Probing substituent effects in phosphinoamine ligands using Mo(CO)5L complexes

Article abstract of DOI:10.1016/j.poly.2014.12.005

Recent work has revealed substantial differences in the structure, spectroscopic properties, and reactivity of heterobimetallic Zr/Co complexes of the general form XZr(R′NPR₂)₃CoY (R′ = ⁱPr, 2,4,6-trimethylphenyl, 3,5-dimethylphenyl; R = Ph, ⁱPr; X, Y = halides or neutral donor ligands) as a function of nitrogen and phosphorus donor atom substituents. To probe the electronic differences between these ligands, a series of Mo(CO)₅(R₂PNHR′) complexes has been synthesized (R = Ph, R′ = ⁱPr (2a); R = ⁱPr, R′ = ⁱPr (2b), 2,4,6-trimethylphenyl (2c), 3,5-dimethylphenyl (2d), 4-methylphenyl (2e), 4-trifluoromethylphenyl (2f), 4-methoxyphenyl (2g)). Thermolysis of Mo(CO)₆ with the corresponding phosphinoamine ligands 1a-1g affords 2a-2g. The infrared carbonyl stretching frequencies of these complexes have been compared to probe the effects of phosphorus and nitrogen substituents on the electronic properties of the phosphinoamine ligands.

Full text of DOI:10.1016/j.poly.2014.12.005

Polyhedron 87 (2015) 354–360
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Probing substituent effects in phosphinoamine ligands using Mo(CO)5L
complexes
⇑
Kyle H. Lee, J.W. Napoline, Mark W. Bezpalko, Bruce M. Foxman, Christine M. Thomas
Department of Chemistry, Brandeis University, 415 South Street, Waltham, MA 02453, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Recent work has revealed substantial differences in the structure, spectroscopic properties, and reactivity
of heterobimetallic Zr/Co complexes of the general form XZr(R0NPR2)3CoY (R0 = iPr, 2,4,6-trimethylphenyl,
3,5-dimethylphenyl; R = Ph, Pr; X, Y = halides or neutral donor ligands) as a function of nitrogen and
phosphorus donor atom substituents. To probe the electronic differences between these ligands, a series
of Mo(CO)5(R2PNHR0) complexes has been synthesized (R = Ph, R0 = iPr (2a); R = iPr, R0 = iPr (2b), 2,4,6-
trimethylphenyl (2c), 3,5-dimethylphenyl (2d), 4-methylphenyl (2e), 4-trifluoromethylphenyl (2f),
4-methoxyphenyl (2g)). Thermolysis of Mo(CO)6 with the corresponding phosphinoamine ligands 1a–
1g affords 2a–2g. The infrared carbonyl stretching frequencies of these complexes have been compared
to probe the effects of phosphorus and nitrogen substituents on the electronic properties of the phosph-
inoamine ligands.
Received 7 September 2014
Accepted 5 December 2014
Available online 12 December 2014
i
Keywords:
Metal carbonyl
Phosphinoamine
Molybdenum
Infrared spectroscopy
Ligand properties
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
CoN2]ꢀ reacts in a manner similar to monometallic Co analogues,
simply undergoing two-electron oxidation at the Co center [25].
In recent years, our group ꢀand others have been utilizing phos-
phinoamide ligands [R0NPR2] to link two metals in both homo-
and hetero-bimetallic complexes [1–16]. These complexes have
demonstrated remarkable reactivity, including CO2 activation
[17,18], E–H bond activation (E = S, O, N) [19,20], and catalytic
activity towards hydrosilylation and cross-coupling reactions
[21–23]. Varying the phosphine substituents in C3-symmetric Zr/
Co complexes ClZr(iPrNPR2)3CoI was shown to have a dramatic
Given the dramatic differences imparted by varying the phos-
phorus donor substituent, we have recently turned our attention
to systematically investigating the implications of the amide donor
substituents on metal–metal interactions and reactivity of hetero-
bimetallic complexes. Comparison of the N-iPr and N-Mes deriva-
tives ClZr(RNPiPr2)3CoI revealed identical Zr–Co distances, but
redox potentials ca. 0.2 V more negative for the more electron-rich
N-iPr derivative [5]. Structural and spectroscopic comparison of the
reduced complexes Zr(iPrNPiPr2)3CoN2 and (THF)Zr(MesNPiPr2)3
CoN2 is complicated by the additional Zr-bound THF ligand on
the N-Mes complex [24]. In a more subtle variation of the phosph-
inoamide N-donor substituent, we recently examined the m-xylyl
derivative [XylNPiPr2]ꢀ (Xyl = 3,5,-dimethylphenyl) [23]. Interest-
ingly, treatment of the metalloligand (iPr2PNXyl)3ZrCl with CoI2
i
effect on the metal–metal interaction. The Pr2P-substituted com-
plex has a Zr–Co distance 0.1 Å shorter than the Ph2P-substituted
complex, demonstrating that more electron-rich donor ligands
increase the electron density at Co and allow for stronger Co ? Zr
dative donation [5]. More interestingly, however, the Zr-bound
halide in the iPr2P-substituted complex ClZr(iPrNPiPr2)3CoI
becomes labile upon reduction, allowing the isolation of a coordin-
leads to the iodide-bridged product (
-I)CoI rather than the C3-symmetric isomer observed for the
N-Mes derivative ClZr(MesNPiPr2)3CoI. Nonetheless, two electron-
g
2-iPr2PNXyl)Zr(iPr2PNXyl)2
atively unsaturated complex Zr(iPrNPiPr2)3CoN2 featuring
a
(l
weakly-bound dinitrogen ligand on Co and an open coordination
site at the trigonal pyramidal Zr center [24]. This, and another
iPr2P-substituted complex (THF)Zr(MesNPiPr2)3CoN2 (Mes = (2,4,6-
trimethylphenyl) [24] have demonstrated cooperative reactivity
in which substrates add across the metal–metal bond, while the
chloride-bound Ph2P-substituted reduced product [ClZr(iPrNPPh2)3
reduction of (g l-I)CoI affords (THF)Zr
2-iPr2PNXyl)Zr(iPr2PNXyl)2(
(XylNPiPr2)3CoN2 for direct comparison with (THF)Zr(MesNPiPr2)3
CoN2. Surprisingly, while the two complexes have similar Zr–Co
distances, a remarkably large 20 cmꢀ1 difference in
m(N2) is
observed by IR spectroscopy (2026 cmꢀ1 versus 2045 cmꢀ1). Given
the number of factors involved, this electronic difference can be
attributed to two possibilities: (1) The amide substituents affect
the electron density at the Zr center and this, in turn, strengthens
⇑
Corresponding author. Tel.: +1 (781)736 2576.
