Syntheses, structures, and reactions of cyrhetrenylphosphines; applications in palladium catalyzed Suzuki cross-coupling reactions

• Syntheses of rhenium containing phosphines.
• Lithiations of bromocyclopentadienyl ligand.
• Palladium catalyzed Suzuki couplings.
• Crystal structures of cyrhetrenylphosphines.

Reaction of bromocyrhetrene (η5-C5H4Br)Re(CO)3 with lithium tetramethylpiperidide (LiTMP; 1.0 equiv, −78 °C) and then ClPR2 (R = a, Ph; b, Cy) gives (η5-1,2-C5H3BrPR2)Re(CO)3 (5a, 48%; 5b, 80%). Analogous reactions with 2.0 equiv of LiTMP and ClPR2 give the 1-bromo-2,5-diphosphidocyclopentadienyl complexes [η5-1,2,5-C5H2Br(PR2)2]Re(CO)3 (6a, 60%; 6b, 80%). These rhenium containing or cyrhetrenylphosphines are combined with Pd(OAc)2 (2:1 mol ratio) to give catalysts for Suzuki couplings of phenylboronic acid and p-bromotoluene or p-bromoacetophenone (1 mol%; Cs2CO3, toluene, 100 °C). The catalyst with 5b exhibits much higher activities than the others, with conversions of 92–64% after 20 min. The crystal structures of 5b and 6a,b are determined.

Bromocyrhetrene may be o-lithiated or o,o′-dilithiated, and reactions with ClPPh2 or ClPCy2 give the corresponding monophosphines and diphosphines, three of which are structurally characterized, and one of which gives, when combined with Pd(OAc)2, an effective catalyst for Suzuki couplings.Figure optionsDownload as PowerPoint slide