 H 5 ) 3 (thf)], ligand substitution of THF for pyridine proceeds readily, but carbometalation of the coordinating pyridine does not take place in the absence of coordinating solvents 83b…”

“…In such reactions, the allyl compounds are significantly more reactive than the corresponding alkyl compounds 76. 83b In the case of [B(C 3 H 5 ) 3 ], the presence of protic solvents is needed to ensure an addition reaction. Bis(allylation) is the favored reaction pathway under these conditions to give a 2,6‐bis(allyl)tetrahydropyridine as the major product 145.…”

Developing Lithium Chemistry of 1,2‐Dihydropyridines: From Kinetic Intermediates to Isolable Characterized Compounds

“…[12] 1-Metallo-1,2-dihydropyridines have been implicated as the active intermediates in the metal catalyzed 1,2-hydroborationo fp yridine, [13] while the presence of am etal salt such as az inc or magnesium dihalide is known to activate the reduction of unactivated ketones and aldehydes by 1-methyl-1,4-dihydropyridines. [14] The addition of metalÀcarbon bonds to pyridines gives either the 1,2-or 1,4-addition product (e.g.,o rganoanion = allyl, M = K; [15] K/Zn; [15] Ca; [16] Al [17] ). Steric blocking at the 2a nd 6p ositions of the pyridine ring for example with imino substituents, does not necessarily promote 1,4 addition.…”