Synthesis of neutral molecular squares composed of bis(phosphine)platinum corner units and dialkynyl linkers. Solid-state characterization of [Pt(μ-C≡CC≡C)(dppp)]4

Article abstract of DOI:10.1021/om049690w

Coupling of dichloroplatinum complexes with ethyne or butadiyne, catalyzed by Cul in the presence of Et₂NH, leads to complexes of the types [Pt(C≡CH)₂L₂] (L₂ = dppe (1), dppp (2); L = PEt₃ (3)) and [P

Full text of DOI:10.1021/om049690w

4382
Organometallics 2004, 23, 4382-4390
Syn th esis of Neu tr a l Molecu la r Squ a r es Com p osed of
Bis(p h osp h in e)p la tin u m Cor n er Un its a n d Dia lk yn yl
Lin k er s. Solid -Sta te Ch a r a cter iza tion of
[P t(µ-CtCCtC)(d p p p )]4
Mesfin J anka, Gordon K. Anderson,* and Nigam P. Rath
Department of Chemistry and Biochemistry, University of MissourisSt. Louis,
One University Boulevard, St. Louis, Missouri 63121
Received May 3, 2004
Coupling of dichloroplatinum complexes with ethyne or butadiyne, catalyzed by CuI in
the presence of Et2NH, leads to complexes of the types [Pt(CtCH)2L2] (L2 ) dppe (1), dppp
(2); L ) PEt3 (3)) and [Pt(CtCCtCH)2L2] (L2 ) dppp (4), dcpe (5); L ) PEt3 (6)). Attempts
to produce tetraplatinum species with ethynyl edges proved unsuccessful, but further coupling
of the butadiynylplatinum complexes with [PtCl2L2] produces the neutral molecular squares
[Pt(µ-CtCCtC)2L2]4 (L2 ) dppp (7), dcpe (8); L ) PEt3 (9)). This two-step approach allows
the synthesis of the unsymmetrical complexes [Pt2(µ-CtCCtC)2(PEt3)2L2] (L2 ) dppp (10);
dcpe (11)). The molecular structure of 7 reveals that each square has a puckered, butterfly-
like structure. These pack in a face-to-face manner, generating series of channels that
accommodate several solvent molecules. Coupling of trans-[Pt(CtCCtC)2(PEt3)2] (6b) with
[PtCl2L2] (L2 ) dcpe, dppp) leads to complexes assigned as neutral octaplatinum derivatives.
The nitrogen-containing complexes [Pt(CtCC5H4N)2(dppp)] (14) and [Pt(CtCC6H4CN)2-
(dppp)] (15) react with AgNO3 to produce Pt4Ag4 adducts.
In tr od u ction
have the advantage of being more soluble in common
organic solvents.
The directional bonding approach, advanced sepa-
rately by Fujita1 and Stang,2 makes use of coordinate
bonds in the preparation of a wide range of two- and
three-dimensional structures. The basis of this method
is that, by selecting suitable corner or angular units and
appropriate linker or spacer moieties, two- or three-
dimensional structures can be formed by a self-assembly
process. A molecular square, for example, may be
constructed from four corner units subtending 90°
angles, such as a cis square-planar metal center, and
four linear linkers.3-6
Charged palladium- or platinum-containing molecular
squares have been prepared using the divalent metals
with neutral bidentate ligands at the corners and
neutral linkers, giving rise to a 2+ charge per metal
center.3-6,8-22 Neutral molecular squares, on the other
hand, may be accessible either by using neutral biden-
tate ligands in the corner units and dianionic linkers
or by employing dianions at the corners and linking the
metal centers by neutral linear units. We chose to
pursue the former approach, using alkynyl groups as
(8) Stang, P. J .; Whiteford, J . A. Organometallics 1994, 13, 3776.
(9) Rauter, H.; Hillgeris, E. C.; Evxleben, A.; Lippert, B. J . Am.
Chem. Soc. 1994, 116, 616.
