Phosphine-borane

Unsaturated Silicon hydride, 4446 BORANES PHOSPHINES SILANES... 

The cryogenic trap section of the line consists of one more large capacity, removable trap, and three U traps leading to the inlet of the Toepler pump. These traps can be used to separate volatile materials on the basis of differing vapor pressures, as is performed routinely for boranes, phosphines, etc, on lines similar in design to this section of the vacuum system. 

IS facilitated after forming the borane ( Phosphine complexes. Mainu in such complexes and enhancement adjacent carbon enable the enantios< complex. Oxidative coupling of the accomplish the synthesis of C,-symm<... 

The previously unknown phosphine-bridged diborane B2PH7 (55) has been obtained in good yield by treating H2P(BHg) Na+ with dry HCl at low temperatures. N.m.r. data exclude the alternative bis(borane)phosphine... 

Since Evans et al. [78] has discovered that prochiral alkyl(dimefliyl) phosphine boranes can undergo the enantioselective deprotonation of one methyl group, using butyllithium and ( )-sparteine 141, these compounds have been widely used for the synthesis of P-chirogenic borane phosphines [79-105]. Lithium alkyls form chiral complexes 142 with sparteine 141 and related chiral diamines, which were investigated by single crystal X-ray analysis (Scheme 43) [82-87]. 

Borohydride salts react with trivalent phosphorus compounds to give a variety of boranes, phosphines and phosphine-borane adducts (9.20-9.23). The reaction between sodium borohydride and phosphorofluoridic acid produces diborane in about 80% yield, and is a convenient method of preparation of the latter. 

SCHEME 4.349 Oxidative alkynylation of borane-phosphines using a functionalized organocopper reagent [523]. 

Borane complexes of P-heterocycles as versatile precursors for the synthesis of chiral phosphine ligands used for asymmetric catalysis 98S1391. 

It is now well-established that unsymmetrical substituted menthylphosphinates, RR P(0)0Men, as well as the corresponding phosphine-boranes RR P(BH3)OMen and phosphinothioates RR P(S)OMen, can be separated readily into the di-astereomeric forms, and subsequently reacted with Grignard reagents to afford P-chirogenic tertiary phosphines with a high degree of stereospecificity [57]. The... 

Phosphine-borane 63a (75% ee) was obtained by reduction of compound (Sp)-62a using LDBB at -60°C and nucleophilic substitution with iodomethane in 72 % yield. The observed loss of optical purity may be ascribed to stereomutation of the generated tricoordinated phosphorus species. Recrystallization afforded (S)-63a in > 99% ee. On the other hand, severe racemization was observed using the same method with (Rp)-62b. An alternative strategy consisted of deborana-tion of (Rp)-62b using ZSl-methylpyrrolidine, methylation with methyl triflate. 

Quenching of the same lithiated species with CO2, followed by reduction of the carboxyUc acid functionality obtained with BH3-THF complex, yielded the next higher analogues 78 to these alcohols [94]. Subsequent treatment of the depro-tonated alcohols with TsCl or MsCl afforded (l )-l-boranato[alkyl(methyl)plios-phino] ethanol-2-tosylates or the mesylate phosphine-boranes in over 90% ee and excellent overall yields. 

P-Chirogenic phosphine/sulfide hybrid phosphine-boranes 80 were synthesized from the reaction between (l )-tosylates 79 [94] and sodium thiolate in DMF at ambient temperature as depicted in Scheme 12, or alternatively by a one pot synthesis consisting of the nucleophilic attack of the chirally induced hthium salt of 74 on phenyl disulfide. Both methodologies provided the desired sul-fide/phosphine boranes in excellent yields [10]. 

The same phosphine-borane used for the synthesis of BisP acted as the starting materials of the construction of MiniPHOS, the next smaller analogue to BisP (Scheme 13). The chirally induced lithium salt was treated with alkylphos-phorus dichloride, methylmagnesium bromide, and borane-THF complex to afford enantiomerically pure MiniPHOS-borane 82a. Recrystallization enabled elimination of a small amount of corresponding raeso-diastereomer formed [29]. Yields were generally low, ranging from 13 to 28%. 

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