CuI click catalysis with cooperative noninnocent pyridylphosphine ligands

Article abstract of DOI:10.1016/j.ica.2011.10.037

We describe the synthesis and characterization of compound L1H, 2-di(tert-butyl)phosphinomethyl-6-methylpyridine, and the first dimeric Cu ^I complex 3 with this novel bidentate NP^tBu ligand. We also demonstrate for the first time tha

Full text of DOI:10.1016/j.ica.2011.10.037

Inorganica Chimica Acta 380 (2012) 336–342
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CuI click catalysis with cooperative noninnocent pyridylphosphine ligands
Sandra Y. de Boer a, Yann Gloaguen a, Martin Lutz b, Jarl Ivar van der Vlugt a,
⇑
a Supramolecular & Homogeneous Catalysis Group, van ’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
b Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 17 October 2011
We describe the synthesis and characterization of compound L1H, 2-di(tert-butyl)phosphinomethyl-6-
methylpyridine, and the first dimeric CuI complex 3 with this novel bidentate NPtBu ligand. We also dem-
onstrate for the first time that this ligand scaffold exhibits noninnocent reactivity through dearomatization
behavior, similar to its well-studied tridentate analog L2H, 2,6-bis((di-tert-butylphosphino)methyl)pyri-
dine PNPtBu. The molecular structure of [Cu(CCPh)(L2H)]2 is reported, which is a rare case of a crystallo-
graphically characterized copper-acetylide dimer. We also demonstrate that copper(I) complexes with
either ligand L1H or L2H or their dearomatized counterparts may act as active, cooperative catalysts for
the [2+3] polar cycloaddition of azides and acetylenes. These results represent the first indications of selec-
tive Cu-based cooperative catalysis, using non-innocent lutidine-based PNP backbone and catalysts 2 and 5
could thus be termed all-inclusive systems for this reaction.
Young Investigator Award Special Issue
Keywords:
Cooperative catalysis
Copper
Pincer ligand
Click reaction
Ligand design
Hybrid ligand
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
pounds are strictly monoanionic frameworks, predominantly with
a deprotonated pivot (heteroatom) donor atom [5–7]. Recently,
Nature often employs cooperative substrate activation to en-
hance selectivity, reactivity or activity, and almost without excep-
tion first row transition metals are utilized in metalloenzyme
active sites [1]. This activation can be roughly separated into two
areas: redox-based reactivity and acid-base related reactivity. Tradi-
tionally, the general concept of cooperative interactions has been ig-
nored in synthetic catalyst designs, where ligand and metal have
strictly separated roles during the catalytic conversion of substrates,
and this is the case for the majority of newly developed systems to
facilitate both existing and new catalytic transformations. Only re-
cently, some convincing examples of productive metal–ligand inter-
play during substrate orientation, activation and/or transformation
have been demonstrated. However, there is a striking dichotomy in
these literature examples, with first-row transition metals mainly
involved in redox-based cooperativity [2], while various expensive
second- or third-row transition metals have been involved in other
types of substrate activation to an appreciable extent [3]. Hence,
the combination of first-row metals and cooperative ligand systems
is a relative barren field of research, with potential applications to
replace existing processes based on scarce metals with benign,
earth-abundant alternatives [4].
neutral lutidine-based PNP and PNN pincer scaffolds, which are
susceptible to selective deprotonation–rearomatization of the li-
gand backbone [8], have also been successfully applied in cooper-
ative catalysis [9], mainly with Ru [10] and to a lesser extent with
Rh [11] and Ir [12]. Upon dearomatization, the ligand system
undergoes a reversible formal charge-switching from neutral to
monoanionic. Compared to the varied chemistry detailed for the
heavier congeners, strikingly little attention has been paid to the
use of first row transition metals with these ligand frameworks
to date [13].
Therefore, we started a research program to explore metal–li-
gand cooperative reactivity with specific focus on first row metals,
utilizing inter alia cooperative PNP ligands as a reactive scaffold.
