Coordination Modes, Oxidation, and Protonation Levels of 2,6-Pyridinediimine and 2,2′:6′,2′-Terpyridine Ligands in New Complexes of Cobalt, Zirconium, and Ruthenium. An Experimental and Density Functional Theory Computational Study

Article abstract of DOI:10.1021/acs.inorgchem.8b01949

The syntheses and molecular and electronic structures of the following complexes have been established by single crystal X-ray crystallography and UV-vis-NIR spectroscopy, and verified by density functional theory calculations (DFT B3LYP): [(η⁵-Cp)₂Zr^IV(tpy^2-)]⁰ (S = 0) 1, [(η⁵-Cp)₂Zr^IV(^OMepdi^2-)]⁰ (S = 0) 2, [Co^II(^OMepdi^?)(η²-BH₄)]⁰ (S = 0) 4, [Ru^II(^OMepdi-H)Cl(PPh₃)₂]⁰ (S = 0) 5, cis-[Ru^II(^OMepdi⁰)Cl₂(PPh₃)]⁰ (S = 0) 6, and [Ru^II(η²-^OMepdi⁰)(η²-^OMepdi-H)₂]⁰ (S = 0) 7, with (tpy⁰) being neutral 2,2′:6′,2′-terpyridine, (tpy^?)^1- its radical anion, (tpy^2-)^2- its dianion; (^OMepdi⁰) neutral 2,6-bis(4-methoxyphenylmethylimine)pyridine, (^OMepdi^?)^1- its radical anion and (^OMepdi^2-)^2- its dianion; (^OMepdi-H)^1- represents the deprotonated form of the (^OMepdi⁰) ligand where deprotonation takes place at the meta-position of the pyridine ring. Density functional theory calculations using the B3LYP functional were performed, establishing geometry optimized molecular and electronic structures. The structural parameter Δ = [(average distance C_py-C_imine) - (av. distance C_py-N_py + av. distance C_imine-N_imime)] is introduced for the characterization of the oxidation level of pdi (and analogously of tpy) ligands of M(pdi) (or M(tpy)) motifs for first row transition metals. The M(L⁰) unit in second and third row low-valent transition metal ion complexes may exhibit significant -backdonation M → L⁰ structural effects.

Full text of DOI:10.1021/acs.inorgchem.8b01949

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Coordination Modes, Oxidation, and Protonation Levels of 2,6-
́
Pyridinediimine and 2,2′:6′,2′-Terpyridine Ligands in New
Complexes of Cobalt, Zirconium, and Ruthenium. An Experimental
and Density Functional Theory Computational Study
†
†
Mei Wang,†,‡ Christina Romelt, Thomas Weyhermuller, and Karl Wieghardt*,†
̈
̈
‡Key Laboratory of Marine Chemistry, Theory and Technology, Ministry of Education, College of Chemistry and Chemical
Engineering, Ocean University of China, Quingdao, 266100, PR China
†Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, D-45470 Mu
̈
lheim an der Ruhr, Germany
S
* Supporting Information
ABSTRACT: The syntheses and molecular and electronic structures of the
following complexes have been established by single crystal X-ray crystallography
and UV−vis-NIR spectroscopy, and verified by density functional theory
calculations (DFT B3LYP): [(η5-Cp)2ZrIV(tpy2−)]0 (S = 0) 1, [(η5-Cp)2ZrIV-
(
OMepdi2−)]0 (S = 0) 2, [CoII(OMepdi•)(η2-BH4)]0 (S = 0) 4, [RuII(OMepdi-
H)Cl(PPh3)2]0 (S = 0) 5, cis-[RuII(OMepdi0)Cl2(PPh3)]0 (S = 0) 6, and
[RuII(η2-OMepdi0)(η2-OMepdi-H)2]0 (S = 0) 7, with (tpy0) being neutral
2,2′:6′,2′-terpyridine, (tpy ) its π radical anion, (tpy2−)2− its dianion; (OMepdi0)
neutral 2,6-bis(4-methoxyphenylmethylimine)pyridine, (OMepdi•)1− its radical
anion and (OMepdi2−)2− its dianion; (OMepdi-H)1− represents the deprotonated
form of the (OMepdi0) ligand where deprotonation takes place at the meta-position
•
1−
́
of the pyridine ring. Density functional theory calculations using the B3LYP functional were performed, establishing geometry
optimized molecular and electronic structures. The structural parameter Δ = [(average distance Cpy−Cimine) − (av. distance
Cpy−Npy + av. distance Cimine−Nimime)] is introduced for the characterization of the oxidation level of pdi (and analogously of
tpy) ligands of M(pdi) (or M(tpy)) motifs for first row transition metals. The M(L0) unit in second and third row low-valent
transition metal ion complexes may exhibit significant π-backdonation M → L0 structural effects.
C−C bonds shrink, whereas the four C−N bonds expand with
increasing reduction. We have recently introduced the single
structural parameter Δ as defined in eq 1 in Scheme 1.1−3 As
shown in Figure 1 Δ varies in a linear fashion with the charge n
of the (tpy)n and (pdi)n ligands in five ZnII(tpy)n and
ZnII(pdi)n complexes.
These Δcalc values are obtained from geometry optimizations
of density functional theory (DFT) (B3LYP) calculations.
Both correlations hold for first row transition metal ions but
not necessarily for second and third row metal ions when
structurally significant π-backdonation effects M → N must be
taken into account.
INTRODUCTION
■
It is now well established that the neutral, potentially
tridentate, N-heterocyclic ligands 2,2′:6′,2′-terpyridine (tpy0)
and the pyridine-2,6-diimines (pdi0) are redox-active li-
gands.1−7 Both neutral forms possess two unoccupied π*-
orbitals which can successively accept up to four electrons
generating (a) a π-radical monoanion (SL = 1/2), (b) a
diamagnetic or triplet dianion, (c) a π-radical trianion (SL = 1/
2), and (d) a diamagnetic tetraanion. The two π* orbitals are
antibonding with respect to the two imine (3, 3′) and two
pyridine C−N bonds (1, 1′) but bonding with respect to the
two Cimine−Cpyridine bonds (2, 2′) in the pdi ligand and,
similarly, the tpy ligand (Scheme 1). In other words, the two
In this work we describe how dramatically the electronic
structures of isostructural complexes of first, second, and third
row transition metal ions can vary within the series
[Cp2M(tpy)]0 (M = Ti, Zr, Hf), and, similarly, [Cp2M(pdi)]0
(M = Ti, Zr, Hf). We also compare the electronic structures of
the series [M(tpy)(η2-BH4)]0 (M = Co, Rh, Ir) and
[M(pdi)(η2-BH4)]0 (M = Co, Rh, Ir).
Scheme 1. Definition of the Structural Parameter Δ
Received: July 12, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Chart 1. Complexes and Ligands
Figure 1. Linear dependences of calculated Δcalc values of (a)
ZnII(pdin) complexes (black squares) and b) ZnII(tpyn) complexes
(red triangles) with the charge n of the respective (tpy)n and (pdi)n
4
ligands. [ZnII(pdi)n(C5H4N-NMe2)]2+,1+,0
,
[ZnII(tpy)n-
(NMe3)2]2+,1+,0,1−,2‑4 and [ZnII(pdi)n(NMe3)]1−,2− (this work).
Finally, this work shows the possibility of generating singly
and doubly deprotonated forms at the meta- and para-positions
of the pyridine rings of the (pdi) ligands.
RESULTS
■
Examples of this type of complexation are shown in Scheme
Synthesis and Characterization of Complexes. Com-
plexes 1−7 of this work are shown in Chart 1. Two neutral
complexes [(η5-Cp)2Zr(L0)]0 1 and 2 have been synthesized
by combining [(η5-Cp)2ZrCl2]0 in tetrahydrofuran (thf)
solution with sodium amalgam beads under strictly anaerobic
conditions (Ar) and the tridentate (L0) ligands 2,2′:6′,2′-
terpyridine (tpy0) and 2,6-bis-[1-(4-methoxyphenyl-
iminoethyl)]pyridine (OMepdi0), eq 2.
2 where the Os species8 is doubly deprotonated in the meta-
Scheme 2. Structures of (a) (pdi0) and (pdi-H)1−, (b)
[{Os(H)3(PR3)2}2(pdi-2H)2−]0, and (c) [FeII(pdi2−)(pdi-
H)Na(thf)2]0
THF
0
0
[(η5‐Cp)2ZrIVCl2]0 + L + 2Na ⎯⎯⎯→⎯ [(η5‐Cp)2Zr(L )]0
(2)
+ NaCl
where L0 = (tpy0) 1; (OMepdi0) 2.