E-mail address: thomasc@brandeis.edu (C.M. Thomas).
http://dx.doi.org/10.1016/j.poly.2014.12.005
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

K.H. Lee et al. / Polyhedron 87 (2015) 354–360
355
or weakens the metal–metal interaction. A less electron-rich Zr
center could withdraw more electron density from Co via a stron-
ger metal–metal interaction, leading to less back-bonding to N2
(2e)) associated with the carbonyl groups trans to the phosphino-
amine ligands. The Mo–P distances of 2c and 2e are 2.5616(4) Å,
and 2.5492(3) Å, respectively. A structure for the Ph2P-substituted
analogue of 2e, namely ((4-methylphenyl)NHPiPr2)Mo(CO)5, was
previously reported and is largely similar to that of 2e [30].
With a series of Mo(CO)5(L) complexes in hand, infrared spec-
troscopy was used to probe the electron-donating ability of the
phosphinamine ligands L. The spectra of all seven complexes fea-
ture three diagnostic carbonyl stretches, as is typical for pseudo
C4v-symmetric tricarbonyl compounds. On the basis of the evalua-
tion of force constants, Cotton determined that the three stretches
typically observed for Mo(CO)5L complexes are most reasonably
assigned as A1, B1, and overlapping A1 and E vibrational modes
[31]. The deviation from ideal C4v symmetry imparted by the tri-
substituted phosphine accounts for the observation of a B1 mode,
which would not be IR active in rigorous C4v symmetry. In the ser-
ies of Mo(CO)5(Ph2PNHR) complexes reported by Gray, there is no
change in the carbonyl stretches as the R group is varied among
and a higher m(N2). (2) The nitrogen substituents affect the donor
ability of the phosphine, leading directly to a more or less elec-
tron-rich Co center. The nearly identical Zr–Co distances in
(THF)Zr(XylNPiPr2)3CoN2 and (THF)Zr(MesNPiPr2)3CoN2 suggest
that the latter hypothesis is more likely. In any case, the electronic
differences between these two complexes have significant implica-
tions for reactivity and (THF)Zr(XylNPiPr2)3CoN2 was shown to be a
less effective catalysts for Kumada coupling reactions.
Herein, we use the Mo(CO)5 fragment as a spectroscopic probe
to investigate the variations in electron-donor ability of the phos-
phine moiety of a series of phosphinoamines in which the ligand
substituents are systematically varied. Gray and coworkers previ-
ously investigated trends in 31P and 95Mo chemical shifts in a series
of Mo(CO)5(PPh2XR) complexes (X = O, NH; R = alkyl, aryl) [26,27],
i
but such a study with Pr2P-substituted phosphinoamines has not
i
been reported. The implications of the electronic differences in a
series of iPr2PNHR ligands are discussed in the context of heterobi-
metallic complexes.
different alkyl substituents (Me, Et, Pr, nBu, etc.) [26], and a very
small (1–2 cmꢀ1) shift to higher frequency was observed upon
changing the nitrogen substituents to aryl groups (Ph, p-tolyl) [27].
In the case of complexes 2a–2g, a comparison of the highest fre-
quency A1 stretches reveals a variation of about 4 cmꢀ1 across the
2. Results and discussion
series, with the highest m(CO) for the Ph2P-substituted phosphino-
amine complex 2a (Table 1).1 While 4 cmꢀ1 does not initially appear
A series of Mo(CO)5L complexes 2a–g was synthesized via heat-
ing Mo(CO)6 with R0NHPR2 1a–g to 66 °C in THF in a sealed reaction
vessel for 3 days (Scheme 1). The resulting products showed charac-
teristic singlets in their 31P NMR spectra shifted ꢁ40–60 ppm down-
field from the resonances observed for the phosphinoamine ligands
(Table 1). Mono-substituted products were formed exclusively with
the N-aryl-substituted ligands regardless of stoichiometry; how-
ever, small amounts of di-substituted Mo(CO)4(L)2 products were
observed by 31P NMR spectroscopy when N-iPr-substituted ligands
were used. For example, heating a 1:1 mixture of Mo(CO)6 and 1a
to 66 °C for 3 days typically leads to an 80:20 ratio of mono- and
di-substituted products. The desired mono-substituted product 2a
can be separated from the mixture using column chromatography.