We have described the stoichiometric reactivity of ligand
PNPtBu(L2H) with CuI, whereby hemilabile coordination of the pyr-
idine-nitrogen donor was observed on going from neutral species 1
to the T-shaped cationic complex A (Scheme 1) [14]. Complex 1
selectively reacted with strong bases at the ligand backbone [15],
mirroring reactivity described for 2nd and 3rd row metals
[10–12] and providing a platform for further investigations with
first row metals. Deprotonation of the reactive CH2-spacer of the
PNP-backbone resulted in bright orange, neutral T-shaped Cu-
complex 2, featuring ligand scaffold L2, which was susceptible to
electrophilic addition (C–C bond formation) reactions on the ligand
backbone. Reprotonation of 2 with thiophenol and benzyl mercap-
tan (pKa = 15.3 in DMSO) occurs smoothly and instantaneously at
room temperature [16], while boiling this species in ethanol
(pKa = 29.8 in DMSO) did not induce any visual change, with the
Pincer ligands have been around for a few decades now, but
research on these well-defined, tridentate scaffolds is still
blossoming. The majority of the developed classes of pincer com-
⇑
Corresponding author. Tel.: +31 20 5256459; fax: +31 20 5255604.
E-mail address: j.i.vandervlugt@uva.nl (J.I. van der Vlugt).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.10.037

S.Y. de Boer et al. / Inorganica Chimica Acta 380 (2012) 336–342
337
SbF6
PtBu2
CuBrSMe2
PtBu2
Cu Br
PtBu2
PtBu2
PtBu2
KSCN
THF
AgSbF6
THF
N
N
N Cu
PtBu2
N
Cu NCS
PtBu2
PtBu2
PNPtBu
A
1
OTf
PtBu2
PtBu2
MeOTf
Et2O
base
Et2O
N Cu
N Cu
PtBu2
PtBu2
2
Scheme 1. Synthesis of CuI complex 2 featuring a dearomatized PNÀP-ligand and the structural resemblance to the cationic derivative A.
persistent bright orange color indicative of the intact dearomatized
heterocycle.
PtBu2
CuBr(SMe2)
PtBu2
Alternatively, a 1D coordination polymer based on L2H and
with the overall formula [Cu2Br2(L2H)]n could be fabricated, which
showed identical response to base-mediated deprotonation of the
PNP backbone. Subsequent treatment with sufficiently acidic thiols
resulted in the formation of unique dinuclear CuI complexes fea-
turing bridging thiolate and PNP ligands [16].
Hence, the methodology of dearomatization–reprotonation of-
fers a flexible and versatile route toward CuI species bearing func-
tionalities that are otherwise difficult to install. We also reported
on the chemistry of ligand PNPtBu with nickel [17] and palladium
N
N Cu Br
Br Cu N
L1H
tBu2P
3
Scheme 2. Synthesis of complex 3.
[18], including
a direct comparison of dearomatized Pd(alk-
yl)(PNÀPtBu) species with their isoelectric PCP analogs in the Suzu-
ki coupling of arylbromides and arylboronic acids.
showed a broad 31P NMR signal at 26.6 ppm as well as the ex-
pected signals in the 1H NMR spectrum for all types of hydrogen
atoms present. IR spectroscopy indicated coordination of the pyri-
Besides tridentate ligands based on lutidine, also picoline and
lutidine-derived NPR-ligands as well as the closely related quino-
line analogs have been employed quite extensively in the last dec-
ade [19], but the potential noninnocent character of these
bidentate analogs of the PNPR ligand class has been almost com-
pletely overlooked to date and practical application of this feature
has not been reported so far [20]. Furthermore, very few reports on
alkyl-substituted PN ligands have appeared. Given our recent
explorations in the first row chemistry of cooperative but very
bulky pincer ligands, it was deemed interesting to probe the coop-
erative reactivity with the sterically more accessible PN ligands
while coordinated to CuI and thereby expand the toolbox of nonin-
nocent, reactive ligands. We herein describe our initial efforts in
this direction with the synthesis and application of Cu-complexes
3 and 4 for the (stoichiometric and catalytic) activation of acety-
lenes and azides. Furthermore, we have applied complexes 2 and
5, featuring PNP ligand L2 and L2H, respectively, in the same
‘click-reaction’. This is the first example of cooperative copper
catalysis with these noninnocent NP and PNP scaffolds.
dine N-atom to the CuI center, with two bands at
m
1590 and
1577 cmÀ1
. High resolution FAB-MS showed a peak at m/z
790.0530 for the parent molecule [M+] and a fragmentation pat-
tern indicative of a dimeric structure, which was confirmed by
an X-ray crystallographic analysis of single crystals, grown by slow
vapor diffusion of pentane into an acetone-d6 solution. The molec-
ular structure for dimeric complex 3 in the solid state, with bridg-
ing bromide ligands, is depicted in Fig. 1.
The complex shows overall centrosymmetry and the geometry
around the CuI-center is distorted tetrahedral, with a more acute
Br1–Cu1–Br1i angle of 103.783(9)° and large P–Cu–Br angles of
127.070(16)° and 118.207(16)°. The Cu–N and Cu–P bond dis-
tances are within the usual regions [14–16,23].
2.2. Cooperative click reactivity of Cu(PNP) complexes
It was reasoned that compound 2 might be a suitable starting
material for the direct preparation of a precatalyst for the [2+3] po-
lar cycloaddition [24] of phenyl acetylene, given that the pKa of this
reagent is 28.8 (in DMSO). Reconstitution of the aromatic pyridine
heterocycle of the PNÀPtBu backbone occurred instantaneously
upon addition of one equiv phenylacetylene to an orange solution
of 2 in diethyl ether, as evidenced by a color change to yellow, and
NMR, IR spectroscopic and mass spectrometric analysis of the iso-
lated light-yellow solid confirmed formation of species 5. Evidently,
proton transfer from the acidic phenylacetylene to the dearoma-
tized L2 backbone, concomitant with formation of the copper–
phenylacetylide adduct proceeded smoothly and rapidly at room
temperature, which is in contrast with the sluggish formation of a
monomeric, two-coordinate CuI-phenylacetylide complex, reported
by Gunnoe [25]. Reaction of the starting (NHC)CuMe-complex with
PhCCH, eliminating methane concomitant with formation of the de-
sired copper species, required heating to 60 °C for 22 h to enable
complete conversion. This hints towards a different mechanism
for both reactions, i.e. intermolecular proton-transfer followed by
2. Results and discussion
2.1. Ligand synthesis and CuI coordination chemistry
Ligand L1H is prepared in a straightforward manner [21] by
careful monolithiation of one of the lutidine methyl-groups, fol-
lowed by phosphorylation using ClPtBu2 to give a white solid after
recrystallization by slow vapor diffusion of hexane into a concen-
trated dichloromethane solution. The 31P NMR signal appears at d
35.3 ppm in acetone-d6. The second, unreacted methyl-group can
act both as a spectroscopic handle and as a steric (and electronic)
tuning factor upon coordination [22]. By using a lutidine-scaffold
instead of picoline, undesirable cyclometallation reactions at the
6-position of the pyridine ring are also efficiently avoided.
Upon combining ligand L1H with CuBr(SMe)2 in diethyl ether a
light-yellow solid was recovered (Scheme 2) after work-up that

338
S.Y. de Boer et al. / Inorganica Chimica Acta 380 (2012) 336–342
Fig. 1. ORTEP plot (50% probability displacement ellipsoids) of complex 3, [Cu(l-Br)(L1H)]2; left – top view; right – side view. Hydrogen atoms and disordered solvent
molecules have been omitted for clarity. Selected bond lengths (Å) and angles (°): Cu1–P1 2.2188(5); Cu1–N1 2.1505(15); Cu1–Br1 2.4580(3); Cu1–Br1i 2.5198(3); P1–C7
1.8506(18); Cu1ÁÁÁCu1i 3.0725(4); P1–Cu1–N1 87.54(4); P1–Cu1–Br1 127.070(16); P1–Cu1–Br1i 118.207(16); N1-Cu1-Br1 109.93(4); Cu1–Br1–Cu1i 76.217(9); Br1–Cu1–Br1i
103.783(9); P1–C7–C6–N1 29.2(2); Cu1–P1–C7–C6 À25.62(14). Symmetry operation i: 0.5 À x, 0.5 À y, Àz.
H
PtBu2
PhC CH
H
PtBu2
PtBu2
N3
Ph
N
N Cu
PtBu2
Ph
+
N
Cu C CPh
PtBu2
N Cu
PtBu2
N
N
Et2O
THF
2
5
2
6
Scheme 3. Reaction of 2 toward phenyl acetylene and subsequent addition of benzyl azide to generate compound 6 via intermediacy of complex 5.
nucleophilic addition in our case versus associative substitution via
intramolecular proton-transfer in the literature case.
