Isolation and characterization of main group and late transition metal complexes using orthometallated imine ligands

Article abstract of DOI:10.1039/c1dt11629k

Several late transition metal and main group orthometallated imine complexes were synthesized by utilizing ortholithiated imine precursors. Magnesium, aluminum, zinc, copper(i), and tin(iv) complexes were isolated and characterized. Subsequent reactions with electrophiles such as Ph ₂PCl, MeI and I₂ yielded several functionalized products, including a new iminophosphine ligand and its corresponding copper(i) complex. The coordination modes of the orthometallated imine ligands, as well as the structures of the metal complexes, were studied in the solid state using small molecule X-ray diffraction when possible.

Full text of DOI:10.1039/c1dt11629k

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 860
www.rsc.org/dalton
PAPER
Isolation and characterization of main group and late transition metal
complexes using orthometallated imine ligands†
John F. Beck and Joseph A. R. Schmidt*
Received 29th August 2011, Accepted 8th October 2011
DOI: 10.1039/c1dt11629k
Several late transition metal and main group orthometallated imine complexes were synthesized by
utilizing ortholithiated imine precursors. Magnesium, aluminum, zinc, copper(I), and tin(IV) complexes
were isolated and characterized. Subsequent reactions with electrophiles such as Ph2PCl, MeI and I2
yielded several functionalized products, including a new iminophosphine ligand and its corresponding
copper(I) complex. The coordination modes of the orthometallated imine ligands, as well as the
structures of the metal complexes, were studied in the solid state using small molecule X-ray diffraction
when possible.
In some cases, “ate” salts have been found to be very useful
reagents. For example, the most productive “ate” salts are the
Recently, our group presented a detailed structural study of a
lithium cuprates, which have found broad utility in organic
Introduction
series of ortholithiated imines.1 The coordination chemistry of
these ortholithiated imines was also investigated with a number of
early transition metals including titanium, zirconium, tantalum,
and niobium.2–5 With the exception of compounds incorporating
imido ligands, most of the metal complexes studied exhibited
very low solubility in ethereal, aromatic or hydrocarbon solvents.
Furthermore, in the course of our studies, it has become apparent
that lithium reagents may not be the best way to access the
chemistry supported by orthometallated imines. Lithium reagents
commonly undergo undesirable side reactions reducing product
yields when used in salt metathesis reactions with transition, main
group, and lanthanide metal halides. One of the most common
problems involves the formation of lithium halide adducts or
“ate” salts, which have been observed in many cases when lithium
reagents are reacted with metal chlorides.6–15 The formation of
“ate” salts may be responsible for the poor solubility observed for
the group (IV) orthometallated imine complexes that we previously
reported.4 In fact, we were recently able to isolate a hafnium
“ate” salt incorporating an orthometallated imine ligand.16 To
help circumvent this difficulty, we decided to pursue alternative
orthometallated imine complexes that could be used as transfer
reagents in place of the lithiated species. In addition, the recent
renaissance of main group organometallics in catalysis17–24 implies
that these main group metal complexes may have applicability in
catalytic transformations in their own right.
synthesis.25,26 There are numerous examples of their use as coupling
reagents, dating back to the early work of Henry Gilman.27
Efforts to avoid the limitations of “ate” salts have led to the
investigation of zinc,28 magnesium,29–32 and tin32,33 compounds,
which have proven to be effective transfer reagents in coupling
chemistry. For example, it has been reported that the yields of
niobium and tantalum alkyls are higher when alkyl zinc species
are used instead of lithium reagents.34 Thus, zinc complexes have
found extensive use as salt metathesis reagents for group (V)
metals. Magnesium species, in the form of bis-alkyls and Grignard
reagents, have also been widely used as alkylating agents in
organometallic synthesis, as well as organic synthesis. Despite
their toxic nature and unpleasant odor, tin reagents such as
nBu3SnCp32 and SnMe4 are often utilized in the alkylation of
35
early transition metals. Thus, the lithium-free orthometallated
imine starting materials based on zinc, magnesium and tin should
provide an advantageous alternative route to organometallic
products utilizing these chelating ligands.
Recent investigations into main group organometallics have
led to a range of interesting chemistry, while reaffirming that
common and inexpensive metals such as magnesium and alu-
minum show great promise in catalysis. Hill and coworkers
at the University of Bath have performed truly pioneering
work on group (II) catalysis, developing calcium-mediated in-
tramolecular hydroamination,36 C–F bond activation,37 and inter-
molecular hydrophosphination.38,39 There has also been a great
deal of interest in calcium catalyzed polymerization.20 Other
recent reports detail several examples of magnesium catalyzed
hydroamination40–42 and the polymerization of lactide.43–46 Ad-
ditionally, several research groups have recently investigated the
polymerization of lactide using aluminum complexes.47–51 Bergman
has demonstrated the aluminum catalyzed hydroamination of
Department of Chemistry, School for Green Chemistry and Engineering,
College of Natural Sciences & Mathematics, The University of Toledo, 2801
W. Bancroft St. MS 602, Toledo, OH 43606-3390, USA
† Electronic supplementary information (ESI) available: Discussion of
(L2)AlCl2 (15). CCDC reference numbers 842465–842471. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt11629k
860 | Dalton Trans., 2012, 41, 860–870
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Scheme 1 The synthesis of ortholithiated imines via Schiff base condensation and regiospecific lithiation (L1: R = H, R¢ = 2,6-iPr2C6H3; L2: R = Me, R¢ =
2,6-iPr2C6H3; L3: R = Me, R¢ = 2,6-Et2C6H3; L4: R = H, R¢ = Cy). Legend: (i) PTSA cat., toluene reflux, 2–4 days; (ii) 0.99 eq. nBuLi, pentane, -78 ◦C.
aminoalkenes using a phenylene-diamine supporting ligand.52
Herein, we detail the synthesis of several new late transition
and main group orthometallated imines and their subsequent
reactions with various electrophiles. These new metal complexes
are expected to show utility as ligand transfer reagents and as
precatalysts for organometallic transformations.
imine ligand backbones or result from reversible decoordina-
1
tion/coordination of the ether ligand. Low temperature H and
13C{ H} NMR spectroscopy at -48 ◦C eliminated most of the
1
broadness attributed to this fluxional behavior; lower temperature
studies were not possible due to the poor solubility of the metal
1
complex at these temperatures. The 1H and 13C{ H} NMR spectra
at -48 ◦C were typical for a C2 symmetric metal complex and
resembled previously reported titanium imido complexes.2 Two
proton resonances at 5.38 and 4.57 ppm, corresponding to the two
chemically inequivalent protons of the methylenedioxy moiety,
were observed, as well as a broad set of resonances at 3.21
and 0.73 ppm, which corresponded to a diethyl ether ligand.
These observations imply a square pyramidal geometry about the
magnesium center; two orthometallated imine ligands bind to the
metal center forming the base of a square pyramid and a diethyl
ether ligand is positioned axially. Other possible isomers of 1 would
not correspond to the observed spectra. A trans arrangement of the
anionic carbon donors of the ligands places the methylenedioxy
protons of one ligand in proximity to the p system of the N-aryl
group of the adjacent ligand. This p interaction causes a downfield
chemical shift of the two methylene protons. This geometry also
minimizes steric interactions between the bulky isopropyl groups
of the N-aryl substituents.
Results and discussion
In order to study the reactivity of ortholithiated imines with main
group and late transition metals, four of our previously reported
ortholithiated imines were employed: Li-L1, Li-L2, Li-L3 and Li-L4
(Scheme 1).2 In our previous work, it was noted that ortholithiated
imines with bulky substituents at the 2- and 6-positions of the
N-aryl group significantly increased the stability of the resulting
lithium salts,1 as well as their early transition metal complexes.2,3
For this reason, ligands L1 and L2 were used primarily, while
L4, the most stable N-alkyl ligand isolated to date, was used in
some cases to ascertain any electronic or steric differences resulting
from the presence of an alkyl group at this position. Initially our
investigation focused on complexes containing magnesium, zinc,
and tin because of their utility in coupling reactions.
The reaction of Li-L1 with ethyl magnesium bromide (EtMgBr)
proceeded readily in a mixture of diethyl ether and toluene. The
presumed product (L1)MgEt then underwent a pseudo-Schlenk
equilibrium resulting in a 1 : 1 mixture of (L1)2Mg and MgEt2.
Recrystallization from diethyl ether yielded (L1)2Mg(OEt2) (1) as
a yellow solid in good yield (Scheme 2). Irreversible redistribution
of ligands around group (II) metal centers has been previously
noted.53 The 1H NMR spectrum of 1 was extremely broad at room
temperature, indicating a great deal of fluxionality in solution.
