Dihydrogen Complexes of Iridium and Rhodium

A series of iridium and rhodium pincer complexes have been synthesized and characterized: [(POCOP)Ir(H)(H-2)] [BAr4f] (1-H-3), (POCOP)Rh(H-2) (2-H-2), [(PONOP)Ir(C2H4)] [BAr4f] (3-C2H4), [(PONOP)Ir(H)(2))] [BAr4f] (3-H-2), [(PONOP)Rh(C2H4)] [BAr4f] (4-C2H4) and [(PONOP)Rh(H-2)] [BAr4f] (4-H-2) (POCOP = kappa(3)-C6H3-2,6-[OP(tBu)(2)](2); PONOP = 2,6-(tBu(2)PO)(2)C5H3N; BAr4f tetralcis3(3,5-trifluoromethylphenyOborate). The nature of the dihydrogen-metal interaction was probed using NMR spectroscopic studies. Complexes 1-H-3, 2-H-2, and 4-H-2 retain the H-H bond and are described as a classical dihydride system. The presence of bound classified as eta(2)-dihydrogen adducts. In contrast, complex 3-H-2 is best dihydrogen was determined using both T-1 and (1)J(HD) coupling values. T-1 = 14 ms, (1)J(HD) = 33 Hz for the dihydrogen ligand in 1-H-3, T-1(min) = 23 ms, (1)J(HD) = 32 Hz for 2-H-2, T-1(min) = 873 ms for 3-H-2, T-1(min) 33 ms, (1)J(HD) = 30.1 Hz for 4-H-2.