Boron heterocycles as ligands

Boron Heterocycles as Ligands in Transition-Metal Chemistry, 18, 301... 

G. E. Herberich, G. Greis, and H. F. Heil, Novel Aromatic Boron Heterocycle as Ligand in a Transition Metal rc-Complex, Angew. Chem. Int. Ed. Engl. 9, 805-806 (1970). 

W. Siebert, Boron Heterocycles as Ligands in Transition-Metal Chemistry, Adv. Orga-nomet. Chem. 18, 301-340 (1980). 

The current year has seen the appearance of comprehensive data on known carbaboranes up to the end of 1976. - Other reviews have discussed Group IV carbaboranes, carbaborane crystal structures, wfo-monocarbaboranes, car-baborane nomenclature, metallocarbaboranes, and triple decker complexes with boron heterocycles as ligands. Theoretical studies have considered molecular orbitals utilized in bonding carbaboranes and their relationship to cage counting rules. ... 

The aforementioned boron heterocycles act as strong electron acceptors toward transition-metal moieties if the other ligands present have... 

The use of the boratabenzene heterocycle as a ligand for transition metal complexes dates back to 1970 with the synthesis of (C H5B-Ph)CpCo+ (1) (Cp = cyclopentadienyl).1 Since boratabenzene and Cp are 6 it electron donors, 1 can be considered isoelectronic to cobaltocenium. Many other transition metal compounds have been prepared that take advantage of the relationship between Cp and boratabenzene.2 In 1996, the synthesis of bis(diisopropylaminoboratabenzene)zirconium dichloride (CsHsB-NPr ZrCh (2) was reported Of particular interest is that 2 can be activated with methylaluminoxane (MAO) to produce ethylene polymerization catalysts with activities similar to those characteristic of group 4 metallocenes.4 Subsequent efforts showed that, under similar reaction conditions, (CsHjB-Ph ZrCh/MAO (3/MAO) gave predominantly 2-alkyl-1-alkenes5 while (CsHsB-OEt ZrCh/MAO (4/MAO) produced exclusively 1-alkenes.6 Therefore, as shown in Scheme 1, it is possible to modulate the specificity of the catalytic species by choice of the exocyclic group on boron. 

We are investigating a series of reactions of aminopyridines and aminopyrimidines and main group compounds. These heterocycles can form adducts with both kinds of nitrogen atoms pyridinic or anilinic. Bonding of several aminopyridines to heteroatoms such as boron, silicon, or phosphorus gives polyfunctional molecules rich in lone pairs and therefore candidates to be used as ligands. 

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