A tripodal benzylene-linked trisamidophosphine ligand scaffold: Synthesis and coordination chemistry with group(IV) metals

Article abstract of DOI:10.1021/ic500163c

A new tripodal trisamidophosphine ligand (1) based on the trisbenzylphosphine backbone has been synthesized in three steps starting from NaPH₂ and phthaloyl-protected 2-aminobenzyl bromide. At elevated temperatures, 1 reacts directly with M(NMe

Full text of DOI:10.1021/ic500163c

Article
pubs.acs.org/IC
A Tripodal Benzylene-Linked Trisamidophosphine Ligand Scaffold:
Synthesis and Coordination Chemistry with Group(IV) Metals
Sonja Batke, Malte Sietzen, Hubert Wadepohl, and Joachim Ballmann*
Anorganisch-Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 276, 69120 Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: A new tripodal trisamidophosphine ligand (1)
based on the trisbenzylphosphine backbone has been synthesized
in three steps starting from NaPH2 and phthaloyl-protected 2-
aminobenzyl bromide. At elevated temperatures, 1 reacts directly
with M(NMe2)4 (M = Zr, Hf) to afford the dimethylamido
complexes [PN3]M(NMe2) (M = Zr, Hf) (2), which are easily
converted into the corresponding triflates [PN3]MOTf (M = Zr,
Hf) (3) via reaction with triethylsilyl trifluoromethanesulfonate.
The related titanium chloro complex [PN3]TiCl (4-Ti) is
obtained from 1 and Bn3TiCl via protonolysis. Triple deprotona-
tion of 1 with n-butyllithium affords the tris-lithium salt Li3[PN3]
(1-Li), which serves as a common starting material for the
preparation of all the group(IV) chlorides [PN3]MCl (M = Ti, Zr,
Hf) (4). Upon treatment of 4-Ti with Bn2Mg(thf)2, formation of a
benzyltitanium species is observed, which is converted cleanly into a ligand-CH-activated species (5-Ti).
ligand scaffold coordinates to numerous transition metals5 and
INTRODUCTION
■
main block elements.6 Complexes of this type have found
widespread applications in organic and inorganic chemistry, for
example, in small molecule activation,7 dehydrocoupling
reactions,8 polymerizations,9 or simply as an effective proton
acceptor (Verkade’s base10). Nowadays, over 50 derivatives of
tren (commonly abbreviated with [NN3])11 and related
trisanionic ligand systems with [NO3],12 [NS3],13 and [PS3]14
donor sets are well-established (c.f. B and C, Chart 1).
Surprisingly, trisanionic [PN3]-systems are rare, and so far, only
the C1-linked (C1 = methylene) system P(CH2NHAr)3 has
been used in coordination chemistry.15 In contrast to A, B, and
C, this particular ligand scaffold coordinates in a tridentate
fashion, leaving the phosphine exo-configured (D, Chart 1). In
the context of dinitrogen activation, beneficial effects upon
formal exchange of the central tren-nitrogen for a phosphine
have been predicted on a theoretical basis,16 but these
theoretical studies suppose a tetradentate coordination of a
trisanionic [PN3]-ligand. Thus, efforts have been made to
access coordination compounds of tris(2-aminoethyl)-phos-
phine (phospha-tren) and other potentially tetradentate
trisamidophosphines. Although C2-linked [PN3]-ligands (C2 =
ethylene, phenylene) have been prepared,17 it seems that their
complexes are not readily accessible, possibly due to formation
of polymeric species.
When Verkade and co-workers reported the first titanium
complex that employs the tren framework as a tetradendate
trisanion in 1991,1 the term metallazatrane was coined to
describe such inherently C3-symmetric complexes, which
incorporate the tren-ligand in its trisanionic form. Soon after
this seminal work, derivatives of the original N,N′,N″-trimethyl-
tren system (A, R = Me, Chart 1) were developed by Verkade,2
Schrock,3 and Gade,4 and it was shown that this privileged
Chart 1. Selection of C3-Symmetric Complexes That Employ
Trisanionic Ligand Scaffolds
Very recently, we demonstrated that the C3-linked
trisamidophosphine ligand E (Chart 1) coordinates in a
Received: January 22, 2014
Published: April 8, 2014
© 2014 American Chemical Society
4144
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
Scheme 1. Ligand Synthesis (Arabic Numbers at 1 are Labels for NMR Signal Assignment)
tetradendate fashion upon ligation to group(IV) metals.18 As
the latter system is based on a triphenylphosphine core, a
limited donor strength of the apical phosphine (compared to
phospha-tren) had to be expected a priori. Nevertheless, the
triatomic C3-linkage in E proved to be appropriate for
tetradentate binding to the central metal and inspired us to
synthesize a [PN3]-ligand with an inverted benzylene-spacer
(i.e., a derivative of 2,2′,2″-trisamino-trisbenzylphosphine,
structure F in Chart 1) in order to establish the coordination
chemistry of such a trisalkylphosphine-based [PN3]-system. In
this study, we focused on the tris-trimethylsilyl derivative of
ligand F (R = SiMe3), as silyl-aryl amines are commonly readily
deprotonated even in cases of sterically demanding sub-
stituents.5a,f−h,r Compared to ligand E (containing three aryl-
alkyl amines), a stabilizing effect has to be expected in
complexes F (R = SiMe3) due to the silyl substituents, which
are located in β-positions with respect to the central metal.
generated and isolated in the form of its tris-hydrochloride
salt. Starting from this salt, a trimethylsilyl substituent was
attached to each of the three amino groups to obtain the
desired ligand 1 as an off-white powder (Scheme 1).
As expected, 1 only exhibits one singlet in the 31P NMR
spectrum at δ = −38.3 ppm, which is shifted upfield compared
25
1
to Bn3P (δ = −11.3 ppm ) (Bn = benzyl). The H NMR
spectrum indicates that a highly symmetric species is present in
solution, as only one set of signals is detected for the three
individual side arms. Thus, one benzylic, one broadend NH,
and one sharp trimethylsilyl signal are observed in addition to
four aromatic resonances. Single crystals were grown by cooling
a saturated solution of 1 in pentane to −40 °C and subjected to
X-ray diffraction (see Figure 1), confirming the formation of
RESULTS AND DISCUSSION
■
Ligand Synthesis. For the synthesis of an F-type ligand,
three strategies were considered, namely, (i) metalation of N-
protected o-toluidine at the benzylic position19 and subsequent
reaction with a phosphorus electrophile (PCl3, P(OPh)3), (ii)
synthesis of tris(o-nitrobenzyl)-phosphine and subsequent
reduction, and (iii) synthesis of an N-protected primary o-
aminobenzyl-phosphine20 and subsequent reaction with the
corresponding N-protected o-aminobenzyl bromide. In pre-
liminary experiments, route (iii) was identified as the most
promising approach as (o-phthalimido)-benzyl bromide21 reacts
cleanly with primary phosphines. However, preparation of the
key building block, (o-phthalimido)-benzyl-phosphine, proved
to be more difficult than expected, although a potentially
explosive procedure for the preparation of o-aminobenzyl-
phosphine20 was optimized successfully (see the Supporting
Information). In an attempt to prepare (o-phthalimido)-benzyl-
phosphine starting from (o-phthalimido)-benzyl bromide21 and
NaPH2,22 no primary phosphine, but a small amount of tris(o-
phthalimidobenzyl)-phosphine, i.e., the phthaloyl-protected
ligand scaffold (1-Phth), was isolated (Scheme 1). Treatment
of NaPH2 with 3 equiv of (o-phthalimido)-benzyl bromide in
the presence of 2 equiv of sodium tert-butanolate in THF
afforded 1-Phth in low yields (approximately 10%). While
changing to other alkali metal PH2− salts23 or substitution of (o-
phthalimido)-benzyl bromide for the respective chloride did
not result in improved yields, the use of DME (DME =
dimethoxyethane) instead of THF led to an enhanced
procedure as the desired product forms in acceptable yields
(approximately 30%) and precipitates straight from the reaction
mixture along with sodium bromide (see Scheme 1). The
inorganic salts are easily removed, and the key intermediate 1-
Phth thus obtained is sufficiently pure for subsequent
deprotection. Employing a standard deprotection protocol via
hydrazinolysis of the phthalimide,24 the free amine was
Figure 1. ORTEP plot of the molecular structure of 1 (carbon-bound
protons omitted for clarity; thermal ellipsoids set at 50% probability).
Selected bond lengths (Å) and angles (deg): Si1−N1 1.7376(14),
Si2−N2 1.7306(13), Si3−N3 1.7428(14), P−C2 1.8532(14), P−C1
1.8542(15), P−C3 1.8576(14); C2−P−C1 99.66(7), C2−P−C3
101.13(7), C1−P−C3 101.46(7).
the target ligand. A particular interesting feature emerging from
the molecular structure of 1 is that the ligand adopts a bowl-
shaped conformation in the solid state, which appears to be
ideally suited to host the targeted metal ions.
Complex Synthesis. Starting from 1, the dimethylamido
species [PN3]M(NMe2) 2 (M = Zr, Hf) were prepared by
reaction with tetrakis(dimethylamido)zirconium and tetrakis-
(dimethylamido)hafnium, respectively (see Scheme 2). Pro-
longed heating (5 days in the case of Zr and 18 days in the case
of Hf) at elevated temperatures (130 °C in toluene) is required
to ensure full conversion, which favors the formation of several
byproducts in addition to the target compounds. While the
yield of crude products is in satisfactory ranges (approximately
65%), analytically pure material is only obtained in relatively
modest yields (33% in the case of Zr and 35% in the case of
1
Hf). According to H and 13C NMR data, complexes 2 (M =
Zr, Hf) are C3-symmetric in solution, which implies free
rotation of the dimethylamido substituent at room temperature.