(10) Fujita, M.; Sasaki, O.; Mitusuhashi, T.; Fujita, T.; Yazake, J .;
Yamaguchi, K.; Ogura, K. J . Chem. Soc., Chem. Commun. 1996, 1535.
(11) Stang, P. J .; Olenyuk, B.; Fan, J .; Arif, A. M. Organometallics
1996, 15, 904.
(12) Olenyuk, B.; Whiteford, J . A.; Stang, P. J . J . Am. Chem. Soc.
1996, 118, 8221.
(13) Stang, P. J .; Olenyuk, B. Angew. Chem., Int. Ed. Engl. 1996,
35, 732.
In the majority of examples reported to date, the
products are highly charged. Attempts to reduce such
charged species to the corresponding neutral ones have
resulted in disintegration of the assemblies.7 The avail-
ability of neutral macrocycles is highly desirable. They
may act as hosts for electron-deficient guests (the
presence of many counterions can block the potential
cavities in charged macrocyclic structures) and as
potential catalytic precursors. In addition, neutral mac-
rocycles, as opposed to their charged analogues, would
(14) Stang, P. J .; Cao, D. H.; Chen, K.; Gray, G. M.; Muddiman, D.
C.; Smith, R. D. J . Am. Chem. Soc. 1997, 119, 5163.
(15) Whiteford, J . A.; Lu, C. V.; Stang, P. J . J . Am. Chem. Soc. 1997,
119, 2524.
(16) Whiteford, J . A.; Stang, P. J .; Huang, S. D. Inorg. Chem. 1998,
37, 5595.
(17) Muller, C.; Whiteford, J . A.; Stang, P. J . J . Am. Chem. Soc.
1998, 120, 9827.
(18) Lee, S. B.; Hwang, S.; Chung, D. S.; Yun, H.; Hong, J . I.
Tetrahedron Lett. 1998, 39, 873.
* To whom correspondence should be addressed. Tel: 314-516-5437.
Fax: 314-516-5342. E-mail: ganderson@umsl.edu.
(1) Fujita, M. Acc. Chem. Res. 1999, 32, 53 and references therein.
(2) Leininger, S.; Olenyuk, B.; Stang, P. J . Chem. Rev. 2000, 100,
853 and references therein.
(3) Fujita, M.; Yazake, J .; Ogura, K. J . Am. Chem. Soc. 1990, 112,
5645.
(4) Fujita, M.; Yazake, J .; Ogura, K. Chem. Lett. 1991, 1031.
(5) Stang, P. J .; Cao, D. H. J . Am. Chem. Soc. 1994, 116, 4981.
(6) Stang, P. J .; Cao, D. H.; Saito, S.; Arif, A. M. J . Am. Chem. Soc.
1995, 117, 6273.
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Chem. 1999, 38, 426.
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(21) Wurthner, F.; Sautter, A. Chem. Commun. 2000, 445.
(22) Schweiger, M.; Seidel, S. R.; Arif, A. M.; Stang, P. J . Inorg.
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10.1021/om049690w CCC: $27.50 © 2004 American Chemical Society
Publication on Web 08/18/2004

Neutral Molecular Squares
Organometallics, Vol. 23, No. 19, 2004 4383
the linkers. Indeed, alkynyl-containing ligands have
been used recently in the preparation of a series of self-
assembled polygons, ranging from triangles to octa-
gons.23 Stang has recently reported the use of dicarbox-
ylates in the construction of neutral platinum-containing
macrocycles.24
When this work began, there was a report in the
literature of the synthesis of the butadiynyl-bridged
square [Pt4(µ-CtCCtC)4(dcpe)4], although it had not
been characterized by X-ray crystallography.25 While
our work was in progress, a report appeared describing
a series of neutral molecular squares of the form
[Pt4(µ-CtCCtC)4L8].26 Whereas the general approach
adopted by Bruce and co-workers was similar to ours,
there are significant differences both in the synthetic
details and in the particular compounds isolated and
characterized.
F igu r e 1. Molecular structure of [Pt(CtCH)2(dppe)] (1),
with atoms represented by thermal ellipsoids at the 50%
level.