In the case of 1b, the mono-substituted product 2b, could be
obtained exclusively by using a slight excess (1.1 equiv) of Mo(CO)6.
The solid state structures of two representative penta-
carbonylmolybdenum complexes 2c and 2e were obtained using
X-ray crystallography and are shown in Fig. 1. The Mo–C distances
are in the 2.00–2.07 Å range, with the shortest Mo–C
distances (Mo–C20 = 1.9973(15) Å (2c); Mo–C18 = 2.0092(11) Å
to be a large variation, the A1 stretches of Mo(CO)5(PR3) complexes
only vary within a ꢁ10 cmꢀ1 range. For example, the A1
m(CO) for
Mo(CO)5(PPh3) is 2078 cmꢀ1 while that for Mo(CO)5(PMe3) is
2071 cmꢀ1 [32]. A comparison of the
m(CO) stretches of the two
N-iPr complexes 2a and 2b reveals that variation of the phosphorus
i
substituents from Ph to Pr leads to a 4 cmꢀ1 decrease in the fre-
quency of the A1 vibrational mode, as expected given the more elec-
tron-releasing nature of the alkyl substituents. Across the series of
iPr2P-substituted complexes 2b–2g, the CO stretches suggest that
the iPr2PNHR ligands become more electron rich as the amine
substituent is varied in the order 4-trifluoromethylphenyl < 4-meth-
ylphenyl = 3,5-dimethylphenyl < 4-methoxyphenyl < 2,4,6-trimeth-
ylphenyl = iPr. Notably, the A1 stretches of 2f and 2a are identical,
suggesting that variation of the N-aryl substituents can affect
electronic changes equivalent to varying the phosphine substituents.
2
A careful examination of the chemical shifts and JP–C coupling
constants associated with the metal carbonyls, particularly the
CO ligand trans to the phosphinoamine phosphorus donor, in the
13C NMR spectrum of 2a–2g did not reveal any clear trends.
The trends in CO stretching frequencies of 2a–2g and the corre-
sponding trends in electron-donating ability of ligands 1a–1g lends
fundamental insight into some of the structural, spectroscopic, and
reactivity trends observed in our group’s heterobimetallic Zr/Co
complexes. As suggested in the Introduction, the substantial differ-
ences in metal–metal interactions and reactivity of heterobimetal-
lic Zr/Co complexes supported by deprotonated ligands 1a and 1b/
1c can be attributed to the more electron-donating isopropyl phos-
phine substituents [5], and this is supported by the Mo(CO)5L
model studies. Based on the similar carbonyl stretching frequen-
cies of 2b and 2c, the ꢁ0.2 V difference in the redox potentials of
ClZr(iPrNPiPr2)3CoI and ClZr(MesNPiPr2)3CoI cannot be explained
by electronic differences between the ligands and may more likely
be the result of steric arguments – the larger mesityl substituent
may better stabilize reduced products. Lastly, we find that the
N-mesityl substituent does render ligand 1c measurably more
electron rich than N-xylyl ligand 1d, a factor that likely plays a
role in the substantial differences in the spectroscopic properties
1
While all three infrared CO stretches generally follow the same trends, we discuss
Scheme 1. Synthesis of complexes 2a–2g.
only the A1 mode here for simplicity.

356
K.H. Lee et al. / Polyhedron 87 (2015) 354–360
Table 1
Infrared
m
(CO) stretches of Mo(CO)5(L) complexes 2a–g. 31P NMR spectroscopic data for the Mo(CO)5(L) complexes and free ligands are also provided for comparison.
L =
m
(CO)a (cmꢀ1
)
d
31P of 1b (ppm)
d
31P of 2b (ppm)
d
13C (2JP–C) for COtrans and COcis in 2b
2071, 1988, 1937d
35.6 [28]
73.5c
211.1 (22.9 Hz)
206.1 (9.2 Hz)
Ph
P
Ph
iPr
HN
HN
1a
2067, 1981, 1925
57.6 [5]
102.0
210.4 (22.9 Hz)
207.5 (9.3 Hz)
iPr
P
1b
2067, 1982, 1935
57.7 [5]
105.8
210.2 (23.7 Hz)
207.1 (8.5 Hz)
iPr
iPr
HN
P
1c
2069, 1984, 1934
47.1 [23,29]
106.0
210.0 (23.7 Hz)
207.2 (9.3 Hz)
iPr
iPr
HN
P
1d
2069, 1983, 1932
48.7
106.1
210.0 (24.6 Hz)
207.2 (9.3 Hz)
iPr
iPr
HN
P
1e
2071, 1983, 1932
49.1
110.5
209.5 (24.4 Hz)
206.8 (9.1 Hz)
F3C
iPr
iPr
HN
P
1f
2068, 1983, 1935
51.0
110.5
210.2 (23.7 Hz)
207.3 (9.3 Hz)
MeO
iPr
iPr
HN
P
1g
a
Spectra collected in C6H6 solution using a KBr solution cell.