This could be caused by fluxionality within the orthometallated
The reactions of Li-L1 with aluminum precursors yielded two
metal complexes (Scheme 3). In the first case, treatment of AlCl3
with Li-L1 resulted in the formation of a bis-ligated aluminum
complex Al(L1)2Cl (2). Regardless of the relative ratio of Li-
L1 to AlCl3 used, 2 was the only product observed by NMR
spectroscopy. Crystallization from toluene at -25 ◦C yielded
crystals suitable for X-ray crystallography. One crystal that was
subjected to data collection was found to be a mono-ligated
aluminum complex (L1AlCl2), which we believe is produced as
a minor reaction product in very low yield (see ESI†). The bulk of
the crystals were found to be the bis-ligated complex, as expected
1
based on 1H and 13C{ H} NMR spectra, as well as the elemental
analysis results. The crystal structure (Fig. 1) showed a square
pyramidal aluminum coordination sphere, in which the anionic
carbons of the two orthometallated imines are trans (C1–Al1–
C21 = 166.5(1)◦) with a C2 axis of symmetry colinear with the
aluminum chloride bond. The 1H NMR spectrum of 2 showed two
resonances for the methylene protons of the methylenedioxy ring at
Scheme 2 The reaction of EtMgBr with Li-L1 yielded the bis-ligated
magnesium complex 1 and an equivalent of Et2Mg (R¢ = 2,6-iPr2C6H3).
Scheme 3 Aluminum complexes incorporating one and two orthometallated imine ligands were synthesized. The use of Et2AlCl allowed for the isolation
of a mono-ligated aluminum complex (R¢ = 2,6-iPr2C6H3).
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 860–870 | 861
©

View Article Online
Fig. 2 ORTEP diagram (50% thermal ellipsoids) ofZn(L1)2 (4). Hydrogen
atoms have been removed for clarity. Bond lengths (in A): Zn1–C1 =
Fig. 1 ORTEP diagram (50% thermal ellipsoids) of Al(L1)2Cl (2).
˚
1.988(2), Zn1–N1 = 2.196(1), C1–C2 = 1.363(2), C1–C6 = 1.418(2); angles
(in ◦): C1–Zn1–N1 = 82.79(6), C1–Zn1–C21 = 135.84(7), N1–Zn1–N2 =
108.46(5), C1–Zn1–N2 = 125.29(6), C2–C1–C6 = 112.8(2).
Hydrogen atoms and 3 toluene solvent molecules removed for clarity.
˚
Bond lengths (in A): Al1–C1 = 2.026(3), Al1–N1 = 2.103(2), Al1–Cl1 =
2.205(1), C1–C2 = 1.368(4), C1–C6 = 1.422(3); angles (in ◦): C1–Al1–N1 =
80.18(9), C1–Al1–C21 = 166.5(1), N1–Al1–N2 = 123.44(8), C2–C1–C6 =
112.4(2).
5.13 and 4.52 ppm, which can again be attributed to an interaction
between these protons and the p system of the neighboring ligand,
as can be readily noted in the crystal structure. The reaction of
Et2AlCl with Li-L1 yielded Et2Al(L1) (3) in good yield. A single
1H NMR resonance for the methylenedioxy protons was observed
at 5.31 ppm, due to a mirror plane of symmetry through the ligand
backbone. Complex 3 may prove to be quite interesting in future
reactivity studies since aluminum alkyls are often good precursors
for the exploration of aluminum organometallic reactivity. For
example, recent reports note that metal complexes containing
aluminum, a non-toxic and inexpensive metal, can be used for
catalytic polymerization of lactide50,51 as well as hydroamination.52
The reactions of Li-L1 and Li-L4 with ZnCl2 resulted in good
yields of the corresponding zinc complexes: Zn(L1)2 (4) and
Zn(L4)2 (5) (Scheme 4). Crystals suitable for X-ray crystallography
were grown from concentrated solutions of pentane (4) and
diethyl ether (5). Both complexes exhibited a distorted tetrahedral
arrangement of the ligands around the zinc centers (Fig. 2 and 3).
Although the zinc–carbon and zinc–nitrogen bond lengths are very
similar for the two complexes, there is a significant difference in
the relative positions of the ligands around the two metal centers.
The C1–Zn–C21 bond angle for 4 is 135.84(7)◦ while the C1–
Zn1–C15 bond angle for 5 is 142.80(6)◦. A similar increase in the
bond angle of N1–Zn–N2 is observed from 108.46(5)◦ for 4 to
Fig. 3 ORTEP diagram (50% thermal ellipsoids) ofZn(L4)2 (5). Hydrogen
atoms have been removed for clarity. Bond lengths (in A): Zn1–C1 =
1.991(2), Zn1–N1 = 2.147(1), C1–C2 = 1.368(2), C1–C6 = 1.422(2); angles
(in ◦): C1–Zn1–N1 = 83.69(6), C1–Zn1–C15 = 142.80(6), N1–Zn1–N2 =
112.08(5), C1–Zn1–N2 = 119.54(6), C2–C1–C6 = 112.5(1).
˚
112.08(5)◦ in 5. At the same time, there is a decrease in the bond
angle of C1–Zn1–N2 from 125.29(6)◦ to 119.54(6)◦ for 4 and 5,
respectively. The bite angles are almost identical for 4 (82.79(6)◦)
and 5 (83.69(6)◦). The observed differences in bond angles are
attributable to the bulky isopropyl groups of 4, as the slight
changes in the relative orientation of the ligands help to decrease
the steric interactions of the isopropyl groups in 4. In solution, 4
1
and 5 exhibit exceptionally different H NMR spectra. A single
resonance at 5.33 ppm, corresponding to all four methylenedioxy
protons, was observed in 4 whereas 5 has two resonances at 5.53
and 5.33 ppm, which is more typical of what one would expect
for a tetrahedral complex incorporating this ligand system. The
single resonance for the methylenedioxy protons of 4 could be due
Scheme 4 The reactions of Li-L1 (R¢ = 2,6-iPr2C6H3) and Li-L4 (R¢ = Cy)
yielded the corresponding zinc complexes 4 and 5, where the ligands adopt
a pseudo tetrahedral geometry around the central zinc atom in each case.
862 | Dalton Trans., 2012, 41, 860–870
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Scheme 5 The reaction of Li-L1 with differing amounts of CuI led to the formation of two different products: a dimeric copper complex and a lithium
cuprate (R¢ = 2,6-iPr2C6H3).
54
˚
to coincidental overlap of the two signals, but is more likely due to
some dynamic behavior of the methylenedioxy ring or complete
ligand in solution. A C2 rotational axis of symmetry relates the
two ligands, making them equivalent, but no symmetry operation
exists to make the two methylenedioxy protons within a given
ligand equivalent. Thus, coordination to the metal center in a
tetrahedral geometry should yield diastereotopic methylenedioxy
protons and lead to a 1H NMR spectrum like that observed for 5.
The reaction of Li-L1 with CuI yielded the copper complex CuL1
(6) in moderate yield (Scheme 5). Its NMR spectra were very
similar to that of the starting material, Li-L1. Crystals suitable
for X-ray diffraction were grown from a saturated diethyl ether
solution, and compound 6 was found to be a dimer in the solid
state, in which each copper center is bound to the anionic carbon
donor of one ligand and the neutral nitrogen of a second ligand
(Fig. 4). The angle between the anionic carbon donor atom, copper
center and the neutral nitrogen atom (C1–Cu1–N2) is 168.9(2)◦.
Unlike the structure of Li-L1, the two ligands in 6 are no longer
coplanar and it appears that the ligands have rotated away from
each other in order to minimize the steric interactions of the
bulky N-aryl groups. This rotation is somewhat limited due to
the presence of a copper–copper bond, with a length of 2.472(1)
a Cu–Cu bond of 2.412(1) A. In contrast, longer Cu–Cu bond
distances have been observed in other copper complexes utilizing
ligands with less similarity to L1. Guastini and coworkers observed
a bond distance of 2.750(2) A for a dinuclear copper(I) benzoate
species,55 while Lai and coworkers reported a bond distance of
˚
˚
2.940(1) A for a copper(I) complex utilizing chelating phosphine
ligands.56 The widely varying bond lengths observed are likely due
to the nature of the ligands used. It seems that bulky chelating C~N
ligands facilitate the formation of dinuclear copper complexes
with relatively short Cu–Cu bonds. Copper complexes supported
by orthometallated N,N-dimethylbenzylamines have been isolated
and structurally characterized by van Koten and Noltes. The lack
of steric bulk found in this ligand set allowed for higher order
clustering, and the tetranuclear copper complex that was isolated
57
˚
exhibited a very short Cu–Cu distance of 2.38 A.
Increasing the ratio of Li-L1 to CuI yielded the lithium cuprate
Cu(L1)2Li (7) (Scheme 5). The H NMR spectrum of 7 clearly
1
showed two inequivalent ligands that exhibit a limited degree
of fluxional behavior. Low temperature NMR spectroscopy at
temperatures down to -60 ◦C did not resolve this fluxionality.