Resu lts a n d Discu ssion
Eth yn yl Com p lexes. Alkynylplatinum(II) complexes
have been prepared by a variety of methods, including
alkynyl transfer from Grignard, organolithium, and
organosodium reagents,27-29 or from less reactive met-
als, such as tin, mercury, and gold.30-32 Base-promoted
methods have also been developed, using NaOH, KOH,
NH3, or NHEt2/CuI.33-37 In attempts to generate bis-
(ethynyl)platinum(II) species, we investigated a number
of methods, and we found the copper-catalyzed reaction
to proceed most smoothly. Thus, treatment of a THF
suspension of [PtCl2(dppe)] with ethyne, in the presence
of CuI (10 mol %) and diethylamine, followed by
purification, allowed isolation of [Pt(CtCH)2(dppe)] (1)
as a yellow solid in high yield. [Pt(CtCH)2(dppp)] (2)
and cis- and trans-[Pt(CtCH)2(PEt3)2] (3a ,b) were
prepared analogously from [PtCl2(dppp)] and cis- and
trans-[PtCl2(PEt3)2], respectively (eq 1).
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for [P t(CtCH)2(d p p e)] (1)
Pt-C(3)
Pt-P(1)
C(3)-C(4)
2.025(5)
2.2851(12)
1.164(8)
Pt-C(5)
Pt-P(2)
C(5)-C(6)
2.102(5)
2.2747(12)
1.184(8)
C(3)-Pt-C(5)
C(3)-Pt-P(2)
C(5)-Pt-P(2)
Pt-C(3)-C(4)
89.3(2)
C(3)-Pt-P(1)
C(5)-Pt-P(1)
P(1)-Pt-P(2)
Pt-C(5)-C(6)
93.07(14)
174.13(15)
85.79(4)
176.80(14)
92.15(14)
177.3(5)
174.3(5)
plexes 3a ,b38,39 were characterized by NMR spectros-
copy. In each of the four complexes a resonance due to
the ethynyl hydrogen is observed between 2.2 and 2.5
ppm, and two 13C signals are detected for the ethynyl
carbons. The signal due to the â-carbon is the more
readily observed (due to the NOE and its shorter
2
relaxation time), and a J PtC value of ca. 300 Hz is found
1
in each case. Only in the trans complex 3b is J PtC
HCtCH
detected, where a value of 485 Hz is found. Each
L2PtCl2
8 L2Pt(CtCH)2
(1)
complex exhibits a single resonance in its 31P{1H} NMR
CuI, Et2NH
1
spectrum, with J PtP values in the range 2200-2300 Hz
for 1, 2, and 3a , where each P atom lies trans to an
ethynyl group, whereas a value of 2368 Hz is found for
the mutually trans P atoms in 3b.
Complex 1 has been characterized by elemental
analysis, NMR spectroscopy, and X-ray crystallography,
whereas 2 has been identified by high-resolution mass
spectrometry and NMR spectroscopy. The known com-
The solid-state structure of 1 has been determined,
and its molecular structure is shown in Figure 1.
Selected bond distances and bond angles are presented
in Table 1. The geometry at platinum is approximately
square planar, the sum of the angles around the metal
center being 360.4°. The smallest angle (85.79(4)°) is
that subtended by the dppe ligand, as anticipated on
the basis of its expected bite angle.40 The ethynylplati-
num units are nearly linear, with the Pt-CtC angles
being 174.3(5) and 177.3(5)°. The Pt-C(3) and Pt-C(5)
distances are 2.025(5) and 2.012(5) Å, respectively, and
the corresponding carbon-carbon distances are 1.164(8)
and 1.184(8) Å, as expected for CtC triple bonds.
Attempts to prepare molecular squares with ethynyl
edges proved unsuccessful. When 1 or 2 was treated
with [PtCl2(dppe)] or [PtCl2(dppp)] in the presence of
(23) J iang, H.; Lin, W. J . Am. Chem. Soc. 2003, 125, 8084.
