Phosphine/sulfide boranes

Treatment of tosylates 37 or 38 with in situ prepared sodium thiolates at room temperature afforded phosphine/sulfide boranes 39 in high yields (Table 5.9). Alternatively, to avoid the preparation of 37, compounds 39 with n=l and R = Ph could also be prepared directly from 4 by enantioselective deprotonation and treatment with diphenyldisulfide. The compounds reported are listed in Table 5.9. 

Scheme 5.16 Different methods to prepare P-stereogenic phosphine/sulfide boranes.

Table 5.9 P-stereogenic phosphine/sulfide boranes 39 of Scheme 5.16.

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]. 

Tris(trimethylsilyl)silane reacts with phosphine sulfides and phosphine selen-ides under free radical conditions to give the corresponding phosphines or, after treatment with BH3-THF, the corresponding phosphine-borane complex in good to excellent yields (Reaction 4.45) [82]. Stereochemical studies on P-chiral phosphine sulphides showed that these reductions proceed with retention of configuration. An example is given in Reaction (4.46). 

Changes in the P-functionality of the dihydrophosphinine oxides (14) made available phosphine sulfides and phosphine boranes (15 and 16, respectively) (Scheme 8)[19, 20],... 

There are no reports on the enantioselective reaction of the carbanion a to non-activated phosphines due to the low acidity of their a-protons. However, formation of phosphine-borane complexes enables deprotonation at the a position [83]. Evans and coworkers have foimd that enantiotopic methyl groups of phos-phine-boranes can be efficiently discriminated by s-BuLi-(-)-sparteine [Eq. (30)] [84]. This result is in accord with many other reports that the chiral complex composed of s-BuLi and (-)-sparteine is generally the most efficient enantioselective deprotonating combination [1,2,3,85]. However, in the reaction of phosphine sulfides this is not the case. The n-BuLi-(-)-sparteine combi-... 

The main difference between phosphine boranes and phosphine sulfides is that for the latter compounds -BuLi rather than i-BuLi is generally used as the... 

The lower enantioselectivity achieved by phosphine sulfides and other practical considerations (like product crystallinity or ease of purification) have made phosphine boranes the reagents of choice in enantioselective deprotonation. Recently, however, it has been showed that in certain cases phosphine sulfides outperform the borane counterparts. O Brien and co-workers developed a strategy to prepare both enantiomers of phosphine derivatives using enantioselective deprotonation with (-)-sparteine (Scheme 5.44). 

It might be more practical to synthesize the protected phosphine (oxide, sulfide, borane) and convert it into the free phosphine following the P—C bond-forming step. Isolation of the target phosphine from the reduction or deboronation reaction is often significantly easier than from the initial P—C bond-forming reaction... 

Bis(a-aminomethyl)phosphines having a mobile hydrogen atom could be expected to undergo a borylation reaction with borane, hydrogen being evolved. In fact, bis(Af-phenylaminomethyl)-phenylphosphine (199) and its sulfide (200) appeared to interact with borane under mild conditions, yielding a new type of phosphorus-boron-containing heterocycle—2-... 

The complexes of borane (BH3) itself with amines, phosphines, dialkyl sulfides and carbon monoxide, the first representatives prepared only in die 1930s were thoroughly discussed in several books and reviews.2,9,25-36 Therefore, in this section, only a brief summary will be given outlining the most basic aspects of these compounds, whereas complexes of substituted boranes will be discussed in more detail. 

Borane monovalent cations with tertiary phosphine bases were first prepared by the action of hydrogen iodide on a mixture of phosphine-borane and phosphine, by the displacement of sulfides from [H2B(SR2)2]+ cations, or directly from phosphine... 

REDUCTION, REAGENTS Bis(triphenyl-phosphine)copper tetrahydroborate. Borane-Pyridine. Calcium-Methylamine/ ethylenediaminc. Chlorobis(cyclopenta-dienyl)tetrahydroboratozirconium(IV). Chromium(II)-Amine complexes. Copper(0)-lsonitrile complexes. 2,2-Dihydroxy-l, 1-binaphthyl-Lithium aluminum hydride. Di-iododimethylsilane. Diisobutyl-aluminum 2,6-di-/-butylphenoxide. Diisobutyl aluminum hydride. Dimethyl sulfide-Trifluoroacetic anhydride. Disodium tetracarbonylferrate. Lithium-Ammonia. Lithium-Ethylenediamine. Lithium bronze. Lithium aluminum hydride. Lithium triethylborohydride. Potassium-Graphite. 1,3-Propanedithiol. Pyridine-Sulfur trioxide complex. 

Ignition or explosive reaction with metals (e.g., aluminum, antimony powder, bismuth powder, brass, calcium powder, copper, germanium, iron, manganese, potassium, tin, vanadium powder). Reaction with some metals requires moist CI2 or heat. Ignites with diethyl zinc (on contact), polyisobutylene (at 130°), metal acetylides, metal carbides, metal hydrides (e.g., potassium hydride, sodium hydride, copper hydride), metal phosphides (e.g., copper(II) phosphide), methane + oxygen, hydrazine, hydroxylamine, calcium nitride, nonmetals (e.g., boron, active carbon, silicon, phosphoms), nonmetal hydrides (e.g., arsine, phosphine, silane), steel (above 200° or as low as 50° when impurities are present), sulfides (e.g., arsenic disulfide, boron trisulfide, mercuric sulfide), trialkyl boranes. 

Organoboranes possessing one B—C bond in the molecule can also be obtained by hydroborating alkenes and alkynes with heterosubstituted borane derivatives, especially dihalogenoboranes, which can be stabilized by complexation with amines, phosphines, ethers and sulfides. The last two are useful complexing agents for both the preparation and the reactions of dihalogenoboranes . The most convenient synthesis of dichloroborane etherate is the reaction of LiBH. with BCl, in Et,0 ... 

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