Two C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes, 1-(BMes(2))-2-R-1,2-C2B10H10 (1, R = H, 2, R = Ph), were synthesised by lithiation of 1,2-dicarba-closo-dodecaborane and 1-phenyl-1,2-dicarba-closo-dodecaborane, respectively, with n-butyllithium and subsequent reaction with fluorodimesitylborane. These novel compounds were structurally characterised by X-ray crystallography. Compounds 1 and 2 are hydrolysed on prolonged exposure to air to give mesitylene and boronic acids 1-(B(OH)(2))-2-R-1,2-C2B10H10 (3, R = H, 4, R = Ph respectively). Addition of fluoride anions to 1 and 2 resulted in boryl-carborane bond cleavage to give dimesitylborinic acid HOBMes(2). UV absorption bands at 318-333 nm were observed for 1 and 2 corresponding to local pi-pi*-transitions within the dimesitylboryl groups while visible emissions at 541-664 nm with Stokes shifts of 11 920-16 170 cm(-1) were attributed to intra-molecular charge transfer transitions between the mesityl and cluster groups. Compound 2 was shown by cyclic voltammetry to form a stable dianion on reduction. NMR spectra for the dianion [2](2-) were recorded from solutions generated by reductions of 2 with alkali metals and compared with NMR spectra from reductions of 1,2-diphenyl-ortho-carborane 5. On the basis of observed and computed B-11 NMR shifts, these nido-dianions contain bowl-shaped cluster geometries. The carborane is viewed as the electron-acceptor and the mesityl group is the electron-donor in C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes.
A series of 1,3-bis(perfluoroaryl)-2-(hetero) aryl-1,3,2-benzodiazaboroles, 1,3-Ar-F(2)-2-Ar-1,3,2-(NBC6H4)-B-2 (Ar = Ph, Ar-F = C6F5 5; Ar = Ph, Ar-F = 4-C5F4N 6; Ar = Ph, Ar-F = 4-NCC6F4 7; Ar = 2-C4H3S, Ar-F = C6F5 8; Ar = 2-C4H3S, Ar-F = 4-C5F4N 9; Ar = 2-C4H3S, FAr = 4-NCC6F4 10), were synthesised by cyclocondensation of the adducts PhBBr2 center dot PPh3 or 2-thienylBBr(2) center dot PPh3 with N, N '-bis(perfluoroaryl)-o-phenylenediamines in the presence of 2,2,6,6-tetramethylpiperidine. Similar treatments of the PPh3 adducts of 4-(1 ', 3 '-diethyl-1 ', 3 ', 2 '-benzodiazaborolyl)-phenyldibromoborane with the corresponding diamines gave rise to the push-pull compounds, C6H4(NEt)(2)B-1,4-C6H4-B((NAr)-Ar-F)(2)C6H4 (Ar-F = C6F5 11; 4-C5F4N 12) and C6H4(NEt)(2)B-2,5-C4H2S-B((NAr)-Ar-F)(2)C6H4 (Ar-F = C6F5 13; 4-C5F4N 14). The X-ray structures of 8, 11, 12 and 13 were determined. Electronic structure calculations reveal that the LUMOs are located at the perfluoroaryl groups in 5-14; thus the fluorinated benzodiazaborolyl groups are considered as electron-withdrawing moieties. These moieties differ from alkylated benzodiazaborolyl groups which are regarded as donors. The emission spectra for 5-14 show charge transfer bands with significant solvatochromism and large Stokes shifts (6100-12 500 cm(-1) in cyclohexane and 8900-15 900 cm(-1) in CH2Cl2). The emissions of the benzodiazaboroles, 5-10, arise from a different charge transfer (CT) process to the local charge transfer (LCT) process typically found in many fluorescent benzodiazaboroles. This novel remote charge transfer (RCT) process involving the perfluoroaryl groups is supported by CAM-B3LYP computations. The push-pull systems 11-14 here give fluorescent emissions with moderate to high fluorescence quantum yields (65-97%) that arise from the usual LCT process only.