Peak broadening was most pronounced for the isopropyl moieties
of a single N-aryl group, possibly indicating that one ligand in 7
is hemilabile. Crystals suitable for single crystal X-ray diffraction
were grown from an evaporated solution of toluene and diethyl
ether. The crystal structure revealed a dimeric metal complex
in which the central copper atom is coordinated by the anionic
carbon donor atoms of two ligands and the nitrogen atom of one
of those ligands (Fig. 5). The lithium atom is bound to the other
imine nitrogen, as well as the oxygen atom of the methylenedioxy
ring on the adjacent ligand. The oxygen atom of a diethyl ether
ligand and a lithium–copper bond complete the lithium center’s
distorted tetrahedral geometry. The distance between the lithium
◦
˚
A. The C1–Cu1–Cu2 angle is 91.6(2) , with each copper having
a T-shaped coordination. The observed Cu–Cu bond distance is
similar to other species previously reported. For example, White
and coworkers published the structure of a dimeric complex
supported by a bulky pyridine-based chelating C~N ligand with
˚
atom and the copper center is 2.46(1) A, which is shorter than that
reported by Power and coworkers for [Li2Cu3Ph6]2[Li4Cl2(Et2O)10]
57
˚
with a Li–Cu bond of 2.62(1) A. Bau and coworkers have also
isolated a lithium copper cluster, [Cu4LiPh6][Li(Et2O)4], with a Li–
58
˚
Cu bond length of 2.52(3) A. The very close contact in 7 seems
to indicate the presence of a true Li–Cu bond. To the best of our
knowledge, there have been no reports of other dinuclear copper
lithium complexes analogous to 7.
The reactivity of ortholithiated imines with various electrophiles
was also investigated. Li-L1 reacted with nBu3SnCl to yield 8,
an air and moisture stable tin complex (Scheme 6). Tin reagents
have shown broad utility as alkyl transfer reagents for both early35
and late transition metals.59 orthoMetallated tin complexes can
also act as air and moisture stable alternatives to ortholithiated
imines in some cases. Treatment of Li-L3 with MeI yielded the
orthomethylated imine (9) (Scheme 6), while the reaction of
Li-L1 with Ph2PCl proved to be more difficult; no product was
Fig. 4 ORTEP diagram (50% thermal ellipsoids) of (CuL1)2 (6). Hydrogen
atoms have been removed for clarity. Bond lengths (in A): Cu1–C1 =
1.908(5), Cu1–N2 = 1.914(4), Cu1–Cu2 = 2.472(1), C1–C2 = 1.390(7),
C1–C6 = 1.417(7); angles (in ◦): C1–Cu1–N2 = 168.9(2), C1–Cu1–Cu2 =
91.6(2), C2–C1–C6 = 111.3(4), N1–Cu2–Cu1 = 98.9(1).
˚
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 860–870 | 863
©

View Article Online
Fig. 5 ORTEP diagram (50% thermal ellipsoids) of [Cu(L1)2][Li(OEt2)]
(7). Hydrogen atoms have been removed for clarity. Bond lengths (in
A): Cu1–C1 = 1.940(6), Cu1–N1 = 2.310(5), C1–C2 = 1.381(8), C1–C6 =
1.437(9), Cu1–Li1 = 2.46(1), Li1–O2 = 2.08(1), Li1–O5 = 1.94(1), Li1–N2 =
2.05(1); angles (in ◦): C1–Cu1–N1 = 80.6(2), C1–Cu1–C21 = 163.8(2),
C1–Cu1–Li1 = 78.0(3), O5–Li1–Cu1 = 117.4(5), O2–Li1–O5 = 120.3(6),
N2–Li1–O2 = 108.5(5), C2–C1–C6 = 111.1(5).
Fig. 6 ORTEP diagram (50% thermal ellipsoids) of CuI(Ph2P-L1) (10).
Hydrogen atoms have been removed for clarity. Bond lengths (in A):
˚
˚
Cu1–I1 = 2.6412(9), Cu1–N1 = 2.100(6), Cu1–P1 = 2.220(2); angles (in ◦):
N1–Cu1–P1 = 92.9(2), I1–Cu1–N1 = 106.4(2), I1–Cu1–P1 = 111.85(6).
Atoms labeled with “i” are generated by the following symmetry operator:
-x + 2/3, -y + 1/3, -z + 4/3.
Scheme 6 The reaction of Li-L1 (R = H, R¢ = 2,6-iPr2C6H3) or Li-L3
(R = Me, R¢ = 2,6-Et2C6H3) yielded the corresponding tin complex (8) and
ortho-methylated compound (9).
Scheme 8 The reaction of 1 with Ph2PCl yielded the free iminophosphine
11 (R¢ = 2,6-iPr2C6H3).
detected under a variety of attempted conditions. As the use of
copper
reagents to generate phosphines has been previously
and the elemental analysis of 11 confirmed that it was free of
magnesium.
reported,60 the reaction of Ph2PCl with Cu(L1) (6), generated
in situ, was attempted and yielded the iminophosphine copper
complex (10) (Scheme 7), although all attempts to isolate the
copper-free iminophosphine from this reaction were unsuccessful.
Crystals suitable for crystallographic analysis were grown from a
saturated acetonitrile solution, and complex 10 was found to be a
dimer in the solid state with bridging iodide ligands spanning two
copper centers, which are both also chelated by iminophosphine
ligands (Fig. 6). In order to produce the free iminophosphine,
it was necessary to treat Ph2PCl with the magnesium complex
1, yielding the iminophosphine 11 in moderate yield (Scheme
8). The 31P NMR spectrum of 11 shows a single resonance at
-23.8 ppm, consistent with a free aromatic iminophosphine,61
The reaction of Li-L2 with I2 yielded an iodinated species 13,
and its subsequent Ullmann homocoupling resulted in an excellent
yield of compound 14 (Scheme 9). The 1H NMR spectrum of 14
has two doublets (2JHH = 0.6 Hz) at 6.01 and 5.94 ppm, consistent
with a C2 symmetric molecule. There are numerous reports of
C2 symmetric diamine62 and diimine ligands63 utilized for many
processes, making 14 a useful new chiral diimine. It is easy to
envision the production of 14 by reductive elimination of two
ligands from a high oxidation state metal. Although we have
previously observed this reaction on occasion in our group (IV)
and (V) metal chemistry, it has been rare and generally not a
problem with this ligand set. In contrast, oxidative coupling of a
clearly related (though much less sterically bulky) orthometallated
imine ligand in bis-ligated titanium complexes was found to be
quite common by Mu and coworkers.64 Our attempts to produce
copper(II) reagents as part of this investigation have always been
thwarted by reductive elimination of 14 from transient copper(II)
complexes that were produced, preventing the successful isolation
of any related copper(II) complexes.
Conclusion
Various magnesium, zinc, and tin complexes with potential uses
as transfer reagents in salt metathesis chemistry for the generation
of new metal complexes were synthesized. Of particular interest
Scheme 7 The investigation of copper reagents in place of lithium
reagents led to the isolation of 10, an iminophosphine copper complex
(R¢ = 2,6-iPr2C6H3).
864 | Dalton Trans., 2012, 41, 860–870
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Scheme 9 The reaction of Li-L2 with I2 yielded 13, which was subsequently reacted with activated copper to give 14, the Ullmann-coupled product
(R¢ = 2,6-iPr2C6H3).
are the zinc and tin complexes. Zinc complexes have been noted
to be superior to lithium reagents when used with group (V)
metals giving higher yields of group (V) alkyls than lithium
or magnesium reagents.34 Tin reagents can be used in some
circumstances as air and moisture stable alternatives to lithium
reagents.32 Several copper complexes were synthesized, including
a lithium cuprate that shows evidence of a copper-lithium bond.
One copper complex (6) was used in the synthesis of a piperonal
imine based iminophosphine copper(I) complex, while the related
magnesium complex (1) allowed the successful synthesis of the
metal free iminophosphine ligand (11). Additionally, the reactivity
of the ortholithiatedimines was investigatedwithelectrophiles such
as I2 and iodomethane. Overall, orthometallated imines based on
a piperonal scaffold have been shown to be excellent ligands for
late transition and main group metals, as well as useful building
blocks for more complex ligands, such as iminophosphines.
were taken using C6D6, CDCl3, C7D8, or CD3CN as the NMR
solvent. H NMR shifts are given relative to the residual solvent
resonances at 7.16, 7.26, 2.08, and 1.94 ppm, respectively, and
13C NMR shifts are given relative to C6D6 (128.1 ppm), CDCl3
(77.2 ppm), C7D8 (20.4 ppm) and CD3CN (118.3 ppm). 31P NMR
1
spectra were externally referenced to 0.00 ppm with 5% H3PO4
3
in D2O. Unless otherwise noted, all coupling constants are JHH
.
IR samples were prepared as Nujol mulls and taken between
KBr plates on a Perkin-Elmer XTL FTIR spectrophotometer.
Melting points were observed on a capillary melting point (Uni-
Melt) apparatus in sealed capillary tubes and are uncorrected.
X-ray structure determinations were performed at the Ohio
Crystallographic Consortium, housed at The University of Toledo.
Elemental analyses were determined by Atlantic Microlab, Inc.,
Norcross, GA or Galbraith Laboratories, Inc., Knoxville, TN.
High resolution mass spectrometry, using electrospray ionization,
was performed at the University of Illinois Mass Spectrometry
Laboratory, Urbana, IL.
