om7b00871_si_001.pdf (3.24 MB)
Syntheses of Heteroleptic Amidinate Strontium Complexes Using a Superbulky Ligand
journal contribution
posted on 2018-01-22, 14:19 authored by Benjamin Freitag, Jürgen Pahl, Christian Färber, Sjoerd HarderStrontium
complexes are presented with two different bulky amidinate
ligands (Am): tBuC(N-DIPP)2 (DIPP = 2,6-diisopropylphenyl), abbreviated here as tBuAmDIPP, and (p-tolyl)C(N-Ar‡)2 (Ar‡ = 2,6-Ph2CH-4-iPr-phenyl) abbreviated here as pTolAmAr‡. The amidine tBuAmDIPP-H was deprotonated by Sr[N(SiMe3)2]2 in benzene at 60 °C. Although the product, tBuAmDIPPSrN(SiMe3)2, could be characterized
by NMR, attempts to isolate it led to ligand scrambling via a Schlenk
equilibrium. Reaction of in situ prepared tBuAmDIPPSrN(SiMe3)2 with PhSiH3 gave PhH2SiN(SiMe3)2 and presumably
the intermediate tBuAmDIPPSrH, but the
latter is not stable and the homoleptic complex (tBuAmDIPP)2Sr was isolated and structurally
characterized. Deprotonation of the bulkier amidine pTolAmAr‡-H with Sr[N(SiMe3)2]2 needed forcing conditions, inevitably giving rise to
deprotonation of the Ph2CH substituent as well. Reaction
of pTolAmAr‡-H with the less bulky
and less basic Sr[N(SiHMe2)2]2, however,
gave the heteroleptic product pTolAmAr‡SrN(SiHMe2)2, which has been structurally characterized.
The latter was also at 60 °C stable toward ligand scrambling.
Reaction with PhSiH3 did give hydride exchange, but the
product pTolAmAr‡SrH decomposed
even at −30 °C. Instead, an amidinate complex with a deprotonated
Ph2CH substituent was isolated and structurally characterized
(7). The latter catalyzed the intramolecular alkene hydroamination.