13
Complexes [CoII(tpy•)(η2-BH4)]0 3 and [CoII(OMepdi•)-
(η2-BH4)]0 4 have been prepared from methanol solutions of
CoCl2 and 1 equiv of (tpy0) or (OMepdi0) affording green solids
of [CoII(tpy0)Cl2]0 and [CoII(OMepdi0)Cl2]0.14,15 The reaction
of these complexes with 1 equiv of Na[BH4] in THF under
strictly anaerobic conditions affords black-purple crystals of 3
and 4, respectively.
CH3OH
0
0
[CoIICl2]0 + L + 2Na ⎯⎯⎯⎯⎯⎯⎯→ [CoII(L )Cl2]0
(3)
0
[CoII(L )Cl2]0 + 2Na[BH4] → [CoII(L)(η2‐BH4)]0
+ 0.5B2H6 + 0.5H2
(4)
where L0 = (tpy0) 3; (OMepdi0) 4.
The reaction of [RuII(PPh3)3Cl2]0 with 1 equiv of Na[BH4]
in THF solution (Ar atmosphere) is known to yield the
hydrido complex [RuII(H)Cl(PR3)3]0,10−12 which in turn
reacts with 1 equiv of the ligand (OMepdi0) affording the
neutral complex [RuII(OMepdi-H)Cl(PPh3)2]0 5 in 70%
isolated yield, eqs 5 and 6.
positions (pdi-2H)2− and in the Fe,Na dinuclear complex9
where the para-position of one pyridine ring is deprotonated.
These meta- and para-deprotonations require C,H-activa-
tion.10−12 Note that the pdi0 oxidation level of the
deprotonated forms does not change.
Here we have synthesized two new complexes 5 and 7
(Chart 1) containing N,C-coordinated, bidentate (OMepdi-
H)1− ligands. We compare their electronic structures with that
of cis-[RuII(OMepdi0)Cl2(PPh3)]0 6.
THF
−
[RuIICl2(PPh3)3]0 + BH4 ⎯⎯⎯→⎯ [RuII(H)Cl(PPh3)3]0
+ Cl− + 0.5B2H6
(5)
(6)
[RuII(H)Cl(PPh3)3]0 + (OMepdi0)
→ [RuIICl(OMepdi‐H)(PPh3)2]0 + PPh3 + H2
B
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Interestingly, from the reaction of [RuII(PPh3)3Cl2]0 with 1
equiv of the ligand (OMepdi0) in a THF/methanol mixture (1:1
−
vol) but without the activator BH4 the neutral, octrahedral
complex cis-[RuII(OMepdi0)Cl2(PPh3)]0 6 has been obtained in
∼60% yield, eq 7.
[RuIICl2(PPh3)3]0 + (OMepdi0) → cis
‐[RuII(OMepdi0)Cl2(PPh3)]0
(7)
Finally, the addition of an excess of KC8 and KOH (∼3
equiv each) to the above THF/methanol solution and heating
to reflux for 48 h under anaerobic conditions affords purple
crystals of [RuII(η2-OMepdi-H)2(η2-OMepdi0)]0 7.
Complexes 1−7 possess a singlet ground state as has been
established by temperature-dependent (3−300 K) magnetic
susceptibility measurements on solid samples (SQUID).
Electronic spectra of new complexes have been recorded in
the range 350−1600 nm in methanol, tetrahydrofuran, or
toluene solution at ambient temperature. The spectra are
shown in Figure 2 (for 1 and 2) in Figure 3 (for
Figure 4. Electronic spectra of [RuII(OMepdi-H)Cl(PPh3)]0 5 (black),
[RuII(OMepdi0)Cl2(PPh3)]0 6 (red), and [RuII(η2-OMepdi-H)2-
(η2-OMepdi0)]0 7 (green) in THF solution at 20 °C.
Table 1. Electronic Spectra of Complexes (300−1600 nm,
20 °C)
complex
solvent
toluene
λmax, nm (ε, M−1 cm−1
)
1
2
3
4
402 (1.75 × 104), 700 (0.3 × 104), 1290
(1.25 × 104), 1480 (1.75 × 104)
toluene
THF
320 (3.0 × 104), 490 (1.8 × 104), 700 (sh),
1250 (0.75 × 104)
320 (sh), 425 (1.3 × 104), 558 (1.1 × 104),
1000 (sh), 1300 (1.9 × 104)
THF/
CH3OH
CH3OH
397 (3.7 × 104), 490 (3.7 × 104), 700 (sh),
780 (2.3 × 104), 1200 (sh)
[CoII(OMepdi0)
Cl2]0
323 (2.4 × 104), 426 (1.8 × 104), 544
(0.3 × 104), 618 (0.1 × 104)
5
6
7
THF
320 (3.3 × 104), 520 (1.5 × 104), 650 (sh
,0.75 × 104), 800 (sh,0.3 × 104)
THF
360 (sh, 2.7 × 104), 450 (1.1 × 104), 495
(1.2 × 104)
THF
400 (sh), 540 (0.9 × 104), 820 (0.1 × 104)
Figure 2. Electronic spectra of [(η5-Cp)ZrIV(tpy2−)]0 1 (black) and
[(η5-Cp)2ZrIV(OMepdi2−)]0 2 (red) in toluene solution at 20 °C.
(tpy•)1− π radical anions, and their corresponding singlet
dianions pdi2− and tpy2−. These bands are absent in the
spectrum of [CoII(pdi0)Cl2]0 (S = 3/2) containing a neutral
OMepdi0 ligand. The spectra of 5 and 7 each containing an η2-
coordinated (η2-OMepdi-H)1− ligand and 6 with a neutral
(
OMepdi0) ligand also lack transitions >900 nm.
Crystal Structure Determinations. Table S1 summarizes
crystallographic details of the structure determinations.
Crystals of 1 consist of neutral molecules of [(η5-
Cp)2ZrIV(tpy2−)]0 and uncoordinated, disordered thf solvent
molecules which have been removed from the final refinement
cycles by using the program Platon/Squeeze.17
Figure 5 (top) shows the structure of the neutral complex 1:
there are two η5-coordinated cyclopentadienyl anions and a
tridentate terpyridine dianion bound to a central ZrIV ion. The
structure of the tpy2− exhibits a small static disorder of one
terminal pyridine ring which has not been possible to resolve
by a split atom model. The anisotropic thermal parameters of
the carbon atoms (C(13) to C(17)) of one-half of the tpy2−
ligand are significantly larger than those of the corresponding
C-atoms of the other half (C(2) to C(7)). This indicates that
the N,N′,N′-coordinated tpy2− ligand is in fact not quite planar
and that the Zr(tpy) moiety is not C2v symmetric.
The C−C bonds in the two terminal pyridine rings display
distinct short−long−short−long bond alternation (see Scheme
3) due to the dearomatization (reduction) of these rings. The
two Cpy−Cpy bonds between the terminal and central pyridine
are among the shortest reported for M(tpy) units at 1.411(8)
Figure 3. Electronic spectra of [CoII(OMepdi0)Cl2]0 (black),
[CoII(OMepdi•)(η2-BH4)]0 4 (red), [CoII(tpy•)(η2-BH4)]0 3 (green)
in MeOH, THF, and THF solution at 20 °C, respectively.
[CoII(pdi0)Cl2]0, [CoII(OMepdi•)η2-BH4)]0, and [CoII(tpy•)-
(η2-BH4)]0), and in Figure 4 (for [RuII(OMepdi-H)Cl(PPh3)]0
5, cis-[RuII(OMepdi0)Cl2(PPh3)]0 6, and [RuII(η2-OMepdi-H)2-
(η2-OMepdi0)]0 7). The spectrum of [Co(tpy0)Cl2]0 has been
reported.16
Table 1 summarizes the observed transitions. The spectra of
1, 2, 3, and 4 display characteristic intense (ε > 104 M−1 cm−1)
transitions in the near-infrared region (∼800−1600 nm) which
are assigned to π,π* transitions of coordinated (pdi•)1−,
C
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 3. Structures and Selected Bond Distances (Å) of
(a) Uncoordinated (tpy0) and (pdi0) Ligands, (b) the
ZrIV(tpy2−) Unit in 1, and (c) the ZrIV(OMepdi2−) Unit in 2
Figure 5. Structures of 1 (top) and 2 (bottom) at 30% and 50%
probability ellipsoids, respectively.
and 1.417(8) Å. This is also typical for a highly reduced
character of the (tpy) ligand (Δexp ≈ 0.02). In contrast, the two
C−N bonds of the central pyridine ring are long (av. 1.414(7)
Å), approaching C−N single bond distances. In summary, we
interpret these structural parameters as indication of an
asymmetrically bound tpy2− dianion. The two Zr−Nt bonds
of the terminal pyridines are also not identical at 2.307(4) and
2.383(4) Å (the Zr−Nc bond distance to the central pyridine is
the shortest at 2.159(4) Å).
