Bifunctional pincer-type organometallics as substrates for organic transformations and as novel building blocks for polymetallic materials

Article abstract of DOI:10.1021/ja0177657

The reactivity of the bifunctionalized ligand NC(Br)N-I 1 [IC₆H₂(CH₂NMe₂)₂- 3,5-Br-4] has been studied as a versatile synthon for organic and/or organometallic synthesis. Chemoselective metalation (M

Full text of DOI:10.1021/ja0177657

Published on Web 04/17/2002
Bifunctional Pincer-type Organometallics as Substrates for
Organic Transformations and as Novel Building Blocks for
Polymetallic Materials
Gema Rodr´ıguez,† Martin Albrecht,† Jeroen Schoenmaker,† Alan Ford,†
Martin Lutz,‡ Anthony L. Spek,‡,§ and Gerard van Koten*,†
Contribution from the Department of Metal-Mediated Synthesis, Debye Institute, and Department
of Crystal and Structural Chemistry, BijVoet Center for Biomolecular Research, Utrecht
UniVersity, Padualaan 8, 3584 CH Utrecht, The Netherlands
Received December 14, 2001
Abstract: The reactivity of the bifunctionalized ligand NC(Br)N-I 1 [IC6H2(CH2NMe2)2-3,5-Br-4] has been
studied as a versatile synthon for organic and/or organometallic synthesis. Chemoselective metalation (M
) Pd, Pt, Li) at the Caryl-I or Caryl-Br bonds was achieved by choosing the appropriate metal precursors.
In this way a series of PtII and PdII complexes were prepared that have a second functional group available
for further reactions. These PtII and PdII complexes were subjected to a wide range of organic and
organometallic reactions, revealing the remarkable stability of their M-C σ-bond and opening an easy
route for the synthesis of mono- and (hetero)bimetallic building blocks. The scope of the chemistry of such
building blocks shows that they are good candidates for use in the synthesis of dendrimers, bioorganometallic
systems, or polymetallic materials. The X-ray crystal structures of the most representative complexes
(2, 3a, 19, 20, and 24) are also reported.
Introduction
methodology, various complexes have been obtained that display
a high thermal stability paired with a high or unprecedented
Organometallic complexes are excellent functional units in
macroscopic devices, e.g., for application in catalysis1 and
sensing.2 Usually the introduction of the active site (the transition
metal) is the last step of the synthetic protocol of such systems
since the organometallic center is considered to be the most
labile and sensitive part of the device. A drawback of this
strategy is the often tedious separation of unreacted ligands and
metal residues due to incomplete metalation. Alternative strate-
gies that are based on metalated building blocks would
circumvent this issue. This new approach requires the avail-
ability of bifunctional ligands that can be selectively metalated
at one position only. This should provide stable organometallic
building blocks containing a second functional group for further
syntheses.
catalytic activity.4 Our work in this field has concentrated on
transition-metal complexes containing terdentate monoanionic
pincer ligands [C6H3{CH2NMe2}2-2,6-R]-, in particular those
that bond in the η3-mer-N,C,N coordination mode (Chart 1).5
In the course of these studies, various useful applications have
been identified in the fields of catalysis,6 sensors,7 and the
construction of switches.8 Therefore, we decided to study the
reactivity of the bifunctional ligand NC(Br)N-I 1 [NC(Br)N-I
is the abbreviation for IC6H2(CH2NMe2)2-3,5-Br-4, Chart 1] for
(transition) metal complexation. In this ligand a Caryl-Br bond
(3) Dehand, J.; Pfeffer, M. Coord. Chem. ReV. 1976, 18, 327-352.
(4) (a) Liu, F.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am.
Chem. Soc. 1999, 121, 4086-4087. (b) Liou, S.-Y.; van der Boom, M. E.;
Milstein, D. Chem. Commun. 1998, 687-688. (c) Herrmann, W. A.;
Brossmer, C.; Reisinger, C.-P.; Riermeier, T. H.; O¨ fele, K.; Beller, M.
Chem. Eur. J. 1997, 3, 1357-1364. (d) Gupta, M.; Hagen, C.; Kaska, W.
C.; Cramer, R. E.; Jensen, C. M. J. Am. Chem. Soc. 1997, 119, 840-841.
(e) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976, 1020-
1024.
(5) (a) Albrecht, M.; van Koten, G. Angew. Chem. 2001, 113, 3866-3898;
Angew. Chem., Int. Ed. 2001, 40, 3750-3781. (b) Rietveld, M. H. P.; Grove,
D. M.; van Koten, G. New J. Chem. 1997, 21, 751-771. (c) van Koten, G.
Pure Appl. Chem. 1989, 61, 1681-1694.
(6) See, for example, (a) Rodr´ıguez, G.; Lutz, M.; Spek, A. L.; van Koten, G.
Chem. Eur. J. 2002, 8, 45-57. (b) Dani, P.; Karlen, T.; Gossage, R. A.;
Gladiali, S.; van Koten, G. Angew. Chem. 2000, 112, 759-761; Angew.
Chem., Int. Ed. 2000, 39, 743-745. (c) Beletskaya, I. P.; Chuchurjukin,
A. V.; Dijkstra, H. P.; van Klink, G. P. M.; van Koten, G.; Tetrahedron
Lett. 2000, 41, 1075-1079. (d) Grove, D. M.; van Koten, G.; Verschuuren,
A. H. M. J. Mol. Catal. 1988, 45, 169-174.
A suitable methodology to stabilize the M-C bond involves
the principles of chelation, i.e. the formation of complexes
containing an M-C bond that is supported by intramolecular
(heteroatom) coordination to the metal center.3 By use of this
* Corresponding author: Phone +31-30-2533120; fax +31-30-2523615;
e-mail g.vankoten@chem.uu.nl.
† Department of Metal-Mediated Synthesis, Debye Institute.
‡ Department of Crystal and Structural Chemistry, Bijvoet Center for
Biomolecular Research.
§ Corresponding author for crystallographic data: Phone +31-30-
2532538; fax +31-30-2523940; e-mail a.l.spek@chem.uu.nl.
(1) (a) Halpern, J. Pure Appl. Chem. 2001, 73, 209-220. (b) Loch, J. A.;
Crabtree, R. H. Pure Appl. Chem. 2001, 73, 119-128. (c) Thomas, J. M.
Angew. Chem. 1999, 113, 3801-3843; Angew. Chem., Int. Ed. 1999, 38,
3588-3628. (d) Zamaraev, K. Pure Appl. Chem. 1997, 69, 865-876.
(2) See, for example, Beer, P. D.; Gale, P. A. Angew. Chem. 2001, 113, 502-
532; Angew. Chem., Int. Ed. 2001, 40, 486-516.
(7) See, for example, (a) Albrecht, M.; Gossage, R. A.; Lutz, M.; Spek, A. L.;
van Koten, G. Chem. Eur. J. 2000, 6, 1431-1445. (b) Albrecht, M.; van
Koten, G. AdV. Mater. 1999, 171-174.
(8) See, for example, (a) Albrecht, M.; Lutz, M.; Spek, A. L.; van Koten, G.
Nature 2000, 406, 970-974. (b) Steenwinkel, P.; Grove, D. M.; Veldman,
N.; Spek, A. L.; van Koten, G. Organometallics 1998, 17, 5647-5655.
9
10.1021/ja0177657 CCC: $22.00 © 2002 American Chemical Society
J. AM. CHEM. SOC. 2002, 124, 5127-5138
5127

A R T I C L E S
Rodr´ıguez et al.
Chart 1. η3-N,C,N-Bonded NCN-R Pincer Ligand in a
MXn(NCN-R)Lm Complex and the Bifunctional Ligand 1 That Can
Be Selectively Metalated
Table 1. Selected 1H NMR and 31P NMR Dataa
b
c
complex Caryl-H (3JH,Pt) ArCH N(3JH,Pt
)
NCH (3JH,Pt
)
aryl−H
δP (1JP,Pt
)
2
3
1
2
7.68
3.48
2.30
1.99
6.71 (57.3) 2.88
7.59-7.53 (m) 21.1 (3030.2)
7.33-7.23 (m)
3a
7.14
7.15
6.80
6.80
6.65
3.97 (46.2) 3.10 (38.0)
3.98 (46.8) 3.17 (38.0)
2.99
2.99
2.86
3b
4ad
4bd
5e
2.48
2.51
1.91
7.55-7.48 (m) 23.7d
7.39-7.34 (m)
7.30-7.25 (m)
7.97 (br)
7.35 (br)
6.41 (br)
Scheme 1. Chemoselective Metalation of the Bifunctional NCN
Ligand 1a
19
6.81
3.41
1.80
16.9 (2988.6)
20
21
6.13 (57.4) 3.30 (44.0) 2.98 (37.0) 7.71-7.55 (m) 22.3 (3091.6)
7.36-7.16 (m)
6.05
3.31 (45.8) 2.99 (39.2) 7.75-7.62 (m) 23.4d
7.57-7.44 (m)
7.42-7.24 (m)
22
23
6.10 (56.1) 3.26
6.06 3.29
2.81
2.79
7.60-7.51 (m) 22.5 (3071.7)
7.40-7.26 (m)
7.57-7.44 (m) 25.9
7.40-7.28 (m)
a Singlet signals from CDCl3 solutions unless otherwise stated; δ values
are given in parts per million, and J values are given in hertz. b In pincer
skeleton. c Of PPh3. d In C6D6. e In CD2Cl2.
a Reagents and conditions: (i) [Pt(PPh3)4], toluene, ∆, 20 h. (ii) [Pt(tol-
4)2(SEt2)]2, benzene, ∆, 2 h. (iii) [Pd(PPh3)4], toluene, 50 °C, 1 d. (iv)
[Pd2(dba)3‚CHCl3], toluene, -80 °C f RT. (v) (a) AgBF4, acetone/CH2Cl2
(1:1), RT, 30 min; (b) NaI, acetone, RT, 3 h.
and a more reactive Caryl-I bond are available for oxidative
addition or metal-halide exchange. Importantly, the two ortho-
chelating amine groups may support metalation but only at the
former position. Variation of metal precursor and reaction
conditions may therefore lead to chemoselective metalation,
since either kinetic (viz., the higher reactivity of the Caryl-I
bond) or thermodynamic arguments (viz., stability through
chelation) may dominate the outcome of the reaction. We report
on the selective preparation of these organometallic systems and
the scope and limitation of the resulting complexes as substrates
in subsequent organic and metal-mediated reactions. Further-
more, these studies provided access to new strategies for the
preparation of multimetallic materials such as periphery-
functionalized dendritic9 structures and polymers.10
Figure 1. Molecular plots of compounds (a) 2 and (b) 3a. The pincer ligand
in 2 is disordered and it was therefore partially refined with isotropic
displacement parameters. Only the major disorder component is displayed
here. The CH2Cl2 solvent molecule in 2 and hydrogen atoms in both
structures have been omitted for clarity.
