mL and DMF and saturated with methylamine gas at 0 OC. The vessel was sealed and agitated for 1 day. The polymer was washed successively in dioxane, ethanol, 2 N NaOH/i-PrOH (l:l), water (until eluate neutral), ethanol, and ether. After drying in vacuo, the polymer (3.7 g/3.8 mequiv of amino groups/l g of dry weight) was suspended in a mixture of water (1.5 mL), ethanol (0.5 mL), triethylamine (7 mL), and 4chloropyridine hydrochloride (4.7 g) in a glass pressure vessel, sealed and heated for 4 days at 140 OC. The polymer was washed as before, and unreacted amino groups were blocked by acetylation (acetic anhydride in CH2C12, then base wash). The washed DMAP polymer was dried at 150 OC in vacuo until constant weight. Incorporation of pyridine groups was determined by potentiometric chloride titration of the hydrochloride salt bound to the polymer: 2.53 mequiv/g compared to 3.15 mequiv/g prior to acetylation.Polymeric l-Acyl-4-(diaUtylamino)pyridinium Chlorides. In a typical experiment, the anhydrous 4-(dialkylamino)pyridine polymer was swelled in methylene chloride (freshly distilled from P205 under argon) and treated with excess benzoyl chloride at 0 OC. The polymer was filtered and washed with methylene chloride under anhydrous conditions until the washings contained negligible amounts of benzoyl chloride-by the silver nitrate test in alcohol (less than 0.1% of total pyridine groups as indicated by GC). The polymer was dried under vacuum at room temperature and was stable at -10 OC for several months. After treatment with a primary (e.g., benzyl) amine in methylene chloride, a pure amide was recovered by filtration and acid/base wash. The amount of amide corresponded to 0.8 mequiv/g of acyl substitution on the polymer. Anhydrous manipulation as above and those involving transfer between two polymers were most conveniently carried out by using a circulating system described in Figure 1, containing Teflon columns (1-4-(10) Warshawsky, A,; Deshe, A.; Rossey, G.; Patchornik, A. React. Polym. 1984, 2, 301.mL volume) joined to the solvent distillation apparatus, waste, and vacuum pump via Teflon tubing.In summary, we have shown for the first time the possibility to perform highly efficient condensation reactions, by transferring polymerbound electrophiles (Le., active esters) via a mediator (shadchan) to polymer-bound nucleophiles (i.e., amines). We have also shown the possibility of on-line monitoring which is relevant for automation.The mediator methodology developed here is believed not to be limited to acylation and related processes but to be expandable to other chemical processes that involve the creation of activated intermediates. These possibilities are currently under investigation. Acknowledgment. We thank the Etta P. Schiff Trust and the Bantrell Fund for financial support. This work is dedicated to Prof. Arieh Berger on t h e 10th anniversary of his death.

A new approach is proposed which allows us to calculate molecular conformations of organometallic molecules within the framework of the MM3 force field. The ligand positions in the coordination sphere of the metal atom are mainly determined by minimization of the interligand nonbonded energy. For a description of the metal-ligand interactions (n-bonding), a very strong but otherwise ordinary (Hill type) van der Waals potential is used. Using this approach, the conformations of the bent sandwich metallocenes MCp2 (where M are metals of main groups I1 or IVA or lanthanides 11) were reproduced. It was shown that, when the interplanar distance between the planes of the Cp ligands are short, the ligands have a parallel orientation. When the distance is large (when the metal atom has a large radius), the interplanar distances become longer and the ligand planes do not stay parallel, but the molecule "bends" so that these planes intersect. The influence of bulky substituents on the bending angle was shown. Calculations were also carried out on crystals of these molecules, to determine the effect of crystal packing. The possibilities for the accurate prediction of the conformations of molecules of this type of structures (not yet investigated experimentally) on the basis of quantum mechanics and molecular mechanics are discussed.

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