Crystal Structure of a Representative Mixed Adduct of Trimethylaluminium and a Lithium Amide and a Theoretical MO Study on Model Systems

Abstract

Reaction of the simple alane adduct [Me,Al . HN(CH,Ph),] existence here can be attributed to the stabilising effect of (2) with the lithium amide [(PhCH,),NLi] leads to the forma-the attached Me3Al ligand. Crystalline 2 adopts the classical, tion of the mixed adduct [Me3A1 . (PhCH2),NLi . distorted-tetrahedral arrangement of simple monomeric HN(CH,Ph),] (1). The crystal structures of 1 and 2 are re-alane adducts. Ab initio MO calculations on model systems ported. Exhibiting a four-membered, mixed-metal, mixed-show that niixed adduct formation from Me3Al and Me,NLi anion = N ring-core, the structure of 1 is unusual in con-is exothermic, while further reaction to give Me,AlNMe, and taining a monomeric lithium dibenzylamide fragment. Such MeLi (i.e., complete transmetallation) is endothermic. fragments generally convert to aza-ally1 derivatives, so its Lithium dibenzylamide has been a key compound in the development of lithium amide structural chemistry. Its crystal structure (solvent-free) ['] and those of a series of solvated derivatives (containing dioxanel'l, ether"], hexamethylphosphoramide[ll or tetrahydrofuran[2]) have contributed much to the understanding of how lithium amide structures self-assemble, for which there are now well-establishedIn addition, a novel form containing a phosphorus ylide molecule as a ligand has been characterisedl'll. Recently, we have introduced this lithium amide into the arena of heterobimetallic chemistry by synthesizing a mixed Group 1 (dilithium-dis~dium) [~] and a pair of mixed Group 1 -Group 2 (monolithium-monomagnesium and dilithium-monomagnesium)[61 derivatives.In this paper, we extend this heterobimetallic work to Group 3 in reporting the trimethylaluminium adduct [Me3AI * (PhCH2)'NLi . HN(CH2Ph)2] (l), which contains the first example of dibenzylamine acting as a ligand in a lithium dibenzylamide structure. As described below, other examples of lithium amide amine interactions are known. They are probably much more widespread than so far appreciated as conceivably they are formed but go undetected during the preparation of lithium amides from amines, either when the amine is genuinely in excess, or in equimolar reactions when the lithium reagent is added to the amine solution, a situation creating a temporary excess. Formally 1 was synthesised by insertion of the lithium amide into the N+AI dative bond of the simple amine adduct [Me3Al .

Synthesis and Characterization of an Orthometalated Aminoalane, [MeAlN(CH2Ph)-μ-(CH2C6H4)]2: Molecular Structures of [MeAlN(CH2Ph)-μ-(CH2C6H4)]2 and [Me2AlN(CH2Ph)2]2

“…The fold angle about the N(1)···N(1a) axis in the gallium analogue is 2.7°. The bond angles and distances for the Al 2 N 2 core are well within the range of values reported for other aminoalane dimers derived from secondary amines. ,, The Al−N distance in 3 , which is formally a dative bond, has been reported as 2.058 Å 2 Molecular structure of 2 showing the atom-labeling scheme. 3 Selected Bond Lengths (Å) and Angles (deg) for 2 Al(1)···Al(2) 2.783 (3) Al(1)−N(1) 1.982 (4) Al(1)−C(1) 1.962 (7) Al(1)−C(2) 1.981 (10) Al(1)−N(1a) 1.982 (4) Al(2)−N(1) 1.984 (4) Al(2)−C(3) 1.977 (9) Al(2)−C(4) 1.951 (11) Al(2)−N(1a) 1.984 (4) N(1)−C(10) 1.512 (7) N(1)−C(20) 1.498 (7) N(1)−Al(1)−C(1) 111.4 (2) C(1)−Al(1)−C(2) 118.0 (4) N(1)−Al(1)−C(2) 111.0 (3) N(1)−Al(1)−N(1a) 90.9 (2) C(1)−Al(1)−N(1a) 111.4 (2) C(2)−Al(1)−N(1a) 111.0 (3) N(1)−Al(2)−C(3) 109.2 (3) C(3)−Al(2)−C(4) 118.5 (5) N(1)−Al(2)−C(4) 112.9 (3) N(1)−Al(2)−N(1a) 90.7 (3) C(3)−Al(2)−N(1a) 109.2 (3) C(4)−Al(2)−N(1a) 112.9 (3) Al(1)−N(1)−Al(2) 89.1 (1) Al(1)−N(1)−C(10) 113.7 (3) Al(2)−N(1)−C(10) 114.2 (4) Al(1)−N(1)−C(20) 114.5 (4) Al(2)−N(1)−C(20) 113.0 (3) C(10)−N(1)−C(20) 110.8 (3) N(1)−C(10)−C(11) 115.2 (4) N(1)−C(20)−C(21) 116.8 (4) …”

