Syntheses and Structures of [CH2(NCnH2n)2]Mo(CO)4 (n = 4,5) Complexes with Bis(cycloamine) Ligands Easily Prepared from CH2Cl2

Article abstract of DOI:10.1021/acs.organomet.5b00396

Dipyrrolidylmethane, CH₂(pyr)₂, and dipiperidylmethane, CH₂(pip)₂, are synthesized via the condensation of their respective secondary amine precursors and dichloromethane at room temperature in the absence of light. Their use as chelating ligands is shown by the isolation and complete characterization of [CH₂(pyr)₂]Mo(CO)₄ and [CH₂(pip)₂]Mo(CO)₄ complexes. X-ray analysis reveals the methylene bis(cycloamines) to possess a sharp bite angle between 61° and 63° and a strong steric impact on the surrounding carbonyl ligands as a result of their ring conformations. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.organomet.5b00396

Article
pubs.acs.org/Organometallics
Syntheses and Structures of [CH2(NCnH2n)2]Mo(CO)4 (n = 4,5)
Complexes with Bis(cycloamine) Ligands Easily Prepared from CH2Cl2
Samuel J. Kyran, Sergio G. Sanchez, Christopher J. Arp, and Donald J. Darensbourg*
Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, Texas 77843 United States
S
* Supporting Information
ABSTRACT: Dipyrrolidylmethane, CH2(pyr)2, and dipiper-
idylmethane, CH2(pip)2, are synthesized via the condensation
of their respective secondary amine precursors and dichloro-
methane at room temperature in the absence of light. Their use
as chelating ligands is shown by the isolation and complete
characterization of [CH2(pyr)2]Mo(CO)4 and [CH2(pip)2]-
Mo(CO)4 complexes. X-ray analysis reveals the methylene
bis(cycloamines) to possess a sharp bite angle between 61° and
63° and a strong steric impact on the surrounding carbonyl
ligands as a result of their ring conformations.
transamination with N,N,N′,N′-tetramethyldiaminomethane
using Sm(NO3)2 or CuCl catalysts.2 The use of fulvenes as a
methylene source has also been noted.13 In their 2014 work,
the authors noticed the formation of dipiperidylmethane from
piperidine at room temperature in the presence of the
bispiperidine complex, cis-(pip)2W(CO)4 with dichlorome-
thane as solvent.12 As the authors were involved in studying
the catalytic properties of molybdenum and tungsten carbonyls
for various chemical transformations, they had prematurely
concluded that the cis-(pip)2W(CO)4 complex acts as the
catalyst for this conversion. In reality, the transformation of
piperidine to dipiperidylmethane with dichloromethane
proceeds on its own (Scheme 1).
INTRODUCTION
Methylene bridged cyclic amines (Figure 1) are used as
heterocyclic building blocks through amino methylations in
■
In this article, we wish to (1) summarize our efforts in
elucidating the reaction conditions involved in preparing
dipyrrolidyl- and dipiperidylmethanes directly from dichloro-
methane and (2) present the syntheses, structures, and
Figure 1. Common methylene bridged cyclic amines.
complete characterizations of Luttringhaus and Kullick’s
molybdenum complexes with said amines as ligands and the
varying steric effects they exhibit around the metal center.
̈
organic synthesis.1−6 They can also be employed as organo-
catalysts in aldol condensations and transesterifications.7−9
Their use in coordination chemistry as chelating ligands,
however, has been largely unexplored. The earliest reported
metal complexes, characterized only by infrared spectroscopy,
were [CH2(pyr)2]Mo(CO)4, 1, and [CH2(pip)2]Mo(CO)4, 2,
RESULTS AND DISCUSSION
■
Our initial interest was driven to understand the role of cis-
(pip)2W(CO)4 complex as a catalyst in producing CH2(pip)2
from piperidine.12 Upon running a series of experiments (Table
1), it soon became apparent that the metal does not play a role
in this chemistry. In fact, both CH2(pyr)2 and CH2(pip)2 can
be easily prepared by stirring pyrrolidine or piperidine,
respectively, in dichloromethane at room temperature in the
absence of light in good yields, as shown in Scheme 1. The
published in a brief communication by Luttringhaus and Kullick
̈
in 1959.10 Jung et al. have used CH2(pip)2 as a coligand in the
preparation of a benzoquinonatocobalt complex back in 2001.11
́
And finally, in a recent 2014 article, Szymanska-Buzar et al.
