Synthesen und Kristallstrukturen der Lithiumphosphide {Li(DME)[P(t-Bu)2]}2 und [Li(DME)PPh2]∞ / Syntheses and Crystal Structures of the Lithium Phosphides {Li(DME)[P(t-Bu)2]}2 and [Li(DME)PPh2]∞
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Cited by 14 publications
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MP(tBu) 2 (M = Li, Na, K), KH and KN(SiMe 3 ) 2 are shown to activate HD reversibly.Inthe case of MP(tBu) 2 this leads to isotopic scrambling and the formation of H 2 ,D 2 , H(D)P(tBu) 2 and MH(D) in C 6 D 6 .Intoluene,KP(tBu) 2 reacts with H 2 but also leads to isotopic scrambling into the methyl groups of the solvent toluene.D FT calculations reveal that these systems effect H 2 activation via cooperative interactions with the Lewis acidic alkali metal and the basic phosphorus, carbanion, or hydride centres,mimicking frustrated Lewis pair (FLP) behaviour.Heterogeneous transition-metal-mediated hydrogenation was discovered by Sabatier in 1899. [1] Ther eduction of multiple bonds has since become au biquitous process throughout academic chemistry and across chemical industry. [2] Moreover,t he field of catalytic hydrogenation has evolved considerably.I nt he 1960-1990s,t he advent of homogeneous precious transition-metal catalysts provided access to specifically designed catalysts allowing for enhanced substrate selectivity and the added sophistication of enantioselectivity. [3] These findings and the numerous successful applications of transition-metal systems established the dogma dictating the need for transition-metal catalysts for hydrogenation.In the early 1960s,W alling and Bollyky [4] reported metalfree hydrogenation of benzophenone in the presence of KOtBu, albeit at temperatures ca. 200 8 8Ca nd H 2 pressure of > 100 bar. This system was subsequently studied in detail by Berkessel et al. [5] Similarly,soluble LiAlH 4 [6] or suspensions of NaH, KH, and MgH 2 [7] were reported to effect catalytic hydrogenation of several olefinic and acetylenic substrates, although again rather extreme temperatures (150-225 8 8C) and H 2 pressures (60-100 bar) were required. Under similar forcing conditions (280 8 8C, 150 bar H 2 pressure), Haenel et al. reported the reductions of polyaromatics in coal via ac atalytic hydroboration/hydrogenolysis process. [8] In 2006, the discovery of frustrated Lewis pairs (FLPs) broadened the scope of hydrogenation catalysts to main-group compounds. [9] Combinations of Lewis acids and bases were found to act in concert to activate dihydrogen in aheterolytic fashion under comparatively mild conditions and have been applied to reduce aw ide range of organic substrates including imines, enamines,olefins,alkynes,polyaromatic species,ketones and aldehydes (Figure 1). [9c, 10] Moreover,c hiral FLP catalysts have yielded highly enantioselective reductions. [11] In 2008, Harder and coworkers [12] reported the use of NacNac dippcalcium and strontium complexes (dipp = 2,6-diisopropylphenyl;N acNac dipp = CH{(CMe)(2,6-iPr 2 C 6 H 3 N)} 2 )t oe ffect the hydrogenation of olefins,a nd showed that related alkalimetal systems require high H 2 pressures (100 bar). Subsequently,t hese Group 2s ystems were expanded to include Okudasw ork on trimetallic calcium [13] and strontium [14] hydride cations,[ (Me 3 TACD) 3 M 3 (m 3 -H) 2 ] + (Me 3 TACD = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane;M= Ca, Sr)...
