Bis(pyridylimino)isoindolato (BPI) Osmium Complexes: Structural Chemistry and Reactivity

A series of osmium complexes with
monoanionic, meridionally coordinating
1,3-bis­(2-pyridylimino)­isoindolates (BPI) as spectator ligands has
been synthesized. Reaction of the dichlorido metal precursor [OsCl2(PPh3)3] with the lithiated BPI ligand
transfer reagent gave the chlorido complex [(tBu-BPIMe)­Os­(PPh3)2Cl] (2) which,
in turn, was reacted with lithium triethylborohydride to yield the
hydrido complex [(tBu-BPIMe)­Os­(PPh3)2H] (3). Treatment of complex 2 with thallium hexafluorophosphate under a nitrogen pressure
afforded the cationic dinitrogen complex [(tBu-BPIMe)­Os­(PPh3)2(N2)]­PF6 (4), which contains an end-on coordinated dinitrogen
molecule trans to the isoindolato nitrogen atom. To synthesize the
alkynyl complex [(tBu-BPIMe)­Os­(PPh3)2(CCPh)] (5), the chlorido
complex 2 was treated with lithium phenylacetylide. Complex 5 was subsequently converted quantitatively by addition of
one or two equivalents of HBF4 to the vinylidene complex
[(tBu-BPIMe)­Os­(PPh3)2(CCHPh)]­BF4 (6), and the
cationic species [(H-tBu-BPIMe)­Os­(PPh3)2(CCHPh)]­(BF4)2 (7), respectively; the latter being formed via
protonation of one imine nitrogen atom of the BPI ligand. Upon stirring,
a toluene solution of the chlorido complex 2 with benzyl
potassium, the four-membered metallacycle [(tBu-BPIMe)­Os­(PPh3)­(o-C6H4PPh2)] (8) was obtained, which reacted
with molecular hydrogen and phenyl acetylene to give the hydrido complex 3 and the acetylide complex 5, respectively.
Stirring of 8 with methyl acetylenedicarboxylate (DMAD)
yielded [(tBu-BPIMe)­Os­(DMAD)­(o-C6H4PPh2)] (9), while
treatment with carbon monoxide gave the acyl complex [(tBu-BPIMe)­Os­(o–C­(O)-C6H4PPh2)­(CO)] (10) by an insertion
of CO into the osmium carbon bond.