H
PtBu2
Cu
The instantaneous formation of an copper-acetylide species sup-
ported by a reprotonated PNPtBu ligand (Scheme 3) was further verified
by an independent synthesis of the complex Cu(C„CPh)(L2H) by reac-
tion of commercially available Cu(C„CPh) with PNPtBu in diethyl ether
to yield a yellow-green solid. We have no definite proof for the mono-
meric or higher-ordered nature of 5, – higher mass aggregates
seem to be absent in the FAB mass spectrum (FAB+ 459.09
[MÀ{CCPh}]observed as major species). The 31P NMR spectrum of pro-
posed complex 5 showed a singlet at d 42.1 ppm in d4-methanol, sim-
ilar to the starting CuBr(PNP) species 1 and markedly different than
dearomatized intermediate 2, indicating that reprotonation and coor-
dination of the acetylide fragment was successful. We have modeled
N
C
CPh
PtBu2
PhC CH
N3
5
PtBu2
H
Ph
PtBu2
N Cu
PtBu2
N
N
N
Cu
PtBu2
B
N
Ph
2
H
6
Ph
(DFT, PM3 level) a dimeric copper species with the acetylene
r-bonded
N
N
Ph
to Cu1 and -bonded to Cu2 – often proposed to be a likely constitution
p
N
for the active species with less bulky ligands present – but this proved
to lead to highly congested complexes. Similar evidence for the possi-
bility of a mononuclear Cu-center to be an active ‘click-catalyst’ was re-
cently provided by Straub, who showed that both Cu(NHC)(OAc) and
Cu(NHC)(CCPh) are active CuAAC catalysts (CuAAC – copper-catalyzed
azide–alkyne cycloaddition) [25].
In a subsequent experiment using complex 5 in the presence of
an equimolar amount of benzyl azide, the orange color of complex
2 was regenerated, along with the product 1-benzyl-4-phenyltriaz-
ole 6 of the [2+3] polar cycloaddition reaction. Obviously, the inter-
mediate copper triazolide adduct B, with a proposed structure
analogous to the isolated compound reported by Straub [26], is ba-
sic enough (and also sterically hindered enough) to induce facile
intramolecular proton transfer, i.e. deprotonation of the PNP-ligand
backbone, to release triazole species 6. This implies that the ‘click’
reaction can thus be performed without the need for additional
base or buffered solution media. The regeneration of complex 2
was also confirmed by in situ 31P NMR spectroscopy.
Scheme 4. Proposed catalytic cycle for the click-reaction of phenyl acetylene and
benzyl azide catalyzed by 1 mol% of species 2 or 5.
To run this reaction in a catalytic fashion we used 1 mol% 5 as
catalyst and diethyl ether as reaction medium (Scheme 4);
alternatively complex 2 could be employed as well. As expected,
compound 6 was obtained in near quantitative yield after 16 h as
a white solid precipitate from the reaction mixture, with NMR
signatures as previously reported for this benchmark product. Fur-
thermore, it may be anticipated that all-inclusive catalysts with a
built-in reactive site may give rise to enhanced rates or unusual
chemoselectivities compared to standard ‘click’ catalysts, as intra-
molecular proton-transfer could suppress side-reactions wherein
the intermediate triazolide undergoes rearrangement. We are cur-
rently testing this hypothesis by extending our screening studies.
Initial reactivity of 2 with benzoxazole confirms that C–H bond

S.Y. de Boer et al. / Inorganica Chimica Acta 380 (2012) 336–342
339
activation may also occur with this heterocyclic compound, which
is also under further investigation.
31P NMR spectrum and 13C NMR signals indicative of the acetylenic
fragment. FAB-MS spectrometry indicated the formation of dinu-
clear species, with the highest-intensity peak at m/z 729.3 for
[Cu2(CCPh)(L1H)2]+. IR spectroscopy indicated that the Cu–N bond
2.3. Cooperative reactivity of Cu(NP) complex 4
remained intact, with bands apparent at
m .
