Catalytic Hydrogenolysis of Biphenylene with Platinum, Palladium, and Nickel Phosphine Complexes

• Published in: Organometallics Vol. 17; no. 22; pp. 4784 - 4794
• Main Authors: Edelbach, Brian L, Vicic, David A, Lachicotte, Rene J, Jones, William D
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 26.10.1998; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; C-C ACTIVATION; CARBON-CARBON BOND; IRIDIUM COMPLEXES; CRYSTAL-STRUCTURE; METAL INSERTION; 1,1-REDUCTIVE ELIMINATION; MECHANISMS; OXIDATIVE ADDITION; REDUCTIVE ELIMINATION; THERMAL-DECOMPOSITION
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om9805281

The catalytic hydrogenolysis of biphenylene was carried out using Pt, Pd, and Ni phosphine complexes under an atmosphere of H2 between 56 and 120 °C. The Pt species Pt(PEt3)3, (PEt3)2Pt(2,2‘-biphenyl), 1, trans-(PEt3)2PtH2, and trans-(PEt3)2Pt(α-biphenyl)H, 4, were all viable catalysts. The resting state species in each case was complex 4. At 80 °C under an atmosphere of H2, 4 reductively eliminates biphenyl and forms trans-(PEt3)2PtH2. Free PEt3 inhibits the rate of reductive elimination from 4 and the overall rate of hydrogenolysis. The novel Pt(IV) dihydride trans,cis-(PEt3)2Pt(2,2‘-biphenyl)H2 was synthesized and characterized by X-ray analysis. trans,cis-(PEt3)2Pt(2,2‘-biphenyl)H2 undergoes unimolecular reductive elimination to give 2. On the basis of these results a catalytic cycle is proposed. A mixture of [(dippe)PtH]2 and (dippe)PtH2 (dippe = bis(diisopropylphosphino)ethane) was also capable of catalyzing the hydrogenolysis of biphenylene under an atmosphere of H2 at 120 °C. The rate of hydrogenolysis increases as the concentration of biphenylene, H2, and (dippe)PtH2 increases. These observations are consistent with the C−C bond activation of biphenylene occurring via (dippe)PtH2, not [(dippe)Pt0]. The rate of catalytic hydrogenolysis was not affected by the length of the chelating phosphine bridge. The Ni complex [(dippe)NiH]2 was the most efficient catalyst for the hydrogenolysis of biphenylene (16 turnovers/day at 56 °C). The resting state species was (dippe)Ni(2,2‘-biphenyl).