Boron-lead bond

Prior to 1958 only nitrile-adducts were reported to result from the reaction of nitriles with trihaloboranes (c.f. 36)). The first reported example of the 1,2-addition of boron-halogen bonds to a C=N group involves the reaction of tri-fluoroacetonitrile with trichloroborane or tribromoborane 4) and leads to dimeric derivatives. A 1 1 ratio of the cis-trans isomers is obtained as indicated on the basis of 19F n.m.r. studies. 

Zirconium-aryne complexes have also found application in the regiose-lective synthesis of halophenols.62 Reaction of 101 with methyl diethylbori-nate or triethylborate leads to insertion of a boron-oxygen bond into a Zr-benzyne bond with formation of 102 and 104, respectively (Scheme 12). Further reactions of 102 and 104 with bromine or iodine followed by excess NaOH and 30% hydrogen peroxide gives halomethyl(methoxy)phe-nols 103 and 105 in good yields. In most cases only one regioisomer of the halophenol was observed. 

The reaction of the porphyrin ligand, TTP (tetra-p-tolylporphyrin) with BF3-OEt2 leads to the oxide fluoride complex, B2OF2(TTP) and the structure has been established using H, 13C, nB and 19F NMR spectroscopy and FAB mass spectrometry [9], The structure contains a B—O—B bridge in which each boron is bonded to fluorine and to a nitrogen of TTP. The structure of the diboron complex was confirmed by an X-ray crystal structure determination of the tetrakis-(p-chlorophenyl)porphyrin (TpCiPP) derivative. 

The presence in the molecule of two kinds of boron-hydrogen bond is indicated both by its Raman spectrum and by the chemical evidence that four only of the hydrogen atoms are replaceable by methyl groups. Electron diffraction leads to B-H 1.19 A, B-H, 1.33 A, B-B 1.77 A, ZHBH 121.5° and Z.H, BHjj 100°. Raman and infrared spectra of the tetramethyl compound suggest an absence of terminal hydrogen atoms, and electron diffraction shows the four carbon atoms and two boron atoms to be coplanar. 

Vinyllead and alkynyllead tricarboxylates can only be prepared by metal-metal exchange, such as mercury-lead,ll6 ll7 tin-lead,ll6,ll7 boron-lead i or zinc-lead.l In the case of tin-lead exchange, cleavage of the methyl-tin bond is much slower than cleavage of the vinyl-tin or alkynyl-tin bond. Therefore (trimethyl)vinyltin derivatives are preferred to the corresponding (tributyl)vinyltin analogues for the synthesis of the unstable vinyllead and alkynyllead compounds. 

X-Rav Diffraction. Borosilicate molecular sieves have been studied by X-ray diffraction (1.16-20 ). X-ray diffraction techniques have been developed to determine the degree of substitution of the silicate framework by borate tetrahedra (291. The boron-oxygen bond is shorter than the the silicon-oxygen bond, which leads to a contraction of the unit cell for a borosilicate molecular sieve as boron substitution increases. The unit cell volume determined from peak positions in the ranges 2O°<20<35< and 45°<20<5O° or an empirical parameter termed ST (sum of four d spacings) correlated with structural boron content (29). 

B. Reactions Leading to Formation of Boron-Nitrogen Bonds. 285... 

A number of reactions of the boranes lead to synthesis of boron-carbon bonds. With boron alkyls the boron hydrides undergo important alkylation reactions, but only in the case of diborane have these reactions been described in detail. When diborane is mixed with trimethylborane at room... 

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