Donor-acceptor ring-in-ring complexes

The self-assembly of three donor-acceptor ring-in-ring complexes, prepared from the π-electron-deficient tetracationic cyclophane, cyclobis(paraquat-4,4'-biphenylene), and three large π-electron-rich crown ethers (each 50-membered rings) containing dioxynaphthalene (DNP) and tetrathiafulvalene (TTF) units in pairs (DNP/DNP, DNP/TTF and TTF/TTF), is reported. (1)H NMR spectroscopic analyses are indicative of the formation of 1:1 complexes in CD(3)CN, whilst the charge-transfer interactions between the DNP and TTF units of the crown ethers and the tetracationic cyclophane have permitted the measurement of binding constants of up to 4×10(3) M(-1) in CH(3)CN to be made using UV/Vis spectroscopy. Ring-in-ring complexes are proposed as intermediates in the stepwise synthesis of molecular Borromean rings (BRs) comprised of three different rings. With the particular choice of crown ethers, the 1:1 complexes have polyether loops that protrude from the donor-acceptor recognition point above and below the mean plane of the tetracationic cyclophane, which, ideally, could conceivably bind dialkylammonium centers present in a third ring. X-ray crystallographic analyses of the solid-state superstructures of two of the three 1:1 complexes reveal, however, the presence of prodigious CH···O interactions between the polyether loops of the crown ethers and the rims of the cyclophane, no doubt stabilizing the complexes, but, at the same time, masking their potential recognition sites from further interactions that are essential to the subsequent emergence of the third ring. The solid-state superstructure of one of the crown ethers binding two dibenzylammonium ions provides some insight into the design requirements for the next generation of these systems; longer polyether loops may be required to allow optimal interactions between all components. It has become clear during a pursuit of the stepwise synthesis of the molecular BRs that, when designing complex mechanically interlocked molecules utilizing multiple recognition sites, the unsullied orthogonality of the recognition motifs is of the utmost importance.     

Donor-acceptor complexes of quinoline N-oxides with boron trifluoride

Molecular n-v complexes of quinoline N-oxides with BF₃ have been studied by electronic and IR spectroscopy. In most case the donor centre is the oxygen atom of the N-oxide group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1092, August, 1994.     

Donor-acceptor complexes of heteroaromatic N-oxides. A review

Petrozavodsk State University, 185640 Petrozavodsk and St. Petersburg State University, 198904 St. Petersburg. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 760–773, June, 1995. Original article submitted December 24, 1994.     

Donor-acceptor complexes of dipyrrolylmethenes with boron trifluoride as intermediates in the synthesis of Bodipy

The formation of donor-acceptor complexes of dipyrrolylmethene and structurally similar biladiene-a,c with boron trifluoride was studied by electronic absorption, IR, and ¹H NMR spectroscopies as well as by quantum chemical calculations. It was shown that the formation of donor-acceptor complexes is the first step of the synthesis of the corresponding boron fluoride chelate complexes (Bodipy). The hydrogen bond N—H...F—B additionaly stabilizes the donor-acceptor complexes. The stability constants, geometric parameters, and energy characteristics of the donoracceptor complexes were determined; the two-step mechanism of Bodipy synthesis was analyzed.     

Synthesis of new borazines containing crosslinkable groups

Three new functional group containing borazine derivatives, 2,4,6-tri（allylamino）borazine, 2,4,6-tri（3-ethynylanilino）borazine, and 2,4,6-tri（4-propargyl oxyanilino）borazine were synthesized by aminolysis reaction of 2,4,6-trichloroborazine ClaB3N3H3（TCB）. The new compounds were characterized by infrared （IR） spectra, nuclear magnetic resonance （NMR）, and mass spectrometry （MS）.     

Donor-acceptor stabilized silaformyl chloride

Formyl chloride (H(Cl)C=O) is unstable at room temperature and decomposes to HCl and CO. Silicon analogue of formyl chloride, silaformyl chloride IPr·SiH(Cl)=O·B(C(6)F(5))(3) (3) (IPr = 1,3-bis(2,6-diisopropyl-phenyl)imidazol-2-ylidene), was stabilized by Lewis donor-acceptor ligands. Compound 3 is not only the first stable acyclic silacarbonyl compound but also the first silacarbonyl halide reported so far.     

