Manganese(II) Alkyl/π-Allyl Complexes Resistant
to Ligand Redistribution
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Abstract
The reaction of [Li(THF)<sub>4</sub>][(Mn{C(SiMe<sub>3</sub>)<sub>3</sub>})<sub>3</sub>(μ-Cl)<sub>4</sub>(THF)] (<b>1</b>) with K(allyl<sup>TMS2</sup>) (allyl<sup>TMS2</sup> = 1,3-C<sub>3</sub>H<sub>3</sub>(SiMe<sub>3</sub>)<sub>2</sub>) afforded [(η<sup>3</sup>-allyl<sup>TMS2</sup>)Mn{C(SiMe<sub>3</sub>)<sub>3</sub>}{ClLi(THF)<sub>3</sub>}] (<b>2</b>). Attempted
sublimation of <b>2</b> yielded [(η<sup>3</sup>-allyl<sup>TMS2</sup>)Mn{C(SiMe<sub>3</sub>)<sub>3</sub>}(THF)] (<b>3</b>), indicating that <b>2</b> extrudes LiCl at elevated temperatures.
Additionally, LiCl
in <b>2</b> was displaced by reaction with PMe<sub>3</sub>,
quinuclidine, and dmap (dmap = 4-(dimethylamino)pyridine), providing
[(η<sup>3</sup>-allyl<sup>TMS2</sup>)Mn{C(SiMe<sub>3</sub>)<sub>3</sub>}(L)] (L = PMe<sub>3</sub> (<b>4</b>), quinuclidine
(<b>5</b>), dmap (<b>6</b>)). Treatment of PMe<sub>3</sub> complex <b>4</b> with BPh<sub>3</sub> yielded bright red [(allyl<sup>TMS2</sup>)Mn{C(SiMe<sub>3</sub>)<sub>3</sub>}] (<b>7</b>)
accompanied by a precipitate of Ph<sub>3</sub>B(PMe<sub>3</sub>).
Mixed alkyl/π-allyl manganese(II) complexes <b>2</b>–<b>7</b> are pyrophoric red solids with a high-spin d<sup>5</sup> configuration, and all were crystallographically characterized.
In the solid-state structures, the allyl ligands in <b>2</b>–<b>6</b> adopt a <i>syn</i>,<i>syn</i> configuration, whereas in base-free <b>7</b>, the allyl ligand
has a <i>syn</i>,<i>anti</i> configuration. Complexes <b>4</b>, <b>5</b>, and <b>7</b> sublimed cleanly (5
mTorr) at 70, 90, and 50 °C, respectively. Complex <b>4</b> exhibited a particularly favorable combination of volatility and
thermal stability, given that its appearance and powder X-ray diffraction
pattern were unchanged after 24 h in a sealed flask at 100 °C.
Compounds <b>2</b>–<b>7</b> are the first high-spin
d<sup>5</sup> mixed alkyl/allyl complexes, and <b>7</b> is the
first room-temperature-stable example of a mononuclear transition-metal
complex bearing only alkyl and allyl ligands