Six new C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes, 1,A-R2-1,A-C2B10H10, where R represents the group 2-(1,3-Et2-1,3,2-N2BC6H4) or 2-(1,3-Ph2-1,3,2-N2BC6H4) and A is 2, 7 or 12, were synthesized from o-, m-, and p-dicarbadodecaboranes (carboranes) by lithiation and subsequent treatment with the respective 2-bromo-1,3,2-benzodiazaboroles. UV-visible and fluorescence spectra of all carboranes display low energy charge transfer emissions. While such emissions with Stokes shifts between 17,330 and 21,290 cm(-1) are typical for C,C'-bis(aryl)-ortho-carboranes, the observed low-energy emissions with Stokes shifts between 8320 and 15,170 cm(-1) for the meta- and para-isomers are unusual as high-energy emissions are typical for meta- and para-dicarbadodecaboranes. Fluorescence quantum yields (φF) for the novel 1,7- and 1,12-bis(benzodiazaborolyl)-carboranes depend on the substituents at the nitrogen atoms of the heterocycle. Thus, the para-carborane with N-ethyl substituents 1,12-(1',3'-Et2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 has a φF value of 41% in cyclohexane solution and only of 9% in the solid state, whereas the analogous 1,12-(1',3'-Ph2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 shows quantum yields of 3% in cyclohexane solution and 72% in the solid state. X-ray crystallographic, computational and cyclic voltammetry studies for these carboranes are also presented.
Fifteen C-diazaborolyl-ortho-carboranes, 1-R'-2-R''-1,2-C(2)B(10)H(10), where R' represents the groups 2-(1,3-Et(2)-1,3,2-N(2)BC(6)H(4))-, 2-(1,3-Ph(2)-1,3,2-N(2)BC(6)H(4))-, 2-(1,3-Ph(2)-5,6-Me(2)-1,3,2-N(2)BC(6)H(2))-, 2-(1,3-(i)Pr(2)-1,3,2-N(2)BC(6)H(4))-, and 2-(1,3,2-N(2)BC(6)H(6))- and where R'' is H, Me, Ph, (t)Bu or SiMe(3), were synthesized. Cyclic voltammetry studies of the compounds showed irreversible oxidation waves which are caused by the oxidation of the heterocycle. Those C-diazaborolyl-ortho-carboranes with Ph, tBu and SiMe(3) substituents at the adjacent C-atom of the cage displayed two one-electron reduction waves reflecting the formation of stable radical monoanions with unusual (2n + 3) skeletal electron counts. The geometries of these anions were determined by combinations of infrared, UV-visible spectroelectrochemical and computational studies. Additionally the structures of seven new C-diazaborolyl-ortho-carboranes and one new 2-bromo-1,3,2-benzodiazaborole were determined by X-ray crystallography and compared with previously obtained structures.
A series of 1,4-phenylenes X-C(6)H(4)-BDB with a 1,3,2-benzodiazaborolyl (BDB) and a phosphorus based end group [X = PPh(2) (2), P(O)Ph(2) (3), P(S)Ph(2) (4), P(Se)Ph(2) (5), P(AuCl)Ph(2) (6) and P(Me)Ph(2) (7)] as well as 2-(2')thienyl-1,3,2-benzodiazaboroles with a second end group X [X = PPh(2) (8), P(S)Ph(2) (9), P(Se)Ph(2) (10) and P(Me)Ph(2) (11)] in the 5' position were synthesised using established methodologies. Molecular structures of 2-9 and 11 were determined by X-ray diffraction. Compounds 3, 4, 6, 7, 9 and 11 show intense blue luminescence in cyclohexane, toluene, chloroform, dichloromethane and tetrahydrofuran with pronounced solvatochromism. Thereby Stokes shifts in the range of 8950-10,440 cm(-1) and quantum yields up to 0.70 were observed in dichloromethane solutions. In contrast to this, for the selenides 5 and 10 quantum yields are small (<0.1). The absorption maxima (298-340 nm) are well reproduced by TD-DFT computations (B3LYB/G-311G(d,p)) and arise from strong HOMO-LUMO transitions. With the exception of 5 and 10 the HOMOs of the molecules under study are mainly located on the benzodiazaborole group. In 5 and 10 the HOMOs are on the selenium atoms. The LUMOs of all new neutral molecules are mainly represented by the phenylene or thiophene bridge. In the phosphonium cations the LUMOs have additional contributions from the phosphonium unit.
