Synthesis, solid-state crystal structure, and reactivity of a monomeric copper(I) anilido complex

Article abstract of DOI:10.1021/ja0353659

Synthesis and isolation of the Cu(I) amido complex (dtbpe)Cu(NHPh) (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) is accomplished upon reaction of [(dtbpe)Cu(μ-Cl)]₂ with LiNHPh. The anilido complex has been fully characterized by IR spectroscopy and multinuclear NMR spectroscopy as well as by single-crystal X-ray diffraction study. Salient features of the solid-state structure include an amido orientation that allows π-interaction of the nitrogen-based lone pair with both the empty copper p-orbital and the π*-system of the phenyl substituent. A solid-state X-ray diffraction study of [(dtbpe)Cu(NH₂Ph)]-[BF₄] has allowed a direct comparison of the structural features upon conversion of the amine ligand to an amido. The reactivity of the amido ligand of (dtbpe)Cu(NHPh) is consistent with nucleophilic character. For example, the formation of Ph₃CNHPh is observed upon treatment with [Ph₃C][BF₄], and reaction at room temperature with EtX (X = Br or I) yields N-ethylaniline. The reactivity of (dtbpe)Cu(NHPh) is compared to that of the octahedral and d⁶ complex TpRu(PMe₃)₂(NHPh) (Tp = hydridotris(pyrazolyl)borate).

Full text of DOI:10.1021/ja0353659

Published on Web 07/11/2003
Synthesis, Solid-State Crystal Structure, and Reactivity of a
Monomeric Copper(I) Anilido Complex
Elizabeth D. Blue,† Amelia Davis,† David Conner,† T. Brent Gunnoe,*,†
Paul D. Boyle,† and P. S. White‡
Contribution from the Department of Chemistry, North Carolina State UniVersity,
Raleigh, North Carolina 27695-8204, and Department of Chemistry, UniVersity of North
Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290
Received March 28, 2003; E-mail: brent_gunnoe@ncsu.edu
Abstract: Synthesis and isolation of the Cu(I) amido complex (dtbpe)Cu(NHPh) (dtbpe ) 1,2-bis(di-tert-
butylphosphino)ethane) is accomplished upon reaction of [(dtbpe)Cu(µ-Cl)]2 with LiNHPh. The anilido
complex has been fully characterized by IR spectroscopy and multinuclear NMR spectroscopy as well as
by single-crystal X-ray diffraction study. Salient features of the solid-state structure include an amido
orientation that allows π-interaction of the nitrogen-based lone pair with both the empty copper p-orbital
and the π*-system of the phenyl substituent. A solid-state X-ray diffraction study of [(dtbpe)Cu(NH2Ph)]-
[BF4] has allowed a direct comparison of the structural features upon conversion of the amine ligand to an
amido. The reactivity of the amido ligand of (dtbpe)Cu(NHPh) is consistent with nucleophilic character. For
example, the formation of Ph3CNHPh is observed upon treatment with [Ph3C][BF4], and reaction at room
temperature with EtX (X ) Br or I) yields N-ethylaniline. The reactivity of (dtbpe)Cu(NHPh) is compared to
that of the octahedral and d6 complex TpRu(PMe3)2(NHPh) (Tp ) hydridotris(pyrazolyl)borate).
amido ligands has been reported.2,8,10,11,14-22 Remarkably, the
Os(IV) anilido complex TpOsCl2(NHPh) is unreactive with HCl,
Introduction
Late transition metal complexes that possess nondative
heteroatomic ligands (e.g., amido, oxide, imido, and oxo) exhibit
diverse patterns of reactivity.1-3 For example, amide and oxide
complexes have been implicated in a variety of metal-mediated
transformations including hydroamination and C-N/C-O
coupling reactions.4-7 The parent amido complexes trans-
(DMPE)Ru(H)(NH2) (DMPE ) 1,2-bisdimethylphosphinoet-
hane), TpRu(L)(L′)(NH2) (Tp ) hydridotris(pyrazolyl)borate),
and cis-(PMe3)4Ru(H)(NH2) deprotonate weakly acidic C-H
bonds, and cis-(PMe3)4Ru(H)(NH2) undergoes an array of
reactivity that demonstrates a highly nucleophilic amido ligand.8-13
The reactivity of other octahedral and d6 complexes that possess
and [TpOsCl2(NH2Ph)][OTf] is deprotonated by chloride an-
ion.23 In contrast to the even-electron reactions of the octahedral
Ru(II) and Os(IV) amido systems discussed above, octahedral
Fe(III) hydroxide and methoxide complexes undergo odd-
electron hydrogen atom abstraction reactions with compounds
that possess relatively weak C-H bonds.24,25 The disparate
nature of these amido and oxide ligands reveals a significant
scope of reactivity for nondative ligands bound to closely related
group 8 octahedral metal centers.
Understanding the factors that control ligand-based reactivity
of late transition metal amido and related complexes requires
access to a variety of coordination environments including
variable ligand sets, metal identities, and oxidation states. The
† North Carolina State University.
‡ University of North Carolina at Chapel Hill.
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10.1021/ja0353659 CCC: $25.00 © 2003 American Chemical Society
J. AM. CHEM. SOC. 2003, 125, 9435-9441
9435

A R T I C L E S
Blue et al.
