Borane-phosphines synthesis

These nucleophilic reagents react with most common electrophiles such as organohalides, tosylates, aldehydes, ketones, epoxides, and activated alkenes. It should be noted that many workers have found much higher yields if the phosphides are protected as phosphine oxide or borane anions (see Section 3). Phosphide reagents also react with activated arenes to give mixed aryl phosphines (Protocol 2). Metal phosphides therefore provide an alternative, complementary tertiary phosphine synthesis to the electrophilic routes outlined in Section 2.1. 

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<... 

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]. 

Juge and eo-workers were the first to use ehlorophosphine boranes as valuable synthons in phosphine synthesis, as Seheme 4.24 depicts. 

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

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%. 

Scheme 17. Improved synthesis of optically active secondary phosphine-boranes...

As mentioned in Sect. 2.2, phosphine oxides are air-stable compounds, making their use in the field of asymmetric catalysis convenient. Moreover, they present electronic properties very different from the corresponding free phosphines and thus may be employed in different types of enantioselective reactions, m-Chloroperbenzoic acid (m-CPBA) has been showed to be a powerful reagent for the stereospecific oxidation of enantiomerically pure P-chirogenic phos-phine-boranes [98], affording R,R)-97 from Ad-BisP 6 (Scheme 18) [99]. The synthesis of R,R)-98 and (S,S)-99, which possess a f-Bu substituent, differs from the precedent in that deboranation precedes oxidation with hydrogen peroxide to yield the corresponding enantiomerically pure diphosphine oxides (Scheme 18) [99]. 

This section is divided into two main subsections. The first describes the synthesis and characterization of phosphine-stabilized gold clusters. The second focuses on the synthesis and characterization of thiol-stabilized gold clusters and the study of other stabilizers such as arsines or boranes are described. 

Although most of the structurally characterized gold clusters are phosphine-based systems, in recent years some studies have focused on the synthesis of gold clusters with other stabilizers coexisting with phosphines such as thiols, arsines and boranes. Certain heteroleptic gold clusters stabilized with these ligands and arylphosphines in the same molecule have been structurally characterized. 

The procedure described for the preparation of ethylenediamine-bisborane is general for the synthesis of amine-boranes and of borane adducts of other electron donors in which elements such as phosphorus and sulfur serve as the donor atom. In addition to the procedure used here for triphenylphosphine-borane, borane adducts of phosphines have been prepared by Analytical reagent grade (Mallinckrodt). 

So far we have discussed the synthesis of useful P-chiral phosphorus intermediates that can be converted into a variety of phosphines by reaction with a nucleophile (and deprotection). However, Imamoto and co-workers found that one-electron reducing agents react with resolved menthyl phosphine oxides and boranes to give metal phosphides that retain their configuration at phosphorus (Scheme 26).49... 

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