Synthesis, characterization and reactivity of vanadium, chromium, and manganese PNP pincer complexes

Article abstract of DOI:10.1016/j.ica.2016.02.064

The synthesis of a series of vanadium, chromium, and manganese PNP complexes of the types [M(PNP)Cl₃] (M = V, Cr) and [M(PNP)Cl₂] (M = Cr, Mn) is reported. Vanadium and manganese PNP pincer complexes are described for the first time. All complexes are characterized by their magnetic moments, elemental analysis, and ESI MS. In addition, some compounds are characterized by X-ray crystallography. In a preliminary study, these complexes catalyze the oxidative homo-coupling of aryl Grignard reagents in the presence of MeI as oxidizing agents to give symmetrical biaryls, but are inactive in Kumada cross-coupling reactions. The reactivity of V(III), Cr(III), Cr(II) and Mn(II) is compared with related Fe(II) and Co(II) complexes of the types [Fe(PNP-iPr)Cl₂], and [Co(PNP-iPr)Cl₂]. In all cases, good to excellent isolated yields are obtained. However, since the respective metal chlorides in the absence of PNP ligands exhibited comparable reactivities, the new PNP complexes offer no real advantage for this type of coupling reactions.

Full text of DOI:10.1016/j.ica.2016.02.064

Inorganica Chimica Acta xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization and reactivity of vanadium, chromium,
and manganese PNP pincer complexes
Matthias Mastalir a, Mathias Glatz a, Berthold Stöger b, Matthias Weil b, Ernst Pittenauer b,
Günter Allmaier b, Karl Kirchner a,
⇑
a Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
b Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of a series of vanadium, chromium, and manganese PNP complexes of the types [M(PNP)
Cl3] (M = V, Cr) and [M(PNP)Cl2] (M = Cr, Mn) is reported. Vanadium and manganese PNP pincer com-
plexes are described for the first time. All complexes are characterized by their magnetic moments,
elemental analysis, and ESI MS. In addition, some compounds are characterized by X-ray crystallography.
In a preliminary study, these complexes catalyze the oxidative homo-coupling of aryl Grignard reagents
in the presence of MeI as oxidizing agents to give symmetrical biaryls, but are inactive in Kumada cross-
coupling reactions. The reactivity of V(III), Cr(III), Cr(II) and Mn(II) is compared with related Fe(II) and Co
(II) complexes of the types [Fe(PNP-iPr)Cl2], and [Co(PNP-iPr)Cl2]. In all cases, good to excellent isolated
yields are obtained. However, since the respective metal chlorides in the absence of PNP ligands exhibited
comparable reactivities, the new PNP complexes offer no real advantage for this type of coupling
reactions.
Received 28 January 2016
Accepted 29 February 2016
Available online xxxx
Keywords:
Vanadium
Chromium
Manganese
Pincer ligands
Homo coupling
Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction
We are currently focusing on the chemistry of non-precious
metal complexes containing PNP pincer ligands based on the 2,6-
Among the many ligand systems that can be found in the chem-
ical literature pincer ligands play an important role and their com-
plexes have attracted tremendous interest due to their high
stability, activity and variability [1]. These tridentate ligands are
often planar scaffolds consisting of neutral central pyridine back-
bone tethered to two, mostly bulky, two-electron donor groups
by different spacers. In this family of ligands steric, electronic,
and also stereochemical parameters can be manipulated by modi-
fications of the substituents at the donor sites and/or the spacers.
Accordingly, many applications of mostly precious second and
third row transition metal pincer complexes in the fields of catal-
ysis, molecular recognition and supramolecular chemistry were
discovered turning this area into an intensively investigated sub-
ject in organometallic chemistry. As non-precious first-row transi-
tion metals are concerned, the chemistry of neutral pyridine-based
iron [2–7] and cobalt [8,9] PNP complexes experienced an impres-
sive upswing in recent years. Reports on chromium [10], nickel
[11,12], and copper [13] PNP pincer complexes are still rare, while
vanadium, manganese, and titanium PNP pincer complexes appear
to be unknown as yet.
diaminopyridine scaffold, where the pyridine ring and the phos-
phine moieties are connected via NH, N-alkyl, or N-aryl linkers
(Scheme 1) [14].
Herein we report on the synthesis, characterization and reactiv-
ity of a series of new vanadium, chromium, and manganese PNP
complexes of the types [M(PNP)Cl3] (M = V, Cr) and [M(PNP)Cl2]
(M = Cr, Mn). In a preliminary study, these complexes were found
to catalyze the homo-coupling of PhMgBr in the presence of MeI
or atmospheric oxygen as oxidizing agents, but were inactive for
cross coupling reactions.
2. Results and discussion
Treatment of [MCl3(THF)3] (M = V, Cr) with the PNP ligands 1a–
g in THF affords the six-coordinate 14e and 15e complexes [V(PNP)
Cl3] (2a–e,2g) and [Cr(PNP)Cl3] (3a–f) in high isolated yields (93–
99%), respectively (Scheme 2). Likewise, the reaction of anhydrous
MCl2 (M = Cr, Mn) with 1 equiv of the PNP ligands 1a–g in THF at
room temperature afforded the five-coordinate 14e and 15e com-
plexes [Cr(PNP)Cl2] (4a–f) and [Mn(PNP)Cl2] (5a–e,5g) in 92–98%
isolated yields (Scheme 3). All complexes display large paramag-
netic shifted and very broad 1H NMR signals and thus were not
⇑
Corresponding author.