Experimental
General methods and instrumentation
Synthesis and characterization of reaction products
Compounds H-L1–4 and Li-L1–4 were prepared in accordance with
All manipulations involving lithium reagents were performed
under an inert N2 atmosphere using standard glove box and
Schlenk techniques. Solvents were predried before use; methylene
previously published literature methods.2,4
˚
chloride was passed through two columns of 4 A molecular sieves
(L1)2Mg(OEt2) (1). Method one: A Schlenk flask was charged
with H-L1 (1.00 g, 3.23 mmol) and toluene (20 ml) was added via
cannula. Then, n-butyl lithium (2.02 ml, 3.23 mmol) was added
dropwise via syringe and allowed to stir for 20 min. The reaction
was cooled to 0 ◦C and EtMgBr (1.08 ml, 3.23 mmol) was added via
syringe. The reaction was allowed to stir for 12 h. The reaction was
filtered to remove lithium salts, and the solvent was then removed
via reduced pressure. The crude material was then crystallized from
diethyl ether yielding 1 as a yellow solid (0.69 g, 60%). Method
two: A Schlenk flask was charged with Li-L1 (0.70 g, 2.2 mmol)
and diethyl ether (20 ml) was added via cannula. The reaction was
and sparged with nitrogen. Pentane, diethyl ether, and toluene
˚
were passed through columns of activated alumina and 4 A
molecular sieves and sparged with nitrogen. Dimethoxyethane
(DME) was dried over sodium metal, freeze-pump-thawed three
times, and vacuum distilled. n-Butyl lithium (1.6 M in hexanes),
ethylmagnesium bromide (3 M in diethyl ether), potassium and
diphenylchlorophosphine were purchased from Strem Chemicals,
Inc., and used as received. Copper(I) iodide was purchased from
Acros and dried via heating at 100 ◦C for 12 h under vacuum. Zinc
chloride (anhydrous), aluminum chloride (anhydrous), diethylalu-
minum chloride (1.0 M in hexanes), tri-n-butyltin chloride, methyl
iodide, iodine, methanol, ethyl acetate, magnesium sulfate and
sodium sulfite were purchased from various commercial sources.
Benzene-d6 was dried over sodium metal, freeze-pump-thawed
◦
cooled to 0 C and EtMgBr (0.71 ml, 2.1 mmol) was added via
syringe. The reaction was allowed to stir for 12 h. The solvent
was removed via reduced pressure. The residue was taken up in
toluene and filtered to remove lithium chloride, and the solvent was
removed via reduced pressure. The crude material was crystallized
˚
three times, vacuum distilled and stored over 4 A molecular
1
sieves. Toluene-d8 was dried over sodium metal, freeze-pump-
thawed three times, and vacuum distilled. Chloroform-d1 was dried
over calcium hydride, freeze-pump-thawed three times, vacuum
from diethyl ether yielding 1 as a yellow solid (0.55 g, 73%). H
NMR (ambient temperature, toluene-d8): d 7.90 (s, 2H), 6.99 (s,
6H), 6.72 (d, 2H, 7.6 Hz), 6.51 (d, 2H, 7.6 Hz), 5.06 (br. s, 4H),
3.63 (br. s, 4H),◦2.95 (br. s, 4H), 1.10 (d, 12H, 6 Hz), 1.09 (m, 18H);
1H NMR (-48 C, toluene-d8): d 7.92 (s, 2H), 7.13 (m, 2H), 7.06
(d, 2H, 7.2 Hz), 6.89 (d, 2H, 7.2 Hz), 6.67 (d, 2H, 7.6 Hz), 6.56
(d, 2H, 7.6 Hz), 5.38 (s, 2H), 4.57 (s, 2H), 4.24 (br. s, 2H), 3.21
(m, 4H), 2.62 (m, 2H), 1.43 (d, 6H, 6.4 Hz), 1.24 (d, 6H, 6.4 Hz),
˚
distilled and stored over 4 A molecular sieves. Silica gel (Porosity:
˚
60 A, Particle size: 40–63 mm) was purchased from Sorbent
Technologies and used as received. H and 13C NMR data were
1
obtained on a 600 MHz Inova NMR or a 400 MHz VXRS
NMR spectrometer at ambient temperature at 599.9 MHz for
1H NMR and 150.8 MHz for 13C NMR and 399.95 MHz for 1H
NMR and 100.56 MHz for 13C NMR, respectively. All spectra
1
1.03 (d, 6H, 6.4 Hz), 0.73 (br. s, 6H), 0.55 (d, 6H, 6.4 Hz); 13C{ H}
NMR (-48 ◦C, toluene-d8): d 174.5, 155.9, 149.8, 148.0, 147.4,
Dalton Trans., 2012, 41, 860–870 | 865
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
140.6, 140.3, 139.4, 124.7, 122.3, 122.2, 105.1, 98.5, 64.3, 29.5,
28.3, 25.7, 24.8, 22.8, 21.1, 13.9 (one aromatic carbon resonance
not observed); IR: 1611 (s), 1555 (s), 1461 (s), 1400 (s), 1333 (m),
1242 (s), 1175 (s), 1096 (s), 1046 (s), 978 (m), 933 (s), 891 (w), 860
(w), 788 (s), 757 (s). Melting point: 151 ◦C dec.
154.9, 150.1, 146.8, 140.7, 137.9, 135.5, 127.6, 125.7, 123.7, 106.4,
99.8, 28.2, 25.0 (br), 22.7 (br); IR: 1617 (s), 1569 (m), 1457 (m),
1416 (s), 1377 (m), 1358 (m), 1237 (s), 1107 (m), 1055 (s), 979 (w),
941 (w), 889 (w), 813 (w), 720 (w); Anal. calcd. for C40H44N2O4Zn:
C, 70.43; H, 6.50; N, 4.11. Found: C, 69.20; H, 6.32; N, 4.11.
Melting point: 159 ◦C dec.
Al(L1)2Cl (2). A Schlenk flask was charged with Li-L1 (0.50 g,
1.6 mmol) and toluene (40 ml) was added via cannula. A second
Schlenk flask was charged with AlCl3 (0.10 g, 0.75 mmol) and
toluene (5 ml) was added via cannula. The solution of Li-L1 was
added via cannula to the stirring slurry of AlCl3. The reaction was
allowed to stir for 12 h. The crude reaction mixture was filtered
through celite and the solvent removed via reduced pressure. The
residue was dissolved in a minimal amount of toluene (5 ml),
layered with pentane and cooled to -25 ◦C. 2 was isolated as a
Zn(L4)2 (5). A Schlenk flask was charged with Li-L4 (0.25 g,
1.1 mmol) and toluene (25 ml) was added via cannula. A second
Schlenk flask was charged with ZnCl2 (68 mg, 0.49 mmol) and
◦
diethyl ether (15 ml) was added via cannula and cooled to 0 C.
The solution of Li-L4 was added via cannula to the stirring slurry
of ZnCl2 and the reaction was allowed to stir for 12 h, during
which time it turned a light blue and then a pale yellow color. The
reaction was filtered and the solvent removed via reduced pressure.
The residue was dissolved in diethyl ether and cooled to -25 ◦C.
5 was isolated as a white crystalline solid (0.25 g, 97%). 1H NMR
(benzene-d6): d 7.77 (s, 2H), 6.85 (d, 2H, 7.8 Hz), 6.76 (d, 2H, 7.8
Hz), 5.53 (d, 2H, 2JHH = 1.8 Hz), 5.33 (d, 2H, 2JHH = 1.8 Hz), 2.98
(tt, 2H, 10.7 Hz, 4.2 Hz), 1.68–1.49 (m, 10H), 1.35–1.26 (m, 4H),
1
yellow crystalline solid (0.32 g, 62%). H NMR (benzene-d6): d
7.91 (s, 2H), 7.06 (d, 2H, 7.8 Hz), 6.96 (t, 2H, 7.8 Hz), 6.77 (d, 2H,
7.8 Hz), 6.55 (d, 2H, 7.8 Hz), 6.41 (d, 2H, 7.8 Hz), 5.13 (d, 2H,
2JHH = 1.2 Hz), 4.52 (d, 2H, 2JHH = 1.2 Hz), 3.52 (sept, 2H, 6.8 Hz),
2.59 (sept, 2H, 6.8 Hz), 1.40 (d, 6H, 6.8 Hz), 0.97 (d, 6H, 6.8 Hz),
1
1
0.92 (d, 6H, 6.8 Hz), 0.52 (d, 6H, 6.8 Hz); 13C{ H} NMR (benzene-
1.11–0.99 (m, 4H), 0.79–0.73 (m, 2H); 13C{ H} NMR (benzene-
d6): d 175.3, 153.9, 152.5, 144.7, 144.4, 141.3, 133.8, 128.6, 126.7,
125.7, 123.5, 121.9, 106.7, 100.5, 30.2, 28.7, 25.7, 25.6, 23.0, 21.1;
IR: 1600 (s), 1548 (s), 1421 (s), 1379 (m), 1250 (s), 1174 (w), 1118
(s), 1056 (m), 987 (w), 929 (w), 798 (m), 727 (w), 695 (w); Anal.
calcd. for C40H44AlClN2O4: C, 70.73; H, 6.53; N, 4.12. Found: C,
70.37; H, 6.50; N, 3.99. Melting point: 182 ◦C dec.
d6): d 167.6, 155.1, 149.2, 139.6, 137.0, 125.8, 106.1, 99.6, 67.2,
34.8, 34.2, 25.5, 25.3, 25.2; IR: 1631 (s), 1609 (s), 1558 (s), 1504
(m), 1416 (s), 1376 (s), 1336 (m), 1323 (m), 1242 (s), 1207 (m),
1176 (s), 1109 (s), 1052 (s), 994 (w), 972 (m), 939 (s), 886 (w), 863
(s), 819 (s), 791 (s), 756 (s), 729 (w), 691 (w), 622 (m); Anal. calcd.
for C28H32N2O4Zn: C, 63.94; H, 6.13; N, 5.33. Found: C, 61.11; H,
5.90; N, 5.02. Melting point: 115 ◦C dec.
