The Conformations of 13-Vertex <i>ML</i><sub>2</sub>C<sub>2</sub>B<sub>10</sub> Metallacarboranes:
Experimental and Computational Studies
Kelly J. Dalby
David Ellis
Stefan Erhardt
Ruaraidh D. McIntosh
Stuart A. Macgregor
Karen Rae
Georgina M. Rosair
Volker Settels
Alan J. Welch
Bruce E. Hodson
Thomas D. McGrath
F. Gordon A. Stone
10.1021/ja067698m.s002
https://acs.figshare.com/articles/dataset/The_Conformations_of_13_Vertex_i_ML_i_sub_2_sub_C_sub_2_sub_B_sub_10_sub_Metallacarboranes_Experimental_and_Computational_Studies/3017566
The docosahedral metallacarboranes 4,4-(PMe<sub>2</sub>Ph)<sub>2</sub>-4,1,6-<i>closo</i>-PtC<sub>2</sub>B<sub>10</sub>H<sub>12</sub>, 4,4-(PMe<sub>2</sub>Ph)<sub>2</sub>-4,1,10-<i>closo</i>-PtC<sub>2</sub>B<sub>10</sub>H<sub>12</sub>, and [N(PPh<sub>3</sub>)<sub>2</sub>][4,4-cod-4,1,10-<i>closo</i>-RhC<sub>2</sub>B<sub>10</sub>H<sub>12</sub>] were prepared by reduction/metalation of either 1,2-<i>closo</i>-C<sub>2</sub>B<sub>10</sub>H<sub>12</sub> or 1,12-<i>closo</i>-C<sub>2</sub>B<sub>10</sub>H<sub>12</sub>. All three species were fully characterized,
with a particular point of interest of the latter being the conformation of the {<i>ML</i><i><sub>2</sub></i>} fragment relative to the
carborane ligand face. Comparison with conformations previously established for six other <i>ML</i><sub>2</sub>C<sub>2</sub>B<sub>10</sub> species
of varying heteroatom patterns (4,1,2-<i>M</i>C<sub>2</sub>B<sub>10</sub>, 4,1,6-<i>M</i>C<sub>2</sub>B<sub>10</sub>, 4,1,10-<i>M</i>C<sub>2</sub>B<sub>10</sub>, and 4,1,12-<i>M</i>C<sub>2</sub>B<sub>10</sub>) reveals
clear preferences. In all cases a qualitative understanding of these was afforded by simple MO arguments
applied to the model heteroarene complexes [(PH<sub>3</sub>)<sub>2</sub>PtC<sub>2</sub>B<sub>4</sub>H<sub>6</sub>]<sup>2-</sup> and [(PH<sub>3</sub>)<sub>2</sub>PtCB<sub>5</sub>H<sub>6</sub>]<sup>3-</sup>. Moreover, DFT
calculations on [(PH<sub>3</sub>)<sub>2</sub>PtC<sub>2</sub>B<sub>4</sub>H<sub>6</sub>]<sup>2-</sup> in its various isomeric forms approximately reproduced the observed
conformations in the 4,1,2-, 4,1,6-, and 4,1,10-<i>M</i>C<sub>2</sub>B<sub>10</sub> species, although analogous calculations on
[(PH<sub>3</sub>)<sub>2</sub>PtCB<sub>5</sub>H<sub>6</sub>]<sup>3-</sup> did not reproduce the conformation observed in the 4,1,12-<i>M</i>C<sub>2</sub>B<sub>10</sub> metallacarborane.
DFT calculations on (PH<sub>3</sub>)<sub>2</sub>PtC<sub>2</sub>B<sub>10</sub>H<sub>12</sub> yielded good agreement with experimental conformations in all four
isomeric cases. Apparent discrepancies between observed and computed Pt−C distances were probed
by further refinement of the 4,1,2- model to 1,2-(CH<sub>2</sub>)<sub>3</sub>-4,4-(PMe<sub>3</sub>)<sub>2</sub>-4,1,2-<i>closo</i>-PtC<sub>2</sub>B<sub>10</sub>H<sub>10</sub>. This still has a
more distorted structure than measured experimentally for 1,2-(CH<sub>2</sub>)<sub>3</sub>-4,4-(PMe<sub>2</sub>Ph)<sub>2</sub>-4,1,2-<i>closo</i>-PtC<sub>2</sub>B<sub>10</sub>H<sub>10</sub>,
but the structural differences lie on a very shallow potential energy surface. For the model compound a
henicosahedral transition state was located 8.3 kcal mol<sup>-1</sup> above the ground-state structure, consistent
with the fluxionality of 1,2-(CH<sub>2</sub>)<sub>3</sub>-4,4-(PMe<sub>2</sub>Ph)<sub>2</sub>-4,1,2-<i>closo</i>-PtC<sub>2</sub>B<sub>10</sub>H<sub>10</sub> in solution.
2007-03-21 00:00:00
2B
PH
conformation
MC
henicosahedral transition state
carborane ligand face
CH
8.3 kcal mol
MO
ML 2C species
DFT calculations
model