published a crystal structure of the [CH2(pip)2]W(CO)4
complex, synthesized photochemically using W(CO)6 thereby
establishing the coordinating nature of CH2(pip)2.12
Preparing these methylene bis(cycloamines) is typically done
by refluxing the mono secondary amines with paraformalde-
hyde in a high-boiling solvent.1,5,9 Another method involves the
Received: May 11, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00396
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 1. Synthesis of Dipyrrolidyl- And Dipiperidylmethanes from Dichloromethane
piperidinium chloride salt as the sole product half the time
(Table 1). Thus, all large-scale syntheses were carried out in
aluminum foil covered flasks. The methylene bis(cycloamines)
were spectroscopically pure after removal of salt and excess
dichloromethane and can be used for further reactions without
the need for distillation.
Table 1. Conditions Investigated for the Reaction of
Piperidine with Dichloromethane
a
addition of metal
complex (mol %)
stirring under ambient light
vs darkness
observed
products
test
1
2
3
4
5
6
7
8
9
10
5% cis-(pip)2W(CO)4
light
dark
light
dark
dark
light
dark
light
dark
dark
only salt
5% cis-(pip)2W(CO)4
ligand + salt
ligand + salt
ligand + salt
ligand + salt
ligand + salt
ligand + salt
only salt
The chelation of CH2(pyr)2 and CH2(pip)2 to molybdenum
carbonyls can be achieved either in a refluxing hexane solution
for a couple days or in heptane over a few hours yielding the
products as yellow solids in moderate yields (Scheme 2).
Complex 2, [CH2(pip)2]Mo(CO)4, containing dipiperidyl-
methane, is air-stable and can be stored in contact with air
for long periods of time unlike its well-known bispiperidine
analogue, cis-(pip)2Mo(CO)4, 3, which decomposes in the
absence of inert atmosphere within a few days. It also exhibits
somewhat better solubility than 3 being fully soluble in DMSO,
partially soluble in CH2Cl2 and THF and minimally soluble in
acetone, MeOH and Et2O. Complex 1, [CH2(pyr)2]Mo(CO)4
has similar if not slightly poorer solubility in the same solvents
and is not air-stable, unlike 2. While some exposure to air is
tolerable, storage for longer than a day needs to be under an
inert atmosphere.
1% cis-(pip)2W(CO)4
1% cis-(pip)2W(CO)4
1% W(CO)6
1% cis-(pip)2Mo(CO)4
1% cis-(pip)2Mo(CO)4
-
-
-
ligand + salt
ligand + salt
a
Test reactions: 0.25 mL piperidine in 20 mL CH2Cl2 with or without
metal addition in an open or Al foil covered vial. Stirred 24 h, excess
1
CH2Cl2 removed and product composition determined via H NMR
on crude mixture.
starting amines themselves can double up as a base driving the
reaction forward to give methylene bis(cycloamines) along with
2 equiv of the respective ammonium chloride salt. In an earlier
work, Matsumoto et al. have shown this to occur for various
secondary cyclic amines, albeit under high pressures, which is
clearly not required.14 Their use of pressure may stem from
alkylated amine byproducts observed in other high pressure
organic reactions carried out in dichloromethane. The pressure
could accelerate the reaction rate for tertiary amines to produce
a chloromethylammonium salt, but it is not required for the
reaction to take place.15,16 Mills et al. followed up with a
detailed NMR study in 1987 showing the reaction of
pyrrolidine with dichloromethane to proceed under ambient
conditions.17 They present evidence for the formation of 1-
methylenepyrrolidinium chloride after the condensation of the
first amine with dichloromethane followed by its rapid reaction
with a second amine to yield dipyrrolidylmethane. The reaction
of piperidine with various halomethanes have also been
described as early as 1964.18 Rapid formation of dipiperidyl-
methane is seen to occur with a benzene solution of
dibromomethane. More recent examples of alkyl and aromatic
amine reactivities without the need of a catalyst or pressing
conditions with dichloromethane can also be found in the
literature.19,20
1H NMR spectroscopy shows distinct changes in the
chemical shifts of the free ligands versus the coordinated
complexes. The bridging methylene protons experience a
downfield shift of 1.2 ppm when bound to molybdenum (δ
3.21 → 4.42 ppm, CH2(pyr)2; δ 2.86 → 4.09 ppm, CH2(pip)2).