1592 and 1575 cmÀ1
Stimulated by the results obtained with complexes 2 and 5 in
this cycloaddition reaction, we also tested the behavior of species
3 for dearomatization and subsequent interaction with phenyl-
acetylene. Gratifyingly, upon addition of one equiv HCCPh to the
orange solution obtained after treating 3 with strong base in
diethyl ether (with presumable formation of a {Cu(L1)(solvent)}
species), the color instantaneously faded to light yellow, indicative
of reprotonation of the ligand-backbone, and after work-up a
greenish-yellow solid was obtained for complex 4. NMR spectro-
scopic analysis of the product indicated formation of the desired
copper(PN)(acetylide) unit, with a broad signal at 32 ppm in the
The existence of a bimetallic constitution for complex 7 was con-
firmed by an X-ray crystallographic analysis of single crystals ob-
tained by slow diffusion of pentane into a concentrated CH2Cl2
solution. The resulting molecular structure for complex [Cu(l-
CCPh)(L1H]2 is depicted in Fig. 2.
The geometry around the CuI metal centers is distorted tetrahe-
dral with angles between 84.46(4)° and 125.59(5)°. The Cu1–C16–
Cu1i angle is acute with 71.35(5). As a consequence of the inver-
sion symmetry of the complex, the Cu1–C16–Cu1i–C16i unit is pla-
nar. The acetylide group is approximately coplanar with this plane,
but bent in the direction of one copper center. The C17–C16–Cu1
and C17–C16–Cu1i angles are thus significantly different with
156.04(14)° and 132.60(13)°. The angle sum at C16 is 360.0(2)°.
The bridging of the acetylide groups results in a short Cu1ÁÁÁCu1i
contact of 2.4417(4) Å.
As a consequence, there is no side-on interaction of the respec-
tive CuI centers with either of the
p-systems of the two triple
bonds, which is also reinforced by the steric hindrance imparted
by the tert-butyl groups. A search of the Cambridge Structural
Database CSD revealed only a few published dimeric structures
featuring related
l-CCR or l-CCAr binding motifs [26]. The C16–
C17 bond length of 1.210(2) Å is in the range of an C„C bond [27].
Subsequent addition of an equimolar amount of benzyl azide
regenerated an orange-colored solution in the course of 4 h, con-
comitant with formation of a white precipitate, which was identi-
fied by NMR spectroscopy as 1-benzyl-4-phenyltriazole, after
comparison with an authentic sample [28].
3. Conclusions
In summary, we have reported the facile, selective and efficient
coupling of azides and acetylenes (click-reaction) using an all-
inclusive CuI complex with a cooperative diphosphinopyridine
(PNP) framework. This reaction sequence relies on the reversible
dearomatization of the PNP-scaffold combined with its affinity to
activate sufficiently protic E–H bonds. The described intramolecu-
lar C–C coupling methodology is believed to provide a general route
to induce selective formation of triazoles. We are currently investi-
gating catalyst tuning by modifications on the ligand framework.
4. Experimental
All commercial starting materials were used as received. THF,
pentane, hexane and diethyl ether were distilled from sodium ben-
zophenone ketyl, CH2Cl2, isopropanol and methanol were distilled
from CaH2, and toluene was distilled from sodium under nitrogen.
NMR spectra (1H, 31P and 13C) were measured on a Varian INOVA
500 MHz or a Varian MERCURY 300 MHz. High resolution mass
spectra were recorded on a JEOL JMS SX/SX102A four sector mass
spectrometer; for FAB-MS 3-nitrobenzyl alcohol was used as ma-
trix. IR spectra were collected on a Bruker alpha-p FT-IR spectrom-
eter with ATR module. Elemental analyses were carried out at
Kolbe Mikroanalytisches Laboratorium in Mülheim an der Ruhr.
CuBr(PNPtBu) 1 and Cu(PNÀPtBu) 2 were prepared following litera-
ture procedures [10,11]. Ligand L1H was prepared according to a
literature procedure [21].
Fig. 2. ORTEP plot (50% probability displacement ellipsoids) of complex 4 [Cu(l-
CCPh)(L1H)]2; top – top view; bottom – side view. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (°): Cu1–P1 2.2735(4);
Cu1–N1 2.2132(13); Cu1–C16 2.0147(16); Cu1–C16i 2.1667(17); C16-C17 1.210(2);
C17–C18 1.444(2); P1–C7 1.8438(16); Cu1ÁÁÁCu1i 2.4417(4); P1–Cu1–N1 84.46(4);
P1–Cu1–C16 125.59(5); P1–Cu1–C16i 115.99(4); N1–Cu1–C16 112.33(6); N1–Cu1–
C16i 105.51(6); C16–Cu1–C16i 108.65(5); Cu1–C16–Cu1i 71.35(5); C17–C16–Cu1
156.04(14); C17–C16-Cu1i 132.60(13). Symmetry operation (i): 1 À x, 1 À y, 1 À z.