[CoII(pdi0)Cl2]18 it is in the range 0.165−0.190 Å, indicating
in both cases the presence of a neutral (tpy0) and a (pdi0)
ligand, respectively.
Figure 6 shows the structure of neutral [CoII(OMepdi•)(η2-
BH4)]0 (4). Scheme 4 compares selected bond lengths in the
Co(tpy•) and Co(OMepdi•) units (see also Table S2). In 4 the
The structure of the neutral complex 2 is shown in Figure 5
(bottom). It consists also of an (η5-Cp)2ZrIV-moiety and an
N,N′,N′′-coordinated (OMepdi) ligand which has the character-
istic C−C and C−N bond distances of a closed-shell dianion
(
OMepdi•)1− ligand is symmetrically coordinated (C2v); no
disorder problems have been identified. The arithmetic mean
value of the two Cpy−Cimine bonds at 1.436(2) Å, the average
Cimine−Nimine bond length at 1.325(2) Å and the av. Cpy−Npy
bond distance at 1.372(2) Å indicate an oxidation level of a
(pdi•)1− π-radical anion; the Δexp value of 0.088 Å is in
reasonable agreement with this notion (Figure 1).
(
OMepdi2−)2−. This pdi2− ligand is also asymmetrically
coordinated (Scheme 3). Here, no static disorder problems
are detected: The C(9)−N(10) bond at 1.333(1) Å is shorter
than its (C2)−N(1) counterpart at 1.360(1) Å, and the former
exhibits more CN double bond character than the latter.
The central pyridine ring is again dearomatized (short−long
alternating C−C bond lengths). Thus, the crystallographic data
support a description of the structure as [(η5-Cp)2ZrIV-
The structures [RuII(OMepdi-H)Cl(PPh3)2]0 (5), cis-
[RuII(OMepdi0)Cl2(PPh3)]0 (6), and [RuII(η2-OMepdi-H)2-
(η2-OMepdi0)]0 (7) are shown in Figure 7, panels a−c,
respectively.
(
OMepdi2−)]0 with Δexp = 0.026 Å and an asymmetrically
The five-coordinate, neutral complex 5 possesses a slightly
distorted trigonal bipyramidal structure where two (PPh3)
groups occupy axial positions; the bidentate N,C-bound anion
η2-(OMepdi-H)1− together with a chloride ion is in the
equatorial plane. Scheme 5 summarizes selected bond
distances (experimental and DFT calculated) of the
RuII(OMepdi-H) unit. Its Δexp value of 0.156 Å suggests that
the oxidation level remains the same as in a protonated, neutral
ligand (OMepdi0).
coordinated (OMepdi2−) dianion (Zr−Nt 2.385(1) and
2.303(1) Å, Zr−Nc 2.154(1) Å).
The structure of [CoII(tpy•)(η2-BH4)]0 (3) has been
determined previously by X-ray and neutron scattering
crystallography.13 The experimental Δexp values of 0.063 and
0.066 Å, respectively, are in excellent agreement with the
notion of a (tpy•)1− radical anion.1−3 We note that the average
Δexp parameter for [CoII(tpy0)Cl2]0 is 0.145 Å,14 and for
D
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 6. Structure of 4 at 50% probability ellipsoids.
Scheme 4. Structures and Selected Bond Distances (Å) of
the CoII(tpy•) Unit in 3 (top) and CoII(OMepdi•) Unit in 4
(bottom)
Figure 7. Structures of 5 (top), 6 (middle), and 7 (bottom) at 50%
probability ellipsoids.
The structure of the neutral, octahedral complex 6 (Figure
7) consists of a RuII(OMepdi0)-unit, two Cl− ions in cis-position
relative to each other and a (PPh3) ligand. Three previously
reported structures of this type exhibit an average Δexp value of
0.122 Å.19,20 The corresponding trans-isomers are also known;
seven structures have been reported (av. Δexp = 0.129
Å).19,21−23 Scheme 6 summarizes selected bond distances of
the tridentate, neutral (OMepdi0) ligand in 6 with a Δexp value of
0.128 Å. As shown below, the rather low Δexp values are a
consequence of some RuII → (pdi0) π-backdonation.
Scheme 5. Structure and Selected Experimental (red) and
Calculated (blue) Bond Distances (Å) of N−C-Coordinated
(
OMepdi-H) Ligand in 5
The complex 7 (Figure 7) contains neutral, octahedral
molecules with two bidentate, N,C-coordinated (OMepdi-H)1−
anions and one, also bidentate but N,N′-coordinated, neutral
(η2-OMepdi0) ligand: [RuII(η2-OMepdi-H)2(η2-OMepdi0)]0 7. The
central Ru ion possesses a low spin + II oxidation state.
Scheme 7 summarizes metrical data of bond distances in
both ligands. Interestingly, the Δexp values for both types of η2-
coordinated (pdi) ligands are within experimental error
identical at 0.15 0.01 Å, which indicates that both ligands
have the same oxidation level.
E
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 6. Structure and Selected Experimental Bond
Distances (Å) of the RuII(OMepdi0) Unit in 6
Table 2. Summary of Δexp and Δcalc Values of Selected
Complexes
complex
Δ
exp, Å
Δ
calc, Å
ref
this
[(η5-Cp)2ZrIV(tpy2−)]0 1
(S = 0)
[(η5-Cp)(η1-Cp)TiIII(tpy•)]0
0.021
0.023
0.083
0.019
0.030
0.122
0.024
0.077
0.101
0.085
0.062
work
this
work
this
work
this
work
this
work
this
work
13
(S = 1)
c
[(η5-Cp)(η1-Cp)HfIV(tpy2−)]0
(S = 0)
[(η5-Cp)2ZrIV(OMepdi2−)]0 2
0.026
(S = 0)
[(η5-Cp)2TiIII(η2-OMepdi•)]0
(S = 1)
Scheme 7. Structures and Selected Experimental Bond
Distances (Å) of the RuII(η2-pdi-H) (top) and RuII(η2-pdi0)
unit in 7
c
[(η5-Cp)(η4-Cp)
HfIV(OMepdi2−)]0 (S = 0)
[CoII(tpy•)(η2-BH4)]0 3
[CoII(OMepdi•)(η2-BH4)]0 4
[RhI(tpy0)(η2-BH4)]0
[IrI(tpy0)(η2-BH4)]0
0.063 (X-ray) 0.066
(neutron)
0.088
this
work
this
work
this
work
25
c
c
[RhI(xylpdi0)(η2-BH4)]0
[IrI(xylpdi0)(η2-BH4)]0
0.100
0.099
0.070
this
work
[PdII(tpy0)(η1-BH4)]1+
[PdII(pdi0)(η1-BH4)]1+
0.125
0.168
0.158
0.133
0.138
0.136
this
work
this
work
this
work
this
work
19,
21−23
19,
21−23
8
8
[RuII(η2-OMepdi-H)Cl
(PPh3)2]0 5
0.152
0.128
0.132
0.140
0.087
cis-[RuII(OMepdi0)Cl2
(PPh3)]0 6
trans-[RuII(xylpdi0)
Cl2(PMe3)]0
trans-[RuII(iPrpdi0)
Cl2(PPh3)]0
c
cis-[OsII(tolpdi0)Cl2(PiPr3)]0
0.093
0.164
a
[RuII(η2-OMepdi0)(η2-OMe
0.157
pdi-H)2]0 7
b
0.154
0.158
8
a
b
Average Δvalues for N,N′-coordinated (OMepdi0) ligands; Δvalue
c
for the N,C-coordinated (OMepdi0−H)1− ligand. For 3rd row
transition metal complexes, the geometry optimization convergence
criteria were slightly loosened (TolE 5e-5, TolRMSG 1e-3, TolMaxG
3e-2, TolRMSD 2e-2, TolMaxD 4e-2).
DFT (B3LYP) Calculations. In order to obtain a better
understanding of the electronic structures of complexes 1−7,
we have performed a series of DFT calculations with the
B3LYP functional for geometry optimizations, employing
experimental X-ray data as a starting point.24 Table 2
summarizes the Δexp and Δcalc values of these complexes and,
in addition, of two reference compounds from the literature.