Two linear pi-conjugated systems with 1,3-diethyl-1,3,2-benzodiazaborolyl [C6H4(NEt)(2)B-] as a donor group and dimesitylboryl (-BMes(2)) as acceptor were synthesised with -ethynylene-phenylene-(-C C-1,4-C6H4-, 3) and -ethynylene-thiophene-(-C C-2,5-C4H2S-12) bridges between the boron atoms. An assembly (20) consisting of two diazaborolyl-ethynylene-phenylene-boryl units, [C6H4(NCy)-(N')B-C C-1,4-C6H4-BMes(2)] joined via a 1,4-phenylene unit at the nitrogen atoms (N') of the diazaborolyl units was also synthesised. The three push-pull systems, 3, 12 and 20, form salts on fluoride addition with the BMes(2) groups converted into (BMes(2)F)(-) anions. The molecular structures of 3, 12 and (NBu4)(12 center dot F) were elucidated by X-ray diffraction analyses. The borylated systems 3, 12 and 20 show intense blue luminescence in cyclohexane with quantum yields (Phi(fl)) of 0.99, 0.44 and 0.94, respectively, but weak blue-green luminescence in tetrahydrofuran (Phi(fl) = 0.02-0.05). The charge transfer nature of these transitions is supported by TD-DFT computations with the CAM-B3LYP functional. Addition of tetrabutylammonium fluoride to tetrahydrofuran solutions of 3 and 20 resulted in strong violet-blue luminescence with emission intensities up to 46 times more than the emission intensities observed prior to fluoride addition. Compounds 3 and 20 are demonstrated here as remarkable 'turn-on' fluoride sensors in tetrahydrofuran solutions.
A series of diphenylacetylenes with one 1,3,2-benzodiazaborolyl end group (BDB) and a second end group X (X = H, OMe, NMe(2), SMe, CN and BDB) were synthesized using established 1,3,2-benzodiazaborole methodologies. The 1,3,2-benzodiazaborolyldiphenylacetylenes with X = p-H (4), p-OMe (5), p-NMe(2) (6), p-SMe (7) and p-CN (8) end groups are functionalized with cyano groups at the central ring in an ortho-position to the triple bond. Molecular structures of 2, 3, 5, 6 and 7 were determined by X-ray diffraction. These borylated systems show intense blue luminescence in cyclohexane, toluene, chloroform, dichloromethane and tetrahydrofuran, whereas green luminescence was observed in acetonitrile solutions. Thereby Stokes shifts in the range 1700-8600 cm(-1) and quantum yields of 0.60-1.00 were observed in cyclohexane solutions. The absorption maxima (308-380 nm) are well reproduced by TD-DFT computations (B3LYP/G-311G(d,p)) and arise from strong HOMO-LUMO transitions. The LUMOs in all the molecules under study are mainly located on the diphenylacetylene bridge, while with the exception of the dimethylamino derivative 6, the HOMO is largely benzodiazaborolyl in character. Thus, the S1←S0 absorption bands are assigned to π(diazaborolyl)-π*(diphenylacetylene) transitions. In contrast to this, in compound 6 the HOMO is mainly represented by the terminal dimethylaminophenyl unit. While calculated ground state dipole moments μ(g) are small (1.1-7.5 D), experimentally determined changes of the dipole moments upon excitation are large (14.8-19.7 D) and reflect a significant charge transfer upon excitation. NLO activities of the rod-structured compounds 2, 4, 6 and 8 are indicated by calculated static first-order hyperpolarizabilities β up to 76.8 × 10(-30) esu.
Spherical protein cages such as an iron storage protein, ferritin, have great potential as nanometer-scale capsules to assemble and store metal ions and complexes. We report herein the synthesis of a composite of an apo-ferritin cage and Ru(p-cymene) complexes. Ru complexes were efficiently incorporated into the ferritin cavity without degradation of its cage structure. X-Ray crystallography revealed that the Ru complexes were immobilized on the interior surface of the cage mainly by the coordination of histidine residues.
New 2-arylalkynyl benzo-1,3,2-diazaboroles, 2-(4'-XC(6)H(4)C[triple bond, length as m-dash]C)-1,3-Et(2)-1,3,2-N(2)BC(6)H(4) (X =Me ; MeO ; MeS ; Me(2)N ), were prepared from B-bromodiazaborole, 2-Br-1,3-Et(2)-1,3,2-N(2)BC(6)H(4), with the appropriate lithiated arylacetylene, ArC[triple bond, length as m-dash]CLi. Molecular structures of , and were determined by X-ray diffraction studies. UV-vis and luminescence spectroscopic studies on these diazaboroles reveal intense blue/violet fluorescence with very large quantum yields of 0.89-0.99 for . The experimental findings were complemented by DFT and TD-DFT calculations. The Stokes shift of only 2600 cm(-1) for , compared to Stokes shifts in the range of 5900-7300 cm(-1) for , is partly explained by the different electronic structures found in compared to (X = H). The HOMO is mainly located on the aryl group in and on the diazaborolyl group in whereas the LUMOs are largely aryl in character for all compounds. Thus, in contrast to other conjugated systems containing three-coordinate boron centers such as B(Mes)(2), (Mes = 2,4,6-Me(3)C(6)H(2)), in which the boron serves as a pi-acceptor, the 10-pi electron benzodiazaborole moiety appears to function as a pi-donor moiety.
A series of pi-conjugated systems with two and three 1,3-diethyl-1,3,2-benzodiazaborolyl end-groups was synthesised in 58-91% yields using established 1,3,2-diazaborole methodologies. The bis(diazaborolyl) compounds contain thiophene -2,5-C4H2S- (2a), dithiophene -5,5'-(2,2'-C4H2S)2- (2b), phenylene -1,4-C6H4- (2c), biphenylene -4,4'-(1,1'-(C6H4)2)- (2d) and dioctylfluorene -2,7-(9,9-(C8H7)2C11H6)- (2e) bridges. The three-way linkers in the tris(diazaborolyl) assemblies contain a central phenylene unit -1,3,5-C6H3- linked to the borolyl end groups via thiophene -2,5-C4H2S- (3a), directly bonded (3b) or via phenylene -1,4-C6H4- (3c) units. Molecular structures of 2a, 2b, 2c, 3a, 3b and 3c were determined by X-ray crystallographic studies. These borolylated systems show intense blue/violet luminescence with Stokes shifts of 6200-9500 cm(-1) and quantum yields of 0.33 to 0.98. The absorption maxima (296-351 nm) of these assemblies are reproduced well by TD-DFT computations (B3LYP/6-31G*), and arise from strong, low energy HOMO-LUMO transitions. From molecular orbital computations on optimised geometries of these diazaborolyl systems, the LUMO is located mainly on the thiophene/benzene bridge (66-92%) while the HOMO is largely benzodiazaborolyl in character (53-83%). The S1 <-- S0 absorption bands are thus assigned to pi(diazaborolyl)-pi*(thiophene/ benzene) transitions. Computations on related bis(boryl) dithiophenes [with diarylboryl e.g. Ph2B, Mes2B, (C6F5)2B and FMes2B (Mes = 2,4,6-Me3C6H2; FMes = 2,4,6-(CF3)3C6H2), dioxaborolyl and other diazaborolyl groups] reveal strong, low energy UV-visible absorption bands arising from pi(thiophene)-pi*(thiophene) transitions, with increasing boron participation in the LUMO of the diarylboryl and especially the highly fluorinated systems.
Reaction of 1,4-bis(dibromoboryl)benzene (1a) with 2 equiv. of the diazabutadiene tBuN=CH-CH=NtBu and subsequent reduction of the obtained bis(1,3,2-diazaborolium)salt 2a with sodium amalgam afforded the 1,4-bis(1,3,2-diazaborolyl)benzene 3a. Similarly, 1,3-bis(dibromoboryl)benzene (1b), 1,3,5-tris(dibromoboryl)benzene (1c) and 4,4'-bis(dibromoboryl)biphenyl (1d) were converted into compounds 3b, 3c and 3d which contain two or three diazaborolyl substituents at the arene core. Treatment of precursors 1a,b,d with two equiv. or with three equiv. of N,N'-di-tert-butylethane-1,2-diamine in the presence of an excess of NEt3 gave rise to the diazaborolidine derivatives 4a-4d. Reaction of 1,3-bis(diiodoboryl)benzene with two equivalents of N,N'-dimethylethane-1,2-diamine in the presence of NEt3 furnished the corresponding 1,3-bis(diazaborolidinyl)benzene 4e. The novel compounds were characterized by elemental analyses and spectroscopy (1H, 13C, 11B NMR, MS). The molecular structures of 3c, 4a and 4e were eludicated by X-ray-diffraction analyses. In addition to this, the oxidative cyclovoltammograms and blue emission spectra of these novel compounds were discussed. Here, the electronic communication between boron heterocycles on the different spacer-units and the luminescence of the oligo-diazaborolylarenes were of interest.
Reaction of 2-bromo-1,3-diethyl-1,3,2-benzodiazaborole (1) with equimolar amounts of thienyl lithium or 2,2-dithienyl lithium led to the generation of benzodiazaboroles 2 and 3 which are functionalized at the boron atom by a 2-thienyl or a 5-(2,2-dithienyl) unit. Similarly 2-bromo-1,3-diethyl-1,3,2-naphthodiazaborole (4) and thienyl lithium or 2,2-dithienyl lithium afforded the naphthoborolyl-substituted thiophene 5 or dithiophene 6. Treatment of 2,5-bis(dibromoboryl)-thiophene 7 with 2 eq. of tBuN=CH-CH=NtBu in n-hexane followed by sodium amalgam reduction of the obtained bis(diazaborolium) salt 8 gave the 2,5-bis(diazaborolyl)thiophene 9. The 2,5-bis(diazaborolidinyl)-thiophene 10 resulted from the cyclocondensation of 7 with 2 eq. of N,N-di-tert-butylethylenediamine in the presence of NEt3. Analogously, cyclocondensation of 7 with N,N-diethylphenylenediamine gave the bis(benzodiazaborolyl) functionalized thiophene 11. The novel compounds were characterized by elemental analysis and spectroscopy (1H-, 11B-, 13C-NMR, MS and UV-VIS). The molecular structure of 3 was elucidated by X-ray diffraction. Cyclovoltammograms show an irreversible oxidation wave at 298-598 vs. Fc/Fc+. The borolylated thiophenes and dithienyls show intense blue luminescence with Stokes shifts of 30-107 nm.
The new diimine ligand 3,8- di- n- pentyl- 4,7- di( phenylethynyl)- 1,10- phenanthroline ( 1) was used for the synthesis of a range of PtII complexes, viz. [ Pt( 1) Cl-2], [ Pt( 1)C C - Ph)(2)], [ Pt( 1)( C C - Fc)(2)] and [ Pt( 1)( C C - p- C6H4- C C - Fc)(2)] ( Fc = ferrocenyl). Crystal structure analyses were performed for [ Pt( 1) Cl-2] and [ Pt( 1)( C C - Ph)(2)] and revealed that the di( acetylide) pi- tweezer of the latter binds a molecule of chloroform through C - H (...) pi hydrogen bonds. The redox and optical properties of 1 and its complexes were investigated by ( spectro-) electrochemistry, UV - Vis and luminescence spectroscopy, and an energy level diagram was derived for [ Pt( 1)( C C - Fc)(2)] and related compounds on the basis of the data collected. The ferrocenyl- substituted PtII complexes are donor - sensitiser assemblies. Intramolecular quenching of the photoexcited PtII diimine unit leads to very short luminescence lifetimes for [ Pt( 1)( C C - p- C6H4 - C C - Fc)(2)] ( 2 ns) and [ Pt( 1)( C C - Fc)(2)] ( 0.3 ns), as opposed to [ Pt( 1)( C C - Ph)(2)] ( 0.7 mu s). Excimer formation has been observed for [ Pt( 1)( C C - Ph)(2)] at room temperature in dichloromethane and at low temperatures in frozen glassy dichloromethane and 2- methyltetrahydrofuran solution, but not in the solid state.
