Synthesis, molecular structure, and EPR analysis of the three-coordinate Ni(I) complex [Ni(PPh3)3][BF4]

Article abstract of DOI:10.1021/jp802462x

The compound [Ni(PPh₃)₃] [BF₄] ·BF₃·OEt₂ was isolated in crystalline form from the olefin oligomerization catalyst system Ni(PPh₃) ₄/BF₃·OEt₂ and structurally characterized by X-ray diffraction. The influence of vibronic coupling on the EPR parameters of three-coordinate metal complexes with a 3d⁹ electronic configuration was investigated within the framework of ligand field theory. Analytical expressions for g-tensor components and isotropic hyperfine coupling constants with ligand nuclei were obtained using first-order perturbation theory. It has been shown that the account of the vibronic interaction in the excited state predicts the existence of three-axial anisotropy of the g-tensor even at the level of first-order perturbation theory; two axes of the g-tensor located in a plane of three-coordinate structure can rotate about the main z axis when a compound is distorted by motion of ligands. It has been shown that in three points of the potential energy surface minimum, for which linear and quadric constants of the vibronic interactions have an identical signs, the HFS isotropic constant from one ligand is larger than HFS constants from the other two; for different vibronic constant signs the ratio between HFS constants varies on opposite. This theoretical researches are in the quality consent with experimental data for a three-coordinate Ni(I) and Cu(II) flat complexes.

Full text of DOI:10.1021/jp802462x

J. Phys. Chem. A 2008, 112, 12449–12455
12449
Synthesis, Molecular Structure, and EPR Analysis of the Three-Coordinate Ni(I) Complex
[Ni(PPh3)3][BF4]
V. V. Saraev,*,† P. B. Kraikivskii,† I. Svoboda,‡ A. S. Kuzakov,† and R. F. Jordan§
Irkutsk State UniVersity, Str. K. Marksa, 1, Irkutsk, 664003, Russia, Darmstadt UniVersity of
Technology, Petersenstr. 23, Darmstadt, 64287, Germany, and UniVersity of Chicago,
5735 S. Ellis AVe., Chicago, Illinois 60637
ReceiVed: March 20, 2008; ReVised Manuscript ReceiVed: September 30, 2008
The compound [Ni(PPh3)3][BF4] · BF3 · OEt2 was isolated in crystalline form from the olefin oligomerization
catalyst system Ni(PPh3)4/BF3 · OEt2 and structurally characterized by X-ray diffraction. The influence of
vibronic coupling on the EPR parameters of three-coordinate metal complexes with a 3d9 electronic
configuration was investigated within the framework of ligand field theory. Analytical expressions for g-tensor
components and isotropic hyperfine coupling constants with ligand nuclei were obtained using first-order
perturbation theory. It has been shown that the account of the vibronic interaction in the excited state predicts
the existence of three-axial anisotropy of the g-tensor even at the level of first-order perturbation theory; two
axes of the g-tensor located in a plane of three-coordinate structure can rotate about the main z axis when a
compound is distorted by motion of ligands. It has been shown that in three points of the potential energy
surface minimum, for which linear and quadric constants of the vibronic interactions have an identical signs,
the HFS isotropic constant from one ligand is larger than HFS constants from the other two; for different
vibronic constant signs the ratio between HFS constants varies on opposite. This theoretical researches are in
the quality consent with experimental data for a three-coordinate Ni(I) and Cu(II) flat complexes.
1. Introduction
of Jahn-Teller distortions for three-coordinate structures with
doubly degenerate electronic states is well appreciated.10–12
The trigonal planar three-coordinate complex [Ni(PPh3)3]+
has a doubly degenerate ground state, resulting in a Jahn-Teller
distortion that reveals itself by three-axial anisotropy of the
g-tensor (gX ) 2.07; gY ) 2.12; gZ ) 2.38) and magnetic
nonequivalence of the phosphine ligands (A(1P)X ) 8.1; A(1P)Y
) 6.4; A(1P)Z ) 6.1; A(2P)X,Y,Z < 3 mT).13,14 In our previous
work,13 the influence of ground-state vibronic interactions on
EPR parameters of three-coordinate 3d9-complexes was inves-
tigated to aid in interpreting the EPR spectra of [Ni(PPh3)3][BF4]
and related complexes. Assuming that the spin-orbital interac-
tion is smaller than the vibronic interaction, analytical expres-
sions that describe the relation between g-tensor components
(g < g|) were developed using first-order perturbation theory.
However, these expressions do not explain existence of three-
axial anisotropy of EPR parameters.
The monovalent oxidation state of nickel has received
increasing attention in recent years, in part due to its active role
in a number of catalytic processes including biochemical
reactions,1 nickel-mediated cross-coupling reactions to make
new C-C bonds,2 alkene oligomerization by heterogeneous3
and homogeneous nickel catalysts,4 and other processes.5 Ni(I)
complexes with phosphine ligands are thermally stable and can
display high activity in the oligomerization of unsaturated
hydrocarbons. For example, in the Ni(PPh3)4/BF3 ·OEt2 catalyst
system, prepared by mixture of the two components in toluene
solution, quantitative oxidation of Ni(0) to Ni(I) with formation
of cationic Ni(I) phosphine complexes was observed.4b–d At a
molar ratio of B/Ni ) 4/1, the major species formed in this
system is the 15-electron, 3-coordinate Ni(I) complex [Ni-
(PPh3)3][BF4], which displays high activity in styrene olig-
omerization.4c
In the present work, the complex [Ni(PPh3)3][BF4]·BF3 ·OEt2
was obtained in crystalline form from the Ni(PPh3)4/BF3 ·OEt2
catalyst system and characterized by X-ray diffraction. Ad-
ditionally, the influence of vibronic interactions on the EPR
parameters for three-coordinate 3d9 complexes has been inves-
tigated in more detail within the framework of the ligand field
theory and considering the electron-oscillator interactions both
in ground and in excited states. Analytical expressions for
g-tensor components and isotropic hyperfine coupling constants
with ligand nuclei were obtained using first-order perturbation
theory. These expressions were used to interpret the EPR spectra
of the [Ni(PPh3)3][BF4] and related species.
