Phosphorus boron halides

N.m.r. studies are reported on the triethylphosphine and trisdi-methylaminophosphine complexes with boron halides, and triethylphos-phine complexes with aluminium chloride. A correlation of Sp with the number of phosphorus ligands in metal carbonyl complexes has led to a qualitative rationalization of 8p in terms of a- and 7r-bonding. ... 

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Boron-11 resonance has been rather frequently investigated in boron containing phosphorus compounds which, in most instances, were borane- or boron halide-adducts (see Section IV). Some data are nevertheless available for typical boron-phosphorus compounds which may be discussed in relation to available nB literature (for a general review see 1969, 24). 

Adduct formation results in well-defined species. Generally speaking, phosphorus compounds act as Lewis bases [exceptions being penta-valent phosphorus halides as reviewed by Webster <1966 106)] for other examples in which the relevant Lewis acids are metalloid derivatives see references 1966, 107 and 1969, 186. Adducts involving boron have recently been reviewed elsewhere(1969 94 andl02) and are by far the most numerous and use has been made of phosphorus, boron, proton and fluorine resonances, in some cases at varying temperature. 

BC13 has a hexagonal bimolecular cell, Cj , P63, with a = 6.08 and c = 6.55 A. The trigonal planar molecules are in A and B positions as for SbCls and Sb(CH3)3Br2 (Figures 4.26 and 4.27). All other boron halides are also planar. Phosphorus trihalides, like NH3 and nitrogen halides, are pyramidal because of the lone electron pair on P and N. 

Many phosphine-borane complexes Y3P BZ3 have been characterized. They include compounds where Y = alkoxy, alkyl, amino, halide, and hydride groups, and Z = alkyl, halide, and hydride. The stabilities of these complexes vary widely depending on the Lewis acidity and basicity of the boron and phosphorus moieties, respectively. The relative stabilities of Lewis acid-base complexes with BH3 are R3P > R3N > RgAs > R3Sb, but with BF3 the order is R3N > R3P > RsAs > R3Sb. The stabilities of the boron halide complexes of phosphines follow the same order as the amine complexes BI3 > BBt3 > BCI3 > BF3. 

In reactions with metal or metalloidal halides, primary amines, because of their difunctionality, tend to yield more complex molecules, such as cyclic, cage, or polymeric structures. For example, cage-type structures of the type P4(NCH3)e and As4(NCH3)e have been prepared by methylaminolysis of phosphorus(III) or arsenic(III) chloride, respectively, and cyclic structures of formula (HNBC1)3 or (RBNC1)4 have been prepared from boron halides and ammonium chloride or mono-alkylamines. 

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