Results and Discussion
Chemoselective Metalation of 1. Refluxing of equimolar
amounts of 1 and [Pt(PPh3)4] in toluene for 20 h afforded
selectively the oxidative addition product 2 (Scheme 1).11 The
aromatic protons of 2 provide a diagnostic probe for the site of
1
platination, since they appear in the H NMR spectrum as a
high-field singlet with satellites due to 195Pt-1H couplings (δH
3
) 6.71, JH,Pt ) 57.3 Hz) (Table 1).
Unequivocal confirmation of the proposed connectivity
pattern was obtained from a single-crystal structure determina-
tion of 2. The molecular structure is shown in Figure 1a and
relevant bond distances and angles are summarized in Table 2.
The overall structural features of 2 are similar to those of
related platinum complexes.12 The metal square-plane is slightly
(9) See, for example, (a) Kreiter, R.; Kleij, A. W.; Klein Gebbink, R. J. M.;
van Koten, G. Top. Curr. Chem. 2001, 217, 163-199. (b) Newkome, G.
R.; He, E.; Moorefield, C. N. Chem. ReV. 1999, 99, 1689-1746.
(10) See, for example, Manners, I. Angew. Chem. 1996, 108, 1712-1731; Angew.
Chem., Int. Ed. Engl. 1996, 35, 1602-1621.
(11) Manna, J.; Whiteford, J. A.; Stang, P. J. J. Am. Chem. Soc. 1996, 118,
8731-8732.
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5128 J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002

Bifunctional Pincer-type Organometallics
A R T I C L E S
Table 2. Selected Bond Lengths and Bond and Torsion Angles of Complexes 2, 3a, 19, 20, and 24
bond lengths (Å)
bond angles (deg)
torsion angles (deg)
Complex 2
176.95(4)
Pt-I
2.6944(4)
2.021(6)
2.3087(10)
2.3068(11)
P1-Pt-P2
I-Pt-C41
I-Pt-P1
I-Pt-P2
Pt-C41-C51-C61
-173.7(4)
172.4(3)
-101.8(3)
74.6(4)
80.1(3)
-103.6(4)
Pt-C41
Pt-P1
Pt-P2
171.9(3)
88.64(3)
93.99(3)
C21-C31-C41-Pt
P1-Pt-C41-C31
P1-Pt-C41-C51
P2-Pt-C41-C31
P2-Pt-C41-C51
Complex 3a
Pt-Br
Pt-C1
Pt-N1
Pt-N2
2.5355(10)
1.927(8)
2.090(7)
2.085(7)
Br-Pt-C1
N1-Pt-N2
Br-Pt-N1
Br-Pt-N2
178.3(2)
163.5(3)
98.09(19)
98.3(2)
Pt-C1-C2-C3
Pt-C1-C6-C5
C1-C2-C7-N1
C1-C6-C10-N2
-178.6(7)
178.7(7)
-24.9(12)
-23.6(12)
Complex 19
Pt-I
2.6979(3)
2.040(3)
2.3132(9)
2.3129(9)
I-Pt-C1
I-Pt-P1
I-Pt-P2
P1-Pt-P2
175.74(10)
92.16(2)
89.34(2)
Pt-C1-C2-C3
Pt-C1-C6-C5
P1-Pt-C1-C2
P1-Pt-C1-C6
P2-Pt-C1-C2
P2-Pt-C1-C6
175.9(2)
-176.1(2)
92.2(2)
-90.1(3)
-85.6(2)
92.1(3)
Pt-C1
Pt-P1
Pt-P2
177.44(3)
Complex 20
Pt1-I1
Pt2-I2
Pt1-C1
Pt2-C4
Pt1-N1
Pt1-N2
Pt2-P1
2.7375(5)
2.7098(6)
1.925(5)
2.021(5)
2.090(5)
2.083(4)
2.3001(11)
I1-Pt1-C1
I2-Pt2-C4
N1-Pt1-N2
I1-Pt1-N1
I1-Pt1-N2
I2-Pt2-P1
P1-Pt2-P1a
179.62(16)
168.46(16)
162.91(18)
98.90(13)
98.19(12)
91.01(2)
Pt1-C1-C2-C3
Pt1-C1-C6-C5
C1-C6-C7-N2
C1-C2-C9-N1
P1-Pt2-C4-C5
P1-Pt2-C4-C3
180.01
180.01
32.0(5)
42.4(5)
84.52(3)
-95.48(3)
169.05(5)
Complex 24
Pt-I1
2.7094(7)
1.931(7)
2.085(5)
2.092(5)
I1-Pt-C1
N1-Pt-N2
I1-Pt-N1
I1-Pt-N2
178.68(18)
163.1(2)
98.15(15)
98.70(17)
Pt-C1-C2-C3
Pt-C1-C6-C5
C1-C2-C7-N1
C1-C6-C10-N2
-179.3(5)
177.9(5)
21.9(7)
Pt-C1
Pt-N1
Pt-N2
24.4(8)
distorted and includes trans-positioned phosphine groups [P1-
Pt-P2 and C41-Pt-I are 176.95(4)° and 171.9(3)°, respec-
tively]. The aromatic ring of the monodentate pincer ligand has
nearly perpendicular orientation to the metal coordination plane
[torsion angle P1-Pt-C41-C31 is -101.8(3)°]. The metal-
carbon bond [Pt-C41 2.021(6) Å] is significantly longer than
in complexes where this bond is supported by chelating
phosphine or nitrogen donors (typically 1.90-1.95 Å, vide
infra). Because of the absence of the chelating coordination,
the pincer ligand is disordered in the crystal.
The present results suggest that coordination of one or both
amine substituents in 1 to the platinum center in the metal
precursor [Pt(tol-4)2(SEt2)]2 must be a key interaction during
the formation of 3a, which leads to attack of the Caryl-Br and
not the Caryl-I bond.
Interestingly, palladation of 1 with [Pd2(dba)3‚CHCl3] as the
metal precursor required low temperatures (-80 °C, toluene
solution) and again occurs selectively into the Caryl-Br bond,
affording pure complex 4a as a yellowish solid (Scheme 1).
The organopalladium complex 4a contains the pincer ligand in
the well-established N,C,N-terdentate bonding mode, which was
established by comparison of the spectroscopic data of 4a with
those of related complexes.14b,15
Chemoselective platinum insertion into the C-Br bond of 1
and formation of complex 3a (Scheme 1) was performed
following a method recently described by Canty et al.13 The
reaction of a benzene solution of 1 with a stoichiometric amount
of the metal precursor [Pt(tol-4)2(SEt2)]2 afforded complex 3a
within 2 h. To unambiguously establish the proposed structure
and hence the selectivity of the platination reaction a single-
crystal structure determination of 3a was performed (Figure 1b,
relevant bond distances and angles in Table 1).
The molecular structure of 3a shows a PtII center in a distorted
square-planar environment and embedded in the coordination
pocket of the terdentate N,C,N framework of the pincer ligand,
which is in agreement with other similar, earlier reported, PtII
complexes.14 A short Pt-C σ-bond [Pt-C1 1.927(8) Å] due to
rigid chelation of the amine groups is noted.
Opposite results were obtained with palladium(0) precursors
containing phosphine ligands. Treatment of a toluene solution
of 1 with [Pd(PPh3)4] at 50 °C for 1 day induced the oxidative
addition of the palladium(0) precursor to 1 via selective Caryl-I
bond activation and complex 5 was isolated as the single product
(Scheme 1). Assignment of the structure of 5 was done on the
basis of spectroscopic data, which are in agreement with those
obtained for 2 (Table 1) and for related palladium(II) complexes
containing a NCN pincer ligand without a bromide substituent.16
(14) (a) Terheijden, J.; van Koten, G.; Muller, F.; Grove, D. M.; Vrieze, K.;
Nielsen, E.; Stam, C. H. J. Organomet. Chem. 1986, 315, 401-417. (b)
van Koten, G.; Timmer, K.; Noltes, J. G.; Spek, A. L. J. Chem. Soc., Chem.
Commun. 1978, 250-252.
(15) Alsters, P. L.; Baesjou, P. J.; Janssen, M. D.; Kooijman, H.; Sicherer-
Roetman, A.; Spek, A. L.; van Koten, G. Organometallics 1992, 11, 4124-
4135.
(12) Manna, J.; Kuehl, C. J.; Whiteford, J. A.; Stang, P. J. Organometallics
1997, 16, 1897-1905.
(13) Canty, A. J.; Patel, J.; Skelton, B. W.; White, A. H. J. Organomet. Chem.
2000, 599, 195-199.
(16) Spee, M. P. R.; Ader, B.; Steenwinkel, P.; Kooijman, H.; Spek, A. L.; van
Koten, G. J. Organomet. Chem. 2000, 598, 24-27.
9
J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002 5129

A R T I C L E S
Rodr´ıguez et al.
Scheme 2. Chemoselective Lithiation of the Bifunctional NCN
Ligand 1a
Scheme 3. Pincer-PtII Complexes for Organic Transformations
a Reagents and conditions: (i) t-BuLi, Et2O, -100 °C. (ii) DMF. (iii)
[Pt(tol-4)2(SEt2)]2, benzene, ∆, 2 h. (iv) [Pd(dba)2‚CHCl3], toluene, -80
°C f RT.
Strict temperature control of this reaction appeared to be
essential, since at lower temperatures (25 °C) only starting
material was recovered, whereas at more elevated temperatures
(80 °C) other metalated products were obtained that could not
be identified.
Finally, a two-step procedure that gives a similar outcome
as route A involves first reaction of t-BuLi (1.9 equiv) with an
Et2O solution of 1 at -100 °C. This afforded quantitative and
selective lithium-iodide exchange to yield the aryllithium
compound 6 (Scheme 2, cf. formation of 5 in route A).
The chemoselectivity of this reaction was unequivocally
demonstrated by quenching a freshly formed solution of 6 at
-80 °C with dry dimethylformamide (DMF), giving rise to the
also bifunctionalized pincer ligand 7. Selective metalation of 7
was achieved by applying a similar protocol as shown for 1.
Reaction of 7 with [Pt(tol-4)2(SEt2)]2 and [Pd2(dba)3‚CHCl3]
gave the corresponding complexes 8a and 9, respectively
(Scheme 2). The aldehyde moiety of 7 remains unaffected and
is accessible for further functionalization.
Organometallic Substrates for Organic Transformations.
