1. Preheat oven to 350°. Stir together buttermilk and baking soda.
2. Beat butter at medium speed with an electric mixer until creamy. Gradually add granulated sugar, beating until light and fluffy and stopping to scrape bowl as needed. Add eggs, 1 at a time, beating just until blended after each addition. Beat in vanilla.
3. Stir together flour and next 4 ingredients in a large bowl; gradually add to butter mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Beat at low speed just until blended after each addition, stopping to scrape bowl as needed. Add preserves, and beat at low speed just until blended. Stir in pecans. Spoon batter into a greased and floured 10-inch tube pan.
4. Bake at 350° for 1 hour and 5 minutes to 1 hour and 10 minutes or until a long wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes; remove from pan to wire rack, and cool completely (about 2 hours). Dust cake with powdered sugar just before serving, if desired.