Stereochemistry of substitution reactions at a chiral ruthenium atom: the crystal structure of (R)-[Ru(h5- C5H4R*)(CO)(PPh3)NCCH3]PF6(R* = neomenthyl)

The stereochemistry of substitution reactions of complexes of the type [Ru(η5-C5H4R*)(CO)(PPh3)L]n+ (R* = menthyl or R = neomenth n = 1, L = NCCH3 or NCCD3 has been studied by X-ray crystallography. Circular Dichroism and 1H, 13C and 31P NMR spectroscopy. All the reactions investigated have been unequivocably proved to occur with ≥ 94% retention of configuration at the ruthenium atom. Thus (S)-Ru(η5-C5H4R*)(CO)(PPh3)Cl reacts with NaI to give (R)-Ru(η5-C5H4R*)(CO)(PPh3)I (R* = menthyl or neomenthyl) and reaction of Ru(η5-C5H4R*)CO(PPh3)X (R*=menthyl, (S)Ru, X = Cl; R* = neomenthyl, (R)Ru, X = I) with AgY in acetonitrile yields the corresponding complex (R)-[Ru(η5- C5H4R*)(CO)(PPh3)(NCCH3)]Y (Y = PF6 or BF4). An X-ray structure determination of [Ru(η5-C5H4R*)(CO)(PPh3)NCCH3]PF6 (R* = neomenthyl) has confirmed that the absolute configuration of the ruthenium centre is R. The crystals are orthorhombic, space group P212121 (No. 19) with a 10.400(2), b 15.850(4), c 24.740(5) Å and Z = 4. The structure was solved via the heavy-atom method and refined to R = 0.036 using 4183 diffractometer data with I ≥ 1.56(I). CD3CN undergoes exchange with the coordinated acetonitrile in (R)-[Ru(C5H4R*)(CO)(PPh3)(NCCH3)]BF4 (R* = neomenthyl) with retention of configuration at ruthenium and reaction of (R)-[Ru(η5-C5H4R*)(CO)(PPh3)NCCD3]BF4 with NaI regenerates (R)-[Ru(η5-C5H4R*)(CO)(PPh3)I] (R* = neomenthyl).