4.1. Complex 3 [Cu(l-Br)(L1H)]2
To a suspension of CuBr(SMe)2 (374.9 mg, 1.82 mmol) in 20 mL
diethyl ether was added a solution of NPtBu (L1H) (458.5 mg,

340
S.Y. de Boer et al. / Inorganica Chimica Acta 380 (2012) 336–342
1.82 mmol) in 10 mL diethyl ether. The light-yellow suspension is
stirred for 16 h and all volatiles are removed in vacuo to leave a
light-yellow solid. Yield: 716.7 mg, 0.91 mmol, 99.5%. 1H NMR
(400 MHz, (CD3)2CO): d 7.70 (t, JH = 7.6 Hz, 1H, ArH), 7.36 (d,
JH = 7.2 Hz, 1H, ArH), 7.20 (d, JH = 6.8 Hz, 1H, ArH), 3.39 (d,
JPH = 7.6 Hz, 2H, CH2), 2.98 (s, 3H, CH3), 1.31 (d, JPH = 12.8 Hz,
18H, tBu-H). 31P NMR (162 MHz, (CD3)2CO): d 26.6 (br s). 13C
NMR (100 MHz, (CD3)2CO): d 159.9 (d, JPC = 17.1 Hz, 2C, Ar-C),
138.7 (s, 1C, Ar-CH), 122.7 (d, JPC = 30 Hz, 2C, Ar-CH), 33.5 (d,
JPC = 7.8 Hz, 2C, tBu-C), 31.1 (d, JPC = 11 Hz, 1C, CH2), 28.2 (d,
5. Copper catalyzed azide alkyne cycloaddition
The appropriate catalyst was charged into a flame-dried Schlenk
of 15 mL volume, together with 100 molar equiv of phenyl acetylene
(182.3 mg) in 10 mL diethyl ether. To this yellow solution was
added benzyl azide (237.7 mg, 100 mol. eq. to catalyst) and the
reaction monitored in time. Progressive formation of a white precip-
itate signaled generation of triazole product. After 16 h the reaction
mixture was filtered and the product analyzed. Yield: 170 mg,
0.723 mmol, 40%. The NMR spectroscopic features of the thus ob-
tained product match that of N-benzyl-4-phenyltriazole [28].
JCH = 10.8 Hz, 6C, tBu-CH3), 26.3 (s, 1C, CH3). IR (ATR, Et2O):
m
1592, 1575 cmÀ1. HR-MS (FAB) calcd for [M]+ C30H52Br2Cu2N2P2
790.0530; found, 790.0530.
6. X-ray crystal structure determination of complex 3
4.2. Complex 4 Cu(CCPh)(L1H)
C
30H52Br2Cu2N2P2 + disordered solvent, Fw = 789.58[⁄], pale yel-
low plate, 0.68 Â 0.39 Â 0.02 mm3, monoclinic, C2/c (no. 15),
To a suspension of [CuBr(NPtBu)]2 3 (33.9 mg, 0.043 mmol) in
10 mL diethyl ether was added KOtBu (1 M solution in THF)
(0.086 mg, 0.086 mmol). The solution immediately turned orange,
indicating the formation of {Cu(L1)}. After stirring the reaction for
20 min., phenyl acetylene (8.8 mg, 0.086 mmol) was added by
syringe, leading to a color change to dark yellow. After stirring
for 2 h, the solution was filtered to remove salts and all volatiles
removed in vacuo to leave a yellow solid. Isolated yield: 26.1%
(9.3 mg, 0.086 mmol). Alternatively, complex 4 could be prepared
by stirring a suspension of NPtBu (329.0 mg, 1.31 mmol) and solid
Cu(phenylacetylide) (215.6 mg, 1.31 mmol) in 25 mL toluene for
18 h at r.t. Yield: 93.6% (509.8 mg, 1.31 mmol). Single crystals
were obtained by slow diffusion of pentane into a concentrated
a = 23.2103(15), b = 12.4802(7), c = 16.1383(9) Å, b = 123.830(4)°,
V = 3883.3(4) Å3, Z = 4, Dx = 1.351 g/cm3[⁄]
,
l .
