para), 127.4 and 125.7 (ortho and para), 55.3 (N(CH3)4+), 53.6 (C0-CH3).N(CH3)4+[/ac-(CO)3(13CO)Re(COCH3)(COC6H5)r (5C). A solution of a 2:1 mixture (0.90 g, 1.83 mmol) of N(CH3)4+[(CO)4Re(CH3)-(COQHs)]-(7): N(CH3)4+[(CO)4Re(C6H5)(COCH3)]" (6) in 10 mL of acetone was placed in a 22-mL stainless steel Parr bomb and degassed by three freeze-pump-thaw cycles on a vacuum line. 13CO (90% !3C, Mound Laboratory) was condensed into the bomb at -196 °C. The bomb was sealed and warmed to 30 °C, where the gauge pressure was 400 psi. After 2 h at 30 °C, the 13CO was vented and recovered for further use.NMR of the crude reaction mixture indicated that it consisted of 59% 5 in addition to 4% unreacted 7 and 37% unreacted 6. The mixture was reacted with HC1 (0.8 mL, 4.2 M in ether, 3.4 mmol) to convert 5C to 10C, which was isolated by column chromatography as for 10A. Purified 10C (0.44 g, 0.98 mmol) was then treated with N(CH3)4+OH~(0.4 mL, 2.76 M in CH3OH, 1.1 mmol) to give pure 5C (0.24 g, 38% yield based on 7): NMR (acetone-^, 270 MHz) ó 7.44 (m, 2 H), 7.23 (m, 3 ), 3.40 (m, 12 H), 2.25 (s, 3 H). I3C NMR (acetone-d6, 0.09 M Cr(acac)3, -30 °C, 50.1 MHz) 5 262.9 (COC6H5), 260.5 (COCH3),