In the proton NMR spectra, diastereotopic resonances are
observed for the methylene protons, indicating that the rotation
of the three side arms along the 3-fold axis is hindered
4145
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
Scheme 2. Synthesis of 1-Li, 2 (M = Zr, Hf), 3 (M = Zr, Hf), and 4 (M = Ti, Zr, Hf) Starting from 1
substantially. Even at 80 °C, no signs of a beginning
coalescence of these signals are detectable, which renders the
complexes configurationally stable. From a theoretical point of
view, racemization in solution is possible via either a C3v- or a
CS-symmetric transition state (see the Supporting Information),
but not observed experimentally for any of the compounds
described herein (2-M to 4-M, M = Ti, Zr, Hf). The 31P NMR
spectra exhibit a single resonance at 17.2 ppm (2-Zr) and 26.7
ppm (2-Hf), respectively. While this rather unusual difference
in 31P NMR shifts (almost 10 ppm) is certainly noteworthy, we
are unable to provide an explanation for this phenomenon, as
the 31P NMR resonances of all other zirconium and hafnium
complexes in this work (vide infra) differ by less than 5.5 ppm
(cf. 4-Zr and 4-Hf). If the apical phosphines in 2-Zr and 2-Hf
are actually coordinated (endo-configuration) or pointing away
from the central metals (exo-configuration) can be extracted
Hf−P = 2.7154(5) Å). All metrical parameters within the ligand
framework display typical values, which is also the case for the
distances between the amido nitrogens and the central metal
ions. The coordination polyhedra in 2 deviate only slightly from
ideally trigonal-bipyramidal structures (N1, N2, and N3 in
equatorial positions) with an averaged Neq−M−Neq angle of
approximately 116° in both cases (M = Zr, Hf). The
dimethylamido nitrogen atom N4 and the central phosphine
of 2-Zr and 2-Hf are found in apical positions (P1−Zr−N4 =
173.55(4)°, P−Hf−N4 = 173.60(5)°) with the central metals
located above the equatorial planes through N1, N2, and N3
(approximately 0.45 Å in 2-Zr and 0.43 Å in 2-Hf). Compared
to 2-Zr (Zr−P1 = 2.7284(13) Å), the dimethylamido
zirconium complex of ligand E (Chart 1, R = 3,5-xylyl; M =
Zr; L = NMe2) exhibits a metal−phosphorus distance of
2.824(1) Å.18a This indicates a weaker interaction between the
metal and the phosphine in the latter complex and
demonstrates that the phosphine in ligand 1 is indeed a more
electron-donating anchor (compared to the trisarylphosphine-
based ligand E).
1
neither from these 31P NMR shifts nor from the H or 13C
NMR data. To address this question, crystals of both the
zirconium and the hafnium derivative of 2 were grown from
saturated toluene solutions and examined by X-ray diffraction
methods (see Figure 2 and Figure S2 in the Supporting
Information). The structural analysis reveals both complexes to
be endo-configured with metal−phosphorus bond distances well
within the usual range26 (2-Zr: Zr−P1 = 2.7284(13) Å; 2-Hf:
Complexes 2 are easily converted into the corresponding
triflates 3 via reaction with triethylsilyl trifluoromethanesulfo-
nate (see Scheme 2). Both triflates 3 (M = Zr, Hf) exhibit 3-
fold symmetry in solution with only one singlet for the TMS
1
groups (TMS = trimethylsilyl) present in the individual H
NMR spectra. Compared to the starting dimethylamido species
2, a downfield shift of the 31P NMR resonances of 3 is observed
and the product signals are detected at 26.3 ppm (3-Zr) and
29.6 ppm (3-Hf). For 3-Hf, single crystals suitable for X-ray
diffraction were obtained by cooling a saturated toluene
solution of the complex to −40 °C (see Figure 3). What is
evident at a glance is that the central phosphine is still
coordinated to the hafnium center and that the triflate occupies
the remaining apical position of the trigonal-bipyramidal
coordination polyhedron. Compared to 2-Hf, a significantly
shorter Hf−P distance (2.647(2) and 2.654(2) Å in 3-Hf vs
2.7154(5) Å in 2-Hf) is noticed, while most other distances and
angles within the [PN3]Hf core differ only slightly or
insignificantly. This stronger Hf−P interaction renders the
phosphine more electropositive and explains the observed
downfield shift in the 31P NMR spectrum of 3-Hf (compared to
2-Hf). Compared to the corresponding hafnium triflate of
ligand E (Chart 1, R = 3,5-xylyl; M = Zr; L = OTf), which
displays a metal phosphorus distance of 2.713(1) Å, a shorter
Hf−P distance is found for 3-Hf.18b This effect is attributed to
Figure 2. ORTEP plot of the molecular structure of 2-Zr (protons
omitted for clarity; thermal ellipsoids set at 50% probability). Selected
bond lengths (Å) and angles (deg): Zr−N4 2.0879(17), Zr−N1
2.0975(18), Zr−N2 2.1252(16), Zr−N3 2.1440(15), Zr−P1
2.7284(13); N4−Zr−N1 104.96(6), N4−Zr−N2 96.69(6), N1−Zr−
N2 115.99(5), N4−Zr−N3 105.23(6), N1−Zr−N3 113.74(6), N2−
Zr−N3 117.09(6), N4−Zr−P1 173.55(4), N1−Zr−P1 78.18(4), N2−
Zr−P1 76.87(4), N3−Zr−P1 78.17(4).
4146
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
formation of unidentified mixtures. In contrast, treatment of 1
with Bn3TiCl proceeds cleanly via the isolable intermediate
[HNPN2]Ti(Bn)(Cl) (see the Supporting Information) and
results in the formation of the desired [PN3]TiCl complex (4-
Ti; see Scheme 2).
As the synthesis of 4 (M = Ti, Zr, Hf) suffered from the
cumbersome preparation of Bn3TiCl29 or from the time-
consuming preparations of the required precursors 2 (M = Zr,
Hf), an alternative synthetic pathway to the entire series 4 (M =
Ti, Zr, Hf) was highly desirable. With the MCl4(THF)2
precursors (M = Ti, Zr, Hf) readily available for all group(IV)
metals,30 the preparation of 4 via the tris-lithium salt Li3[PN3]
(1-Li) was explored. The required lithium salt 1-Li was easily
prepared in high yield (89%) by treatment of a cold solution of
1 in pentane with 3 equiv of n-butyl lithium and isolated as a
1
THF adduct. According to H NMR integration, 1 equiv of
Figure 3. ORTEP plot of the molecular structure of 3-Hf (protons
omitted for clarity; thermal ellipsoids set at 50% probability). In
addition to the shown molecule, there is a second independent
molecule with fairly similar metrical parameters present in the unit cell.
Selected bond lengths (Å) and angles (deg) (values in square brackets
refer to the second molecule): Hf1−P1 2.647(2) [2.654(2)], Hf1−O1
2.143(7) [2.144(7)], Hf1−N2 2.067(8) [2.085(9)], Hf1−N1
2.080(9) [2.082(8)], Hf1−N3 2.088(9) [2.074(9)]; O1−Hf1−P1
178.8(2) [178.5(2)], N2−Hf1−P1 79.8(2) [80.5(3)], N2−Hf1−O1
100.3(3) [99.7(3)], N2−Hf1−N1 114.6(3) [118.1(4)], N2−Hf1−N3
117.9(3) [115.9(4)], N1−Hf1−P1 80.2(2) [79.2(3)], N1−Hf1−O1
100.7(3) [99.5(3)], N1−Hf1−N3 118.4(4) [116.9(4)], N3−Hf1−P1
79.7(3) [80.0(2)], N3−Hf1−O1 99.2(3) [101.2(3)].
THF is present per cation, and all three lithium nuclei are
7
equivalent according to Li NMR (δ = 0.29 ppm). The 31P
NMR spectrum of 1-Li in THF-d8 exhibits a singlet at −32.3
ppm, i.e., downfield shifted with respect to the protioligand 1 (δ
= −38.3 ppm). Thus, a weak coordinative interaction between
the lithium and the phosphorus nuclei seems to be present at
room temperature, although no coupling between the two
nuclei was observed. Single crystals of 1-Li suitable for X-ray
diffraction were obtained from saturated Et2O/THF solutions
and subjected to X-ray diffraction (see Figure 4). The molecular
structure in the solid state does not reflect the structure present
in solution, as one of the lithium ions is coordinated by solvent
the different designs of ligands E and 1 and was expected a
priori. Once attached to the metal, however, complexes of
ligands E and 1 react in a rather similar way, which is noticed,
for example, in the preparation of the [PN3]MOTf complexes
(M = Zr, Hf, [PN3] = ligand E, 1), as equivalent synthetic
routes starting from the respective dimethylamido complexes
are employed in both cases.18
Similar to the triflates 3, the corresponding chlorides
[PN3]MCl (4-Zr and 4-Hf) are readily prepared by addition
of trimethylsilyl chloride to solutions of 2 (M = Zr, Hf) in
toluene (see Scheme 2). The proton NMR spectra of 3-Zr and
4-Zr exhibit only minor differences, and the 31P NMR
resonances are almost identical (26.3 ppm for 3-Zr vs 26.2
ppm for 4-Zr). For hafnium, the former differences are slightly
more pronounced with 31P NMR resonances found at 29.6
ppm for 3-Hf and at 31.7 ppm for 4-Hf, although 3 and 4 can
be considered equivalent from a chemical point of view.
Interestingly, zirconium and hafnium react almost identically
when attached to the trisamidophosphine ligand 1. This was
also noticed in the preparation of 2 (M = Zr, Hf), as the
reaction of M(NMe2)4 (M = Zr, Hf) with 1 occurs for
zirconium as well as for hafnium employing rather similar
reaction conditions. In contrast to its heavier homologues, a
mixture of unidentified products was obtained upon reaction of
1 with tetrakis(dimethylamido)titanium. According to 31P
NMR spectroscopy, at least five species in approximately
equal amounts had formed and no signal corresponding to a
titanium-bound dimethylamido substituent was detected by 1H
NMR spectroscopy. Similarly, treatment of 1 with (Me2N)2-
TiCl227/LiNMe2 or with (Me2N)3TiCl28 failed to produce
closed-cage complexes, but resulted in the formation of a
species with one dangling side arm or in a trinuclear species
([HNPN2]TiCl2, [(TMS)1PN3]2Ti3; see the Supporting
Information). Reaction of 1 with Bn4Ti29 also results in the
Figure 4. ORTEP plot of the molecular structure of the anion of 1-Li
(top) (hydrogen atoms and Li(OEt2)2(THF)2 counterion are omitted
for clarity; thermal ellipsoids set at 50% probability) and detailed view
of the core structure (bottom) (peripheral phenyl carbons, selected
silylmethyl and hydrogen atoms omitted). Selected bond lengths (Å)
and angles (deg): Li1···Li2 2.504(7), P1−Li1 2.602(5), P1−Li2
2.588(5), O1−Li1 2.240(6), O1−Li2 2.087(5), N1−Li1 1.969(6),
N2−Li1 2.068(6), N2−Li2 2.138(6), N3−Li2 1.970(6); Li2−P1−Li1
57.69(16), Li2−O1−Li1 70.6(2), Li1−N2−Li2 73.1(2), O1−Li1−P1
91.87(19), O1−Li2−P1 95.9(2).