Donor-acceptor complexes of linear oligopyrroles with boron trifluoride. Spectral studies and quantum-chemical simulation

Intermediate products of synthesis of the boron trifluoride complexes with linear oligopyrroles are found. By means of electronic spectroscopy it was shown that the reaction of linear oligopyrroles with boron trifluoride in solutions resulted in the formation of stable donor-acceptor complexes. Their composition was established and the formation constants were evaluated. It was shown that transformation of these complexes in the corresponding borofluoride complexes is possible only while boiling the reaction mixture. By means of quantum-chemical methods the structural and energy parameters of the donor-acceptor complexes under study were calculated.     

Theoretical investigation of the symmetric trisubstituted borazines

The bonding in borazine and four symmetric tri-substituted derivatives, B-trifluoroborazine, N-trifluoroborazine, B-trimethylborazine and N-trimethylborazine, is discussed by means of all electron ab initio SCFMO calculations. B-trifluoroborazine is predicted to be 12·9 eV more stable than the N-trifluoro derivative and B-trimethylborazine 2·8 eV more stable than the N-trimethyl derivative. The calculated wavefunctions are used to interpret the low energy photoelectron spectra of these molecules. The calculated sequence for the three highest filled orbitals is πσπ in all derivatives except B-trifluoroborazine, where the sequence ππσ is realised.     

Donor-acceptor molecular figures-of-eight

The intermolecular template-directed synthesis, separation and characterisation of two constitutional isomers that are self-complexing donor-acceptor [1]rotaxanes has been achieved by click chemistry, starting from a π-electron deficient tetracationic cyclophane containing two azide functions and a π-electron rich 1,5-dioxynaphthalene-containing polyether chain terminated by propargyl groups.     

Donor-acceptor phthalocyanine nanoaggregates

A novel donor-acceptor bisphthalocyanine (bis-Pc, 1) in which two different Pc units (Zn(II)-Pc and Ni(II)-Pc) are linked via vinylene spacers to the pseudopara positions of a central [2.2]paracyclophane moiety is described. The synthesis of 1 is achieved by two successive Heck reactions of pseudopara-divinyl[2.2]paracyclophane 9 with, sequentially, a zinc(II)- and a nickel(II)-iodophthalocyanine (4 and 5, respectively). The self-assembly ability of 1, which is the result of the complementary donor-acceptor character of its phthalocyanine units, has been assessed by a variety of techniques. It is revealed that 1 forms one-dimensional aggregates of nanometer-sized dimension, whereas equimolar mixtures of the donor and acceptor Pc subunits 2 and 3, although strongly interacting, do not give large arrays. The aggregates of 1 represent a novel type of supramolecular polymers based mainly upon donor-acceptor interactions.     

Donor-acceptor heteroleptic open sandwiches

A series of donor-acceptor heteroleptic open sandwiches with formula CpM-M'Pyl (M = B, Al, Ga; M' = Li, Na; Cp = cyclopentadienyl; Pyl = pentadienyl) has been designed in silico using density functional theory. The most stable complexes are those containing boron as a donor atom. A molecular orbital analysis shows that the s character of the lone pair located at the group 13 element is mainly responsible for the complex stabilization. It is also found that the surrounding medium has a similar effect on these sandwiches such as in the "classical" donor-acceptor complexes, showing a decrement in the group 13 element-alkaline metal bond lengths.     

Donor-acceptor complexes of excited states on silica surface and in hexane solution at liquid nitrogen temperature

It is shown that an exciplex between pyrene (Py) and N,N-dimethylaniline (DMA) forms at low temperature (77 K) on the nonporous silica surface and in a solid hexane solution. The fluorescence lifetime of pyrene in the adsorption state increases when the quencher concentration grows at 77 K. The exciplex fluorescence spectra in the adsorption state shifts to a blue wavelength range when the temperature decreases as a result of the dipole-dipole interaction of the exciplex with the hydroxy groups of the silica surface. On the basis of the model suggested the hydroxyl group concentration on the dehydrated at 770 K silica surface has been estimated.