The synthesis and reactivity of out-of-plane
(Me8taa)MX2 and
(Me8taa)MX+ complexes
(M=
Zr, Hf; X= Cl, hydrocarbyl, NR2, OR) containing the
dianionic tetraaza-macrocycle ligand
octamethyldibenzotetraazaannulene
(Me8taa2-) are described. The
reaction of
[Li(Et2O)]2[Me8taa] (1) with MCl4(THF)2 yields
(Me8taa)MCl2 complexes
(2a, M = Zr; 2b, M = Hf).
Alkylation
of 2a,b with
LiCH2SiMe3 or LiMe in hydrocarbon solvents
yields
(Me8taa)M(CH2SiMe3)2
(3a, M = Zr; 4a, M = Hf) or
(Me8taa)MMe2 (3b, M =
Zr; 4b, M = Hf) complexes. Compound
3b rearranges by migration of a Me group from Zr to a
Me8taa imine carbon in coordinating
solvents. The reaction of
(Me8taa)H2 with the appropriate
ZrR4 compound yields
(Me8taa)Zr(CH2Ph)2 (3c) and
(Me8taa)Zr(CH2CMe3)2
(3d). The reaction of
(Me8taa)H2 and
Zr(NR2)4
yields
(Me8taa)Zr(NR2)2
(6a, R = Me; 6b, R = Et). Spectroscopic
data for (Me8taa)MX2
compounds 2, 3, 4, and 6
are consistent with cis,
C
2
v
-symmetric structures.
Dialkyl complexes
3 and 4 and bis(amide) complexes
6 react with chlorinated solvents
(1,1,2,2-tetrachloroethane,
CH2Cl2) to yield 2.
Compound 6a reacts with AlMe3 to afford the
heterobimetallic μ-amido
complex
[(Me8taa)Zr(μ-NMe2)2AlMe2][AlMe4]
(8), which does not undergo further reaction
to yield 3b. The reaction of dialkyl complexes
3 and 4a with HNR3
+
reagents yields cationic
[(Me8taa)MR][B(C6F5)4]
compounds (10a, M = Zr, R =
η2-CH2Ph; 10b, M = Zr, R
= CH2SiMe3; 10c, M = Zr, R =
CH2CMe3; 10d, M = Hf, R =
Me). These species form labile adducts
with PMe2Ph and THF. Cation 10a
polymerizes ethylene to a linear polymer with low
activity, while 10d is unreactive with ethylene.
10a reacts with
HOCMe2CH2CH2CHCH2
to yield the mononuclear alkoxide complex
(Me8taa)Zr(OCMe2CH2CH2CHCH2)+
(13), in
which the pendant alkene is not coordinated. 10a also
reacts with water or ethanol to yield
binuclear complexes
[{(Me8taa)Zr(μ-OR)}2]2+
(14a, R = H; 14b, R = Et). An X-ray
structural
analysis of 14a reveals that one of the
(Me8taa)Zr units has an unusual
inverted
conformation, and NMR data suggest that 14a,b
adopt similar structures in solution. 10d
reacts with 2-butyne to yield the double insertion product
[(Me8taa)Hf(CMeCMeCMeCMe2)]+
(15) and with MeC⋮CSiMe3 to afford
[(Me8taa)Hf(C(SiMe3)CMe2)]+
(16), while 10a and
10b are unreactive with these alkynes. 10a
and 10c react with terminal alkynes by
protonolysis to afford binuclear
[{(Me8taa)Zr(μ-C⋮CR)}2]2+
complexes (17a, R = Ph; 17b, R
= Pr). Complex 17a reacts reversibly with
PMe3 to yield the mononuclear cation
(Me8taa)Zr(C⋮CPh)(PMe3)+ (18a).
(Me8taa)MR+ species are less
reactive for alkene and alkyne
insertion than are Cp2MR+ species.