Scheme 1. Preparation of (BINAP)Cu-OTf (1) and
[(BINAP)Cu(NCMe)][PF6] (2)
chemistry of well-defined late transition metal amido complexes
is primarily dominated by systems of the Fe, Co, and Ni
triads.2,3,8,10-12,14-22,26-35 In contrast, the chemistry of copper
complexes that possess nondative heteroatomic ligands is limited
in scope. Copper complexes possessing aryloxide or bridging
oxo ligands have been prepared and studied.36-43 Although an
isolable copper nitrene complex has not been reported, copper
nitrene systems have been implicated as intermediates in olefin
aziridination reactions.44-50 The chemistry of copper amido
complexes is limited to bridging amido ligands and amido
moieties that are incorporated into chelating ligands as well as
the reactivity of poorly defined copper amido complexes.51-57
Although the isolation and reactivity of well-defined monomeric
copper amido complexes have not been described, recent reports
of catalytic reactions that involve C-N bond forming steps
underscore the potential importance of such substrates.58-64 We
report herein the isolation and full characterization of a
monomeric Cu(I) anilido complex as well as initial reactivity
studies of this system.
Results and Discussion
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Synthesis and Characterization of Cu(I) Aniline and
Anilido Complexes. Our strategy to isolate a Cu(I) amido
system was to incorporate a bis-chelating phosphine into the
copper coordination sphere along with a ligand capable of facile
displacement. Along these lines, (BINAP)Cu(OTf) (1) and
[(BINAP)Cu(NtCMe)][PF6] (2) (BINAP ) 2,2′-bis(diphe-
nylphosphino)-1,1′-binaphthyl); OTf ) trifluoromethanesulfonate)
can be prepared by reaction of Cu(I) triflate with BINAP or
[Cu(NCMe)4][PF6] with BINAP, respectively (Scheme 1).
Unfortunately, all efforts to convert the BINAP-copper com-
plexes 1 or 2 to corresponding Cu(I) amido complexes failed.
Reactions of 1 or 2 with (1) lithium or sodium amides, (2)
amines followed by strong bases, or (3) mixtures of amines and
lithium or sodium amide bases resulted in the formation of free
BINAP.
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Assuming that reduction of Cu(I) was problematic, efforts
to prepare systems with more reducing phosphine ligands were
made. The combination of [Cu(NCMe)4][PF6] and the bispho-
sphine 1,2-bis(di-tert-butylphosphino)ethane (dtbpe) yields [(dt-
bpe)Cu(NCMe)][PF6] (3) in 95% yield after workup (Scheme
2). Complex 3 is characterized by a singlet at 2.33 ppm in the
1H NMR spectrum and resonances at 119.2 and 2.5 ppm in the
13C NMR spectrum due to the coordinated acetonitrile. In
addition, IR spectroscopy reveals νCN ) 2276 cm-1, and the
cyclic voltammogram of complex 3 exhibits a reversible
oxidation at 1.3 V (vs NHE).
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The reaction of complex 3 with LiNHPh followed by
chromatography on silica gel yields the Cu(I) amine complex
[(dtbpe)Cu(NH2Ph)][PF6] (4) (Scheme 2). Complex 4 is char-
acterized by a singlet at 29.8 ppm and a septet at -143.7 ppm
(1JPF ) 714 Hz) in the 31P NMR spectrum. A broad singlet at
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1
5.46 ppm in the H NMR is assigned as the resonance due to
the amine protons. The IR spectrum of 4 exhibits two high-
(55) Tsuda, T.; Miwa, M.; Saegusa, T. J. Org. Chem. 1979, 44, 3734-3736.
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ν
NH at 3345 and 3295 cm-1. A chemically irreversible oxidation
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1975, 22, 1859-1862.
of the amine complex 4 is observed at 1.3 V (vs NHE). Attempts
to deprotonate the amine complex 4 or to isolate the putative
Cu(I) anilido complex from the reaction of 3 and LiNHPh (prior
to column chromatography) resulted in decomposition. The
(58) Klapars, A.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124,
7421-7428.
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9
9436 J. AM. CHEM. SOC. VOL. 125, NO. 31, 2003

Monomeric Copper(I) Anilido Complex
A R T I C L E S
Scheme 2. Preparation of [(dtbpe)Cu(NCMe)][PF6] (3) and
[(dtbpe)Cu(NH2Ph)][PF6] (4).
Figure 1. ORTEP diagram (50% probability) of [(dtbpe)Cu(µ-Cl)]2 (5)
(hydrogen atoms omitted for clarity).
(dtbpe)Cu(NHPh) (6) is a ligand-centered oxidation. In contrast,
conversion of octahedral Ru(II) amine complexes to corre-
sponding amido systems results in a change in oxidation
potential of approximately 2.0 V.15 The two phosphine moieties
are symmetry inequivalent if the amido Cipso-Namido-H plane
is aligned approximately parallel with the P-Cu-P plane (this
geometry is observed in the solid state, see below), and hindered
Cu-Namido rotation should be detected by variable-temperature
31P NMR spectroscopy. However, no evidence of decoalescence
of the single phosphine resonance is observed down to -80 °C
in toluene-d8. Thus, either the ∆Gq for Cu-Namido bond rotation
is small or the amido ligand prefers an alignment in solution
that is approximately perpendicular to the solid-state orientation
(see below). Espinet et al. have attributed Pt-N bond rotational
barriers primarily to steric effects for square-planar d8 arylamido
complexes.29 The Cu(I) amido complex 6 is highly air-sensitive
and decomposes within minutes upon exposure to air in either
the solid state or solution. Under a dinitrogen atmosphere,
complex 6 is persistent in the solid state for at least 1 day at
room temperature and several days at low temperature. In
methylene chloride, 6 decomposes to uncharacterized products
after approximately 2 h at room temperature.