The characterization of Ni(I) species by EPR is hindered by
the lack of a strict theoretical description of EPR spectra for
3-coordinate, homoleptic d9 species. The EPR theory which is
advanced well for cubic structures6 and their derivatives7 cannot
be applied for three-coordinate compounds without corrections
as wave functions of a doubly degenerate state in three-co-
ordinate structures are bound by a spin-orbit interaction among
themselves.8
The influence of covalence on the g-tensor and hyperfine
interaction with ligands in heteroleptic three-coordinate Cu(II)
complexes has been studied in detail,9 but vibronic interactions
were not taken into account. On the other hand, the importance
2. Experimental Section
* Corresponding author. E-mail: saraev@admin.isu.ru.
† Irkutsk State University.
All operations were carried out under argon using Schlenk
techniques. Toluene and benzene (Merck) were distilled from
‡ Darmstadt University of Technology.
§ University of Chicago.
10.1021/jp802462x CCC: $40.75
2008 American Chemical Society
Published on Web 11/08/2008

12450 J. Phys. Chem. A, Vol. 112, No. 48, 2008
Saraev et al.
TABLE 1: Crystal Data for Complex
[Ni(PPh3)3]BF4 ·BF3 ·OEt2
empirical formula
C58H55B2F7NiOP3
formula mass
1073.29
crystal size
crystal system
space group
a (Å)
b (Å)
c (Å)
0.36 × 0.20 × 0.10
triclinic
j
P1
13.318(1)
13.946(1)
17.017(1)
76.880(9)
68.233(9)
83.948(8)
2857.9(3)
2
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
Dcalcd (g/cm3)
µ(Mo KR) (mm-1
temperature (K)
1.387
0.491
100
Figure 1. Three-coordinate complex of D3h symmetry.
)
data collection range (deg)
H
K
L
no. reflections measured
no. unique data
parameters
GoF on F2
R1 [I g 2σ(I)]
wR2 (all data)
4.09 g 2Θ g 26.37
-16 g h g 16
-17 g k g 17
-21 g l g 20
34892
3. Theoretical Analysis
Three-coordinate d9-complexes of D3h symmetry (Figure 1)
have the ground E(|x2 - y2 ,|xy ) and excited E(|yz ,|xz ) doubly
degenerate states.8
Molecular orbitals (MOs) can be represented as linear
combinations of metal d-orbitals and corresponding to them by
symmetry group orbitals of ligands.16 In the general form, the
MO on which there is unpaired electron is
11644 [R(int) ) 0.0878]
1.033
0.0845
0.2042
|Ψ ) a|d - b|ΦL
(1)
sodium/benzophenone prior to use. BF3(OEt2) (Merck) was
distilled over LiH before use. Ni(PPh3)4 was synthesized by a
literature method.15
where |d is d-orbital of the central atom; |ΦL is corresponding
by symmetry group orbital of ligands; a and b are coefficients
corresponding to the contribution to MO of combining orbitals.
Atom orbital (AO) overlapping is not taken into account, and
only σ-orbitals of ligands are considered which consist of
s-orbits of atoms from the first coordination sphere.
Infrared spectra were recorded on a Bruker FRA 106
spectrometer. EPR spectra were recorded on a CMS-8400
instrument (9.6 GHz) at 77 K.
The ligand group orbitals that combine only with the AOs
Crystal Structure Analysis. Crystal data are listed in Table
1. Data collection: a crystal was sealed under argon in a glass
capillary and mounted on an Oxford Excalibur diffractometer.
Reflections were measured (ω-scans) using graphite-monochro-
mated Mo KR radiation; Lp correction and absorption correction
based on ψ-scans were applied. The structure was solved by
direct and conventional Fourier methods. All non-hydrogen
atoms were treated with a riding model in idealized positions.
of a ground orbital doublet have the form:16
1
1
|Φx2-y2
)
(2σ1 - σ2 - σ3), |Φxy
)
(σ2 - σ3) (2)
√
√
2
6
the corresponding MOs can be presented as follows:
|Θ(0) ) a|x2 - y2 - b|Φx2-y2 |ε(0) ) a|xy - b|Φxy
|Θ(1) ) |xz , |ε(1) ) |yz (3)
,
,
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre.
Copies of the data [CCDC 682428] can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [Fax: (international) + 44(1223)336-033, E-mail:
deposit@ccdc.cam.ac.uk].
where |Θ(i) and |ε(i) are symmetrical and asymmetrical MO of
orbital doublets, respectively. MO of the excited state includes
only d-functions under symmetry conditions.
Vibronic Interaction. Doubly degenerate e-vibrations are
active in Jahn-Teller interactions in three-coordinate d9-
complexs having D3h symmetry (Figure 1).17
[Ni(PPh3)3][BF4]·BF3 ·OEt2. BF3 ·OEt2 (0.23 mL) was added
to a stirred solution of Ni(PPh3)4 (0.5 g) in toluene (10 mL)
over 10 min at 20°. The mixture was cooled to -10 °C,
maintained at this temperature for 3 h, and filtered. Pentane (5%
by volume) was added to the brown filtrate. The compound
[Ni(PPh3)3][BF4]·BF3 ·OEt2 was obtained in 73% yield as
yellow crystals from the filtrate by slow crystallization at -20
°C (5-7 days) and filtration at -20 °C. Calcd for
C58H55B2F7NiOP3 (1073.29): C 64.85, H 5.12, P 8.66. Found:
C 65.23, H 4.82, P 8.37. IR (cm-1) 3060 w (ν H-C)),
1580-1980 m (ν CdC), 1460 s (δas PPh), 1440 s (δas PPh),
1290 m (δs PPh), 1100-1000 s (ν BF4-), 890 vs (F1 PPh),
743 m (ν BF4-), 690 w (F1 PPh), 575 s (νas PC3), 520 m (νs
PC3). EPR (toluene, 77 K): gX ) 2.07; gY ) 2.12; gZ ) 2.38;
A(1P)X ) 8.1; A(1P)Y ) 6.4; A(1P)Z ) 6.1; A(2P)X,Y,Z < 3 mT.