Spectra collected in C6D6.
b
c
Previously reported 31P NMR chemical shift of 74.18 ppm in CDCl3 [26].
d
Previously reported m(CO) stretches of 2072, 1990, 1956, and 1947 in n-hexane using NaCl solution cell [26].
and reactivity of heterobimetallic Zr/Co complexes supported by
these ligands [23]. The modulation of phosphine electronic proper-
ties by variation of para-phenyl substituents on the amine nitrogen
is particularly remarkable given the distance of that substituent
from the phosphorus donor atom.
electronic properties of the phosphinoamine ligands as a function
of nitrogen and phosphorus substituents. Variation of the phos-
phine substituents from aryl to alkyl leads to the expected
decrease in m(CO) as the phosphinoamines become more electron
rich. A remarkably significant variation in the electronic properties
of the phosphine donors was also observed upon varying the N-aryl
substituents of the phosphinoamines. The ability to modulate
ligand electronic properties via N-aryl substitution is in line with
3. Conclusions
In summary, we have synthesized a series of Mo(CO)5(R2PNHR0)
complexes 2a–2g and used infrared spectroscopy as a probe of the

K.H. Lee et al. / Polyhedron 87 (2015) 354–360
357
Fig. 1. Displacement ellipsoid (50%) representations of the solid state structures of 2c and 2e. Hydrogen atoms have been omitted for clarity. Relevant interatomic distances
for 2c (Å): Mo–P1, 2.5616(4); Mo–C16, 2.0528(14); Mo–C17, 2.0534(15); Mo–C18, 2.0468(14); Mo–C19, 2.0390(15); Mo–C20, 1.9973(15). Relevant interatomic distances for
2e (Å): Mo–P1, 2.5492(3); Mo–C14, 2.0698(10); Mo–C15, 2.0539(10); Mo–C16, 2.0294(10); Mo–C17, 2.0377(10); Mo–C18, 2.0092(11).
the substantial differences we observe when these phosphino-
amine ligands are deprotonated and used as a ligand platform to
support C3-symmetric heterobimetallic Zr/Co complexes. We do,
however, expect that steric factors also play an important role
and studies are currently underway to explore a series of heterobi-
metallic Zr/Co complexes in which the steric and electronic prop-
erties of the N-aryl substituents are systematically varied.
hours to ensure that a complete deprotonation had taken place.
The resulting solution was cooled to ꢀ35 °C and a similarly cooled
solution of chlorodiisopropylphosphine (7.4 mL, 47 mmol) in tolu-
ene (30 mL) was added dropwise. The reaction was warmed slowly
to room temperature. After stirring for four hours, the reaction
mixture was filtered through a pad of Celite, removing sodium
chloride. The solvent was removed from the filtrate in vacuo. The
resulting oily residue was redissolved in diethyl ether and filtered
through a plug of silica gel. Removal of the solvent in vacuo yielded
analytically pure product as a yellow oil (9.2 g, 88%). 1H NMR
(400 MHz, CD2Cl2): d = 7.03 (d, 2H, 2J = 8.4 Hz, Ar-H), 6.96 (m, 2H,
4. Experimental
4.1. General considerations
2
J = 8.0 Hz, Ar-H), 3.74 (d, 1H, JH–P = 10.8 Hz, NH), 2.31 (s, 3H,
Me), 1.82 (m, 2H, CH(CH3)2), 1.15 (m, 12H, CH-(CH3)2). 31P{1H}
NMR (161.8 MHz, C6D6): d = 48.9 (s). 13C NMR (100.5 MHz, CD2Cl2):
d = 147.3 (d, J = 16.1 Hz, N-ipso-Ar), 130.1 (s, Ar), 127.9 (s, ipso-Ar),
116.4 (d, J = 12.3 Hz, Ar), 27.4 (d, J = 12.1 Hz, CH(CH3)2), 20.8 (s,
tolyl-Me) 19.3 (d, J = 20.3 Hz, CH(CH3)2) 17.5 (d, J = 8.1 Hz,
CH(CH3)2). Anal. Calc. for C13H19F3NP: C, 69.93; H, 9.93; N, 6.27.
Found: C, 69.79; H, 9.87; N, 6.30%.
Unless specified otherwise, all manipulations were performed
under an inert atmosphere using standard Schlenk or glovebox
techniques. Glassware was oven dried before use. Tetrahydrofuran
and pentane were purged with ultra high purity argon gas and
dried using a Glass Contours solvent system with successive drying
columns. All solvents were stored over 3 Å molecular sieves. Ben-
zene-d6 was degassed via repeated freeze–pump–thaw cycles
and dried over 3 Å molecular sieves. iPrNHPPh2 (1a) [28,33],
iPrNHPiPr2 (1b) [5], (2,4,6-trimethylphenyl)NHPiPr2 (1c) [5], and
(3,5-dimethylphenyl)NHPiPr2 (1d) [23,29] were synthesized using
literature procedures. All other chemicals were purchased from
commercial vendors and used without further purification. All
NMR spectra were recorded at ambient temperature unless other-
wise noted and chemical shifts are reported in ppm. For 1H and
13C{1H} NMR spectra, the solvent resonance was referenced as an
internal standard, and for 31P{1H} NMR spectra the 85% H3PO4 res-
onance was referenced as an external standard (0 ppm). 19F NMR
spectra were referenced to 1% Trifloroacetic acid (ꢀ76.5 ppm). IR
spectra were recorded on a Varian 640-IR spectrometer controlled
by Resolutions Pro software. Elemental analyses were performed at
Complete Analysis Laboratory Inc., Parsippany, NJ.
