Treatment of dilithium dialkyl compounds derived from dilithiation
of 3,3‘-dimethyl-2,2‘-bipyridine and its trimethylsilylated compound with
R‘2MCl2 afford axially asymmetric
metal
dialkyls R‘2M(LL) (R‘ = Me, LL =
(CH2C5H3N)2, M = Si
(2), Sn (3)) and R‘2M(L‘L‘) (R‘
= Me,
L‘L‘ =
(CHSiMe3C5H3N)2, M =
Si (4), Ge (5), Sn (6); R‘ = Ph, M
= Sn (7)), respectively.
Compounds 5−7 can react further with
W(CO)6 to form bimetallic complexes
R‘2M(L‘L‘)W(CO)4 (R‘ = Me, M = Ge (8), Sn
(9); R‘ = Ph, M = Sn (10)) via the
coordination of the two
pyridyl nitrogens. The variable-temperature 1H NMR
spectra of 2−4 have been recorded
to
investigate the fluxional behavior due to the torsional motion along
the C−C axis that joins
the two pyridine groups. X-ray structures of compounds
4, 6, and 9 have been
determined.
Metalation of 3,3‘-dimethyl-2,2‘-bipyridine and
its trimethylsilyl derivatives
(2-RCH2C5H3N)2
(R = H, SiMe3) using appropriate stoichiometries of
BunLi/tmeda yields the corresponding
mono- and dilithiated compounds. Deprotonation was found to occur
selectively at the
α-methyl carbon, as established by quenching the lithiated compounds
with Me3SiCl or D2O
and analyzing the products by NMR spectroscopy. The
C
2 molecular structure of the
dilithium compound
[{2-CH(SiMe3)C5H3N}2{Li(tmeda)}2]
(2a) has been determined by X-ray
structure analysis, which shows that each lithium atom is C,N-chelated
by the α-carbon
atom and the nitrogen atom of the other pyridine ring within the
molecule. The Li−Cα and
the Li−Npyridyl distances are 2.274(10) and
2.046(9) Å, respectively, and the torsion angle
between the pyridine rings is 50.7°. In the lithiation of the
gem-bis-silylated derivative
2-CH(SiMe3)2C5H3N-C5H3NCH3,
the anionic species
2-CH(SiMe3)2C5H3N-C5H3NC̄H2
undergoes a 1,6-silyl migration to form the α,α‘-bis-silylated anionic
species
[2-C̄H(SiMe3)C5H3N−C5H3NCH2(SiMe3)].
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