The operator of the vibronic interaction is well-known:17
1
2
U ) ω(i)2(Q(Θi)2 + Q(εi)2)σˆ0 + V(i)(QΘ(i)σˆz + Qε(i)σˆx) +
ˆ (i)
W(i)[(Q(Θi)2 - Q(εi)2)σˆz - 2QΘ(i)Qε(i)σˆx] (4)
where σˆj are Pauli matrices:
0 1
1 0
1
0
1 0
0 1
σ
)
,
σ
)
, σˆ0 )
(
)
(
)
(
)
0 -1
ω(i) is the frequency of e(i)-vibrations; Q(ji) are symmetrized
coordinates of e(i)-vibrations; V(i) is the constant of a linear
vibronic bond; W(i) is the constant of a quadric vibronic bond;
I takes on values 0, 1 for the ground and excited states,
respectively.

Synthesis of [Ni(PPh3)3][BF4]·BF3 ·OEt2
J. Phys. Chem. A, Vol. 112, No. 48, 2008 12451
If it is assumed that the vibronic interactions in the ground
and excited states are independent of each another, the energies
of adiabatic potential surfaces and wave functions corresponding
to them can be written as17
gzz ) 2 +|Lz + 2Sz| +
gxx ) -|Lx + 2Sx| + + +|Lx + 2Sx|-
gxy ) -i( -|Lx + 2Sx| + - +|Lx + 2Sx|- )
gyx ) -|Ly + 2Sy| + + +|Ly + 2Sy|-
1
ε((i)(F, ) ) ω(i)2F(i)2 ( ε(i)
(5)
gyy ) -i( -|Ly + 2Sy| + - +|Ly + 2Sy|- )
(14)
2
ε(i) ) [V(i)2F(i)2 + 2V(i)W(i)F(i)3 cos 3 (i) + W(i)2F(i)4 1/2
|Ψ(-i) ) cos Ω(i)|Θ(i) - sin Ω(i)|ε(i)
]
(6)
(7)
Leaving in matrix elements (14) only members of the zero
and first order of smallness, it is possible to obtain the following
expressions for g-tensor components:
|Ψ(+i) ) sin Ω(i)|Θ(i) + cos Ω(i)|ε(i)
(8)
(9)
gzz ) 2(1 + 2a2 sin 2γ)
2λa2
(15)
V(i)sin (i) - W(i)F(i)sin 2
(i)
tan 2Ω(i) )
V(i)cos (i) + W(i)F(i)cos 2
(i)
gyy ) 2 cos 2γ -
gxx ) 2 cos 2γ -
[∆ cos2γ - ε(1)(cosγ - sin γ)2 ×
∆2 - ε(1)2
(i)
cos 2(Ω(0) + Ω(1))] (16)
where tan
) Q(εi)/Q(Θi), F(i)2 ) QΘ(i)2 + Q(εi)2
.
Extremes of adiabatic potential surfaces correspond to the
2λa2
∆2 - ε(1)2
[∆ cos 2γ + ε(1)(cosγ - sinγ)2 ×
(i)
points where cos
) ((1, -1/2) The upper sign in this
0
expression complies with the minimum at V(i)W(i) > 0 (
)
(i)
0
0°, 120°, 240°), the lower one at V(i)W(i) < 0 ( (i) ) 60°, 180°,
cos 2(Ω(0) + Ω(1))] (17)
0
300°).17 In these points, the wave function of the lower adiabatic
potential sheet |Ψ- turns into |Θ or |ε , symmetrical or
asymmetrical relative to the plane orthogonal to the distortion
direction, respectively.
2a2λε(1)
∆2 - ε(1)2
gxy ) gyx )
(cos γ - sin γ)2 sin 2(Ω(0) + Ω(1))
(18)
Spin-Orbital Interaction. The operator of the spin-orbital
interaction for the central atom has the form8
From here it is seen that the consideration of the vibronic
interaction in the excited state predicts the existence of three-
axial anisotropy of the g-tensor even at the level of first-order
perturbation theory, the g-tensor being of a nondiagonal form
(gxy ) gyx * 0) which indicates the variance of g-tensor main
axes in the plane (xy) with molecular axes x, y. Using standard
techniques,6 it is possible to obtain the main components of the
g-tensor in the plane (xy) and the relation between the molecular
coordinate system and the coordinate system in which the
g-tensor is diagonal:
HλS ) λLS
(10)
where λ is the spin-orbit coupling constant.
It is necessary to precisely solve the secular equation to allow
for this interaction in the ground state in the limits of the vibronic
doublet. Wave spin-orbital functions in the zero-order ap-
proximation have the following form at that
| ( 0 ) cos γ|Ψ(- ( i sin γ|Ψ+(
(11)
(0)
(0)
2λa2
∆2 - ε(1)2
g1,2 ) 2 cos 2γ -
[∆ cos 2γ ( ε(1)(sin γ - cos γ)2]
where tan 2γ ) ελ/ε(0) ελ ) -a2λ is the energy of the
spin-orbital interaction in the limits of the lower orbital doublet.
(19)
Perturbation theory can be used to take into account the
spin-orbit interaction between the ground and excited states.
Considering the first-order corrections, let us write the equation
2gxy
gyy - gxx
tan 2R )
) tan 2(Ω(0) + Ω(1))
(20)
where R is the turning angle of x and y axes in the plane (xy).
In expression (19) the functional dependence on Ω is absent
for g1,2. It indicates that the main axes of the g-tensor 1 and 2
will rotate in coordination about the z axis when a three-
coordinate complex is distorted by motion of ligands.
1
2
| ( ) | ( 0 - a2λ(sin γ - cos γ)[cos(Ω(0) + Ω(1)) -
i
1
i sin(Ω(0) + Ω(1))] ·
|Ψ--
-
|Ψ-+
(1)
(1)
(1)
∆ + ε(1)
[
]
∆ - ε
Figure 2 displays the dependence of the g-tensor main
components on the ratio of energies of the spin-orbit and
vibronic interactions (ελ/ε(0)). In order to diminish the number
of variable parameters, the following simplifications were
assumed: (i) energies of the vibronic interaction in the ground
and excited states are equal (ε(0) ) ε(1)); (ii) the factor a (the
portion of d-orbitals in the ground-state MO) is taken to equal
0.9, which is typical of coordination compounds;18 (iii) the
relation ε/∆ ) 0.29 reflects the fact that that under these
conditions the difference between g1 and g2 is maximal and
satisfies the condition of smallness of the vibronic interaction
in comparison with electronic. For example, when ε/∆ ) 0.10
the curves for g1 and g2 virtually merge into one line. It is seen
from Figure 2 that when the ελ/ε(0) f 0 components of the
g-tensor tend to the pure spin value (ge ) 2). Within the range
(12)
where ∆ is the energy gap between the ground and excited
orbital doublets.