The observed high selectivity of 1 toward different metalating
agents gives access to molecules containing two functional sites,
i.e., a (potentially catalytically) active organometallic site and
an organic site accessible for further transformations. Extended
stability of the M-C σ-bond has been illustrated recently for
pincer-type systems comprising two supporting M-N bonds.19
For example, Si-O bond cleavage in the organometallic silyl
ether 10 occurs quantitatively in the presence of Bu4NF to give
the corresponding organoplatinum phenol [PtCl(NCN-OH)] 11
(Scheme 3).19d
Hence, reaction conditions have been established that promote
oxidative addition of a palladium or platinum precursor selec-
tively to either the Caryl-I bond (route A, Scheme 1) or the
Caryl-Br bond (route B, Scheme 1), leaving the other carbon-
halide bond of the ligand precursor unaffected. This chemose-
lectivity is remarkable, since it is well-known that oxidative
addition of transition metals to aryl halides follows the order
ArI > ArBr . ArCl.17 Oxidative addition of [M(PPh3)4] to 1
(i.e., route A) proceeds according to this reactivity sequence
and obviously is kinetically controlled, whereas the opposite
selectivity is observed when the phosphine-free compounds [Pt-
(tol-4)2(SEt2)]2 and [Pd2(dba)3‚CHCl3] are used as metal precur-
sors (route B), and therefore the thermodynamic products 3a
and 4 were obtained.18 In route B, prior coordination of the
nitrogen donor atoms of 1 to the metal center can occur since
the metal precursor lacks strongly bound ligands. This directs
the addition of the metal to the Caryl-Br bond, which as a
consequence leaves the C-I bond unaffected. Apparently when
[M(PPh3)4] is used, phosphine coordination to platinum or
palladium reduces the relevance of the nitrogen donors of 1
significantly since the M-P bond is considerably stronger than
the corresponding M-N bond. Consequently the more reactive
C-I bond is preferentially cleaved.16 In either case, a reactive
C-X bond (X ) Br in 2 and 5, X ) I in 3a and 4a) remains
available for further functionalization.
Subsequent esterification of the phenolic OH-group with
various acid chlorides was also achieved with full conservation
(17) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and
Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987.
(18) Although no oxidative addition of [Pd2(dba)3‚CHCl3] to the Caryl-I bond
of 1 has been observed, it cannot be excluded with the present data.
However, if such a hypothetical complex would indeed be formed, it is, in
contrast to the characterized complex 4, apparently not stable enough and
reductive elimination takes place, affording the starting materials again.
(19) (a) Albrecht, M.; Hovestad, N.; Boersma, J.; van Koten, G. Chem. Eur. J.
2001, 7, 1289-1294. (b) Albrecht, M.; Gossage, R. A.; Spek, A. L.; van
Koten, G. Chem. Commun. 1998, 1003-1004. (c) Davies, P. J.; Grove, D.
M.; van Koten, G. Organometallics 1997, 16, 800-802. (d) Davies, P. J.;
Veldman, N.; Grove, D. M.; Spek, A. L.; Lutz, B. T. G.; van Koten, G.
Angew. Chem. 1996, 108, 2078-2081; Angew. Chem., Int. Ed. Engl. 1996,
35, 1959-1961.
9
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Bifunctional Pincer-type Organometallics
A R T I C L E S
Table 3. Resistance of the NCN-Metal Site during Transformations of the Para Functional Center under Specific Reaction Conditions
M
functional group
type of reaction
desilylation
reagents, conditions
BuF4N
HCl (2 N), 55 °C
acid chloride, amine
alkyl bromide, K2CO3
NaOH, 80 °C
amine
Ph3PdCHPh
LiAlH4
NaBH4
NaCNBH3
acetylene, Pd-cat
[M(PPh3)4]
resistance of Pt
resistance of Pd
Pt or Pd
Pt or Pd
Pt or Pd
Pt or Pd
Pt
Ar-OSiMe2tBu
Ar-OSiMe2tBu
Ar-OH
Ar-OH
Ar-OH
stable
stable
stable
stable
decomposes
stable
decomposes
decomposes
decomposes
stable
stable
decomposes
stable
desilylation
etherification
esterification
deprotonation
Schiff base reaction
Wittig reaction
reduction
reduction
reduction
Sonogashira coupling
oxidative addition
lithiation
stable
Pt
Pt
Pt
Pt
Ar-CHO
Ar-CHO
Ar-CHO
Ar-CHO
Ar-CHO
Ar-I
Pt or Pd
Pt or Pd
Pt or Pd
Pt or Pd
decomposes
stable
stable
stable
stable
stable
Ar-I
Ar-I
t-BuLi, 100 °C
decomposes
Scheme 4. Pincer-PtII Complexes for Organic Transformationsa
of the platinum-carbon bond.7a,19b,c Similarly, etherification
reactions of 10 with benzyl bromides has been successfully
applied for dendrimer synthesis.19a These results prompted us
to use para-functionalized pincer-platinum complexes and their
palladium analogues as substrates for organic transformations.
The applied reaction range from mild organic transformations
to relatively harsh metal-mediated procedures are compiled in
Table 3.
The organometallic substrate 11 can be prepared from the
corresponding silyl ether 10 with HCl in air as an alternative
procedure to fluoride-mediated O-Si bond cleavage.19d Quan-
titative deprotection with 2 N aqueous HCl in acetone occurred
at room temperature in 24 h and at 55 °C already in 5 h.
Platinum(IV) products from metal oxidation have not been
detected under these reaction conditions but start to appear when
the reaction mixture is left at elevated temperature for prolonged
periods (12 h). Although the detailed mechanism of this reaction
is not yet understood, it might involve the formation of a highly
reactive arenium intermediate A (Scheme 3), which originates
from oxidative addition of HCl to the metal center and
subsequent shift of the proton along the Pt-C bond. Similar
complexes have been reported to be highly reactive and to
readily cleave the oxygen-silicon bond, thus resulting in the
elimination of the tert-butyldimethylsilyl group.20
The resistance of the η3-N,C,N-coordinated NCN-platinum
unit toward an acidic or oxidizing environment prompted us to
further investigate these complexes as organometallic substrates
for reductions. The reaction of [PtBr(NCN)] with LiAlH4 has
been reported to yield decomposition products, probably via
formation of a highly unstable complex containing a platinum-
bound hydride, although the expected halfway-formed cationic
intermediate [NCNPtHPtNCN]+ is stable.21 This undesired
reactivity was anticipated to be circumvented by use of NaBH4
as reducing agent, since LiAlH4 and NaBH4 are often comple-
mentary in terms of reactivity.22 When a solution of 8a was
treated with NaBH4 (2.0 equiv) in methanol at 0 °C, 50%
conversion to the benzylic alcohol 14 was observed after 30
min (Scheme 4).
a Reagents and conditions: (i) AcOH, NaBH3CN, MeOH, 10 °C f RT,
1 h. (ii) (a) L-Val-OMe‚HCl, NEt3, RT, 12 h; (b) AcOH, NaBH3CN, MeOH,
10 °C f RT, 2 h.
protons. Unfortunately, longer reaction times led to decomposi-
tion products and pure 14 could not be isolated from this
reaction. Ultimately, the aldehyde functionality in 8a was
successfully reduced by using NaBH3CN as a less reactive
hydride source. Treatment of a methanol solution of 8a and
AcOH (1.0 equiv) at a temperature below 10 °C with NaBH3-
CN (2.0 equiv) led to the stable platinated complex 14.
The remarkable stability of the pincer-platinum(II) unit
toward reducing conditions has been applied in, for example,
the functionalization of biologically active substances with
pincer-metal units.23 Thus, covalent attachment of the pincer-
platinum building block 8a, via the aldehyde functionality, to
the N-terminus of the C-protected amino acid Val-OMe was
achieved under Schiff base reaction conditions. Subsequent
reduction of the resulting imine with NaBH3CN gave the
N-functionalized amino acid 15 in good yields (Scheme 4).
The NCN-palladium site is less resistant to these reagents
than the corresponding platinum analogues. For example,
reaction of the palladium analogue of 10 with HCl leads to
concomitant Si-O and Pd-C bond cleavage (Scheme 3).24
Also, NaBH3CN-mediated reduction reactions with the pal-
ladium complex 9 failed and the expected benzylic alcohol was
1
not obtained. H NMR analysis of the crude reaction mixture
clearly revealed that the nitrogen groups are not coordinated to
the Pd center since the resonance signals of the ArCH2N and
the NMe2 protons appeared at a field typical for the metal-free
ligand precursor. Moreover, the presence of one signal at 10
ppm typical for aldehyde moieties and another one at 7.58 ppm
The presence of 14 was clearly indicated by a new singlet in
the 1H NMR spectrum at 4.50 ppm for the benzylic ArCH2OH
and a reduced integral of the resonance due to the aldehyde
(20) Albrecht, M.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2001, 123,
7233-7246.
(21) (a) Terheijden, J.; van Koten, G.; Grove, D. M.; Vrieze, K.; Spek, A. L. J.
Chem. Soc., Dalton Trans. 1987, 1359-1366. (b) Grove, D. M.; van Koten,
G.; Ubbels, H. J. C.; Spek, A. L. J. Am. Chem. Soc. 1982, 104, 4285-
4286.
(23) Albrecht, M.; Rodr´ıguez, G.; Schoenmaker, J.; van Koten, G. Org. Lett.
2000, 2, 3461-3464.
(24) Notably, the softer deprotection method using fluoride anions induces Si-O
bond cleavage and affords the desired organopalladium phenol in good
yields.
(22) March, J. AdVanced Organic Chemistry; 4th ed., Wiley: New York, 1992.
9
J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002 5131

A R T I C L E S
Rodr´ıguez et al.
Scheme 5. Metal-Mediated Transformations of Pincer-MII
NCN-platinum but also the NCN-palladium complex proved
to be suitable substrates. Compound 5 is the proposed inter-
mediate in the Sonogashira coupling with 1 as substrate.29
Accordingly, stoichiometric amounts of 5 were reacted with
trimethylsilylacetylene in Et2NH as a solvent, affording the
exclusive formation of ligand 18.30 Thus, the transformation of
3a and 4a into the acetylenic products 16 and 17, respectively,
involves the transient formation of a (hetero)bimetallic arenediyl-
bridged intermediate B (Scheme 5).
Complexesa
(Hetero)Bimetallic Complexes as Building Blocks for New
Materials. Bimetallic transition-metal complexes with π-delo-
calized bridging ligands display intriguing electronic and
photophysical properties since electronic “communication”
between the metal centers is facilitated.31 Therefore, such species
can be used as building blocks for the synthesis of conducting
organometallic oligomers and polymers (“molecular wires”)32
and for materials exhibiting nonlinear optical (NLO) properties.33
This wide range of possible applications prompted us to study
the synthesis and isolation of stable bimetallic complexes from
ligand 1 by a double oxidative addition strategy. The results
obtained in the Sonogashira C-C coupling reaction are already
good evidence for the formation of these systems since the
heterobimetallic complex B (Scheme 5) is supposed to be a key
intermediate.
a Reagents and conditions: (i) [PdCl2(PPh3)2], CuI, Et2NH, RT, 12 h.
(ii) Me3SiCtCH. (iii) Me3SiCtCH, Et2NH, RT, 12 h.