Scheme 3. Preparation of [(dtbpe)Cu(µ-Cl)]2 (5) and
(dtbpe)Cu(NHPh) (6).
amine complex 4 can also be made by reacting [(dtbpe)Cu-
(NCMe)][PF6] (3) with aniline (Scheme 2).
Solid-State Structures. An X-ray diffraction study of [(dt-
bpe)Cu(µ-Cl)]2 (5) revealed a binuclear species with bridging
chloride ligands (Figure 1). Table 1 presents crystal data, and
Table 2 displays selected bond distances and angles for complex
5. The Cu-Cl (∼2.38 Å) and Cu-P bond distances (∼2.28 Å)
are typical of related Cu(I) systems.65-70
A solid-state X-ray diffraction study of the Cu(I) amine
complex [(dtbpe)Cu(NH2Ph)][BF4] reveals a three-coordinate
monomeric cation with tetrafluoroborate anion (Figure 2).
Selected crystal data and bond distances and angles are depicted
in Tables 1 and 2, respectively. The coordination geometry is
distorted trigonal planar around Cu with a small P(1)-Cu-
Reaction of dtbpe and CuCl in methylene chloride yields
[(dtbpe)Cu(µ-Cl)]2 (5). In the solid state complex 5 is binuclear
(see below). The cyclic voltammogram of complex 5 reveals
two oxidations at E1/2 ) 0.55 V (vs NHE, quasi-reversible if
the return scan is made before the second oxidation) and Ep,a
) 0.88 V. The reaction of the chloride complex 5 with LiNHPh
yields the Cu(I) amido complex (dtbpe)Cu(NHPh) (6) as a pale
yellow solid after workup (Scheme 3). Complex 6 can also be
prepared by reaction of the previously reported [Cu(NHPh)]4
with dtbpe (Scheme 3).56 A solid-state X-ray diffraction study
of the anilido complex 6 reveals a monomeric structure (see
below). The amido proton resonates as a broad singlet at 4.70
ppm in the 1H NMR spectrum (C6D6), and the 31P NMR
spectrum displays a resonance at 30.2 ppm. The cyclic volta-
mmogram of the amido complex 6 reveals a chemically
irreversible oxidation at 0.10 V (vs NHE). Thus, the shift in
oxidation potential upon deprotonation of the amine complex
4 is approximately 1.2 V (both oxidations are chemically
irreversible). It is possible that the observed oxidation of
(65) Yam, V. W.-W.; Lee, W.-K.; Cheung, K. K.; Lee, H.-K.; Leung, W.-P. J.
Chem. Soc., Dalton Trans. 1996, 2889-2891.
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Organometallics 1984, 3, 1444-1445.
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K.-K.; Phillips, D. L.; Leung, K.-H. Angew. Chem. Int. Ed. 2000, 39, 4084-
4088.
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Chem. Soc., Dalton Trans. 1987, 1275-1278.
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9
J. AM. CHEM. SOC. VOL. 125, NO. 31, 2003 9437

A R T I C L E S
Blue et al.
Table 1. Selected Crystallographic Data for [(dtbpe)Cu(NH2Ph)][BF4] (4), [(dtbpe)Cu(µ-Cl)]2 (5), and (dtbpe)Cu(NHPh) (6)
4
5
6
formula
mol wt
cryst syst
space group
a, Å
C24H47BCuF4NP2
561.93
monoclinic
P21/c
11.199(3)
16.080(3)
15.882(3)
97.36(3)
2836.5(11)
4
C18H40ClCuP2
417.46
monoclinic
P21/c
11.3260(7)
15.3216(9)
13.7667(9)
112.7524(18)
2203.1(2)
4
C29H56CuNP2O0.5
552.26
monoclinic
P21/n
19.486(4)
14.682(3)
21.649(8)
99.58(3)
6107(3)
8
b, Å
c, Å
â, deg
V, Å3
Z
D
calcd, g cm-3
1.316
1.259
1.201
total no. of reflns
6765
15 186
10 641
no. of unique reflns
6765
5254
10641
R
0.041
0.051
0.067
Rw
0.042
0.060
0.068
temp (°C)
-100
-125
-125
Table 2. Selected Bond Distances (Å) and Angles (deg) for
[(dtbpe)Cu(NH2Ph)][BF4] (4), [(dtbpe)Cu(µ-Cl)]2 (5), and
(dtbpe)Cu(NHPh) (6)
4
5
6
Bond Distances
Cu1-Cl1
Cu1-P1
Cu1-P2
Cu1-N1
N1-C1
C1-C2
C2-C3
C3-C4
C4-C5
C5-C6
C1-C6
2.3844(9)
2.2863(8)
2.2832(9)
2.2719(10)
2.2637(9)
2.010(2)
1.444(4)
1.390(4)
1.385(4)
1.378(5)
1.383(5)
1.386(4)
1.385(4)
2.298(2)
2.261(2)
1.890(6)
1.354(9)
1.421(10)
1.382(11)
1.380(12)
1.381(12)
1.370(11)
1.415(11)
Bond Angles
Cl1-Cu-Cl1a
Cl1-Cu-P1
Cl1-Cu-P2
P1-Cu-P2
Cu1-Cl1a-Cu1a
N1-Cu-P1
N1-Cu-P2
Cu-N1-C1
95.73(3)
118.71(3)
115.23(3)
94.40(3)
84.27(3)
Figure 3. ORTEP diagram (50% probability) of (dtbpe)Cu(NHPh) (6)
(most hydrogen atoms omitted for clarity).
