10.1021/om950836o.s001
James M. Boncella
James M.
Boncella
Mary L. Cajigal
Mary L.
Cajigal
Khalil A. Abboud
Khalil A.
Abboud
Competition between π Donation and α-C−H Agostic
Interactions in Complexes of the Type
Tp‘Ta(CH-<i>t</i>-Bu)(X)(Y) (X = Halide; Y = Halide, NR<sub>2</sub>, OR;
Tp‘ = Hydrotris(3,5-dimethylpyrazolyl)borate)
American Chemical Society
1996
PrC 6 H 3
THF
alkylidene carbon
proton
NR
CH
π donor properties
Cl
KN
Tp
1996-04-02 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Competition_between_Donation_and_-C_H_Agostic_Interactions_in_Complexes_of_the_Type_Tp_Ta_CH-_i_t_i_-Bu_X_Y_X_Halide_Y_Halide_NR_sub_2_sub_OR_Tp_Hydrotris_3_5-dimethylpyrazolyl_borate_/3776754
The compounds
Tp‘Ta(CHC(CH<sub>3</sub>)<sub>3</sub>)X<sub>2</sub>
(<b>2</b> (X = Cl), <b>3</b> (X = Br)) (Tp‘ =
hydrotris(3,5-dimethylpyrazolyl)borate), have been synthesized by the reaction of
KTp‘ with Ta(CHC(CH<sub>3</sub>)<sub>3</sub>)X<sub>3</sub>(thf)<sub>2</sub>
in THF. One Cl ligand in <b>2</b> can be substituted with
OR<sup>-</sup> (R = <i>i</i>-Pr, Me) or
NMe<sub>2</sub><sup>-</sup>. The values of
<sup>1</sup><i>J</i><sub>C-H</sub> for the alkylidene carbon
are uniformly low due to the α-H
agostic interaction between the metal center and the alkylidene proton.
The magnitude of
<sup>1</sup><i>J</i><sub>C-H</sub> in these compounds depends
upon the π donor properties of the remaining ligands.
Attempted synthesis of monoarylamide complexes by displacement of
Cl<sup>-</sup> from <b>2</b> with
N(H)Ar<sup>-</sup> results in proton transfer from N to C and
formation of the imido complexes Tp‘Ta(CH<sub>2</sub>C(CH<sub>3</sub>)<sub>3</sub>)(NAr)Cl
(Ar = 2,6-<i>i</i>-PrC<sub>6</sub>H<sub>3</sub> (<b>7</b>),
Ph (<b>8</b>)). When <b>2</b> reacts with
KN(Me)Ph, proton
transfer occurs from the Me group to the alkylidene carbon giving the
imine complex Tp‘Ta(η<sup>2</sup>-CH<sub>2</sub>NPh)(CH<sub>2</sub>CMe<sub>3</sub>)Cl
(<b>9</b>). A single-crystal X-ray diffraction study of
<b>9</b> confirmed the
structure and suggested that <b>9</b> is best described as an
azametallacyclopropane complex.