“…Addition of Me 3 Al to HN(CH 2 Ph) 2 in 1:1 mol ratio at −70 °C leads to the formation of the Me 3 Al·HN(CH 2 Ph) 2 adduct ( 3 ), whose synthesis, characterization, and molecular structure have been reported. Careful thermolysis of 3 at 120 °C in toluene solution yields the aminoalane dimer, [Me 2 AlN(CH 2 Ph) 2 ] 2 , 2 , via CH 4 elimination .…”

Neutron Diffraction Characterization of C–H···Li Interactions in a Lithium Aluminate Polymer

“…Hitherto, studies on the bridging action of the AlMe groups in lithium aluminates have only used X-ray diffraction, where the direct observation of the H atoms during Fourier synthesis is absent. Information on the role of H in such bridges has been inferred from short Li–C(alkyl) bonds that have been noted to complete four-membered metallacycles in several aluminate structures. − However, while the negatively hyperconjugated dimer of (2-C 5 H 4 N)(Me 3 Si) 2 CLi has been probed thoroughly, a survey of the Cambridge Structural Database reveals that only one single-crystal neutron diffraction study of a lithium aluminate has ever been reported . In fact, the current volume of literature devoted to a detailed structural analysis of any type of metal–methyl agostic interaction remains modest, as the positions of methyl hydrogen atoms are notoriously difficult to locate using any method other than neutron diffraction. − As yet, only one comprehensive neutron study focusing on agostic interactions to lithium ions has been reported, though interactions of this type had been identified before the formal classification of agostic interactions. , In addition, few compounds incorporating intermolecular C–H···Li agostic interactions have been reported; rarer still are those involving di- and trifurcated interactions, for which only a handful of structures are known, few being neutron-derived structures.…”

Bis(dibenzylamine)silver(I) nitrate

“…The title compound, (I), was formed by accident, instead of the expected sulfenamide. A search in the Cambridge Structural Database (Version 5.26;Allen, 2002) for coordination compounds with dibenzylamine yielded only ten structures, namely chloro(dibenzylamine-N)dimethylaluminium(III) (Craig et al, 1998), bis(dibenzylamine-N)bis(N,N-dibenzylcarbamato-O)copper (II) (Dell'Amico et al, 2002), ( 2 -dibenzylamido)dibenzylaminetrimethylaluminiumlithium (Armstrong et al, 1996), dibenzylaminotrimethylaluminium (Armstrong et al, 1996), bis[( 2 -tetrahydridoborate-H,H,H 0 ,H 0 )bis(dibenzylamino)lithium] (Giese et al, 2001), dibenzylaminotrimethylgallium (Lake et al, 1999), dibenzylaminotrimethylindium (Lake et al, 1999), bis(dibenzylamine)bis(ethylthioacetato)copper(II) (Sato & Ouchi, 1982), catena-bis(dibenzylamine-N)bis( 2 -thiocyanato-S,N)cadmium(II) (Taniguchi & Ouchi, 1987) and trichlorobis(dibenzylamino)indium (Pauls et al, 2001). Here, we present the crystal structure of the title compound, (I).…”