Synthesis, Characterization and Reactivity of Group 4 Metallocene Bis(diphenylphosphino)acetylene ComplexesA Reactivity and Bonding Study
dataset
posted on 2013-11-20, 00:00 authored by Martin Haehnel, Sven Hansen, Kathleen Schubert, Perdita Arndt, Anke Spannenberg, Haijun Jiao, Uwe RosenthalA study of the coordination
chemistry of bis(diphenylphosphino)acetylene,
Ph<sub>2</sub>P–CC–PPh<sub>2</sub>, with selected
group 4 metallocenes is presented. By substitution of the alkyne in
complexes of the type Cp′<sub>2</sub>M(L)(η<sup>2</sup>-Me<sub>3</sub>SiC<sub>2</sub>SiMe<sub>3</sub>) (M = Ti, no L; M
= Zr, L = pyridine; Cp′ = substituted or unsubstituted bridged
or unbridged η<sup>5</sup>-cyclopentadienyl), the expected mononuclear
complexes Cp*<sub>2</sub>Ti(η<sup>2</sup>-Ph<sub>2</sub>PC<sub>2</sub>PPh<sub>2</sub>) (<b>4Ti</b>), (<i>rac</i>-ebthi)Ti(η<sup>2</sup>-Ph<sub>2</sub>PC<sub>2</sub>PPh<sub>2</sub>) (<b>5Ti</b>), and (<i>rac</i>-ebthi)Zr(η<sup>2</sup>-Ph<sub>2</sub>PC<sub>2</sub>PPh<sub>2</sub>) (<b>5Zr</b>) [ebthi = ethylenebis(tetrahydroindenyl)] were obtained. When [Cp<sub>2</sub>Zr] was used in the reaction of Cp<sub>2</sub>Zr(py)(η<sup>2</sup>-Me<sub>3</sub>SiC<sub>2</sub>SiMe<sub>3</sub>) with Ph<sub>2</sub>P–CC–PPh<sub>2</sub>, the dinuclear
complex [Cp<sub>2</sub>Zr(η<sup>2</sup>-Ph<sub>2</sub>PC<sub>2</sub>PPh<sub>2</sub>)]<sub>2</sub> (<b>6</b>) was formed
and isolated in the solid state. In solution, this complex is in equilibrium
with the very spectacular structure of complex <b>7b</b> as
the first example of such a highly strained four-membered heterometallacycle
of a group 4 metal, involving the rare R<sub>2</sub>PCCR′ fragment
in the cyclic unit. Both the stability and reactivity of heterodisubstituted
alkynes X–CC–X (X = NR<sub>2</sub>, PR<sub>2</sub>, SR, SiR<sub>3</sub>, etc.) themselves and also of their complexes
are of general interest. Complex <b>6</b> did not react with
a second [Cp<sub>2</sub>Zr] fragment to form a homobimetallic complex.
In contrast, for (<i>rac</i>-ebthi)Zr(η<sup>2</sup>-Ph<sub>2</sub>PC<sub>2</sub>PPh<sub>2</sub>) (<b>5Zr</b>)
this reaction occurs. In the reaction of complex <b>4Ti</b> with
the Ni(0) complex (Cy<sub>3</sub>P)<sub>2</sub>Ni(η<sup>2</sup>-C<sub>2</sub>H<sub>4</sub>) (Cy = cyclohexyl), C–P bond cleavage
of the alkyne ligand resulted in the formation of the isolated complex
[(Cy<sub>3</sub>P)Ni(μ-PPh<sub>2</sub>)]<sub>2</sub> (<b>11</b>). The structure and bonding of the complexes were investigated
by DFT analysis to compare the different possible coordination modes
of the R<sub>2</sub>P–CC–PR<sub>2</sub> ligand.
For compound <b>7b</b>, a <i>flip</i>-<i>flop</i> coordination of the phosphorus atoms was proposed. Complexes <b>4Ti</b>, <b>5Ti</b>, <b>5Zr</b>, <b>6</b>, and <b>11</b> were characterized by X-ray crystallography.
