Boron atomic copper

Recent theoretical studies of reductive elimination from MeaCu-S in the presence of BF3 suggest that reaction rate of the conjugate addition can increase if one of the Me groups is detached from the copper(III) to bind with a boron atom (Scheme 10.12) [129]. 

The so-called metaborates of empirical formula B02 can take several forms. The infinite linear (B02) T ion is found in the low-temperature form of LiB02 (449), Ca(B02)2 (275), and Sr(B02)2 (46). At high temperatures and pressures, the lithium compound possesses a sphaleritelike structure with boron in four-coordination (278). The triborate isolated B3Or group is found in the barium (297), sodium (276), and potassium (361) compounds, and the framework B30 " group, in which all the boron atoms are tetrahedral, exists for a high-pressure calcium metaborate phase (280) and copper metaborate (284). Two other anhydrous calcium metaborates are known to give the series... 

Wu, H. T. Micca, P. L. Makar, M. S. Miura, M. Total syntheses of three copper (E) tetracarboranylphe-nylporphyrins containing 40 or 80 boron atoms and their biological properties in EMT-6 tumor-bearing mice. Bioorg. Med Chem. 2006,14, 5083—5092. 

Six categories of 7V-hetero atom derivatives are considered N-M (M = boron, copper), N-N (e.g., N-nitro, A-nitroso), N-oxides (used to protect teriary amines), N-P (e.g., phosphinamides, phosphonamides), N-SiR3 (R = CH3), and N-S (e.g., sulfonamides, sulfenamides). 

These results may be explained either by Cram s cyclic model in the case of lithium alkyls or by Cornforth s dipolar model if copper-boron trifluoride reagents are used. Boron trifluoride causes double complexation of both nitrogen and oxygen atoms which results in the formation of an adduct with rigid antiperiplanar conformation due to electrostatic repulsion (see 4 and 5)9. 

Copper preferentially occupies the holes in /3-rh boron as shown by powder diffraction . In the CuB solid solution the D hole is represented by two crystallographic positions (denoted 2 and 2" in Fig. 1) " situated 40 pm from each other. The accommodation of the Cu atoms in three (or four) different holes in the preferred order shown in Fig 1 demonstrates the complex nature of the solid solution. 

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