An Approach Towards Functional Dendrimers Based on the Hydroboration Reaction and Spontaneous Boron–Nitrogen Bond Formation

Abstract

The reaction of 1,4‐bis‐ or 1,3,5‐tris(bromoboryl)benzenes 4 and 6, respectively, with 2 or 3 equiv. of 4,4′‐bis(but‐3′′‐enyl)‐2,2′‐bipyridyl (2) leads to the corresponding 2,2′‐bipyridylboronium cations 5 and 7 in almost quantitative yield. Using the monocation [(MeC6H4)B(Br){4,4′‐bis(but‐3′′‐enyl)‐2,2′‐bipyridyl}]+ (3Br) as a model system, it is shown that the olefinic side‐chains of such compounds are readily transformed into alkyldibromoborane functionalities by hydroboration with HBBr2. Subsequent addition of 4,4′‐dimethyl‐2,2′‐bipyridyl leads to the formation of a branched system of three 2,2′‐bipyridylboronium cations (9Br). The species 5 and 7 can be regarded as generation zero (G0) 2,2′‐bipyridylboronium dendrimers, and the hydroboration/B–N adduct formation sequence offers a convenient route for the assembly of higher generations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Two Directing Groups Used for Metal Catalysed Meta‐C−H Functionalisation Only Effect Ortho Electrophilic C−H Borylation

“…of BBr 3 and heated and then dried in-vacuo) showed a gradual change in the 11 B NMR spectra whereby the boron centre in the cationic component was shifted gradually downfield from δ 11B = 37.5 to δ 11B ca. 42 ppm (in the range expected for an ArylB(OR)Br species), [19] whereas the second resonance was shifted upfield from δ 11B = À 16.6 to δ 11B = À 25 ppm (Figure 6), the latter is as expected for a discrete BBr 4 À anion. Thus, it can be concluded that upon cooling of the sample, the product favours the salt form, 8 A.…”

Amides as modifiable directing groups in electrophilic borylation

“…The δ 11B = 40.4 is consistent with boron in an ArB(OR)Br environment. 18 Finally, it should be noted that leaving mixtures containing 3 for longer reaction times led to the conversion of 3 into 2a , suggesting 3 is an intermediate in the production of 2a .…”

“…However, the identity of 3 is supported by comparison to Me 3 N/BHBr 2 which displays a d 11B = −0.7 doublet with an identical 1 J B-H coupling constant (156 Hz) to that observed in 3. 17 18 Finally, it should be noted that leaving mixtures containing 3 for longer reaction times led to the conversion of 3 into 2a, suggesting 3 is an intermediate in the production of 2a.…”

Recent Progress on Synthesis of N,N′-Chelate Organoboron Derivatives

“…In 2005, Matthias Wagner’s team reported other N , N ′-chelate organoboron complexes in this reaction. They used dibromo(phenyl)borane, bromo(methyl)(phenyl)borane, bromo(ethoxy)(phenyl)borane to give bipyridine adducts with satisfactory yields ( 15 – 18 , 76–89%) [ 41 ], as shown in Scheme 4 . This reaction indicated that different N , N ′-chelate organoboron compounds could be obtained by adding distinct boron reagents under ambient temperature.…”

“…The data presented in this study are openly available in references [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , …”