Thomas A. Kaden

Metal carbonyl syntheses XXII. Low pressure carbonylation of [MOCl4]− and [MO4]−: the technetium(I) and rhenium(I) complexes [NEt4]2[MCl3(CO)3]☆

Low pressure carbonylation (1 atm) of [MOCl4]− or [MO4]− in the presence of BH3-tetrahydrofuran and halides X− results in the clean formation of [NEt4]2[MX3(CO)3] containing monovalent rhenium or technetium (MRe or Tc; X Cl or Br). In the case of the radioactive element technetium this low pressure synthesis is an important progress since potential hazards of traditional high pressure carbonylations are thus avoided. The complex [NEt4]2[ReBr3(CO)3] crystallizes in the space group P1 with a = 10.166(2), b = 16.393(4), c = 17.243(5) A, and α = 69.27(20, β = 86.42(2), γ = 88.61(2)°, Z = 4 and V = 2682(1) A3. [NEt4]2[MX3 (CO)3] is a versatile precursor compound of other Re(I) and Tc(I) complexes; substitution of the halide ligands by a variety of σ-donor ligands is facile even under mild conditions. Examples include reactions with CNtBu to yield quantitatively TcCl(CNtBu)2(CO)3 and with a tetradentate phosphine ligand to yield the dinuclear complex [Re2Br2(CO)6(tetraphos)]. The x-ray structures of both compounds were determined. Dissolution of [NEt4]2[MX3(CO)3] in water under aerobic conditions results in the unusual organometallic aqua cation [(M(OH2)3(CO)3] +; this species is stable in water for days (IR spectroscopy).

TITFIT, a comprehensive program for numerical treatment of potentiometric data by using analytical derivatives and automatically optimized subroutines with the Newton—Gauss—Marquardt algorithm

TITFIT, a computer program written in HP-enhanced BASIC is able to fit potentiometric titration curves with up to 400 points by using the Newton-Gauss-Marquardt technique supplemented by the use of analytical derivatives. The program contains a part which writes an optimized subroutine as needed by the model. The program also has additional facilities such as visual interactive adjustment of parameters and a plotting subroutine for graphical presentation of the final results. Data can be entered either manually through the keyboard or automatically through an RS-232 serial interface. The performance of the program is discussed for the well studied Ni(2+) glycine system; the results are similar to those already published in the literature.

Reactions with the technetium and rhenium carbonyl complexes (NEt4)2[MX3(CO)3]. Synthesis and structure of [Tc(CN-But)3(CO)3](NO3) and (NEt4)[Tc2(μ-SCH2CH2OH)3(CO)6]

Abstract Starting from [MO4]− (M = Tc, Re) the low-pressure (1 atm.) synthesis of the important starting material (NEt4)2[MCl3(CO)3] could be improved in terms of yield and time. These MI complexes were used for the preparation of compounds containing the “fac-M(CO)3” moiety under ambient conditions. The substitution with the isocyanide ligand CN-But is described. In the case of rhenium, IR spectroscopical investigations in the CO stretching region allowed the observation of the stepwise formation of [Re(CN-But)3(CO)3]+. It could be demonstrated that 99Tc NMR spectroscopy allows similar investigations, although not all types of intermediates could be detected. The structure of the complex [Tc(CN-But)3(CO)3](NO3) was elucidated by X-ray diffraction analysis. Substitution with the protic ligand 2-mercaptoethanol HSCH2CH2OH revealed similar behaviour. Two intermediates were observed with IR spectroscopical methods. The final product was the dimer (NEt4)[Tc2(μ-SCH2CH2OH)3(CO)6], the structure of which was determined by X-ray diffraction.

Synthesis and metal complexes of aza-macrocycles with pendant arms having additional ligating groups

In view of new strategies in coordination chemistry macrocycles with functionalized pendant arms represent an interesting class of ligands, which combine both the properties of a macrocyclic structural unit with those of a flexible side-chain to which the functional group is bound. With such systems it is possible to study the effect of axial coordination even for weak ligating groups, since they are brought close to the metal ion, the changes in the properties of the metal ion when the pendant arm becomes coordinated and finally the influence of the metal ion on the reactivity of the functional group.

Microprocessor-controlled system for automatic acquisition of potentiometric data and their non-linear least-squares fit in equilibrium studies☆

A microprocessor-controlled potentiometric titration apparatus for equilibrium studies is described. The microprocessor controls the stepwise addition of reagent, monitors the pH until it becomes constant and stores the constant value. The data are recorded on magnetic tape by a cassette recorder with an RS232 input-output interface. A non-linear least-squares program based on Marquardts modification of the Newton-Gauss method is discussed and its performance in the calculation of equilibrium constants is exemplified. An HP 9821 desk-top computer accepts the data from the magnetic tape recorder. In addition to a fully automatic fitting procedure, the program allows manual adjustment of the parameters. Three examples are discussed with regard to performance and reproducibility.