E-mail address: kkirch@mail.tuwien.ac.at (K. Kirchner).
http://dx.doi.org/10.1016/j.ica.2016.02.064
0020-1693/Ó 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Mastalir et al., Inorg. Chim. Acta (2016), http://dx.doi.org/10.1016/j.ica.2016.02.064

2
M. Mastalir et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
R'
R'
N
N
N
PR2
PR2
Ph
Ph
PR2
=
P
P
P
P
P
P
P
1a (R' = H) 1b (R' = H) 1c (R' = H) 1d
1e
PNP-Et
1f (R' = Ph) 1g
(R' = Me)
(R' = H)
(R' = Ph)
PNP-Ph
PNP-Cy
PNP-iPr
PNPMe-iPr
PNPPh-Et
PNPPh-nPr
Scheme 1. PNP ligands used in this work (labeling of complexes refers to letters of
ligands depicted here).
Fig. 1. Structural view of [V(PNP-Ph)Cl3]ꢀ3.5(CH3)2CO (2aꢀ3.5(CH3)2CO) showing
50% displacement ellipsoids (H atoms and solvent molecules omitted for clarity).
R'
R'
N
N
N
R'
Cl
M
PR2
PR2
N
PR2
Cl
1a-f
MCl3(THF)3
M = V, Cr
N
THF, r.t.
N
PR2
1a R = Ph; R' = H
1b R = Cy; R' = H
1c R = iPr; R' = H
1d R = iPr; R' = Me
1e R = Et; R' = H
1f R = Et; R' = Ph
1g R = nPr; R' = Ph
Cl
R'
2a-e,g
3a-f
M = V
M = Cr
Fig. 2. Structural view of [V(PNPPh-nPr)Cl3] (2g) showing 50% displacement
ellipsoids (H atoms omitted for clarity).
Scheme 2. Synthesis of V(III) and Cr(III) complexes [V(PNP)Cl3] (2) and [Cr(PNP)Cl3]
(3).
very informative. 13C{1H} and 31P{1H} NMR could not be detected
at all. Complexes 2–5 exhibit solution magnetic moments leff of
2.7–2.9 lB, 3.9 lB, 4.9–5.0 lB, and 5.9–6.0 lB (Evans method, in
CH3OH) [15], in agreement with d2, d3, high spin d4, and high spin
d5 electron configurations, respectively.
In order to unequivocally establish the ligand arrangement
around the metal centers, the solid state structure of complexes
[V(PNP-Ph)Cl3] (2a), [V(PNPPh-nPr)Cl3] (2g), [Cr(PNP-iPr)Cl3] (3d),
[Cr(PNPMe-iPr)Cl2] (4d), and [Mn(PNP-iPr)Cl2] (5c) was determined
by X-ray diffraction. Representations of these molecules are shown
in Figs. 1–5 with selected metrical parameters given in Table 1. The
structures of 2a, 2g and 3d show a distorted-octahedral trivalent
vanadium and chromium center surrounded by three meridionally
placed donor atoms of the PNP ligand. The three chlorine atoms
Fig. 3. Structural view of [Cr(PNPMe-iPr)Cl3] (3d) showing 50% displacement
ellipsoids (H atoms and a second independent complex are omitted for clarity).
R'
R'
N
N
N
R'
Cl
M
PR2
PR2
N
PR2
Cl
1a-g
MCl2
N
THF, r.t.
M = Cr, Mn
N PR2
R'
M = Cr 4a-f
M = Mn 5a-e,g
Scheme 3. Synthesis of Cr(II) and Mn(II) complexes [Cr(PNP)Cl2] (4) and [Mn(PNP)
Cl2] (5).
Fig. 4. Structural view of [Cr(PNPMe-iPr)Cl2]ꢀ0.5CH2Cl2 (4dꢀ0.5CH2Cl2) showing 50%
displacement ellipsoids (H atoms and solvent molecules omitted for clarity).
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M. Mastalir et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
3
atmosphere, traces of oxygen in the mass spectrometer are
unavoidable. For the Cr(III) complex 3c the sodiated complex [M
(Cr3+)+Na]+ and also [M(Cr3+)ꢁCl]+), where one chloride ligand is
lost, were found as the main fragment ions in the full mass spec-
trum at m/z 521.1 and 463.1, respectively, (spectrum B).
In the divalent M(II) series, the various fragments are shown in
Scheme 4. The Cr(II) complex 4d undergoes oxidation to form Cr
(III) complexes (spectrum C). Signals of the formal NaCl adduct
[M(Cr3+)+NaCl]+ and [M(Cr3+)]+ are detected at m/z 549.1 and
491.1, respectively. In the case of Mn(II), the fully intact but sodi-
ated complex [M(Mn2+)+Na]+ was observed at m/z 489.1 (spectrum
D). Both Fe(II) and Co(II) complexes [Fe(PNP-iPr)Cl2] and [Co(PNP-
iPr)Cl2] lose one chloride ligand giving rise to the cationic frag-
ments [M(Fe2+)ꢁCl]+ and [M(Co2+)ꢁCl]+ at m/z 432.1 and 435.1
(spectra E, F). In addition, the iron complex forms a methanol
adduct [M(Fe2+)+CH3OHꢁCl]+ (m/z 464.1) revealing the high affin-
ity of CH3OH towards Fe(II) complexes. Similar observations were
made recently with Fe(II) PNP pincer complexes based on R,R-TAD-
DOL in combination with bulky iPr and tBu substituents [14i].