In 2001 Nitschke and Tilley26 reported the synthesis and
crystal structure of diamagnetic [(η5-Cp)2Zr(bpy)]0 (S = 0)
(bpy = 2,2′-bipyridine) and discuss the nature of the N,N′-
coordinated (bpy) ligand from the observation of regular bond
alternations and “partial” dearomatization of both pyridine
rings as originating from the donation of electron density from
a ZrII center (4d2) into antibonding π* levels of the neutral
(bpy0) unit: [(η5-Cp)2ZrII(bpy0)]0. As we have shown
subsequently from DFT (B3LYP) calculations27 an electronic
structure description as [(η5-Cp)2ZrIV(bpy2−)]0 (S = 0) is the
correct formulation (Δexp = 0.003 Å; Δcalc = 0.005 Å). Its
HOMO possesses only 23% Zr d but 72% bpy character. The
Zr−N bonds are quite covalent with, possibly, some π-
donation of electron density ZrIV ← N. Thus, the (η5-Cp)2ZrIV
unit (4d0) is a π-acid and the closed-shell dianion (bpy2−)2− is
a good π-donor ligand.
Interestingly, the first row transition metal analogue [(η5-
Cp)2Ti(bpy)]0 (S = 0) has also been synthesized and
structurally characterized.28 Its electronic structure has been
elucidated by DFT (B3LYP) calculation27 and shows an open-
shell diradical [(η5-Cp)2TiIII(bpy•)]0 (S = 0). A broken
symmetry (BS(1,1)) calculation [BS(a,b): a and b stand for
the number of unpaired electrons at the metal and the ligand,
respectively] for an open-shell (S = 0) species is 9 kcal/mol
lower in energy than the corresponding closed shell singlet.
The Δexp and Δcalc values of 0.042 and 0.037 Å, respectively,
are in excellent agreement with the presence of a π-radical
anion (bpy•)1−. The HOMO (spin up) possesses ∼2% Ti-d,
and the HOMO (spin down) has 89% Ti-d-character.
In contrast to experiments the closed-shell optimized
geometries of the Zr complexes 1 and 2 show the presence
of symmetrically coordinated Zr(η3-tpy) and Zr(η3-pdi)
moieties, respectively. It is remarkable that in spite of these
small structural differences the Δexp and Δcalc values are nearly
identical (see Table 2); they indicate the presence of (tpy2−)2−
F
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
and (OMepdi2−)2− dianions. The very small structural differ-
ences between calculated and experimental structures may be
because the experimental data are derived from solid-state
single crystals, whereas the calculated structures represent gas-
phase structures. There are five unoccupied 4d orbitals,
characteristic for a central ZrIV ion in 1 and 2. The two
HOMOs are predominantly ligand-based orbitals (∼9% Zr-d-
character). Therefore, we describe their electronic structures as
closed-shell singlet speciesno BS(1,1) solutions have been
The corresponding hypothetical hafnium complex
[(Cp)2Hf(tpy)]0 also exhibits η5,η1-coordination of the Cp
ligands. However, the electronic ground state is found to be S
= 0 (closed shell, [(η5-Cp)(η1-Cp)HfIV(η3-tpy2−)]0) with Δcalc
0.019 Å, in close resemblance to the Zr complex. The S = 1
excited state lies 6 kcal/mol higher in energy than the ground
state.
For the hypothetical molecule [(Cp)2Ti(OMepdi)]0, the
geometry optimization also yields a triplet ground state,
which is 13 kcal/mol more stable than the closed shell singlet
(S = 0) and 6.9 kcal/mol more stable than the open shell (BS
1,1 S = 0) solution.
found. A significant structural contribution of ZrIV
(heterocycle2−) π-donation has also not been identified.
←
In the following we present our DFT calculations of the
corresponding hypothetical titanium and hafnium analogues of
1 and 2, namely, [(Cp)2Ti(tpy)]0, [(Cp)2Ti(OMepdi)]0,
[(Cp)2Hf(tpy)]0, and [(Cp)2Hf(OMepdi)]0, all of which have
not been synthesized to date. In all cases we have geometry
optimized the structures of the (S = 1) and (S = 0) states
(open shell, closed shell, and BS(1,1)). The geometry
optimizations of [(Cp)2Ti(tpy)]0 in its closed shell (S = 0)
state, and the open shell (BS 1,1 S = 0) and (S = 1) states
reveal an unexpected structural change: the (S = 1) state is the
ground state which is 5.6 kcal/mol more stable than the
BS(1,1), S = 0 solution, and 8.2 kcal/mol more stable than the
closed shell S = 0 solution. Figure 8 shows the structure of the
Figure 9 shows the structure of the (S = 1) ground state
which possesses two η5-coordinated Cp− ligands, but the
(
OMepdi•)1− is only η2-coordinated and has an uncoordinated
imine arm: [(η5-Cp)2TiIII(η2-OMepdi•)]0 (S = 1). The excited S
= 0 state possesses a different structure with one (η2-Cp)1−,
one (η3-Cp)1− monoanion, and a tridentate (OMepdi2−)2−
dianion: [(η2-Cp)2TiIV(η3-OMepdi2−)]0. The Hf analogue
exhibits a closed shell (S = 0) ground state (Δcalc = 0.024
Å), yielding [(η5-Cp)(η4-Cp)HfIV(OMepdi2−)]0.
Using BS(1,1) DFT calculations, we have previously shown
that the electronic structure of [Co(tpy)(η2-BH4)]0 (S = 0)
(3), which has been synthesized and crystallographically
characterized by X-ray and neutron diffraction,13 is best
described as [CoII(tpy•)(η2-BH4)]0 with a central low spin
CoII ion (d7, SCo= 1/2) coupled antiferromagnetically to a
(tpy•)1− π-radical anion.1−3 Here the BS(1,1) solution is 5
kcal/mol lower in energy than the closed shell solution. The
Δ
exp value of 0.066 Å (neutron data) is close to the Δcalc value
of 0.077 Å from the geometry optimized structure. Similar
calculations for complex 4 reveal the same electronic
properties, also with a 5 kcal/mol more stable BS(1,1)
solution. The calculated Mulliken spin population displays 0.81
electrons at the low spin CoII ion and 0.88 electrons at the
(
OMepdi•)1− radical.
In contrast, for hypothetical [RhI(tpy0)(η2-BH4)]0 (S = 0)
and its (also hypothetical) iridium analogue [IrI(tpy0)(η2-
BH4)]0 (S = 0), we found only closed shell singlet solutions.
The same is true for [RhI(xylpdi0)(η2-BH4)]0 which has been
synthesized and structurally characterized (X-ray)25 as well as
its hypothetical Ir analogue [IrI(OMepdi0)(η2-BH4)]0 (S = 0).
Interestingly, the structural parameters Δexp (and Δcalc) are all
in the narrow range 0.062−0.100 Å, which could be typical for
an open shell singlet with π-radical anions and low spin RhII
and IrII. However, this cannot be the case because attempts to
find energetically low lying BS(1,1) solutions converge to
closed shell solutions. Here we encounter a case where the
Figure 8. Geometry optimized structure of the (S = 1) ground state of
hypothetical [(η5-Cp)(η1-Cp)TiIII(η3-tpy•)]0.
ground state which contains one η5-coordinated Cp− and one
η1-bound Cp− as well as a tridentate (tpy•)1− π-radical anion.
Thus, the structure is best described as [(η5-Cp)(η1-Cp)-
TiIII(η3-tpy•)]0 (S = 1). Δcalc of 0.083 Å is in excellent
agreement with this assignment. The excited state singlet
structure with a Δcalc of 0.045 Å is in accord with a structure
[(η5-Cp)(η2-Cp)TiIV(η3-tpy2−)]0 (S = 0).
Figure 9. Geometry optimized structure of the (S = 1) ground state of hypothetical [(η5-Cp)2TiIII(η2-OMepdi•)]0 (left) and of the closed-shell (S =
0) excited state [(η2-Cp)(η3-Cp)TiIV(η3-OMepdi2−)]0 (right).
G
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
observed structural ligand parameters alone do not allow an
unambiguous assignment of the oxidation level of the ligand or
metal ion. The closed shell calculations show that the neutral
forms (tpy0) and (pdi0) experience a structurally significant π-
Δexp value of 0.087 Å.8 Here the closed shell DFT calculation
yields a Δcalc value of 0.093 Å in good agreement with
experiment. No BS(1,1) solution has been found, which rules
out a description as [OsIII(pdi•)Cl2(PR3)]0. Analysis of the
closed shell computational results reveals three occupied 5d
metal orbitals with 45, 54, and 62% Os d character; the latter
orbital is the HOMO. The LUMO is a predominantly (pdi0)
ligand centered orbital (which still has 20% Os d character)
which is followed by a second unoccupied (pdi0) ligand orbital
still with 11% Os d character. This analysis indicates
substantial OsII → (pdi0) π-backdonation: cis-[OsII(pdi0)-
Cl2(PR3)]0 (S = 0). The closed shell calculation of the
hypothetical carbonyl analogue cis-[OsII(tolpdi0)Cl2(CO)]0 (S
= 0) yields Δcalc = 0.127 Å, indicating a much “electron poorer”
OsII central ion with less π-backdonation OsII → (pdi0).