4.3. (4-trifluoromethylphenyl)NHPiPr2 (1f)
A solution of 4-(trifluoromethyl)aniline (5.00 g, 31.0 mmol) in
toluene (60 mL) was cooled to ꢀ35 °C. To this was added a solution
of sodium bis(trimethylsilyl)amide (6.25 g, 34.1 mmol) in toluene
(40 mL) dropwise over five minutes. The resulting yellow solution
was allowed to warm slowly to room temperature. The reaction
was stirred at room temperature for four hours to ensure that
deprotonation had proceeded completely. The resulting solution
was cooled to ꢀ35 °C and to this a similarly cooled solution of chlo-
rodiisopropylphosphine (4.93 mL, 31.0 mmol) in toluene (30 mL)
was added dropwise. The reaction was warmed slowly to room
temperature. After stirring for four hours at room temperature,
the reaction mixture was filtered through a pad of Celite, removing
sodium chloride. The solvent was removed from the filtrate in
vacuo and the resulting oily residue was redissolved in diethyl
ether and filtered through a plug of silica gel. Removal of the sol-
vent from the filtrate in vacuo yielded analytically pure product
as a yellow oil (7.90 g, 91.7%). 1H NMR (400 MHz, C6D6): d 7.32
(d, J = 7.6 Hz, 2H, Ar), 6.78 (d, J = 7.6 Hz, 2H, Ar), 3.56 (d,
J = 6.8 Hz, 1H, NH), 1.39 (m, 2H, CH(CH3)2), 0.87 (m, 12H,
4.2. (4-methylphenyl)NHPiPr2 (1e)
A solution of p-toluidine (5.00 g, 46.7 mmol) in toluene (60 mL)
was cooled to ꢀ35 °C. To this was added a solution of sodium
bis(trimethylsilyl)amide (8.56 g, 46.7 mmol) in toluene (40 mL)
dropwise over five minutes. The resulting yellow solution was
allowed to warm slowly to room temperature and stirred for four

358
K.H. Lee et al. / Polyhedron 87 (2015) 354–360
CH(CH3)2). 13C{1H} NMR (100.5 MHz, CD2Cl2):
d
153.0 (d,
sure flask under N2. The flask was sealed tightly and heated to
66 °C for 3 days. The reaction vessel was then brought into a
glovebox and the reaction mixture was filtered to remove insoluble
impurities. The filtrate was then dried under vacuum. The remain-
ing solids were washed with cold pentane (2 mL) and the product
was dried in vacuo, leaving a yellow solid (324.2 mg, 78%). Note:
Small amounts of disubstituted product, (iPrNHPiPr2)2Mo(CO)4,
were formed when stoichiometry was not carefully controlled.
1H NMR (400 MHz, C6D6): d 3.04 (m, 1H, NCH(CH3)2), 1.51 (m,
2H, PCH(CH3)2), 0.96 (m, 6H, PCH(CH3)2), 0.85 (m, 6H, PCH(CH3)2),
0.85 (d, 6H, NCH(CH3)2), 0.61 (m, 1H, NH). 13C{1H} NMR
(100.5 MHz, C6D6): d 210.4 (d, J = 22.9 Hz, Mo–CO), 207.5 (d,
J = 9.3 Hz, Mo–CO), 47.4 (s, NCH(CH3)2), 30.1 (d, J = 22.8,
PCH(CH3)2), 26.9 (d, J = 2.6 Hz, NCH(CH3)2), 18.1 (d, J = 6.7 Hz,
PCH(CH3)2), 17.5 (s, PCH(CH3)2). 31P{1H} NMR (161.8 MHz, C6D6):
d 102.0. FT-IR (C6H6, KBr): 2067 cmꢀ1, 1981 cmꢀ1, 1925 cmꢀ1. Anal.
Calc. for C14H22MoNO5P: C, 40.89; H, 5.39; N, 3.41. Found: C, 41.11;
H, 5.44; N, 2.91%.
2
J = 16.3 Hz, N-ipso-Ar), 126.3 (m, Ar), 119.5 (q, JC–F = 33.3 Hz,
1
ipso-CF3), 125.2 (q, JC–F = 270.4 Hz, CF3), 115.3 (d, J = 13.0 Hz, Ar),
26.6 (d, J = 11.4 Hz, CH(CH3)2), 18.5 (d, J = 20.3 Hz, CH(CH3)2),
16.8 (d, J = 7.3 Hz, CH(CH3)2). 31P{1H} NMR (161.8 MHz, C6D6): d
49.1 (s). 19F NMR (376.1 MHz, C6D6): d 14.96 (s). Anal. Calc. for
C13H19F3NP: C, 56.31; H, 6.91; N, 5.05. Found: C, 56.36; H, 6.89;
N, 5.09%.
4.4. (4-methoxyphenyl)NHPiPr2 (1g)
A solution of p-anisidine (5.00 g, 40.6 mmol) in toluene (60 mL)
was cooled to ꢀ35 °C. To this was added a solution of sodium
bis(trimethylsilyl)amide (7.44 g, 40.6 mmol) in toluene (40 mL)
dropwise over five minutes. The resulting yellow solution was
allowed to warm slowly to room temperature. The reaction was
stirred at room temperature for four hours to ensure that a com-
plete deprotonation had taken place. The resulting solution was
cooled to ꢀ35 °C and to this a cold solution of chlorodiisopropyl-
phosphine (6.46 mL, 40.6 mmol) in toluene (30 mL) was added
dropwise. The reaction was warmed slowly to room temperature.
