Boron, lithium complexes methyl

Flow fluorination of the 4,4 -bipyridine —boron trifluoride complex gives only mono-fluorinated l-fluoro-4-(4-pyridyl)pyridinium boron trifluoride tetrafluoroborate (31), while fluorination of l-methyl-4-(4-pyridyl)pyridinium triflate in the presence of lithium triflate provides l-fluoro-l -methyl-4,4 -bipyridinium ditriflatc (32) 67... 

Allylic t ganranetallics modified at the metal center by chiral adjuvants add to aldehydes and ketones to provide optically active hranoallylic alcohols. This process has been described for reagents containing boron, tin and chromium metd centers. Gore and coworkers have shown that a chrranium-medi-ated addition reaction of allylic brranides to simple aldehydes that uses a complex of lithium N-methyl-nt ephedrine and chromium(Il) chloride occurs with modest (6-16% ee) enantioselectivity (equation 61, Table 8). 

Fehlhammer et al also demonstrated that the lithium complex of the monoan-ionie, tridentate hydrotris(3-methyl-imidazol-2-ylidene)borate carbene 8, could be transmetallated to Fe , Co and Re , affording cationic complexes 9, 10, and 11, respectively (Seheme 5.2). Lithium complex 8 was implieated in the formation of 9-11 as these eomplexes formed only when n-BuLi was used to generate the carbene in situ, with Na[N(SiMej)2] or KOt-Bu affording boron-substitution products. The strueture of the purported Li carbene complex was verified by the isolation and structural characterization of 8 (R = Et). 

If the pKa of the corresponding acid R1 - H from the stabilized carbanion is smaller than 35, the migration of R1 fails in (dichloromethyl)borate complexes. Failure to convert pinanediol [(phenylthio)methyl]boronate to an a-chloro boronic ester has been reported15. Reaction of (dichloromethyl)lithium with an acetylenic boronic ester resulted in loss of the acetylenic group to form the (dichloromethyl)boronate, and various attempts to react (dichloromethyl)boronic esters with lithium enolates have failed17. Dissociation of the carbanion is suspected as the cause, but in most cases the products have not been rigorously identified. 

The reactivity profiles of the boronate complexes are also diverse.43 For example, the lithium methyl-trialkylboronates (75) are inert, but the more reactive copper(I) methyltrialkylboronates (76) afford conjugate adducts with acrylonitrile and ethyl acrylate (Scheme 16).44 In contrast, the lithium alkynylboronates (77) are alkylated by powerful acceptors, such as alkylideneacetoacetates, alkylidene-malonates and a-nitroethylene, to afford the intermediate vinylboranes (78) to (80), which on oxidation (peracids) or protonolysis yield the corresponding ketones or alkenes, respectively (Scheme 17).45a Similarly, titanium tetrachloride-catalyzed alkynylboronate (77) additions to methyl vinyl ketone afford 1,5-diketones (81).4Sb Mechanistically, the alkynylboronate additions proceed by initial 3-attack of the electrophile and simultaneous alkyl migration from boron to the a-carbon. 

DEHALOGENATION Diiron nonacarbonyl. Lithium amalgam. Phenanthrcnc-Sodium. Sodium thiosulfate. Triethyl phosphite. DEHYDRATION Alumina. Boron trifluo-ride n-butyl etherate. Dimethyl sulfoxide. Hcxamethylphosphoric triamidc. Iodine. Methyl N-suIfonylurethanc tricthylamine complex. Phosphonitrilic chloride. Thio-nyl chloride. Triphenylphosphite methlo-dide. 

Miscellaneous.—The 2-hydroxymethylene-ketone (310) forms a reasonably stable crystalline mesomeric complex (311) by reaction with boron trifluoride. Reaction of the complex with methyl-lithium, followed by acid, gave the 2-ethylidene-ketone (312), though in low yield. 

Rathice and Kow first reported the preparation of a boron-stabilized carbanion by direct deprotonation of the carbon acid. They made the important observation that the deprotonation needed a sterically demanding base to prevent its complexation with boron. Thus the anion of B-methyl-9-borabicy-clo[3.3.1]nonane, prepared by deprotonation with lithium 2,2,6,6-tetramethylpiperidine (LiTMP) in benzene, can be alkylated successfully. 

The reaction of the lithium enolate of 2-methyl-1-indanone with the thiophenium salt (35) leading to the 2-trifluoromethyl derivative in 51% yield is an exception. With all other in situ generated enolates of ketones, no trifluoromethylation was observed. To moderate the reactivity of the enolates, a boron Lewis acid (40) was added to form the boron complexes. This made a regio-, diastereo- and enantio-selective trifluoromethylation possible in good to high yields. ... 

Carboranyl derivatives of lanthanum, thulium and ytterbium are formed when the C-mercuro derivatives of methyl- and phenylcarboranes react with the rare earth metals in tetrahydrofuran at 20°C (Suleimanov et al., 1982a), or from the lithium derivatives of methyl- and phenylcarboranes with the rare earth trichlorides in benzene-ether at 20°C (Bregadze et al., 1983) as complexes with THF. A carboranyl derivative with a thulium-boron bond is also described. The reaction (eq. 62) may proceed via the formation of B-Tm-C derivatives, followed by disproportionation. 

Electrical conductivity measurements have been reported on a wide range of polymers including carbon nanofibre reinforced HOPE [52], carbon black filled LDPE-ethylene methyl acrylate composites [28], carbon black filled HDPE [53], carbon black reinforced PP [27], talc filled PP [54], copper particle modified epoxy resins [55], epoxy and epoxy-haematite nanorod composites [56], polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) blends [57], polyacrylonitrile based carbon fibre/PC composites [58], PC/MnCli composite films [59], titanocene polyester derivatives of terephthalic acid [60], lithium trifluoromethane sulfonamide doped PS-block-polyethylene oxide (PEO) copolymers [61], boron containing PVA derived ceramic organic semiconductors [62], sodium lanthanum tetrafluoride complexed with PEO [63], PC, acrylonitrile butadiene [64], blends of polyethylene dioxythiophene/ polystyrene sulfonate, PVC and PEO [65], EVA copolymer/carbon fibre conductive composites [66], carbon nanofibre modified thermotropic liquid crystalline polymers [67], PPY [68], PPY/PP/montmorillonite composites [69], carbon fibre reinforced PDMS-PPY composites [29], PANI [70], epoxy resin/PANI dodecylbenzene sulfonic acid blends [71], PANI/PA 6,6 composites [72], carbon fibre EVA composites [66], HDPE carbon fibre nanocomposites [52] and PPS [73]. 

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