4147
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
Table 1. Selected Metrical Parameters and 31P NMR Shifts of 4 (M = Ti, Zr, Hf)
4-Ti
2.5387(12)
4-Zr
2.6796(14)
4-Hf
2.6616(3)
M−P (Å)
M−N (Å)
M−Cl (Å)
1.9525(13)−1.9642(15)
2.3645(11)
2.0839(16)−2.0911(18)
2.4794(13)
2.0732(11)−2.0779(11)
2.4471(3)
P−M−Cl (deg)
δ
173.119(17)
40.7
172.108(17)
26.2
172.909(11)
31.7
a
31P (ppm)
a
Recorded in toluene-d8 at room temperature.
molecules only (two THF and two Et2O molecules). The latter
lithium solvate serves as counterion for a monoanionic
[PN3]Li2(μ-THF) arrangement with two lithium ions located
within the ligand’s half-cage framework. In consequence, two
7Li NMR signals in a 2 to 1 ratio are to be expected if this
structure was also present in solution. Upon dissolution of the
crystals in THF-d8, only the above-mentioned singlet was
to be removed by filtration over rigorously dried aluminum
oxide. This rather unusual purification methodology works on
small scales only, as prolonged contact with the aluminum
oxide induces degradation of the complex. Despite numerous
efforts to optimize this procedure, yields of pure 4-Ti were
consistently in the range of 20% only. Nevertheless, this
procedure is preferred over the reaction of 1 with Bn3TiCl
(vide supra). Complex 4-Ti is also generated by reaction of 1-
Li with TiCl3(thf)3 and in situ oxidation with PbCl2.
Unidentified impurities (approx 15% by 31P NMR spectrosco-
py), however, could not be removed efficiently, which renders
this procedure inapplicable.
7
detected in the Li NMR (1-Li is almost insoluble in C6D6 or
toluene-d8 and decomposes immediately in DMSO-d6 or
CD2Cl2; therefore, THF-d8 is required for NMR spectroscopic
studies). At −80 °C, all NMR signals (1H NMR and 31P{1H}
NMR) are broadened significantly or completely absent, which
precludes a meaningful analysis. This is also the case if
crystalline [Li(THF)2(OEt2)2]{[PN3]Li2(μ-THF)} is dissolved
in precooled THF-d8 (−80 °C) and the NMR spectra recorded
at −80 °C (precooled spectrometer). In the 7Li NMR
spectrum, a sharp peak (tentatively assigned to the solvated
lithium cation) is observed at low temperatures in addition to
unresolved broad signals (see the Supporting Information).
Proton NMR spectra of all three complexes 4 indicate that
the complexes are C3-symmetric in solution with only one
resonance each observed for the equivalent sets of atoms of the
individual side arms. A singlet in the 31P NMR spectrum is
detected for each complex, and an increasing shift to more
positive δ values in the order 4-Zr (δ = 26.2 ppm) > 4-Hf (δ =
31.7 ppm) > 4-Ti (δ = 40.7 ppm) is noticed (see Table 1). As
the ionic radii of the group(IV) metals decrease in the above
order, the Lewis acidities increase in just the same way, if
oxidation states and coordination numbers remain constant.
Thus, the above trend of the 31P NMR shifts might be
explained by an increasingly stronger interaction between the
metal and the phosphine donor provoked by an increasing
Lewis acidity of the metal ion, as stronger M−P interactions
lead to a deshielding of the 31P nucleus. To substantiate this
simple explanation, single crystals of 4 (M = Ti, Zr, Hf) for X-
ray diffraction analysis were required in order to determine the
metal phosphorus distances and to ensure that coordination
numbers and other metrical parameters are within comparable
boundaries. Fortunately, single crystals of all three complexes
were obtained readily via diffusion of pentane into saturated
solutions of the complexes in toluene (see Figure 5). Trigonal-
bipyramidal coordination polyhedra with the amido donors
occupying equatorial positions are found for all type-4
complexes. The chlorides and phosphines are located in axial
positions, and a similar deviation from linearity is observed for
the individual P−M−Cl vectors (see Table 1). Comparison of
the metal phosphorus distances in 4 (M = Ti, Zr, Hf) confirms
the expected trend as the respective bond lengths decrease in
the order of Zr−P > Hf−P > Ti−P.
7
Unfortunately, the observed Li NMR shift for 1-Li does not
allow for a conclusive statement on coordination numbers or
7
geometries, as Li NMR signals of related lithium amides are
found within −1.8 and +4.9 ppm (see the Supporting
Information). On the basis of these observations, we propose
that a dynamic exchange process sets in upon dissolution of 1-
Li in THF-d8 and that this process renders all lithium atoms
equivalent at room temperature.
Although unexpected at first, the molecular structure of 1-Li
in the solid state exhibits several interesting features (see Figure
4). Each of the lithium ions situated within the ligands half-cage
is bound to one individual amido side arm, and both metals are
bridged by the remaining third amido side arm, by the
phosphine, and by a THF molecule. In addition, an agostic
interaction between Li1 and one of the silylmethyl groups
seems to be present, as indicated by one unusual H−C19−H
angle of approximately 95° and a short distance between the
center of the respective C−H bond and Li1 (approximately
2.68 Å). Thus, the coordination geometry around Li1 is best
described as distorted trigonal-bipyramidal with P1 and C19-H
in axial positions and N1, N2, and O1 in the equatorial plane.
For Li2, a distorted tetrahedral coordination environment is
found. Particularly noteworthy is a relatively short intermetallic
distance of 2.504(7) Å within the triply bridged bimetallic
assembly.31
With 1-Li in hand, the [PN3]M chlorides 4 (M = Ti, Zr, Hf)
were generated by addition of a precooled suspension of 1-Li in
toluene to a suspension of MCl4(thf)2 in toluene at −40 °C,
and the respective products were isolated after the reaction
mixtures had been warmed to room temperature over the
course of 4−6 h. For zirconium and hafnium, this procedure led
to the desired compounds 4-Zr and 4-Hf in high purity and
acceptable yields (approximately 50%). For titanium, however,
side-products formed in addition to the target material and had
With all chloro complexes 4 available, we turned the focus to
the preparation of [PN3]M(alkyl) species (M = Ti, Zr, Hf) and
examined the reactions of 4 with Grignard reagents and
dialkylmagnesium species, such as Bn2Mg(THF)2.32 To our
surprise, 4-Zr and 4-Hf do not react with different magnesium
alkyls (MeMgBr, Me2Mg(THF)2, PhMgBr, BnMgCl, Bn2Mg-
(THF)2) not even after prolonged reaction times (up to 2
weeks) at elevated temperatures (90 °C). In contrast, 4-Ti
reacts slowly with Bn2Mg(THF)2, and a new 31P NMR signal
appears at δ = −31.4 ppm after several days at room
temperature. However, incomplete conversion was observed
4148
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
that the 3-fold symmetry is lost and that a compound with
different side arms had formed. Six methylene protons of the
ligands’ benzyl moieties are observed along with overall 12
partially overlapping aryl signals. In addition to two singlets for
the TMS groups, which integrate to 18 protons, two other
methylsilyl resonances are detected at δ = 0.77 ppm and δ =
0.00 ppm with an intensity of three protons each. No signals for
a titanium-bound benzyl ligand are detected, but two coupled
doublets corresponding to one proton each are present at 2.38
and 1.21 ppm, respectively.
On the basis of this analysis, formation of a CH-activated
species as shown in Scheme 3 is proposed. This is corroborated
by 13C, 13C-DEPT, 1H,13C-HSQC, 1H,13C-HMBC, 1H,1H-
1
COSY, H,31P-HMBC, and 29Si NMR spectra, all of which are
in agreement with the anticipated structure of 5-Ti. As all
attempts to crystallize 5-Ti for single-crystal X-ray diffraction
failed, the acquired NMR data were also compared to related
systems known in literature. With trimethylsilyl substituted
tren-ligands for example, two group(IV) azatranes that show a
similar type of intraligand CH activation have been reported,
namely, the TMS[NN3]-titanium3b,c and TMS[NN3]-zirco-
nium5h,33 derivatives. In both cases, similar proton NMR
data, especially with respect to the metal-bound methylene
group, are well-documented, thus supporting our structural
assignment of 5-Ti (see Scheme 3). In this context, it is
noteworthy that the titanium−methyl complex of ligand E (see
Chart 1) is prone to intraligand CH activation as well, while the
corresponding zirconium and hafnium complexes do not show
such reactivity.18 Thus, the titanium derivatives of the [PN3]-
ligands E and F are directly comparable, while surprising
differences in the initial complexation of titanium are apparent.
With both ligands in hand, we will now continue to explore
their (possibly dissimilar) coordination chemistry with other
early transition metals and also focus on the reactivity of the
CH-activated titanium complexes. While attempts to hydro-
genate 5-Ti were not productive yet, efforts to react 5-Ti, for
example, with silanes are ongoing in our laboratories and
directed toward the application of this system as “hydride
surrogate”.34
Figure 5. ORTEP plots of the molecular structures of 4-Ti (top), 4-Zr
(middle), and 4-Hf (bottom) (protons omitted for clarity; thermal
ellipsoids set at 50% probability). Selected bond lengths (Å) and
angles (deg) of 4-Ti: Ti−Cl 2.3645(11), Ti−P 2.5387(12), Ti−N1
1.9525(13), Ti−N2 1.9642(15), Ti−N3 1.9559(14); Cl−Ti−P
173.119(17), N1−Ti−Cl 95.90(4), N1−Ti−P 79.86(4), N1−Ti−N2
122.03(6), N1−Ti−N3 116.66(6), N2−Ti−Cl 96.41(4), N2−Ti−P
81.47(4), N3−Ti−Cl 103.98(4), N3−Ti−P 82.82(4), N3−Ti−N2
114.62(5). Selected bond lengths (Å) and angles (deg) of 4-Zr: Zr−Cl
2.4794(13), Zr−P 2.6796(14), Zr−N1 2.0911(18), Zr−N2
2.0839(16), Zr−N3 2.0891(17); Cl−Zr−P 172.108(17), N1−Zr−Cl
98.76(4), N1−Zr−P 78.78(4), N2−Zr−Cl 97.85(5), N2−Zr−P
77.13(5), N2−Zr−N1 119.05(7), N2−Zr−N3 116.26(6), N3−Zr−
Cl 107.93(4), N3−Zr−P 79.87(4), N3−Zr−N1 113.18(6). Selected
bond lengths (Å) and angles (deg) of 4-Hf: Hf−Cl 2.4471(3), Hf−P
2.6616(3), Hf−N1 2.0779(11), Hf−N2 2.0732(11), Hf−N3
2.0777(11); Cl−Hf−P 172.909(11), N1−Hf−Cl 98.24(3), N1−Hf−
P 79.53(3), N2−Hf−Cl 97.54(3), N2−Hf−P 77.99(3), N2−Hf−N1
119.74(4), N2−Hf−N3 116.62(4), N3−Hf−Cl 106.35(3), N3−Hf−P
80.66(3), N3−Hf−N1 113.64(4).
