2 research outputs found
Dicarbonyl{[2-(diphenylphosphino)ethyl]cyclopentadienyl} Group VI Metal Hydrides, Halides, and Anions: Precursors for Olefin Epoxidation Catalysts
No full textOxidative decarbonylation of (η<sup>5</sup>-C<sub>5</sub>R<sub>5</sub>)Mo(CO)<sub>3</sub>X and isoelectronic four-legged
piano-stool
Mo(II) precursors to homogeneous olefin epoxidation catalysts has
garnered significant attention as an alternative to organorhenium
oxides RReO<sub>3</sub>. An emerging theme has been the introduction
of donor-functionalized cyclopentadienyl ligands to tune catalyst
performance. However, the utility of the [2-(diphenylphosphino)ethyl]cyclopentadienyl
(Cp<sup>PPh</sup>) ligand under oxidative decarbonylation conditions
has not been explored. The application of Mo(VI) and W(VI) compounds
containing mono- and bidentate phosphine oxide ligands as epoxidation
catalysts suggests that screening MoX(CO)<sub>2</sub>(η<sup>5</sup>:η<sup>1</sup>-Cp<sup>PPh</sup>) as catalyst precursors
is a worthy objective. To this end, HM(CO)<sub>2</sub>(η<sup>5</sup>:η<sup>1</sup>-Cp<sup>PPh</sup>) (M = Cr (<b>1</b>), Mo (<b>2</b>), W (<b>3</b>)) were synthesized; the
hydrides <b>1</b> and <b>3</b> are of interest, since <b>2</b> is an established precursor for ionic hydrogenation catalysts.
Hydrogen–halogen exchange using <b>1</b>–<b>3</b> afforded MX(CO)<sub>2</sub>(η<sup>5</sup>:η<sup>1</sup>-Cp<sup>PPh</sup>) (M = Cr, X = I (<b>4</b>); M = Mo,
X = Cl (<b>5</b>), Br (<b>6</b>), I (<b>7</b>);
M = W, X = Br (<b>8</b>)), while deprotonation of <b>1</b>–<b>3</b> provided [K(18C6)][M(CO)<sub>2</sub>(η<sup>5</sup>:η<sup>1</sup>-Cp<sup>PPh</sup>)] (M = Cr (<b>9</b>), Mo (<b>10</b>), W (<b>11</b>)). Complexes <b>1</b> and <b>3</b>–<b>11</b> have been characterized
in solution and by X-ray crystallography. Treatment of <b>5</b>–<b>7</b> with <i>t</i>-BuOOH resulted in
active cyclooctene and 1-dodecene epoxidation catalysts, with conversion
curves and activities similar to those afforded by MoCl(CO)<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>R<sub>5</sub>) and MoR(CO)<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>R<sub>5</sub>) precursors
Group VI Metal Carbonyl Complexes of Bis((diphenylphosphino)methyl)diphenylborate and an Assessment of Their Utility for Template Ligand Syntheses
No full textZerovalent
group VI metal chemistry of anionic bis((diphenylphosphino)methyl)diphenylborate
(Ph<sub>2</sub>BP<sub>2</sub>) offers some surprises in comparison
to the chemistry of analogous complexes of neutral bidentate phosphines.
The enhanced donor ability of Ph<sub>2</sub>BP<sub>2</sub> relative
to related bis-PPh<sub>2</sub> ligands is confirmed by IR spectral
analysis of [ASN][M(CO)<sub>4</sub>(Ph<sub>2</sub>BP<sub>2</sub>)]
(ASN = 5-azoniaspiro[4.4]nonane; M = Cr, Mo, W). The mononitriles
[ASN][<i>fac</i>-M(CO)<sub>3</sub>(RCN)(Ph<sub>2</sub>BP<sub>2</sub>)] (M = Cr, R = Me; M = Mo, R = Et; M = W, R = Et) are useful
reagents for the introduction of sulfur dioxide and isocyanides to
the π-basic M(CO)<sub>3</sub>(Ph<sub>2</sub>BP<sub>2</sub>)
fragment. While the fundamental coordination chemistry of this anionic
fragment mostly mirrors that of its conventional neutral cousins,
the electronic impact of Ph<sub>2</sub>BP<sub>2</sub> leads to divergent
reactivity in some cases. For example, the sulfur dioxide complexes
[ASN][<i>mer</i>-M(CO)<sub>3</sub>(SO<sub>2</sub>)(Ph<sub>2</sub>BP<sub>2</sub>)] (M = Mo, W) are unreactive toward CH<sub>2</sub>N<sub>2</sub>, dramatically different from the case for <i>mer</i>-M(CO)<sub>3</sub>(SO<sub>2</sub>)(L<sub>2</sub>) (L<sub>2</sub> = dppm, dppe, dppp). The spectral data of [ASN][Mo(CO)<sub>3</sub>(CNC<sub>6</sub>H<sub>4</sub>(2-NH<sub>2</sub>))(Ph<sub>2</sub>BP<sub>2</sub>)] and [ASN][Mo(CO)<sub>3</sub>(CNCH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>)(Ph<sub>2</sub>BP<sub>2</sub>)], salts containing
the first anions of 2-aminophenyl isocyanide and 2-aminoethyl isocyanide,
respectively, indicate that the anionic M(CO)<sub>3</sub>(Ph<sub>2</sub>BP<sub>2</sub>) fragment may be more useful than neutral M(CO)<sub>3</sub>(dppe) for the π-back-bonding induced stabilization
of ligands prepared via template syntheses
