Used individually or combinatorially, unique isocyanate-based dendritic monomers generate homo- and heterofunctional materials (the sketch shows schematically a molecule with a heterofunctional surface). Tier construction by combinatorial monomer addition offers new avenues to macromolecular architectural design and the control of physical properties.
Abstract-The synthesis of a novel series of 1 → 3 C-branched, isocyanate-based building blocks (monomers) useful for the rapid construction of dendritic architectures is reported. More specifically, the preparation of di-t-butyl 4-isocyanato-4- (9), and dimethyl 6-isocyanato-6-(4-carbomethoxy-2-oxabutyl)-4,8-dioxaundecanedioate (11), via treatment of the corresponding amines with triphosgene, is described. Characteristic features of each monomer include a triad of protected functionality connected to a single, air-stable isocyanate moiety. Isocyanate stability is postulated to arise from the close proximity of the tertiary alkyl branching center. This series of dendritic building blocks facilitates the introduction of a variety of functional groups, such as alcohol, amines, carboxylic acids, esters, nitriles, and ethers, onto the surface of dendrimers as well as other suitable materials. Isocyanate utility is demonstrated by reaction of a DSM-based, 32-amine-terminated dendrimer with the triscarbamate isocyanate monomer (7d) to afford a poly(t-butyl carbamate)-'coated' dendrimer (12).
Iron(II) and nickel(II) bis(ligand) complexes of
6-(5-methyl-1,2,4-oxadiazol-3-yl)-2,2′-bipyridine (L) are described. The
ligand field in the iron complex is close to that at the singlet (
1 A1) ? quintet (
5 T2) crossover and magnetic and
Mössbauer spectral evidence indicates that a spin transition occurs in
salts of the iron complex but is centred above room temperature. The
structures of [FeL2]
[CF3SO3]2.CH3CN
and [NiL2]
[BF4]2.CH3CN
were determined and both are very similar to the structures of the
corresponding terpyridine complexes. Spectroscopic data indicate that for the
iron complex π-interaction between the metal and the ligand is less than
that in the terpyridine system. [FeL2]
[CF3SO3]2.CH3CN
is monoclinic, space group P
21/c; a
8 . 232(5), b 25 . 273(10),
c 17 . 306(10) Å, β 92 .
37(3)°, Z 4; [NiL2]
[BF4]2.CH3CN
is monoclinic, space group P
21/c; a
8 . 136(2), b 17 . 558(2),
c 23 . 783(7) Å, β 109 .
32(1)°, Z 4.
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