A series of new bis(phosphinite) p-XPCPIrHCl pincer complexes {[PCP = eta(3)-5-X-C6H2[OP(tBU)(2)](2)-1,3], X = MeO (4a), Me (4b), H (4c), F (4d), C6F5 (4e), and Ar-F [=3,5-bis (trifluoromethyl)phenyl] (4f)} have been synthesized. Treatment of compounds 4a-f with NatOBu in cyclooctane (COA)/tert-butylethylene (TBE) mixtures generates species with unprecedented catalytic activity for the catalyzed transfer dehydrogenation of COA with TBE as acceptor to form cyclooctene (COE) and tert-butylethane (TBA). With substrate: precatalyst ratios of 3030COA:3030TBE:1p-XPCPIrHCl (4):1.1NaOtBu, turnover numbers (TONS) between 1400 and 2200 (up to 72% conversion in TBE) and initial turnover frequencies (TOFs) between 1.6 and 2.4 s(-1) have been observed at 200degreesC.