Reversible oxidative Addition an Kohlenstoff

Abstract

Es wird die ReaktivitätN -heterocyclischer Carbene (NHCs) und cyclischer Alkylaminocarbene (cAACs) gegenüber Arylboronsäureestern vorgestellt. Die Reaktionen mit NHCs führen zur reversiblen Bildung thermischs tabiler Lewis-Säure-Base-Addukte Ar-B(OR) 2 ·NHC (Add1-Add6)

Reactivity of NHC Alane Adducts towards N‐Heterocyclic Carbenes and Cyclic (Alkyl)(amino)carbenes: Ring Expansion, Ring Opening, and Al−H Bond Activation

“…Molecular structure of (iPr 2 Im)·AlH 3 (3)i nthe solid state (ellipsoids set at the 50 %p robability level). Selectedbondlengths []a nd angles [ 8]: Al1ÀC1 2.0405 (17), Al1ÀH1 1.54(2), Al1ÀH2 1.56(2), Al1ÀH3 1.492 (19), Al2À C112 .0375 (17),Al2ÀH4 1.53(2), Al2ÀH5 1.52(2), Al2ÀH6 1.53(2), C1-Al1-H1 108.5 (7), C1-Al1-H2 104.1 (8), C1-Al1-H3 105.4 (8), H1-Al1-H2 112.1(11), H1-Al1-H3 113.5(10), H2-Al1-H3 112.5(11), C11-Al2-H4 104.5 (8), C11-Al2-H51 09.2(7), C11-Al2-H6 106.5 (8), H4-Al2-H5 112.2(10),H 4-Al2-H61 11.4(11), H5-Al2-H6 112.5(11). Figure 3.…”

“…The bond distances of approximately 2.179 between the aluminuma tom and the NHCs in the cation are larger than that in (iPr 2 Im)·AlH 3 (3;A l ÀC NHC : 2.039 ), as expected for higher coordination numbers, whereas the AlÀCd istances of the anionic part of 8 (2.048(3) and 2.006(3) )a re in perfect agreement with those observed for 3. [19] To our knowledge, 8 is the first example of [8]for 7:Al ÀC1 2.0709 (18), AlÀC111.999(2), AlÀN4 1.8514(17), AlÀO1 1.6996(6), C1-Al1-C11108.01 (8), C1-Al1-O1 108.38(6), C11-Al1-O1 114.48(6), N4-Al1-O1118.69(6),C 1-Al1-N4 104.10(7),C 11-Al1-N41 02.29 (8).…”

“…Selectedbondlengths []a nd angles [8]for 8 for the cation:Al1ÀC1 2.181(3), Al1ÀC112 .189(3), Al1ÀC21 2.170(3), Al1ÀC31 2.176(3), Al1ÀH101 1.62(2), Al1À H100 1.60(3),C 1-Al1-C119 1.43(11), C1-Al1-C21 179.23(12), C1-Al1-C3189.94(11), C11-Al1-C21 88.88(11), C11-Al1-C31177.97(12), C21-Al1-C31 89.77(11), C1-Al1-H100 88.7(9),C 1-Al1-H101 90.4(9), C11-Al1-H10091.8(9),C11-Al1-H101 89.4 (8), C21-Al1-H100 90.6(9), C21-Al1-H101 90.3(9), C31-Al1-H1008 9.7(9), C31-Al1-H101 89.1 (8),H 100-Al1-H101 178. 5(13).…”

“…5(13). Selected bond lengths []and angles [8] an NHC-stabilized cationic aluminumc enter with the coordination number six. However,i fc rystalso f8 were dissolved in solvents like benzene, toluene, diethyl ether,o rT HF,w ei solated the adduct (iPr 2 Im) 2 ·AlH 3 (5)a st he main component, usually contaminated with traces of 6.N MR investigations in C 6 D 6 revealed the formation of 3, 5, 6,a nd someh ydrogenated NHC iPr 2 ImH 2 from thesec rystals in solution.T hus, complex 5 seems to be in ar ather complicated equilibrium with other speciesi ns olution,f rom which ionic 8 seemst oc rystallize preferentially.…”

“…It was demonstrated earlier,f or example, that cyclic (alkyl)-(amino)carbenes (cAACs) provide ar obust environment for SiÀ H, BÀH, and PÀHb ond activation, and more recently we and others reported that even CÀHa nd CÀF [7] bond activation occurs with the formation of EÀHa nd EÀE( E= H, B, C, N, Si, P) bond-cleavagep roducts,r espectively.I na ddition, we also showedr ecently that the insertion of cAACs into the BÀC bond of selected aryl boronate esters is reversible and this reversibility may lead to the development of novel carbon-centered organocatalysts. [8] We currently assume that EÀHo rE ÀEb ond activation is also the key step for any further reactivity of NHCs and cAACs. In the last few years reactions of NHCs with Lewis acidic hydrides such as silanes, [9] boranes, [10] and beryllium hydrides [11] have been reported that lead to ring expansion of the NHC, with EÀ Ho rE ÀEb ond activation considered to be the crucial step of the reaction sequence.…”