After stirring for four hours, the reaction mixture was filtered
through a pad of Celite, removing sodium chloride. The solvent
was removed from the filtrate in vacuo. The resulting oily residue
was redissolved in diethyl ether and filtered through a plug of silica
gel. Removal of the solvent from the filtrate in vacuo yielded ana-
lytically pure product as a yellow oil (8.73 g, 89.9%). 1H NMR
(400 MHz, C6D6): d 6.93 (d, J = 8.8 Hz, 2H, Ar), 6.78 (d, J = 10.4 Hz,
2H, Ar), 3.37 (s, 3H, MeO), 3.14 (d, J = 10.4 Hz, 1H, NH), 1.46
(m, 2H, CH(CH3)2), 0.96 (m, 12H, CH(CH3)2). 31P{1H} NMR
(161.8 MHz, C6D6): d 51.0 (s). 13C{1H} NMR (100.5 MHz, CD2Cl2):
d 152.6 (s, ipso-OMe), 142.9 (d, J = 16.3 Hz, N-ipso-Ar), 116.8 (d,
J = 10.6 Hz, Ar), 114.5 (s, Ar), 55.52 (s, OMe), 26.85 (d, J = 11.4 Hz,
CH(CH3)2), 18.8 (d, J = 20.3 Hz, CH(CH3)2), 17.0 (d, J = 8.0 Hz,
CH(CH3)2). Anal. Calc. for C13H19F3NP: C, 65.25; H, 9.27; N, 5.85.
Found: C, 65.28; H, 9.36; N, 5.84%.
4.7. ((2,4,6-trimethylphenyl)NHPiPr2)Mo(CO)5 (2c)
Solid Mo(CO)6 (264.0 mg, 1.000 mmol) and (2,4,6-trimethyl-
phenyl)NHPiPr2 (251.4 mg, 1.000 mmol) were combined in THF
(10 mL) in a pressure flask under N2. The flask was sealed tightly
and heated to 66 °C for 3 days. The reaction vessel was then
brought into the glovebox and the reaction mixture was filtered
to remove insoluble impurities. The filtrate was then dried under
vacuum. The remaining solids were washed with cold pentane
(2 mL) and the product was dried in vacuo, leaving an off-white
solid (374.3 mg, 77%). 1H NMR (400 MHz, C6D6): d 6.69 (s, 2H,
Mes-Ar), 2.58 (s, 1H, NH), 2.11 (s, 6H, Mes-CH3), 2.04 (m, 2H,
CH(CH3)2), 0.92–1.04 (m, 12H, CH(CH3)2). 13C{1H} NMR
(100.5 MHz, C6D6): d 210.2 (d, J = 23.7 Hz, Mo–CO), 207.1 (d,
J = 8.5 Hz, Mo–CO), 138.7 (d, J = 2.6 Hz, Mes-Ar), 136.4 (d,
J = 2.5 Hz, Mes-Ar), 135.9 (d, J = 1.7 Hz), 130.4 (s, Mes-Ar), 32.3
(d, J = 18.7 Hz, CH(CH3)2), 21.1 (s, Mes-Me), 20.9 (s, Mes-Me),
19.3 (m, CH(CH3)2,
2
peaks overlapping). 31P{1H} NMR
4.5. (iPrNHPPh2)Mo(CO)5 (2a)
(161.8 MHz, C6D6): d 105.8. FT-IR(C6D6): 2067 cmꢀ1, 1982 cmꢀ1
,
1935 cmꢀ1. Anal. Calc. for C20H26MoNO5P: C, 49.29; H, 5.38; N,
Solid Mo(CO)6 (264.0 mg, 1.000 mmol) and iPrNHPPh2
(243.4 mg, 1.000 mmol) were combined in THF (10 mL) in a pres-
sure flask under N2. The flask was sealed tightly and heated to
66 °C for 3 days. The reaction vessel was then brought into a glove-
box and the reaction mixture was filtered to remove insoluble
impurities. The filtrate was then dried under vacuum. The remain-
ing solids were washed with cold pentane (2 mL) and the product
was dried in vacuo, leaving an off-white solid. Isolated product typ-
ically contains a small amount (20% or less) of disubstituted prod-
uct, (iPrNHPPh2)2Mo(CO)4, which can be separated using column
chromatography (5:1 CH2Cl2/hexanes) (yield: 291.5 mg, 61%). 1H
NMR (400 MHz, C6D6): d 7.52 (m, 4H, Ph), 7.05 (m, 6H, Ph), 2.90
(m, 1H, CH(CH3)2), 1.73 (m, 1H, NH), 0.55 (d, J = 6.0 Hz, 6H).
13C{1H} NMR (100.5 MHz, C6D6): d 211.1 (d, J = 22.9 Hz, Mo–CO),
206.1 (d, J = 9.2 Hz, Mo–CO), 139.1 (d, J = 40.7 Hz, P-ipso-Ph),
131.9 (d, J = 13.5 Hz, Ph), 130.5 (s, Ph), 129.0 (d, J = 9.3 Hz, Ph),
47.2 (d, J = 5.9 Hz, CH(CH3)2), 25.6 (d, J = 3.3 Hz, CH(CH3)2).