= 3.26 mmÀ1[⁄]
29182 Reflections were measured on a Bruker Kappa ApexII dif-
fractometer with sealed tube and Triumph monochromator
(k = 0.71073 Å) up to a resolution of (sin h/k)max = 0.65 ÅÀ1 at a
temperature of 150(2) K. Intensity data were integrated with the
Eval14 software [29], taking a large anisotropic mosaicity about
hkl = (010) into account. An analytical absorption correction and
the scaling was performed with SADABS [30] (0.22–0.97 correction
range). 4442 Reflections were unique (Rint = 0.025), of which
3808 were observed [I > 2r(I)]. The structure was solved with
Direct Methods using the program SHELXS-97 [31] and refined with
SHELXL-97 [31] against F2 of all reflections. Non-hydrogen atoms
were refined with anisotropic displacement parameters. Hydrogen
atoms were introduced in calculated positions and refined with a
riding model. The crystal structure contains solvent accessible
voids (655 Å3/unit cell) filled with disordered solvent molecules.
Their contribution to the structure factors was secured by back-
Fourier transformation using the SQUEEZE routine of PLATON [32]
resulting in 153 electrons/unit cell). 179 Parameters were refined
CH2Cl2 solution. 1H NMR (400 MHz, (CD3)2CO):
d 7.61 (t,
JH = 7.6 Hz, 1H, ArH), 7.52 (br s, 1H, ArH), 7.17 (m, 2H, ArH),
7.11 (m, 3H, ArH), 7.01 (m, 1H, ArH), 3.33 (d, JPH = 4.8 Hz, 2H,
CH2), 2.81 (s, 3H, CH3), 1.29 (d, JPH = 12.4 Hz, 18H, tBu-H). 31P
NMR (162 MHz, (CD3)2CO): d 32.0 (br s).13C NMR (100 MHz,
(CD3)2CO): d 160.0 (d, JPC = 4.5 Hz, 1C, pyC), 159.3 (d, JPC = 9.1 Hz,
1C, pyC), 138.1 (s, 1C, pyCH), 131.6 (s, 2C, PhCH), 128.6 (s, 2C,
PhCH), 125.7 (s, 1C, PhCH), 122.5 (d, JPC = 3.8 Hz, 1C, pyCH),
122.1 (s, 1C, pyCH), 113.1 (s, 1C, PhC), 82.6 (d, JPC = 3.7 Hz, 1C,
Cu–C„C), 75.2 (s, 1C, C„C-Ph), 33.7 (d, JPC = 2.7 Hz, 2C, tBu-
CH3), 31.8 (d, JPC = 7.4 Hz, 1C, CH2), 30.1 (s, 6C, tBu-CH3), 26.0
with no restraints. R1/wR2 [I > 2r(I)]: 0.0230/0.0520. R1/wR2 [all
reflections]: 0.0313/0.0555. S = 1.108. Residual electron density be-
tween À0.38 and 0.43 e/Å3. Geometry calculations and checking
for higher symmetry were performed with the PLATON program
[32]. [⁄] derived values do not contain the contribution of the dis-
ordered solvent.
(d, JPC = 1.3 Hz, 1C, CH3). IR (ATR, Et2O):
m
2037, 1592, 1575 cm-
1
.
HR-MS (FAB) calcd for [MÀCCPh]+ C23H31CuNP 314.1099;
found, 314.1152.