(both integrate for one proton) suggested that the borohydride
reagent is preferentially consumed by addition to the Pd-C bond
rather than to the CdO aldehyde functionality.
Notably, bases such as NaNH2, NaOMe, n-BuLi, or other
n-alkyllithium reagents25 except for t-BuLi (vide infra) have
been found to be incompatible with all of the studied complexes
since they promote demetalation reactions. This susceptibility
of the M-C bond to nucleophilic bases may be due to an anion
exchange of the base with the metal-bound halide and subse-
quent decomplexation, perhaps via R- or â-hydrogen elimination
pathways. Accordingly, Wittig-type reactions with 8a as the
substrate failed due to the presence of NaOMe for ylide
formation.
Palladium-mediated C-C bond formation reactions at the
para position of pincer-metal complexes have been examined
by using substrates 3a and 4, which both contain, in addition
to a C-M bond, a reactive Caryl-I bond. For example, Caryl-Caryl
bond formation was probed by using the Suzuki coupling
protocol.26 However, even after prolonged heating of the
platinum(II) complex 3a in the presence of PhB(OH)2 and
catalytic amounts of a suitable palladium salt and Na2CO3, the
anticipated coupling was not observed. Instead, the starting
material 3a was recovered along with another organoplatinum
product, which most probably resulted from bonding of a
derivative of the boronic acid to the metal center of the NCN-
platinum complex.
A logical strategy for the preparation of such bimetallic
complexes comprises the oxidative addition of [M(PPh3)4] to
the aryl-iodide bond of 3. Previous reports have shown,
however, that the hard amine ligands in cyclometalated platinum
complexes are replaced quantitatively by PPh3.14b,34 Since the
oxidative addition of [M(PPh3)4] includes the release of PPh3,
partial substitution of the amines in 3 and hence product
mixtures such as C were expected (Scheme 6). To avoid this,
phosphine complex 19 has been used as starting material
(Scheme 6). This complex was readily obtained after 3a was
first stirred in a NaI/acetone mixture and subsequently in
benzene in the presence of stoichiometric amounts of PPh3. The
singlet at 16.88 ppm in the 31P NMR spectrum (1JPtP ) 2988.6
Hz) is indicative for platinum-bound PPh3 groups in mutual trans
position.
An X-ray crystal structure determination of 19 confirmed the
proposed connectivity pattern (Figure 2; relevant bond distances
and angles are given in Table 1). The molecular structure of 19
shows a square-planar platinum(II) complex that possesses two
PPh3 ligands in mutual trans configuration and a monodentate
η1-C-bonded NCN ligand, i.e. the two o-amino substituents are
not coordinated. The coordination plane of the platinum(II)
center is perpendicular to the NCN plane, which is in agreement
with the structural features of other closely related compounds
earlier reported.34 This perpendicular conformation has also been
found for 2 containing a Pt-C bond at the para position of the
NCN site (cf. Figure 1a).
Milder reaction conditions, which avoid the use of inorganic
bases such as Na2CO3 (vide supra), are used in the Sonogashira
reaction.27 Reaction of 3a with (trimethylsilyl)acetylene in the
presence of catalytic amounts of CuI and [PdCl2(PPh3)2]
afforded the desired para-alkynylated NCN-Pt(II) complex 16
in reasonable yield (60%; Scheme 5).28
The same reactivity and stability were observed for the
NCN-Pd complex 4a, i.e., under these conditions, not only the
(29) Katritzky, R. A.; Meth-Cohn, O.; Rees, W. C. ComprehensiVe Organic
Functional Transformations, Pergamon: Oxford, U.K., 1995.
(30) Back, S.; Albrecht, M.; Spek, A. L.; Rheinwald, G.; Lang, H.; van Koten,
G. Organometallics 2001, 20, 1024-1027.
(25) In contrast, aryllithium compounds or lithium acetylides react with NCN-
platinum and palladium halide complexes in an anion-exchange reaction;
for details, see ref 14a.
(26) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457-2483.
(27) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron, Lett. 1975, 16,
4467-4470. (b) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara,
N. Synthesis 1980, 627-630.
(28) James, S. L.; Verspui, G.; Spek, A. L.; van Koten, G. Chem. Commun.
1996, 1309-1310.
(31) Sauvage, J.-P.; Collin, J.-P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.
Chem. ReV. 1994, 94, 993-919.
(32) Martin, R. E.; Diederich, F. Angew. Chem. 1999, 111, 1440-1469; Angew.
Chem., Int. Ed. 1999, 38, 1350-1357.
(33) Long, N. J. Angew. Chem. 1995, 107, 37-54; Angew. Chem., Int. Ed. Engl.
1995, 34, 21-38.
(34) Albrecht, M.; Dani, P.; Lutz, M.; Spek, A. L.; van Koten, G. J. Am. Chem.
Soc. 2000, 122, 11822-11833.
9
5132 J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002

Bifunctional Pincer-type Organometallics
A R T I C L E S
Scheme 6. Synthesis of (Hetero)Bimetallic Complexesa
Figure 3. Displacement ellipsoid plot (50% probability) of the pincer-
diplatinum(II) compound 20. The pincer ligand is disordered over the
crystallographic mirror plane of space group Pnma. Only one disorder
component is shown. Hydrogen atoms and the C6H6 solvent molecule have
been omitted for clarity. Symmetry operation: x, 0.5 - y, z.
a Reagents and conditions: (i) (a) AgBF4, acetone/CH2Cl2, RT, 30 min;
(b) NaI, acetone, RT, 12 h. (ii) PPh3, benzene, RT, 12 h. (iii) [Pt(PPh3)4],
toluene, 50 °C, 12 h. (iv) [Pd(PPh3)4], toluene, RT, 15 min.
clearly reflected by the Pt-C bond length, which is shorter in
the η3-N,C,N platinum moiety than in the η1-C platinum
monodentate site [cf. Pt1-C1 1.925(5) Å vs Pt2-C4 2.021(5)
Å]. Notably, the NCN aryl ring is disordered over a crystal-
lographic mirror plane and is therefore essentially perpendicular
to the coordination plane of Pt2 containing symmetry-related
phosphine ligands.
Remarkably, the expected compound C has not been detected.
Instead the Pt center, which is initially η1-C-bound in 19, has
become η3-N,C,N-coordinated in 20. Species C may be an
unstable intermediate rather than an end product as a result of
the steric hindrance of the four PPh3 groups at the para positions.
It must be noted that the repulsion of the ortho substituents on
the bridging arene ring would force the two coordination planes
and the arenediyl ring to be in mutually perpendicular orienta-
tions.
Figure 2. Displacement ellipsoid plot (50% probability) of compound 19.
Hydrogen atoms and the disordered CH2Cl2 solvent molecules have been
omitted for clarity.
Moreover, bimetallic complexes 20 and 21 were also directly
prepared from 3b and [M(PPh3)4]. Indeed, formation of the
1
intermediate C could be observed by H NMR, but as earlier
Metal insertion into the para Caryl-I bond of the η1-C pincer-
platinum compound 19 was accomplished by oxidative addition
with stoichiometric amounts of [M(PPh3)4] (M ) Pt, Pd). These
reactions afforded the homobimetallic Pt2 species 20 and the
heterobimetallic analogue 21, respectively (Scheme 6). Most
interestingly, the formed product showed only one type of
indicated, these compounds were not stable enough and they
converted within 1 h into 20 and 21, respectively.
Metal insertion into the para Caryl-Br bond of the η1-C
pincer-platinum complex 2 was also accomplished by oxidative
addition of [Pd(PPh3)4]. This procedure gave the corresponding
bimetallic complex 22 with an η3-N,C,N-coordinated palladium
center (Scheme 7). Notably, scrambling of the palladium-bound
halide was observed during this reaction, thus affording a
mixture of iodide and bromide species. Complete anion
exchange was accomplished by addition of NaI. The NMR
1
platinum-bound phosphines (δP ) 22.3, JPtP ) 3091.6 Hz for
1
20, δP ) 23.4 for 21). Moreover, the H NMR spectra of both
complexes clearly reveal 195Pt satellites on the resonances
attributed to the ArCH2N and NMe2 protons. This strongly
indicates that the nitrogen donors of the NCN ligand are
coordinated to the platinum center. A single-crystal structure
determination of 20 unambiguously confirmed these assign-
ments. The molecular structure is depicted in Figure 3 and shows
two square-planar platinum(II) centers that are interconnected
by the aryl ring of the NCN ligand.
spectroscopic properties of 22 are closely related to those of
195
the parent platinum complexes 20 and 21, except for the
-
Pt-1H couplings (3JPtH ) 56.1 Hz, Table 1) for the aromatic
protons, which were not observed in 21.
The synthesis of the bispalladated complex 23 required the
preparation and immediate reaction of 4b with [Pd(PPh3)4] due
to its low stability. The resulting bimetallic complex is more
stable than 4b and could be easily analyzed (Scheme 7).
Another interesting and successful strategy toward the
preparation of bimetallic complexes involves the substitution
One platinum center is bound to two phosphine ligands as
well as via an η1-C bond to the para position of the pincer ligand.
The other metal center is bound in a well-established η3-N,C,N
terdentate coordination mode.14 The difference in binding is
9
J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002 5133

A R T I C L E S
Rodr´ıguez et al.
Scheme 7. Synthesis of Pincer-(Hetero)Bimetallic Complexesa
Scheme 8. Synthesis of Organometallic Polymers (cf. 25) and
Dendrimer Mimics (cf. 24) from Pincer-Platinum Building Blocksa
a Reagents and conditions: (i) [Pd2(dba)3‚CHCl3], benzene, ∆, 15 min.
(ii) NaI, acetone, RT, 12 h. (iii) (a) AgBF4, acetone/CH2Cl2, RT, 30 min;
(b) NaI, acetone, RT, 12 h. (iv) [Pd(PPh3)4], benzene, 0 °C, 1 h.
of an aryl-bound halide by a lithium/halide exchange reaction.
When a tetrahydrofuran (THF) solution of 3a at -100 °C was
treated with t-BuLi (2.0 equiv), lithium/iodide exchange took
place and a bimetallic Li/Pt species D was formed (Scheme 8).
The chemoselectivity of the lithiation was unambiguously
demonstrated by quenching this solution with DMF, which
yielded the air-stable aldehyde 8a. Remarkably, the η3-N,C,N-
metal unit remains unaffected during this two-step process.
Concomitant formation of LiI caused partial anion exchange,
which was completed by subsequent addition of excess NaI.
This reaction sequence afforded the iodide compound 8b.
