Boron interactions

The presence of two heteroatoms with different electronic properties in one molecule (one atom possessing a lone electron pair and another one with a vacant orbital, donor and acceptor, base and acid) separated by some fragment results in an interaction between the heteroatoms. Three types of the phosphorus-boron interactions have been revealed through-bond, intramolecular trans-annular (dative P—B bond), and intermolecu-lar (dative P—B bond) (Fig. 3). 

The migration of borane from the phosphorus atom in 1,3,2,5-dioxa-boraphosphorinane to the phosphorus atom in 1,5,3,7-diazadiphospha-cyclooctane is evidence of a lower phosphorus nucleophilicity in the P(III)—C—O—B(III) system than in the P—C—N fragment, which may result from the phosphorus-boron interaction in 1,3,2,5-dioxaboraphosph-orinane (90IZV1120). 

The crystallographically determined structure of 15 confirms the presence of a butterfly arrangement of iron atoms within which the boron atom resides in contact with all four metal atoms [Fe—B = 2.044(6), 2.047(6), 1.966(6), and 1.974(6) A] and 0.31 A above the Fe —Fe vector the internal dihedral angle of the Fe4 butterfly is 114.0°. These parameters are compared in Table II with those of related clusters. Compound 15 was first isolated as a product from the reaction of Fe2(CO)6B2H6 with Fe2(CO)9 (60), and evidence for increased iron-boron interaction is observed in a dramatic change in nB-NMR spectral shift (8) from S — 24.2 to +116.0. 

Tris(acetonitrile)tricarbonylchromium and tris(acetonitrile)tricarbonyl-tungsten react with tris(dimethylamino)borane to give yellow, readily sublimable crystalline products of the type [(CH3)2N]3BM(CO)3. On the basis of their 11B nmr spectrum, -coordination of the aminoborane with a relatively strong, metal-boron interaction is suggested.8,9... 

The presence of adequate supplies of boron has been shown to be essential for the proper development of frogs and fish, and considerable evidence indicates that boron plays a vital role in other animals and humans." Although precise biochemical mechanisms are yet to be revealed for animals, it appears likely that boron interacts through reversible ester formation in significant and necessary ways with membrane components and enzymes in animal cells. 

This effect is due to strong metal-boron interactions leading to an increased coordination number of the B atoms and, additionally, to a much better electronic shielding of the B nuclei. 

The empty 2/j,-orbital on boron interacting with the ji-electrons of the butadienylidene system in borole (5) is proved by the pronounced bathochromic shift in the visible spectrum compared with that of its pyridine adduct. This Ti-electron delocalization in boroles is destabilizing and produces a 471-electron antiaromatic system. The antiaromaticity is further evidenced by the rapidity of reactions that remove the 2p ,-orbital on boron from conjugation. These reactions include Lewis complexation, transition metal complexation, or borole ring opening reactions such as Diels-Alder addition, oxidation, and protodeboration. This removal of the antiaromaticity from borole results in transforming the compound to a typical, low reacting, sterically hindered arylborane. 

Scheme 12 Compound 92 combines Lewis acidic boron interaction with a neighboring hydrogen-bonding interaction to selectively extract fluoride across a biphasic barrier.

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