CONCLUSION
■
In conclusion, the new trisamidophosphine ligand 1 was
synthesized and comprehensively characterized, and its
coordination chemistry was examined with all of the group(IV)
metals. For zirconium and hafnium, the dimethylamido and
triflato species 2 and 3 were prepared and their structures were
elucidated by X-ray crystallography. A synthetic pathway that
affords the [PN3]MCl (4, M = Ti, Zr, Hf) species via the
lithium salt 1-Li was developed, and all complexes 4 and the
lithium salt 1-Li were studied in detail. Reaction of Bn2Mg-
(THF)2 with 4-Ti results in a ligand-CH-activated species (5-
Ti) and provides a basis for further studies employing 5-Ti, for
example, in dehydrocoupling reactions.34
EXPERIMENTAL SECTION
■
General Methods. All manipulations were performed under an
atmosphere of dry and oxygen-free argon by means of standard
Schlenk or glovebox techniques. Solvents were either taken from an M.
Braun Solvent Purification System (THF, Et2O, toluene, n-hexane, and
n-pentane) or dried over CaH2 and distilled (TMS2O, CH2Cl2)
(TMS2O = hexamethyldisiloxane). Toluene-d8, THF-d8, and benzene-
d6 were refluxed over sodium and purified by distillation. NEt3 was
dried over CaH2 and purified by distillation. DME was dried over
even in the case of an excess of Bn2Mg(THF)2. On the basis of
1H NMR analysis, the new species at δ(31P) = −31.4 ppm is
tentatively assigned to [PN3]TiBn. Upon heating a mixture of
unreacted 4-Ti, Bn2Mg(THF)2, and [PN3]TiBn, complete
conversion to a new species at δ(31P) = 24.3 ppm was observed,
and the resulting product 5-Ti was isolated in 66% yield after
work-up. What emerges from the 1H NMR spectrum of 5-Ti is
4149
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
Scheme 3. Synthesis of 5-Ti Starting from 4-Ti
sodium benzophenone ketyl and EtOH over magnesium tunings, and
both were purified by distillation. Hydrazine monohydrate was
degassed by three freeze−pump−thaw cycles and kept under an
atmosphere of dry argon. Triethylsilyl trifluoromethanesulfonate and
trimethylsilyl chloride were purified by simple distillation prior to use.
31P, 1H, and 13C NMR spectra were recorded on a Bruker Avance 600
MHz or a Bruker Avance 400 MHz spectrometer at room temperature.
1H and 13C NMR spectra were referenced to residual proton signals of
the lock solvents. 31P NMR spectra were referenced to external
P(OMe)3 (141.0 ppm with respect to 85% H3PO4 at 0.0 ppm).
Assignments of the NMR signals (see Scheme 1 for atom numbering)
and coupling constants (JH,P vs JH,H) were ascertained by 1H,1H−
COSY, 13C-DEPT, 1H,13C-HSQC, 1H,13C-HMBC, and 1H{31P} NMR
spectroscopy. Microanalyses (C, H, N) were performed at the
Department of Chemistry at the University of Heidelberg. Especially
in the case of the zirconium and hafnium complexes, severe difficulties
were encountered in obtaining satisfactory elemental analyses. As
carbon values were found reproducibly too low, it is assumed that
carbides of the metals form during combustion. This hypothesis is
supported by the fact that almost all elemental analyses are satisfactory,
if a stoichiometric amount of carbon is deducted from the theoretical
carbon value. However, unambiguous proof for this assumption cannot
be provided; therefore, theoretical values are given without subtraction
of a carbon atom. The starting materials (o-phthalimido)-benzyl
bromide,21 NaPH2,22a Bn3TiCl,29 MCl4(THF)2 (M = Ti, Zr, Hf),30
ether and excess hydrogen chloride were then removed under reduced
pressure, and the suspension was cooled to 0 °C. Insoluble
phthaloylhydrazide was filtered off, and the filtrate was condensed to
dryness. The residual solid was suspended in methylene chloride (200
mL), and triethylamine (11.5 mL, 85 mmol, 7.6 equiv) was added
subsequently. The reaction mixture was stirred for 20 min at room
temperature, and trimethylsilyl chloride (21.7 mL, 170 mmol, 15.2
equiv) was added dropwise over a period of 15 min. Stirring was
continued for 16 h at room temperature, and all volatiles were then
removed in vacuum. The resulting white residue was extracted with
pentane (3 × 50 mL), and the filtrate was condensed to dryness. The
residual crude product was triturated with TMS2O, and the insoluble
product was isolated via filtration. After removal of residual TMS2O in
vacuum, the product was obtained as an off-white solid (1.89 g, 3.35
1
mmol, 29%). H NMR (600 MHz, C6D6): δ [ppm] = 7.12−7.06 (m,
5-ArH, 3 H), 6.94 (d, 3JH,H = 7.4 Hz, 3-ArH, 3 H), 6.86 (d, 3JH,H = 8.0
Hz, 6-ArH, 3 H), 6.75 (t, 3JH,H = 7.4 Hz, 4-ArH, 3 H), 3.34 (s, NH, 3
H), 2.58 (s, PCH2, 6 H), 0.08 (s, SiMe3, 27 H). 13C NMR (151 MHz,
3
3
C6D6): δ [ppm] = 145.5 (d, JC,P = 3.4 Hz, 1-ArC), 131.0 (d, JC,P
=
5.2 Hz, 3-ArCH), 128.4 (s, 5-ArCH), 124.2 (d, 2JC,P = 5.3 Hz, 2-ArC),
118.4 (d, 4JC,P = 2.3 Hz, 4-ArCH), 117.0 (d, JC,P = 1.6 Hz, 6-ArCH),
4
32.4 (d, JC,P = 17.4 Hz, PCH2), 0.10 (s, SiMe3). 31P{1H} NMR (243
1
MHz, C6D6): δ [ppm] = −38.3 (s). MS (FAB+): m/z (%) = 566.3 [M
+ H]+ (100%). HRMS (FAB+): calcd. for C30H48N3PSi3: 565.2894,
found 565.2992. M (C30H48N3PSi3) = 565.95 g mol−1. Elemental
analysis calcd. for C30H48N3PSi3: C 63.29, H 8.35, N 5.27; found: C
62.80, H 8.91, N 4.73.
32
and Bn2Mg(thf)2 were synthesized according to published
procedures. The dimethylamido precursors M(NMe2)4 (M = Ti, Zr,
Hf), n-butyl lithium solutions (2.5 M in hexanes), sodium tert-
butanolate, and hydrogen chloride solutions (2.0 M in Et2O) were
purchased from Aldrich and used as received.
Li3[PN3](thf)3 (1-Li). THF (1.00 mL, 800 mg, 11.0 mmol, 12
equiv) was added to a suspension of 1 (500 mg, 885 μmol, 1.0 equiv)
in pentane (20 mL), and the mixture was stirred at room temperature
until all solids dissolved (5−10 min). The resulting solution was
cooled to −78 °C, and n-BuLi (2.5 M in hexane, 1.11 mL, 2.77 mmol,
3.14 equiv) was added dropwise within 10 min. The solution was
stirred for 30 min at −78 °C and brought to 0 °C. After stirring for 90
min at 0 °C, the reaction mixture was filtered at this temperature and
washed with cold pentane (3 × 10 mL). The remaining solids were
dried in vacuum, and the product was obtained as a beige powder (628
mg, 786 μmol, 89%). 1H NMR (600 MHz, THF-d8): δ [ppm] = 6.71
(phth)3[PN3] (1-Phth). To a stirred suspension of NaPH2 (0.78 g,
14 mmol, 1.0 equiv) and NaOtBu (2.24 g, 28 mmol, 2.0 equiv) in
DME (50 mL) was added solid (o-phthalimido)-benzyl bromide (13.3
g, 42 mmol, 3.0 equiv) in portions over a period of 20 min, and the
resulting mixture was stirred for 7 h at room temperature. The crude
product precipitated over the course of the reaction and was filtered off
subsequently. The obtained pale yellow solid was washed with DME
(2 × 10 mL) and dried in vacuum. Residual NaBr was removed by
washing the crude material with deoxygenated water (3 × 30 mL) to
afford the product as a colorless solid (8.5 g, 11.4 mmol, 82%) (phth =
3
3
(d, JH,H = 6.8 Hz, 6-ArH, 3 H), 6.56 (t, JH,H = 7.8 Hz, 4-ArH, 3 H),
6.49 (d, 3JH,H = 7.8 Hz, 3-ArH, 3 H), 6.02 (t, 3JH,H = 7.0 Hz, 5-ArH, 3
H), 3.61 (s, THF, 12 H), 2.91 (s, PCH2, 6 H), 1.77 (s, THF, 12 H),
−0.07 (s, SiMe3, 27 H). 13C NMR (101 MHz, THF-d8): δ [ppm] =
160.7 (s, 1-ArC), 131.0 (s, 2-ArC), 129.2 (d, 4JC,P = 4.9 Hz, 6-ArCH),
124.9 (s, 4-ArCH), 123.2 (s, 3-ArCH), 110.9 (s, 5-ArCH), 33.0 (s,
PCH2), 2.7 (s, SiMe3). 31P{1H} NMR (243 MHz, THF-d8): δ [ppm]
1
phthaloyl). H NMR (600 MHz, DMSO-d6): δ [ppm] = 8.01−7.93
3
(m, Phth-ArH, 6 H), 7.89−7.81 (m, Phth-ArH, 6 H), 7.22 (d, JH,H
=
3
7.6 Hz, 5-ArH, 3 H), 7.19 (t, JH,H = 7.4 Hz, 6-ArH, 3 H), 7.07 (d,
3JH,H = 7.6 Hz, 3-ArH, 3 H), 7.03 (t, 3JH,H = 7.4 Hz, 4-ArH, 3 H), 2.54
(s, PCH2, 6 H). 13C NMR (151 MHz, DMSO-d6): δ [ppm] = 167.4
(s, NCO), 137.3 (d, 3JC,P = 6.8 Hz, 1-ArC), 134.9 (s, Phth-ArC), 132.2
(s, 3-ArCH), 131.2 (d, 2JC,P = 3.7 Hz, 2-ArC) 130.1 (d, 4JC,P = 0.9 Hz,
6-ArCH), 129.2 (s, 4-ArCH), 127.1 (s, 5-ArCH), 124.1 (s, Phth-
7
= −32.3 (s). Li NMR (155 MHz, THF-d8): δ [ppm] = 0.29 (s). MS
(ESI+): m/z (%) = 578.3 [M − 3THF − Li + 2H]+ (100%). M
(C30H45Li3N3PSi3 × 3THF) = 800.07 g mol−1. Elemental analysis
calcd. for C42H66Li3N3O3PSi3: C 63.29, H 8.35, N 5.27; found: C
63.49, H 9.06, N 4.75.