Zeeman Interaction. The effect of magnetic field B on a
doubly spin-degenerate ground state |( can be described with
the well-known operator for the Zeeman interaction:6
Hz ) ꢀe(L+2S)B
where ꢀe is the Bohr magneton.
Nonzero components of the effective g-tensor of a paramag-
netic system are associated with angular mechanical moments
by the following relations:6
(13)

12452 J. Phys. Chem. A, Vol. 112, No. 48, 2008
Saraev et al.
Figure 3. Dependence of HFS isotropic constants on the angle (tan
2γ ) 0.3).
Figure 2. Dependence of g-tensor components on ratio of energies of
spin-orbital and the vibronic interactions (a ) 0.9; ∆/ε(i) ) 3.5).
0 < ελ/ε(0) < 0.5, all components of the g-tensor are larger than
the pure spin value.
Hyperfine Interaction (HFI) with Ligand Nucleus. The
Hamiltonian for the contact HFI between electronic and nuclear
magnetic moments has the following form6
8π
3
HSI ) P ′
δ(r )I S
(21)
∑
i
i
i
where P′ ) 2gNꢀeꢀN; δ(ri) is the Dirac delta function; Ii is spin
of the ith nucleus; S is electron spin; ri is a distance from the
ith nucleus to electron.
HFS isotropic constants are associated with the contact
Figure 4. Dependence of HFS isotropic constants on the ratio of
vibronic and spin-orbital interactions; li, mi, ni are numbers of ligands
alternately taking on values 1, 2, 3; i ) 1 under the condition VW >
interaction operator as follows:6
8π
( )
Aisio ) 2P ′ +
0 ( ) 0°, 120°, 240°) and i ) 2 under the condition VW < 0 (
60°, 180°, 300°).
)
δ r S +
(22)
( )
i
z
|
|
3
Isotropic constants for each of the ligands were found using
this expression:
two equivalent ligands remarkably change when the angle
slightly changes, while the constant from the third ligand stays
virtually invariant. Hence, one may expect the lines from
pairwise equivalent nuclei to broaden in the EPR spectrum.
Figure 4 displays the dependence of HFS isotropic constants
on the ratio of energies of the spin-orbital and vibronic
interactions in the ground state (ελ/ε(0)). It follows from the
curves that the more the vibronic interaction prevails over
spin-orbital, the larger differences in HFS isotropic constants
in potential energy minima. On the other hand, in the extreme
case when the spin-orbital interaction prevails over vibronic,
(ελ/ε(0)) f ∞, all these three constants will equal each other
16π
9
(1)
iso
A
)
P′b2(cos2 γ cos2 Ω(0) + sin2 γ sin2 Ω(0)
)
8π
3
1
6
A
)
P ′ b2 (cos2 γ cos2 Ω(0) + sin2 γ sin2 Ω(0)) +
(2)
iso
[
1
2
1
(cos2 γ sin2 Ω(0) + sin2 γ cos2 Ω(0))+
cos 2γ sin 2Ω(0)
]
√
2 3
8π
3
1
6
(3)
iso
A
)
P ′ b2 (cos2 γ cos2 Ω(0) + sin2 γ sin2 Ω(0)) +
[
1
2
1
(cos2 γ sin2 Ω(0) + sin2 γ cos2 Ω(0))-
cos 2γ sin 2Ω(0) (23)
and tend to the value A ) (8ꢀ2/9)πP′b2.
(i)
]
√
2 3
iso
It should be noted that, allowing for the accepted in the
(i)
From expressions (23) it follows that A are functions of
iso
present paper hierarchy of the spin-orbital and vibronic
interactions, formulas (23) may be used for the description of
experimental data only when the vibronic interaction prevails
over spin-orbital.
Ω(0), and hence, of the angle (eq 9)).
Figure 3 illustrates angular dependences of the isotropic HFS
constants with nuclei of ligands in the linear approximation of
the vibronic interaction. From the curves obtained it is seen
that in three points of the potential energy surface minimum,
) 0°, 120°, 240°, the HFS isotropic constant from one ligand
is larger than HFS constants from the other two, and in the
4. Results and Discussion
Table 2 contains selected geometrical parameters for
[Ni(PPh3)3][BF4]·BF3 ·OEt2, and literature data for several
similar three-coordinate Ni(0) and Ni(I) phosphine complexes.
As shown in Figure 5, the molecular structure of [Ni-
(PPh3)3][BF4]·BF3 ·OEt2 contains the salt [Ni(PPh3)3][BF4] and
1 equiv of the adduct BF3 ·OEt2. The [Ni(PPh3)3]+ cation has a
flat, approximately T-shaped geometry at Ni (the sum of all
points
) 60°, 180°, 300°, on the contrary, HFS isotropic
constants from two equivalent ligands are larger than from the
third ligand. Therefore, if the static Jahn-Teller effect is
realized, pairwise magnetic equivalence should be expected. The
fact draws attention that in the points of the potential surface
minimum both in the first and in the second case constants from

Synthesis of [Ni(PPh3)3][BF4]·BF3 ·OEt2