(24) Mukherjee, P. S.; Das, N.; Kryschenko, Y. K.; Arif, A. M.; Stang,
P. J . J . Am. Chem. Soc. 2004, 126, 2464.
(25) Al Qaisi, S. M.; Galat, K. J .; Chai, M.; Ray, D. G.; Rinaldi, P.
L.; Tessier, C. A.; Youngs, W. J . J . Am. Chem. Soc. 1998, 120, 12149.
(26) Bruce, M. I.; Costuas, K.; Halet, J .-F.; Hall, B. C.; Low, P. J .;
Nicholson, B. K.; Skelton, B. W.; White, A. H. Dalton 2002, 383.
(27) Bruce, M. I.; Harbourne, D. A.; Waugh, F.; Stone, F. G. A. J .
Chem. Soc. 1968, 356.
(28) Bell, R. A.; Chisholm, M. H.; Couch, D. A.; Rankel, L. A. Inorg.
Chem. 1977, 16, 677.
(29) Collamati, I.; Furlani, A. J . Organomet. Chem. 1969, 17, 209.
(30) Cardin, C. J .; Cardin, D.; Lappert, M. F. J . Chem. Soc., Dalton
Trans. 1977, 767.
(31) Cross, R. J .; Gemmill, J . J . Chem. Soc., Dalton Trans. 1984,
199 and 205.
(32) Cross, R. J .; Davidson, M. F. J . Chem. Soc., Dalton Trans. 1986,
411.
(33) Cross, R. J .; Davidson, M. F. J . Chem. Soc., Dalton Trans. 1986,
1987.
(34) Almeida, J . F.; Pidcock, A. J . Organomet. Chem. 1981, 209, 415.
(35) Anderson, G. K.; Lumetta, G. J . J . Organomet. Chem. 1985,
295, 257.
(36) Furlani, A.; Licoccia, S.; Russo, M. V. J . Chem. Soc., Dalton
Trans. 1984, 2197.
(38) Brooks, E. H.; Glockling, F. J . Chem. Soc. A 1967, 1030.
(39) Sonogashira, K.; Yataki, T.; Tohda, Y.; Takahashi, S.; Hagihara,
N. J . Chem. Soc., Chem. Commun. 1971, 291.
(40) Dierkes, P.; van Leeuwen, P. W. N. M. J . Chem. Soc., Dalton
Trans. 1999, 1519.
(37) Cross, R. J .; Davidson, M. F. Inorg. Chim. Acta 1985, 97, L35.

4384 Organometallics, Vol. 23, No. 19, 2004
J anka et al.
CuI/Et2NH in THF solution, no reaction was observed
even after refluxing for 4 days. Treatment of 1 or 2 with
BuLi, followed by addition of the dichloroplatinum
complex, resulted in decomposition. These results may
suggest that the ethynyl moiety is too short to allow
formation of a stable square, due to the steric repulsions
between the phenyl groups that would result. Similarly,
whereas reactions of [M(OTf)2(dppp)] (M ) Pd, Pt) with
4,4′-bipyridine were used to generate cationic squares,
the analogous reactions with the more compact pyrazine
ligand give the monomeric species [M(C4H4N2)2(dppp)]
only.41 This was attributed to the unfavorable steric
interactions that would result if the smaller square were
formed. In our case, even with the sterically less
demanding PEt3 ligands in 3a , coupling with cis-[PtCl2-
(PEt3)2] was unsuccessful.