The DFT geometry optimized structure of diamagnetic, five-
coordinate complex 5 with a bidentate N,C-coordinated η2-
backdonation M → (heterocycle0). Nu
̈
ckel and Burger have
proposed this for their [RhI(xylpdi0)(η2-BH4)]0 complex.25
We have also computationally studied the two hypothetical
diamagnetic monocations [Pd(tpy)(BH4)]1+ (S = 0) and
[Pd(OMepdi)(BH4)]1+ (S = 0) which are isoelectronic with the
above neutral RhI and IrI complexes. The closed shell geometry
optimizations yield a square planar geometry with an η1-
−
coordinated BH4 anion (Scheme 8) with an agostic Pd···H
interaction at ∼2.3 Å (2.422 Å for the tpy complex and 2.296
Å for the pdi species).
Scheme 8. Selected Bond Distances (Å) of Geometry
Optimized Structure of Hypothetical [PdII(OMepdi0)(η1-
BH4)]1+ (top) and Selected Bond Distances of
[RhI(pdi0)(η2-BH4)]0 (bottom)
(
OMepdi-H)1− monoanion is in very good agreement with
experiment (Scheme 5). The η2-N,C coordinated anion
displays average C−N and Cimine−Cpy distances from which
Δexp and Δcalc values of 0.152 and 0.158 Å, respectively, are
derived. This is characteristic for neutral (pdi0) ligands. There
are three occupied 4d metal orbitals of which the HOMO
possesses 77% Ru d character, and the LUMO is a (pdi0)
centered ligand orbital (3.7% Ru d character): [RuII(η2-OMepdi-
H)Cl(PPh3)]0.
Closed shell geometry optimization of the structure of
diamagnetic, octahedral [RuII(η2-OMepdi-H)2(η2-OMepdi0)]0 (S
= 0) (7) is again in very good agreement with experiment:
average Δexp = 0.157 Å and Δcalc = 0.164 Å for the neutral
N,N-coordinated (η2-pdi0) ligand, and 0.158 and 0.157 Å,
respectively, for the (η2-pdi-H) monoanion. The HOMO is
one of the three filled 4d orbitals (75%, 67%, 65% Ru d
character) confirming the RuII assignment, whereas the LUMO
(7.4% Ru d) is ligand centered.
The Δcalc values at 0.125 Å for the [PdII(tpy0)(BH4)]1+ and
0.168 Å for the corresponding [PdII(pdi0)(BH4)]1+ complex
are in relatively good agreement with the presence of neutral
(pdi0) ligands with little structurally significant π-back-
donation. Another structural aspect needs consideration. A
weak direct M−B bonding interaction has been proposed in
[RhI(xylpdi0)(η2-BH4)]0.25 Our DFT calculations for the Rh, Ir,
and Pd species confirm this notion (see Discussion section).
The closed shell geometry optimized structure of octahedral,
diamagnetic 6 yields a Δcalc value of 0.133 Å in fair agreement
with a neutral (pdi0) oxidation level. There are five trans-
[RuII(pdi0)Cl2(PPh3)]0 structures in the literature19,21−23
DISCUSSION AND CONCLUSION
■
Three aspects of the present work are discussed: (a) the
characteristic features of the structural parameter Δ of
tridentate π-radical anions and their corresponding dianions
coordinated to first, second, and third row transition metal
ions; (b) the nature of the M···B interaction in complexes
[M(tpy)(BH4)]0 and [M(pdi)(BH4)]0 (M = Co, Rh, Ir); and
(c) the observed variations of Δ in bidentate N,N′-coordinated
(pdi)n ligands (n = 0, 1−, 2−) in transition metal ion
complexes.
Inspection of good to excellent quality structures1−3,30,31 of
transition metal ions coordinated to a tridentate dianion
(tpy2−) revealed that the Δexp value is found in the narrow
range 0.041 0.02 Å, which agrees with the Δexp value of 1.
Notably, the M(pdi2−) unit does not show structurally
significant π-bonding effects (M → N or M ← N), neither
in “electron rich” nor “electron poor” complexes (TiIV, VIV,
MoIV, UIV).
exhibiting such a low average Δexp value of 0.13
0.01 Å.
Furthermore, three cis-structures as in 6 exhibit an average Δexp
= 0.122 Å.19,20 These structures (including 6) may display
structurally significant RuII → (pdi0) π-backdonation. The
DFT calculations identify three doubly occupied 4d orbitals
(RuII 4d6), and the HOMO is one of these with 59% Ru d
character, whereas the LUMO is a (pdi0) π*-orbital (13% Ru
d). Note that PR3 ligands are strong σ-donors but weak π-
acceptors, and, therefore, one must consider 6 (and the other
complexes of this type) as “electron rich” species. Replacement
of PR3 by a CO ligand (which is a strong π-acceptor) generates
an electron poorer RuII center in [RuII(pdi0)Cl2(CO)]0 (S = 0)
which has an average Δexp of 0.150 Å (Δcalc = 0.159 Å).29
The corresponding experimental structure of the complex
cis-[Os(tolpdi0)Cl2(PiPr3)]0 (S = 0) exhibits an extremely low
The available database for M(pdi2−) complexes is dramat-
ically larger. We have identified 54 first row transition metal
ion complexes with a κ3-coordinated (pdi2−) dianion, all of
which display Δexp values in the narrow range of 0.05 0.02 Å
irrespective of their dn electron configuration.32 Complex 2
with Δexp = 0.026 Å is therefore a further example for the
notion that (pdi2−)-to-metal π-bonding is structurally not
effective.
H
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Nu
Article
̈
ckel and Burger25 have proposed that in [RhI(pdi0)(η2-
coordinated at the pyridine ring deprotonated (pdi) ligands
BH4)]0 a weak Rh···B bonding interaction exists by employing
DFT (B3LYP) calculations. The experimental Rh···B inter-
action at 2.271(3) Å is relatively short, and the Mulliken
overlap population analysis confirms a direct bonding Rh···B
interaction (0.21 e). Table 3 summarizes the M···B distances
display Δ values indicating their pdi0 parentage.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were carried out under an
argon atmosphere using standard Schleck techniques or a glovebox in
the strict absence of water and dioxygen using rigorously dried
solvents. The reagents [(Cp)2ZrCl2]0 (Cp = cyclopentadienyl1−),
sodium amalgam beads (10%), 2,2′:6′2″-terpyridine (tpy), [Ru-
(PPh3)3Cl2]0, CoCl2, and NaBH4 are commercially available. The
ligand 2,6-bis[1-(4-methoxyphenyliminoethyl)]pyridine (OMepdi0)
was prepared according to the literature.36 The complexes [Co(tpy)-
Table 3. Distances (Å) and Mayer Bond Order of M···B
interactions
exp.
calcd.
d(M···B), Å
Mayer bond
order
complex
d(M···B), Å
[CoII(tpy•)(η2-
2.16(3)
2.173
0.40
(BH4)]0 (3),13 [Co(tpy)Cl2]0,37 and [Co(OMepdi0)Cl2]0 have been
38
BH4)]0
synthesized as described in the literature.
[CoII(pdi•)(η2-
2.123(2)
2.148
0.42
[(η5-Cp)2Zr(tpy)]0 (S = 0) (1). The complex was prepared in 27%
yield (0.12 g) via an analogous procedure as described below for (2)
by using the ligand tpy instead of (OMepdi0). X-ray quality black-
brown crystals were grown at −20 °C by vapor diffusion of diethyl
ether into a saturated tetrahydrofuran (THF) solution of 1. Anal.
Calcd for C25H21N3Zr: C, 66.04; H, 4.66; N, 9.24. Found: C, 65.79;
H, 4.68; N, 9.13.