The methylene protons on the rings become diastereotopic
with their signals splitting into pairs upon coordination. Hence,
two pairs of multiplets for CH2(pyr)2 and three pairs of
multiplets for CH2(pip)2 are observed for their complexes. This
effect was also noted for the [CH2(pip)2]W(CO)4 complex.12
In the 13C{1H} NMR spectra, the bridging methylene carbons
have a discrete signal between 80 and 90 ppm for all species.
Furthermore, two downfield signals at 206 and 222 ppm
representing the axial (cis to N) and equatorial (trans to N)
carbonyl carbons on the molybdenum can be observed for the
complexes. Infrared data reveal similar carbonyl stretching
frequencies for complexes 1 and 2 indicating the electron
donating capability to be nearly identical for both ligands
(Figure 2).
Single crystals for X-ray diffraction studies were obtained via
slow evaporation of Et2O and CH2Cl2 solutions for complexes
1 and 2, respectively. Thermal ellipsoid plots and relevant bond
distances are shown in Figure 3. Comparison of 2,
[CH2(pip)2]Mo(CO)4, with the previously determined struc-
ture of 3,21 cis-(pip)2Mo(CO)4, shows the CH2(pip)2 ligand to
An interesting observation from our test runs was the effect
of ambient light on this reaction. While we do not have a
complete understanding of its role, what can be said of a
reaction under light is its unpredictability, yielding the
Scheme 2. Synthesis of [CH2(pyr)2]Mo(CO)4, 1, (n = 1) and [CH2(pip)2]Mo(CO)4, 2, (n = 2) Complexes
B
DOI: 10.1021/acs.organomet.5b00396
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
carboxylate group in the 2-position, are the only other
structural examples thus far with a N,N′-methylene bridged
bis(cycloamine)-type ligand.22,23 The N−M−N angles measure
65.5(1)° (CoII), 67.5(2)° (NiII), and 63.5(3)° (ZnII), displaying
again the severe bite angles imposed by these constrained
chelates. Diamines with two carbons separating the nitrogen
atoms show a much larger bite angle. The N−Mo−N angle for
the less electron-releasing 1,10-phenanthroline ligand in the air-
stable complex, (phen)Mo(CO)4, is seen to be 73.62(7)°, while
the more electron-donating N,N,N′,N′-tetramethylethylenedi-
amine ligand reveals a bite angle of 77.98(9)° for its air-stable
complex, (TMEDA)Mo(CO)4.24−27 Moving down the periodic
group, methylene bridged phosphines display bite angles
toward the higher end of the observed range for methylene
bridged amines and larger. For example, dicyclohexylphosphi-
nomethane shows 67.397(17)° and 75.70(2)° for (dcpm)Mo-
(CO)4 and (dcpm)NiCl2 complexes, respectively.28,29
Figure 2. Infrared spectra of [CH2(pyr)2]Mo(CO)4, 1 (red), and
[CH2(pip)2]Mo(CO)4, 2 (blue), complexes in dichloromethane.
have a larger steric impact on the surrounding carbonyls leading
to a distorted octahedral geometry (Figure 4). With the amines
tied back by the methylene group, a small bite angle of
62.55(14)° is observed and the six-membered rings adopt a
conformation that points toward the metal center, compressing
the equatorial carbonyls and giving a C(2)−Mo(1)−C(2)′
angle of 86.0(2)°. The average distance calculated between the
equatorial carbonyl carbons and the closest ligand hydrogens is
only 2.82 Å. This distance is a bit longer, 2.90 Å, and hence a
lesser compression of the equatorial carbonyls, 88.76(13)°, is
noted for the tungsten analogue.12 The angle between the axial
carbonyls of 2 is also compressed, with C(1)−Mo(1)−C(4)
measuring 166.9(2)°, about 5° less than what is seen for
complex 3.
