Roland Leo

Highly Enantiomerically Enrichedα-Haloalkyl Grignard Reagents

alpha-Chloro- and alpha-bromoalkyl Grignard reagents 11 and 30 with > 97% ee (enantiomeric excess) were generated by a sulfoxide/magnesium exchange reaction from the enantiomerically and diastereomerically pure sulfoxides 25 and 27. The resulting alpha-haloalkyl Grignard reagents are configurationally stable at -78 degrees C. Racemization sets in at or above -60 degrees C, especially when the solution contains bromide ions. In the absence of halide ions, the configurational stability extends up to -20 degrees C, when chemical decomposition commences.

Synthese eines Titana-Oxacyclohexanringes durch kontrollierte Ringöffnung von Tetrahydrofuran. Kristallstrukturen von [Ti(CH2)4O{Me2Si(NBut)2}]2, [TiCl{Me2Si(NBut)2}]3(μ3-O)(μ3-Cl) und [Li2(THF)3{Me2Si(NBut)2}]

[TiCl3(THF)3] reagiert mit [(ButNLi)2 · SiMe2]2 in Diethylether bei –35 °C unter Redox-Disproportionierung und Bildung des gelben Titana(IV)-Oxacyclohexan-Komplexes [Ti(CH2)4O{Me2Si(NBut)2}]2. Nach der Kristallstrukturanalyse sind die Titanatome uber die O-Atome der Ti(CH2)4O-Sechsringe, die in der Sesselkonformation vorliegen, zu zentrosymmetrischen Dimeren verknupft. Zusammen mit den N-Atomen der chelatisierenden [Me2Si(NBut)2]2–-Liganden erreichen die Titanatome verzerrt trigonal-bipyramidale Umgebung. Als Nebenprodukt wird hierbei [TiCl{Me2Si(NBut)2}]3(μ3-O)(μ3-Cl) mit clusterahnlichem Aufbau erhalten. Nach der Kristallstrukturanalyse des an der Synthesereaktion beteiligten [Li2(THF)3 · {Me2Si(NBut)2}] sind die beiden Lithiumatome mit beiden N-Atomen der t-Butylamid-Gruppen verbunden und uber ein O-Atom eines der THF-Molekule verbruckt. Synthesis of a Titana-Oxacyclohexane Ring by Controlled Ring Opening of Tetrahydrofurane. Crystal Structures of [Ti(CH2)4O{Me2Si(NBut)2}]2, [TiCl{Me2Si(NBut)2}]3(μ3-O)(μ3-Cl), and [Li2(THF)3{Me2Si(NBut)2}] [TiCl3(THF)3] reacts with [(ButNLi)2SiMe2]2 in diethyl ether at –35 °C under redox disproportionation and formation of the yellow titana(IV)-oxacyclohexane complex [Ti(CH2)4O{Me2Si(NBut)2}]2. According to the crystal structure analysis the titanium atoms are linked to form centrosymmetric dimers via the oxygen atoms of the Ti(CH2)4O six-membered rings, which are in chair conformation. Along with the nitrogen atoms of the chelating [Me2Si(NBut)2]2– ligands the titanium atoms obtain a distorted trigonal-bipyramidal surrounding. While [TiCl{Me2Si(NBut)2}]3(μ3-O)(μ3-Cl) with a cluster-like structure is obtained as a by-product. According to the crystal structure analysis of [Li2(THF)3 · {Me2Si(NBut)2}], which is involved in the synthesis reaction, the two lithium atoms are connected with both the nitrogen atoms of the t-butyl amide groups and bridged via an oxygen atom of one of the THF molecules.

Phosphaniminato-Acetato-Komplexe von Cobalt und Cadmium mit M4N4-Heterocuban-Struktur