Having a series of well-defined V(III), Cr(III), Cr(II), and Mn(II)
PNP complexes in hands, we decided to investigate their catalytic
activity in the Kumada cross-coupling of PhMgBr and aryl halides.
Unfortunately, no cross coupling took place and only homo-cou-
pling product (biphenyl) was obtained. Thus, complexes 2a–c, 3c,
4a–d, and 5c as well as [Fe(PNP-iPr)Cl2], and [Co(PNP-iPr)Cl2] were
reacted with PhMgBr in the presence of MeI in THF as solvent at
room temperature. For comparison, also the chloride salts of V
(III), Cr(III), Cr(II), Mn(II), Fe(II) and Co(II) in the absence of PNP
ligands were tested as catalysts. This reaction constitutes an easy
and efficient method to obtain symmetrical biaryl compounds. In
recent years, several non-precious metal complexes were found
to catalyze this reaction including manganese [16,17] and iron
complexes [17,18]. As oxidants typically 1,2-dichloroethane or
atmospheric oxygen are used. As shown in Table 2, excellent iso-
lated yields (62–93%) of biphenyl were obtained by using 0.1 mol
% of catalyst with very short reaction times (15 min with MeI
and 45 min in the presence of dry air). Yields up to 93% were
achieved with Cr(II) PNP complexes and MeI. It has to be noted that
all reactions with MeI proceed with gas evolution presumably due
to the formation of ethane. The reactions with the chloride salts
were less efficient in the case of V(III), Cr(III), and Mn(II), but only
slightly worse with Cr(II), Fe(II), and Co(II) chlorides. Accordingly,
the new PNP complexes offer no real advantage for homo coupling
reactions.
Fig. 5. Structural view of [Mn(PNP-iPr)Cl2]ꢀTHF (5cꢀTHF) showing 50% displacement
ellipsoids (H atoms and solvent molecules omitted for clarity).
occupy the three remaining positions. In all complexes the Cl1–
metal–Cl3 angles deviate from linearity being 165.92(2)°, 168.13
(3)°, and 172.30(3)°, respectively, and are contracted towards the
pyridine ring. The same pattern is observed for the P1–metal–P2
angles which are 156.25(2)°, 158.38(3)°, and 162.41(3)°, respec-
tively. The coordination geometry of the metal center in 4d and
5c is distorted square pyramidal with the chromium and man-
ganese atoms lying 0.463(1) and 0.416(1) Å out of the pyridine
plane. For comparison, in [Fe(PNP-iPr)Cl2] [14b] and [Fe(PNPMe
-
iPr)Cl2] [14k] these values are 0.288(1) and 0.708(1) Å. The
Cr–Cl1 (basal) bond length is significantly shorter (2.3381(5) Å)
than the distance to the apical chlorine (Cr–Cl2 2.4684(5) Å). This
order is reversed in 5c, where the Mn–Cl1 (basal) bond length is
slightly longer (2.3940(5) Å) than the Mn-Cl2 distance being
2.3658(5) Å as well as for [Fe(PNPMe-iPr)Cl2] (2.347(1) versus
2.301(1) Å) and [Fe(PNP-iPr)Cl2] (2.3708(7) versus 2.3040(6) Å)
(Table 1). Thus, the metal–Cl2 (apical) bond distance is most
sensitive to the nature of the metal decreasing in the order Cr(II)
> Mn(II) > Fe(II) > Co(II).
Since ESI-MS enables not only the detection and the study of
reaction substrates and products but also short-lived reaction
intermediates and decomposition products as they are present in
solution, representative PNP complexes were investigated by
means of this technique. Methanol solutions of [V(PNPMe-iPr)Cl3]
(2d), [Cr(PNP-iPr)Cl3] (3c), [Cr(PNPMe-iPr)Cl2] (4d), [Mn(PNP-iPr)
Cl2] (5c), and, for comparison, [Fe(PNP-iPr)Cl2] and [Co(PNP-iPr)
Cl2] in the presence of NaCl were subjected to ESI-MS analysis in
the positive ion mode. The full scan ESI-MS spectra are depicted
in Fig. 6 (spectra A – F).
[Cr(PNP-iPr)Cl2] (4c) was also tested as catalyst for the oxida-
tive homo-coupling of several aryl magnesium bromides and
PhMgCl with MeI as oxidant. The results of this study are presented
in Table 3. With 4c and aryl magnesium bromides excellent yields
of symmetrical biaryls were obtained (entries 1 and 3–6, 62–91%).
Also with PhMgCl biphenyl was formed in high yields but required
a slightly longer reaction time (entry 2).