The selective reactivity patterns and the outstanding stability
properties of the η3-N,C,N-pincer platinum unit toward alkyl-
lithium reagents have been used for the development of a novel
straightforward protocol for the synthesis of metallodendrimers
containing one or several pincer-(transition) metal sites in their
structure (at the core or periphery). Metallodendrimers have
found use as homogeneous catalysts, light-harvesting antennas,
and sensor materials.35
a Reagents and conditions: (i) t-BuLi, Et2O, -100 °C. (ii) (a) DMF; (b)
AgBF4, acetone, RT; (c) NaI, acetone, RT. (iii) Me3SiCl. (iv) HCl. (v) Ac2O/
D2O. (vi) NaI.
So far, peripheral functionalization of carbosilane dendrimers
with catalytically active NCN-metal moieties has been ac-
complished by coupling of the para-lithiated pincer ligand
precursor with Si-Cl bonds on the dendritic periphery, followed
by metal insertion para to the Si-C bond.36 This metalation is
often incomplete, especially for higher-generation dendrimers
containing a large number of peripheral sites, thus causing the
introduction of mistakes in the dendritic structure of the
metallodendrimer. The use of organometallic building blocks
Figure 4. Displacement ellipsoid plot (50% probability) of p-silyl-
functionalized pincer-PtII 24. Hydrogen atoms have been omitted for clarity.
such as 3 avoids this final metalation step and provides
convergent synthetic protocols for the synthesis of periphery-
functionalized dendritic structures. We have tested this approach
by reacting lithiated 3b with Me3SiCl as the simplest model
substrate of a reactive carbosilane dendritic surface. This
afforded 24 containing a new para C-Si bond in nearly
quantitative yield (Scheme 8). According to NMR spectroscopy
and also an X-ray structure determination (see Figure 4), no
metal decomplexation occurred under these reaction conditions.
(35) See, for example, (a) Fischer, M.; Vo¨gtle, F. Angew. Chem. 1999, 111,
934-955; Angew. Chem., Int. Ed. 1999, 38, 884-905. (b) Hearshaw, M.
A.; Moss, J. R. Chem. Commun. 1999, 1-8. (c) Newkome, G. R.; He, E.;
Moorefield, C. N. Chem. ReV. 1999, 99, 1689-1746. (d) Bosman, A. W.;
Janssen, H. M.; Meijer, E. W. Chem. ReV. 1999, 99, 1665-1688.
(36) For examples, see (a) Kleij, A. W.; Gossage, R. A.; Klein Gebbink, R. J.
M.; Brinkmann, N.; Reijerse, E. J.; Kragl, U.; Lutz, M.; Spek, A. L.; van
Koten, G. J. Am. Chem. Soc. 2000, 122, 12112-12124. (b) Ko¨llner, C.;
Pugin, B.; Togni, A. J. Am. Chem. Soc. 1998, 120, 10274-10275. (c) Reetz,
M. T.; Lohmer, G.; Schwickardi, R. Angew. Chem. 1997, 109, 1559-1562;
Angew. Chem., Int. Ed. Engl. 1997, 36, 1526-1529. For exceptions, i.e.,
metal insertion before the last steps, see e.g. ref 15 and (d) Constable, E.
C. Chem. Commun. 1997, 1073-1080.
9
5134 J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002

Bifunctional Pincer-type Organometallics
A R T I C L E S
oxide (Merck). Please note that a full description of the experimental
procedures and analytical data for the synthesis of compound 1 has
been deposited as Supporting Information. The metal salts [Pt(tol-4)2-
(SEt2)]2,39 [Pd2(dba)3‚CHCl3],40 and [Pd(PPh3)4]40 and complex 1019d
were synthesized according to literature procedures. All other chemicals
were obtained commercially and used without further purification. NMR
spectra were recorded at 25 °C and were referenced to SiMe4 (δ )
Strict control of the temperature is essential during the lithium/
halide exchange reaction of 3b, since selective para-lithiation
of 3b occurs selectively only at temperatures around -100 °C.
At higher temperatures a white precipitate formed, which was
isolated by repeated washing with THF. The material, which
appeared to be insoluble in water and common organic solvents,
has been tentatively assigned a polymeric structure [Pt(NCN)]n
25 (Scheme 8). Such a product may result from substitution of
the metal-bound halide by the aryl anion of the pincer-lithium
species, which is known to give complexes of the type [Pt-
(aryl)(NCN)] containing a new Pt-Caryl bond (cf. [Pt(NCN)-
{1-C6H2(CH2NMe2)-3,5}].14a,37 Condensation of the bifunctional
intermediate D obviously provides polymeric structures. The
postulation of 25 as polymeric material is further supported by
the reactivity of this solid. For example, addition of HCl to a
suspension of 25 in acetone induced a rapid formation of a clear
solution. Spectroscopic analysis (1H, 13C NMR) of this solution
revealed the presence of [PtCl(NCN)] 26 exclusively, as it was
established by comparison with an authentic sample.21a Simi-
larly, reaction of 25 with a mixture of Ac2O/D2O resulted in
the clean formation of the deuterated complex 27, which was
easily converted in its iodide analogue 28 by treatment of the
reaction mixture with NaI.38 Due to the insolubility of 25, we
have not been able yet to determine the polydispersity index
(PDI) nor the average molecular weight of the polymeric
material.
1
0.00, J values are given in hertz; H and 13C NMR) or H3PO4 (31P
NMR). Elemental analyses were performed by Dornis and Kolbe,
Mikroanalytisches Laboratorium (Mu¨lheim a.d. Ruhr, Germany).
Residual solvent molecules were identified by 1H NMR spectroscopy.
Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF)
mass spectra were acquired by use of a Voyager-DE BioSpectrometry
Workstation (PerSeptive Biosystems Inc., Framingham, MA) mass
spectrometer equipped with a nitrogen laser emitting at 337 nm. The
instrument was operated in the linear mode at an accelerating voltage
in the range 22 000 V. External calibration was performed with C60/
C70, and detection was performed by means of a linear detector and
digitizing oscilloscope operating at 500 MHz. Sample solutions with
∼10 mg/mL in THF were used, and the matrix was 3,5-dihydroxy-
benzoic acid or 5-chlorosalicylic acid in THF (10 mg/mL). A solution
of silver(I) trifluoroacetate in THF was added in some cases to the
sample in order to improve the peak resolution. The sample solution
(0.2 µL) and the matrix solution (0.2 µL) were combined and placed
on a gold MALDI target and analyzed after evaporation of the solvents.
[PtI(PPh3)2(NC(Br)N)] 2. A solution of 1 (0.18 g, 0.45 mmol) and
[Pt(PPh3)4] (0.56 g, 0.45 mmol) in toluene (50 mL) was refluxed for
20 h. Subsequently, all volatiles were evaporated and the residual solid
was dissolved in CH2Cl2 (5 mL). Hexane (60 mL) was added, and a
white solid precipitated. This precipitate was collected and washed two
more times with hexane to give 2 as a white powder (0.37 g, 74%).
13C NMR (75 MHz, CD2Cl2) δ ) 45.6 (N(CH3)2), 64.5 (CH2), 121.9
Conclusions
We have established methods for the selective monometala-
tion of the bifunctional ligands of which 1 is a representative
example. Excellent chemoselectivites have been obtained by
appropriate variation of the metal precursors and reaction
conditions, which allowed for product distributions that were
controlled by kinetic (e.g., higher reactivity of the Caryl-I bond)
or by thermodynamic factors (e.g., stability through chelation).
This provided organometallic building blocks that contain a
second functional group for further functionalization. A range
of synthetic protocols have been developed that allow for the
modification of these groups by organic and also organometallic
reactions without affecting the M-C σ-bond of the organome-
tallic moiety. This disclosed a novel strategy for the fabrication
of materials with organometallic active sites, which is based
on the use of metalated building blocks. This has been illustrated
by the synthesis of dendritic mimics, biomolecular pincer-
platinum structures,23 and by the preparation of polymers
containing organometallic main chains, cf. [Pt(NCN)]n, 25.
Currently, we are investigating the application potential of such
structures in molecular electronics.
3
(C), 128.2 (t, JPC ) 4.3 Hz, Cmeta, PPh3), 130.5 (Cpara, PPh3), 130.6,
3
3
131.8 (t, JPC ) 28.7 Hz, Cipso, PPh3), 135.5 (t, JPC ) 6.1 Hz, Cortho
,
PPh3), 137.5, 138.6 (Cipso). MS (MALDI-TOF): m/z 1115.7 [M]+ (calcd
1115.1), 988.5 [M - I]+ (calcd 988.2). Anal. Calcd for C48H48BrIN2P2-
Pt‚0.5CH2Cl2 (1159.2): C, 50.25; H, 4.26; N, 2.42. Found: C, 50.66;
H, 3.88; N, 2.12.
[PtBr(NCN-I-4)] 3a. A mixture of 1 (1.00 g, 2.52 mmol) and [Pt-
(tol-4)2(SEt2)]2 (1.17 g, 1.26 mmol) in dry benzene (50 mL) was stirred
at reflux temperature for 2 h. The slightly yellow solution was allowed
to cool to room temperature, all volatiles were removed in vacuo, and
the crude product was recrystallized from benzene/pentane to afford
1.17 g (78%) of 3a as colorless needles. 13C NMR (75 MHz, CDCl3)
δ ) 55.6 (N(CH3)2), 76.7 (CH2), 86.1 (Cpara), 128.1 (3JPtC ) 37.4 Hz,
C
meta), 145.7 (Cortho), 146.1 (Cipso). MS (MALDI-TOF): m/z 591.4 [M]+
(calcd 590.9), 510.4 [M - Br]+ (calcd 512.0). Anal. Calcd for C12H18-
BrIN2Pt (590.93): C, 24.34; H, 3.06; N, 4.73. Found: C, 24.26; H,
3.15; N, 4.75.
[PtI(NCN-I-4)] 3b. A solution of 3a (0.54 g, 0.92 mmol) and AgBF4
(0.20 g, 1.01 mmol) in acetone/CH2Cl2 (1:1, 30 mL) was stirred for 30
min. The suspension formed was filtered over Celite to yield a yellowish
filtrate. The solvent was removed from the filtrate in vacuo, and the
residue obtained was dissolved in acetone (25 mL). To this solution
was added NaI (2.00 g, 13.3 mmol), and the resulting suspension was
stirred overnight. After this time solvent was removed in vacuo, and
the crude product was dissolved in CH2Cl2 (25 mL) and washed with
water (10 mL) and brine (10 mL). The organic layer was dried over
MgSO4 and evaporated to dryness to afford 0.54 g (93%) of 3b as an
yellow powder. 13C NMR (75 MHz, CDCl3) δ ) 56.3 (N(CH3)2), 76.1
(CH2), 86.3 (ArI), 128.1 (Cmeta), 145.8 (Cortho), 149.1 (Cipso). MS
(MALDI-TOF): m/z 511.5 [M - I]+ (calcd 512.0), 317.8 [M - PtI]+
Experimental Section
General. All manipulations involving organolithium compounds
were performed under a dry and deoxygenated nitrogen atmosphere
by standard Schlenk techniques. Solvents were carefully dried and
distilled from sodium benzophenone (pentane, hexane, toluene, C6H6,
THF, Et2O) or CaH (CH2Cl2, DMF) prior to use. Flash chromatography
was performed on 230-400 mesh silica or 70-300 mesh aluminum
(37) Albrecht, M.; James, S. L.; Veldman, N.; Spek, A. L.; van Koten, G. Can.