BH4)]0
[RhI(tpy0)(η2-BH4)]0
[RhI(pdi0)(η2-BH4)]0
[IrI(tpy0)(η2-BH4)]0
[IrI(pdi0)(η2-BH4)]0
2.310
2.284
2.280
2.252
2.434
0.23
0.18
0.50
0.45
0.26
2.271(3)
[PdII(tpy0)(η1-
BH4)]1+
[(η5-Cp)2Zr(OMepdi0)]0 (S = 0) (2). The ligand (OMepdi0) (0.37 g,
1.0 mmol) was added to a suspension of [(Cp)2ZrCl2]0 (0.29 g, 1.0
mmol), and sodium amalgam (10 wt %, 0.5 g, ∼2 mmol Na) in 25 mL
of THF and stirred at 20 °C for 24 h. The resulting dark-brown
solution was filtered, and the volume was reduced to 10 mL under a
vacuum. Diethyl ether was added (10 mL) which initiated the
precipitation of a brown-black solid which was collected by filtration
and dried in vacuo. Yield: 0.13 g (22%). X-ray quality crystals were
grown by vapor diffusion of diethyl ether into a saturated THF
solution of 2. Anal. Calcd for C33H33N3O2Zr: C, 66.63; H, 5.59; N,
7.06. Found: C, 66.35; H, 6.18; N, 6.71.
[PdII(pdi0)(η1-
2.398
0.27
BH4)]1+
(experimental and calculated) for the corresponding Co, Rh,
Ir, and Pd complexes with tpy and (pdi) ligands, respectively.
In our DFT calculations we have analyzed the Mayer bond
order for the M···B interactions. We confirm the presence of a
weak M···B interaction (Table 3).
Finally, we discuss the metrical details of bidentate, η2-
coordinated (pdi)n ligands (n = 0, 1−, 2−) (Table 4). It is
[Co(OMepdi0)(η2-BH4)]0 (S = 0) (4). A mixture of CoCl2 (0.13 g,
1.0 mmol) and the ligand (OMepdi0) (0.37 g, 1.0 mmol) in methanol
(10 mL) was stirred at 20 °C for 12 h after which time the solvent was
removed in vacuo. The residual green solid of [CoII(OMepdi0)Cl2]0
and 2 equiv of NaBH4 (0.076 g, 2.0 mmol) were suspended in 20 mL
of THF and stirred at 20 °C for 12 h. After filtering, the solvent was
removed under reduced pressure affording dark, almost black
microcrystals in ∼80% yield (0.38 g) of 4. X-ray quality crystals
were grown by vapor diffusion of diethyl ether into a saturated THF
solution of 4 at 20 °C. Anal. Calcd for C23H27BCoN3O2: C, 61.77; H,
6.09; N, 9.40. Found: C, 61.92; H, 5.81; N, 9.20.
Table 4. Summary of Structurally Characterized η2-
Coordinated (pdi) Complexes (Δ )
a
complex
Δ, Å
0.130
ref
[RuII(η2-pdi0)(η2-pdi-H)2]0
[Mo0(η2-pdi0)(CO)4]0
[MnII(η2-pdi•)2]0
this work
0.150
av. 0.075
0.019
34
35
21
[RuII(η2-pdi2−)(η6-toluene)]0
a
Δ is defined in eq 1.
[Ru(OMepdi-H)Cl(PPh3)2]0 (S = 0) (5). A mixture of (OMepdi0)
(0.37 g, 1.0 mmol), [Ru(PPh3)3Cl2]0 (0.96 g, 1 mmol) and NaBH4
(0.019 g, 0.5 mmol) in 30 mL of THF was heated to reflux at 66 °C
for 24 h. The resulting dark-red solution was filtered, and all volatiles
were removed under reduced pressure yielding a black-red micro-
crystalline solid which was washed with diethyl ether and dried. Yield:
0.37 g (37%). X-ray quality crystals were grown by vapor diffusion of
diethyl ether into a saturated toluene solution of 5 at −20 °C. Anal.
Calcd for C59H52ClN3O2P2Ru: C, 68.56; H, 5.07; N, 4.07. Found: C,
68.13; H, 5.37; N, 4.98.
notable that the uncoordinated (dangling) imine part of the
(pdi)n ligand possesses a nearly invariant C = N imine double
bond at 1.29 0.01 Å and a Cimine−Cpy single bond at 1.48
0.02 Å irrespective of the transition metal ion to which the
(pdi) ligand is bound. This is a consequence of the fact that
the planar η2-coordinated part and the plane of the dangling
part are not coplanar as in η3-coordinated (pdi) ligands. The
observed dihedral angle between the planes is not 0° but in the
range of 50−90° which inhibits electronic π-communication
between the dangling imine and the η2-coordinated part. Thus,
the redox activity of η2-ligands can only be observed in the
coordinated pyridine-imine part. The structural coordination
chemistry of redox-noninnocent iminopyridine ligands in first
row transition metal ions has been reported.33
cis-[Ru(OMepdi0)Cl2(PPh3)]0 (S = 0) (6). A mixture of (OMepdi0)
(0.37 g, 1.0 mmol) and [Ru(PPh3)3Cl2]0 (0.96 g, 1 mmol) in 30 mL
of THF/methanol (1:1) was heated to reflux for 18 h. The red-black
solution was filtered, and all volatiles were removed in vacuo. The
black residue was washed with diethyl ether and dried. Yield: 0.47 g
(51%). X-ray quality black-purple crystals of 6·Et2O·0.5 THF were
grown by vapor diffusion of diethyl ether into a saturated THF
solution of 6 at −20 °C. Anal. Calcd for C47H52ClN3O3.5PRu: C,
61.50; H, 5.71; N, 4.58. Found: C, 62.31; H, 5.72; N, 5.54.
[RuII(η2-OMepdi0)(η2-OMepdi-H)2]0 (S = 0) (7). A mixture of
Table 4 summarizes a few structurally characterized η2-
coordinated (pdi)n complexes where Δ represents the
structural parameter as defined in eq 1 (Scheme 1) of the
η2-bound iminopyridine part. Δ is ∼0.14 Å for a neutral
iminopyridine ligand, ∼0.075 Å for an iminopyridine π-radical
anion, and ∼0.02 Å for a dianion. It is notable that the η2-
(
OMepdi0) (1.12 g, 3.0 mmol), [Ru(PPh3)3Cl2]0 (0.96 g, 1 mmol),
KC8 (0.41 g, 3 mmol), and KOH (0.17 g, 3 mmol) in 30 mL of THF
was heated to reflux for 48 h. The resulting red-black solution was
filtered, and all volatiles were removed in vacuo. The residue was
washed with diethyl ether and dried. Yield: 0.33 g (27%). X-ray
quality crystals were grown by vapor diffusion of diethyl ether into a
I
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
saturated THF solution of 7 at −20 °C. Anal. Calcd for
C69H67N9O6Ru: C, 67.96; H, 5.54; N, 10.34. Found: C, 67.65; H,
4.92; N, 9.75.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01949.
■
S
X-RAY CRYSTALLOGRAPHIC DATA COLLECTION
AND REFINEMENT OF THE STRUCTURES
■
Computational details, model input file, Cartesian
coordinates of the geometry optimized structures as
well as crystallographic data of the complexes (PDF)
Single crystals of complexes were coated with perfluoropo-
lyether, picked up with nylon loops, and were mounted in the
nitrogen cold stream of the diffractometers at 100 K. Graphite
monochromated Mo−Kα radiation (λ = 0.71073 Å) from a
Mo-target rotating-anode X-ray source was used throughout.
Final cell constants were obtained from least-squares fits of
several thousand strong reflections. Intensity data were
corrected for absorption using intensities of redundant
reflections with the program SADABS.17 The structures were
readily solved by Patterson methods and subsequent difference
Fourier techniques. The Siemens ShelXTL39 software package
was used for solution, refinement, and artwork of the
structures. All non-hydrogen atoms were anisotropically
refined, and hydrogen atoms were placed at calculated
positions and refined as riding atoms with isotropic displace-
ment parameters.
A methoxyphenyl group (fragment C19 to C26) in the pdi
ligand of [Co(pdi)(BH4)]0 was found to be disordered next to
a crystallographic center of inversion. A split atom refinement
with occupation factors of 0.67:0.33 was used to satisfactorily
model the disorder. SADI and EADP restraints in ShelXL were
used (18 restraints).
Methoxo groups in crystals of 7 were found to be disordered
and two groups containing carbon atoms C24 and C84 were
split on two positions with occupation factors of about 0.55
and 0.52 respectively. O−C distances were restrained to be
equal (SADI), and thermal displacement parameters were
restrained to be equal using the EADP instruction of ShelXL
(6 restraints).
Accession Codes
CCDC 1565814, 1811210, 1819350, and 1854899−1854902
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge via www.ccdc.ca-
m.ac.uk/data_request/cif, or by emailing data_request@ccdc.
cam.ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
+44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: karl.wieghardt@cec.mpg.de.