J. Phys. Chem. A, Vol. 112, No. 48, 2008 12453
TABLE 2: Selected Bond Lengths (Å) and Angles (deg) of Molecular Structure for Three-Coordinate Ni(I) and Ni(0)
Complexes
complex
bond
length (Å)
angle
size (deg)
ref
[Ni(PPh3)3]BF4 ·BF3 ·OEt2
Ni1-P1
Ni1-P2
Ni1-P3
Ni-Paverage
B1-F1
B1-F3
B1-F4
B1-F2
2.215(2)
2.209(2)
2.183(2)
2.202(5)
1.348(8)
1.359(8)
1.387(8)
1.398(9)
P1-Ni1-P2
P1-Ni1-P3
P2-Ni1-P3
∑(Li-Ni-Lj)
F1-B1-F2
F1-B1-F3
F1-B1-F4
F2-B1-F3
F2-B1-F4
F3-B1-F4
P1-Ni1-P2
P1-Ni1-P3
P2-Ni1-P3
∑(Li-Ni-Lj)
P4-Ni2-P5
P4-Ni2-P6
P5-Ni2-P6
∑(Li-Ni-Lj)
P1-Ni-P2
P1-Ni-Cl
P2-Ni-Cl
∑(Li-Ni-Lj)
P1-Ni-P2
P1-Ni-Cl
P2-Ni-Cl
∑(Li-Ni-Lj)
P1-Ni-P2
P1-Ni-N
107.00(6)
141.98(7)
110.91(6)
359.90(9)
106.6(6)
112.3(6)
111.9(6)
106.5(6)
107.6(6)
111.5(6)
121.2(1)
118.5(1)
120.2(1)
359.9(3)
118.0(1)
121.7(1)
120.3(1)
360.0(3)
111.52(2)
121.33(2)
126.98(2)
359.83(6)
114.94(2)
121.12(2)
123.56(2)
359.62(6)
107.0(2)
130.4(4)
122.5(4)
360.0(0)
this work
a
Ni(PPh3)3
Ni1-P1
Ni1-P2
Ni1-P3
Ni-Paverage
Ni2-P4
Ni2-P5
Ni2-P6
Ni-Paverage
Ni-P1
2.154(2)
2.148(2)
2.156(1)
2.152(8)
2.143(2)
2.144(2)
2.139(1)
2.142(1)
2.2091(6)
2.2012(6)
2.1481(6)
2.2052(1)
2.2536(5)
2.2393(5)
2.1666(6)
2.2465(0)
2.220(4)
2.213(4)
1.88(1)
19
19
25
26
27
b
Ni(PPh3)3
[(Ph3P)2NiCl]•THF
(Ph3P)2NiCl
Ni-P2
Ni-Cl
Ni-Paverage
Ni-P1
Ni-P2
Ni-Cl
Ni-Paverage
Ni-P1
(Ph3P)2Ni{N(SiMe3)}2
Ni-P2
Ni-N
P2-Ni-N
Ni-Paverage
2.216(9)
∑(Li-Ni-Lj)
angles ∑(Pi-Ni-Pj) ) 359.90(9)°). The largest difference in
Ni-P bond lengths is 0.032 Å and that in P-Ni-P bond angles
is 34.98(1)°. For comparison, the corresponding largest differ-
ences for Ni(PPh3)3, a diamagnetic Ni(0) complex that exists
as two geometrical isomers in a unit cell of single crystal,19 are
0.007(9) Å and 2.7(0)° for a-isomer and 0.005(1) Å and 3.7(0)°
for b-isomer. Apparently, the distortion from trigonal symmetry
in [Ni(PPh3)3]+ is caused by the Jahn-Teller effect which has
static character in the crystal. This conclusion is consistent with
ab initio and DFT calculations for [Au(PH3)3]+ (5d10).20
Calculations for the singlet ground state (1A1′) predict a trigonal
planar geometry (D3h) with the HOMO being the degenerate e′
antibonding Au-P character. Calculations for the lowest triplet
excited state (3E′′) predict a T-shaped geometry due to a
Jahn-Teller distortion.
The average Ni-P bond length in [Ni(PPh3)3]+ (2.202(5) Å)
is slightly greater than that in Ni(PPh3)3 (2.152(8) and 2.142(1)
Å for a-and b-isomers, respectively19). A similar trend in metal
- phosphorus bond lengths was observed for a large number of
phosphine complexes with an electron configurations ranging
from d1 to d10.21–24 The M-P bond lengthening upon going to
a higher oxidation state is usually ascribed to a reduction in
d-π* backbonding, the π* orbitals in this case being combina-
tions of the P-C 2ex,y MOs and the P 3d orbitals.21–23
2
2
orbital, which has a predominant 5dxy, 5dx -y contribution with
On the other hand, the average Ni-P bond length in
[Ni(PPh3)3]+ (2.202(5) Å) is slightly smaller than that in the
heteroleptic neutral complexes [(Ph3P)2NiCl]·THF (2.2052(1)
Å),25 (Ph3P)2NiCl (2.246(1) Å),26 and (Ph3P)2Ni{N(SiMe3)2}
(2.216(9) Å).27 The average length of the Ni-P bonds in all of
complexes listed in Table 2 is less than the Ni-P bond lengths
in tetrahedral four-coordinate Ni(I) complexes: (Ph3P)3NiCl
(2.2979(2) Å);25 [(Ph3P)3NiCl]·C7H8 (2.3055(5) Å);28 (Ph3P)3-
NiBr (2.315(6) Å);29 [(Ph3P)3NiJ]·0.5THF (2.2949(3) Å).30
EPR data for homoleptic d9 [Ni(PR3)3]+ complexes (R ) Ph,
Cy), and several heteroleptic Ni(I) and Cu(II) complexes whose
structures were established by X-ray diffraction, are listed Table
3. The EPR parameters for (Ph3P)2NiX complexes were
determined from spectra of these compounds in (Ph3P)2-
CuX·0.5C6H6 single crystals;31 data for the other complexes in
Table 3 were determined from spectra of frozen solutions.
According to Table 3, g-tensors are rhombic anisotropic for
all Ni(I) complexes, and the ratio g3 - g2 > g2 - g1 is generally
observed both for homoleptic and the majority of heteroleptic
complexes. There is generally good agreement between the
experimental values of a g-tensor for the considered compounds
Figure 5. Molecular structure of a unit cell for [Ni(PPh3)3]-
BF4 ·BF3 ·OEt2 crystal.

12454 J. Phys. Chem. A, Vol. 112, No. 48, 2008
Saraev et al.