J. Chem. 2001, 79, 709-718.
(38) The p-deuterated compound 28 was identified by its 1H NMR spectrum,
which was identical to that of [PtI(NCN)] except for the aromatic part,
where a singlet at 6.82 ppm is observed instead of the doublet at 6.83 ppm
and the triplet at 7.03 ppm corresponding to [PtI(NCN)].21b
(39) Steele, B. R.; Vrieze, K. Transition Met. Chem. 1977, 2, 140-144.
(40) Komiya, S. Synthesis of Organometallic Compounds; Wiley: Chichester,
U.K., 1997.
9
J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002 5135

A R T I C L E S
Rodr´ıguez et al.
(calcd 317.0). Anal. Calcd for C12H18I2N2Pt (639.18): C, 22.55; H,
2.84; N, 4.38. Found: C, 22.65; H, 2.88; N, 4.32.
aqueous solution of NH4Cl (5 mL). The resulting suspension was
allowed to warm to room temperature and all volatiles were removed
in vacuo. The residue was dissolved in CH2Cl2, washed with brine,
dried over MgSO4, and evaporated to dryness. The resulting mixture
was dissolved in acetone and AgBF4 (0.13 g, 0.65 mmol) was added.
The suspension formed was stirred for 30 min and then filtered over
Celite. The solvent from the filtrate was removed in vacuo and the
residue obtained was dissolved in acetone (30 mL). To this solution
was added NaI (0.89 g, 5.90 mmol), and the resulting suspension was
stirred overnight. After this time solvent was removed in vacuo, and
the crude product was dissolved in CH2Cl2 (30 mL) and washed with
water (10 mL) and brine (10 mL). The organic layer was dried over
MgSO4 and evaporated to dryness to afford 0.23 g of 8b (74%) as a
yellow powder. H NMR (300 MHz, CDCl3) δ ) 3.21 (s, 12H, JPtH
) 37.5 Hz, N(CH3)2), 4.10 (s, 4H, 3JPtH ) 44.1 Hz, CH2), 7.36 (s, 2H,
ArH), 9.88 (s, 1H, CHO). 13C NMR (75 MHz, CDCl3) δ ) 56.4
(N(CH3)2), 76.3 (CH2), 121.5 (3JPtC ) 36 Hz, Cmeta), 133.1 (Cpara), 144.3
(3JPtC ) 77.3 Hz, Cortho), 163.0 (Cipso), 191.8 (CHO). Anal. Calcd for
C13H19IN2OPt (541.29): C, 28.85; H, 3.54; N, 5.18. Found: C, 29.08;
H, 3.59; N, 5.12.
[PdBr(NCN-I-4)] 4a. Solid [Pd2(dba)3‚CHCl3] (2.71 g, 1.58 mmol)
was added to a stirred solution of 1 (1.25 g, 3.15 mmol) in toluene (50
mL) at - 80 °C. The resulting solution was allowed to warm to room
temperature and stirred overnight. The reaction mixture was filtered
through Celite and the solvent was removed under reduced pressure.
The solid residue was dissolved in wet acetone (20 mL), AgBF4 (0.61
g, 3.15 mmol) was added, and the suspension was stirred for 1 h. After
this time, the resulting cloudy solution was filtered through Celite, and
the solvent was concentrated to ca. 5 mL. Then Et2O was added (20
mL), which resulted in the formation of a precipitate that was collected
and purified by repetitive washing with Et2O. The solid was dissolved
in CH2Cl2 (20 mL) and stirred with an excess of LiBr (0.33 g, 3.80
mmol) for 2 h. The suspension was subsequently filtered over Celite.
The filtrate was washed with water and brine, dried over MgSO4, and
evaporated to dryness to give 4a as an yellow solid (yield 0.37 g, 25%).
13C NMR (75 MHz, C6D6) δ ) 53.3 (N(CH3)2), 73.7 (CH2), 88.4 (Cpara),
128.6 (Cmeta), 147.8 (Cortho), 158.1 (Cipso). MS (MALDI-TOF): m/z 531.4
[(M - Br) + Ag]+ (calcd 529.8), 423.8 [M - Br]+ (calcd 423.0).
1
3
[PdBr(NCN-CHO-4)] 9. A solution of 7 (0.19 g, 0.64 mmol) and
[Pd2(dba)3‚CHCl3] (0.36 g, 0.35 mmol) in dry benzene (20 mL) was
refluxed for 3 h. After this time the reaction mixture was cooled to
room temperature and filtered through Celite. Subsequently, all volatiles
were evaporated and the residual solid was dissolved in CH2Cl2 (5 mL).
Hexane (50 mL) was then added and a yellow solid precipitated. This
precipitate was collected and washed several times with pentane to give
9 as a yellow powder (0.17 g, 64%).1H NMR (200 MHz, CDCl3) δ )
2.99 (s, 12H, N(CH3)2), 4.07 (s, 4H, CH2), 7.31 (s, 2H, ArH), 9.85 (s,
1H, CHO). 13C NMR (75 MHz, CDCl3) δ ) 53.7 (N(CH3)2), 74.1
(CH2), 121.4 (Cmeta), 128.9 (Cpara), 134.0 (Cortho), 145.7 (Cipso), 191.6
(CHO). MS (MALDI-TOF): m/z 323.3 [M - Br]+ (calcd 325.0), 217.8
[M - PdBr]+ (calcd 219.1). Anal. Calcd for C13H19BrN2OPd·0.5H2O
(414.6): C, 37.66; H, 4.86; N, 6.76. Found: C, 37.86; H, 4.50; N,
6.50.
[PdI(PPh3)2(NC(Br)N)] 5. A solution of 1 (1.06 g, 2.67 mmol) and
[Pd(PPh3)4] (2.74 g, 2.67 mmol) in toluene (75 mL) was stirred at 50
°C for 1 day. Subsequently, all volatiles were evaporated and the
residual solid was dissolved in CH2Cl2 (10 mL). Hexane (60 mL) was
then added, and a yellow solid precipitated. This precipitate was
collected and washed several times with hot hexane to give 5 as a yellow
powder (2.00 g, 73%). 13C NMR (75 MHz, CD2Cl2) δ ) 45.4 (NCH3),
64.3 (ArCH2), 122.6 (Cpara), 128.1 (t, 3JPC ) 5.1 Hz, Cmeta, PPh3), 130.2
(Cpara, PPh3), 132.2 (t, 3JPC ) 23.1 Hz, Cipso, PPh3), 135.2 (t, 3JPC ) 6.2
Hz, Cortho, PPh3), 137.1 (Cmeta), 137.5 (Cortho), 155.9 (Cipso). Anal. Calcd
for C48H48BrIN2P2Pd‚0.5CH2Cl2 (1070.6): C, 54.41; H, 4.61; N, 2.62;
P, 5.79. Found: C, 54.52; H, 4.98; N, 2.20; P, 5.77.
[NC(Br)N-CHO-4] 7. To a solution of 1 (2.19 g, 5.52 mmol) in
dry Et2O (30 mL) was added dropwise t-BuLi (6.2 mL, 1.7 M in hexane,
10.5 mmol) at -100 °C. The solution was stirred for 10 min at low
temperature and then treated with DMF (15 mL, large excess). After
warming to room temperature, the mixture was stirred for 14 h. H2O
was added (20 mL), and stirring was continued for 1 h. The mixture
was diluted with NaOH (2 M, 40 mL) and extracted with Et2O (3 ×
50 mL). The organic layers were combined, washed with brine, dried
over MgSO4, and evaporated to dryness. The crude product was further
purified by column chromatography [Al2O3 (4% NH4OH), pentane/
ethyl acetate, 3:1], yielding 7 as a yellowish oil (1.43 g, 87%). 1H NMR
(200 MHz, CDCl3) δ ) 2.33 (s, 12H, NCH3), 3.60 (s, 4H, CH2), 7.86
(s, 2H, ArH), 10.02 (s, CHO). 13C NMR (75 MHz, CDCl3) δ ) 45.7
(N(CH3)2), 63.7 (CH2), 129.8, 133.6, 134.8, 140.1, 191.8 (CHO). Anal.
Calcd for C13H19BrN2O (298.07): C, 52.18; H, 6.40; N, 9.37. Found:
C, 52.22; H, 7.07; N, 9.37.
[PtCl(NCN-OH-4)] 11. Complex 10 (1.65 g, 3.0 mmol) was
suspended in a mixture of acetone (40 mL) and HCl (2 M, 10 mL) and
stirred in air at 55 °C for 6 h. During this time a precipitate formed,
which was collected, washed with portions of Et2O (3 × 40 mL), and
dried in vacuo to leave 11 as a white solid (0.57 g, 78%). All analytical
data were consistent with those reported in the literature.19d
[PtBr(NCN-CH2OH-4)] 14. To a cooled (10 °C) suspension of 8a
(0.15 g, 0.27 mmol) in MeOH (15 mL) and AcOH (17 mg, 96 µL,
0.28 mmol) were added portions of NaBH3CN (in total 34 mg, 0.54
mmol). The reaction mixture was allowed to warm to room temperature
and stirred for an additional 2 h. All volatiles were removed in vacuo,
and the residue was diluted in NaOH (2M, 4 mL) and extracted with
EtOAc (3 × 10 mL). The combined organic extracts were dried over
MgSO4 and concentrated to give 14 (88 mg, 59%). 1H NMR (200 MHz,
[PtBr(NCN-CHO-4)] 8a. A mixture of 7 (200 mg, 0.67 mmol) and
[Pt(tol-4)2(SEt2)]2 (312 mg, 0.67 mmol) was stirred for 3 h in benzene
(20 mL) at reflux temperature. The yellowish solution was allowed to
cool to room temperature, volatiles were removed, and the residue
crystallized from CH2Cl2/pentane to afford 8a as needle-shaped crystals
3
CDCl3) δ ) 1.85 (br s, 1H, OH), 3.10 (s, 12H, JPtH ) 38.4 Hz,
3
N(CH3)2), 4.00 (s, 4H, JPtH ) 46.4 Hz, CH2), 4.50 (s, 2H, CH2OH),
6.83 (s, 2H, ArH). 13C NMR (50 MHz, CDCl3) δ ) 55.0 (N(CH3)2),
66.0 (CH2OH), 77.3 (CH2), 118.7 (Cmeta), 124.7 (Cpara), 136.1 (3JPtC
)
(0.25 g, 76%). 1H NMR (200 MHz, CDCl3) δ ) 3.14 (s, 12H, 3JPtH
)
77.3 Hz, Cortho), 143.5 (Cipso). MS (MALDI-TOF): m/z 415.2 [M -
Br]+ (calcd 414.0). Anal. Calcd for C13H19BrN2OPt (493.03): C, 31.46;
H, 4.26; N, 5.64. Found: C, 31.55; H, 4.26; N, 5.57.