The effects of pressure and temperature on the energy (Eop) of the metal-to-metal charge transfer (MMCT, FeII-->CoIII) transition of the cyano-bridged complexes trans-[L14CoNCFe(CN)5]- and cis-[L14CoNCFe(CN)5]- (where L14=6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus-Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in Eop due to both pressure and temperature were found to be less than the shifts in the energy difference (DeltaE degrees]) between the CoIII-FeII and CoII-FeIII redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of CoII, are discussed in order to account for this trend. To study the effect of pressure on CoIII electronic absorption bands, a new cyano-bridged complex, trans-[L14CoNCCo(CN)5], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans-[L14CoNCFe(CN)5].5H2O.
Multi-stage mass spectrometry (MSn) on [(M + Ag - H)x + Ag]+ precursor ions (where M = an amino acid such as glycine or N,N-dimethylglycine) results in the formation of stable silver (Ag3+, Ag5+ and Ag7+) and silver hydride (Ag2H+, Ag4H+ and Ag6H+) cluster cations in the gas phase. Deuterium labelling studies reveal that the source of the hydride can be either from the alpha carbon or from one of the heteroatoms. When M = glycine, the silver cyanide clusters Ag4CN+ and Ag5(H,C,N)+ are also observed. Collision induced dissociation (CID) and DFT calculations were carried out on each of these clusters to shed some light on their possible structures. CID of the Agn+ and Ag(n-1)H+ clusters generally results in the formation of the same Ag(n-2)+ product ions via the loss of Ag2 and AgH respectively. DFT calculations also reveal that the Agn+ and Ag(n-1)H+ clusters have similar structural features and that the Ag(n-1)H+ clusters are only slightly less stable than their all silver counterparts. In addition, Agn+ and Ag(n-1)H+ clusters react with 2-propanol and 2-butylamine via similar pathways, with multiple ligand addition occurring and a coupled deamination-dehydration reaction occurring upon condensation of a third (for Ag2H+) or a fourth (for all other silver clusters) 2-butylamine molecule onto the clusters. Taken together, these results suggest that the Agn+ and Ag(n-1)H+ clusters are structurally related via the replacement of a silver atom with a hydrogen atom. This replacement does not dramatically alter the cluster stability or its unimolecular or bimolecular chemistry with the 2-propanol and 2-butylamine reagents.
The molecular structure of 1,1,2,2-tetra-tert-butyldisilane has been determined by gas-phase electron diffraction supported by ab initio calculations, in the solution phase by Raman spectroscopy, and in the solid phase by Raman spectroscopy and X-ray crystallography. The gas-phase structure (C2 symmetry) was found to be almost anticlinal, a most unusual and unexpected result. In the favoured conformation, contact between tert-butyl groups at each end of the molecule is avoided by a large deviation of the angles around the silicon atoms from the parent tetrahedral angle of 109.5 degrees. In fact, the Si-Si-C angles returned from the gas electron diffraction refinement are 117.0(5) and 110.7(6) degrees, indicating the large degree of flexibility about the silicon centres. The ab initio methods and gas electron diffraction results indicate that there is only one conformer of But2HSiSiHBut2 in the gaseous mixture. Variable temperature Raman studies indicate the possibility of a further higher energy conformer existing in the liquid phase. However, this seems quite improbable from other observations made for the Raman spectra at all temperatures. The X-ray structure is close to that observed in the gas phase, with phiHSiSiH = 94.2(18) degrees. There is a large amount of disorder about one of the silicon postions and one of the tert-butyl groups within the crystal structure, which makes detailed direct comparison with the gaseous structure difficult.