In the case of the V(III) complex 2d, the most abundant signal at
m/z 443.1 corresponds to an oxidized mono chloro V(IV) species
bearing an oxo ligand [M(V4+)+O-2Cl]+ emphasizing the sensitivity
of this complex towards oxygen (spectrum A). It has to be noted
that, even though solutions are prepared under an argon
Table 1
Selected bond distances and angles (U+00C5, °) of the square pyramidal high-spin Cr(II), Mn(II), Fe(II), and Co(II) complexes [Cr(PNPMe-iPr)Cl2] (4d), [Mn(PNP-iPr)Cl2] (5c), [Fe
(PNP-iPr)Cl2] [14b], [Fe(PNPMe-iPr)Cl2] [14k], and [Co(PNP-Ph)Cl2] [2c].
4d
5c
Fe(PNP-iPr)Cl2
Fe(PNPMe-iPr)Cl2
Co(PNP-Ph)Cl2
M–Cl1 (basal)
M–Cl2 (apical)
M–N1
M–P1
M–P2
Cl1–M–Cl2
P1–M–P2
N1–M–Cl2
2.3381(5)
2.4684(5)
2.1270(9)
2.4257(5)
2.4301(5)
101.10(1)
148.31(2)
157.10(3)
2.3940(5)
2.3658(5)
2.356(5)
2.5931(5)
2.5794(5)
113.19(2)
142.16(1)
139.71(1)
2.3708(7)
2.3040(6)
2.250(2)
2.4631(7)
2.4844(7)
107.60(3)
146.56(3)
144.13(6)
2.347(1)
2.301(1)
2.290(3)
2.464(1)
2.443(1)
106.71(4)
140.89(4)
145.45(8)
2.247(2)
2.279(2)
2.097(5)
2.550(2)
2.542(2)
117.68(8)
155.36(6)
130.4(2)
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M. Mastalir et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
Fig. 6. Positive-ion ESI full scan mass spectra of complexes 2d, 3c, 4d, 5c, [Fe(PNP-iPr)Cl2], and [Co(PNP-iPr)Cl2]. All mass calculations and mass assignments are based on the
most abundant metal isotope (51V, 52Cr, 55Mn, 56Fe, 59Co-isotopes) and the Cl isotope of lowest mass (35Cl).
glovebox. The solvents were purified according to standard proce-
dures [19]. The deuterated solvents were purchased from Aldrich
and dried over 4 Å molecular sieves. The ligands N,N0-bis
(diphenylphosphino)-2,6-diaminopyridine (PNP-Ph) (1a) [10a] N,
N0-bis(dicyclohexyl)-2,6-diaminopyridine (PNP-Cy) (1b) [14k] N,
N0-bis(diisopropylphosphino)-2,6-diaminopyridine (PNP-iPr) (1c)
[14a], N,N0-bis(diisopropylphosphino)-N,N0-dimethyl-2,6-diamino-
pyridine (PNPMe-iPr) (1d) [20], N,N0-bis(diethylphosphino)-2,
6-diaminopyridine (PNP-Et) (1e), N,N0-bis(ethylphosphino)-N,
N0-diphenyl-2,6-diaminopyridine (PNPPh-Et) (1f), and N,N0-bis(n-
propylphosphino)-N,N0-diphenyl-2,6-diaminopyridine (PNPPh-nPr)
(1g) [14h] and complexes [Fe(PNP-iPr)Cl2] [14b], and [Co(PNP-
iPr)Cl2] [8d] were prepared according to the literature. 1H, 13C
{1H}, and 31P{1H} NMR spectra were recorded on Bruker
AVANCE-250, AVANCE-300 DPX, and AVANCE-400 spectrometers.
1H and 13C{1H} NMR spectra were referenced internally to
residual protio-solvent, and solvent resonances, respectively, and
are reported relative to tetramethylsilane (d = 0 ppm). 31P{1H}
NMR spectra were referenced externally to H3PO4 (85%)
(d = 0 ppm). Room-temperature solution (CH3OH) magnetic
moments were determined by 1H NMR spectroscopy using the
method of Evans [15].
3. Conclusion
In sum, we describe here the synthesis of a series of vanadium,
chromium, and manganese PNP complexes of the types [M(PNP)
Cl3] (M = V, Cr) and [M(PNP)Cl2] (M = Cr, Mn). Vanadium and man-
ganese PNP pincer complexes were as yet not reported. All com-
plexes are characterized by their magnetic moments, elemental
analysis and ESI MS. In addition, some compounds were character-
ized by X-ray crystallography. In a preliminary study, these com-
plexes catalyze the oxidative homo-coupling of aryl Grignard
reagents in the presence of MeI as oxidizing agents to give sym-
metrical biaryls, but are inactive in Kumada cross-coupling reac-
tions. The reactivity of V(III), Cr(III), Cr(II) and Mn(II) is compared
with related Fe(II) and Co(II) complexes of the types [Fe(PNP-iPr)
Cl2], and [Co(PNP-iPr)Cl2]. In all cases, good to excellent isolated
yields are obtained. However, since the respective metal chlorides
in the absence of PNP ligands exhibited comparable reactivities,
the new PNP complexes offer no real advantage for this type of
coupling reactions.
4. Experimental
All mass spectrometric measurements were performed on an
Esquire 3000plus 3D-quadrupole ion trap mass spectrometer (Bru-
ker Daltonics, Bremen, Germany) in positive-ion mode by means
of electrospray ionization (ESI). Mass calibration was done with a
4.1. General
All manipulations were performed under an inert atmosphere
of argon by using Schlenk techniques or in an MBraun inert-gas
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M. Mastalir et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
5
H
CH3
R
R
N
O
+
+
N
PiPr2
Cl
N
PiPr2
+II
+II
Fe
N
Fe
+
N
Cl
N
PiPr2
PiPr2
R = H
R
R = H
m/z 432.1
CH3OH -Cl-
m/z 464.1
-Cl-
R
N
Cl
R
+
Cl
R
N
N
PiPr2
N
PiPr2
Cl
+II
N
PiPr2
Cl
+II
Co
Na+
N
M
+II
Mn
Cl
N
N
PiPr2
N
PiPr2
R = Me
m/z 435.1
PiPr2
Na+
R
R
R
M = Cr, Mn, Fe, Co
R = H
m/z 489.1
- e- NaCl
R
R
Cl
Cl
+
N
PiPr2
N
PiPr2
+III
+III
+
N
Cr
Cl
N
Cr
Cl
N PiPr2
Cl
N
PiPr2
Na+
R
R
R = Me
R = Me
m/z 549.1
m/z 491.1
Scheme 4. Fragmentation pathways of M(II) complexes [M(PNPR-iPr)Cl2] (M = Cr, Mn, Fe, Co; R = H or Me) in CH3OH in the presence of NaCl as established by ESI MS
experiments.
Table 2
ion formation. Direct infusion experiments were carried out using
a Cole Parmer model 74900 syringe pump (Cole Parmer Instru-
Catalyst screening in the homo-coupling of PhMgBr with MeIa as oxidizing agents.
ments, Vernon Hills, IL, USA) at a flow rate of 2 lL/min. Full scan
and MS/MS (low energy CID)-scans were measured in the range
m/z 100–1100 with the target mass set to m/z 1000. Further exper-
imental conditions include: drying gas temperature: 150 °C; capil-
lary voltage: ꢁ4 kV; skimmer voltage: 40 V; octapole and lens
voltages: according to the target mass set. All mass calculations
are based on the most abundant metal isotopes (50V, 52Cr, 55Mn,
56Fe, 59Co-isotopes) and the Cl isotope of lowest mass (35Cl). Mass
spectra were averaged during data acquisition time of 1–2 min and
one analytical scan consisted of five successive micro scans result-
ing in 50 and 100 analytical scans, respectively, for the final full
scan mass spectrum.
catalyst (0.1 mol%)
MeI
PhMgBr
THF, 15 min, r.t.
Oxidation state
Catalyst
Additive
t (min)
Yieldb (%)
V(III)
V(III)
V(III)
V(III)
V(PNP-Ph)Cl3 (2a)
V(PNP-iPr)Cl3 (2c)
V(PNPMe-iPr)Cl3 (2d)
VCl3
Cr(PNP-iPr)Cl3 (3c)
CrCl3
Cr(PNP-Ph)Cl2 (4a)
Cr(PNP-Cy)Cl2 (4b)
Cr(PNP-iPr)Cl2 (4c)
Cr(PNPMe-iPr)Cl2 (4d)
CrCl2
Mn(PNP-iPr)Cl2 (5c)
MnCl2
Fe(PNP-iPr)Cl2
FeCl2
Co(PNP-iPr)Cl2
CoCl2
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
MeI
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
81
85
85
59
82
33
89
92
91
93
73
81
38
73
69
88
71
Cr(III)
Cr(III)
4.2. Synthesis
Cr(II), h. s.c
Cr(II), h. s.
Cr(II), h. s.
Cr(II), h. s.
Cr(II), h. s.
Mn(II), h. s.
Mn(II), h. s.
Fe(II), h. s.
Fe(II), h. s.
Co(II), h. s.
Co(II), h. s.
4.2.1. [CrCl3(THF)3]
Anhydrous CrCl3 (20 g, 126.3 mmol) and Zn powder (200 mg,
3.05 mmol) were mixed in a glass frit and extracted with dry
THF (400 mL) in a Soxhlet extractor under inert conditions for
48 h. The extracted suspension was reduced to 100 mL, the purple
powder was collected by filtration and dried under reduced pres-
sure. Yield: 33.5 g (89%) [21].
4.2.2. [V(PNP-Ph)Cl3] (2a)
a
The reactions were carried out using PhMgBr (10.5 mmol), MeI (10.0 mmol),
A suspension of PNP-Ph (1a) (477 mg, 1.0 mmol) and VCl3(-
THF)3 (374 mg, 1.0 mmol) in THF (15 mL) was stirred for 3 h. The
suspension was then reduced to 4 mL and n-hexane (15 mL) was
added for precipitation. The solid was collected on a glass frit as
a brown powder, washed with n-hexane, and dried under reduced
pressure. Yield: 628 mg (99%). Anal. Calc. for C29H25Cl3N3P2V
(634.78): C, 54.87; H, 3.97; N, 6.62. Found: C, 54.95; H, 4.06; N,
and catalyst (0.01 mmol) in THF (8.5 mL).
b
Isolated yields after column chromatography.
h. s. = high spin.
c
commercial mixture of perfluorinated trialkyl-triazines (ES Tuning
Mix, Agilent Technologies, Santa Clara, CA, USA). All analytes were
dissolved in methanol ‘‘hypergrade for LC–MS Lichrosolv” quality
(Merck, Darmstadt, Germany) to form a concentration of roughly
1 mg/mL and doped with sodium chloride to suppress dissociation
of chloride ligands from the metal complexes and/or to promote
the corresponding [M+Na]+ or [M+NaCl]+ (formally added by oxi-
dation of the central metal cation by a one electron oxidation step)
6.54%. leff = 2.7 lB.
