An alternative synthetic route to
η5-pentamethylcyclopentadienylgallium
(Me5C5Ga,
Cp*Ga, 1) via reductive dehalogenation of
(pentamethylcyclopentadienyl)diiodogallane
(Cp*GaI2, 2) is reported. In addition, the
behavior of compound 1 as a ligand in
transition
metal chemistry is examined. In the reaction of 1 with
Cr(CO)5(C8H14)
(C8H14 = cis-cyclooctene), Fe2(CO)9,
Fe(CO)3CHT (CHT = cycloheptatriene),
Co2(CO)8, and Ni(CO)4
the
new complexes Cr(Cp*Ga)(CO)5 (3),
Fe(Cp*Ga)(CO)4 (4),
Fe2(μ-Cp*Ga)3(CO)6
(5), Co2(μ-Cp*Ga)2(CO)6 (6), and
Ni4(μ-Cp*Ga)4(CO)6
(8), respectively, were obtained. They
were
characterized by analytical and spectroscopic methods; solid-state
structures were determined
by X-ray diffraction analysis. In the reaction of 1
with Ni(CO)4, the complex
Ni(Cp*Ga)(CO)3 (7) is an intermediate, which was
characterized by IR and NMR data. The
η5-bonding
mode within the Cp*Ga ligand is maintained, apart from one Cp*Ga unit
in 5 which exhibits
η3/η1-bonding. The cone angle of
η5-Cp*Ga is 112°, as determined on the basis of
structural
data of 3 and 4. Concerning the
σ-donor/π-acceptor properties, 1 is classified as
a
predominant electron donor.
The reaction of LiB(C 6 F 5 ) 4 with HCl in diethyl ether afforded the new oxonium acid [H(OEt 2 ) 2 ] + -[B(C 6 F 5 ) 4 ] -(1) as a colorless crystalline solid, which was characterized by NMR spectroscopy, by elemental analysis, and by single-crystal X-ray diffraction. The application of 1 is demonstrated in the generation of the complex {[η 5 -C 5 H 3 (CH 2 CH 2 NMe 2 )CMe 2 -η 5 -C 13 H 8 ]ZrCH 3 } + -[B(C 6 F 5 ) 4 ] -(3), containing an intramolecularly donorstabilized alkylzirconocene cation.
The reaction of decamethylsilicocene, (Me5C5)2Si, with the proton-transfer reagent Me5C5H2+B(C6F5)4- produces the salt (Me5C5)Si+ B(C6F5)4(2), which can be isolated as a colorless solid that is stable in the absence of air and moisture. The crystal structure reveals the presence of a cationic pi complex with an eta5-pentamethylcyclopentadienyl ligand bound to a bare silicon center. The 29Si nuclear magnetic resonance at very high field (delta = - 400.2 parts per million) is typical of a pi complex of divalent silicon. The (eta5-Me5C5)Si+ cation in 2 can be regarded as the "resting state" of a silyliumylidene-type (eta1-Me5C5)Si+ cation. The availability of 2 opens new synthetic avenues in organosilicon chemistry. For example, 2 reacted with lithium bis(trimethylsilyl)amide to give the disilene E-[(eta1-Me5C5)[N(SiMe3)2]Si]2(3).
on the occasion of his 60th birthdayWe recently reported the syntheses of the decamethylmetallocenes of germanium and tin starting from the bis(pentamethylcyclopentadieny1) dihalides of these elements."] We have now been able to synthesize the analogous silicon compound using this procedure. Reaction of dichloro[bis(pentamethylcyclopentadienyl)]silane lrZ1 with naphthalenelithium, naphthalenesodium, or naphthalenepotassium in tetrahydrofuran (THF) affords bis(pentamethylcyclopentadienyl)silanediyl (decamethylsilicocene) 2.l3l (MesCs) (MesCs)2Si (M = Li, Na, K)
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