1
ArCH), 123.9 (s, Phth-ArCH), 30.0 (d, JC,P = 18.6 Hz, PCH2).
31P{1H} NMR (162 MHz, DMSO-d6): δ [ppm] = −15.6 (s). MS
(FAB+): m/z (%) = 762.2 [M + Na]+ (100%). M (C45H30N3O6P) =
739.71 g mol−1. HRMS (FAB+): calcd. for C45H30N3NaO6P:
762.1770, found 762.1748.
[PN3]Zr(NMe2) (2-Zr). A solution of Zr(NMe2)4 (120 mg, 451
μmol, 1.2 equiv) in toluene (10 mL) was added dropwise to a stirred
solution of 1 (200 mg, 353 μmol, 1.0 equiv) in toluene (10 mL). The
resulting yellow solution was heated to 130 °C for 5 days, and the
dimethylamine byproduct was removed periodically by evacuating the
headspace of the reaction vessel once per day. The solvent was then
removed in vacuum, and the residue was washed with benzene (3 mL)
and pentane (2 × 5 mL). The product was obtained as a colorless solid
H3[PN3] (1). To a suspension of 1-Phth (8.30 g, 11.2 mmol, 1.0
equiv) in ethanol (150 mL) was added hydrazine monohydrate (1.85
g, 37.1 mmol, 3.2 equiv) dropwise, and the resulting reaction mixture
was refluxed for 2 h. After cooling to room temperature, a solution of
hydrogen chloride in Et2O (2.0 M, 37 mL, 74.2 mmol, 6.6 equiv) was
added and the mixture was refluxed for an additional hour. Diethyl
1
(90 mg, 129 μmol, 33%). H NMR (600 MHz, Tol-d8): δ [ppm] =
4150
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
7.06−7.03 (m, 6-ArH, 3 H), 7.02 (d, 3JH,H = 5.7 Hz, 5-ArH, 3 H), 6.93
[ppm] = 29.6 (s). MS (LIFDI): m/z (%) = 742.7 [M − OTf]+. M
(C31H45F3HfN3O3PSSi3) = 890.49 g mol−1. Elemental analysis calcd.
for C31H45F3HfN3O3PSSi3: C 41.81, H 5.09, N 4.72; despite numerous
attempts, low values for carbon were obtained, e.g., C 39.87, H 5.17, N
4.57.
3
(d, 3JH,H = 7.4 Hz, 3-ArH, 3 H), 6.83 (t, JH,H = 7.2 Hz, 4-ArH, 3 H),
3.33 (s, NMe2, 6 H), 2.71 (d, 2JH,P = 12.9 Hz, PCH2, 3 H), 2.28−2.11
(m, PCH2, 3 H), −0.01 (s, SiMe3, 27 H). 13C NMR (151 MHz, Tol-
3
3
d8): δ [ppm] = 150.5 (d, JC,P = 8.1 Hz, 1-ArC), 131.9 (d, JC,P = 2.9
3
Hz, 5-ArCH), 131.6 (s, 2-ArC), 130.9 (d, JC,P = 6.0 Hz, 3-ArCH),
[PN3]TiCl (4-Ti). Method A. A suspension of 1-Li (200 mg, 250
μmol, 1.0 equiv) in toluene (5 mL) was added to a stirred suspension
of TiCl4(THF)2 (91 mg, 270 μmol, 1.1 equiv) in toluene (5 mL) at
−40 °C. An immediate color change to deep red was observed, and the
reaction mixture was allowed to warm to room temperature. Stirring at
room temperature was continued for 6 h. The reaction mixture was
then filtered through a plug of aluminum oxide. The orange-red filtrate
was condensed to dryness, and the residual crude product was washed
with a minimal amount of pentane. The product was obtained as a red
solid after drying in vacuum for several hours (30 mg, 46 μmol, 19%).
127.2 (s, 6-ArCH), 122.9 (s, 4-ArCH), 46.5 (s, NMe2), 27.0 (d, 1JC,P
=
4.4 Hz, PCH2), 2.8 (s, SiMe3). 31P{1H} NMR (243 MHz, Tol-d8): δ
[ppm] = 17.2 (s). MS (LIFDI): m/z (%) = 696.1 [M]+ (100%). M
(C32H51N4PSi3Zr) = 698.23 g mol−1. Elemental analysis calcd. for
C32H51N4PSi3Zr: C 55.05, H 7.36, N 8.02; despite numerous attempts,
low values for carbon were obtained, e.g., C 53.81, H 7.08, N 8.14.
[PN3]Hf(NMe2) (2-Hf). A solution of Hf(NMe2)4 (160 mg, 451
μmol, 1.2 equiv) in toluene (10 mL) was added slowly to a stirred
solution of 1 (200 mg, 353 μmol, 1.0 equiv) in toluene (10 mL). An
immediate color change to orange was observed, and the solution was
heated to 130 °C for 18 days. Over this time, the dimethylamine
byproduct was removed periodically by evacuating the headspace of
the reaction vessel every third day. Subsequently, all volatiles were
removed in vacuum and the residue was washed with benzene (5 mL)
and pentane (5 mL). The product was obtained as a colorless solid (96
mg, 122 μmol, 35%). 1H NMR (600 MHz, Tol-d8): δ [ppm] = 7.07−
7.02 (m, 6-ArH, 3 H), 7.02 (d, 3JH,H = 10.4 Hz, 5-ArH, 3 H), 6.90 (d,
3JH,H = 7.4 Hz, 3-ArH, 3 H), 6.80 (t, 3JH,H = 7.0 Hz, 4-ArH, 3 H), 3.40
(s, NMe2, 6 H), 2.77 (dd, 2JH,P = 12.8 Hz, 3JH,H = 2.6 Hz, PCH2, 3 H),
3
1H NMR (600 MHz, Tol-d8): δ [ppm] = 7.15 (d, JH,H = 8.1 Hz, 6-
3
3
ArH, 3 H), 7.01 (d, JH,H = 6.5 Hz, 5-ArH, 3 H), 6.87 (d, JH,H = 7.4
3
Hz, 3-ArH, 3 H), 6.79 (t, JH,H = 7.3 Hz, 4-ArH, 3 H), 2.51 (dd, J =
13.1 Hz, 4.0 Hz, PCH2, 3 H), 2.02 (dd, J = 15.9 Hz, 13,5 Hz, PCH2, 3
H), 0.27 (s, SiMe3, 27 H). 13C NMR (151 MHz, Tol-d8): δ [ppm] =
3
3
154.4 (d, JC,P = 10.1 Hz, 1-ArC), 130.1 (d, JC,P = 5.6 Hz, 3-ArCH),
129.3 (s, 2-ArC), 127.3 (s, 6-ArCH), 127.2 (s, 5-ArCH), 123.7 (s, 4-
ArCH), 26.9 (d, 1JC,P = 4.4 Hz, PCH2), 3.26 (s, SiMe3). 31P{1H} NMR
(243 MHz, Tol-d8): δ [ppm] = 40.7 (s). MS (LIFDI): m/z (%) =
645.1 [M]+ (100%). M (C30H45ClN3PSi3Ti) = 646.25 g mol−1.
Elemental analysis calcd. for C30H45ClN3PSi3Ti: C 55.76, H 7.02, N
6.50; found: C 55.38, H 6.38; N 6.18.
2
2.22 (t, JH,P = 12.7 Hz, PCH2, 3 H), −0.01 (s, SiMe3, 27 H). 13C
NMR (151 MHz, Tol-d8): δ [ppm] = 150.0 (d, 3JC,P = 7.9 Hz, 1-ArC),
3
Method B. To a solution of 1 (60 mg, 106 μmol, 1.0 equiv) in
toluene (0.5 mL) was added Bn3TiCl (38 mg, 106 μmol, 1.0 equiv) at
room temperature, resulting in an immediate color change to red. The
resulting solution was heated to 55 °C for 4 h, and the solvent was
removed in vacuum. The residue was extracted with a mixture of Et2O
and TMS2O, and the extracts were kept at −40 °C for several days.
Crystals of the intermediate [HNPN2]Ti(Bn)(Cl) formed over this
132.7 (s, 5-ArCH), 131.7 (s, 2-ArC), 130.7 (d, JC,P = 5.7 Hz, 3-
ArCH), 127.2 (d, 4JC,P = 2.5 Hz, 6-ArCH), 123.0 (s, 4-ArCH), 46.5 (s,
NMe2), 27.1 (d, 1JC,P = 4.4 Hz, PCH2), 2.9 (s, SiMe3). 31P{1H} NMR
(243 MHz, Tol-d8): δ [ppm] = 26.7 (s). MS (LIFDI): m/z (%) =
786.04 [M]+ (100%). M (C32H51N4PSi3Hf) = 785.49 g mol−1.
Elemental analysis calcd. for C32H51HfN4PSi3: C 48.93, H 6.54, N
7.13; despite numerous attempts, low values for carbon were obtained,
e.g., C 47.18, H 6.52, N 6.71.
