Abstract (English)
The synthesis and reactivity of Lewis base stabilized pnictogenylboranes has been investigated.
The systematic coordination of different pnictogenylboranes towards group 6 metal Lewis acids is investigated. The resulting complexes with phosphanylboranes [(CO)4M(PH2BH2•NMe3)2] (M = Cr, Mo, W), arsanylboranes ([(CO)4M(AsH2BH2•NMe3)2] (M = Cr, Mo, W) and tBu-substituted phosphanylborane ...
Abstract (English)
The synthesis and reactivity of Lewis base stabilized pnictogenylboranes has been investigated.
The systematic coordination of different pnictogenylboranes towards group 6 metal Lewis acids is investigated. The resulting complexes with phosphanylboranes [(CO)4M(PH2BH2•NMe3)2] (M = Cr, Mo, W), arsanylboranes ([(CO)4M(AsH2BH2•NMe3)2] (M = Cr, Mo, W) and tBu-substituted phosphanylborane [(CO)4M(tBuPHBH2•NMe3)2] (M = Cr, W) are fully characterized by multinuclear NMR spectroscopy, single crystal X-ray diffraction and IR spectroscopy. The systematic nature of the approach of the synthesis and the high purity of the compounds enables the comparative investigation of the coordination behavior of pnictogenylboranes. The observed trends allow to make qualitative statements concerning the influence of the metal center, the pnictogen atom and the substituent at the pnictogen atom on the coordination behavior of pnictogenylboranes.
The synthesis and reactivity of the tert-butyl-substituted arsanylborane tBuAsHBH2NMe3 (1) stabilized by a Lewis base are reported. Compound 1 is obtained by the reaction of in situ generated NatBuAsH with IBH2•NMe3. By the reaction of compound 1 with Lewis acids the neutral compounds BBr3•tBuAsHBH2•NMe3 and BH3•tBuAsHBH2•NMe3 as well as coordination products towards Group 6 metal complexes [M(CO)4(tBuAsHBH2•NMe3)2] (M = Cr, Mo, W) are obtained. Upon reaction with IBH2•LB (LB = SMe2, NMe3), the cationic oligomeric arsanylboranes [(Me3NBH2tBuAsHBH2•NMe3)]I and [H2B(tBuAsHBH2•NMe3)2]I were isolated. Compound 1 was also used as starting material for the synthesis of first oligomeric arsanylboranes obtained by thermal oligomerization under different conditions. DFT computations support the experimental observations.
The reactivity of the substituted arsanylborane tBuAsHBH2NMe3 (1) towards different elemental chalcogenes as well as organic oxidants such as O-NMe3, Me3Si-O-O-SiMe3, MesCNO and cyclohexenesulfide is reported. By reaction of 1 with grey selenium the selenium oxidation product tBuAs(Se)HBH2NMe3 was isolated and fully characterized. For the oxidation with sulfur two oxidation products tBuAs(S)HBH2NMe3 and tBuAs(S)SHBH2NMe3 could be isolated as oils and fully characterized. The structural investigation of As(tBuAs(S)SHBH2NMe3)3 as well as DFT calculations allow preliminary insights in the decomposition behavior of the sulfur compounds. For the reaction of MesCNO the formation of an unusual As-H activation product Mes-C(NOH)-AstBu-BH2NMe3 is reported. In the case of Me3N-O, the first isolatable oxo-arsanylboranes tBuAs(O)HBH2NMe3 and tBuAs(O)OHBH2NMe3 are reported, with the latter also being accessible via the controlled reaction of 1 with air. Both compounds were fully characterized.
A new synthetic pathway to various mono-alkyl substituted phosphinoboranes HRP–BH2–NMe3 has been developed. The new synthetic route starting from alkyl halides and NaPH2 followed by metalation and salt metathesis is performed in a one-pot procedure and leads to higher yields and purity of the resulting phosphinoboranes compared to previously reported routes. Additionally, the scope of accessible compounds could be expanded from short-chained linear alkyl substituents to longer chained linear alkyl substituents as well as secondary or functionalized alkyl substituents. The reported examples include primary alkyl substituted phosphinoboranes RHP-BH2-NMe3 (R = n-butyl, n-pentyl, n-hexyl), the secondary alkyl substituted iPrPH-BH2-NMe3 and the functionalized alkyl substituted 4-bromo-butyl-phosphinoborane (BrC4H8)PH-BH2-NMe3. These new pnictogenylboranes have additionally been used for preliminary polymerization reactions via a thermal and a transition metal catalyzed pathway, revealing the formation of high molecular weight polymers under certain conditions. Detailed investigations on the influence of temperature, concentration, substituents and reaction time on the respective polymerization reactions have been performed.
Translation of the abstract (German)
Die Synthese und Reaktivität von Lewis Base stabilisierten Pnictogenylboranen wurde untersucht.
Der Fokus lag dabei auf der systematischen Untersuchung des Koordinationsverhaltens verschiedener Pnictogenylborane gegenüber Gruppe 6 Lewis Säuren, der Synthese und Reaktivität eines Lewis-Base stabilisierten Tert-butyl Arsanylborans sowie dessen Oxidationschemie und der Entwicklung eines optimierten Synthesewegs zu alkylsubstituierten Phosphanylboranen als Startmaterialien für Polymerisationen.
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