95.95(3)
93.19(8)
The amido complex 6 crystallizes as a monomeric complex
from a solution of THF and cyclohexane. Crystal data and
selected bond distances and angles are depicted in Tables 1 and
2, and the structure of complex 6 is displayed in Figure 3. Two
independent molecules were observed; however, the structural
details are similar (see Supporting Information). The Cu-N(1)
bond distance of complex 6 (1.890(6) Å) is shorter than that of
complex 4 by approximately 0.12 Å. The shorter Cu-N bond
distance of 6 compared to 4 could be due to Coulombic
interactions between the positively charged metal center and
negatively charged amido ligand, amido to copper π-donation
(see below), or a combination of these two effects. Parkins et
al. have reported a binuclear Cu(II) complex that possesses
p-tolylmethylamido ligands with Cu-N bond distances of
1.993(4) Å, while tetranuclear copper complexes with bridging
amido groups display shorter Cu-N bond distances of ap-
proximately 1.88-1.99 Å.51,52,54,72 The P(2)-Cu(1)-N(1)-C(1)
torsional angle of the amido complex 6 is approximately 13°
(Figure 4). Thus, the amido ligand is oriented for π-donation
(orientation for maximum orbital overlap would result in an
approximate torsional angle of 0°) into the empty p-orbital of
the Cu(I) system that is perpendicular to the P-Cu-P plane
(Scheme 4). The amido orientation is approximately perpen-
dicular to that observed by Hillhouse and Mindiola for Ni(I)
131.33(8)
132.36(8)
114.28(18)
125.63(16)
141.00(16)
134.5(5)
Figure 2. ORTEP diagram (50% probability) of [(dtbpe)Cu(NH2Ph)][BF4]
(4) (counterion and most hydrogen atoms omitted for clarity).
P(2) bond angle of 95.95(3)°. The Cu(1)-N(1) bond distance
is 2.010(2) Å, and the N(1)-C(1) bond distance {1.444(4) Å}
is slightly longer than that of free aniline (1.398 Å).71
(71) Fukuyo, M.; Hirotsu, K.; Higuchi, T. Acta Crystallogr. Sect. B 1982, 38,
640-643.
(72) Nyburg, S. C.; Parkins, A. W.; Sidi-Boumedine, M. Polyhedron 1993, 12,
1119-1122.
9
9438 J. AM. CHEM. SOC. VOL. 125, NO. 31, 2003

Monomeric Copper(I) Anilido Complex
A R T I C L E S
bonds.1,74-76 Even though Cu(I) is a high d-electron count metal
center, the three-coordinate copper anilido complex 6 has a
vacant p-orbital available for π-bonding with the amido ligand
(Scheme 4), and the solid-state structure of 6 indicates that the
orientation of the amido ligand is correct for π-overlap (see
above). It might be anticipated that the empty metal p-orbital
could serve to attenuate amido-based reactivity; however, the
extent to which transition metal p-orbitals can engage in
π-bonding with electron-donating ligands is unclear. In addition
to the empty p-orbital, the higher electronegativity of copper
compared with earlier transition metal centers could serve to
mitigate amido-based reactivity due to increased covalency of
the Cu-N bond. Thus, we sought to explore the reactivity of
complex 6.
Figure 4. Structure of (dtbpe)Cu(NHPh) (6) showing amido orientation.
Scheme 4. Orientation of Amido Ligand Allows Interaction of
Amido Lone Pair with Cu p-Orbital and Phenyl π*
The combination of (dtbpe)Cu(NHPh) (6) with [Ph3C][PF6]
results in an immediate reaction at room temperature. Analysis
1
by H NMR spectroscopy indicates the formation of the free
organic amine Ph3CNHPh (eq 1).77 No evidence of electron
Scheme 5. Comparison of Bond Angles around Copper for
Complexes 4 and 6
transfer to form trityl radical or net hydride abstraction to yield
triphenylmethane and a Cu nitrene complex is observed. The
II/I potential of (dtbpe)Cu(NHPh) (6) (Ep,a ) 0.1 V vs NHE)
does not preclude single-electron transfer chemistry since trityl
cation is reduced at approximately 0.44 V (vs NHE in methylene
chloride).78 Thus, the high nucleophilicity of the anilido ligand
likely renders N-C bond formation kinetically competitive with
single-electron oxidation. In contrast, upon combination with
single-electron oxidants, octahedral ruthenium(II) anilido
complexes of the type TpRu(L)(L′)(NHPh) (L ) L′ ) PMe3
or P(OMe)3 or L ) CO and L′ ) PPh3) undergo aryl-aryl
coupling reactions.79 The Ru(III/II) oxidation potentials of the
TpRuL2(NHPh) (L ) P(OMe)3 or PMe3) complexes (-0.28 and
-0.25 V; chemically reversible) indicate that single-electron
oxidation is more facile than for (dtbpe)Cu(NHPh) (Ep,a ) 0.10
V).15 Thus, the difference in reactivity between TpRuL2(NHPh)
and (dtbpe)Cu(NHPh) might be explained by the relative
oxidation potentials. However, TpRu(CO)(PPh3)(NHPh) under-
goes analogous reactivity {i.e., similar to TpRuL2(NHPh)}, and
its Ru(III/II) potential (Ep,a ) 0.11 V) is Virtually identical to
the copper amido complex (dtbpe)Cu(NHPh) (6).80 Thus, redox
potential does not explain the dissimilar reactivity of the TpRu
anilido complexes and (dtbpe)Cu(NHPh).
