Dihydrogen Complexes of Iridium and Rhodium

A series of iridium and rhodium pincer complexes have been synthesized and characterized: [(POCOP)­Ir­(H)­(H2)] [BArf 4] (1-H 3 ), (POCOP)­Rh­(H2) (2-H 2 ), [(PONOP)­Ir­(C2H4)] [BArf 4] (3-C 2 H 4 ), [(PONOP)­Ir­(H)2)] [BArf 4] (3-H 2 ), [(PONOP)­Rh­(C2H4)] [BArf 4] (4-C 2 H 4 ) and [(PONOP)­Rh­(H2)] [BArf 4] (4-H 2 ) (POCOP = κ3-C6H3-2,6-[OP­(tBu)2]2; PONOP = 2,6-(tBu2PO)2C5H3N; BArf 4 = tetrakis­(3,5-trifluoromethylphenyl)­borate). 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 classified as η2-dihydrogen adducts. In contrast, complex 3-H 2 is best described as a classical dihydride system. The presence of bound dihydrogen was determined using both T1 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 .