ref
TABLE 3: EPR Data for Selected Three-Coordinate Ni(I) and Cu(II) Complexesa
complex
g1
g2
g3(z)
A1(P), mT
A2(P), mT
A3(z)(P), mT
[Ni(PR3)3]BF4
R ) Ph
2.07
2.10
2.12
2.17
2.38
2.40
8.1(P1), <3(P2,3)
6.4(P2,3), <3(P1)
6.4(P1), <3(P2,3)
6.1(P2,3), <3(P1)
6.1(P1), <3(P2,3)
6.0(P2,3), <3(P1)
13, 14
13
R ) Cy
(Ph3P)2NiX
X ) Cl
2.111
2.112
2.167
2.209
2.446
2.435
6.8(P1), 4.2(P2)
7.3(P1), 3.5(P2)
5.4(P1), 3.8(P2)
5.1(P1), 3.4(P2)
4.8(P1), 3.1(P2)
4.7(P1), 3.0(P2)
31
31
X ) Br
(N^N)MeNiL
L ) PCy3
L ) dppm
L ) CO
2.03
2.03
2.01
2.07
2.17
2.16
2.17
2.11
2.54
2.43
2.19
2.51
32
32
33
34
(N^N)t-BuNi(THF)
(N^N)MeCuX
X ) OC6H4OMe
X ) Cl
2.02
2.05
2.037
2.07
2.05
2.037
2.22
2.20
2.169
9.0(Cu)
12.6(Cu)
10.5(Cu)
1.4(N)
35
36
9, 36
0.8(Cu)
0.49(Cu)
1.0(N)
0.8(Cu)
0.97(Cu)
1.0(N)
X ) SCPh3
X ) SC6H3Me2
2.04
2.04
2.18
1.4(Cu)
1.4(Cu)
11.3(Cu)
9
a
and theoretically designed values of these parameters in a wide
range of energy ratio for spin-orbital and Jahn-Teller interac-
tions (Figure 2). One exception is (N^N)MeNi(CO), for which
the opposite ratio g3 - g2 < g2 - g1 is observed. Apparently,
in this case, the influence of the differences in the ligands
overrides the effects of the vibronic interaction. A first-order
Jahn-Teller effect is not present in (N^N)MeNi(CO).33
(N^N)MeCuX complexes (X ) Cl, SCPh3, SC6H3Me2),9,36 for
which g3 > g2 ) g1, are another exception.
The experimental EPR data for (Ph3P)2NiX obtained from
(Ph3P)2CuX·0.5C6H6 single crystal31 are useful for testing
theoretical constructions. It has been shown31 that the main axis
3(Z) of the g-tensor in a flat (Ph3P)2NiX complex is perpen-
dicular to the complex plane and to the main axes Y1-3 of the
HFS tensors of nonequivalent 31P nucleus. The chosen theoreti-
cal design (Figure 1) corresponds to the single-crystal EPR
data.31 The magnetic nonequivalence of the 31P nuclei in a
heteroleptic (Ph3P)2NiX complex is coordinated with geo-
metrical nonequivalence of phosphorus atoms and it is the proof
of vibronic interactions in heteroleptic complexes too.
Comparing calculated values for the g-tensor components
(Figure 2) with experimental values for three-coordinate com-
plexes, we come to the conclusion that the calculated values
correctly reproduce the experimental data at ελ/ε(0) in the range
from 0.05 to 0.5. The experimentally determined HFS constant
from PPh3 ligand substantially exceeds those from the other
two in homoleptic cationic [Ni(PPh3)3]+ complex, indicating
the static nature of the Jahn-Teller effect. In compliance with
theoretically found values for HFS constants, these points of
the minimum are characterized by the identical sign of linear
and quadric constants of the vibronic bond (V(i)W(i) > 0).
The theoretical expressions derived here can be used to
interpret the EPR spectra for other three-coordinate metal
complexes with a 3d9 electronic configuration. For example,
the g-tensor for [Ni(PCy3)3][BF4] has rhombic anisotropy also
(g1 ) 2.10; g2 ) 2.17; g3(z) ) 2.40); however, in this case the
HFS constant from the two equivalent 31P nucleus is greater
than that from the third 31P (A(2P)1 ) 6.4; A(2P)2 ) 6.1;
A(2P)3(z) ) 6.0; A(1P)1,2,3(z) < 3.0 mT).13 Hence, the linear and
quadric constants of the vibronic interactions for
[Ni(PCy3)3][BF4] have different signs (V(i)W(i) < 0).
5. Conclusion
The compound [Ni(PPh3)3][BF4]·BF3 ·OEt2 was isolated in
crystalline form from the olefin oligomerization catalyst system
Ni(PPh3)4/BF3 ·OEt2 and structurally characterized by X-ray
diffraction. The [Ni(PPh3)3]+ cation has a flat T-shaped geometry
at Ni. To understand the EPR spectra of [Ni(PPh3)3]+ and related
three coordinate d9 complexes, the influence of vibronic
interactions in both the ground and excited states on the EPR
parameters has been investigated within the framework of ligand
field theory. Having assumed that spin-orbit interactions are
less important than vibronic interactions, analytical expressions
for g-tensor components and isotropic hyperfine coupling
constants with ligand nuclei were obtained using first-order
perturbation theory. It has been shown that the account of the
vibronic interaction in the excited-state predicts the existence
of three-axial anisotropy of the g-tensor even at the level of
first-order perturbation theory; two axes of the g-tensor located
in a plane of three-coordinate structure can rotate about the main
z axis when a compound is distorted by motion of ligands. It
has been shown that, in three points of the potential energy
surface minimum, for which linear and quadric constants of the
vibronic interactions have an identical signs, the HFS isotropic
constant from one ligand is larger than HFS constants from the
other two; for different vibronic constant signs the ratio between
HFS constants varies on opposite. Results of theoretical
researches are in quality equal to experimental data for three-
coordinate Ni(I) and Cu(II) flat complexes.
Acknowledgment. This work was supported by the RFBR
(Russia) and CRDF (USA) (international grant No. RUC1-2862-
IR-07). We thank Dr. Ian Steele for assistance with the X-ray
crystallographic analysis. P.K. thanks DAAD for a research
stipend.

Synthesis of [Ni(PPh3)3][BF4]·BF3 ·OEt2
J. Phys. Chem. A, Vol. 112, No. 48, 2008 12455
(6) (a) Abragam A.; Bleaney, B. Electron Paramagnetic Resonance
of Transition Ions; Clarendon Press: Oxford, UK, 1970. (b) Wertz, J. E.;
Bolton J. R. Electron Spin Resonance. Elementary Theory and Practical
Applications; McGraw-Hill Book Co.: New York, 1972. (c) Carrington,
A.; McLachlan, A. D. Introduction to Magnetic Resonance; Chapman and
Hall: London, 1967. (d) Al’tshuler, C. A.; Kozirev B. M. Electron
Paramagnetic Resonance of Intermediate Group Elements; Science: Mos-
cow, 1972.
(7) (a) McGarvey, B. R. Can. J. Chem. 1975, 53 (16), 2498–2511. (b)
Nowlin, T.; Subramanian, S.; Kim, C. Inorg. Chem. 1972, 11, 2907–2912.