1
time and were isolated by filtration (approximately 20 mg). H NMR
3
(600 MHz, Tol-d8): δ [ppm] = 6.96 (d, JH,H = 8.1 Hz, ArH, 2 H),
[PN3]ZrOTf (3-Zr). A solution of triethylsilyl trifluoromethanesul-
fonate (7.7 mg, 29 μmol, 1.2 equiv) in toluene (5 mL) was slowly
added to a solution of 2-Zr (17 mg, 24 μmol, 1.0 equiv) in toluene (5
mL) at −40 °C. The reaction mixture was allowed to warm to room
temperature, and stirring at room temperature continued for 1 h. All
volatiles were then removed in vacuum, and the residue was washed
with a minimal amount of pentane and TMS2O. The product was
6.92 (m, ArH, 2 H), 6.84 (m, ArH, 4 H), 6.73 (m, ArH, 1 H), 6.69 (d,
3JH,H = 7.8 Hz, 1 H), 6.58 (m, ArH, 1 H), 6.37 (d, 3JH,H = 7.4 Hz, ArH,
1 H), 3.59 (m, PCH2, 1 H), 3.17−3.10 (m, PCH2, 1 H), 3.03 (sbr, Bn-
CH2, 2 H), 2.53−2.48 (m, PCH2, 1 H), 2.41−2.40 (m, PCH2, 1 H),
2.27 (d, J = 13.1 Hz, PCH2, 1 H), 2.18 (m, PCH2, 1 H), 0.53 (s,
SiMe3, 9 H), 0.22 (s, SiMe3, 9 H), 0.13 (s, SiMe3, 9 H). One crystal
was selected for X-ray diffraction, and the remaining material was
redissolved in toluene. The resulting solution (0.5 mL) was heated to
80 °C for 5 h and then condensed to dryness. No further work-up was
required, and the product was obtained as a red solid (10 mg, 15 μmol,
15%). Analytical data are identical with the data reported above (see
method A).
1
obtained as a white powder (10 mg, 12 μmol, 51%). H NMR (600
MHz, Tol-d8): δ [ppm] = 7.09−7.08 (m, 6-ArH, 3 H), 7.00−6.94 (m,
5-ArH, 3 H), 6.87 (d, 3JH,H = 7.1 Hz, 3-ArH, 3 H), 6.79 (t, 3JH,H = 7.6
Hz, 4-ArH, 3 H), 2.64 (m, PCH2, 3 H), 2.14−2.03 (m, PCH2, 3 H),
0.03 (s, SiMe3, 27 H). 13C NMR (151 MHz, Tol-d8): δ [ppm] = 148.6
(d, 3JC,P = 8.0 Hz, 1-ArC), 137.3 (s, 2-ArC), 130.9 (d, 3JC,P = 5.5 Hz, 3-
ArCH), 130.6 (d, 5JC,P = 2.6 Hz, 5-ArCH), 129.5 (d, 4JC,P = 2.1 Hz, 6-
[PN3]ZrCl (4-Zr). Method A. A suspension of 1-Li (400 mg, 495
μmol, 1.0 equiv) in toluene (5 mL) was added to a stirred suspension
of ZrCl4(THF)2 (190 mg, 504 μmol, 1.0 equiv) in toluene (5 mL) at
−40 °C, and the resulting reaction mixture was warmed to room
temperature. The orange suspension was stirred at room temperature
for 6 h and then filtered through Celite. The filtrate was condensed to
dryness, and the residual yellowish material was washed with minimal
amounts of pentane and TMS2O. After drying in vacuum, a white
powder of the product was obtained (149 mg, 231 μmol, 47%).1H
NMR (600 MHz, Tol-d8): δ [ppm] 7.10−7.09 (m, 6-ArH, 3 H), 7.03
(d, 3JH,H = 7.6 Hz, 5-ArH, 3 H), 6.91 (d, 3JH,H = 7.4 Hz, 3-ArH, 3 H),
6.80 (t, 3JH,H = 7.2 Hz, 4-ArH, 3 H), 2.64 (dd, 2JH,P = 13.2, 2JH,H = 3.3
Hz, PCH2, 3 H), 2.14−2.12 (m, PCH2, 3 H), 0.15 (s, SiMe3, 27 H).
1
ArCH), 124.0 (s, 4-ArCH), 26.8 (d, JC,P = 10.6 Hz, PCH2), 1.65 (s,
SiMe3). 31P{1H} NMR (243 MHz, Tol-d8): δ [ppm] = 26.3 (s). M
(C31H45F3ZrN3O3PSSi3) = 803.22 g mol−1. Elemental analysis calcd.
for C31H45F3N3O3PSSi3Zr: C 46.35, H 5.65, N 5.23; despite numerous
attempts, low values for carbon were obtained, e.g., C 45.32, H 5.96, N
5.02.
[PN3]HfOTf (3-Hf). A solution of triethylsilyl trifluoromethanesul-
fonate (10 mg, 38 μmol, 1.2 equiv) in toluene (5 mL) was slowly
added to a solution of 2-Hf (25 mg, 32 μmol, 1.0 equiv) in toluene (5
mL) at −40 °C. The reaction mixture was warmed to room
temperature and stirred for 1 h. After removal of the solvent in
vacuum, the residue was washed with a small amount of pentane and
TMS2O to afford the product as a white solid (16 mg, 18 μmol, 47%).
1H NMR (600 MHz, Tol-d8): δ [ppm] = 7.09−7.08 (m, 6-ArH, 3 H),
7.08−7.07 (m, 5-ArH, 3 H), 6.87 (d, 3JH,H = 7.1 Hz, 3-ArH, 3 H), 6.78
3
13C NMR (151 MHz, Tol-d8): δ [ppm] = 150.2 (d, JC,P = 8.4 Hz, 1-
ArC), 130.9 (d, 3JC,P = 5.3 Hz, 3-ArCH), 130.0 (s, 2-ArC), 129.7 (s, 6-
ArCH), 127.7 (s, 5-ArCH), 123.3 (s, 4-ArCH), 26.8 (d, 1JC,P = 4.4 Hz,
PCH2), 2.3 (s, SiMe3). 31P{1H} NMR (243 MHz, Tol-d8): δ [ppm] =
26.2 (s). MS (LIFDI): m/z (%) = 687.0 [M]+ (100%). M
(C30H45ClN3PSi3Zr) = 689.61 g mol−1. Elemental analysis calcd. for
C30H45ClN3PSi3Zr: C 52.25, H 6.58, N 6.09; despite numerous
attempts, low values for carbon were obtained, e.g., C 50.43, H 7.20, N
6.44.
3
2
(t, JH,H = 6.5 Hz, 4-ArH, 3 H), 2.75 (m, PCH2, 3 H), 2.19 (t, JH,P
=
14.0 Hz, PCH2, 3 H), 0.03 (s, SiMe3, 27 H). 13C NMR (151 MHz,
Tol-d8): δ [ppm] = 148.0 (d, 3JC,P = 7.5 Hz, 1-ArC), 131.8 (d, JC,P
=
=
=
4
3
5
2.7 Hz, 6-ArCH), 130.8 (d, JC,P = 5.8 Hz, 3-ArCH), 130.1 (d, JC,P
2.6 Hz, 5-ArCH), 128.4 (s, 2-ArC), 124.1 (s, 4-ArCH), 26.9 (d, 1JC,P
4.4 Hz, PCH2), 1.82 (s, SiMe3). 31P{1H} NMR (243 MHz, Tol-d8): δ
4151
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
Method B. A solution of trimethylsilyl chloride (43 μL, 353 μmol,
2.6 equiv) in toluene (1 mL) was slowly added to a solution of 2-Zr
(90 mg, 129 μmol, 1.0 equiv) in toluene (5 mL), and the resulting
mixture was stirred for 3 days at room temperature. All volatiles were
removed in vacuum, and the residual material was washed with small
amounts of pentane. The product is obtained as a white powder (35
mg, 54 μmol, 42%). Analytical data are identical with the data reported
above (see method A).
ASSOCIATED CONTENT
* Supporting Information
Additional experimental details; selected NMR spectra;
ORTEP plots of the molecular structures of 2-Hf, [HNPN2]-
TiCl2, [HNPN2]Ti(Bn)(Cl), and [(TMS)1PN3]2Ti3, crystallo-
graphic data, and details of the structure determinations for 1−
4. This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
[PN3]HfCl (4-Hf). Method A. A suspension of 1-Li (100 mg, 125
μmol, 1.0 equiv) in toluene (5 mL) was added to a suspension of
HfCl4(THF)2 (64 mg, 138 μmol, 1.1 equiv) in toluene (5 mL), at −40
°C. After warming the reaction mixture to room temperature, stirring
was continued 6 h. The resulting suspension was filtered through
Celite, and the filtrate was condensed to dryness. The residual crude
material was washed with minimal amounts of pentane and TMS2O to
AUTHOR INFORMATION
Corresponding Author
*E-mail: joachim.ballmann@uni-heidelberg.de. Tel: (+ 49)
6221-548596.
■
1
afford the product as a pale yellow solid (54 mg, 70 μmol, 56%). H
Notes
NMR (600 MHz, Tol-d8): δ [ppm] = 7.12 (d, 3JH,H = 7.9 Hz, 6-ArH, 3
The authors declare no competing financial interest.
3
3
H), 7.03 (d, JH,H = 6.5 Hz, 5-ArH, 3 H), 6.89 (d, JH,H = 7.5 Hz, 3-
ArH, 3 H), 6.78 (t, 3JH,H = 7.3 Hz, 4-ArH, 3 H), 2.72 (dd, 2JH,P = 13.1
Hz, 2JH,H = 4.2 Hz, PCH2, 3 H), 2.20 (m, PCH2, 3 H), 0.15 (s, SiMe3,
27 H). 13C NMR (151 MHz, Tol-d8): δ [ppm] = 149.9 (d, 3JC,P = 10.1
ACKNOWLEDGMENTS
■
Support for this research by a Liebig-Stipendium for J.B. and a
FCI-Doktorandenstipendium for M.S. from the Fonds der
Chemischen Industrie (FCI) is gratefully acknowledged. We
thank Prof. L. Gade for generous support and continued
interest in our work. We are grateful to Lukas Merz for
experimental help with the synthesis of selected starting
materials.
Hz, 1-ArC), 130.9 (d, 4JC,P = 5.6 Hz, 6-ArCH), 130.7 (s, 2-ArC), 129.9
1
(s, 3-ArCH), 127.7 (s, 5-ArCH), 123.4 (s, 4-ArCH), 26.8 (d, JC,P
=
4.4 Hz, PCH2), 2.4 (s, SiMe3). 31P{1H} NMR (243 MHz, Tol-d8): δ
[ppm] = 31.7 (s). MS (LIFDI): m/z (%) = 776.94 [M]+ (100%). M
(C30H45ClN3PSi3Hf) = 776.87 g mol−1. Elemental analysis calcd. for
C30H45ClHfN3PSi3: C 46.38, H 5.84, N 5.41; found: C 46.87, H 6.29,
N 5.09.
