Boron-nitrogen complexes

While the mercury compound shows localized N—Hg bonds, the TADB-system (which is isoelectronic with cyclopentadiene) forms a low-spin complex with iron. This was the first identified example of a sandwich-compounds of a boron-nitrogen ring. The complex is prepared by adding an etheric solution of TADBLi to a suspension of FeCl2 in tetra-hydrofuran. 

The chemistry of boron-phosphorus compouuds has been reviewed. Numerous boron-phosphorus derivatives have been reported, but relatively few boron-arsenic or boron-antimony compounds have been described. Boron-phosphorus compounds are similar in many ways to boron nitrogen derivatives, but the teudeucy to share boudiug electrons in covalent tetrahedral compounds is much more evident with phosphorus thau with uitrogeu. lu fact, most boron phosphorus chemistry iuvolves tetrahedral borou. They are typically either phosphiue-boraue complexes, such as R3P BR j, or phosphinoboranes (R2PBR2) , cyclic or polymeric derivatives of the hypothetical H3P BH3. The chemistry of these compounds and that of boron phosphate and thiophosphate is described below. Boron phosphides are discussed in Section 2.6. 

In covalent azides, the pseudohalogen azide RN3 has an angular structure as in HN3. Triazidoborazine [H3N3B3(N3)3] and other boron azides, for example, salts of the tetraazidoborate ion B(N3 (4 have been considered as boron nitride precursors (see Boron-Nitrogen Compounds). The M(Ns)3 azido complexes of the other group 13 elements (Al, Ga, In, Tl) and their M(N3)4 tetraazido anions are all known. They and their derivatives are also used as precursors for the nitrides. 

The 6-membered B3O3 ring also occurs in many more complex borate anions. Cyclic boron-nitrogen molecules are considered later in this chapter. The cyclic molecule (c), X = SH, is the predominant species in the vapour of HBS2 at temperatures below 100°C. In the crystalline tribromo compound of type (c), (BrBS)3, the molecular structure (d) was found. 

Some boron-nitrogen compounds have similar structures to those of carbon. Structurally complex borides are formed with many metals. 

Boron-nitrogen and boron-phosphorous compounds are classical textbook examples of donor-acceptor complexes. The chemical bonds of the Lewis-acid Lewis-base complexes are usually explained in terms of frontier orbital interactions and/or quasiclassical electrostatic attraction in the framework of the Hard and Soft Acid and Base (HSAB) model [73]. We were interested in seeing if the differences between the bond strengths of boron-nitrogen and boron-phosphorous complexes for different boranes, amines and phosphanes can be explained with the EDA method. 

Boron-Nitrogen Compounds.35 Compounds of the type R 3N->BR3 have already been mentioned amongst the many donor-acceptor complexes formed by BR3 compounds. In this Section we are concerned with compounds containing the —NR —BR— unit. This unit is similar to a —CR =CR— group and can replace it in many compounds. This analogy is often justified by the assumption that the actual electron distribution in the N to B bond can be described by the resonance (8-XIX), whereby approx. / + -/... 

When manganese vapour and a mixture of nitric oxide, trifluorophosphine and boron trifluoride are co-condensed the compound Mn(PF3)(NO)3 is produced [280]. Co-condensation of nickel and carbon dioxide results in the formation of some nickel tetracarbonyl [280]. Burdett and Turner [298] showed that co-condensation of nickel and nitrogen at 20°K resulted in a nickel—nitrogen complex. Moskovits and Ozin [299] have recently repeated the experiment and have shown from the infrared spectrum of the matrix that the major product is NiN2, with the nickel atom bonded to the end of the nitrogen molecule. 

---