Do carbenium ion additions toward alkenes proceed via .pi. complexes? A stereochemical investigation.

(0.70 mmol) of dibenzothiophene was added. After 48 h at 55 OC the mixture was worked up, first with glacial acetic acid and then with 6 N aqueous HCI. A sample of the biphenyl (95%) was analyzed by MS and IR measurements. The product was a mixture of 14.3% 2,2'-dideuterio-and 25.3% 2-deuteriobiphenyl, together with 60.4% biphenyl. (e) Workup with o-Deuterioacetic Acid. The reaction between (COD)2Ni, 2,2'-bipyridyl, and LiAIH, in 15 mL of T H F was conducted on a 1.5 mM scale as in section d. Workup with CH3C02D gave 94.5% biphenyl and a mixture of 2.3% 2-deuterio-and 3.2% 2,2'-dideuteriobi-phenyl. Hydrodesulfurization of Dibenzothiophene (3) with Nickel Salts and Metal Hydrides. (a) 2,2'-Bipyridyl and LiAIH4. A solution of 200 mg (0.73 mmol) of nickel(I1) acetylacetonate and 113 mg (0.73 mmol) of 2,2'-bipyridyl in 15 mL of T H F was treated with 26 mg (0.73 mmol) of LiAIH,. After the brown solution was stirred for 30 min at 25 OC, 67 mg (0.36 mmol) of 3 was added. The reaction mixture was heated for 48 h at 55 OC and then given the usual protolytic workup. A GLPC analysis showed a 36% conversion to biphenyl. A reaction in which 6 molar equiv of LiAIH4 was used with 2 molar equiv each of Ni(acac), and 2,2'-bipyridyl to desulfurize 1 molar equiv dibenzothiophene gave 32% biphenyl. (b) Use of NaBH4. A reaction analogous to that in section a, except that NaBH, was substituted for LiAIH4, gave a 6% conversion to bi-phenyl, either in T H F (55 " C) or in triglyme (130 " C). (c) Use of Diisobutylaluminum Hydride. A green solution of 290 mg (1.83 mmol) of Ni(acac), and 285 mg (1.83 mmol) of 2,2'-bipyridyl in 15 mL of toluene was stirred while being treated with 260 mg (1.83 mmol) of (i-Bu),AIH. Then 160 mg (0.87 mmol) of 3 was added to the brown solution. After 24 h at reflux and the usual protolytic workup, a GLPC analysis showed a 38% conversion to biphenyl.violet solution of 1, prepared from 560 mg (2.03 mmol) of (COD),Ni and 220 mg (2.03 mmol) of 2,2'-bipyridyl in 15 mL of THF, was treated first with 80 mg (2.03 mmol) of LiAIH, and after 30 min with 212 mg (1.0 mmol) of 9. After 48 h at 55 OC hydrolytic workup gave an 82% yield of 3,3'-dimethylbiphenyI. A reaction mixture of 560 mg (2.03 mmol) of …