RESUMO
Titration calorimetry has been used to determine the enthalpies of protonation (DeltaH(HM)) for the reaction of (L(3))M(CO)(3) complexes, where M = W and Mo and L(3) = cyclic and noncyclic tridentate ligands of the N, S, and P donor atoms, with CF(3)SO(3)H in 1,2-dichloroethane solution at 25 degrees C to give (L(3))M(CO)(3)(H)(+)CF(3)SO(3)(-). The basicities (-DeltaH(HM)) increase with the ligand donor groups (X, Y, or Z) in the order S = PPh << NR (R = Me, Et) for both cyclic and noncyclic ligand complexes that have the same structure of the protonated product. Although the metal basicity (-DeltaH(HM)) generally increases as the ligand donor group basicities (pK(a)'s of the conjugate acids) increase, the large difference between the pK(a) values of thioethers (-6.8) and phosphines (6.25) suggests that thioether donor groups should be much weaker donors than phosphines. The observation that thioether groups contribute nearly as much as phosphine groups to the basicity of the metal in the (L(3))M(CO)(3) complexes may be explained by suggesting that repulsion between the pi-symmetry lone electron pair on sulfur and the filled metal d orbitals increases the energies of the d orbitals thereby making the metal more basic than expected from only the sigma-donor ability of the sulfur. There is a good correlation (r = 0.973) between -DeltaH(HM) and average nu(CO) values of the eight (L(3))W(CO)(3) complexes that have the same structure of their protonated forms. A plot of the average of the three nu(CO) frequencies for the (L(3))W(CO)(3) complexes vs the average nu(CO) frequencies for the analogous Mo complexes is linear (r = 0.9996), and the slope of 1.07 indicates that the tridentate ligands have nearly the same electronic effects on both W and Mo complexes. Noncyclic ligands make the metal more basic by 1.6 +/- 0.3 kcal/mol than cyclic ligands with the same donor atoms. The tungsten complexes are 2.8 +/- 0.1 kcal/mol more basic than their molybdenum analogs. Determinations of DeltaH(HM) values for both fac- and mer-(PNP)M(CO)(3) complexes (M = W, Mo; PNP = MeN(C(2)H(4)PPh(2))(2)) allowed the calculation of enthalpies of mer-to-fac isomerization for both the tungsten (-2.0 kcal/mol) and molybdenum (-4.8 kcal/mol) complexes. These studies demonstrate that the metal, ligands, and geometry of the protonated products all substantially affect the heats of protonation (DeltaH(HM)) of (L(3))M(CO)(3) complexes.
RESUMO
Selection of optimum process conditions in combinatorial microreactors is essential if the combinatorial synthesis process is to be correlated with the synthesis process on a more conventional scale and the materials are to have the desired chemical properties. We have developed a new methodology for the high-throughput multiparameter optimization of polymerization reaction conditions in arrays of microreactors. Our strategy is based on the application of nondestructive spectroscopic techniques to measure chemical properties of polymers directly in individual microreactors followed by the multivariate spectral descriptor analysis for rapid determination of the optimal process conditions. We have demonstrated our strategy in the high-throughput multiparameter optimization of process conditions in thin-film melt polymerization reactions performed in 96-microreactor arrays for combinatorial screening of new polymerization catalysts. The combinatorial polymerization system was optimized for the best processing parameters using a set of input variables that included reactant parameters (relative amounts of starting components and catalyst loading) and processing variables (reaction time, reaction temperature, and inert gas flow rate). The measured output parameters were the chemical properties of materials and reproducibility of the material formation in replicate polymerizations in microreactors. Spatially resolved nondestructive evaluation of polymer formation was performed directly in individual microreactors and provided information about the spatial homogeneity of polymers in microreactors. It showed to be another powerful indicator of the reproducible polymerization process on the combinatorial scale. Although the methodology described here was implemented for high-throughput optimization of polymerization conditions, it is more general and can be further implemented for a variety of applications in which optimization of process parameters can be studied in situ or off-line using spectroscopic and other tools.