With the aim of improving ionic and electronic conductivities of Li2ZnTi3O8 for high performance lithium ion battery applications, Li2Zn0.9M0.1Ti3O8 (M = Li+, Cu2+, Al3+, Ti4+, Nb5+, Mo6+) compounds are successfully...
We
report a new method to synthesize cobalt arylborohydrides and
incorporate the borane-amine unit into the coordination sphere of
a half-sandwich cobalt system based on activation of primary amines.
Insertion of BH3 into the Co(II)–C(aryl) bond of
the phosphinoaryl cobalt compound Cp*Co(2-C6H4PPh2) (1) provided the cobalt arylborohydride
Cp*Co(κ3-H,H,P-H3BC6H4PPh2) (2), which was
oxidized to the cationic cobalt(III) arylborohydride (2
+
). Complex 2
+
can be synthesized alternatively by oxidation of the cobalt(II)
aryl compound (1), followed by BH3 insertion
into the Co(III)-C(aryl) unit. This cationic borohydride enables alkyl
amines activation. As exemplified by the reaction with cyclohexylamine,
the phosphinoborohydride moiety in 2
+
undergoes B–N bond coupling with the two amine molecules
by release of 2 equiv of H2, leading to the borane-amino
cobalt(III) hydride (3) featuring a phosphinoborane-diamine
ligand, 1,2-Ph2PC6H4B(NHCy)2.
The reactions of [Cp*Co(μ-Cl)]2 with various aryl
lithium reagents (ArLi) were performed with a view to access bridging
diaryl dicobalt(II) complexes. Treatment of [Cp*Co(μ-Cl)]2 with 1 equiv of ArLi provided bridging aryl Co(II) complexes
with the formula [(Cp*Co)2(μ-Cl)(μ-Ar)] (Ar = C6H5
–, 1; p-CH3C6H4
–, 2). With 2 equiv of C6H5Li or p-CH3C6H4Li, the reaction provided triple-decker dicobalt(I) complexes
[(Cp*Co)2-μ-(η4:η4-biphenyl)] (3) and [(Cp*Co)2-μ-(η4:η4-dimethyl-biphenyl)] (4).
The biphenyl ligands in 3 and 4 underwent
dissociation resulting in formation of the more stable triple-decker
tricobalt complexes [(Cp*Co)3-μ-(η4:η4:η4-biphenyl)] (5) and [(Cp*Co)3-μ-(η4:η4:η4-dimethyl-biphenyl)] (6),
respectively. The bridging diaryl complex [(Cp*Co)2(μ-η1:η1-Ar)2] was proposed as the
intermediate in the formation of triple-decker dicobalt(I) complexes
through the reductive coupling of the aryl ligand, because the diaryl
cobalt(II) complex[(Cp*Co)2-μ-(o-CH3C6H4)2] (7) is stabilized by increased steric hindrance at the o-position of the aryl ligand.
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