(dtbpe)Ni(NH(2,6-CHMe2)2C6H3).73 The bond angles around the
amido nitrogen sum to 359.1(9)°; however, the amido hydrogen
was placed at an idealized position. Structural similarities
between the amine complex 4 and the amido complex 6 include
three-coordinate copper with one small and two large bond
angles around the central copper atom (Scheme 5). However,
the P(1)-Cu-N(1) and P(2)-Cu-N(1) bond angles for the
amine complex 4 are nearly identical (the bond angle difference
is approximately 1°), while the P(1)-Cu-N(1) bond angle of
the amido complex 6 is approximately 15° smaller than the
P(2)-Cu-N(1) bond angle. The amido ligand seemingly
exhibits an electronic predilection toward an orientation that
maximizes overlap of the amido lone pair with the empty Cu
p-orbital as well as the π*-system of the phenyl substituent.
The amine complex lacks this electronic influence, and the plane
of the phenyl ring for complex 4 is oriented approximately
perpendicular to that of complex 6 (see Figures 2-4). The amido
nitrogen to phenyl ipso carbon bond distance of complex 6
{1.354(9) Å} is shorter than a N-C single bond (∼1.54 Å)
and the corresponding bond of the amine complex 4 {1.444(4)
Å}. To our knowledge, this is the first example of a structurally
characterized monomeric copper complex that possesses a
simple nonchelating amido ligand.
The anilido complex (dtbpe)Cu(NHPh) (6) reacts with
ethylbromide to yield N-ethylaniline and a copper product whose
Reactivity of (dtbpe)Cu(NHPh) (6). Highly basic amido
complexes coordinated to octahedral and d6 complexes have
been reported.2,8,10,11,14-22 The reactivity of such complexes is
likely derived from the combination of filled dπ manifolds (i.e.,
amido to metal π-donation is disrupted) and highly ionic M-N
(74) Holland, P. L.; Andersen, R. A.; Bergman, R. G. Comments Inorg. Chem.
1999, 21, 115-129.
(75) Mayer, J. M. Comments Inorg. Chem. 1988, 8, 125-135.
(76) Caulton, K. G. New J. Chem. 1994, 18, 25-41.
(77) Canle, M.; Clegg, W.; Demirtas, I.; Elsegood, M. R. J.; Maskill, H. J. Chem.
Soc., Perkin Trans. 2 2000, 85-92.
(78) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877-910.
(79) Conner, D.; Jayaprakash, K. N.; Gunnoe, T. B.; Boyle, P. D. Organome-
tallics 2002, 21, 5265-5271.
(80) Jayaprakash, K. N.; Gunnoe, T. B.; Boyle, P. B. Inorg. Chem. 2001, 40,
6481-6486.
(73) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem. Soc. 2001, 123, 4623-
4624.
9
J. AM. CHEM. SOC. VOL. 125, NO. 31, 2003 9439

A R T I C L E S
Blue et al.
Scheme 6. Reaction of Copper and Ruthenium Amido Complexes
purified by passage through a column of activated alumina. THF and
benzene were dried by distillation over sodium/benzophenone. Aceto-
nitrile was distilled over calcium hydride. Benzene-d6 was purified by
distillation from CaH2, degassed, and stored over 4 Å sieves. CDCl3
and CD2Cl2 were degassed via three freeze-pump-thaw cycles and
with EtBr or EtI Results in Nucleophilic Substitutiona
1
stored over 4 Å sieves. H and 13C NMR spectra were obtained on a
1
Varian Mercury 300 or 400 MHz. All H and 13C NMR spectra were
referenced against tetramethylsilane using residual proton signals (1H
NMR) or the 13C resonances of the deuterated solvent (13C NMR). 31
P
NMR spectra were obtained on a Varian 300 or 400 MHz spectrometer
and referenced against external 85% H3PO4. Variable-temperature NMR
experiments were performed on a Varian Mercury 300 MHz spectrom-
eter. IR spectra were obtained on a Mattson Genesis II spectrometer
either as thin films on a KBr plate or in solution using a KBr solution
cell. Electrochemical experiments were performed under a nitrogen
atmosphere using a BAS Epsilon Potentiostat. Cyclic voltammograms
were recorded in a standard three-electrode cell from -2.00 V to +2.00
V with a glassy carbon working electrode and tetrabutylammonium
hexafluorophosphate as electrolyte. Tetrabutylammonium hexafluoro-
phosphate was dried under dynamic vacuum at 140 °C for 48 h prior
to use. All potentials are reported versus NHE (normal hydrogen
electrode) using cobaltocenium hexafluorophosphate as an internal
standard. Elemental analyses were performed by Atlantic Microlabs,
Inc. LiNHPh was generated by reaction of aniline with 1 equiv of
n-BuLi in benzene followed by vacuum filtration to collect the resulting
white precipitate. Tetrakis(acetonitrile)copper(I) hexafluorophosphate,
TpRu(PMe3)2(NHPh), and bis(di-tert-butyl)phosphinoethane (dtbpe)
were prepared according to reported procedures.15,81,82 [Cu(NHPh)]4 was
prepared according to a previously reported procedure.56 All other
reagents were used as purchased from commercial sources.
a
*Resonances consistent with the formation of [(dtbpe)Cu(µ-X)]2
(X ) Br or I) are observed for the reaction of 6 with EtBr and EtI.