3
38.7 Hz, N(CH3)2), 4.08 (s, 4H, JPtH ) 46.2 Hz, CH2), 7.34 (s, 2H,
ArH), 9.85 (s, 1H, CHO). 13C NMR (75 MHz, CDCl3) δ ) 55.0
(N(CH3)2), 76.8 (CH2), 121.3 (3JPtC ) 36 Hz, Cmeta), 133.1 (Cpara), 144.1
(3JPtC ) 77.3 Hz, Cortho), 157.5 (Cipso), 191.8 (CHO). Anal. Calcd for
C13H19BrN2OPt (493.03): C, 31.59; H, 3.87; N, 5.67. Found: C, 31.80;
H, 3.95; N, 5.59.
[PtBr(NCN-{CH2-L-Val-OMe}-4)] 15. A mixture of 8a (110 mg,
0.23 mmol), L-valine methyl ester hydrochloride (75 mg, 0.45 mmol),
triethylamine (0.06 mL, 0.45 mmol), and MgSO4 (1.0 g) was stirred in
CH2Cl2 (10 mL) at room temperature for 2 days. Subsequently, all solids
were filtered off and the filtrate was evaporated under reduced pressure.
The residue was dissolved in MeOH (10 mL) and AcOH (17 mg, 96
µL, 0.28 mmol). This solution was kept below 10 °C while portions of
NaBH3CN (27.9 mg, 0.44 mmol) were added. The reaction mixture
was allowed to warm to room temperature and stirred for an additional
[PtI(NCN-CHO-4)] 8b. To a solution of 3a (0.38 g, 0.59 mmol) in
dry THF (30 mL) was added dropwise t-BuLi (0.78 mL, 1.5 M in
hexane, 1.18 mmol) at -100 °C. The solution was stirred for 5 min
and subsequently treated with DMF (1.5 mL, large excess). After being
stirred for 15 min, the reaction mixture was quenched with a saturated
9
5136 J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002

Bifunctional Pincer-type Organometallics
A R T I C L E S
Table 4. Crystallographic Data for Compounds 2, 3a, 19, 20, and 24
2
3a
19
20
24
formula
fw
C48H48BrIN2P2Pt‚0.5(CH2Cl2) C12H18BrIN2Pt
C48H48I2N2P2Pt‚1.8(CH2Cl2) C48H48I2N2P2Pt2‚C6H6 C15H27IN2PtSi
1159.19
592.16
1316.58
1436.91
585.47
crystal size [mm3] 0.34 × 0.16 × 0.04
0.50 × 0.30 × 0.15
0.48 × 0.36 × 0.12
0.36 × 0.30 × 0.12
yellowish
Nonium KappaCCD
0.71073
0.40 × 0.25 × 0.16
colorless
Enraf-Nonius CAD4T
0.71073
crystal color
diffractometer
λ [Å]
temperature [K]
crystal system
space group
a [Å]
colorless
Nonius KappaCCD
0.71073
colorless
colorless
Enraf-Nonius CAD4T Nonium KappaCCD
0.71073
150(2)
0.71073
150(2)
150(2)
150(2)
150(2)
triclinic
monoclinic
P21/c (no. 14)
10.7151(13)
7.3901(5)
21.018(3)
90
114.673(9)
90
1512.4(3)
4
monoclinic
P21/c (no. 14)
15.4841(1)
21.1002(2)
21.8256(2)
90
orthorhombic
Pnma (no. 62)
23.794(3)
16.816(3)
12.502(3)
90
monoclinic
P21/c (no. 14)
13.6334(15)
14.1668(19)
10.1738(8)
90
P1h (no. 2)
12.0481(1)
13.9921(1)
14.2119(2)
88.5840(4)
83.4641(4)
84.0046(5)
2367.03(4)
2
b [Å]
c [Å]
R [deg]
â [deg]
133.6230(3)
90
90
90
100.739(8)
90
γ [deg]
V [Å3]
5161.95(8)
4
5002.3(16)
4
1930.6(4)
4
Z
D
calc [g/cm3]
1.626
2.601
1.694
1.908
2.014
µ [mm-1
]
4.618
13.943
4.197
6.923
8.923
sin (θ/λ)max [Å-1
abs. correction
transm range
refl meas/unique
parameters
]
0.65
0.65
0.65
0.65
0.65
analytical
0.24-0.81
44 077/10 841
559
DELABS
0.10-0.56
7127/3466
158
analytical
0.27-0.67
69 290/11 820
563
analytical
0.20-0.57
67 537/5943
325
DELABS
0.26-0.71
9301/4399
188
restraints
68
0
16
24
0
R1 (obs/all refl)
wR2 (obs/all refl)
GoF
0.0339/0.0430
0.0913/0.0955
1.042
0.0432/0.0547
0.0986/0.1034
1.062
0.0311/0.0439
0.0728/0.0773
1.034
0.0260/0.0419
0.0527/0.0596
1.063
0.0383/0.0520
0.0833/0.0885
1.022
res. density [e/Å3] -1.74/1.18
-2.30/2.58
-1.10/1.91
-1.20/1.05
-1.70/2.06
2 h. All volatiles were then removed in vacuo, and the residue was
extracted with NaOH (2 M, 20 mL) and CH2Cl2 (3 × 20 mL). The
combined organic layers were washed with brine, dried over MgSO4,
and concentrated. The resulting oil was purified by column chroma-
tography (SiO2, hexane/CH2Cl2/acetone) to give 14 as a yellowish solid
(85 mg, 64%). Analytical data are consistent with those reported in
the literature.23
(N(CH3)2), 63.6 (CH2), 93.2 (ArCtCSiMe3), 105.8 (ArCtCSiMe3),
122.9 (C), 129.9 (C), 130.8, 140.2 (C).30
[PtI(η1-C-C6H3{CH2NMe2}2-2,6-I-4)(PPh3)2] 19. Addition of PPh3
(0.33 g, 1.26 mmol) to a solution of 3b (0.38 g, 0.60 mmol) in C6H6
(20 mL) afforded, after stirring overnight and removal of all volatiles,
the crude title product. Purification was achieved by repeated crystal-
lization of 19 from CH2Cl2/pentane. Yield: 0.53 g (99%). Crystals
suitable for X-ray structure determination were grown by recrystalli-
zation from CH2Cl2/pentane. 13C NMR (75 MHz, CDCl3) δ ) 45.5
(NCH3), 70.0 (CH2), 89.1 (Cpara), 127.9-136.1 (m, CH, PPh3), 145.8
(Cmeta), 146.1 (Cipso). MS (MALDI-TOF): m/z 1034.0 [M - I]+ (calcd
1036.2), 899.0 [M - PPh3]+ (calcd 901.0). Anal. Calcd for C48H48I2N2P2-
Pt (1163.8): C, 49.54; H, 4.16; N, 2.41. Found C, 49.63; H, 4.23; N,
2.40.
[PtBr(NCN-CtCSiMe3-4)] 16. To a suspension of 3a (0.12 g, 0.2
mmol), CuI (2 mg, 0.01 mmol), and [PdCl2(PPh3)2] (2 mg, 0.01 mmol)
in Et2NH (10 mL) was added trimethylsilylacetylene (21 mg, 31 µL,
0.22 mmol). The reaction mixture was stirred at room temperature for
16 h and subsequently evaporated to dryness. The residue was
redissolved in CH2Cl2 (10 mL) and washed with AcOH (1 M), brine,
and water. After being dried over MgSO4, the solution was concentrated
to 1 mL and pentane (15 mL) was added, which caused the precipitation
of 16 as an off-white solid (68 mg, 60%). 1H NMR (300 MHz, CDCl3)
[PtI(η1-C-C6H3{CH2NMe2}2-3,5-PtI-4)(PPh3)2] 20. Method A: A
solution of 19 (0.30 g, 0.33 mmol) and [Pt(PPh3)4] (0.33 g, 0.41 mmol)
in benzene (30 mL) was refluxed for 1 h. Volatiles were then removed
under reduced pressure. The crude product was isolated by repetitive
precipitation of a CH2Cl2 solution with pentane and it was finally
recrystallized from CH2Cl2/benzene/pentane to afford 0.29 g of 20
(64%).
3
δ ) 0.19 (s, 9H, SiMe3), 3.14 (s, 12H, JPtH ) 40.2 Hz, N(CH3)2),
3.96 (s, 4H, 3JPtH ) 44.7 Hz, CH2), 6.92 (s, 2H, ArH). For an alternative
preparation of such complexes, see ref 28.
[PdBr(NCN-CtCSiMe3-4)] 17. This complex was obtained by a
procedure similar to the one applied for the preparation of 16, starting
from 4a (64 mg, 0.12 mmol), CuI (2 mg, 0.06 mmol), [PdCl2(PPh3)2]
(5 mg, 0.06 mmol), and trimethylsilylacetylene (14 mg, 0.14
Method B: A solution of 3b (50 mg, 0.08 mmol) and [Pt(PPh3)4]
(97 mg, 0.08 mmol) in benzene (30 mL) was refluxed for 1 h. Volatiles
were then removed under reduced pressure and the crude product was
isolated by repetitive precipitation of a CH2Cl2 solution with pentane,
affording 100 mg (94%) of 20. 13C NMR (75 MHz, CD2Cl2) δ ) 56.6
(NCH3), 77.3 (CH2), 127.1, 128.0, (t, 3JPC ) 5.3 Hz, Cmeta, PPh3), 130.5
1
mmol).Yield: 40 mg (66%). H NMR (300 MHz, C6D6) δ ) 0.30 (s,
9H, SiMe3), 2.55 (s, 12H, N(CH3)2), 3.14 (s, 4H, CH2), 6.82 (s, 2H,
ArH). 13C NMR (75 MHz, C6D6) δ ) 0.2 (SiMe3), 53.3 (N(CH3)2),
74.0 (CH2), 92.9 (ArCtCSiMe3), 107.2 (ArCtCSiMe3), 119.3 (Cpara),
123.4 (Cmeta), 145.6 (Cortho), 160.8 (Cipso). MS (MALDI-TOF): m/z 393.0
[M - Br]+ (calcd 393.1). Anal. Calcd for C17H27BrN2SiPd (473.8):
C, 43.09; H, 5.74; N, 5.91. Found: C, 42.81; H, 5.63; N, 5.71.
3
(Cpara, PPh3), 132.2 (t, JPC ) 28.1 Hz, Cipso, PPh3), 132.4, 135.6 (t,
3JPC ) 6.0 Hz, Cortho, PPh3), 139.9, 143.6. MS (MALDI-TOF): m/z
1356.4 [M]+ (calcd 1358.1), 1228.6 [M - I]+ (calcd 1231.2). Anal.