4.2.3. [V(PNP-Cy)Cl3] (2b)
This complex was prepared analogously to 2a using PNP-Cy
(1b) (502 mg, 1.0 mmol) and VCl3(THF)3 (374 mg, 1.0 mmol) as
Please cite this article in press as: M. Mastalir et al., Inorg. Chim. Acta (2016), http://dx.doi.org/10.1016/j.ica.2016.02.064

6
M. Mastalir et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
Table 3
Homo-coupling of aryl magnesium halides with MeI as oxidizing agents utilizing [Cr(PNP-iPr)Cl2] (4c) as catalysts.a
catalyst (0.1 mol%)
MeI
MgBr
THF, 15 min, r.t.
R
R
R
Entry
1
Catalyst
RMgX
Product
Additive
MeI
t (min)
Yieldb (%)
91
Cr(PNP-iPr)Cl2
15
MgBr
MgCl
2
3
MeI
MeI
30
15
79
91
MgBr
4
5
MeI
MeI
15
15
65
62
MeO
OMe
MeO
MgBr
MgBr
MgBr
6
MeI
15
83
a
The reactions were carried out using ArMgX (10.5 mmol), MeI (10.0 mmol), and catalyst (0.01 mmol) in THF (8.5 mL).
Isolated yields after column chromatography.
b
starting materials. Yield: 633 mg (96%). Anal. Calc. for C29H49Cl3N3-
4.2.8. [Cr(PNP-Ph)Cl3] (3a)
P2V (658.97): C, 52.86; H, 7.49; N, 6.38. Found: 52.92; H, 7.55; N,
6.31%. leff = 2.7 lB.
A solution of PNP-Ph (1a) (477 mg, 1.0 mmol) and CrCl3(THF)3
(374 mg, 1.0 mmol) in THF (10 mL) was stirred for 16 h at 50 °C.
The purple solution was then reduced to 2 mL and n-hexane
(10 mL) was added for precipitation. The purple powder was col-
lected on a glass frit, washed with n-hexane, dried under vacuum.
Yield: 616 mg (97%). Anal. Calc. for C29H25Cl3CrN3P2 (635,83): C,
54.76; H, 3.95; N, 6.60. Found: C, 54.65; H, 3.89; N, 6.70%.
4.2.4. [V(PNP-iPr)Cl3] (2c)
This complex was prepared analogously to 2a using PNP-iPr
(1c) (341 mg, 1.0 mmol) and VCl3(THF)3 (374 mg, 1.0 mmol) as
starting materials. Yield: 450 mg (95%). Anal. Calc. for C17H33Cl3N3-
P2V (498.71): C, 40.94; H, 6.67; N, 8.43. Found: C, 41.10; H, 6.68; N,
leff = 3.9lB.
8.52%. leff = 2.7 lB.
4.2.9. [Cr(PNP-Cy)Cl3] (3b)
4.2.5. [V(PNPMe-iPr)Cl3] (2d)
This complex was prepared analogously to 3a using PNP-Cy
(1b) (501 mg, 1.0 mmol) and CrCl3(THF)3 (374 mg, 1.0 mmol).
Yield: 620 mg (94%). Anal. Calc. for C29H49Cl3CrN3P2 (660.03): C,
52.77; H, 7.48; N, 6.36. Found: C, 52.83; H, 7.65; N, 6.21%.
This complex was prepared analogously to 2a using PNPMe-iPr
(1d) (370 mg, 1.0 mmol) and VCl3(THF)3 (374 mg, 1.0 mmol) as
starting materials. Yield: 511 mg (97%). Anal. Calc. for C19H37Cl3N3-
P2V (526.77): C, 43.32; H, 7.08; N, 7.98. Found: C, 43.34; H, 7.09; N,
leff = 3.9 lB.
7.97. leff = 2.7 lB.
4.2.10. [Cr(PNP-iPr)Cl3] (3c)
4.2.6. [V(PNP-Et)Cl3] (2e)
This complex was prepared analogously to 3a using PNP-iPr
(1c) (341 mg, 1.0 mmol) and CrCl3(THF)3 (374 mg, 1.0 mmol).
Yield: 464 mg (93%). Anal. Calc. for C17H33Cl3CrN3P2 (499.77): C,
40.85; H, 6.65; N, 8.41. Found: C, 40.85; H, 6.65; N, 8.41%.
This complex was prepared analogously to 2a using PNP-Et (1e)
(285 mg, 1.0 mmol) and VCl3(THF)3 (374 mg, 1.0 mmol) as starting
materials. Yield: 438 mg (99%). Anal. Calc. for C13H25Cl3N3P2V
(442.61): C, 35.28; H, 5.69; N, 9.49. Found: C, 35.31; H, 5.68; N,
leff = 3.9 lB.