NMR spectra are consistent with [(dtbpe)Cu(µ-Br)]2 (Scheme
6). At room temperature, TpRu(PMe3)2(NHPh) does not react
with ethylbromide after 24 h; however, at 80 °C a slow
conversion (t1/2 ≈ 22 h) to TpRu(PMe3)2(Br) and N-ethylaniline
is observed (Scheme 6). This reaction is consistent with
observations made for cis-(PMe3)4Ru(H)(NH2).11 The copper
amido complex 6 also reacts with ethyliodide to yield N-
ethylaniline and a copper complex whose spectroscopic features
are consistent with [(dtbpe)Cu(µ-I)]2. Monitoring the reactions
of the Ru and Cu anilido complexes with 10 equiv of EtX (X
) Br or I) reveals substantial differences. For example, the
conversion of 6 and EtI is complete within 10 min at room
temperature, while the reaction between 6 and approximately
10 equiv of EtBr occurs with a t1/2 of approximately 13.5 min
at room temperature (kobs ) 8.5 × 10-4 M-1 s-1; Scheme 6).
These results are consistent with a simple nucleophilic SN2 type
reaction. The reaction of TpRu(PMe3)2(NHPh) with EtBr is
slower than the reaction of the copper anilido complex 6. The
half-life for the reaction of the ruthenium complex is ap-
proximately 22 h at 80 °C (kobs ) 8.6 × 10-6 M-1 s-1; Scheme
6).
(BINAP)CuOTf (1). BINAP (0.775 g, 1.25 mmol) was dissolved
in 5 mL of CH3CN and was slowly added to a solution of CuOTf-
benzene (0.402 g, 1.24 mmol) in 30 mL of CH2Cl2. The resulting
solution was stirred for 3 h at room temperature, and the solvent was
removed in vacuo. A yellow solid was recrystallized from CH2Cl2 and
1
hexanes (0.863 g, 83% yield). H NMR (CD2Cl2, δ): 7.84 (4H, m),
7.61 (4H, m), 7.50 (6H, m), 7.34 (2H, t, J ) 7 Hz), 7.27 (2H, m), 7.10
(6H, m), 6.79 (2H, t, J ) 7 Hz), 6.74 (2H, d, J ) 9 Hz), 6.64 (4H, t,
J ) 7 Hz). 13C{1H} NMR (CD2Cl2, δ): 135.3 (t, J ) 9 Hz), 133.7
(m), 131.5 (t, J ) 10 Hz), 128.6 (s), 128.1 (m), 127.8 (d, J ) 25 Hz),
127.1 (s). 31P{1H} NMR (CD2Cl2, δ): -0.8 (s, BINAP). Anal. Calc
for C44H32Cu1F3O3P2S1: C, 64.71; H, 3.86; N, 5.75. Found: C, 64.78;
H, 3.90; N, 5.66.
[(BINAP)Cu(NCMe)][PF6] (2). A solution of [Cu(NCMe)4][PF6]
(0.195 g, 0.52 mmol) in 5 mL of THF was added to a THF solution of
35 mL with BINAP {(()-2,2′-bis(diphenylphosphino)-1,1′-binaphtha-
lene} (0.327 g, 0.53 mmol). The solution was allowed to stir for 3 h,
and the solvent was reduced in vacuo to 15 mL. Approximately 20
mL of hexanes was added to precipitate a white solid. The resulting
solid was collected by vacuum filtration and dried under reduced
Summary and Conclusions
The synthesis, isolation, and full characterization of a
monomeric Cu(I) anilido system has been accessed using a bulky
bisphosphine ligand to stabilize the amido complex. Even though
the tert-butyl groups of the bisphosphine ligand result in a
sterically crowded coordination sphere, the amido ligand of
(dtbpe)Cu(NHPh) has been demonstrated to undergo nucleo-
philic reactivity, and reactions with ethylbromide suggest that
complex 6 is more reactiVe than a corresponding octahedral
and d6 ruthenium anilido system. These results suggest that while
the anilido ligand of 6 may interact with the empty metal
p-orbital, its reactivity is not significantly attenuated. In addition,
the increased electronegativity of Cu(I) versus Ru(II) does not
seemingly decrease amido-based nucleophilicity.
1
pressure (0.417 g, 91% yield). H NMR (CD2Cl2, δ): 7.80 (4H, m),
7.60 (10H, m), 7.35 (2H, t, J ) 7 Hz), 7.17 (2H, m), 7.05 (6H, m),
6.78 (2H, t, J ) 7 Hz), 6.72 (2H, d, J ) 8 Hz), 6.60 (4H, t J ) 7.2
Hz), 2.47 (3H, s, CH3CN). 13C{1H} NMR (CD2Cl2, δ): 139.7 (bs,
CH3CN), 135.3 (t, JPC ) 9 Hz), 133.9 (s), 133.6 (t, J ) 9 Hz), 132.1
(s), 130.5 (s), 130.2 (t, J ) 5 Hz), 129.8 (s), 128.6 (s), 128.2 (t, J ) 6
Hz), 127.7 (s), 127.5 (s), 127.3 (s), 3.6 (s, CH3CN). 31P{1H} NMR
1
(CD2Cl2, δ): 2.5 (s, BINAP), -144.2 (septet, JPF ) 710 Hz, PF6).
Anal. Calc for C46H35Cu1F6N1P3: C, 63.34; H, 4.04; N, 1.61. Found:
C, 63.20; H, 4.11; N, 1.70.
Experimental Section
[(dtbpe)Cu(NCMe)][PF6] (3). The bisphosphine dtbpe (0.213 g, 0.67
mmol) was dissolved in approximately 50 mL of CH2Cl2, and
[Cu(NCMe)4][PF6] (0.249 g, 0.67 mmol) was added to the solution.