Calcd for C48H48I2N2P2Pt2‚C6H6 (1437.0): C, 45.14; H, 3.79; N, 1.95.
Found: C, 44.77; H, 3.87; N, 1.96.
[NC(Br)N-CtCSiMe3-4)] 18. This compound was obtained by a
procedure similar to the one applied for the preparation of 16, starting
from 5 (44 mg, 0.04 mmol) and trimethylsilylacetylene (7 mg, 0.08
mmol).Yield: 9 mg (62%). 1H NMR (200 MHz, (CD3)2CO): δ ) 0.24
(s, 9H, SiMe3), 2.17 (s, 12H, N(CH3)2), 3.37 (s, 4H, CH2), 7.30 (s, 2H,
ArH).13C NMR (50 MHz, (CD3)2CO) δ ) -0.4 (SiMe3), 45.0
[PdI(η1-C-C6H3{CH2NMe2}2-3,5-PtI-4)(PPh3)2] 21. A solution of
3b (110 mg, 0.17 mmol) and [Pd(PPh3)4] (199 mg, 0.17 mmol) in
benzene (30 mL) was stirred at room temperature for 3 h. The formed
precipitated was collected and washed with pentane (2 × 15 mL) to
yield 160 mg (73%) of 21. 13C NMR (75 MHz, CDCl3) δ ) 56.1
9
J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002 5137

A R T I C L E S
Rodr´ıguez et al.
(NCH3), 76.7 (CH2), 126.0, 127.5, (t, 3JPC ) 5.2 Hz, Cmeta, PPh3), 129.7
(Cpara, PPh3), 132.2 (t, 3JPC ) 22.9 Hz, Cipso, PPh3), 134.8 (t, 3JPC ) 6.1
Hz, Cortho, PPh3), 142.5, 143.4, 150.6. Anal. Calcd for C48H48I2N2P2-
PdPt‚C6H6 (1348.3): C, 48.10; H, 4.04; N, 2.08. Found: C, 48.50; H,
4.20; N, 2.24.
) -1.0 (SiMe3), 56.3 (N(CH3)2), 76.9 (CH2), 124.0 (Cmeta), 134.7 (Cpara),
143.1 (Cortho), 150.8 (Cipso). MS (MALDI-TOF): m/z 460.7 [M - I]+
(calcd 458.2). Anal. Calcd for C15H27IN2SiPt (585.5): C, 30.77; H,
4.65; N, 4.78. Found: C, 30.61; H, 4.65; N, 4.72.
[Pt(NCN)]n 25. To a solution of 3b (0.6 g, 1.0 mmol) in THF (20
mL) was added dropwise t-BuLi (1.3 mL, 1.5 M in hexane, 2.0 mmol)
at -100 °C. Immediately, a precipitate was formed. The suspension
was stirred for 5 min and subsequently allowed to slowly reach room
temperature. The precipitate was collected, washed repeatedly with THF
(3 × 20 mL), and dried in vacuo to give 25 as an insoluble white solid
(0.23 g).
[PtI(η1-C-C6H3{CH2NMe2}2-3,5-PdI-4)(PPh3)2] 22. A solution of
2 (60 mg, 0.05 mmol) and [Pd2(dba)3‚CHCl3] (24 mg, 0.025 mmol) in
benzene (15 mL) was refluxed for 15 min. After this time the reaction
mixture was cooled to room temperature and the formed precipitate
was collected and washed with pentane (2 × 10 mL). The resulting
powder was then dissolved in acetone and an excess of NaI was added.
The suspension was stirred overnight. After filtration of the reaction
mixture, solvent was removed and the residue was dissolved in CH2-
Cl2. The organic phase was washed with water and brine and dried
over MgSO4. After removal of the solvent, 22 was obtained as a yellow
powder. Yield: 44 mg (64%). 13C NMR (50 MHz, CDCl3) δ ) 54.7
(NCH3), 73.7 (CH2), 125.9, 127.5 (t, 3JPC ) 5.1 Hz, Cmeta, PPh3), 130.0
[PtCl(NCN)] 26. A suspension of 25 (25 mg) in acetone (5 mL)
was treated with gaseous HCl. Immediately, the reaction mixture
became homogeneous. All volatiles were removed in vacuo. Analysis
of the residue gave identical NMR spectroscopic data (1H, 13C) as
reported for 26.21b 1H NMR (200 MHz, CDCl3): δ ) 3.08 (s, 12H,
3
3JPtH ) 38.2 Hz, N(CH3)2), 4.02 (s, 4H, JPtH ) 45.6 Hz, CH2), 6.95
3
3
3
(Cpara, PPh3), 131.4 (m, Cipso, PPh3), 132.0, 135.0 (t, JPC ) 6.0 Hz,
(d, JHH ) 7.0 Hz, 2H, ArH), 6.99 (t, JHH ) 7.0 Hz, 1H, ArH).
[PtCl(NCN-D-4)] 28. A suspension of 25 (25 mg) in Ac2O (2 mL)
and D2O (2 mL) was refluxed for 5 min and the reaction mixture
became homogeneous. All volatiles were removed in vacuo, the residue
was dissolved in CH2Cl2, and the mixture was stirred in the presence
of an excess of NaI for 1 h. 1H NMR (300 MHz, CDCl3): δ ) 3.19 (s,
C
ortho, PPh3), 135.9, 144.5. MS (MALDI-TOF): m/z 1140.7 [M - I]+
(calcd 1142.1). Anal. Calcd for C48H48I2N2P2PdPt‚CH2Cl2 (1355.12):
C, 43.43; H, 3.72; N, 2.07. Found: C, 43.50; H, 4.11; N, 1.70.
[PdI(η1-C-C6H3{CH2NMe2}2-3,5-PdI-4)(PPh3)2] 23. Solid [Pd2-
(dba)3‚CHCl3] (0.27 g, 0.26 mmol) was added to a stirred solution of
1 (0.2 g, 0.56 mmol) in toluene (15 mL) at -80 °C. The resulting
solution was allowed to warm to room temperature and stirred
overnight. The reaction mixture was filtered through Celite and the
solvent was removed under reduced pressure. The solid residue was
dissolved in wet acetone (15 mL), AgBF4 (0.21 g, 1.12 mmol) was
added, and the suspension was stirred for 15 min. After this time, the
resulting cloudy solution was filtered through Celite, and the solvent
was concentrated to ca. 5 mL. Then Et2O was added (20 mL), which
resulted in the formation of a precipitate that was collected and purified
by repetitive washing with Et2O. The solid was dissolved in CH2Cl2
(20 mL), an excess of LiI (0.20 g, 1.50 mmol) was added, and the
mixture was stirred for 3 h. The suspension was subsequently filtered
over Celite and the filtrate was washed with brine and water, dried
over MgSO4, and concentrated. 4b was obtained as a yellow solid (yield
0.10 g, 39%).
3
3
12H, JPtH ) 37.5 Hz, N(CH3)2), 4.03 (s, 4H, JPtH ) 42.9 Hz, CH2),
6.82 (s, 2H, ArH).38
Crystal Structure Determinations. The crystal structures presented
in this paper were solved with automated Patterson methods41 and
refined with SHELXL-9742 against F2 of all reflections. Structure
drawings, calculations and checkings were performed with the PLATON
package.43 Further details of the crystal structures are given in
Table 4.
Crystallographic data (excluding structure factors) for the structures
in this paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications CCDC 175142 (2), 175143
(3a),175144 (19), 175145 (20), and 175146 (24). Copies of the data
can be obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. (fax +44 1223 336033 or e-mail
deposit@ccdc.cam.ac.uk).
To a benzene solution of freshly prepared 4b (72 mg, 0.13 mmol)
at 0 °C was added Pd(PPh3)4 (75 mg, 0.065 mmol). The reaction mixture
was allowed to warm to room temperature and stirred during 1 h. The
formed precipitate was collected and washed with pentane (2 × 5 mL)
to yield 73 mg (50%) of 23. 13C NMR (75 MHz, CD2Cl2) δ ) 55.1
(NCH3), 74.3 (CH2), 127.1, 128.2, (t, 3JPC ) 4.9 Hz, Cmeta, PPh3), 130.4
(Cpara, PPh3), 132.9 (t, 3JPC ) 23.2 Hz, Cipso, PPh3), 135.4 (t, 3JPC ) 6.1
Hz, Cortho, PPh3), 145.7, 153.5, 154.1. Anal. Calcd for C48H48I2N2P2-
Pd2‚2C6H6 (1337.7): C, 53.87; H, 4.52; N, 2.09. Found: C, 53.65; H,
4.15; N, 2.51.
[PtI(NCN-SiMe3-4)] 24. To a solution of 3b (0.55 g, 0.86 mmol)
in THF (40 mL) was added dropwise t-BuLi (1.10 mL, 1.5 M in hexane,
1.63 mmol) at -100 °C. The solution was stirred for 5 min at low
temperature and subsequently treated with Me3SiCl (0.45 mL, 3.5
mmol). After being stirred for 15 min, the reaction mixture was
quenched with a saturated aqueous solution of NH4Cl (5 mL). The
resulting suspension was allowed to warm to room temperature and
all volatiles were removed in vacuo. This crude product was dissolved
in CH2Cl2, washed with brine, dried over MgSO4, and concentrated to
afford 0.41 g of 24 (75%). 1H NMR (200 MHz, CDCl3): δ ) 0.22 (s,
9H, SiMe3), 3.19 (s, 12H, 3JPtH ) 38.8 Hz, N(CH3)2), 4.03 (s, 4H, 3JPtH
) 45.8 Hz, CH2), 6.95 (s, 2H, ArH). 13C NMR (75 MHz, CDCl3): δ
Acknowledgment. G.R. thanks the European Commission
for a Marie Curie TMR Grant (Contract HPMF-CT-1999-
00236). This work was supported in part (M. L. and A.L.S.) by
the Council for Chemical Sciences from the Dutch Organization
for Scientific Research (CW-NWO).
Supporting Information Available: A complete list of the
experimental procedure and analytical data for compound 1
(PDF), a listing of tables of atomic coordinates, bond lengths
and angles, thermal parameters and relevant crystallographic
data for compounds 2, 3a, 19, 20, and 24 (CIF). This material
is available free of charge via the Internet at http://pubs.acs.org.
JA0177657
(41) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF97
Program System; Technical Report of the Crystallography Laboratory;
University of Nijmegen: Nijmegen, The Netherlands, 1997.
(42) Sheldrick, G. M. SHELXL-97. Program for crystal structure refinement;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(43) Spek, A. L. PLATON. A multipurpose crystallographic tool; Utrecht
University: Utrecht, The Netherlands, 2001.
9
5138 J. AM. CHEM. SOC. VOL. 124, NO. 18, 2002