PNP-Ligated Heterometallic Rare-Earth/Ruthenium Hydride
Complexes Bearing Phosphinophenyl and Phosphinomethyl Bridging Ligands
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Abstract
The reaction of rare-earth bis(alkyl)
complexes containing a bis(phosphinophenyl)amido pincer (PNP), LnPNP<sub><i>i</i>Pr</sub>(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub> (<b>1-Ln</b>, Ln = Y, Ho, Dy), with ruthenium trihydride phosphine
complexes, Ru(C<sub>5</sub>Me<sub>5</sub>)H<sub>3</sub>PPh<sub>3</sub> and Ru(C<sub>5</sub>Me<sub>5</sub>)H<sub>3</sub>PPh<sub>2</sub>Me,
gave the corresponding bimetallic Ln/Ru complexes bearing two hydride
ligands and a bridging phosphinophenyl (μ-C<sub>6</sub>H<sub>4</sub>PPh<sub>2</sub>-κ<i>P</i>:κ<i>C</i><sup>1</sup>, <b>2a-Ln</b>) or a bridging phosphinomethyl ligand
(μ-CH<sub>2</sub>PPh<sub>2</sub>-κ<i>P</i>:κ<i>C</i>, <b>2b-Ln</b>), respectively. Reaction of <b>2a-Y</b> with CO gas at 1 atm and at 20 °C in toluene-<i>d</i><sub>8</sub> afforded the complex <b>3a-Y</b>, which
bears a bridging pseudooxymethylene ligand (μ-OCH(<i>o</i>-C<sub>6</sub>H<sub>4</sub>)PPh<sub>2</sub>-κ<i>P</i>:κ<i>O</i>) and a bridging hydride ligand on the
Y/Ru centers. Computational studies by the DFT method suggested that <b>3a-Y</b> was formed in two steps: first the coordination of CO
(Δ<i>G</i>(B3PW91) = 22.9; Δ<i>G</i>(M06) = 14.9 kcal/mol) and migratory insertion of the Y–C<sub>6</sub>H<sub>4</sub> group (Δ<i>G</i><sup></sup><sup>⧧</sup>(B3PW91) = 13.3; Δ<i>G</i><sup>⧧</sup>(M06) = 16.7 kcal/mol), followed by a rapid intramolecular hydride
migration to the resulting acyl group. Complex <b>2b-Y</b> reacted
with organic nitriles (<i>t</i>BuCN, CH<sub>3</sub>CN, PhCN),
an aldimine (PhNCHPh), an isonitrile (<i>t</i>BuNC), and
group IX transition-metal carbonyls (M(C<sub>5</sub>Me<sub>5</sub>)(CO)<sub>2</sub>, M = Rh, Ir) via insertion of the reactive Y–CH<sub>2</sub> group into the unsaturated bond. These reactions afforded
complexes with new ligand scaffolds, including a bridging alkylideneamidophosphine
(<b>4b-Y</b>), an amidophosphine (<b>7b-Y</b>), an η<sup>2</sup>-iminoacylphosphine (<b>8b-Y</b>), and oxycarbenephosphine
(<b>9b-Y</b> and <b>10b-Y</b>) ligands at the binuclear
Y/Ru core. All of these reaction products were structurally characterized
by X-ray crystallography, NMR spectroscopy, and elemental analyses