2.87. Found: C, 49.40; H, 5.42; N, 3.02%.
4.8. ((3,5-dimethylphenyl)NHPiPr2)Mo(CO)5 (2d)
Solid Mo(CO)6 (152.0 mg, 0.578 mmol) and (3,5-dimethyl-
phenyl)NHPiPr2 (137.4 mg, 0.578 mmol) were combined with
THF (10 mL) in a pressure flask under N2. The flask was sealed
tightly and heated to 66 °C for 3 days. The reaction was then
brought into a glovebox and the reaction mixture was filtered to
remove insoluble impurities. The filtrate was then dried under vac-
uum. The remaining solids were washed with cold pentane (2 mL)
and the product was dried in vacuo, leaving an off-white solid
product (180.8 mg, 66%). 1H NMR (400 MHz, C6D6): d 6.52 (s, 1H,
Ar), 6.44 (s, 2H, Ar), 3.51 (d, 1H, J = 8.0 Hz, NH), 2.11(s, 6H, ArMe),
2.00 (m, 2H, CH(CH3)2), 0.92–1.03 (m, 12H, CH(CH3)2). 13C{1H}
NMR (100.5 MHz, C6D6): d 210.0 (d, J = 23.7 Hz, Mo–CO), 207.2
(d, J = 9.3 Hz, Mo–CO), 143.9 (d, J = 5.1 Hz, N-ipso-Ar), 139.3 (s,
Ar), 125.2 (s, Ar), 120.3 (s, Ar), 31.1 (d, J = 20.3 Hz, CH(CH3)2),
21.6 (s, Ar-Me), 18.8 (d, J = 8.5 Hz, CH(CH3)2), 18.1 (s, CH(CH3)2).
31P{1H} NMR (161.8 MHz, C6D6): d 106.0. FT-IR (C6D6, KBr):
2069 cmꢀ1, 1984 cmꢀ1, 1934 cmꢀ1. Anal. Calc. for C19H24MoNO5P:
C, 48.21; H, 5.11; N, 2.96. Found: C, 48.17; H, 5.08; N, 3.05%.
31P{1H} NMR (161.8 MHz, C6D6):
d 73.5. FT-IR(C6D6, KBr):
2071 cmꢀ1, 1988 cmꢀ1, 1937 cmꢀ1. Anal. Calc. for C20H19MoNO5P:
C, 50.01; H, 3.99; N, 2.92. Found: C, 50.08; H, 3.91; N, 3.01%. Spec-
troscopic properties are consistent with those previously reported
for 2a synthesized via a different route.[26].
4.6. (iPrNHPiPr2)Mo(CO)5 (2b)
4.9. ((4-methylphenyl)NHPiPr2)Mo(CO)5 (2e)
Solid Mo(CO)6 (290.4 mg, 1.100 mmol) and iPrNHPiPr2
(175.3 mg, 1.000 mmol) were combined in THF (10 mL) in a pres-
Solid Mo(CO)6 (264.0 mg, 1.000 mmol) and (4-methyl-
phenyl)NHPiPr2 (223.3 mg, 1.087 mmol) were combined with

K.H. Lee et al. / Polyhedron 87 (2015) 354–360
359
Table 2
THF (10 mL) in a pressure flask under N2. The flask was sealed
X-ray diffraction data collection and refinement details for 2c and 2e.
tightly and heated to 66 °C for 3 days. The reaction vessel was then
brought into a glovebox and the reaction mixture was filtered to
remove insoluble impurities. The filtrate was then dried under vac-
uum. The remaining solids were washed with cold pentane (2 mL)
and the product was dried in vacuo, leaving an off-white solid
product (316.9 mg, 69%). 1H NMR (400 MHz, C6D6): d 6.87 (d,
J = 7.2 Hz, 2H, Ar), 6.59 (d, J = 8.0 Hz, 2H, Ar), 3.52 (d, J = 10 Hz,
1H, NH), 2.10 (s, 3H, Ar-Me), 1.97 (m, 2H, CH(CH3)2), 0.85–1.02
(m, 12H, CH(CH3)2). 13C{1H} NMR (100.5 MHz, C6D6): d 210.0 (d,
J = 24.6 Hz, Mo–CO), 207.2 (d, J = 9.3 Hz, Mo–CO), 141.3 (d,
J = 6.8 Hz, N-ipso-Ar), 132.8 (s, ipso-Ar), 130.3 (s, Ar), 122.8 (d,
J = 3.4 Hz, Ar), 30.9 (d, J = 21.2 Hz, CH(CH3)2), 21.0 (s, p-CH3), 18.8
(d, J = 8.4 Hz, CH(CH3)2), 18.1 (s, CH(CH3)2). 31P{1H} NMR
2c 2e
Chemical formula
Formula Weight
T (K)
C
20H26MoNO5P
C18H22MoNO5P
459.29
120
487.34
120
k (Å)
a (Å)
b (Å)
c (Å)
0.71073
8.6036(4)
9.552(4)
13.7106(6)
94.4000(19)
93.502(2)
105.3196(19)
1079.66(5)
P1
2, 1
1.499
0.711
0.0213
0.0541
0.71073
8.9673(8)
9.4854(8)
13.1572(12)
98.406(3)
95.418(4)
111.829(3)
1014.15(16)
a
(°)
b (°)
c
(°)
V (Å3)
ꢀ
ꢀ
Space group
Z, Z0
P1
2, 1
(161.8 MHz, C6D6):
d ,
106.1. FT-IR (C6H6, KBr): 2069 cmꢀ1
Dcalc (g cmꢀ3
)
1.504
0.752
0.0162
0.0429
(cm–1
)
1983 cmꢀ1, 1932 cm.ꢀ1 Anal. Calc. for C18H22MoNO5P: C, 47.07; H,
l
a
R1 (I > 2
wR2 (all data)
r
)
4.83; N, 3.05. Found: C, 46.96; H, 4.79; N, 3.10%.
a
P
P
P
P
a
R1
=
(||Fo| ꢀ |Fc||)/ |Fo|, wR2 = { [w(F2o ꢀ Fc2)2]/ [w(Fo2)2]}1/2
.
