Jl. Bookham et al., Dynamic coordinative exchange in rhodium(I) complexes of chiral diphosphines bearing pendant pyridyl donor groups, J CHEM S DA, (6), 2000, pp. 975-980
Citations number
35
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
meso-{Ph2PCH(Ph)CH(Ph)PPh2}, meso-{Ph2PCH(pyr)CH(pyr)PPh2}, erythro-{Ph2PCH
(Ph)CH(pyr)PPh2}, rac-{Ph2PCH(pyr)CH(pyr)PPh2}, threo-{Ph2PCH(Ph)CH(pyr)PPh
2}, and threo-{Ph2PCH(Ph)CH(pym)PPh2}, [pyr = 2-pyridyl, pym = 2-pyrimidyl]
reacted with [Rh(COD)Cl](2) (COD = 1,5-cyclooctadiene) to give cationic rh
odium(I) complexes [Rh(COD){L}](+) (L = diphosphine ligand), which were iso
lated as their PF6- salts, 1-6 respectively. In 2 and in 3 the phosphine li
gand adopts a P,P',N-coordination mode whereas 1, and 4-6 exhibit simple P,
P'-coordination for the parent ligands and no evidence for N-coordination i
s observed. In solution 2 undergoes a fluxional process involving interchan
ge of the coordinated and non- coordinated pyridyl environments. Variable t
emperature NMR studies revealed an enthalpy of activation (Delta H double d
agger) of 64.3 kJ mol(-1) and an entropy of activation (Delta S double dagg
er) of 0.005 kJ K-1 mol(-1) for this process in ortho-dichlorobenzene solut
ion. Complex 3 exhibits no similar uxional behaviour. A single-crystal X-ra
y analysis of 2 revealed a nitrogen-rhodium distance of 2.369(3) Angstrom f
or the coordinated pyridyl group, which is slightly longer than each of the
phosphorus-rhodium distances [2.2868(7) Angstrom and 2.3649(8) Angstrom].
This suggests a relatively weak nitrogen- rhodium bonding interaction.