The crystal structure of 1 reveals the CH2(pyr)2 ligand to
have a slightly smaller bite angle than CH2(pip)2 measuring at
61.25(8)°. The five-membered ring size of the pyrrolidyl
groups exerts less influence sterically on the equatorial carbonyl
carbons with the average distance separating them from the
closest ligand hydrogens now at 3.16 Å. Thus, the angle
between the equatorial carbonyls is closer to 90° with C(2)−
Mo(1)−C(3) measuring 89.28(12)°. The influence on the axial
carbonyls, however, remains similar to CH2(pip)2 with C(1)−
Mo(1)−C(4) measuring 166.53(10)°. CoII, NiII, and ZnII
complexes bearing the tetradentate N2O2 ligand CH2(pyr-2-
COO)2, where each pyrrolidyl ring is substituted with a
CONCLUSIONS
■
The search for new ligands, especially those that offer a
modular approach to their synthesis, is of constant interest to
the inorganic community. We have demonstrated here that a
sterically demanding diamine ligand can be prepared by the
simple condensation of piperidine with dichloromethane. The
coordination environment of the [CH2(pip)2]Mo(CO)4
complex is starkly different to its untied cis-(pip)2Mo(CO)4
analogue as a result of the dipiperidylmethane rings now
directed around the metal center as seen via single-crystal X-ray
diffraction studies. The steric effect has less influence on
neighboring ligands when the ring size is reduced by one
carbon as with the dipyrrolidylmethane complex, [CH2(pyr)2]-
Mo(CO)4. This ligand synthesis can be extended to less basic
cyclic amines such as morpholine,30 while on the other hand,
employing substituted piperidines (ex: 3,5-dimethylpiperidine)
could introduce even more bulk around the metal center.
Sterically encumbering ligands are used in various transition
metal chemistries and the surprisingly bulky nature of these
methylene bis(cycloamines) with its extreme bite angles could
prove useful as a new ligand toolset.
Figure 3. Structures of [CH2(pyr)2]Mo(CO)4, 1 (left), and [CH2(pip)2]Mo(CO)4, 2 (right). Thermal ellipsoids, probability level 50%, with select
atom labeling. Hydrogen atoms omitted for clarity. Select bond distances (Å): Complex 1: N−Moave = 2.326(2); axial C−Oave = 1.147(3); equatorial
C−Oave = 1.166(3). Complex 2: N−Moave = 2.338(3); axial C−Oave = 1.123(7); equatorial C−Oave = 1.157(4).
C
DOI: 10.1021/acs.organomet.5b00396
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 4. View down the axial carbonyls of cis-(pip)2Mo(CO)4,21 3 (left), [CH2(pip)2]Mo(CO)4, 2 (center), and [CH2(pyr)2]Mo(CO)4, 1 (right).
Capped stick representations with angles around the molybdenum center. Average distance to the closest ligand hydrogens from the equatorial
carbonyl carbon is shown by arrow. Inset figures display the angle facing away from ligand and between the axial carbonyls.
under an argon atmosphere in hexane (30 mL). After 3 days, a bright
EXPERIMENTAL SECTION
■
yellow product was filtered and washed with hexanes (0.166 g, 77%).
Methods and Materials. Piperidine and pyrrolidine were
IR data in CH2Cl2 (νCO): 1832 (m), 1870 (sh), 1887 (s), 2014 (w).
purchased from Alfa Aesar and used as received. Mo(CO)6 was
obtained from Strem and GC grade heptane was purchased from EMD
chemicals. Dichloromethane and hexane were purified by an MBraun
Manual Solvent Purification System packed with Alcoa F200 activated
1H NMR (CDCl3): δ 1.87 (m, 4H), 2.13 (m, 4H), 2.77 (m, 4H), 3.45
(m, 4H), 4.42 (s, 2H, NCH2N). 13C{1H} NMR (d6-DMSO): δ 22.5,
63.5, 82.7 (NCH2N), 206 (CO), 223 (CO). Anal. Calcd for
C13H18MoN2O4: C, 43.10; H, 5.01; N, 7.73. Found: C, 42.47; H,
5.19; N, 7.61%.
alumina desiccant. NMR spectra were recorded on either a Varian
INOVA 300 or 500 MHz spectrometer. H and 13C NMR spectra
1
were referenced to residual solvent resonances. Infrared spectra were
obtained on a Bruker Tensor 27 FTIR spectrometer. Elemental
ASSOCIATED CONTENT
* Supporting Information
CIF file giving X-ray structural data for 1 and 2. The
Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00396.
