We have performed Monte Carlo simulations to reproduce the intrinsic viscosity corresponding to different generation of several types of dendrite molecules: polyamidoamine dendrimers with an ethylendiamine core, polypropylene-imine with a diaminobutane core, and monodendrons and tridendrons of polybenzylether. With this end, we have employed coarse-grained idealizations of the molecules constituted by only two beads in each repeat unit (one in a branching or end unit and one intermediate along the repeat unit) and a simple hard-sphere potential between non-neighboring beads. Our goal is to investigate if this simple model is able to provide a reasonable description of some differences between these systems that have been observed experimentally, in particular, the location of the maximum in the intrinsic viscosity as a function of the generation number. Experimental radii of gyration in a given solvent are reproduced by a fit of the hard-sphere potential diameter. Subsequently, intrinsic viscosities are calculated by the variational approach of Fixman, which yields an accurate lower-bound value with an additional hydrodynamic interaction parameter (the friction radius of the beads). The results show a pronounced variation of the maximum location with the value of the friction radius and the structural details that cannot be mimicked with simpler models. The initial conformations for the Monte Carlo procedure are taken from atomistic configurations thermalized by means of a molecular dynamics.

The reaction of the chlorosilyl-substituted cyclopentadienyltitanium compound [Ti(η 5 -C 5 H 4 -SiMe 2 Cl)Cl 3 ] with N,N′-dimethylethylenediamine in the presence of 2 equiv of NEt 3 gave a mixture of two complexes, [Ti{η 5 -C 5 H 4 SiMe 2 NMe(CH 2 ) 2 -η-NMe}Cl 2 ] (1) and [Ti{η 5 -C 5 H 4 SiMe 2η-N(CH 2 ) 2 -η-NHMe}Cl 2 ] (2), in a molar ratio of 3:1. However, a similar reaction with N-methylethylenediamine afforded complex 2 regiospecifically. The dialkyl derivatives [Ti- 3), CH 2 Ph (4)) were prepared by reacting the dichloride complex 1 with 2 equiv of MgClMe or 1 equiv of Mg(CH 2 Ph) 2 •2THF, respectively. The analogous reaction with LiNMe 2 afforded the diamido derivative [Ti{η 5 -C 5 H 4 SiMe 2 NMe(CH 2 ) 2 -η-NMe}(NMe 2 ) 2 ] (5) in high yield. Complex 1 reacts with dry CO 2 via insertion of a molecule of CO 2 into each of the Ti-N and Si-N bonds to yield the dicarbamate compound [Ti{(η 5 -C 5 H 4 SiMe 2 OC(O)NMe(CH 2 ) 2 NMe(η 2 -CO 2 )}Cl 2 ] (6), in which the carbamate groups are bound in η 2 -and η 1 -fashion. Thermal decomposition of complex 6 afforded the known oxo derivatives [Ti{µ-(η 5 -C 5 H 4 SiMe 2 -η-O)}Cl 2 ] 2 and [(TiCl 2 ) 2 (µ-O)-[µ-{(η 5 -C 5 H 4 SiMe 2 ) 2 -(µ-O)}] with elimination of CO 2 and 1,3-dimethyl-2-imidazolidinone. The conformational interconversion of 1 and 6 and the reversible coordination of the terminal "NHMe" group to the metal center in 2 were studied in solution by DNMR spectroscopy. The crystal structure of 1 was determined by X-ray diffraction methods.

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A method previously proposed for calculating the radius of gyration and the intrinsic viscosity of dendrimers is modified to give a more accurate description of existing experimental data. The new method includes some features that were not previously considered, namely: a) a correction term to take into account the contribution of individual friction beads, whose volumes are not negligible in comparison with the molecule size, b) a realistic distribution of internal angles between successive beads that define branching points in the molecule, c) a distribution of distances between branching points computed from Molecular Dynamics simulations of a small dendrimer with explicit solvent. Modification a) alone is able to give a good description of the experimental results obtained for polypropylene-imide with a diaminobutane core in water, while the simultaneous use of the three modifications is needed to adequately describe the experimental data of monodendrons and tridendrons of polybenzylether in THF.

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