Method B. A solution of trimethylsilyl chloride (8.2 μL, 65 μmol,
1.3 equiv) in toluene (0.2 mL) was slowly added to a solution of 2-Hf
(35 mg, 50 μmol, 1.0 equiv) in toluene (0.3 mL). The resulting
solution was kept at room temperature for 3 days, and all volatiles
were then removed in vacuum. The residual material was washed with
small amounts of pentane to afford the product as a colorless powder
(18 mg, 23 μmol, 46%). Analytical data are identical with the data
reported above (see method A).
REFERENCES
■
(1) Naiini, A. A.; Menge, W. M. P. B.; Verkade, J. G. Inorg. Chem.
1991, 30, 5009−5012.
(2) (a) Duan, Z.; Naiini, A. A.; Lee, J.-H.; Verkade, J. G. Inorg. Chem.
1995, 34, 5477−5482. (b) Duan, Z.; Verkade, J. G. Inorg. Chem. 1995,
34, 4311−4316.
(3) (a) Cummins, C. C.; Lee, J.; Schrock, R. R.; Davis, W. M. Angew.
Chem., Int. Ed. 1992, 31, 1501−1503. (b) Cummins, C. C.; Schrock, R.
R.; Davis, W. M. Organometallics 1992, 11, 1452−1454. (c) Schrock,
R. R.; Cummins, C. C.; Wilhelm, T.; Lin, S.; Reid, S. M.; Kol, M.;
Davis, W. M. Organometallics 1996, 15, 1470−1476.
(4) Schubart, M.; O’Dwyer, L.; Gade, L. H.; Li, W.-S.; McPartlin, M.
Inorg. Chem. 1994, 33, 3893−3898.
(5) (a) Cummins, C. C.; Schrock, R. R. Inorg. Chem. 1994, 33, 395−
396. (b) Duan, Z.; Verkade, J. G. Inorg. Chem. 1995, 34, 1576−1578.
(c) Scott, P.; Hitchcock, P. B. J. Chem. Soc., Chem. Commun. 1995,
579−580. (d) Freundlich, J. S.; Schrock, R. R. Inorg. Chem. 1996, 35,
7459−7461. (e) Neuner, B.; Schrock, R. R. Organometallics 1996, 15,
5−6. (f) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9−16. (g) Roussel,
P.; Alcock, N. W.; Scott, P. Chem. Commun. 1998, 801−802.
(h) Morton, C.; Munslow, I. J.; Sanders, C. J.; Alcock, N. W.; Scott,
P. Organometallics 1999, 18, 4608−4613. (i) Chen, J.; Woo, L. K. J.
Organomet. Chem. 2000, 601, 57−68. (j) Schrock, R. R.; Rosenberger,
C.; Seidel, S. W.; Shih, K. Y.; Davis, W. M.; Odom, A. L. J. Organomet.
Chem. 2001, 617−618, 495−501. (k) Filippou, A. C.; Schneider, S.
Organometallics 2003, 22, 3010−3012. (l) Filippou, A. C.; Schneider,
S.; Schnakenburg, G. Angew. Chem., Int. Ed. 2003, 42, 4486−4489.
(m) Balazs, G.; Sierka, M.; Scheer, M. Angew. Chem., Int. Ed. 2005, 44,
4920−4924. (n) Leshinski, S.; Shalumova, T.; Tanski, J. M.;
Waterman, R. Dalton Trans. 2010, 39, 9073−9078. (o) King, D. M.;
Tuna, F.; McInnes, E. J. L.; McMaster, J.; Lewis, W.; Blake, A. J.;
Liddle, S. T. Science 2012, 337, 717−720. (p) King, D. M.; Tuna, F.;
McInnes, E. J. L.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T.
Nat. Chem. 2013, 5, 482−488. (q) Tereniak, S. J.; Carlson, R. K.;
Clouston, L. J.; Young, V. G., Jr.; Bill, E.; Maurice, R.; Chen, Y.-S.;
Kim, H. J.; Gagliardi, L.; Lu, C. C. J. Am. Chem. Soc. 2014, 136, 1842−
1855. (r) Gardner, B. M.; Cleaves, P. A.; Kefalidis, C. E.; Fang, J.;
Maron, L.; Lewis, W.; Blake, A. J.; Liddle, S. T. Chem. Sci. 2014,
DOI: 10.1039/C4SC00182F. (s) Parsell, T. H.; Yang, M.-Y.; Borovik,
A. S. J. Am. Chem. Soc. 2009, 131, 2762−2763. (t) England, J.;
[Me2SiCH2NPN2]Ti (5-Ti). A precooled solution of Bn2Mg(thf)2
(50 mg, 137 μmol, 0.55 equiv) in toluene (4 mL) was slowly added to
a solution of 4-Ti (160 mg, 250 μmol, 1.0 equiv) in toluene (5 mL) at
−40 °C. The resulting deep red reaction mixture was allowed to warm
to room temperature, kept at this temperature for 1 h, and then heated
to 90 °C for 9 h. After cooling the reaction mixture to room
temperature, all volatiles were removed in vacuum and the residue was
extracted with pentanes (25 mL). The pentane extracts were
condensed to approximately 10 mL and left standing at −40 °C
overnight. The formed precipitate was filtered off and dried in vacuum
to afford the product as an orange-red powder (100 mg, 164 μmol,
66%). 1H NMR (600 MHz, C6D6): δ [ppm] = 7.14−7.11 (m, ArH, 2
H), 7.07−7.04 (m, ArH, 2 H), 6.93−6.87 (m, ArH, 2 H), 6.88−6.85
(m, ArH, 1 H), 6.84−6.80 (m, ArH, 2 H), 6.75−6.73 (m, ArH, 1 H),
2
2
2
2.69 (dd, JH,P = 13.4, JH,H = 4.1 Hz, PCH2, 1 H), 2.59 (dd, JH,P
=
12.8, 2JH,H = 5.8 Hz, PCH2, 1 H), 2.50 (dd, 2JH,P = 13.9, 2JH,H = 5.4 Hz,
PCH2, 1 H), 2.38 (d, 2JH,H = 11.7 Hz, TiCH2, 1 H), 2.25 (m, PCH2, 1
H), 2.05−1.91 (m, PCH2,2 H), 1.21 (d, 2JH,H = 11.6 Hz, TiCH2, 1 H),
0.77 (s, SiMe2, 3 H), 0.21 (s, SiMe3, 9 H), 0.19 (s, SiMe3, 9 H), −0.00
(s, SiMe2, 3 H). 13C NMR (101 MHz, C6D6): δ [ppm] = 155.3 (d, J =
11.6 Hz, ArC), 151.5 (d, J = 6.3 Hz, ArC), 150.6 (d, J = 11.3 Hz, ArC),
142.2 (s, ArC), 131.5 (d, J = 5.6 Hz, ArCH), 131.1 (d, J = 6.0 Hz,
ArCH), 130.3 (d, J = 5.7 Hz, ArCH), 130.0 (s, ArC), 129.6 (d, J = 2.1
Hz, ArC), 129.0 (d, J = 3.2 Hz, ArCH), 128.5 (s, ArCH), 128.3 (d, J =
1.4 Hz, ArCH), 128.0 (d, J = 3.3 Hz, ArCH), 127.8 (d, J = 2.4 Hz,
ArCH), 123.6 (s, ArCH), 123.1 (s, ArCH), 121.7 (d, J = 3.4 Hz,
ArCH), 120.7 (s, ArCH), 28.1 (d, J = 4.6 Hz, PCH2), 27.1 (d, 1JC,P
=
11.9 Hz, PCH2), 25.0 (d, 1JC,P = 9.1 Hz, PCH2), 6.7 (s, TiCH2), 6.6 (s,
TiCH2), 3.5 (s, SiMe2), 2.6 (s, SiMe3), 2.5 (s, SiMe3). 31P{1H} NMR
(243 MHz, C6D6): δ [ppm] = 24.3 (s). M (C31H48N3PSi3Ti) = 625.83
g mol−1. Elemental analysis calcd. for C30H44N3PSi3Ti: C 59.09, H
7.27, N 6.89; found: C 60.09, H 6.97, N 6.08.
4152
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153

Inorganic Chemistry
Article
Farquhar, E. R.; Guo, Y.; Cranswick, M. A.; Ray, K.; Munck, E.; Que,
L., Jr. Inorg. Chem. 2011, 50, 2885−2896.
L.; Wu, R.-R.; Liao, J.-H.; Liu, Y.-H.; Hsu, H.-F. J. Am. Chem. Soc.
2011, 133, 5708−5711. (g) Lee, C.-M.; Chuo, C.-H.; Chen, C.-H.; Hu,
C.-C.; Chiang, M.-H.; Tseng, Y.-J.; Hu, C.-H.; Lee, G.-H. Angew.
Chem., Int. Ed. 2012, 51, 5427−5430.
̈
(6) (a) Pinkas, J.; Gaul, B.; Verkade, J. G. J. Am. Chem. Soc. 1993,
115, 3925−3931. (b) Plass, W.; Verkade, J. G. Inorg. Chem. 1993, 32,
5153−5159. (c) Pinkas, J.; Wang, T.; Jacobson, R. A.; Verkade, J. G.
Inorg. Chem. 1994, 33, 5244−5253. (d) Pinkas, J.; Wang, T.; Jacobson,
R. A.; Verkade, J. G. Inorg. Chem. 1994, 33, 4202−4210. (e) Duan, Z.;
Young, V. G., Jr.; Verkade, J. G. Inorg. Chem. 1995, 34, 2179−2185.
(f) Plass, W.; Pinkas, J.; Verkade, J. G. Inorg. Chem. 1997, 36, 1973−
1978. (g) Morton, C.; Alcock, N. W.; Lees, M. R.; Munslow, I. J.;
Sanders, C. J.; Scott, P. J. Am. Chem. Soc. 1999, 121, 11255−11256.
(h) Shutov, P. L.; Karlov, S. S.; Harms, K.; Tyurin, D. A.; Churakov, A.
V.; Lorberth, J.; Zaitseva, G. S. Inorg. Chem. 2002, 41, 6147−6152.
(i) Shutov, P. L.; Sorokin, D. A.; Karlov, S. S.; Harms, K.; Oprunenko,
Y. F.; Churakov, A. V.; Antipin, M. Y.; Zaitseva, G. S.; Lorberth, J.
Organometallics 2003, 22, 516−522. (j) Shutov, P. L.; Karlov, S. S.;
Harms, K.; Churakov, A. V.; Lorberth, J.; Zaitseva, G. S. Eur. J. Inorg.
Chem. 2004, 2123−2129. (k) Verkade, J. G. Acc. Chem. Res. 1993, 26,
483−489.