General Methods. All reactions and procedures were performed
under anaerobic conditions in a nitrogen-filled glovebox or using
standard Schlenk techniques. Glovebox purity was maintained by
periodic nitrogen purges and monitored by an oxygen analyzer {O2(g)
< 15 ppm for all reactions}. Hexanes and methylene chloride were
(81) Po¨rschke, K. R.; Pluta, C.; Proft, B.; Lutz, F.; Kru¨ger, C. Z. Naturforsch.
B 1993, 48, 608.
(82) Kubas, G. J. Inorg. Synth. 1979, 19, 90.
9
9440 J. AM. CHEM. SOC. VOL. 125, NO. 31, 2003

Monomeric Copper(I) Anilido Complex
A R T I C L E S
The solution was stirred at room temperature for 2 h, and the solvent
was removed in vacuo. A light yellow solid was isolated (0.362 g,
95% yield). Complex 3 can be further purified by dissolution in
added to the solution and allowed to stir for 1 h. The pale yellow
solution was filtered through a fine-porosity frit to remove the LiCl.
The filtrate was dried in vacuo, and the product was isolated as a yellow
powder (0.2176 g, 75% yield). Crystals suitable for a solid-state X-ray
diffraction study were grown at room temperature by layering a THF
solution of 6 with cyclohexane. 1H NMR (C6D6, δ): 7.34 (2H, t, 3JHH
1
methylene chloride followed by precipitation with hexanes. H NMR
(CDCl3, δ): 2.33 (3H, s, NCCH3), 1.88 (4H, s, methylene), 1.27 (36H,
vt, N ) 14 Hz, t-Bu). 13C{1H} NMR (CDCl3, δ): 119.2 (s, NCMe),
33.8 (vt, N ) 15 Hz, quat t-Bu), 29.7 (s, methyl), 20.7 (vt, N ) 25 Hz,
methylene), 2.5 (s, NCCH3). 31P{1H}NMR (CD2Cl2, δ): 31.8 (bs,
3
3
) 7 Hz, m-Ph), 7.23 (2H, d, JHH ) 7 Hz, o-Ph), 6.67 (1H, t, JHH
)
7 Hz, p-Ph), 4.70 (1H, bs, NH), 1.37 (4H, bs, methylene), 1.06 (36H,
vt, N ) 12 Hz, t-Bu). 13C{1H} NMR (C6D6, δ): 162.3 (bs, ipso Ph),
129.6, 117.0, and 110.9 (all s, phenyl o, m, and p), 33.6 (br s, quat
t-Bu), 30.5 (vt, N ) 10 Hz, methyl), 21.3 (vt, N ) 24 Hz, methylene).
31P{1H} NMR (C6D6, δ): 30.2 (s). IR (C6H6): VNH ) 3332 cm-1. CV
(THF, TBAH, 100 mV/s): Ep,a ) 0.10 V (II/I). Satisfactory elemental
analysis was not obtained due to the air-sensitive nature of the material.
Method B. The copper complex [Cu(NHPh)]4 (0.056 g, 0.36 mmol)
was added to a benzene (30 mL) solution of dtbpe (0.114 g, 0.358
mmol). The solution immediately turned yellow and was allowed to
stir at room temperature for 20 min. The volatiles were removed under
1
dtbpe), -143.7 (septet, JPF ) 710 Hz, PF6). IR (CCl4): VCN ) 2276
cm-1. CV (CH2Cl2, TBAH, 100 mV/s): E1/2) 1.28 V (II/I). Anal.Calc
for C20H43Cu1F6N1P3: C, 42.29; H, 7.63; N, 2.47. Found: C, 42.06;
H, 7.64; N, 2.23.
[(dtbpe)Cu(NH2Ph)][PF6] (4). Method A. To a stirred THF solution
(50 mL) of [(dtbpe)CuNCMe][PF6] (0.6265 g, 1.1 mmol) was added
LiNHPh (0.1085 g, 1.1 mmol). The resulting solution was stirred for
2 h at room temperature; then the solvent was removed in vacuo. The
nonvolatiles were dissolved in approximately 10 mL of CH3CN and
applied to a silica column, which was eluted with approximately 50
mL of CH3CN. The solvent was removed in vacuo, and the resulting
white powder was dissolved in CH2Cl2. The product was precipitated
upon addition of hexanes and filtered to isolate a white powder (0.3824
g, 78% yield). Prior to the solid-state X-ray diffraction study, a
counterion metathesis reaction to yield [(dtbpe)Cu(NH2Ph)][BF4] was
performed. Crystals suitable for a solid-state X-ray diffraction study
were grown at room temperature by layering a THF solution of 4 with
cyclohexane. 1H NMR (CDCl3, δ): 7.28 (2H, t, 3JHH ) 7 Hz, m-phenyl),
1
reduced pressure to yield a yellow powder (0.167 g, 98% yield). H
and 31P NMR spectra of the isolated yellow solid are consistent with
the quantitative formation of (dtbpe)Cu(NHPh) (6).
Reactions with Ethylbromide or Ethyliodide. The general proce-
dures for all reactions with ethylbromide or ethyliodide were similar.
A representative procedure is provided: In a screw cap NMR tube,
TpRu(PMe3)2(NHPh) (0.0140 g, 0.0251 mmol) was dissolved in 0.82
g of C6D6. A small amount of Cp2Fe was added as an internal standard.
Bromoethane (18.0 µL, 0.243 mmol) was added using a microsyringe.