Et2Al(L1) (3). A Schlenk flask was charged with H-L1 (1.00 g,
3.23 mmol) and pentane (30 ml) was added via cannula. n-Butyl
lithium (2.02 ml, 3.23 mmol) was added dropwise via syringe at
room temperature. The slurry of Li-L1 was allowed to stir for 30
min, following which Et2AlCl (3.23 ml, 3.23 mmol) was added via
syringe. The reaction was allowed to stir for 12 h. The solvent
was then removed via reduced pressure. The residue was dissolved
in toluene and filtered, and the solvent was again removed via
reduced pressu◦re. The crude product was dissolved in pentane and
cooled to -25 C. 3 was isolated as a yellow solid (0.92 g, 72%).
1H NMR (benzene-d6): d 7.79 (s, 1H), 7.11–7.03 (m, 3H), 6.72 (d,
1H, 7.6 Hz), 6.55 (d, 1H, 7.6 Hz), 5.31 (s, 2H), 3.09 (sept, 2H,
6.8 Hz), 1.53 (t, 6H, 7.9 Hz), 1.22 (d, 6H, 6.8 Hz), 0.92 (d, 6H,
Cu(L1) (6). A Schlenk flask was charged with Li-L1 (4.00 g,
12.7 mmol) and toluene (40 ml) was added via cannula. A second
Schlenk flask was charged with CuI (3.65 g, 19.2 mmol) and diethyl
ether (20 ml) was added via cannula. The solution of Li-L1 was
added via cannula to the stirring slurry of CuI. The reaction was
allowed to stir for 12 h. The crude reaction mixture was filtered
through celite twice and the solvent removed via reduced pressure.
The residue was washed with pentane (2 ¥ 30 ml) and dissolved in
diethyl ether and cooled to -25 ◦C. 6 was isolated as a red micro-
1
crystalline solid (2.47 g, 52%). H NMR (benzene-d6): d 8.03 (s,
1H), 7.17 (m, 3H, overlapping with C6D5H), 6.75 (d, 1H, 7.8 Hz),
6.58 (d, 1H, 7.8 Hz), 5.21 (s, 2H), 3.57 (sept, 2H, 6.6 Hz), 1.27 (d,
1
1
6.8 Hz), 0.54–0.41 (m, 4H); 13C{ H} NMR (benzene-d6): d 175.3,
6H, 6.6 Hz), 1.12 (d, 6H, 6.6 Hz); 13C{ H} NMR (benzene-d6):
155.0, 151.4, 142.4, 142.3, 136.1, 128.7, 127.9, 124.3, 107.8, 100.7,
28.3, 25.8, 22.9, 10.1, -0.20 (one aromatic carbon resonance is
unobserved); IR: 1633 (s), 1610 (m), 1549 (s), 1462 (s), 1378 (s),
1333 (w), 1291 (m), 1255 (s), 1173 (m), 1103 (m), 1050 (m), 941
(w), 884 (w), 804 (s). Melting point: 95 ◦C dec.
d 177.3, 156.7, 148.5, 146.8, 141.4, 136.6 (br), 133.2 (br), 126.5,
123.9, 105.6, 99.1, 28.6, 14.7, 13.4 (one aromatic carbon resonance
not observed); IR: 1594 (s), 1585 (s), 1543 (s), 1488 (w), 1465 (s),
1406 (s), 1342 (m), 1322 (m), 1264 (s), 1213 (w), 1172 (s), 1124 (m),
1118 (m), 1061 (m), 1043 (w), 980 (m), 945 (m), 889 (w), 853 (w),
794 (s), 755 (m); Anal. calcd. for C20H22CuNO2: C, 64.58; H, 5.96;
N, 3.77. Found: C, 62.26; H, 5.84; N, 3.64. Melting point: 125 ◦C
dec.
Zn(L1)2 (4). A Schlenk flask was charged with Li-L1 (0.50 g,
1.6 mmol) and toluene (30 ml) was added via cannula. A second
Schlenk flask was charged with ZnCl2 (0.10 g, 0.73 mmol) and
◦
diethyl ether (15 ml) was added via cannula and cooled to 0 C.
Cu(L1)2Li (7). A Schlenk flask was charged with Li-L1 (1.00 g,
3.17 mmol) and toluene (25 ml) was added via cannula. A second
Schlenk flask was charged with CuI (0.28 g, 1.5 mmol) and diethyl
ether (10 ml) was added via cannula. The solution of Li-L1 was
added via cannula to the stirring slurry of CuI. The reaction was
allowed to stir for 12 h. The crude reaction mixture was filtered
through celite and the solvent removed via reduced pressure. The
residue was washed with pentane (2 ¥ 25 ml) and isolated as an
orange-red powder (0.91 g, 90%). 1H NMR (benzene-d6): 8.19 (s,
The solution of Li-L1 was added via cannula to the stirring slurry of
ZnCl2 and the reaction was allowed to stir for 12 h. The reaction
was filtered and the solvent removed via reduced pressure. The
residue was dissolved in diethyl ether and cooled to -25 ◦C. 4
was isolated as a white crystalline solid (240 mg, 47%). 1H NMR
(benzene-d6): d 7.90 (s, 2H), 7.03–6.97 (m, 6H), 6.75 (d, 2H, 7.8
Hz), 6.63 (d, 2H, 7.8 Hz), 5.33 (s, 4H), 3.26 (sept, 4H, 6.6 Hz), 1.09
1
(br. s, 12H), 0.72 (br. s, 12H); 13C{ H} NMR (benzene-d6): d 172.7,
866 | Dalton Trans., 2012, 41, 860–870
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
1H), 8.05 (d, 1H, 8.4 Hz), 7.84 (s, 1H), 7.69 (br. s, 1H), 7.13–7.03
(m, 4H), 6.95 (d, 1H, 7.8 Hz), 6.87 (d, 1H, 7.2 Hz), 6.55 (d, 1H,
8.4 Hz), 6.51 (d, 1H, 7.8 Hz), 5.17 (s, 1H), 5.15 (s, 2H), 5.05 (s,
1H), 3.51 (v. br. s, 1H), 3.22 (v. br. s, 1H), 3.12–3.09 (m, 2H), 1.12
(d, 6H, 7.2 Hz), 1.07 (d, 6H, 7.2 Hz), 1.04 (d, 6H, 7.2 Hz), 0.94 (v.
indicating formation of a copper complex. The reaction was
allowed to stir for 30 min. Ph2PCl (0.66 ml, 0.81 g, 3.7 mmol)
was added via syringe; upon addition, a precipitate formed and
the flask became slightly warm. The reaction was allowed to stir
for 20 min. The solvent was removed via reduced pressure. The
residue was taken up in warm dichloromethane (200 ml) and
filtered through celite. The celite was rinsed with an additional
portion of dichloromethane (100 ml). The dichloromethane was
then removed from the combined solutions via reduced pressure.
The crude material was washed with pentane (200 ml) and dried
1
br. s, 6H); 13C{ H} NMR (benzene-d6): 161.1, 159.2, 150.9, 150.1,
149.9, 149.8, 148.9, 148.6, 146.7, 138.0, 131.6, 129.3, 125.7, 124.7,
124.5, 123.5, 123.4, 122.9, 116.2, 109.4, 108.4, 106.9, 101.6, 101.5,
28.7, 28.5, 28.3, 23.9, 23.7, 23.6; IR: 1634 (m), 1609 (s), 1576 (m),
1553 (m), 1460 (s), 1380 (s), 1259 (s), 1176 (m), 1096 (s), 1041
(s), 934 (m), 861 (w), 800 (s), 754 (m), 728 (w); Anal. calcd. for
C40H44CuLiN2O4: C, 69.90; H, 6.45; N, 4.08. Found: C, 58.01; H,
6.42; N, 3.63 Melting point: 84 ◦C dec.