(15) (a) Han, H.; Elsmaili, M.; Johnson, S. A. Inorg. Chem. 2006, 45,
7435−7445. (b) Han, H.; Johnson, S. A. Organometallics 2006, 25,
5594−5602. (c) Hatnean, J. A.; Raturi, R.; Lefebvre, J.; Leznoff, D. B.;
Lawes, G.; Johnson, S. A. J. Am. Chem. Soc. 2006, 128, 14992−14999.
(d) Keen, A. L.; Doster, M.; Han, H.; Johnson, S. A. Chem. Commun.
2006, 1221−1223. (e) Han, H.; Johnson, S. A. Eur. J. Inorg. Chem.
2008, 471−482. (f) Raturi, R.; Lefebvre, J.; Leznoff, D. B.; McGarvey,
B. R.; Johnson, S. A. Chem.Eur. J. 2008, 14, 721−730.
(16) (a) Holscher, M.; Leitner, W. Eur. J. Inorg. Chem. 2006, 4407−
̈
4417. (b) Schenk, S.; Reiher, M. Inorg. Chem. 2009, 48, 1638−1648.
(17) (a) Smythe, N. C. Ph.D. Dissertation, Massachusetts Institute of
Technology, Cambridge, MA, 2006 (available via the Internet at
http://hdl.handle.net/1721.1/37838). (b) Fryzuk, M. D. Personal
communication. (c) Hounjet, L. J.; Bierenstiel, M.; Ferguson, M. J.;
McDonald, R.; Cowie, M. Dalton Trans. 2009, 4213−4226.
(18) (a) Sietzen, M.; Wadepohl, H.; Ballmann, J. Organometallics
2014, 33, 612−615. (b) Sietzen, M.; Wadepohl, H.; Ballmann, J.
Unpublished results.
(7) (a) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76−78.
(b) Reithofer, M. R.; Schrock, R. R.; Muller, P. J. Am. Chem. Soc. 2010,
̈
132, 8349−8358. (c) Kinney, R. A.; McNaughton, R. L.; Chin, J. M.;
Schrock, R. R.; Hoffman, B. M. Inorg. Chem. 2011, 50, 418−420.
(d) Cain, M. F.; Forrest, W. P., Jr.; Peryshkov, D. V.; Schrock, R. R.;
(19) (a) Chen, H. G.; Hoechstetter, C.; Knochel, P. Tetrahedron Lett.
́ ́
1989, 30, 4795−4798. (b) Andres, J. I.; Alonso, J. M.; Fernandez, J.;
Iturrino, L.; Martínez, P.; Meert, T. F.; Sipido, V. K. Bioorg. Med.
Chem. Lett. 2002, 12, 3573−3577. (c) Schroer, J.; Wagner, S.; Abram,
U. Inorg. Chem. 2010, 49, 10694−10701.
Muller, P. J. Am. Chem. Soc. 2013, 135, 15338−15341. (e) MacBeth, C.
̈
E.; Golombek, A. P.; Young, V. P., Jr.; Yang, C.; Kuczera, K.; Hendrich,
M. P.; Borovik, A. S. Science 2000, 289, 938−941.
(20) Issleib, K.; Winkelmann, H.; Abicht, H. P. Synth. React. Inorg.
Met.-Org. Chem. 1974, 4, 191−203.
(8) (a) Waterman, R. Chem. Soc. Rev. 2013, 42, 5629−5641.
(b) Waterman, R. Curr. Org. Chem. 2012, 16, 1313−1331.
(c) Ghebreab, M. B.; Newsham, D. K.; Waterman, R. Dalton Trans.
2011, 40, 7683−7685.
(21) Upadhyay, S. K.; Jursic, B. S. Synth. Commun. 2011, 41, 3177−
3185.
(22) (a) Albers, H.; Schuler, W. Ber. Dtsch. Chem. Ges. 1943, 76B,
23−26. (b) Jacobs, H.; Hassiepen, K. M. Z. Anorg. Allg. Chem. 1985,
531, 108−118.
(9) Schwarz, A. D.; Herbert, K. R.; Paniagua, C.; Mountford, P.
Organometallics 2010, 29, 4171−4188.
(10) (a) Lensink, C.; Xi, S. K.; Daniels, L. M.; Verkade, J. G. J. Am.
Chem. Soc. 1989, 111, 3478−3479. (b) Arumugam, S.; Verkade, J. G. J.
Org. Chem. 1997, 62, 4827−4828. (c) Kisanga, P. B.; Verkade, J. G.;
Schwesinger, R. J. Org. Chem. 2000, 65, 5431−5432. (d) Chintareddy,
V. R.; Wadhwa, K.; Verkade, J. G. J. Org. Chem. 2009, 74, 8118−8132.
(e) Wadhwa, K.; Chintareddy, V. R.; Verkade, J. G. J. Org. Chem. 2009,
74, 6681−6690. (f) Wadhwa, K.; Verkade, J. G. J. Org. Chem. 2009, 74,
5683−5686. (g) Chintareddy, V. R.; Ellern, A.; Verkade, J. G. J. Org.
Chem. 2010, 75, 7166−7174. (h) Raytchev, P. D.; Martinez, A.;
Gornitzka, H.; Dutasta, J.-P. J. Am. Chem. Soc. 2011, 133, 2157−2159.
(i) Chatelet, B.; Joucla, L.; Dutasta, J.-P.; Martinez, A.; Szeto, K. C.;
Dufaud, V. J. Am. Chem. Soc. 2013, 135, 5348−5351.
(23) Schafer, H.; Fritz, G.; Holderich, W. Z. Anorg. Allg. Chem. 1977,
̈
̈
428, 222−224.
(24) Easton, C. J.; Hutton, C. A. Synlett 1998, 457−466.
(25) Landaeta, V. R.; Peruzzini, M.; Herrera, V.; Bianchini, C.;
Sanchez-Delgado, R. A.; Goeta, A. E.; Zanobini, F. J. Organomet. Chem.
2006, 691, 1039−1050.
(26) (a) MacLachlan, E. A.; Hess, F. M.; Patrick, B. O.; Fryzuk, M. D.
J. Am. Chem. Soc. 2007, 129, 10895−10905. (b) Morello, L.; Joao
Ferreira, M.; Patrick, B. O.; Fryzuk, M. D. Inorg. Chem. 2008, 47,
1319−1323. (c) Menard, G.; Jong, H.; Fryzuk, M. D. Organometallics
2009, 28, 5253−5260. (d) Zhu, T.; Wambach, T. C.; Fryzuk, M. D.
Inorg. Chem. 2011, 50, 11212−11221.
(11) (a) Blackman, A. G. Polyhedron 2005, 24, 1−39. (b) C
̧elenligil-
(27) Wang, C.; Erker, G.; Kehr, G.; Wedeking, K.; Frohlich, R.
̈
C
̧
etin, R.; Paraskevopoulou, P.; Dinda, R.; Staples, R. J.; Sinn, E.; Rath,
Organometallics 2005, 24, 4760−4773.
N. P.; Stavropoulos, P. Inorg. Chem. 2008, 47, 1165−1172.
(c) Paraskevopoulou, P.; Ai, L.; Wang, Q.; Pinnapareddy, D.;
(28) Benzing, E.; Kornicker, W. Chem. Ber. 1961, 94, 2263−2267.
(29) Zucchini, U.; Albizzati, E.; Giannini, U. J. Organomet. Chem.
1971, 26, 357−372.
Acharyya, R.; Dinda, R.; Das, P.; Çelenligil-Çetin, R.; Floros, G.;
Sanakis, Y.; Choudhury, A.; Rath, N. P.; Stavropoulos, P. Inorg. Chem.
2010, 49, 108−122.
(30) Manzer, L. E. Inorg. Synth. 1982, 21, 135−140.
(31) Reich, H. J. Chem. Rev. 2013, 113, 7130−7178.
(32) Bailey, P. J.; Coxall, R. A.; Dick, C. M.; Fabre, S.; Henderson, L.
C.; Herber, C.; Liddle, S. T.; Lorono-Gonzalez, D.; Parkin, A.; Parsons,
S. Chem.Eur. J. 2003, 9, 4820−4828.
(12) (a) Groysman, S.; Segal, S.; Goldberg, I.; Kol, M.; Goldschmidt,
Z. Inorg. Chem. Commun. 2004, 7, 938−941. (b) Lehtonen, A.;
Sillanpaa, R. Organometallics 2005, 24, 2795−2800. (c) Licini, G.;
̈
̈
Mba, M.; Zonta, C. Dalton Trans. 2009, 5265−5277.
(33) Waterman, R. Organometallics 2007, 26, 2492−2494.
(34) Roering, A. J.; Maddox, A. F.; Elrod, L. T.; Chan, S. M.;
Ghebreab, M. B.; Donovan, K. L.; Davidson, J. J.; Hughes, R. P.;
Shalumova, T.; MacMillan, S. N.; Tanski, J. M.; Waterman, R.
Organometallics 2009, 28, 573−581.
(13) (a) Govindaswamy, N.; Quarless, D. A., Jr.; Koch, S. A. J. Am.
Chem. Soc. 1995, 117, 8468−8469. (b) Motekaitis, R. J.; Martell, A. E.;
Koch, S. A.; Hwang, J.; Quarless, D. A., Jr.; Welch, M. J. Inorg. Chem.
1998, 37, 5902−5911.
(14) (a) Block, E.; Ofori-Okai, G.; Zubieta, J. J. Am. Chem. Soc. 1989,
111, 2327−2329. (b) Chu, W.-C.; Wu, C.-C.; Hsu, H.-F. Inorg. Chem.
2006, 45, 3164−3166. (c) Conradie, J.; Quarless, D. A., Jr.; Hsu, H.-F.;
Harrop, T. C.; Lippard, S. J.; Koch, S. A.; Ghosh, A. J. Am. Chem. Soc.
2007, 129, 10446−10456. (d) Lee, C.-M.; Chen, C.-H.; Liao, F.-X.;
Hu, C.-H.; Lee, G.-H. J. Am. Chem. Soc. 2010, 132, 9256−9258. (e) Ye,
S.; Neese, F.; Ozarowski, A.; Smirnov, D.; Krzystek, J.; Telser, J.; Liao,
J.-H.; Hung, C.-H.; Chu, W.-C.; Tsai, Y.-F.; Wang, R.-C.; Chen, K.-Y.;
Hsu, H.-F. Inorg. Chem. 2010, 49, 977−988. (f) Chang, Y.-H.; Su, C.-
4153
dx.doi.org/10.1021/ic500163c | Inorg. Chem. 2014, 53, 4144−4153