|
|
|
Journal
Publications |
|
Comparative Study of Diastereoisomer
Interconversion in Chiral BINOL-ate and Diamine Platinum Complexes of
Conformationally Flexible NUPHOS Diphosphines.
Simon Doherty, Colin R. Newman, Rakesh K.
Rath, Jan-Albert van den Berg, Christopher Hardacre, Mark Nieuwenhuyzen
and Julian G. Knight, Organometallics, 2004, 23,
1055. |
|
Abstract: A thorough and detailed study of
diastereointerconversion in the chiral platinum complexes [(NUPHOS)Pt{(S)-BINOL}]
(3a-e) has been undertaken and compared with the results
of a similar study with [(BIPHEP)Pt{(S)-BINOL}]. Rate data
revealed that this process obeys first-order relaxation kinetics, and
rate constants for conversion of the minor to the major diastereoisomer
have been obtained. Eyring analysis of the data gave
DH‡ and
DS‡
values of 22-25 kcal mol-1 and -1 to -16 eu, respectively. In
combination with computational analysis, these studies indicate that
atropinversion most likely occurs via an on-metal pathway involving a
planar seven-membered transition state. Substitution of (S)-BINOL
for (S,S)-DPEN results in a marked reduction in the
barrier to atropinversion; a DH‡
value of 17 kcal mol-1 has been determined for the conversion
of d-[(Ph4-NUPHOS)Pt{(S,S)-DPEN}]Cl2
to l-[(Ph4-NUPHOS)Pt{(S,S)-DPEN}]Cl2,
which could indicate that an alternative mechanism operates. |
| |
|
|
|