1
under vacuum, yielding 10 as an orange solid (2.06 g, 83%). H
4
NMR (acetonitrile-d3): d 8.13 (d, 1H, JPH = 1.2 Hz), 7.59–7.56
(m, 4H), 7.48–7.41 (m, 6H), 7.32 (dd, 1H, 8.4 Hz, 4JPH = 1.8 Hz),
7.17–7.16 (m, 3H), 7.09 (d, 1H, 8.4 Hz), 5.72 (s, 2H), 2.99 (sept,
2H, 8.4 Hz), 0.99 (d, 12H, 8.4 Hz);65 IR: 1620 (s), 1575 (s), 1460 (s),
1420 (s), 1379 (s), 1339 (m), 1255 (s), 1175 (s), 1143 (m), 1099 (m),
1050 (s), 983 (w), 947 (m), 854 (w), 823 (m), 788 (m), 738 (s), 689
nBu3Sn(L1) (8). A Schlenk flask was charged with Li-L1 (1.00 g,
3.17 mmol) and toluene (30 ml) was added via cannula. The
reaction was cooled to 0 ◦C and nBu3SnCl (0.78 ml, 0.93 g,
2.9 mmol) was added via syringe. The reaction was allowed to stir
for 12 h. The crude reaction mixture was filtered and the solvent
removed via reduced pressure. The residue was purified via column
chromatography (silica gel; 9 : 1 pentane/ethyl acetate) and 8 was
(s); HRMScalc: 556.1467 for C32H32CuNO2P [M - I]+; HRMSmeas
:
556.1470. Melting point: 188 ◦C dec.
Ph2P-L1 (11). A Schlenk flask was charged with 1 (0.28 g,
0.39 mmol) and diethyl ether (20 ml) was added via cannula.
Then, Ph2PCl (0.15 ml, 0.18 g, 0.86 mmol) was added dropwise via
syringe to the stirring solution of 1. The reaction was allowed to
stir for 14 h, after which time silica gel was added and the volatiles
were removed via reduced pressure. The crude reaction adsorbed
on the silica gel was added to the top of a column of silica gel and
eluted with 5 : 1 pentane/ethyl acetate. The iminophosphine 11
was crystallized from pentane as a green-yellow crystalline solid
1
isolated as a yellow oil (1.15 g, 68%). H NMR (benzene-d6): d
8.19 (s, 1H), 7.33 (d, 1H, 7.2 Hz), 7.19 (d, 2H, 7.8 Hz), 7.14–7.12
(m, 1H), 6.64 (d, 1H, 7.2 Hz), 5.27 (s, 2H), 3.25 (sept, 2H, 7.2 Hz),
1.68–1.63 (m, 6H), 1.41–1.36 (m, 8H), 1.33–1.30 (m, 4H), 1.25 (d,
1
12H, 7.2 Hz), 0.83 (t, 9H, 8.4 Hz); 13C{ H} NMR (benzene-d6): d
164.5, 155.4, 149.9, 148.6, 138.6, 136.4, 136.3, 124.8, 123.7, 120.2,
108.8, 100.1, 29.7, 28.2, 27.9, 24.3, 14.0, 12.9; IR: 1623 (s), 1564
(m), 1446 (s), 1329 (m), 1245 (s), 1178 (m), 1124 (m), 1053 (s), 945
(m), 846 (w), 807 (m), 737 (w), 653 (w); HRMScalc: 600.2864 for
C32H50NO2Sn [M + H]+; HRMSmeas: 600.2868.
1
4
(123 mg, 64%). H NMR (benzene-d6): d 9.42 (d, 1H, JPH = 3.0
Hz), 8.14 (dd, 1H, 8.4 Hz, 4JPH = 3.0 Hz), 7.47–7.44 (m, 4H), 7.18
(d, 2H, 7.2 Hz), 7.13 (t, 1H, 7.2 Hz), 7.06–7.04 (m, 6H), 6.68 (d,
1H, 8.4 Hz), 4.89 (s, 2H), 3.23 (sept, 2H, 6.6 Hz), 1.18 (d, 12H,
Me-L3 (9). A Schlenk flask was charged with H-L3 (5.00 g,
16.9 mmol) and toluene◦(100 ml) was added via cannula. The
reaction was cooled to 0 C and nBuLi (10.6 ml, 16.9 mmol) was
added via syringe. The reaction was allowed to stir for 30 min,
after which time methyl iodide (1.16 ml, 2.64 g, 18.6 mmol) was
added via syringe and the reaction was allowed to stir for 30 min.
The crude reaction mixture was filtered through celite and the
solvent removed via reduced pressure. Crystallization from diethyl
ether yielded 9 as a yellow crystalline solid (3.3 g, 63%). 1H NMR
(benzene-d6): d 7.12 (d, 2H, 7.2 Hz), 7.06–7.04 (m, 1H), 6.89 (d,
1H, 8.4 Hz), 6.57 (d, 1H, 8.4 Hz), 5.32 (s, 2H), 2.56 (s, 3H), 2.54–
2.47 (m, 2H), 2.43–2.38 (m, 2H), 1.74 (s, 3H), 1.36 (t, 6H, 7.2 Hz);
1H NMR (CDCl3): d 7.18 (d, 2H, 7.2 Hz), 7.12–7.07 (m, 2H), 6.80
(d, 1H, 7.8 Hz), 6.03 (s, 2H), 2.61–2.45 (m, 7H), 2.06 (s, 3H), 1.28
1
6.6 Hz); 13C{ H} NMR (benzene-d6): d 160.9 (d, 3JPC = 29.1 Hz),
151.3 (d, 3JPC = 2.2 Hz), 150.2 (d, 2JPC = 7.5 Hz), 150.1, 138.1, 136.3
(d, 2JPC = 9.3 Hz), 135.4 (d, 1JPC = 20.5 Hz), 133.5 (d, 2JPC = 19.5
Hz), 128.6, 128.5 (d, 3JPC = 6.9 Hz), 124.6, 123.5, 123.4 (d, 4JPC
=
5.3 Hz), 118.4 (d, 1JPC = 27.3 Hz), 110.6, 100.9, 28.5, 23.8; 31P{ H}
NMR (benzene-d6): d -23.8; IR: 1633 (s), 1603 (s), 1435 (s), 1381
(s), 1339 (s), 1259 (s), 1240 (s), 1226 (s), 1179 (s), 1135 (s), 1096
(s), 1052 (s), 1005 (w), 953 (s), 900 (w), 857 (m), 836 (m), 803 (m),
788 (w), 753 (s), 739 (s), 692 (s); Anal. calcd. for C32H32NO2P: C,
77.87; H, 6.53; N, 2.84. Found: C, 77.00; H, 6.44; N, 2.82. Melting
point = 111–113 ◦C.
1
I-L1 (12). A Schlenk tube was charged with Li-L1 (0.39 g,
1.2 mmol) and toluene (20 ml) was added via cannula. Then,
solid I2 (0.32 g, 1.2 mmol) was added. The reaction was allowed
to stir for two hours at ambient temperature. The reaction was
subsequently quenched with a saturated aqueous sodium sulfite
solution (20 ml). The layers were then separated and the organic
layer washed with deionized water (2 ¥ 30 ml). The organic
layer was dried over magnesium sulfate and the solvent removed
via reduced pressure, yielding a dark brown solid following
crystallization from methanol (0.29 g, 55%). 1H NMR (benzene-
d6): d 8.50 (s, 1H), 7.96 (d, 1H, 8.4 Hz), 7.20 (d, 2H, 7.2 Hz), 7.16
(t, 1H, obscured by residual C6D5H), 6.43 (d, 1H, 8.4 Hz), 5.08
1
(t, 6H, 7.6 Hz); 13C{ H} NMR (CDCl3): d 168.7, 147.9, 147.3,
146.9, 135.9, 131.3, 126.1, 123.2, 121.7, 117.6, 105.8, 101.1, 24.7,
21.7, 14.1, 13.3; IR: 1856 (m), 1580 (s), 1468 (s), 1386 (s), 1271 (s),
1201 (m), 1117 (m), 1061 (s), 949 (m), 864 (m), 815 (s), 780 (s),
633 (s); HRMScalc: 310.1807 for C20H24NO2 [M + H]+; HRMSmeas
310.1808. Melting point: 65–66 ◦C.
:
CuI(Ph2P-L1) (10). A Schlenk flask was charged with H-L1
(1.13 g, 3.65 mmol) and toluene (25 ml) was added via cannula.
nBuLi (2.3 ml, 3.7 mmol) was added via syringe. The reaction
was allowed to stir for 30 min. A Schlenk flask was charged
with CuI (0.71 g, 3.7 mmol) and diethyl ether (20 ml) was added
via cannula. The toluene solution was then added to the slurry
of CuI in diethyl ether; upon addition, a red color developed
1
(s, 2H), 3.22 (sept, 2H, 7.2 Hz), 1.24 (d, 12H, 7.2 Hz); H NMR
(chloroform-d1): d 8.31 (s, 1H), 7.87 (d, 1H, 8.9 Hz), 7.22–7.13 (m,
3H), 6.91 (d, 1H, 8.9 Hz), 6.13 (s, 2H), 3.00 (sept, 2H, 6.5 Hz),
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 860–870 | 867
©

View Article Online
868 | Dalton Trans., 2012, 41, 860–870
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
1
1.22 (d, 12H, 6.5 Hz); 13C{ H} NMR (chloroform-d1): d 163.8,
to 140 K using a nitrogen-flow low-temperature apparatus that
had been previously calibrated by a thermocouple placed at the
same position as the crystal. An arbitrary hemisphere of data
was collected using 0.3◦ w scans, and the data were integrated
by the program SAINT.68 The final unit cell parameters were
determined by a least-squares refinement of the reflections with I >
2s(I). Data analysis using Siemens XPREP69 and the successful
solution and refinement of the structure determined the space
group. Empirical absorption corrections were applied for 2, 4, 5,
6, 7 and 10 using the program SADABS.70 Equivalent reflections
were averaged, and the structures were solved by direct methods
using the SHELXTL software package.71 Unless otherwise noted,
all non-hydrogen atoms were refined anisotropically.