Bu ta d iyn yl Com p lexes. We next turned our atten-
tion to the synthesis of butadiynyl-bridged species. As
noted earlier, the preparation of [Pt4(µ-CtCCtC)4-
(dcpe)4] had been described previously.25 During the
course of our work, other complexes of the general form
[Pt4(µ-CtCCtC)4L8] were reported by Bruce and co-
workers, who prepared the angular units [Pt(CtCCt
CH)2L2] (L2 ) dppe, dppp; L ) PEt3) by reaction of
[PtCl2L2] with 1,3-butadiyne in the presence of CuI in
DMF/Et2NH solution.26 We prepared [Pt(CtCCtCH)2L2]
(L2 ) dppp (4), dcpe (5); L ) PEt3 (6a )) similarly, but
using THF as solvent. We also generated trans-[Pt(Ct
CCtCH)2(PEt3)2] (6b) from trans-[PtCl2(PEt3)2]. Com-
plexes 4-6 each exhibit a single 31P resonance, with
1J PtP values of 2200-2300 Hz. In contrast to complexes
1-3, in which the ethynyl hydrogen appears in the
range 2.2-2.5 ppm, the butadiynyl hydrogen in com-
plexes 4-6 appears between 1.6 and 1.8 ppm. In 6a ,b,
five-bond couplings to 195Pt of 9 Hz are observed. Four
13C signals are observed for the butadiynyl group in each
complex. In 5, for example, resonances are observed at
60.9, 72.8, 93.4, and 99.2 ppm due to the δ-, γ-, â-, and
R-carbons, respectively. The two highest frequency
signals exhibit coupling to 31P, whereas the R-, â-, and
γ-carbons each show coupling to 195Pt, the magnitude
of the latter diminishing from 1130 to 311 and then to
36 Hz as the distance from platinum increases. Com-
plexes 4 and 6a proved difficult to isolate in pure form,
because decomposition occurred slowly in solution.
We have determined the solid-state structures of 6a ,b;
the former was reported by Bruce,26 and so it is not
included here. The molecular structure of 6b is shown
in Figure 2, and selected bond distances and bond angles
are given in Table 2. The complex exhibits square-
planar geometry, each of the angles at platinum lying
between 89.42(13) and 90.87(13)°. The sum of the angles
around platinum is 360.0°. The butadiynyl groups are
nearly perfectly linear. The Pt-C distances of 1.995(5)
and 2.007(5) Å are similar to those found in 1. The C-C
bond distances reflect the formal bond orders, with short
bonds between the R- and â- carbons and γ- and
δ-carbons and longer bonds between the â- and γ-car-
bons.
F igu r e 2. Molecular structure of trans-[Pt(CtCCtCH)2-
(PEt3)2] (6b), with atoms represented by thermal ellipsoids
at the 50% level.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for tr a n s-[P t(CtCCtCH)2(P Et3)2] (6b)
Pt(1)-C(1)
Pt(1)-P(1)
C(1)-C(2)
C(3)-C(4)
C(6)-C(7)
2.007(5)
2.3154(12)
1.202(6)
1.171(7)
1.387(6)
Pt(1)-C(5)
Pt(1)-P(2)
C(2)-C(3)
C(5)-C(6)
C(7)-C(8)
1.995(5)
2.3188(12)
1.387(6)
1.211(6)
1.204(7)
C(1)-Pt(1)-C(5) 179.5(2)
C(1)-Pt(1)-P(1)
89.83(13)
89.88(13)
179.24(5)
178.4(5)
C(1)-Pt(1)-P(2)
C(5)-Pt(1)-P(2)
90.87(13) C(5)-Pt(1)-P(1)
89.42(13) P(1)-Pt(1)-P(2)
Pt(1)-C(1)-C(2) 178.1(4)
C(1)-C(2)-C(3)
Pt(1)-C(5)-C(6) 177.2(4)
C(6)-C(7)-C(8) 178.3(5)
C(2)-C(3)-C(4)
C(5)-C(6)-C(7)
179.1(5)
177.5(5)
Sch em e 1. Syn th esis of Neu tr a l Molecu la r
Squ a r es (7, L2 ) d p p p ; 8, L2 ) d cp e; 9, L ) P Et3)
[Pt(CtCCtCH)2L2] (4-6). Further reaction of 4, 5, or
6a with the corresponding [PtCl2L2] complex at 55 °C
for 2 days resulted in formation of the neutral molecular
squares [Pt(µ-CtCCtC)L2]4 (7, L2 ) dppp; 8, L2 ) dcpe;
9, L ) PEt3) in good yields (Scheme 1). Thus, coupling
of the first C-H bond with platinum occurs relatively
easily, whereas more forcing conditions are needed to
Neu tr a l Molecu la r Squ a r es. As described above,
treatment of [PtCl2L2] with butadiyne in the presence
of a catalytic amount of CuI in THF/Et2NH solution at
0 °C resulted in coupling to produce the angular unit
(41) Stang, P. J .; Cao, D. H. J . Am. Chem. Soc. 1994, 116, 4981.