MP(tBu) 2 (M = Li, Na, K), KH and KN(SiMe 3 ) 2 are shown to activate HD reversibly.Inthe case of MP(tBu) 2 this leads to isotopic scrambling and the formation of H 2 ,D 2 , H(D)P(tBu) 2 and MH(D) in C 6 D 6 .Intoluene,KP(tBu) 2 reacts with H 2 but also leads to isotopic scrambling into the methyl groups of the solvent toluene.D FT calculations reveal that these systems effect H 2 activation via cooperative interactions with the Lewis acidic alkali metal and the basic phosphorus, carbanion, or hydride centres,mimicking frustrated Lewis pair (FLP) behaviour.Heterogeneous transition-metal-mediated hydrogenation was discovered by Sabatier in 1899. [1] Ther eduction of multiple bonds has since become au biquitous process throughout academic chemistry and across chemical industry. [2] Moreover,t he field of catalytic hydrogenation has evolved considerably.I nt he 1960-1990s,t he advent of homogeneous precious transition-metal catalysts provided access to specifically designed catalysts allowing for enhanced substrate selectivity and the added sophistication of enantioselectivity. [3] These findings and the numerous successful applications of transition-metal systems established the dogma dictating the need for transition-metal catalysts for hydrogenation.In the early 1960s,W alling and Bollyky [4] reported metalfree hydrogenation of benzophenone in the presence of KOtBu, albeit at temperatures ca. 200 8 8Ca nd H 2 pressure of > 100 bar. This system was subsequently studied in detail by Berkessel et al. [5] Similarly,soluble LiAlH 4 [6] or suspensions of NaH, KH, and MgH 2 [7] were reported to effect catalytic hydrogenation of several olefinic and acetylenic substrates, although again rather extreme temperatures (150-225 8 8C) and H 2 pressures (60-100 bar) were required. Under similar forcing conditions (280 8 8C, 150 bar H 2 pressure), Haenel et al. reported the reductions of polyaromatics in coal via ac atalytic hydroboration/hydrogenolysis process. [8] In 2006, the discovery of frustrated Lewis pairs (FLPs) broadened the scope of hydrogenation catalysts to main-group compounds. [9] Combinations of Lewis acids and bases were found to act in concert to activate dihydrogen in aheterolytic fashion under comparatively mild conditions and have been applied to reduce aw ide range of organic substrates including imines, enamines,olefins,alkynes,polyaromatic species,ketones and aldehydes (Figure 1). [9c, 10] Moreover,c hiral FLP catalysts have yielded highly enantioselective reductions. [11] In 2008, Harder and coworkers [12] reported the use of NacNac dippcalcium and strontium complexes (dipp = 2,6-diisopropylphenyl;N acNac dipp = CH{(CMe)(2,6-iPr 2 C 6 H 3 N)} 2 )t oe ffect the hydrogenation of olefins,a nd showed that related alkalimetal systems require high H 2 pressures (100 bar). Subsequently,t hese Group 2s ystems were expanded to include Okudasw ork on trimetallic calcium [13] and strontium [14] hydride cations,[ (Me 3 TACD) 3 M 3 (m 3 -H) 2 ] + (Me 3 TACD = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane;M= Ca, Sr)...
MP(tBu) (M=Li, Na, K), KH and KN(SiMe ) are shown to activate HD reversibly. In the case of MP(tBu) this leads to isotopic scrambling and the formation of H , D , H(D)P(tBu) and MH(D) in C D . In toluene, KP(tBu) reacts with H but also leads to isotopic scrambling into the methyl groups of the solvent toluene. DFT calculations reveal that these systems effect H activation via cooperative interactions with the Lewis acidic alkali metal and the basic phosphorus, carbanion, or hydride centres, mimicking frustrated Lewis pair (FLP) behaviour.
Treatment of the thioether-substituted secondary phosphanes R(2)PH(C6H4-2-SR(1)) [R(2) = (Me3Si)2CH, R(1) = Me (1PH), iPr (2PH), Ph (3PH); R(2) = tBu, R(1) = Me (4PH); R(2) = Ph, R(1) = Me (5PH)] with nBuLi yields the corresponding lithium phosphanides, which were isolated as their THF (1-5Pa) and tmeda (1-5Pb) adducts. Solid-state structures were obtained for the adducts [R(2)P(C6H4-2-SR(1))]Li(L)n [R(2) = (Me3Si)2CH, R(1) = nPr, (L)n = tmeda (2Pb); R(2) = (Me3Si)2CH, R(1) = Ph, (L)n = tmeda (3Pb); R(2) = Ph, R(1) = Me, (L)n = (THF)1.33 (5Pa); R(2) = Ph, R(1) = Me, (L)n = ([12]crown-4)2 (5Pc)]. Treatment of 1PH with either PhCH2Na or PhCH2K yields the heavier alkali metal complexes [{(Me3Si)2CH}P(C6H4-2-SMe)]M(THF)n [M = Na (1Pd), K (1Pe)]. With the exception of 2Pa and 2Pb, photolysis of these complexes with white light proceeds rapidly to give the thiolate species [R(2)P(R(1))(C6H4-2-S)]M(L)n [M = Li, L = THF (1Sa, 3Sa-5Sa); M = Li, L = tmeda (1Sb, 3Sb-5Sb); M = Na, L = THF (1Sd); M = K, L = THF (1Se)] as the sole products. The compounds 3Sa and 4Sa may be desolvated to give the cyclic oligomers [[{(Me3Si)2CH}P(Ph)(C6H4-2-S)]Li]6 ((3S)6) and [[tBuP(Me)(C6H4-2-S)]Li]8 ((4S)8), respectively. A mechanistic study reveals that the phosphanide-thiolate rearrangement proceeds by intramolecular nucleophilic attack of the phosphanide center at the carbon atom of the substituent at sulfur. For 2Pa/2Pb, competing intramolecular β-deprotonation of the n-propyl substituent results in the elimination of propene and the formation of the phosphanide-thiolate dianion [{(Me3Si)2CH}P(C6H4-2-S)](2-).
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