(c) Nishida, Y.; Sumita, A.; Kida, S. Bull. Chem. Soc. Jpn. 1977, 50 (9),
2485–2489. (d) Chacko, V. P.; Manoharan, P. T. J. Magn. Reson. 1974, 16
(1), 75–81. (e) Kalbacher, B. J.; Bereman, R. D. Inorg. Chem. 1973, 12,
2997–3000. (f) Murakami, Y.; Matsuda, Y.; Sakata, K. Inorg. Chem. 1971,
10, 1734–1738.
(8) Bersuker, I. B. Electronic Structure and Properties of Coordination
Compounds (in Russian); Khimiya: Leningrad, 1976.
(9) Randall, D. W.; George, S. D.; Holland, P. L.; Hedman, B.;
Hodgson, K. O.; Tolman, W. B.; Solomon, E. I. J. Am. Chem. Soc. 2000,
122, 11632–11648.
(10) Elian, M.; Hoffmann, R. Inorg. Chem. 1975, 14, 1058–1076.
(11) Komiya, S.; Albright, T. A.; Hoffmann, R.; Kochi, J. K. J. Am.
Chem. Soc. 1976, 98, 7255–7265.
Supporting Information Available: Crystal structure report
for PK5: C54H45NiP3 + C4H10OBF3 + BF4 + C7H8. This
material is available free of charge via the Internet at http://
pubs.acs.org.
References and Notes
(1) (a) Medina, M.; Williams, R.; Cammack, R. J. Chem. Soc., Faraday
Trans. 1994, 90 (19), 2921–2924. (b) James, T. L.; Cai, L.; Muetterties,
M. C.; Holm, R. H. Inorg. Chem. 1996, 35, 4148–4161. (c) Ge, P.; Riordan,
C. G.; Yap, G.-P. A.; Rheingold, A. L. Inorg. Chem. 1996, 35, 5408–5409.
(d) George, S. J.; Seravalli, J.; Ragsdale, S. W. J. Am. Chem. Soc. 2005,
127, 13500–13501. (e) Piskorski, R.; Jaun, B. J. Am. Chem. Soc. 2003,
125, 13120–13125. (f) Finazzo, C.; Harmer, J.; Bauer, C.; Jaun, B.; Duin,
E. C.; Mahlert, F.; Goenrich, M.; Thauer, R. K.; Doorslaer, S. V.; Schweiger,
A. J. Am. Chem. Soc. 2003, 125, 4988–4989. (g) Duin, E. C.; Cosper, N. J.;
Mahlert, F.; Thauer, R. K.; Scott, R. A. J. Biol. Inorg. Chem. 2003, V. 8
(1-2), 141–148. (h) Gu, W.; Gencic, S.; Cramer, S. P.; Grahame, D. A.
J. Am. Chem. Soc. 2003, 125, 15343–15351. (i) Craft, J. L.; Horng, Y.-C.;
Ragsdale, S. W.; Brunold, T. C. J. Am. Chem. Soc. 2004, 126, 4068–4069.
(j) Funk, T.; Gu, W.; Friedrich, S.; Wang, H.; Gencic, S.; Grahame, D. A.;
Cramer, S. P. J. Am. Chem. Soc. 2004, 126, 88–95. (k) Yang, N.; Reiher,
M.; Wang, M.; Harmer, J.; Duin, E. C. J. Am. Chem. Soc. 2007, 129, 11028–
11029. (l) Dey, M.; Telser, J.; Kunz, R. C.; Lees, N. S.; Ragsdale, S. W.;
Hoffman, B. M. J. Am. Chem. Soc. 2007, 129, 11030–11032. (m) Kieber-
Emmons, M. T.; Riordan, C. G. Acc. Chem. Res. 2007, 40, 618–625. (n)
Harmer, J.; Finazzo, C.; Piskorski, R.; Ebner, S.; Duin, E. C.; Goenrich,
M.; Thauer, R. K.; Reiher, M.; Schweiger, A.; Hinderberger, D.; Jaun, B.
J. Am. Chem. Soc. 2008, 130, 10907–10920.
(2) (a) Amatore, C.; Jutand, A. Organometallics 1988, 7, 2203–2214.
(b) Amatore, C.; Jutand, A.; Mottier, L. J. Electroanal. Chem. 1991, 306
(1-2), 125–140. (c) Amatore, C.; Jutand, A. J. Am. Chem. Soc. 1991, 113,
2819–2825. (d) Courtois, V.; Barhdadi, R.; Troupel, M.; Pe’rrichon, J.
Tetrahedron 1997, 53 (34), 11569–11576. (e) Amatore, C.; Jutand, A.;
Pe’rrichon, J.; Rollin, Y. Monatsh. Chem. 2000, 131 (12), 1293–1304. (f)
Budnikova, Y. H.; Pe’rrichon, J.; Yakhvarov, D. G.; Kargin, Y. M.;
Sinyashin, O. G. J. Organomet. Chem. 2001, 630 (2), 185–192. (g) Klein,
A.; Budnikova, Y. H.; Sinyashin, O. G. J. Organomet. Chem. 2007, 692
(15), 3156–3166.
(3) (a) Kazansky, V. B.; Elev, I. V.; Shelimov, B. N. J. Mol. Catal.
1983, 21 (1-3), 265–274. (b) Elev, I. V.; Shelimov, B. N.; Kazansky, V. B.
J. Catal. 1984, 89 (2), 470–477. (c) Barth, A.; Kirmse, R.; Stach, J. Z.
Chem. 1984, 24 (5), 195–196. (d) Cai, F. X.; Lepetit, C.; Kermarec, M.;
Oliver, D. J. Mol. Catal. 1987, 43 (1), 93–116. (e) Lepetit, C.; Kermarec,
M.; Oliver, D. J. Mol. Catal. 1989, 51 (1), 95–113. (f) Bogus, W.; Kevan,
L. J. Phys. Chem. 1989, 93, 3223–3226. (g) Ghosh, A. K.; Kevan, L. J.
Phys. Chem. 1990, 94, 3117–3221. (h) Bonneviot, L.; Olivier, D.; Che, M.
J. Mol. Catal. 1983, 21 (1-3), 415–430. (i) Sohn, J. R.; Shin, D. C. J.
Catal. 1996, 160 (2), 314–316. (j) Sohn, J. R.; Park, W. C. J. Mol. Catal.
