Angewandte
Chemie
than the Cu···Cu separations in [Cu{N-
[2,25,28]
(
SiMe ) }] ,
2.6770(7) and 2.6937(7) . Con-
3
2
4
sistent with its bridging character, the average NiÀ
N bond length in 4 (1.916 ) is longer than those in
II
two-coordinate Ni
amides (1.803(9)–1.885-
[15,18–20]
I
(4) )
and in the three-coordinate Ni
amides (Ph P) NiN(SiMe ) (1.88(1) ), [{CHN-
[
29]
3
2
3 2
[30]
(
(
(
Dipp)} C]NiN(SiMe )
(1.865(2) ),
Bu PCH CH P Bu )Ni{N(H)Dipp}
and
(1.882-
2
3 2
t
t
2
2
2
2
[
31]
2) ).
Magnetic studies of 4 yielded a cT versus T plot
(
Figure S14, Supporting Information) indicative of
I
antiferromagnetic exchange between Ni centers.
Since the coordination of the four nickels is
essentially the same, the magnetic data were fit
with the Hamiltonian H = À2 J (S S + S S +
Figure 1. Thermal ellipsoid (50%) plots of Ni{N(SiMe ) } (THF) (2, left) and
3
2 2
Ni{N(SiMe ) } (py) (3, right). Selected bond lengths () and angles (8) for 2: Ni1–
3
2
2
2
N1 1.8646(2), Ni1–N2 1.8570(2), Ni1–O1 2.0143(2); N1-Ni1-N2 140.664(5), N1-
Ni1-O1 109.42(19), N2-Ni1-O1 109.78(19); 3: Ni1–N1 1.9394(4), Ni1–N2 1.9449-
1
2
2 3
S S + S S ), assuming a single exchange coupling
3
4
4 1
(4), Ni1–N3 1.9305(4), Ni1–N4 1.9314(4); N1-Ni1-N2 179.2607(3), N3-Ni1-N4
I
I
constant, J, for the Ni –Ni exchange. The best fit
1
79.0992(2).
[
12,23,24]
Co analogs.
The NiÀN (1.8646(2) and 1.8570(2) ) and
NiÀO (2.0143(2) ) bonds in 2 are shorter by 0.05 and 0.02
than the CoÀN and CoÀO bonds in its Co analog (Table S2).
However, the NiÀN bond lengths are similar to those in
[15,16]
Ni{N(Mes)BMes } (avg. 1.866 ).
The bis(pyridine)
2
2
complex 3 has nearly ideal square planar coordination at Ni
with interligand angles near 908. The NiÀN(SiMe ) bonds
3
2
(
1.9394(4) and 1.9449(4) ) are longer than those in 2 by
0
.08 , which is likely due to the higher coordination number
and increased steric crowding in 3. The NiÀN bonds are
[
16]
longer than those in Ni{N(Mes)BMes } , (avg. 1.866 ),
2
2
[21]
Ni{N(SiMe )Dipp}2 (1.8029(9) ),
{Ni(NPh ) } (avg.
2 2 2
and Ni{N(H)Ar}2
3
[14]
Figure 2. Thermal ellipsoid (50%) plot of [Ni{N(SiMe ) }] (4, without
1
.828 for terminal NiÀN bonds),
3
2
4
[17,18]
H atoms). Selected bond lengths () and angles (8): Ni1–N1 1.9127-
2), Ni1–N2 1.9151(2), Ni2–N2 1.9166(2), Ni2–N3 1.9189(2), Ni1···Ni2
(
Ar= terphenyl) (avg. 1.821 ).
(
Originally, Bürger and Wannagat reported that blood red
Ni{N(SiMe ) } ” (probably Ni{N(SiMe ) } (THF)) turned
2
1
.4328(4), Ni1···Ni1A 2.4347(5); Ni1-N2-Ni2 78.77(1), N1-Ni1-N2
68.80(4), N2-Ni2-N3 168.90(4).
“
3
2
2
3 2 2
[2]
black after a short time at room temperature. We also
found that 1 and 2 became black within 30 min at 258C, but
had greater stability as hydrocarbon solutions, whose red
colors persist for 2–3 days at 258C. A sample of 1 in toluene
decomposed over 4–5 weeks during which time the red
solution became black and precipitated black crystals that
were shown to be [Ni{N(SiMe ) }] (4) by X-ray crystallog-
1
was obtained with S = = and g = 2 for the Ni ions, and
i
2
À1
yielded J = À102(2) cm , a value typical for the exchange
pathways involved. The singlet ground state of 4 is well
reproduced by calculations at the CASSCF/NEVPT2 level of
theory (see Supporting Information), but there are low-lying
triplet and quintet states whose population at higher temper-
3
2
4
1
raphy. H NMR spectroscopy of 2 in C D indicated that
6
6
decomposition to 4 yielded a second product which is
atures accounts for the meff value of 2.70 m measured for 4 at
B
I
HN(SiMe ) based on the observed singlet at ca. 0.1 ppm
300 K. The only other Ni species similar to 4 is [Ni-
3
2
t
[32]
(
Figure S7, Supporting Information). Compound 4 can also
(NP Bu )] . However, the two complexes differ structurally
3 4
[25]
t
be synthesized from LiN(SiMe ) and NiCl (DME) in Et O.
and magnetically. The N-Ni-N angles in [Ni(NP Bu )] are
3 4
3
2
2
2
Workup of the dark amber solution afforded black crystals of
suitable for X-ray crystallography.
The structure of 4 (Figure 2) has four Ni ions in an
1808, and the Ni N core is folded along one of the N···N axes
4 4
4
to yield a Ni···Ni separation of 2.375(3) (ca. 0.06 shorter
I
t
than 4). The magnetic moment of [Ni(NP Bu )] at 278C is
3
4
approximate square plane and bridged by four -N(SiMe3)2
4.40 m and indicates a larger contribution from higher spin
B
ligands. A C axis bisects the N1 and N3 atoms, to give two
states.
2
crystallographically unique Ni1 and Ni2 sites on adjacent
edges of the Ni4 square. The N-Ni-N units deviate from
linearity such that the Ni nuclei are displaced toward each
other with Ni···Ni distances of 2.4328(4) and 2.4347(5) (cf.
sum of single bond covalent radii for two Ni atoms =
The ground state wave function for 4 is strongly multi-
configurational in character, as is evident from the CASSCF
CI-vector or from the CASSCF natural orbital occupation
numbers (Figure 3). Four electrons occupy four natural
orbitals, roughly one each, that are composed of a set of
nickel d-orbitals in four possible combinations. The natural
[
27]
2
.20 ). The Ni···Ni distances in 4 are ca. 0.25 shorter
Angew. Chem. Int. Ed. 2015, 54, 12914 –12917
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim