Isomers of Re(CO) 3(CN tBu)LX: Synthetic strategies starting from MnRe(CO) 8(CN tBu)L and Re(CO) 4LX (X  halogen; L Group 15 donor ligand)

Abstract

Reaction of Re(CO) 4LX (L  PMePh 2, PMe 2Ph, PPh 3, P(OMe) 3, P(O iPr) 3, P(O- o-tol) 3; X  Br, I) with tBuNC in the presence of PdO catalyst gave the new complexes Re(CO) 3(CN tBu)LX in high yield (> 60%). The new complexes were shown by spectroscopic techniques (IR, 1H and 31P NMR) to comprise a mixture of mer and fac isomers. The mer/fac ratio decreased with reaction temperatures ( e.g. L  P(OMe) 3; 10°C, ratio = 3; 45°C, ratio = 0.25). At high temperatures (90°C) isomerization of the mer to the fac isomers (L  PMe 2Ph, P(OMe) 3) occurred, suggesting that the mer isomer was the kinetic product of the catalysed reaction. Reactions induced by Me 3NO gave similar effects. Halogen cleavage of MnRe (CO) 8(CN tBu)L, prepared from MnRe(CO) 9(CN tBu) and L in the presence of Me 3NO, yielded either one or two isomers of Re(CO) 3(CN tBu)(L)X (X  I, Br; 40% yield). For large L ( e.g. PPh 3) a new mer isomer with L trans to X was synthesized, and characterized by IR and NMR spectroscopy. For small L ( e.g. P(OMe) 3) a mixture of the two different mer products was obtained. The product isomer ratio was determined predominantly by the position of L in the starting dimer.