N,N-Diisopropylaminomethyllithium: Synthesis, Oxidative Degradation, and Organoaluminum and -gallium Derivatives

From polygons to polyhedra through intermediate structures. A shape measures study of six-atom inorganic rings and clusters

Among the wealth of well-established molecular structures, inorganic rings and clusters present an overwhelming variety of geometries that chemists try to describe with a limited assortment of regular polygons and polyhedra. In the case of six-atom structures we usually employ the hexagon, the pentagonal pyramid, the trigonal prism and the octahedron. More often than not, however, real world structures deviate from those ideal geometries, and we try to cope with non-ideality by adding adjectives such as distorted, twisted, puckered or flattened, additionally nuanced by adverbs such as slightly, significantly or severely. This contribution presents a systematic structural perspective of six-atom groups in molecules by means of a continuous shape measures (CShM) analysis. The shape of a group of N points is defined by all the sets of 3 N Cartesian coordinates that can be generated by rigid translation, rotation, or isotropic scale change. Among all possible arrangements of N points in space, we select as reference shapes the corresponding regular N-vertex polygons and polyhedra, together with univocally defined combinations thereof (e.g., two coplanar or perpendicular edge-sharing squares). The present CShM study allows us to classify most of the structures not only by their closeness to a particular regular shape, but also by quantifying their position along minimal distortion interconversion pathways between two regular shapes.

Trifunctional organometallic frameworks and cages based on all-cis-1,3,5-triethynyl-1,3,5-trisilacyclohexanes

All-cis-1,3,5-triethynyl-1,3,5-triorganyl-1,3,5-trisilacyclohexanes (organyl R = Me, Ph) offer flexible scaffolds with three concordantly oriented ethynyl groups. Lithiation with n-BuLi affords the dimeric {[CH2Si(R)(C2Li)]3(THF)3}2 with a drum-like structure in high yields. They can be transformed into other trinuclear organometallic derivatives like the trimercury cage species [CH2Si(R)C2HgC2(R)SiCH2]3.

Transmetallation and silylation products of aminal carbanions

Reactions of the lithiated carbanion [(RLi)(2).(RH)] (R = MeN[CH(2)N(Me)](2)CH, 2,4,6-trimethyl-2,4,6-triazacyclohex-1-yl) with dialkylaluminium and -gallium chlorides lead to the corresponding dialkylaluminium and -gallium compounds (RAlMe(2))(2), (RAlEt(2))(2) and (RGaEt(2))(2). They were characterised by elemental analyses, NMR spectroscopy ((1)H, (13)C, (27)Al) and crystal structure determinations. In the solid state the aluminium and gallium compounds form dimers by intermolecular coordination between the metal acceptor and the nitrogen donor leading to six-membered M(2)C(2)N(2) rings in chair conformation. As a first test for the synthetic utility of [(RLi)(2).(RH)], nucleophilic aminomethylation of chlorotrimethylsilane was performed to give RSiMe(3). Further deprotonation of RSiMe(3) with tBuLi occurs at one of the methyl groups bound to the silicon atom leading to RMe(2)SiCH(2)Li. Reactions with dimethylaluminium and -gallium chlorides gave RMe(2)SiCH(2)AlMe(2) and RMe(2)SiCH(2)GaMe(2). The compounds were characterised by NMR spectroscopy ((1)H, (13)C, (29)Si, (27)Al), elemental analyses and single crystal X-ray diffraction. The compounds are monomeric in the solid state with intramolecular M-N bonds (M = Al, Ga) leading to five-membered rings.

Two diamino-substituted lithiocarbanions in one molecule

tert-Butyllithium deprotonates bis(3-methyl-1,3-diazacyclohex-1-yl)methane and its five-ring analogue regioselectively at both endocyclic NCH2N units; a deprotonation intermediate has been isolated and structurally characterised.

Organoaluminium and -gallium compounds with N,N-diisopropylaminomethyl groups

The N,N-diisopropylaminomethyl aluminium compound [tBu2AlCH2NiPr2 x LiCl]2(1) and the gallium compounds Li[tBu2Ga(CH2NiPr2)2](2) and [tBu2GaCH2N(H)iPr2]Cl x tBu3Ga (3) were prepared by transmetallation of N,N-diisopropylaminomethyllithium LiCH2NiPr2 with di-tert-butylaluminium or -gallium chloride, and characterised by elemental analyses, multinuclear NMR spectroscopy (1H, 13C, 27Al, 7Li) and IR spectroscopy. The crystal structures have been determined by single crystal X-ray diffraction. Compound aggregates as a centrosymmetric dimer, with two Al-C-N units connected by a frame of two LiCl molecules [Al-Cl 2.367(1), Cl-Li 2.339(4) and 2.374(4), Li-N 1.977(4)A]. Compound 2 is a lithium organogallate with two weak LiN bonds [1.965(7) and 1.937(7)A]. Compound 3 contains two different moieties: tBu3Ga and a [tBu2GaCH2N(H)iPr2]+ cation, which are bridged by a Cl- anion [Ga-Cl 2.445(1) and 2.579(1), HCl 2.362(3)A].

Solvent-free methylthiomethyllithium [LiCH2SMe]∞: solid state structure and thermal decomposition

Solvent-free [LiCH2SMe]infinity forms a layer structure consisting of four- (Li2C2), five- (Li2CS2), and six-membered (Li2C2S2) rings in the solid state; the compound violently explodes upon heating to T=160+/-5 degrees C under an argon atmosphere.