ORCID
■
̈
Christina Romelt: 0000-0003-1673-1484
ller: 0000-0002-0399-7999
Thomas Weyhermu
̈
Karl Wieghardt: 0000-0003-0600-7855
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors are grateful to the Max-Planck Society for financial
support. C.R. wishes to thank Dr. Michael Romelt for valuable
input on theoretical work and helpful discussions. Further, this
work was supported by the National Natural Science
Foundation of China (No. 21601171) and Natural Science
Foundation of Shandong Province (No. ZR2016BB08).
■
̈
Crystals of MePhtpy contained a large solvent accessible void
of about 1260 Å3 in which THF and Et2O molecules could be
identified. These solvent molecules were severely disordered
and could not be satisfactorily refined. Platon/SQUEEZE17,40
was used to remove solvent contributions from the refinement
(about 196 electrons in the void). Crystallographic data of
complexes are summarized in Table S1.
REFERENCES
(1) Scarborough, C. C.; Lancaster, K. M.; DeBeer, S.; Weyhermu
■
̈
ller,
T.; Sproules, S.; Wieghardt, K. Experimental Fingerprints for Redox-
Active Terpyridine in [Cr(tpy)2](PF6)n (n = 3−0), and the
Remarkable Electronic Structure of [Cr(tpy)2]1. Inorg. Chem. 2012,
51 (6), 3718−3732.
(2) Wang, M.; Weyhermuller, T.; Bill, E.; Ye, S.; Wieghardt, K.
̈
Structural and Spectroscopic Characterization of Rhenium Complexes
Containing Neutral, Monoanionic, and Dianionic Ligands of 2,2’-
Bipyridines and 2,2’:6,2″-Terpyridines: An Experimental and Density
Functional Theory (DFT)-Computational Study. Inorg. Chem. 2016,
55 (10), 5019−5036.
COMPUTATIONAL DETAILS
■
All calculations have been performed with the ORCA program
in its version 4.0.x.41 Geometry optimizations were carried out
on structures derived from experimental X-ray data if available
(references thereof are given in the manuscript). We employed
the B3LYP functional42−44 together with the def2-TZVP basis
set45,46 in combination with Weigends auxiliary basis set
(def2/J)47 (for Ti, Co, Zn), the scalar-relativistic recontraction
of the TZVP basis set (old-Zora-TZVP) in combination with
the SARC/J auxiliary basis set (for Zr, Ru, Rh, Pd) or the
SARC-ZORA-TZVP basis set48−52 in combination with the
SARC/J auxiliary basis set (for Os, Ir, Hf). During integral
generation, the resolution of identity and chain of spheres
approximations (RIJCOSX)53 have been applied to Coulomb
and exchange integrals, respectively. Counterions were not
included in any calculation.
(3) Knijnenburg, Q.; Gambarotta, S.; Budzelaar, P. H. M. Ligand-
Centred Reactivity in Diiminepyridine Complexes. Dalton Trans.
2006, No. 46, 5442−5448.
(4) Bart, S. C.; Chlopek, K.; Bill, E.; Bouwkamp, M. W.; Lobkovsky,
E.; Neese, F.; Wieghardt, K.; Chirik, P. J. Electronic Structure of
Bis(imino)pyridine Iron Dichloride, Monochloride, and Neutral
Ligand Complexes: A Combined Structural, Spectroscopic, and
Computational Study. J. Am. Chem. Soc. 2006, 128 (42), 13901−12.
(5) de Bruin, B.; Bill, E.; Bothe, E.; Weyhermuller, T.; Wieghardt, K.
̈
Molecular and Electronic Structures of Bis(pyridine-2,6-diimine)-
metal Complexes [ML2](PF6)n(n = 0, 1, 2, 3; M = Mn, Fe, Co, Ni,
Cu, Zn). Inorg. Chem. 2000, 39 (13), 2936−2947.
(6) Budzelaar, P. H. M.; de Bruin, B.; Gal, A. W.; Wieghardt, K.; van
Lenthe, J. H. Metal-to-Ligand Electron Transfer in Diiminopyridine
Complexes of Mn−Zn. A Theoretical Study. Inorg. Chem. 2001, 40
(18), 4649−4655.
J
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(7) Scott, J.; Gambarotta, S.; Korobkov, I.; Knijnenburg, Q.; de
Bruin, B.; Budzelaar, P. H. Formation of a Paramagnetic Al Complex
and Extrusion of Fe During the Reaction of (Diiminepyridine)Fe
With AlR3 (R = Me, Et). J. Am. Chem. Soc. 2005, 127 (49), 17204−6.
(8) Esteruelas, M. A.; Masamunt, A. B.; Olivan, M.; Onate, E.;
Valencia, M. Aromatic Diosmatricyclic Nitrogen-containing Com-
pounds. J. Am. Chem. Soc. 2008, 130 (35), 11612−3.
(9) Scott, J.; Vidyaratne, I.; Korobkov, I.; Gambarotta, S.; Budzelaar,
P. H. Multiple Pathways for Dinitrogen Activation During the
Reduction of an Fe Bis(iminepyridine) Complex. Inorg. Chem. 2008,
47 (3), 896−911.
(10) Aranyos, A.; Csjernyik, G.; Szabo, K. J.; Backvall, J.-E. Evidence
for a Ruthenium Dihydride Species as the Active Catalyst in the
RuCl2(PPh3)-Catalyzed Hydrogen Transfer Reaction in the Presence
of Base. Chem. Commun. 1999, No. 4, 351−352.
(11) Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. The
Preparation and Reactions of Hydridochlorotris(triphenylphosphine)-
ruthenium(II) Including Homogeneous Catalytic Hydrogenation of
Alk-1-enes. J. Chem. Soc. A 1968, No. 0, 3143−3150.
(24) Details of the computational setup are provided in the
Supporting Information.
̈
(25) Nuckel, S.; Burger, P. Transition Metal Complexes with
Sterically Demanding Ligands. 3.1 Synthetic Access to Square-Planar
Terdentate Pyridine−Diimine Rhodium(I) and Iridium(I) Methyl
Complexes: Successful Detour via Reactive Triflate and Methoxide
Complexes. Organometallics 2001, 20 (21), 4345−4359.
(26) Nitschke, J. R.; Tilley, T. D. Novel Templating Effect in the
Macrocyclization of Functionalized Diynes by Zirconocene Coupling.
Angew. Chem., Int. Ed. 2001, 40 (11), 2142−2145.
(27) Scarborough, C. C.; Wieghardt, K. Electronic Structure of 2,2’-
Bipyridine Organotransition-Metal Complexes. Establishing the
Ligand Oxidation Level by Density Functional Theoretical Calcu-
lations. Inorg. Chem. 2011, 50 (20), 9773−9793.
(28) McPherson, A. M.; Fieselmann, B. F.; Lichtenberger, D. L.;
McPherson, G. L.; Stucky, G. D. Electronic Properties of Bis(η5-
cyclopentadienyl)titanium 2,2’-bipyridyl. A Singlet Molecule with a
Low-lying Triplet Excited State. J. Am. Chem. Soc. 1979, 101 (13),
3425−3430.
(12) Chaudret, B. N.; Cole-Hamilton, D. J.; Nohr, R. S.; Wilkinson,
G. The Reactions of Chlorohydrido- and Dichloro-tris-
(triphenylphosphine)ruthenium(II) With Alkali Hydroxides and
Alkoxides. Hydridohydroxobis(triphenylphosphine Ruthenium(II)
Monosolvates, Their Reactions and Related Compounds. J. Chem.
Soc., Dalton Trans. 1977, No. 16, 1546−1557.
(29) Lu, X.-Y.; Xu, H.-J.; Chen, X.-T. Synthesis, Structure and
Catalytic Activities for the Hydrogen Transfer Reactions of the
Ruthenium(II) Carbonyl Chloride Complexes with Pyridine-2,6-
diimine. Inorg. Chem. Commun. 2009, 12 (9), 887−889.
(30) Wang, M.; Weyhermuller, T.; England, J.; Wieghardt, K.
̈
Molecular and Electronic Structures of Six-Coordinate “Low-Valent”
[M(Mebpy)3]0 (M = Ti, V, Cr, Mo) and [M(tpy)2]0 (M = Ti, V, Cr),
and Seven-Coordinate [MoF(Mebpy)3](PF6) and [MX(tpy)2](PF6)
(M = Mo, X = Cl and M = W, X = F). Inorg. Chem. 2013, 52 (21),
12763−12776.
(13) Corey, E. J.; Cooper, N. J.; Canning, W. M.; Lipscomb, W. N.;
Koetzle, T. F. Preparation, Unusual Spectral Properties, and Structural
Characterization of (Terpyridine)(tetrahydroborato-H,H’)cobalt.
Inorg. Chem. 1982, 21 (1), 192−199.