The resulting solution was heated to 80 °C and monitored at regular
time intervals by 1H NMR. The formation of N-ethylaniline was
confirmed by addition of pure N-ethylaniline to the final reaction
products. In addition, analysis using gas chromatography confirmed
the formation of N-ethylaniline. The formation of TpRu(PMe3)2(Br)
was based upon the close relationship of the final TpRu complex to
TpRu(PMe3)2(Cl). The formation of [(dtbpe)Cu(µ-X)]2 (X ) I or Br)
3
3
7.14 (2H, d, JHH ) 7 Hz, o-phenyl), 7.05 (1H, t, JHH ) 7 Hz,
p-phenyl), 5.46 (2H, bs, NH2), 1.88 (4H, s, methylene), 1.17 (36H, vt,
N ) 14, tert-butyl). 13C{1H} NMR (CDCl3, δ): 142.5 (bs, ipso-Ph),
129.8, 123.6 and 119.2 (all s, phenyl o, m, and p), 33.9 (vt, N ) 12
Hz, quat t-Bu), 30.4 (vt, N ) 8 Hz, methyl), 20.9 (vt, N ) 25 Hz,
methylene). 31P{1H} NMR (CD2Cl2, δ): 29.8 (s, dtbpe), -143.7 (septet,
1JPF ) 714 Hz, PF6). IR (CH2Cl2): VNH ) 3345, 3295 cm-1. CV (CH2-
Cl2, TBAH, 100 mV/s): Ep,a ) 1.31 V (II/I). Anal. Calc for C24H47-
Cu1F6N1P3: C, 46.48; H, 7.64; N, 2.26. Found: C, 46.23; H, 7.50; N,
2.59.
1
complexes was ascertained by similarities of the H NMR spectra to
that of [(dtbpe)Cu(µ-Cl)]2; however, these complexes have not been
isolated.
Method B. To a stirred THF solution (30 mL) of [(dtbpe)Cu(NCMe)]-
[PF6] (3) (0.2367 g, 0.42 mmol) was added aniline (38 µL, 0.42 mmol).
The resulting solution was stirred for 1 h at room temperature, and the
solvent was removed in vacuo. The resulting pale yellow solid (0.228
g, 97% yield) was vacuum-dried overnight. 1H NMR spectroscopy
revealed clean formation of complex 4.
Solid-State X-ray Diffraction Studies of [(dtbpe)Cu(µ-Cl)]2 (5),
[(dtbpe)Cu(NH2Ph)][BF4] (4), and (dtbpe)Cu(NHPh) (6). For details
of X-ray data collection and analysis see Supporting Information.
Acknowledgment. The National Science Foundation
(CAREER Award; CHE 0238167) and North Carolina State
University are acknowledged for support of this research. E.B.
acknowledges support from the National Science Foundation
via a Predoctoral Graduate Fellowship. The authors also wish
to thank the National Science Foundation (NSF) for funding
(CHE-9509532) to obtain the X-ray diffractometer, the research
group of Professor Hillhouse (University of Chicago), and a
reviewer for useful suggestions.
[(dtbpe)Cu(µ-Cl)]2 (5). The white solid dtbpe (bis(di-tert-butyl)-
phosphino ethane; 0.5455 g, 1.71 mmol) was dissolved in approximately
30 mL of methylene chloride. CuCl (0.1672 g, 1.69 mmol) was added
to the dtbpe solution and allowed to stir until all of the CuCl dissolved
(approximately 2 h). The solvent was then removed under reduced
pressure, and the resulting white solid product was isolated (0.6342 g,
90% yield). Complex 5 can be further purified by dissolution in
methylene chloride followed by precipitation with hexanes. Crystals
suitable for a solid-state X-ray diffraction study were grown at room
temperature by layering a methylene chloride solution of 5 with
1
Supporting Information Available: Complete tables of
crystal data, collection and refinement data, atomic coordinates,
bond distances and angles, and anisotropic displacement coef-
ficients for [(dtbpe)Cu(NH2Ph)][BF4] (4), [(dtbpe)Cu(µ-Cl)]2 (5),
and (dtbpe)Cu(NHPh) (6). Kinetic plots for the reactions of
(dtbpe)Cu(NHPh) (6) or TpRu(PMe3)2(NHPh) with EtBr. This
material is available free of charge via the Internet at
http://pubs.acs.org.
cyclohexane. H NMR (CD2Cl2, δ): 1.86 (4H, br s, methylene), 1.25
(36H, vt, N ) 13 Hz). 13C{1H} NMR (CD2Cl2, δ): 33.9 (vt, N ) 9
Hz, quat t-Bu), 30.4 (vt, N ) 9 Hz, methyl), 20.8 (vt, N ) 25 Hz,
methylene).31P{1H} NMR (CD2Cl2, δ): 25.6 (s). CV (CH2Cl2, TBAH,
100 mV/s): E1/2 ) 0.55 V (II/I, quasi-reversible), Ep,a ) 0.88 V (II/I).
Anal. Calc for C36H80Cl2Cu2P4: C, 51.79; H, 9.66. Found: C, 51.64;
H, 9.74.
(dtbpe)Cu(NHPh) (6). Method A. The white powder [(dtbpe)Cu-
(µ-Cl)]2 was weighed out (0.257 g, 0.62 mmol) and dissolved in
approximately 40 mL of benzene. LiNHPh (0.063 g, 0.64 mmol) was
JA0353659
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J. AM. CHEM. SOC. VOL. 125, NO. 31, 2003 9441