4.10. ((4-trifluoromethylphenyl)NHPiPr2)Mo(CO)5 (2f)
Solid Mo(CO)6 (264.0 mg, 1.000 mmol) and (p-CF3-C6H4)NHPiPr2
(277.1 mg, 1.000 mmol) were combined with THF (10 mL) in a pres-
sure flask under N2. The flask was sealed tightly and heated to 66 °C
for 3 days. The reaction vessel was then brought into a glovebox and
the reaction mixture was filtered to remove insoluble impurities.
The filtrate was then dried under vacuum. The remaining residue
was washed with cold pentane (2 mL) and the product was dried
in vacuo, leaving a yellow oily product (356.0 mg, 66%). 1H NMR
(400 MHz, C6D6): d 7.25 (d, J = 8.4 Hz, 2H, Ar), 6.34 (d, J = 8.4 Hz,
2H, Ar), 3.80 (d, J = 10.4 Hz, 1H, NH), 1.91 (m, 2H, CH(CH3)2),
0.79–0.94 (m, 12H, CH(CH3)2). 13C{1H} NMR (100.5 MHz, C6D6): d
209.5 (d, J = 24.4 Hz, Mo–CO), 206.8 (d, J = 9.1 Hz, Mo–CO), 147.2
(d, J = 7.6 Hz, N-ipso-Ar), 127.1 (q, J = 3.8 Hz, Ar), 125.5 (q,
ation. All diffractometer manipulations, including data collection,
integration, scaling, and absorption corrections were carried out
using the Bruker Apex2 software [34]. Preliminary cell constants
were obtained from three sets of 12 frames. All crystal structure
refinements were performed on F2. Data collection and refinement
parameters are presented in Table 2, and fully labelled diagrams
and data collection and refinement details are included in the Sup-
plementary Information File.
Acknowledgment
The authors are grateful to the U.S. Department of Energy –
Office of Basic Energy Sciences under grant DE-SC0004019.
2
1JC–F = 270.7 Hz, CF3), 124.2 (q, JC–F = 32.0 Hz, ipso-CF3), 120.0 (d,
J = 3.0 Hz, Ar), 30.8 (d, J = 19.1 Hz, CH(CH3)2), 19.0 (d, J = 9.1 Hz,
CH(CH3)2), 18.2 (s, CH(CH3)2). 19F NMR (376.1 MHz, C6D6): d -65.9.
Appendix A. Supplementary data
31P{1H} NMR (161.8 MHz, C6D6):
d 110.5. FT-IR(C6H6, KBr):
2071 cmꢀ1, 1983 cmꢀ1, 1932 cmꢀ1. Anal. Calc. for C18H19F3MoNO5P:
CCDC 1023206–1023207 contain the supplementary crystallo-
graphic data for 2c and 2e. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2014.12.005.
C, 42.12; H, 3.73; N, 2.73. Found: C, 42.25; H, 3.77; N, 2.96%.
4.11. ((4-methoxyphenyl)NHPiPr2)Mo(CO)5 (2g)
Solid Mo(CO)6 (264.0 mg, 1.000 mmol) and (p-OMe-C6H4)-
NHPiPr2 (223.3 mg, 0.934 mmol) were combined with THF
(10 mL) in a pressure flask under N2. The flask was sealed tightly
and heated to 66 °C for 3 days. The reaction vessel was then
brought into a glovebox and the reaction mixtures was filtered to
remove insoluble impurities. The filtrate was then dried under vac-
uum. The remaining solids were washed with cold pentane (2 mL)
and the product was dried in vacuo, leaving an off-white solid
(396.5 mg, 86.3%). 1H NMR (400 MHz, C6D6): d 6.67 (br, 4H, over-
lapping Ar), 3.46 (d, J = 8.8 Hz, 1H, NH), 3.33 (s, 3H, OMe), 1.88
(m, 2H, CH(CH3)2), 0.91–1.06 (m, 12H, CH(CH3)2). 13C{1H} NMR
(100.5 MHz, C6D6): d 210.2 (d, J = 23.7 Hz, Mo–CO), 207.3 (d,
J = 9.3 Hz), 157.1 (s, ipso-OMe), 136.5 (d, J = 5.9 Hz, N-ipso-Ar),
126.0 (d, J = 2.6 Hz, Ar), 114.9 (s, Ar), 55.4 (s, OCH3), 30.8 (d,
J = 21.2 Hz, CH(CH3)2), 18.6 (d, J = 7.6 Hz, CH(CH3)2), 17.9 (s,
CH(CH3)2). 31P{1H} NMR (161.8 MHz, C6D6): d 110.5. FT-IR (C6H6,
KBr): 2068 cmꢀ1, 1983 cmꢀ1 1935 cmꢀ. 1 Anal. Calc. for C18H22-
MoNO6P: C, 45.49; H, 4.67; N, 2.95. Found: C, 45.62; H, 4.71; N,
3.09%.
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