(14) Goldschmied, E.; Stephenson, N. C. The Crystal Structure of
Dichloro-2,2’,2″-terpyridylcobalt(II). Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 1970, 26 (11), 1867−1875.
́
̀
(31) Mehdoui, T.; Berthet, J.-C.; Thuery, P.; Salmon, L.; Riviere, E.;
Ephritikhine, M. Lanthanide(III)/Actinide(III) Differentiation in the
Cerium and Uranium Complexes [M(C5Me5)2(L)]0,+ (L = 2,2-
Bipyridine, 2,2’:6’,2″-Terpyridine): Structural, Magnetic, and Reac-
tivity Studies. Chem. - Eur. J. 2005, 11 (23), 6994−7006.
́
(15) Campora, J.; Naz, A. M.; Palma, P.; Rodríguez-Delgado, A.;
Alvarez, E.; Tritto, I.; Boggioni, L. Iron and Cobalt Complexes of 4-
́
Alkyl-2,6-diiminopyridine Ligands: Synthesis and Ethylene Polymer-
ization Catalysis. Eur. J. Inorg. Chem. 2008, 2008 (11), 1871−1879.
(16) Hogg, R.; Wilkins, R. G. 57. Exchange Studies of Certain
Chelate Compounds of the Transitional Metals. Part VIII. 2,2’,2″-
Terpyridine Complexes. J. Chem. Soc. 1962, 0, 341−350.
̈
̈
(32) Romelt, C.; Weyhermuller, T.; Wieghardt, K. Coord. Chem. Rev.
2019, 380, 287−317.
(33) Lu, C. C.; Bill, E.; Weyhermuller, T.; Bothe, E.; Wieghardt, K.
̈
Neutral Bis(α-iminopyridine)metal Complexes of the First-Row
Transition Ions (Cr, Mn, Fe, Co, Ni, Zn) and Their Monocationic
Analogues: Mixed Valency Involving a Redox Noninnocent Ligand
System. J. Am. Chem. Soc. 2008, 130 (10), 3181−3197.
(34) Lu, S.; Selbin, J. The Molecular Structure of a Complex of a
2,6-Diimino-pyridine as a Bidentate Ligand with Molybdenum
Carbonyl. Inorg. Chim. Acta 1987, 134 (2), 229−232.
(35) Russell, S. K.; Bowman, A. C.; Lobkovsky, E.; Wieghardt, K.;
Chirik, P. J. Synthesis and Electronic Structure of Reduced
Bis(imino)pyridine Manganese Compounds. Eur. J. Inorg. Chem.
2012, 2012 (3), 535−545.
(36) Alyea, E. C.; Merrell, P. H. Terdentate N,N,N Donor Ligands
Derived from 2,6-Diacetylpyridine. Synth. React. Inorg. Met.-Org.
Chem. 1974, 4 (6), 535−544.
(37) Harris, C. M.; Lockyer, T. N.; Stephenson, N. C. 5-
Coordinated 2,2’,2-Terpyridyl Complexes of Cobalt(II), Manganese-
(II) and Copper(II). Aust. J. Chem. 1966, 19 (9), 1741.
(38) Bowman, A. C.; Milsmann, C.; Bill, E.; Lobkovsky, E.;
Weyhermuller, T.; Wieghardt, K.; Chirik, P. J. Reduced N-alkyl
Substituted Bis(imino)pyridine Cobalt Complexes: Molecular and
Electronic Structures for Compounds Varying by Three Oxidation
States. Inorg. Chem. 2010, 49 (13), 6110−23.
(39) ShelXTL MP, Version 2013-2; Bruker AXS Inc., 1993−2013.
(40) Spek, A. L. Structure Validation in Chemical Crystallography.
Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65, 148−155.
(41) Neese, F. The ORCA program system. Wiley Interdisciplinary
Reviews: Computational Molecular Science 2012, 2 (1), 73−78.
(42) Becke, A. D. Density Functional Calculations of Molecular
Bond Energies. J. Chem. Phys. 1986, 84 (8), 4524−4529.
(43) Becke, A. D. Density-Functional Thermochemistry. III. The
Role of Exact Exchange. J. Chem. Phys. 1993, 98 (7), 5648−5652.
(17) Sheldrick, G.M. Platon/SQUEEZE program as given in the
program SADABS, Bruker-Siemens Area Detector Absorption and Other
̈
Corrections, Version 2012/1; University of Gottingen: Germany, 2012.
(18) Bowman, A. C.; Milsmann, C.; Hojilla Atienza, C. C.;
Lobkovsky, E.; Wieghardt, K.; Chirik, P. J. Synthesis and Molecular
and Electronic Structures of Reduced Bis(imino)pyridine Cobalt
Dinitrogen Complexes: Ligand Versus Metal Reduction. J. Am. Chem.
Soc. 2010, 132 (5), 1676−1684.
̈
(19) Wallenhorst, C.; Kehr, G.; Frohlich, R.; Erker, G. Unsym-
metrical Bis(iminoethyl)pyridine Metal Complexes with a Pendant
Alkenyl Substituent. Part B: Internal Olefin Coordination to
Ruthenium. Organometallics 2008, 27 (24), 6557−6564.
(20) Booysen, I. N.; Maikoo, S.; Akerman, M. P.; Xulu, B. Novel
Ruthenium(II) and (III) Compounds With Multidentate Schiff Base
Chelates Bearing Biologically Significant Moieties. Polyhedron 2014,
79, 250−257.
(21) Gallagher, M.; Wieder, N. L.; Dioumaev, V. K.; Carroll, P. J.;
Berry, D. H. Low-Valent Ruthenium Complexes of the Non-Innocent
2,6-Bis(imino)pyridine Ligand. Organometallics 2010, 29 (3), 591−
603.
(22) Burkill, H. A.; Vilar, R.; White, A. J. P. Synthesis of a Series of
Ruthenium and Rhodium Complexes With Tridentate Pyridine-Based
Ligands Containing Hydrogen Bonding Groups. Inorg. Chim. Acta
2006, 359 (11), 3709−3722.
(23) Ozdemir, N.; Dincer, M.; Dayan, O.; Cetinkaya, B. (2,6-Bis[1-
[4-(dimethylamino)phenylimino]ethyl]pyridine)dichlorido-
(triphenylphosphine-κP)ruthenium(II): A Zigzag Chain of Fused
Centrosymmetric R(2)(2)(12) Rings. Acta Crystallogr., Sect. C: Cryst.
Struct. Commun. 2007, 63 (6), m264−m266.
K
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(44) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-
Salvetti Correlation-Energy Formula into a Functional of the Electron
Density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37 (2),
785−789.
(45) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence,
Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn:
Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7
(18), 3297−3305.
̈
(46) Andrae, D.; Haußermann, U.; Dolg, M.; Stoll, H.; Preuß, H.
Energy-Adjusted Ab Initio Pseudopotentials for the Second and Third
Row Transition Elements. Theor. Chim. Acta 1990, 77 (2), 123−141.
(47) Weigend, F. Accurate Coulomb-Fitting Basis Sets for H to Rn.
Phys. Chem. Chem. Phys. 2006, 8 (9), 1057−1065.
(48) Pantazis, D. A.; Chen, X.-Y.; Landis, C. R.; Neese, F. All-
Electron Scalar Relativistic Basis Sets for Third-Row Transition Metal
Atoms. J. Chem. Theory Comput. 2008, 4 (6), 908−919.
(49) Pantazis, D. A.; Neese, F. All-Electron Scalar Relativistic Basis
Sets for the 6p Elements. Theor. Chem. Acc. 2012, 131 (11), 1292.
(50) Buhl, M.; Reimann, C.; Pantazis, D. A.; Bredow, T.; Neese, F.
̈
Geometries of Third-Row Transition-Metal Complexes from Density-
Functional Theory. J. Chem. Theory Comput. 2008, 4 (9), 1449−1459.
(51) Pantazis, D. A.; Neese, F. All-Electron Scalar Relativistic Basis
Sets for the Lanthanides. J. Chem. Theory Comput. 2009, 5 (9), 2229−
2238.
(52) Pantazis, D. A.; Neese, F. All-Electron Scalar Relativistic Basis
Sets for the Actinides. J. Chem. Theory Comput. 2011, 7 (3), 677−684.
(53) Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Efficient,
Approximate and Parallel Hartree−Fock and Hybrid DFT Calcu-
lations. A ‘Chain-of-Spheres’ Algorithm for the Hartree−Fock
Exchange. Chem. Phys. 2009, 356 (1), 98−109.
L
DOI: 10.1021/acs.inorgchem.8b01949
Inorg. Chem. XXXX, XXX, XXX−XXX