■
S
analyses were determined by Atlantic Microlab (Norcross, GA).
Synthesis of Dipiperidylmethane, CH2(pip)2. Piperidine (10
mL, 8.62 g, 0.101 mol) and CH2Cl2 (20 mL) were stirred together in
an aluminum foil covered vial. After 24 h, the solution was filtered to
remove the white piperidinium chloride salt and the filtrate rotovaped
to remove excess CH2Cl2. The resulting cloudy oil was treated with
THF followed by filtration to precipitate and remove any additional
salt. Removal of THF yields a pale yellow liquid product (4.21 g,
91%). Distillation was not required for further experiments. The NMR
spectrum is clean and matches that previously reported:12 1H (CDCl3)
δ 1.43 (m, 4H), 1.55 (m, 8H), 2.42 (m, 8H), 2.86 (s, 2H, NCH2N).
Synthesis of Dipyrrolidylmethane, CH2(pyr)2. A similar
procedure to CH2(pip)2 was followed to give CH2(pyr)2 in greater
than 70% yield. When crashing out pyrrolidinium chloride salt, Et2O is
used instead of THF. This salt is very hygroscopic and tends to
dissolve in THF. Pure by NMR:17 1H (CDCl3) δ 1.76 (m, 8H), 2.57
(m, 8H), 3.20 (s, 2H, NCH2N).
Synthesis of [CH2(pip)2]Mo(CO)4. Mo(CO)6 (0.200 g, 0.757
mmol) and CH2(pip)2 (0.150 g, 0.823 mmol) were brought to reflux
under an argon atmosphere in heptane (20 mL). After 2 h, a bright
yellow product was filtered and washed with hexanes (0.122 g, 41%).
IR data in CH2Cl2 (νCO): 1830 (m), 1870 (sh), 1890 (s), 2015 (w).
1H NMR (CDCl3): δ 1.17 (m, 2H), 1.71 (m, 4H), 1.77 (m, 2H), 2.00
(m, 4H), 2.55 (m, 4H), 3.20 (m, 4H), 4.09 (s, 2H, NCH2N). 13C{1H}
NMR (d6-DMSO): δ 22.1, 24.9, 63.7, 89.1 (NCH2N), 206 (CO), 222
(CO). Anal. Calcd for C15H22MoN2O4: C, 46.16; H, 5.68; N, 7.18.
Found: C, 45.86; H, 5.60; N, 7.06%.
AUTHOR INFORMATION
Corresponding Author
*E-mail: djdarens@chem.tamu.edu.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the financial support of the National
Science Foundation (CHE-1057743) and the Robert A. Welch
Foundation (A-0923).
REFERENCES
■
(1) Love, B. E. J. Org. Chem. 2007, 72, 630−632.
(2) Shaibakova, M. G.; Makhmudiyarov, G. A.; Ibragimov, A. G.;
Dzhemilev, U. M. Russ. J. Org. Chem. 2010, 46, 43−48.
(3) Prishchenko, A. A.; Livantsov, M. V.; Novikova, O. P.;
Livantsova, L. I.; Petrosyan, V. S. Heteroat. Chem. 2010, 21, 441−445.
(4) Zhou, Y.; Xie, Y.; Yang, L.; Xie, P.; Huang, H. Tetrahedron Lett.
2013, 54, 2713−2716.
Synthesis of [CH2(pyr)2]Mo(CO)4. Mo(CO)6 (0.157 g, 0.594
mmol) and CH2(pyr)2 (0.106 g, 0.687 mmol) were brought to reflux
(5) Bondarenko, S. P.; Frasinyuk, M. S. Chem. Nat. Compd. 2013, 49,
841−844.
D
DOI: 10.1021/acs.organomet.5b00396
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(6) Hu, J.; Xie, Y.; Huang, H. Angew. Chem., Int. Ed. 2014, 53, 7272−
7246.
