Manganese(II) Alkyl/π-Allyl Complexes Resistant to Ligand Redistribution

The reaction of [Li­(THF)4]­[(Mn­{C­(SiMe3)3})3(μ-Cl)4(THF)] (1) with K­(allylTMS2) (allylTMS2 = 1,3-C3H3(SiMe3)2) afforded [(η3-allylTMS2)­Mn­{C­(SiMe3)3}­{ClLi­(THF)3}] (2). Attempted
sublimation of 2 yielded [(η3-allylTMS2)­Mn­{C­(SiMe3)3}­(THF)] (3), indicating that 2 extrudes LiCl at elevated temperatures.
Additionally, LiCl
in 2 was displaced by reaction with PMe3,
quinuclidine, and dmap (dmap = 4-(dimethylamino)­pyridine), providing
[(η3-allylTMS2)­Mn­{C­(SiMe3)3}­(L)] (L = PMe3 (4), quinuclidine
(5), dmap (6)). Treatment of PMe3 complex 4 with BPh3 yielded bright red [(allylTMS2)­Mn­{C­(SiMe3)3}] (7)
accompanied by a precipitate of Ph3B­(PMe3).
Mixed alkyl/π-allyl manganese­(II) complexes 2–7 are pyrophoric red solids with a high-spin d5 configuration, and all were crystallographically characterized.
In the solid-state structures, the allyl ligands in 2–6 adopt a syn,syn configuration, whereas in base-free 7, the allyl ligand
has a syn,anti configuration. Complexes 4, 5, and 7 sublimed cleanly (5
mTorr) at 70, 90, and 50 °C, respectively. Complex 4 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 2–7 are the first high-spin
d5 mixed alkyl/allyl complexes, and 7 is the
first room-temperature-stable example of a mononuclear transition-metal
complex bearing only alkyl and allyl ligands.