Neutral Molecular Squares
Organometallics, Vol. 23, No. 19, 2004 4385
promote reaction of the second C-H bond. Our results
stand in contrast to the report by Bruce and co-workers,
who observed that copper-catalyzed coupling of [PtCl2L2]
with [Pt(CtCCtCH)2L2] resulted in polymer formation.
They were able to generate the molecular squares from
[Pt(OTf)2L2] and [Pt(CtCCtCH)2L2] in the presence of
NaOAc or Et2NH only under high-dilution conditions.26
Complexes 7-9 are off-white, air-stable solids. Each
is characterized by a single 31P resonance. As expected,
no signal corresponding to an alkynyl CH is detected
1
in the H NMR spectrum. Only in the case of 7 could
the alkynyl carbons be detected in the 13C{1H} NMR
spectrum. Here, the R-carbons appear as a doublet of
doublets at 92.0 ppm (2J PC ) 146 Hz (trans) and 19 Hz
(cis)), although the coupling to 195Pt could not be
determined, whereas the â-carbons exhibit a broad
2
singlet at 96.1 ppm, with J PtC ) 316 Hz. In complex 4
the R-carbon is more deshielded than the â-carbon, but
this trend is reversed in 7.
Unsymmetrical molecular squares were also obtained
in good yield by reaction of cis-[Pt(CtCCtCH)2(PEt3)2]
with [PtCl2L2] under similar conditions. The complexes
[Pt4(µ-CtCCtC)4(dppp)2(PEt3)4] (10) and [Pt4(µ-Ct
CCtC)4(dcpe)2(PEt3)4] (11) were isolated as light yellow,
air-stable solids. Each exhibited two 31P NMR reso-
F igu r e 3. Top view of the molecular structure of [Pt4(µ-
CtCCtC)4(dppp)4] (7), with atoms represented by thermal
ellipsoids at the 50% level.
1
nances, again with J PtP values between 2200 and 2300
It is unclear how the cations are incorporated into the
neutral molecular squares, but the fact that they are
difficult to remove by extraction and the interactions
are maintained under the conditions of mass spectrom-
etry suggests that the interactions are quite strong. It
is also uncertain whether the ammonium ions and the
alkali-metal ions bind in similar ways. Bruce and co-
Hz. Attempts to prepare a mixed-metal derivative by
reaction of 4 with [PdCl2(dppp)] were unsuccessful,
producing only a black, intractable material. Also,
reaction of [PdCl2(dppp)] with butadiyne produced a
dark solid; it may be that diphosphinepalladium species
catalyze polymerization of the dialkyne.42
We have found that it is extremely difficult to remove
the diethylammonium chloride byproduct from the
isolated molecular squares. Signals arising from the Et2-
+
workers suggested that the N-H bond(s) of the Et2NH2
cation may interact with the CtC bonds of the square.26
That may indeed be the case, and the alkali-metal ions
may bind to the triple bonds also. Such “tweezer”
interactions are well-known, particularly when Ag+ ions
are involved.43 It is also possible that the cations
interact with the aromatic rings of the dppp ligands,
but the incorporation of cations is just as effective in
the alkylphosphine-containing complexes, suggesting
that this explanation is less likely.
NH2+ cation are always found in their H NMR spectra.
