10.1021/om980945d.s001
Thomas H. Peterson
Thomas H.
Peterson
Jeffery T. Golden
Jeffery T.
Golden
Robert G. Bergman
Robert G.
Bergman
Deprotonation of the Transition Metal Hydride
(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)IrH<sub>2</sub>. Synthesis and Chemistry of the
Strongly Basic Lithium Iridate (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)Ir(H)(Li)
American Chemical Society
1999
p K
IrH 2
THF
DME
Cp
PMe
S N 2 displacement
acidic transition metal hydride
NMR
C 5
lithium iridate 2
DMSO
1999-04-25 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Deprotonation_of_the_Transition_Metal_Hydride_sup_5_sup_-C_sub_5_sub_Me_sub_5_sub_PMe_sub_3_sub_IrH_sub_2_sub_Synthesis_and_Chemistry_of_the_Strongly_Basic_Lithium_Iridate_sup_5_sup_-C_sub_5_sub_Me_sub_5_sub_PMe_sub_3_sub_Ir_H_Li_/3783912
Treatment of (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)IrH<sub>2</sub> (<b>1</b>) with <i>tert</i>-butyllithium gives (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)Ir(H)(Li) (<b>2</b>) as a bright yellow solid. NMR evidence indicates that the lithium iridate <b>2</b> is
aggregated in benzene, is converted to a single symmetrical species in THF, and is present
as a dimer in DME. Treatment of <b>2</b> with 3,3-dimethylbutane trifluoromethanesulfonate-1,2-<i>syn-d</i><sub>2</sub> (<b>3-</b><b><i>syn-d</i></b><b><sub>2</sub></b>) gave the alkylated hydridoiridium complex <b>4a-</b><b><i>anti-d</i></b><b><sub>2</sub></b>, which was
converted to the corresponding chloride Cp*(PMe<sub>3</sub>)Ir(CHDCHDCMe<sub>3</sub>)(Cl) (<b>4c-</b><b><i>anti-d</i></b><b><sub>2</sub></b>) by
treatment with CCl<sub>4</sub>. Analysis of this material by NMR spectroscopy showed that it was
contaminated with ≤15% syn isomer. The alkylation therefore proceeds with predominant
inversion of configuration at carbon, indicating that the major pathway is an S<sub>N</sub>2
displacement and not an outer-sphere electron-transfer reaction. Protonation studies carried
out on iridate <b>2</b> with organic acids of varying p<i>K</i><sub>a</sub> allowed us to estimate that the p<i>K</i><sub>a</sub> of the
dihydride <b>1</b> falls in the range 38−41, making it less acidic than DMSO and more acidic
than toluene. This represents the least acidic transition metal hydride whose p<i>K</i><sub>a</sub> has been
quantitatively estimated. Treatment of <b>2</b> with main group electrophiles allowed the
preparation of several other hydridoiridium derivatives, including Cp*(PMe<sub>3</sub>)Ir(SnPh<sub>3</sub>)(H)
(<b>5a</b>), Cp*(PMe<sub>3</sub>)Ir(SnMe<sub>3</sub>)(H) (<b>5b</b>), and Cp*(PMe<sub>3</sub>)Ir(BR<sub>2</sub>)(H) (<b>6a</b>, R = F; <b>6b</b>, R = Ph). Reaction
of <b>2</b> with acid chlorides and anhydrides leads to acyl hydrides Cp*(PMe<sub>3</sub>)Ir(COR)(H), and
fluorocarbons also react, giving products such as Cp*(PMe<sub>3</sub>)Ir(C<sub>6</sub>F<sub>5</sub>)(H) in the case of
hexafluorobenzene as the electrophile.