The initiation process in the polymerization of tetrahydrofuran with carbonium ion salts

The initiation process for the polymerization of tetrahydrofuran with (C₆H₅)₃C⁺SbCl₆^? has been studied. Two mechanisms have been considered: a cation-addition process, and a process in which tetrahydrofuran donates a hydride ion to the cation of the initiator to form triphenylmethane. The biscarbonium salt [(C₆H₅)₂C⁺C₆H₄CH₂]₂(SbCl₆^?)₂ has been synthesized and used to initiate the polymerization of tetrahydrofuran. The results are consistent with the hydride-ion mechanism but may be inconclusive because of chain transfer. NMR experiments with 0.05–0.2M solutions of initiator in tetrahydrofuran show that triphenylmethane is rapidly produced in an amount equal to the molar amount of initiator originally present. Some NMR evidence for the presence of an acetal end group in the polymer has been obtained. It is concluded that the initiation process in this system definitely involves the formation of triphenylmethane, although a detailed, unique mechanism cannot be selected at this time.     

Synthesis and characterization of novel 99gTc(V) and Re(V) complexes with water-soluble tetraaza diamido dipyridino ligands: single-crystal X-ray structural investigations of mono- and dinuclear complexes

Rhenium and technetium are known for their useful applications in nuclear medicine with similar properties. In this study, new diamido dipyridino (N(4)) water-soluble ligands (2-C(5)H(4)NCH(2)NHCO)(2)CH(2), 1 (L(1)H2), (2-C(5)H(4)NNHNHCO)(2)CH(2), 2, and [2-C(5)H(4)N(+)(O)(-)CH(2)NHCO](2)CH(2), 3, were synthesized. Reaction of L(1)H2 with ReOCl(3)(PPh(3))(2) resulted in the novel six-coordinated rhenium(V) complex, trans-ReO(L(1))(OEt), 4. The complex was characterized by spectroscopic methods, and its X-ray crystallographic analysis revealed that rhenium is coordinated to four nitrogen atoms of the ligand and to two oxygen atoms from the deprotonated ethanol and the oxo group respectively in a distorted octahedral geometry. In solution, complex 4 was transformed to a new complex 5, which was proved to be the dinuclear complex mu-oxo [ReO(L(1))](2)O. Reaction of 1 with [n-Bu(4)N][ReOCl(4)] resulted in the neutral complex 6, trans-[ReO(L(1))]Cl. Similarly, when ligand 1 was reacted with [n-Bu(4)N][(99g)TcOCl(4)], the neutral trans-[(99)TcO(L(1))]Cl complex 7 was formed, which upon dissolution transformed into a cationic complex 8, trans-[(99)TcO(L(1))(OH(2))](+)Cl(-). The single-crystal X-ray structure of 8 reveals that the coordination sphere about technetium is a distorted octahedron with four nitrogen atoms in the equitorial plane, while doubly bonded oxygen and coordinated water occupy the apical positions. Further dissolution of 8 resulted in the formation of dinuclear mu-oxo [TcO(L(1))](2)O, 9. This study shows that Tc and Re have similar metal core structures in solution for diamido dipyridino systems, besides similarity in geometrical structure, proved by the X-ray structures on the same ligands.     

Polymerization of isobutylene by the adamantane bromide–diethylaluminum chloride catalyst system

Isobutylene has been polymerized in a continuous stirred tank reactor using a catalyst system comprised of 1-bromoadamantane and diethylaluminum chloride. The polymerization was carried out in hexane solvent at ?15 to ?27°C and gave 100% conversion to polyisobutylene (PIB) of 1000–3000 M_w. The results of pyrolysis–gas chromatography–mass spectrometry analyses are consistent with a mechanism involving the formation of the adamantyl cabocation and its addition to an isobutylene molecule to initiate polymerization. ¹³C-NMR analyses show that the PIB products contain R₂C? CR₂ and R₂C? CHR olefin types. Information on the nature of these olefins and the route to their formation has been developed.     

The formation of Na+ and Na ions from Na*(2P) atoms near a tungsten surface. II. Extended diatomics-in-molecules models

Potential energy surfaces (PES ) for Na(²S, ²P) interacting with a tungsten surface partially covered with sodium ions are computed within the framework of the diatomics-in-molecules (DIM) method. A small number (1 to 10) of adsorbed sodium atoms are considered explicitly, the effect of the rest being taken into account through the fragment matrix elements in the DIM formulation. A physical model proposed previously to account for the experimental observation of Na⁺ and Na ions is supported by these calculations and, in addition, a new pathway to Na products is identified. The effect of including extra adsorbed atoms is discussed in terms of the molecular wave functions and a sensitivity analysis.     

Cocatalysis by epoxides in the polymerization of tetrahydrofuran with trityl hexachloroantimonate initiator

The polymerization of tetrahydrofuran (THF) with (C₆H₅)₃C⁺SbCl₆^- initiator is markedly accelerated by small concentrations of propylene oxide or other epoxides. Molar concentrations of propylene oxide 4 to 10 times those of the carbonium-ion salt showed increasing conversion to polymer. The equilibrium conversion level at different temperatures with epoxides is the same as in their absence; the approach to equilibrium is first-order in THF. NMR experiments in the presence of propylene oxide indicate the formation of a trityl ether intermediate. The cocatalysis effect is interpreted on the basis of an acceleration in the initiation process in the system.     

Constraint qualifications in quasidifferentiable optimization

The classical linearization procedure for differentiable nonlinear programming problems can be naturally generalized to the quasidifferentiable case. As in the classical case one has to impose so-called constraint qualifications on the constraint functions in order to ensure that optimality of a feasible point implies optimality of the nullvector for the corresponding quasilinearized problem. We present various constraint qualifications in a unified setting, propose a new one, and investigate the relations between these conditions.Supported by DFG Grant Pa 219/5-1.     

The Complexed Triphosphaallyl Radical,Cation, and Anion Family

Radically complex : The photolytic reaction of [Cp*P{W(CO)₅}₂] (Cp*=C₅Me₅) with a diphosphene produces, via a radical intermediate, an air‐stable complexed triphosphaallyl radical, in which the unpaired electron is evenly distributed over both terminal P atoms. Oxidation of the radical leads to a triphosphaallyl cation, which is only stable at low temperatures in solution, whereas the stable triphosphaallyl anion is formed by reduction (see picture, Mes*=2,4,6‐tri‐tert‐butylphenyl).