Molecularly Simple Dimethylaminomethyl Compounds of Aluminum, Gallium, and Indium

Methylene-bridged, intramolecular donor–acceptor systems based on rare-earth metals and phosphinomethanides

Geminally bonded intramolecular Lewis-pairs based on rare-earth metal phosphinomethanides were prepared, characterized and tested for their reactivity towards H₂, CO₂and alkynes.

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.

(Dimethylaminomethyl)trifluorosilane, Me2NCH2SiF3—A Model for the α-Effect in Aminomethylsilanes

F3SiCH2NMe2 was prepared as a model for the investigation of the nature of the alpha-effect in alpha-aminosilanes, by fluorination of Cl3SiCH2NMe2 with SbF3. Under less mild conditions Si--C bond cleavage was also observed, leading to the double adduct F4Si(Me2NCH2SiF3)2, which was characterised by a crystal structure analysis showing that the central SiF4 unit is connected to Me2NCH2SiF3 via SiN dative bonds and FSi contacts. F3SiCH2NMe2 was characterised by multinuclear NMR spectroscopy (1H, 13C, 15N, 19F and 29Si), gas-phase IR spectroscopy and mass spectrometry. It is a dimer in the crystal (X-ray diffraction, crystal grown in situ), held together by two Si--N dative bonds. In solution and in the gas phase the compound is monomeric. The structure of the free molecule, determined by gas-phase electron diffraction, showed that, in contrast to former postulates, there are no attractive SiN interactions. Ab initio calculations have been carried out to explain the nature of the bonding. F3SiCH2NMe2 has an extremely flat bending potential for the Si-C-N angle; the high degree of charge transfer from the Si to the N atoms which occurs upon closing the Si-C-N angle is in the opposite direction to that expected for a dative bond. The topology of the electron density of F3SiCH2NMe2 was analysed. Solvent simulation calculations have shown virtually no structural dependence on the medium surrounding the molecule. The earlier postulate of Si-->N dative bonds in SiCN systems is discussed critically in light of the new results.

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].