9.51%. leff = 2.8 lB.
4.2.7. [V(PNPPh-Pr)Cl3] (2g)
4.2.11. [Cr(PNPMe-iPr)Cl3] (3d)
This complex was prepared analogously to 2a using PNPPh-nPr
(1g) (494 mg, 1.0 mmol) and VCl3(THF)3 (374 mg, 1.0 mmol) as
starting materials. Yield: 631 mg (97%). Anal. Calc. for C29H41Cl3N3-
P2V (650.90): C, 53.51; H, 6.35; N, 6.46. Found: 53.48; H, 6.32; N,
This complex was prepared analogously to 3a using PNP-iPr
(1d) (369 mg, 1.0 mmol) and CrCl3(THF)3 (374 mg, 1.0 mmol) as
starting materials. Yield: 506 mg (96%). Anal. Calc. for C19H37Cl3-
CrN3P2 (527.82): C, 43.23; H, 7.07; N, 7.95. Found: C, 43.15; H,
6.49%.
leff = 2.8 lB
.
7.15; N, 8.00%. leff = 3.9 lB.
Please cite this article in press as: M. Mastalir et al., Inorg. Chim. Acta (2016), http://dx.doi.org/10.1016/j.ica.2016.02.064

M. Mastalir et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
7
4.2.12. [Cr(PNPPh-Et)Cl3] (3f)
4.2.21. [Mn(PNPMe-iPr)Cl2] (5d)
This complex was prepared analogously to 3a using PNPPh-Et
(1f) (437 mg, 1.0 mmol) and CrCl3(THF)3 (374 mg, 1.0 mmol) as
starting materials. Yield: 567 mg (93%). Anal. Calc. for C25H33Cl2-
CrN3P2 (595.84): C, 50.37; H, 5.57; N, 7.04. Found: C, 50.15; H,
This complex was prepared analogously to 5a using PNPMe-iPr
(1d) (369 mg, 1.0 mmol) and anhydrous MnCl2 (126 mg, 1.0 mmol)
as starting materials. Yield: 466 mg (94%). Anal. Calc. for C19H37Cl2-
MnN3P2 (495.31): C, 46.07; H, 7.53; N, 8.48. Found: C, 46.16; H,
5.45; N, 7.11%.
leff = 3.9 lB
.
7.59; N, 8.41%.
leff = 6.0 lB.
4.2.13. [Cr(PNP-Ph)Cl2] (4a)
solution of PNP-Ph (1a) (477 mg, 1.0 mmol) and CrCl2
4.2.22. [Mn(PNP-Et)Cl2] (5f)
A
This complex was prepared analogously to 5a using PNP-Et (1f)
(285 mg, 1.0 mmol) and anhydrous MnCl2 (126 mg, 1.0 mmol) as
starting materials. Yield: 402 mg (98%). Anal. Calc. for C13H25Cl2-
MnN3P2 (411.15): C, 37.98; H, 6.13; N, 10.22. Found: C, 37.89; H,
(122 mg, 1.0 mmol) in THF (10 ml) was stirred for 16 h. The green
solution was reduced to 2 mL and n–hexane (10 mL) was added for
precipitation. The dark green powder was collected on a glass frit,
and dried under reduced pressure. Yield: 557 mg (95%). Anal. Calc.
for C29H25Cl2CrN3P2 (600.38): C, 58.01; H, 4.19; N, 7.00. Found: C,
6.23; N, 10.30%. leff = 6.1 lB.
4.2.23. [Mn(PNPPh-Pr)Cl2] (5g)
58.15; H, 4.15; N, 6.91%.
leff = 5.0 lB.
This complex was prepared analogously to 5a using PNPPh-nPr
(1g) (494 mg, 1.0 mmol) and anhydrous MnCl2 (126 mg, 1.0 mmol)
as starting materials. Yield: 588 mg (95%). Anal. Calc. for C29H41Cl2-
MnN3P2 (619.45): C, 56.23; H, 6.67; N, 6.78. Found: C, 56.18; H,
4.2.14. [Cr(PNP-Cy)Cl2] (4b)
This complex was prepared analogously to 4a using PNP-Cy
(1b) (501 mg, 1.0 mmol) and CrCl2 (122 mg, 1.0 mmol) as starting
materials. Yield: 607 mg (97%). Anal. Calc. for C29H49Cl2CrN3P2
(624.58): C, 55.77; H, 7.90; N, 6.72. Found: C, 55.85; H, 7.65; N,
6.55; N, 6.86%. leff = 6.0 lB.
6.82%. leff = 5.0 lB.
4.3. General procedure for the oxidative homocoupling of ArMgBr with
MeI
4.2.15. [Cr(PNP-iPr)Cl2] (4c)
This complex was prepared analogously to 4a using PNP-iPr
(1c) (341 mg, 1.0 mmol) and CrCl2 (122 mg, 1.0 mmol) as starting
materials. Yield: 441 mg (95%). Anal. Calc. for C17H33Cl2CrN3P2
(464.32): C, 43.91; H, 7.14; N, 9.04. Found: C, 43.99; H, 7.25; N,
A 3.0 M solution of ArMgBr in Et2O (3.5 mL, 10.5 mmol) was
mixed with 1 mL of a 10 mM stock solution of the catalyst
(0.01 mmol) in THF under stirring. A 5 M solution of MeI (2 mL,
10.0 mmol) was added and the mixture was allowed to react for
15 min and was then quenched with iPrOH (0.5 mL). The product
was purified by silica column chromatography.
