Unexpected isomerization of a cis- into a trans-dihydride complex. A neutral late transition metal complex as a hydride donor

Reaction of HIr(PPh3)(3)(CO) (1) with 1,3-bis[(diisopropylphosphino)methyl]benzene (2) in THF or benzene at 60 degrees C affords trans-H2Ir(CO)L (3; L = C6H3(CH2P(i-Pr-2)(2)). The cationic complex [HIr(PPh3)(CO)L]Br (5) was obtained in the reaction of 1 with 1,3-bis[(diisopropylphosphino)methyl]-2-bromobenzene (4), Reaction of 5 with KO-t-Bu leads to the Ir(I) complex Ir(CO)L (6), which adds methyl iodide to form IIr(CO)(CH3)L (7). Addition of H-2 to 6 results in formation of cis-(L)Ir(H)(2)(CO) (8). This reaction is reversible, due to the rigid square-planar geometry of 6. Under H-2 pressure 8 isomerizes into 3, demonstrating cis-into trans-dihydride isomerization, which is unprecedented for octahedral complexes. The trans-dihydride six-coordinate complex 3 exhibits hydridic reactivity which is unusual for a neutral late transition metal complex and is due to the strong mutual trans influence of the hydride ligands. Various electrophiles ([Ph3C]BF4, PhC(O)Cl, CS2, MeI) directly attack the hydride ligand of 3, forming products of selective hydride transfer. Abstraction of the hydride ligand with the electrophiles affords the iridium complexes [HIr(PPh3)(CO)L]Br (9), HIr(Cl)(CO)L (10), HIr(CO)(SC)(S)H)L (11), and HIr(I)(CO)L (12).