SYNTHESIS AND STRUCTURE OF SILICON-CONTAINING CAGES Joseph A. Hankin, Ray W. Howe, Niels H. Damrauer, Kelly A. Peterson, Stephen J. Bruner, and Robert Damrauer* Chemistry Department, University of Colorado at Denver, Denver, Colorado 80217-3364, USA Abstract: The synthesis and properties of two new silicon-containing cage systems are reported. These are prepared by transition metal-catalyzed cyclotrimerizations of silicon- containing tripod triynes. Trimerizations of this type give both 1,2,4 and 1,3,5 benzene ring isomers. These isomers have been separated and characterized by a variety of means including multi-nuclear NMR and X-ray analysis. Collaborativetoniba ab initio computations have been carried out to examine the stability of in versus out isomers in related cage systems. Introduction: We recently reported the synthesis of silicon cage molecules 1 and 2 for t-Bu t-Bu 1 (1,2,4 isomer) 2 (1,3,5 isomer) n= 3. 1 Our interest in such molecules was stimulated by studies by Pascal and coworkers who have prepared several macrocyclics including 3 and 4. 2-6 Their work has clearly demonstrated that molecules like 3 and 4 are more stable with the hydrogen on their quaternary atom directed inside the cage. The synthetic strategy employed by Pascal and coworkers to prepare compounds like 3 and 4 begins with 1,3,5-trisubstituted benzenes and subsequently assembles the cage. Our studies were undertaken with two goals: (1) to develop other general synthetic pathways that would efficiently prepare silicon-containing macrocyles of varying structure and (2) to answer the question of whether a hydrogen on a quaternary atom would in general prefer an inside or outside orientation. In this paper, we report the synthesis of 1 and 2 for n= 2 and 9. We also will briefly summarize our collaborative studies on ab initio computations bearing on the inside-outside isomerization question. Materials and Methods: All the reported reactions were carried out under an inert gas atmosphere using handling standard techniques. Solvents were dried and all reagents were purified using standard methods. The following instruments were used for characterization purposes: GC - HP5989 (FID): GC-MS - HP5970 : NMR - IBM-NR80, Varian VXR-300, and Bruker WM250: UV - PE552A: X-ray - Nicolet P3F auto diffractometer using Siemens SHELXTL. General Preparation of Silicon-Containing Cages: Tripod Synthesis (eq. 1 for n= 2, 3, and 9): The corresponding yne-1-ol (0.24 mol) in 30 ml benzene was added to a flask containing t-butyltrichlorosilane (0.08 mol), pyridine (0.23 mol), and copper powder (0.005 mol) 391