2: X-ray quality crystals were grown from a toluene solution
at -25 ◦C. Three toluene solvent molecules were present in the
asymmetric unit. The carbon atoms of two solvent molecules
were refined anisotropically. The third toluene molecule was
disordered over two positions; its carbon and hydrogen atoms
were both modeled isotropically. Restraints were used to ensure a
planar arrangement of the carbon atoms within the rings of the
toluene solvent molecules and rigid group fitting was employed
to force a hexagonal structure. The final cycle of full-matrix least-
squares refinement was based on 8984 observed reflections and
570 variable parameters and converged yielding final residuals:
Robs = 0.0727, Rall = 0.0854, and GoF = 1.048.
149.9, 148.9, 148.7, 137.9, 130.4, 124.4, 123.7, 123.3, 108.8, 101.2,
77.5, 28.1, 23.8; IR: 1633 (s), 1591 (s), 1456 (s), 1327 (s), 1252 (s),
1182 (m), 1114 (m), 1041 (s), 930 (s), 856 (w), 829 (m), 804 (w),
747 (s); HRMScalc: 436.0774 for C20H23INO2 [M + H]+; HRMSmeas
436.0775. Melting point: 164–165 ◦C.
:
I-L2 (13). A Schlenk tube was charged with Li-L2 (0.51 g,
1.6 mmol) and toluene (30 ml) was added via cannula. Subse-
quently solid I2 (0.40 g, 1.6 mmol) was added. The reaction was
allowed to stir for two hours at ambient temperature. The reaction
was quenched with a saturated aqueous sodium sulfite solution
(30 ml) and the organic fraction was washed with deionized water
(2 ¥ 30 ml). The organic fraction was dried over magnesium sulfate
and the solvent removed via reduced pressure, yielding 12 as a
brown solid following crystallization from methanol (0.51 g, 74%).
1H NMR (chloroform-d1): d 7.21 (d, 2H, 7.8 Hz), 7.13 (t, 1H, 7.8
Hz), 6.98 (d, 1H, 7.8 Hz), 6.86 (d, 1H, 7.8 Hz), 6.08 (s, 2H), 3.09
(sept, 2H, 6.6 Hz), 2.10 (s, 3H), 1.27 (d, 6H, 6.6 Hz), 1.21 (d, 6H, 6.6
Hz); 13C{ H} NMR (chloroform-d1): d 170.1, 149.8, 146.1, 145.2,
1
140.6, 136.3, 123.9, 123.2, 122.5, 108.5, 100.8, 70.3, 27.9, 23.6,
23.3, 22.1; IR: 1647 (m), 1590 (m), 1453 (s), 1373 (m), 1242 (s),
1140 (w), 1098 (w), 1033 (s), 918 (m), 805 (m), 770 (w); HRMScalc
450.0930 for C21H25INO2 [M + H]+; HRMSmeas: 450.0934. Melting
point: 138–139 ◦C.
:
(L2)2 (14). A Schlenk tube was charged with CuI (2.61 g,
13.7 mmol) and potassium metal (0.53 g, 14 mmol) in the glove box
and dimethoxyethane (30 ml) was added via cannula. The reaction
was allowed to stir for four hours at ambient temperature. Then
13 (0.50 g, 1.1 mmol) was added as a solid and the reaction was
allowed to stir an additional 12 h. The reaction was quenched
with water (20 ml) and filtered through a plug of celite, which
was washed with diethyl ether (2 ¥ 20 ml). The layers were then
separated and the organic layer washed with deionized water (4 ¥
30 ml). The organic layer was dried over magnesium sulfate and
the solvent removed via reduced pressure. Crystallization from
pentane yielded 14 as a dark brown solid (0.33 g, 92%). 1H NMR
(chloroform-d1): d 7.30 (d, 2H, 7.8 Hz), 7.08 (d, 4H, 7.2 Hz), 7.03
(t, 2H, 7.2 Hz), 6.93 (d, 2H, 7.8 Hz), 6.01 (d, 2H, 2JHH = 0.6 Hz),
4: X-ray quality crystals were grown from a pentane solution at
-25 ◦C. The final cycle of full-matrix least-squares refinement was
based on 7032 observed reflections and 425 variable parameters
and converged yielding final residuals: Robs = 0.0392, Rall = 0.0521,
and GoF = 1.024.
5: X-ray quality crystals were grown from a diethyl ether
solution at -25 ◦C. The final cycle of full-matrix least-squares
refinement was based on 5448 observed reflections and 316
variable parameters and converged yielding final residuals: Robs
0.0331, Rall = 0.0372, and GoF = 1.052.
=
6: X-ray quality crystals were grown from a diethyl ether
solution at -25 ◦C. The final cycle of full-matrix least-squares
refinement was based on 4650 observed reflections and 433
variable parameters and converged yielding final residuals: Robs
0.0823, Rall = 0.0896, and GoF = 1.011.
=
2
5.94 (d, 2H, JHH = 0.6 Hz), 2.67 (sept, 2H, 7.2 Hz), 2.55 (sept,
7: X-ray quality crystals were grown from an evaporating
diethyl ether/toluene solution. The final cycle of full-matrix least-
squares refinement was based on 5455 observed reflections and
478 variable parameters and converged yielding final residuals:
Robs = 0.0897, Rall = 0.1171, and GoF = 1.215.
2H, 7.2 Hz), 1.91 (s, 6H), 1.08 (d, 6H, 7.2 Hz), 1.07 (d, 6H, 7.2
1
Hz), 1.05 (d, 6H, 7.2 Hz), 1.03 (d, 6H, 7.2 Hz); 13C{ H} NMR
(chloroform-d1): d 168.2, 147.9, 146.4, 146.3, 136.4, 136.3, 136.0,
123.4, 123.1, 123.0, 122.5, 115.6, 108.2, 101.7, 27.9, 27.7, 24.1,
23.6, 23.5, 23.3, 21.2; IR: 1641 (m), 1458 (s), 1362 (w), 1334 (w),
10: X-ray quality crystals were grown from an acetonitrile
solution at ambient temperature. Additional electron density
corresponding to diffuse disordered solvent was observed, but not
modeled, in the final crystallographic model. The highest residual
1185 (w), 1099 (w), 1048 (s), 936 (w), 801 (m), 758 (m); HRMScalc
:
645.3692 for C42H49N2O4 [M + H]+; HRMSmeas: 645.3685. Melting
point: 186–188 ◦C.
˚
electron density is 3.69 A from O2, the nearest atom. The final
Crystallography
cycle of full-matrix least-squares refinement was based on 3977
observed reflections and 343 variable parameters and converged
yielding final residuals: Robs = 0.0407, Rall = 0.0789, and GoF =
1.037.
A summary of crystal data and collection parameters for crystal
structures of 2, 4, 5, 6, 7 and 10 are provided in Table 1.
Detailed descriptions of data collection, as well as data solution,
are provided below. ORTEP diagrams were generated with the
ORTEP-3 software package.66 For each sample, a suitable crystal
was mounted on a glass fiber using Paratone-N hydrocarbon oil.
The crystal was transferred to a Siemens SMART67 diffractometer
with a CCD area detector, centered in the X-ray beam, and cooled
Acknowledgements
We gratefully acknowledge The University of Toledo for generous
start-up funding, as well as the staff of the Ohio Crystallographic
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 860–870 | 869
©

View Article Online
Consortium housed at The University of Toledo and Dr Allen
Oliver (University of Notre Dame) for assistance with X-ray
crystallography. We would also like to recognize Mr Pascal
Marillier (Hillsdale College) for his assistance in the synthesis
of Me-L3 and I-L2.
34 S. Moorhouse and G. Wilkinson, J. Chem. Soc., Dalton Trans., 1974,
2187–2190.
35 C. Santini-Scampucci and J. G. Riess, J. Chem. Soc., Dalton Trans.,
1973, 2436–2440.
36 M. R. Crimmin, I. J. Casely and M. S. Hill, J. Am. Chem. Soc., 2005,
127, 2042–2043.