́
(7) Cerro-Alarcon, M.; Corma, A.; Iborra, S.; Martínez, C.; Sabater,
M. J. Appl. Catal., A 2010, 382, 36−42.
́
(8) Boronat, M.; Climent, M. J.; Corma, A.; Iborra, S.; Monton, R.;
Sabater, M. J. Chem. - Eur. J. 2010, 16, 1221−1231.
(9) Climent, M. J.; Corma, A.; Domínguez, I.; Iborra, S.; Sabater, M.
J.; Sastre, G. J. Catal. 2007, 246, 136−146.
(10) Luttringhaus, A.; Kullick, W. Tetrahedron Lett. 1959, 1, 13−15.
̈
(11) Jung, O.-S.; Lee, Y.-A.; Park, S. H.; Kim, Y. J.; Yoo, K. H.; Kim,
D. C. Bull. Chem. Soc. Jpn. 2001, 74, 305−309.
(12) Kocięcka, P.; Kochel, A.; Szyman
Commun. 2014, 45, 105−107.
́
ska-Buzar, T. Inorg. Chem.
(13) Taber, D.; Becker, E. I.; Spoerri, P. E. J. Am. Chem. Soc. 1954,
76, 776−781.
(14) Matsumoto, K.; Hashimoto, S.; Ikemi, Y.; Otani, S. Heterocycles
1984, 22, 1417−1420.
(15) Nevstad, G. O.; Songstad, J. Acta Chem. Scand. 1984, 38, 469−
477.
(16) Mas, M.; Sola, J. Inorg. Chim. Acta 1987, 133, 217−219.
(17) Mills, J. E.; Maryanoff, C. A.; McComsey, D. F.; Stanzione, R.
C.; Scott, L. J. Org. Chem. 1987, 52, 1857−1859.
(18) Williams, H. J. Org. Chem. 1964, 29, 2046−2047.
(19) Lee, J.-J.; Stanger, K. J.; Noll, B. C.; Gonzalez, C.; Marquez, M.;
Smith, B. D. J. Am. Chem. Soc. 2005, 127, 4184−4185.
(20) Rudine, A. B.; Walter, M. G.; Wamser, C. C. J. Org. Chem. 2010,
75, 4292−4295.
(21) (a) Grundy, J.; Coles, M. P.; Hitchcock, P. B. Dalton Trans.
2003, 2573−2577. (b) The authors overlooked the N-H protons in
the empirical formula and therefore did not locate them in the
structure of cis-(pip)2Mo(CO)4.
(22) Teo, S.-B.; Ng, C.-H.; Teoh, S.-G.; Wei, C. J. Coord. Chem.
1995, 36, 141−148.
(23) Teo, S.-B.; Teoh, S.-G.; Ng, C.-H. Polyhedron 1995, 14, 1447−
1451.
(24) Bakar, M. A.; Fun, H.-K.; Chinnakali, K.; Teoh, S.-G.;
Shawkataly, O. B.; Lopez, F. M. Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1993, 49, 582−584.
(25) Kromer, L.; Coelho, A. C.; Bento, I.; Marques, A. R.; Romao, C.
̃
C. J. Organomet. Chem. 2014, 760, 89−100.
(26) Slot, H. J. B.; Murrall, N. W.; Welch, A. J. Acta Crystallogr., Sect.
C: Cryst. Struct. Commun. 1985, 41, 1309−1312.
(27) Ardon, M.; Hogarth, G.; Oscroft, D. T. W. J. Organomet. Chem.
2004, 689, 2429−2435.
(28) Hogarth, G.; Kilmartin, J. J. Organomet. Chem. 2007, 692, 5655−
5670.
(29) Schultz, M.; Eisentrager, F.; Regius, C.; Rominger, F.; Hanno-
̈
Igels, P.; Jakob, P.; Gruber, I.; Hofmann, P. Organometallics 2012, 31,
207−224.
(30) (a) Preparing dimorpholinylmethane requires reflux in
dichloromethane over many days. Adding a base could accelerate
the reaction as well as convert all the cyclic amine to the desired ligand
(see ref 17). (b) Dimorpholinylmethane (CAS# 5625−90−1) and
dipiperidylmethane (CAS# 880−09−1) can be purchased commer-
cially from Alfa Aesar. Last checked on May 01, 2015.
E
DOI: 10.1021/acs.organomet.5b00396
Organometallics XXXX, XXX, XXX−XXX