7. X-ray crystal structure determination of complex 4
4.3. Complex 5 Cu(CCPh)(L2H)
C
46H62Cu2N2P2, Fw = 832.00, yellow plate, 0.21 Â 0.15 Â
3
To a solution of CuBr(PNPtBu) 1 (200 mg, 0.371 mmol) in 10 mL
diethyl ether was added a solution of NaN(SiMe3)2 (68.4 mg,
0.371 mmol) in 7 mL THF. The solution immediately turned orange,
indicating the formation of Cu(PNÀPtBu) 2. After stirring the reac-
tion for 15 min, phenyl acetylene (37.9 mg, 0.371 mmol) was
added by syringe, leading to a color change to light yellow. After
stirring for 1 h, the solution was evaporated to dryness. The crude
was then retaken in toluene, filtered over celite to separate salts,
and toluene was then removed in vacuo to leave a light-yellow
solid. Yield: 90 mg, 0.161 mmol, 43%. Alternatively, complex 3
can be prepared by stirring a suspension of PNPtBu (130 mg,
0.329 mmol) and solid Cu(phenylacetylide) (54.1 mg, 0.329 mmol)
in 20 mL toluene for 15 h at r.t. Yield: 84 mg, 0.150 mmol, 45%. 1H
NMR (400.13 MHz, CD3OD): d 7.87 (t, JH = 7.6 Hz, 1H, ArH), 7.50 (d,
JH = 7.6 Hz, 2H, ArH), 7.10–7.47 (m, 5H, ArH), 1.33 (d, JPH = 14.4 Hz,
36H, tBu-H). 31P NMR (CD3OD, 161.98 MHz): d 42.1 (br s). 13C NMR
(CD3OD, 100.62 MHz): d 141.4 (s, CHar), 133.0 (s, CHar), 129.7 (s,
CHar), 129.5 (s, CHar), 123.6 (s, CHar), 34.0 (t, JPC = 6.5 Hz, either
0.08 mm , triclinic, P1 (no. 2), a = 9.1681(4), b = 10.8102(4), c =
ꢀ
11.7608(5) Å,
a
= 96.7585(12), b = 112.5160(11),
c = 92.9488(12)°,
V = 1063.33(8) Å3, Z = 1, Dx = 1.299 g/cm3,
l
= 1.11 mmÀ1. 22911
Reflections were measured on a Bruker Kappa ApexII diffractome-
ter with sealed tube and Triumph monochromator (k = 0.71073 Å)
up to a resolution of (sin h/k)max = 0.65 ÅÀ1 at a temperature of
150(2) K. Intensity data were integrated with the SAINT software
[33]. An absorption correction based on multiple measured reflec-
tions and the scaling was performed with SADABS [30] (0.67–0.75
correction range). 4813 Reflections were unique (Rint = 0.025), of
which 4105 were observed [I > 2r(I)]. The structure was solved
with Direct Methods using the program SHELXS-97 [31] and refined
with SHELXL-97 [31] against F2 of all reflections. Non-hydrogen
atoms were refined with anisotropic displacement parameters.
All hydrogen atoms were located in difference Fourier maps and
refined with a riding model. 242 Parameters were refined with
no restraints. R1/wR2[I > 2r(I)]: 0.0259/0.0584. R1/wR2 [all reflec-
tions]: 0.0359/0.0618. S = 1.057. Residual electron density between
À0.24 and 0.38 e/Å3. Geometry calculations and checking for high-
er symmetry were performed with the PLATON program [32].
PC(CH3)3 or PCH2), 29.8 (t, JPC = 3.9 Hz, PC(CH3)3. IR (ATR, solid):
m
2036 cmÀ1. MS (FAB) 459.09 [MÀCCPh].

S.Y. de Boer et al. / Inorganica Chimica Acta 380 (2012) 336–342
341
(2009) 3146; (c) S.W. Kohl, L. Weiner, L. Schwartsburd, L. Konstantinovski,
L.J.W. Shimon, Y. Ben-David, M.A. Iron, D. Milstein, Science 324 (2009) 74; (e)
D.G.H. Hetterscheid, J.I. van der Vlugt, B. de Bruin, J.N.H. Reek, Angew. Chem.,
Int. Ed. 48 (2009) 8178.
Acknowledgements
This research was funded by an VENI Innovative Research grant
from the Netherlands’ Organisation for Scientific Research – Chem-
ical Sciences (NWO-CW Grant 700.56.403) to J.I.v.d.V., with further
financial support from the University of Amsterdam. We thank
Prof. Dr. Joost N.H. Reek for continuous interest in our work on
first-row transition metal cooperative catalysis. Support from the
EU-FP7 COST network CM0802 ‘PhoSciNet’ is appreciated as well.
Han Peeters is thanked for the HR-MS measurements and Dr. Evg-
eny A. Pidko (TU/e) for scientific discussions.
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Appendix A. Supplementary material
CCDC 834114 and 846882 contain the supplementary crystallo-
graphic data for complexes 3 and 4, respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2011.10.037.
[15] J.I. van der Vlugt, E.A. Pidko, D. Vogt, M. Lutz, A.L. Spek, Inorg. Chem. 48 (2009)
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