37 A. G. M. Barrett, M. R. Crimmin, M. S. Hill, P. B. Hitchcock and P.
A. Procopiou, Angew. Chem., Int. Ed., 2007, 46, 6339–6342.
38 M. R. Crimmin, A. G. M. Barrett, M. S. Hill, P. B. Hitchcock and P.
A. Procopiou, Organometallics, 2008, 27, 497–499.
39 M. R. Crimmin, A. G. M. Barrett, M. S. Hill, P. B. Hitchcock and P.
A. Procopiou, Organometallics, 2007, 26, 2953–2956.
40 X. Zhang, T. J. Emge and K. C. Hultzsch, Organometallics, 2010, 29,
5871–5877.
References
1 J. F. Beck, A. Neshat and J. A. R. Schmidt, Eur. J. Inorg. Chem., 2010,
5146–5155.
2 A. Neshat, C. L. Seambos, J. F. Beck and J. A. R. Schmidt, Dalton
Trans., 2009, 4987–5000.
3 J. F. Beck, T. I. Baiz, A. Neshat and J. A. R. Schmidt, Dalton Trans.,
2009, 5001–5008.
4 T. I. Baiz and J. A. R. Schmidt, Organometallics, 2007, 26, 4094–4097.
5 A. Neshat and J. A. R. Schmidt, Organometallics, 2010, 29, 6219–6229.
6 P. B. Hitchcock, Q. G. Huang, M. F. Lappert, X. H. Wei and M. S.
Zhou, Dalton Trans., 2006, 2991–2997.
7 Z. Z. Wu, J. B. Diminnie and Z. L. Xue, Inorg. Chem., 1998, 37, 2570–
2574.
8 E. Witt and D. W. Stephan, Inorg. Chem., 2001, 40, 3824–3826.
9 A. V. Firth, E. Witt and D. W. Stephan, Organometallics, 1998, 17,
3716–3722.
41 J. F. Dunne, D. B. Fulton, A. Ellern and A. D. Sadow, J. Am. Chem.
Soc., 2010, 132, 17680–17683.
42 M. R. Crimmin, M. Arrowsmith, A. G. M. Barrett, I. J. Casely, M. S.
Hill and P. A. Procopiou, J. Am. Chem. Soc., 2009, 131, 9670–9685.
43 J. Ejfler, K. Krauzy-Dziedzic, S. Szafert, L. B. Jerzykiewicz and P.
Sobota, Eur. J. Inorg. Chem., 2010, 3602–3609.
44 Y. C. Liu, C. H. Lin, B. T. Ko and R. M. Ho, J. Polym. Sci., Part A:
Polym. Chem., 2010, 48, 5339–5347.
45 L. Y. Wang and H. Y. Ma, Macromolecules, 2010, 43, 6535–6537.
46 X. Xu, Y. F. Chen, G. Zou, Z. Ma and G. Y. Li, J. Organomet. Chem.,
2010, 695, 1155–1162.
47 M. H. Thibault and F. G. Fontaine, Dalton Trans., 2010, 39, 5688–5697.
48 S. G. Gong and H. Y. Ma, Dalton Trans., 2008, 3345–3357.
49 M. A. Munoz-Hernandez, M. L. McKee, T. S. Keizer, B. C. Yearwood
and D. A. Atwood, J. Chem. Soc., Dalton Trans., 2002, 410–414.
50 M. H. Chisholm, C. C. Lin, J. C. Gallucci and B. T. Ko, Dalton Trans.,
2003, 406–412.
10 T. V. Lubben, P. T. Wolczanski and G. D. Vanduyne, Organometallics,
1984, 3, 977–983.
11 M. J. Nelsen and G. S. Girolami, J. Organomet. Chem., 1999, 585,
275–284.
12 M. Polamo and M. Leskela, Acta Chem. Scand., 1997, 51, 44–48.
13 C. Schadle, C. Meermann, K. W. Tornroos and R. Anwander, Eur. J.
Inorg. Chem., 2010, 2841–2852.
14 J. Hannedouche, J. Collin, A. Trifonov and E. Schulz, J. Organomet.
Chem., 2011, 696, 255–262.
15 M. A. Guino-o, C. F. Campana and K. Ruhlandt-Senge, Chem.
Commun., 2008, 1692–1694.
51 M. H. Chisholm, N. J. Patmore and Z. P. Zhou, Chem. Commun., 2005,
127–129.
52 J. Koller and R. G. Bergman, Chem. Commun., 2010, 46, 4577–4579.
53 R. Han and G. Parkin, J. Organomet. Chem., 1990, 393, C43–C46.
54 R. I. Papasergio, C. L. Raston and A. H. White, J. Chem. Soc., Dalton
Trans., 1987, 3085–3091.
55 A. Toth, C. Floriani, A. Chiesivilla and C. Guastini, Inorg. Chem., 1987,
26, 236–241.
56 Y. Y. Lin, S. W. Lai, C. M. Che, W. F. Fu, Z. Y. Zhou and N. Y. Zhu,
Inorg. Chem., 2005, 44, 1511–1524.
57 G. van Koten and J. G. Noltes, J. Organomet. Chem., 1975, 84, 129–138.
58 S. I. Khan, P. G. Edwards, H. S. H. Yuan and R. Bau, J. Am. Chem.
Soc., 1985, 107, 1682–1684.
59 E. V. Salo and Z. B. Guan, Organometallics, 2003, 22, 5033–5046.
60 J. D. Hicks, A. M. Hyde, A. M. Cuezva and S. L. Buchwald, J. Am.
Chem. Soc., 2009, 131, 16720–16734.
61 K. R. Reddy, W. W. Tsai, K. Surekha, G. H. Lee, S. M. Peng, J. T. Chen
and S. T. Liu, J. Chem. Soc., Dalton Trans., 2002, 1776–1782.
62 G. Evano, N. Blanchard and M. Toumi, Chem. Rev., 2008, 108, 3054–
3131.
16 J. F. Beck, Ph.D. Dissertation, University of Toledo, 2011.
17 H. W. Roesky, Inorg. Chem., 2004, 43, 7284–7293.
18 P. P. Power, Nature, 2010, 463, 171–177.
19 H. Lei, J. C. Fettinger and P. P. Power, Organometallics, 2010, 29, 5585–
5590.
20 S. Harder, Chem. Rev., 2010, 110, 3852–3876.
21 M. Arrowsmith, M. S. Hill and G. Kociok-Kohn, Organometallics,
2011, 30, 1291–1294.
22 S. Krieck, H. Gorls and M. Westerhausen, Inorg. Chem. Commun.,
2010, 13, 1466–1469.
23 S. P. Sarish, S. Nembenna, S. Nagendran and H. W. Roesky, Acc. Chem.
Res., 2011, 44, 157–170.
24 C. Lichtenberg, P. Jochmann, T. P. Spaniol and J. Okuda, Angew. Chem.,
Int. Ed., 2011, 50, 5753–5756.
25 C. Eaborn, P. B. Hitchcock, J. D. Smith and A. C. Sullivan, J.
Organomet. Chem., 1984, 263, C23–C25.
26 B. Breit and Y. Schmidt, Chem. Rev., 2008, 108, 2928–2951.
27 J. J. Eisch, Organometallics, 2002, 21, 5439–5463.
28 M. Schormann, S. P. Varkey, H. W. Roesky and M. Noltemeyer, J.
Organomet. Chem., 2001, 621, 310–316.
29 P.-J. Sinnema, L. von der Veen, A. L. Spek, N. Veldman and J. H.
Teuben, Organometallics, 1997, 16, 4245–4247.
30 J. R. Hagadorn and J. Arnold, Organometallics, 1998, 17, 1355–
1368.
63 A. Nakamura, S. Ito and K. Nozaki, Chem. Rev., 2009, 109, 5215–5244.
64 D. P. Zhao, B. Gao, W. Gao, X. Y. Luo, D. H. Tang, Y. Mu and L. Ye,
Inorg. Chem., 2011, 50, 30–36.
1
65 13C{ H} NMR spectrum could not be determined due to low solubility.
66 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
67 SMART: Area-Detector Software Package, 5.625; Bruker AXS, Inc:
Madison, WI, 1997–2001.
68 SAINT: SAX Area-Detector Integration Program, 6.22; Bruker AXS,
Inc: Madison, WI, 1997–2001.
31 J. K. F. Buijink, A. Meetsma, J. H. Teuben, H. Kooijman and A. L.
Spek, J. Organomet. Chem., 1995, 497, 161–170.
32 T. Ishiyama, T. Mizuta, K. Miyoshi and H. Nakazawa, Organometallics,
2003, 22, 1096–1105.
33 S. L. Shaw, R. J. Morris and J. C. Huffman, J. Organomet. Chem., 1995,
489, C4–C6.
69 XPREP: Reciprocal Space Exploration Program, 6.12; Bruker AXS,
Inc: Madison, WI, 2001.
70 SADABS: Bruker/Siemens Area Detector Absorption Program, 2.03;
Bruker AXS, Inc: Madison, WI, 2001.
71 SHELXTL-97 Structure Solution Program, 6.10; Bruker AXS, Inc:
Madison, WI, 2000.
870 | Dalton Trans., 2012, 41, 860–870
This journal is
The Royal Society of Chemistry 2012
©