1
Bruce and co-workers noted that when they used Et2NH
as base, the products also contained Et2NH2+OTf-.26
Thus, it has proved impossible to obtain satisfactory
elemental analyses for the squares. In addition to NMR
spectroscopy, we have used mass spectrometry as a
characterization method. The low-resolution FAB mass
spectrum of 7 in nitrobenzyl alcohol (NBA) produced the
anticipated parent mass envelope centered at m/z 2622
(corresponding to 7 + H+), whereas the electrospray
mass spectrum contained a cluster centered at m/z 1311
also, due to a doubly charged ion (7 + 2H+). In both
cases, in addition to the expected pattern, a second set
of peaks was observed that was shifted to higher mass
by 74 mass units, corresponding to the inclusion of one
The squares do not crystallize readily. After many
unsuccessful attempts, we were able to grow crystals
of 7 by slow diffusion of diethyl ether into a chloroform
solution. The compound crystallizes in the orthorhombic
space group Ibca, with eight half-molecules in the
asymmetric unit: i.e., four square molecules centered
around the inversion center, per unit cell. In addition
to 7, the asymmetric unit contains three water mol-
ecules, three molecules that we have modeled as aceto-
nitrile, and 1.5 molecules that we have modeled as
ethanol. The ethanol would have been present in small
amount in the solvents used, but the acetonitrile may
have been absorbed adventitiously from the atmosphere
or from solutions stored in the same location. A top view
of the molecular structure of 7 is shown in Figure 3,
and selected bond distances and angles are presented
in Table 3. The square consists of four platinum centers
at the corners, each coordinated by a chelated dppp
ligand and linked by butadiynyl groups. The Pt-C, Ct
+
Et2NH2 ion. When CsI was introduced during the
measurements, both of the above sets of peaks disap-
peared, and a new mass envelope was observed centered
at m/z 2754, corresponding to 7 + Cs+. Thus, the square
shows a greater affinity for Cs+ than for the Et2NH2
+
cation. Similar behavior was found for complexes 8-11.
When 7 was exposed to a solution containing several
alkali-metal cations, the intensities of the clusters of
peaks in the mass spectrum indicated that its affinity
for the ions decreased in the order Cs+ > K+ > Na+
>
Li+. Complexes 7 and 8 have been characterized satis-
factorily by high-resolution mass spectrometry as their
Cs+ adducts.
(43) Manna, J .; Kuehl, C. J .; Whiteford, J . A.; Stang, P. J .; Muddi-
man, D. C.; Hofstadler, S. A.; Smith, R. D. J . Am. Chem. Soc. 1997,
119, 11611.
(42) Zhan, X.; Yang, M.; Sun, H. J . Mol. Catal. A 2001, 169, 63.

4386 Organometallics, Vol. 23, No. 19, 2004
J anka et al.
F igu r e 4. Side view of [Pt4(µ-CtCCtC)4(dppp)4] (7),
showing the folding of the square to generate a butterfly-
shaped unit.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for [P t4(CtCCtC)4(d p p p )4] (7)
Pt(1)-C(1)
Pt(1)-P(1)
Pt(2)-C(4)
Pt(2)-P(3)
C(1)-C(2)
C(3)-C(4)
C(6)-C(7)
2.022(10)
2.286(2)
1.993(10)
2.281(2)
1.191(13)
1.192(13)
1.374(13)
Pt(1)-C(5)
Pt(1)-P(2)
Pt(2)-C(8#)
Pt(2)-P(4)
C(2)-C(3)
C(5)-C(6)
C(7)-C(8)
2.007(10)
2.288(2)
2.024(9)
2.285(3)
1.394(13)
1.194(13)
1.186(12)
C(1)-Pt(1)-C(5)
C(1)-Pt(1)-P(2)
C(5)-Pt(1)-P(2)
C(4)-Pt(2)-C(8#)
C(4)-Pt(2)-P(4)
85.9(4)
171.7(3)
85.9(3)
89.5(4)
87.3(3)
C(1)-Pt(1)-P(1)
C(5)-Pt(1)-P(1)
P(1)-Pt(1)-P(2)
C(4)-Pt(2)-P(3)
C(8#)-Pt(2)-P(3)
P(3)-Pt(2)-P(4)
C(1)-C(2)-C(3)
92.7(3)
178.5(3)
95.52(9)
175.0(3)
86.1(2)
97.13(9)
176.5(12)
178.4(10)
178.9(12)
C(8#)-Pt(2)-P(4) 176.8(2)
Pt(1)-C(1)-C(2)
C(2)-C(3)-C(4)
Pt(1)-C(5)-C(6)
C(6)-C(7)-C(8)
174.1(9)
177.9(11) C(3)-C(4)-Pt(2)
177.7(9) C(5)-C(6)-C(7)
176.5(11) C(7)-C(8)-Pt(2#) 175.1(8)
C, and C-C distances are similar to those found for 4.