1998, 133 (3), 297–301. (k) Cai, T. Catal. Today 1999, 51 (1), 153–160.
(l) Sohn, J. R. Catal. Today 2002, 73 (1-2), 197–209. (m) Sohn, J. R.;
Park, W. C.; Kim, H. W. J. Catal. 2002, 209 (1), 69–74. (n) Sohn, J. R.;
Park, W. C. Appl. Catal. A: Gen. 2003, 239 (1-2), 269–278.
(4) (a) Shmidt, F. K.; Saraev, V. V.; Larin, G. M.; Lipovich, V. G.
IzV. Akad. Nauk SSSR, Ser. Khim. 1974, No 1, 209. (b) Saraev, V. V.;
Shmidt, F. K. Russ. J. Coord. Chem. 1997, 23 (1), 40–52. (c) Saraev, V. V.;
Kraikivskii, P. B.; Annenkov, V. V.; Vilms, A. I.; Matveev, D. A.;
Danilovtseva, E. N.; Ermakova, T. G.; Kuznetsova, N. P.; Lammertsma,
K. Kinet. Catal. 2005, 46 (5), 712–718. (d) Saraev, V. V.; Kraikivskii, P. B.;
Matveev, D. A.; Vilms, A. I.; Zelinskiy, S. N.; Lammertsma, K. Kinet.
Catal. 2006, 47 (5), 699–703. (e) Saraev, V. V.; Kraikivskii, P. B.; Vilms,
A. I.; Zelinskii, S. N.; Yunda, A.Yu.; Danilovtseva, E. N.; Kuzakov, A. S.
Kinet. Catal. 2007, 48 (6), 778–784. (f) Wang, H. Y.; Meng, X.; Jin, G. X.
Dalton Trans. 2006, 7 (21), 2579–2585. (g) Otman, Ya. Ya.; Manulik, O. S.;
Flid, V. R. Kinet. Catal. 2008, 49 (4), 479–483.
(12) Burdett, J. K. Inorg. Chem. 1975, 14, 375–382.
(13) Saraev, V. V.; Kraikivskii, P. B.; Lazarev, P. G.; Myagmarsuren,
G.; Tkach, V. S.; Schmidt, F. K. Russ. J. Coord. Chem. 1996, 22 (9), 615–
621.
(14) Kraikivskii, P. B.; Saraev, V. V.; Matveev, D. A.; Zelinskii, S. N.;
Tkach, V. S. Russ. J. Coord. Chem. 2003, 29 (6), 431–434.
(15) Creaves, E. O.; Lock, C. J. L.; Mailtlis, P. M. Can. J. Chem. 1968,
46 (24), 3879–3891.
(16) Dyatkina, M. E. Basics of the Molecular Orbital Theory (in
Russian); Nauka: Moscow, 1975.
(17) Bersuker, I. B.; Polinger, V. Z. The Vibronic interactions in
Molecules and Crystals (in Russian); Nauka: Moscow, 1983.
(18) Kuska, H. A.; Rogers, M. T. Electron Spin Resonance of First Row
Transition Metal Complex Ions; Interscience: New York, 1968.
(19) Dick, D. G.; Stephan, D. W.; Campana, C. F. Can. J. Chem. 1990,
68, 628–632.
(20) Barakat, K. A.; Cundari, T. R.; Omary, M. A. J. Am. Chem. Soc.
2003, 125, 14228–14229.
(21) Orpen, A. G.; Connelly, N. G. J. Chem. Soc., Chem. Commun.
1985, 1310–1311.
(22) Orpen, A. G.; Connelly, N. G. Organometallics 1990, 9, 1206–
1210.
(23) Davies, M. S.; Aroney, M. J.; Buys, I. E.; Hambley, T. W.; Calvert,
J. L. Inorg. Chem. 1995, 34, 330–336.
(24) Berning, D. E.; Noll, B. C.; DuBois, D. L. J. Am. Chem. Soc. 1999,
121, 11432–11447.
(25) Ellis, D. D.; Spek, A. L. Acta Crystallogr. I 2000, 56 (9), 1067–
1070.
(26) Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Whittell, G. R. Acta
Crystallogr. I 2002, 58 (3), m160–m161.
(27) Bradley, D. C.; Hursthouse, M. B.; Smallwood, R. J.; Welch, A. J.
J. Chem. Soc., Chem. Commun. 1972, 872–873.
(28) Cassidy, J. M.; Whitmire, K. H. Acta Crystallogr. I 1991, 47, 2094–
2098.
(29) Mealli, C.; Dapporto, P.; Sriyunyongwat, V.; Albright, T. A. Acta
Crystallogr. I 1983, 39, 995–996.
(30) Eckert, N. A.; Riordan, C. G.; Yap, G. P. A. Acta Crystallogr. (E)
2006, 62, m1766–m1767.
(31) Nilges, M. J.; Barefield, E. K.; Belford, R. L.; Davis, P. H. J. Am.
Chem. Soc. 1977, 99, 755–760.
(32) Bai, G.; Wei, P.; Stephan, D. W. Organometallics 2005, 24, 5901–
5908.
(33) Eckert, N. A.; Dinescu, A.; Cundari, T. R.; Holland, P. L. Inorg.
Chem. 2005, 44, 7702–7704.
(34) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
Lachicotte, R. J. J. Am. Chem. Soc. 2002, 124, 14416–14424.
(35) Jazdzewski, B. A.; Holland, P. L.; Pink, M.; Young, V. G.; Spencer,
D. J. E.; Tolman, W. B. Inorg. Chem. 2001, 40, 6097–6107.
(36) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121,
7270–7271.
(5) (a) Dahm, C. E.; Peters, D. G. J. Electroanal. Chem. 1996, 406
(1-2), 119–129. (b) Gennaro, A.; Isse, A. A.; Maran, F. J. Electroanal.
Chem. 2001, 507 (1-2), 124–134. (c) Guyon, A. L.; Klein, L. J.; Goken,
D. M.; Peters, D. G. J. Electroanal. Chem. 2002, 526 (1-2), 134–138. (d)
Ischay, M. A.; Mubarak, M. S.; Peters, D. G. J. Org. Chem. 2006, 71,
623–628. (e) Esteves, A. P.; Ferreira, E. C.; Medeiros, M. J. Tetrahedron
2007, 63 (14), 3006–3009.
JP802462X