9.11%. leff = 5.0 lB.
4.2.16. [Cr(PNPMe-iPr)Cl2] (4d)
This complex was prepared analogously to 4a using PNPMe-iPr
(1d) (369 mg, 1.0 mmol) and CrCl2 (122 mg, 1.0 mmol) as starting
materials. Yield: 472 mg (96%). Anal. Calc. for C19H37Cl2CrN3P2
(492.37): C, 46.34; H, 7.56; N, 8.52. Found: C, 46.25; H, 7.61; N,
4.4. Crystal structure determination
X-ray diffraction data of 2aꢀ3.5(CH3)2CO, 2g, 3d, 4dꢀ0.5CH2Cl2,
and 5cꢀTHF were collected at T = 100 K in a dry stream of nitrogen
on a Bruker KAPPA APEX II diffractometer system with graphite
8.62%. leff = 5.0 lB.
monochromatized Mo K
a radiation (k = 0.71073 Å) and fine sliced
4.2.17. [Cr(PNPPh-Et)Cl2] (4f)
u- and -scans. Data were reduced to intensity values with SAINT
x
This complex was prepared analogously to 4a using PNPPh-Et
(1f) (437 mg, 1.0 mmol) and CrCl2 (122 mg, 1.0 mmol) as starting
materials. Yield: 515 mg (92%). Anal. Calc. for C25H33Cl2CrN3P2
(560.40): C, 53.57; H, 5.94; N, 7.49. Found: C, 53.65; H, 5.85; N,
and an absorption correction was applied with the multi-scan
approach implemented in SADABS [22]. The structures of 2aꢀ3.5
(CH3)2CO, 3d, 4dꢀ0.5CH2Cl2, and 5cꢀTHF were solved by charge-flip-
ping implemented in SUPERFLIP [23] and refined using JANA2006
[24] against F. The structure of 2g was solved with direct methods
implemented in SHELXS and refined using SHELXL [25] against F2. Non-
hydrogen atoms were refined with anisotropic displacement
parameters. The H atoms connected to C atoms were placed in cal-
culated positions and thereafter refined as riding on the parent
atoms. The H atoms of the amine groups were located in difference
Fourier maps. The N–H distances were restrained to 0.870(1) Å in
2a. In 5c the H atoms attached to N were freely refined. Molecular
graphics were generated with the program MERCURY [26].
7.44%. leff = 5.0 lB.
4.2.18. [Mn(PNP-Ph)Cl2] (5a)
PNP-Ph (1a) (477 mg, 1.0 mmol) and anhydrous MnCl2 (126 mg,
1.0 mmol) were suspended in THF (10 mL) and stirred for 16 h. The
suspension was reduced to 4 mL and n-hexane (20 mL) was added
for precipitation. The off-white powder was collected by filtration
and dried under reduced pressure. Yield: 579 mg (96%). Anal. Calc.
for C29H25Cl2MnN3P2 (603.32): C, 57.73; H, 4.18; N, 6.96. Found: C,
57.71; H, 4.17; N, 6.94%.
leff = 6.0 lB.
Acknowledgements
4.2.19. [Mn(PNP-Cy)Cl2] (5b)
This complex was prepared analogously to 5a using PNP-Cy
(1b) (501 mg, 1.0 mmol) and anhydrous MnCl2 (126 mg, 1.0 mmol)
as starting materials. Yield: 596 mg (95%). Anal. Calc. for C29H49Cl2-
MnN3P2 (627.51): C, 55.51; H, 7.87; N, 6.70. Found: C, 55.56; H,
Financial support by the Austrian Science Fund (FWF) is grate-
fully acknowledged (Project No. P24583-N28). The X-ray center of
the Vienna University of Technology is acknowledged for financial
support and for providing access to the single-crystal
diffractometer.
7.84; N, 6.74%. leff = 5.9 lB.
4.2.20. [Mn(PNP-iPr)Cl2] (5c)
This complex was prepared analogously to 5a using PNP-iPr
(1c) (341 mg, 1.0 mmol) and anhydrous MnCl2 (126 mg, 1.0 mmol)
as starting materials. Yield: 450 mg (96%). Anal. Calc. for C17H33Cl2-
MnN3P2 (467.26): C, 43.70; H, 7.12; N, 8.99. Found: C, 43.82; H,
Appendix A. Supplementary material
CCDC 1434128–1434132 contains the supplementary crystallo-
graphic data for compounds 2aꢀ3.5(CH3)2CO, 2g, 3d, 4dꢀ0.5CH2Cl2,
and 5cꢀTHF. These data can be obtained free of charge from The
7.15; N, 9.05%. leff = 6.1 lB.
Please cite this article in press as: M. Mastalir et al., Inorg. Chim. Acta (2016), http://dx.doi.org/10.1016/j.ica.2016.02.064

8
M. Mastalir et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
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Please cite this article in press as: M. Mastalir et al., Inorg. Chim. Acta (2016), http://dx.doi.org/10.1016/j.ica.2016.02.064