Boron trichloride structure, 7

It is especially important to investigate the molecular structure of coordination compounds in the vapor phase because the relatively weak coordination interactions may be considerably influenced by intermolecular interactions in solutions and especially in crystals. It has been shown that the geometrical variations can be correlated with other properties of the molecular complexes ). In particular the structural changes in the F3B N(CH3)3 and CI3B N(CH3)3 molecules ) relative to the respective monomeric species unambiguously indicated boron trichloride to be a stronger acceptor than boron trifluoride. Data on the geometry and force field have also been correlated ). 

Bis(dichloroboryl)benzene (6) is an important starting material which lends itself to facile derivatization. As shown by Piers, it cleanly reacts with bis(penta-fluorophenyl)zinc to afford the corresponding bidentate Lewis acid 13 (Scheme 7) The molecular structure of diborane 13 has been determined and is shown in Fig. 1. In this structure, the vicinal boron atoms are held at 3.26 A and from one another and seem to be ideally positioned to cooperatively interact with monoatomic anions. The fully fluorinated version of this bidentate Lewis acid has also been prepared. Original efforts focused on the use of 1,2-bis(dichloroboryl)tetrafluorobenzene 14 as a starting material (Scheme 8). This compound could be observed in the early stage of the reaction of trimeric perfluoro-o-phenylenemercury (4) with boron trichloride, but was found to be unstable toward condensation into 9,10-dichloro-9,10-dihydro-9,10-diboraoctafluoroanthracene 15. The successful synthesis of the fully fluorinated... 

Reaction of H2(OEP) and diborane in THF and subsequent alkolysis gave (ROB)20 (OEP) (Scheme 3), while (HO)2B 2(TPP) was obtained after chromatographic purification of the unstable reaction product of H2(TPP) and boron trichloride (Scheme 4).24 Their structures have not been confirmed. They are slowly hydrolyzed in aqueous ethanol and rapidly in acid. 

The structures of l,8-di(silyl)naphthalene and its mono- and di(p-anisyl) derivatives have been determined and are shown in Fig. 3-5. While the naphthalene part of the molecules appears to be largely undistorted, the two silyl groups are clearly bent away from each other in the molecular plane in order to avoid closer repulsive contacts. This steric crowding enhances the chemical reactivity of the molecule and makes the eompound a versatile starting material for numerous derivatives. For substitution control the conversion into the symmetrical dichlorosilane is possible using boron trichloride (Scheme 5). 

Boron trichloride will be a resonance hybrid of the following structures... 

BeCU or BCIj Boron trichloride is expected to be the stronger Lewis acid because the oxidation number of boron in BCI3 is +3, whereas for the beryllium atom in BeCl2 it is only +2. The second reason has to do with structure. The boron atom in BCI3 is three-coordinate, leaving a vacant site to which a Lewis base can coordinate. On the other hand, BeCl2 is polymeric, each beryllium atom is four-coordinate, and some Be-CI bonds must be broken before adduct formation can take place. 

Boron has the structure ls22s22plx, and we know that it forms a covalent compound, boron trichloride experimental work shows that there are three equal strength B—Cl bonds in the molecule. A good explanation of this is that hybrid orbitals are formed from boron 2s, 2pv and 2pv orbitals. This is illustrated in Figure 15b. The hybrid orbitals lie in the same plane and are known as sn2 hybrids, since they are formed from one s and two p orbitals. Note that each of the hybrid orbitals will be only partly filled, since there are only three electrons of principal quantum number 2 to be allocated. The layout of the BC13 molecule is shown in Figure 15c. The calculated bond angle for sp2 hybrids is 120°, and this is confirmed experimentally. 

It is of interest to note in passing that In more recent work (ref.72), use has been made in synthesis of the transformation of chalcones to isoflavones with thallium(lll) nitrate. Thus, 6-acetyl-2,2-dimethyl-7-hydroxy-5-methoxychromanone was converted to the chalcone with 2,4-dibenzyloxybenzaldehyde. The O-acetyl derivative by treatment with the thallium reagent followed by acidic cyclisation gave a bischromanone structure. Selective reduction of the least hindered carbonyl group in the bischromanone, acidic dehydration of the resultant alcohol and final debenzylation with boron trichloride gave the linear isofiavone. 

Two boron phosphides have been isolated, BP and Bi2P2-Heating elemental boron and red phosphorus at 900-1100 °C yields BP as refractory brown crystals having a cubic zinc blende structure similar to cubic boron nitride. This material can also be prepared by a number of other methods including the pyrolysis of CHP-BCH, reaction of boron or boron trichloride with zinc phosphide or phosphine, and hydrogen reduction of CRP-BCls. 

For instance, attempts at isolating donor-free alkynylboranes have been hampered by spontaneous polymerization. The first donor-free tris(alkynyl)borane, tris(3,3-dimethyl-l-butynyl)borane (30), has only recently been obtained by reaction of deprotonated 3,3-dimethyl-l-butyne with boron trichloride at —78°C in pentane (equation 32). The alkynylborane (30) was fully characterized by multinuclear NMR spectroscopy, mass spectrometry, and X-ray crystallography. The NMR signal of (30) shows a remarkable shift of 5 = 48, which is upfield from typical shifts of alkyl-and alkenylboranes. The crystal structure of (30) shows similar C-C bond lengths, but significantly shorter B-C bonds in comparison to those observed for the donor-stabilized complexes (30) D indicative of a small degree of p - p interactions between the sp -boron atom and the sp-hybridized carbon. Weak r-overlap was further confirmed by ab initio calculations. It is this r-interaction that has been exploited for the development of nonlinear optical (NLO) materials based on alkynylboranes as described in Section 7.1. ... 

Boron nitride Calcium carbide alloy refining Boron trichloride alloy, aluminum structural parts Magnesium alloy, bearing Cadmium alloy, brazing Cadmium... 

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