Die Phosphaniminato-Acetato-Komplexe [M(NPEt3)(O2C–CH3)]4 mit M = Co und Cd werden aus den wasserfreien Metall(II)acetaten mit uberschussigem Me3SiNPEt3 bei 180 °C gebildet. Durch Kristallisation aus Diethylether lassen sich blaue, feuchtigkeitsempfindliche Einkristalle von [Co(NPEt3)(O2C–CH3)]4 erhalten, wahrend farblose Einkristalle von [Cd(NPEt3)(O2C–CH3)]4 · 2 CH2Cl2 aus Dichlormethan-Losung entstehen. Im Vakuum wird das eingelagerte CH2Cl2 abgegeben. Die Komplexe werden durch die IR-Spektren und durch Kristallstrukturanalysen charakterisiert. In beiden Komplexen sind die Metallatome uber μ3–N-Brucken der (NPEt3–)-Gruppen zu Heterocubanen assoziiert. Im Cobalt-Komplex sind die Acetato-Liganden mit je einer kurzen Co–O- und einer langen Co–O-Bindung semichelatartig gebunden (Co–O-Abstande im Mittel 199,5 und 257,4 pm). Im Cadmium-Komplex bilden die Acetato-Gruppen nahezu symmetrische Chelate aus (Cd–O-Abstande im Mittel 232,1 und 237,8 pm), was zu verzerrt trigonal-bipyramidaler Anordnung an den Cd-Atomen fuhrt. [Co(NPEt3)(O2C–CH3)]4: Raumgruppe P 1, Z = 4, Gitterkonstanten bei –60 °C: a = 1110,1(2); b = 2051,3(5); c = 2169,5(4) pm; α = 100,03(2)°; β = 103,404(15)°; γ = 97,63(2)°; R = 0,0480. [Cd(NPEt3)(O2C–CH3)]4 · 2 CH2Cl2: Raumgruppe C2/c, Z = 4, Gitterkonstanten bei –80 °C: a = 1550,2(1); b = 2101,1(1); c = 1706,1(1) pm; β = 91,09(1)°; R = 0,0311. Phosphoraneiminato-Acetato Complexes of Cobalt and Cadmium with M4N4 Heterocubane Structure The phosphoraneiminato-acetato complexes [M(NPEt3)(O2C–CH3)]4 with M = Co and Cd are formed from the anhydrous metal(II) acetates with excess Me3SiNPEt3 at 180 °C. By crystallization from diethyl ether blue, moisture sensitive single crystals of [Co(NPEt3) · (O2C–CH3)]4 can be obtained, while colourless single crystals of [Cd(NPEt3)(O2C–CH3)]4 · 2 CH2Cl2 originate from dichloromethane solution. In vacuo the intercalary CH2Cl2 is released. The complexes are characterized by their IR spectra and by crystal structure analyses. In both complexes the metal atoms are associated via μ3–N bridges of the (NPEt3–) groups to form heterocubanes. In the cobalt complex the acetato ligands are bonded in a semichelate fashion with a short Co–O and a long Co–O bond each (Co–O distances in average 199.5 and 257.4 pm). In the cadmium complex the acetato groups form almost symmetrical chelates (Cd–O distances in average 232.1 and 237.8 pm); this leads to a distorted trigonal-bipyramidal arrangement at the cadmium atoms. [Co(NPEt3)(O2C–CH3)]4: Space group P 1, Z = 4, lattice dimensions at –60 °C: a = 1110.1(2), b = 2051.3(5), c = 2169.5(4) pm, α = 100.03(2)°, β = 103.404(15)°, γ = 97.63(2)°, R = 0.0480. [Cd(NPEt3)(O2C–CH3)]4 · 2 CH2Cl2: Space group C2/c, Z = 4, lattice dimensions at –80 °C: a = 1550.2(1), b = 2101.1(1), c = 1706.1(1) pm, β = 91.09(1)°, R = 0.0311.

Kristallstruktur des Molybdän(V)‐Imido‐Komplexes [MoCl3(NtBu)(H2NtBu)]2 · 1/2 C7H8

Crystal Structure of the Molybdenum(V) Complex [MoCl3(NtBu)(H2NtBu)]2 · 1/2 C7H8 Green moisture sensitive single crystals of [MoCl3(NtBu)(H2NtBu)]2 (1 · 1/2 C7H8) have been prepared from molybdenum pentachloride with Me2Si(HNtBu)2 in toluene solution; they were suitable for a crystal structure determination. 1 · 1/2 C7H8: Space group P 1, Z = 2, lattice dimensions at –83 °C: a = 696.9(1), b = 1470.9(2), c = 1579.0(2) pm, α = 96.673(13)°, β = 92.014(14)°, γ = 94.852(14)°, R = 0.0321. 1 forms centrosymmetric molecules in which the molybdenum atoms are linked by two μ-Cl-bridges with MoCl bond lengths of 245.7 and 270.2 pm in average of the two crystallographically independent individuals. The longer MoCl bond is in trans-position to the nitrogen atom of the imido ligand (MoN distance 169.0 pm, MoNC bond angle 167.0° in average).