Phosphate and phosphonate ester hydrolysis promoted by dinuclear metal complexes

Abstract The kinetics and mechanism of the hydrolysis of bis(4-nitrophenyl)phosphate and (4-nitrophenyl)phenylphosphonate were studied in the presence of the dinuclear Ni 2+ , Cu 2+ , and Zn 2+ complexes of 1,1-[(1H-pyrazole-3,5-diyl)bis(methylene)]bis(octahydro-1H-1,4,7-triazonine) (LH). Whereas the dinuclear Cu 2+ complex does not promote the hydrolysis of these substrates, the dinuclear complexes of Zn 2+ and Ni 2+ are good catalysts for it. It has been shown by kinetical and 31 P NMR studies that the monohydroxo complex [M 2 (LH −2 )] 2+ binds the substrate to give an intermediate species, in which an intramolecular attack of the coordinated OH − onto the substrate takes place. Phosphate monoester or phenylphosphonate which are the products of the hydrolysis remain coordinated to the dinuclear complex, and, thus inhibit the further reaction. From the Michaelis–Menten type reactivity which we have observed at high substrate concentrations, K M and k cat values were obtained. The values of K M are very similar to each other as well as for the two substrates as for the two metal ions. In contrast, k cat values are distinctly different, the phosphonate ester being more reactive than the phosphate diester by a factor of 3–4. The major effect is however, due to the metal ion, the dinuclear Ni 2+ complex being 50–60 times more reactive than the Zn 2+ complex.

Metal-ion-dependent biological properties of a chelator-derived somatostatin analogue for tumour targeting.

Somatostatin-based radioligands have been shown to have sensitive imaging properties for neuroendocrine tumours and their metastases. The potential of [(55)Co(dotatoc)] (dotatoc =4,7,10-tricarboxymethyl-1,4,7,10-tetraazacyclododecane-1-ylacetyl-D-Phe-(Cys-Tyr-D-Trp-Lys-Thr-Cys)-threoninol (disulfide bond)) as a new radiopharmaceutical agent for PET has been evaluated. (57)Co was used as a surrogate of the positron emitter (55)Co and the pharmacokinetics of [(57)Co(dotatoc)] were investigated by using two nude mouse models. The somatostatin receptor subtype (sst1-sst5) affinity profile of [(nat)Co(dotatoc)] on membranes transfected with human somatostatin receptor subtypes was assessed by using autoradiographic methods. These studies revealed that [(57)Co(dotatoc)] is an sst2-specific radiopeptide which presents the highest affinity ever found for the sst2 receptor subtype. The rate of internalisation into the AR4-2J cell line also was the highest found for any somatostatin-based radiopeptide. Biodistribution studies, performed in nude mice bearing an AR4-2J tumour or a transfected HEK-sst2 cell-based tumour, showed high and specific uptake in the tumour and in other sst-receptor-expressing tissues, which reflects the high receptor binding affinity and the high rate of internalisation. The pharmacologic differences between [(57)Co(dotatoc)] and [(67)Ga(dotatoc)] are discussed in terms of the structural parameters found for the chelate models [Co(II)(dota)](2-) and [Ga(III)(dota)](-) whose X-ray structures have been determined. Both chelates show six-fold coordination in pseudo-octahedral arrangements.

Synthesis and X-ray structural characterisation of seven co-ordinate macrocyclic In3+ complexes with relevance to radiopharmaceutical applications

With a view to radiopharmaceutical aplication, four In3+ complexes of mono- and bi-functional carboxymethylated tetra-azamacrocyclic ligands were prepared, the structures of two of them were solved by X-ray diffraction and their stability was determined by measuring the exchange to transferrin in blood serum.

Stability and structure of mono- and dinuclear Cu(ii), Ni(ii) and Zn(ii) complexes of pyrazole and triazole bridged bis-macrocyclesElectronic supplementary information (ESI) available: titration curves and species distribution curves. See http://www.rsc.org/suppdata/dt/b2/b212113a/

The two ligands L1 and L2, consisting of two 1,4,7-triazacyclononane rings bridged by a pyrazole or a triazole group, form with Cu2+, Ni2+ and Zn2+ a series of mononuclear [MLHn](n + 2)+ (n = −3, −2, −1, 0, 1, 2) and dinuclear species [M2LHm](m + 4)+ (m = 0, −1, −2, −3), the stabilities of which have been determined by potentiometric titrations. The triazole bridged ligand L1 forms complexes which are more stable than those of the pyrazole bridged system L2. It also shows a higher tendency to form dinuclear species compared to L2. In addition two dinuclear species [Cu2(L2H−1)(μ-Ph2PO2)](ClO4)2·MeCN and [Cu4(L2H−1)2(μ4-PO4)](ClO4)3·MeCN·H2O have been isolated as solids and their X-ray structures have been determined. In the first complex we find a dinuclear Cu2+ species which is bridged by the pyrazolide group as well as by the exogenous diphenyl phosphinate. In the second case a μ4-phosphate ion bridges two dinuclear units, resulting in a tetranuclear species.

Handling of electronic absorption spectra with a desk top computer—I A fully automatic spectrophotometric titration system with on-line data acquisition

A fully automatic system for combined spectrophotometric and pH titrations with on-line digital data acquisition is described for a Cary 118C spectrophotometer. The system consists of a temperature-controlled titration cell, a motor burette, a digital ph-meter, and an HP9820 desk-top computer. The computer controls the stepwise addition of reagent, the wavelength and paper drives, and the recorder pen; the absorption data and the pH-values are obtained on-line. A special interface was constructed from CMOS components. This is compatible with other computers or microprocessors having the necessary input/output facilities. The performance of the system has been tested critically. In 50 min more than 200 data points, each representing the mean of ten individual readings, can be collected, and the number of data points which can be obtained in one run is practically unlimited. The system avoids the cumbersome and error-prone manual handling of a large amount of data, it saves time, and, most important, the results have a high reproducibility.