The lowest excited state of [Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, dppz = dipyrido[3,2-a:2',3'-c]phenazine) 1 is strongly luminescent, even in water, and very oxidizing. Therefore it is able to oxidise not only guanosine-5'-monophosphate (GMP), as demonstrated by laser flash photolysis, but also guanine-containing polynucleotides such as calf thymus DNA and [poly(dG-dC)]2. The luminescence quenching was found to be faster in H2O than in D2O, as is the back reaction, indicating that both processes probably proceed by proton-coupled electron transfer. These properties, that are controlled by the triplet MLCT state in which the charge has been transferred from the Ru to a TAP ligand, contrast with those of the well known [Ru(phen)2(dppz)]2+ 2.
Two novel symmetric polytopic ligands L(1) and L(2) have been synthesized. They are composed of three 1,4,8,11-tetraazacyclotetradecane macrocycles which are connected to a central tren moiety via an ethylene and a trimethylene bridge, respectively. The complexation potential and the speciation diagrams of L(1) and L(2) towards Cu(2+) and Ni(2+) were determined by spectrophotometric and potentiometric titrations. Insight into the geometry of the Cu(2+) complexes is provided by UV-VIS and EPR spectroscopy. The simplified ligands L(3) and L(4) are utilized as references for an aminoethyl- and a tren-substituted tetraaza macrocycle to help assign the EPR spectra of the polytopic ligands L(1) and L(2). At a metal-to-ligand ratio of 3 : 1, the metal cations are preferentially bound to the tetraaza macrocycles of L(1) and L(2) in a square planar geometry. At high pH values, a nitrogen atom of the tren moiety in L(1) serves as an additional ligand in an axial position leading to a square pyramidal coordination around Cu(2+), whereas in L(2) no such geometry change is observed. At a metal-to-ligand ratio of 4 : 1, the additional metal cation resides in the central tren moiety of L(1) and L(2). However, in contrast to the typical trigonal bipyramidal geometry found in the [Cutren](2+) complex, the fourth Cu(2+) has a square pyramidal coordination caused by the interaction with the Cu(2+) cations in the macrocycles (as evidenced by EPR spectra). Since the sequence of metal complexation is such that the first three metal ions always bind to the three macrocycles of L(1) and L(2) and the fourth to the tren unit, it is possible to prepare heteronuclear complexes such as [Cu(3)NiL](8+) or [Ni(3)CuL](8+), which can be unambiguously identified by their spectral properties.
Reaction of 2-cyano-1,3,2-diazaborole (BuNCH)-Bu-t=CHN(Bu-t)BCN (2) with half an equivalent of isopropyllithium afforded compound (BuNCH)-Bu-t=CHN(Bu-t)BC(Pr-i)=N-BN(Bu-t)CH=(CHNBu)-Bu-t (7). In contrast to this, a 1:1 stoichiometry of the reactants led to (BuNCH)-Bu-t=CHN(Bu-t)(BPr)-Pr-i ( 6) as the product of a nucleophilic substitution process at the boron atom. Similarly, regardless of the molar ratio of reactants employed, treatment of 2 with cyclopropyllithium, isobutyllithium or phenyllithium afforded solely substitution products (BuNCH)-Bu-t=CHN(Bu-t)BR. [R=cPr (12); Ph (13); Bu-i (14)].
Several new Cu(II) derivatives of the 1,3-bis(dimethylamino)-2-propanolato (bdmap) ligand with formula [Cu(2)(bdmap)(acac)(NH(3))(3)(MeOH)](ClO(4))(2), [Cu(2)(bdmap)(NO(2))(3)(H(2)O)](4) and [Cu(2)(bdmap)(OH)(ox)(0.5)(H(2)O)(2)](n)(ClO(4))(n)xnH(2)O were synthesized and characterized both structurally and magnetically. Dinuclear compound crystallizes in the monoclinic system, space group P2(1)/c, octanuclear compound crystallizes in the triclinic space group P1 and the 1-D alternating system crystallizes in the monoclinic system, space group P2/n. Magnetic analysis indicates strong antiferromagnetic coupling for all derivatives, mainly due to the interaction through the alkoxo O-atom of the bdmap ligand. The effect on the magnetic behaviour of the additional bridging ligands is analysed.
