Boron-containing heterocyclic

Interactions between non-halogen-containing IIIB compounds and transition-metal complexes are found in 6.5.3. Most of these IIIB compounds are boron-containing heterocycles. A series of interesting sandwich compounds, including triple- and tetradecked complexes, are synthesized by methods in 6.5.2.1-6.5.3. 

In Chapter 8.34 of CHEC-II(1996) synthesis and properties of the boron-containing heterocycles with ring junction boron atom 1-6 have been considered <1996CHEC-II(8)889>. However, only a few papers have been published during the last decade concerning the systems 1-4 (Figure 1) and so they are discussed in Section 12.13.6. 

Bis(a-aminomethyl)phosphines having a mobile hydrogen atom could be expected to undergo a borylation reaction with borane, hydrogen being evolved. In fact, bis(Af-phenylaminomethyl)-phenylphosphine (199) and its sulfide (200) appeared to interact with borane under mild conditions, yielding a new type of phosphorus-boron-containing heterocycle—2-... 

Boryl nitronates (75-78), (217, 229-231) which have been poorly studied, are as a rule unstable. It should be noted that dimers (75) are crystalline compounds, which decompose in the solid state within a few days to give boron-containing heterocycles (79) (Scheme 3.74). 

Boron-11 NMR spectroscopy can be used for structural elucidation of complex boron containing heterocycles. Hydrolytic stabilities of dioxazabora heterocycles (19) and their corresponding N Mannich bases with different carboxamides have been determined by nB NMR studies (82M1025). 

In the past decade, X-ray crystallography has become a more routine method of characterization. Consequently, there are many structures of boron-containing heterocycles. The heterocycles relevant to this chapter are separated into structures which do not contain transition metals and the transition metal complexes of the Cp-like 1,2-azaborolyl, 1,2-thiaborolyl, and 1,2-oxaborolyl rings. 

The chemistry of boron-containing heterocycles is diverse. A variety of heteroaromatic compounds having a boron atom in the ring, borazaro-matics for example, has been investigated, mostly due to their interesting... 

There have been enormous developments in organo-boron chemistry during the last few decades, but boron-containing heterocycles are still somewhat rareties. The field is ripe for exploitation, and the chapter on this subject by Terashima and Ishikura should help in this respect. 

Boron-containing Heterocycles.—The enthalpies of adduct formation between pyridine, 2-picoline, 4-picoline, or 2,4,6-collidine and a number of heterocyclic boron derivatives (2-Br- or 2-organo-l,3,2-dihetero-borolans, -borinans, and -boroles) have been measured.282 The presence of Br greatly increases the Lewis acidity of the B atom. 

A new boron-containing heterocycle, l,l,3,3-tetramethyl-l,3-diazonia-2,4-diboratocyclopentane (47), has been prepared by the reaction of... 

Compared with NMR spectroscopy, vibrational spectroscopy plays a much less deeisive role in the characterization of boron-containing heterocycles because of the lack of vibrations which could give characteristic information about structure and bonding in most cases. Best suited for IR spectroscopic investigations are unsaturated rings with <2=C double bonds. For instance, 2,2,3-triethyl-1,1,4-trimethyl- l/f-2,5-dihydro-l,2-azoniaboratole and 2,2,3,4-tetraethyl-l-methyl-2,5-dihydro-l,2-oxoniaboratole display easily determined v (C=C) vibrations at 1636 cm <75CB395) and 1640 cm <74S350), respectively. 

These selected examples show impressively the significance of H NMR investigations of five-membered boron-containing heterocycles. Not only can structural details be deduced, but rotation barriers and rearrangement processes are also rendered observable. 

Boron-containing Heterocycles.—Pyrolysis of BMcs produces yields of up to 25%... 

Bis-(2-hydroxyethyl)-ether or -thioether undergoes condensation reactions with phenyldihydroxyborane, to give new eight-membered boron-containing heterocycles (59). ... 

Several different groups of compounds are consistent with the title of this chapter saturated heterocycles, unsaturated heterocycles, carboranes, etc. However, only the studies of saturated boron-containing heterocycles with ring junction boron atoms connected to three carbon atoms are discussed here (structures (l)-(6)). 

No special review of the chemistry of boron-containing heterocycles with ring junction boron atoms has been made however, compounds (l)-(4) <77T233l> and 1-boraadamantane (5) <80Mi 834-01,83PAC1439) were reviewed separately as parts of more general surveys. 

Boron-containing Heterocycles.—Ab initio MO calculations on the hypothetical 1,3,2,3-diazadiboretidine (65), the B—analogue of cyclobutadiene,... 

Synthetic routes have been described for the new boron-containing heterocycles (31), (32), and (33). ... 

The dimesitylbotyl borepin (169) underwent [2 + 2] photocycloaddition to give (169). A cast firm of (169) from a toluene solution showed photochromic behaviour with a colour change from colourless to deep blue. On the other hand, the bis-boron bridged stilbene (170) upon 254 nm irradiation afforded the novel boron-containing heterocyclic compound (171). ... 

A series of boron-containing heterocycles (e.g. 66) have been prepared using Pd-catalyzed A-arylation reactions between polyhalogenated aromatic amines 63 and 64. (Fig. 14) [406]. Selective reactivity of the aryl iodide cleanly provided the desired product 65, which was transformed to 66 in subsequent steps. Spectroscopic studies indicate these materials have extended conjugated 71-systems. 

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