The angles at the carbon atoms along the edges range
from 174.1 to 178.9(1)°. The geometry at platinum is
approximately square planar, the sum of the angles
around platinum being 360.0°. The largest angle (95.5°)
is that subtended by the dppp ligand. The two P-Pt-C
angles differ considerably (85.9 and 92.7°), and the
C-Pt-C angle is less than 90°. The separations of the
platinum atoms along the edges are 7.775 Å. When the
square is viewed from the side, it may be seen to have
a puckered, butterfly-like structure. Figure 4 shows a
view along one of the Pt‚‚‚Pt diagonals. Due to the
puckered nature of the ring, the diagonal Pt‚‚‚Pt dis-
tances are quite different: namely, 9.973 and 10.725
Å. This differs from the structure of [Pt(µ-CtCCtC)-
(dppe)]4, reported by Bruce and co-workers, in which the
four platinum atoms deviate from the mean plane by
only 0.08 Å.26
Consideration of the extended structure reveals some
interesting features. The puckered rings do not stack
like a series of bowls, as might be expected, but rather
they pack in a face-to-face manner, with the tips of the
butterfly pointing toward each other. This creates sets
of channels, in which the solvent molecules are located.
Figure 5 shows the view down the a axis, where the
puckered squares may be seen to form ladderlike arrays.
This results in two distinct types of channels, those
between the “rungs” of the ladder and those between
the ladders. Water and acetonitrile molecules are lo-
cated in the channels between the rungs of the ladder,
whereas all three types of solvent molecules are found
in the channels between the ladders. The view down
F igu r e 5. Packing diagram for [Pt4(µ-CtCCtC)4(dppp)4]
(7), in a view down the a axis.
the b axis (not shown) provides another perspective of
these same channels. The view along the c axis, how-
ever, directly on the face of the squares reveals no such
features, the squares being offset relative to one another
and the aromatic rings of subsequent layers also serving
to block the anticipated channels through the centers
of the squares. This is in contrast to the dppe analogue
where, although the squares are offset slightly relative
to one another, the squares do stack and this results in
narrow channels running through the centers of the
squares.26
Eth yn yl Com p lexes w ith Nitr ogen Don or s. We
have also used pyridylethynyl and (4-cyanophenyl)-
ethynyl ligands in the construction of metal-containing
arrays. Reaction of [PtCl2(dppp)] with 4-pyridylethyne
in the presence of CuI in THF/Et2NH solution gave the
angular unit [Pt(CtCC5H4N)2(dppp)] (14) in nearly
quantitative yield. [Pt(CtCC6H4CN)2(dppp)] (15) was
prepared from [PtCl2(dppp)] and (4-cyanophenyl)ethyne
under similar conditions. Each complex has been char-
acterized by NMR spectroscopy, and 15 has been
characterized by elemental analysis and 14 by an X-ray
diffraction study. Each complex exhibits a single reso-
1
nance in its 31P{1H} NMR spectrum, with a J PtP
1
coupling of about 2200 Hz. The H and 13C{1H} NMR
spectra contain the expected numbers of signals. The
resonances due to the R-carbons of the alkynyl groups

Neutral Molecular Squares
Organometallics, Vol. 23, No. 19, 2004 4387
not surprising that they should be cleaved under these
conditions. Attempts to prepare neutral macrocyclic
species using 14 or 15 have proved unsuccessful to date.
Exp er im en ta l Section
NMR spectra were recorded on a Bruker ARX-500, Varian
1
Unity plus 300, or Bruker Avance 300 spectrometer. H and
13C chemical shifts are given relative to the residual solvent
resonance; 31P chemical shifts are relative to external H3PO4.
Positive shifts represent deshielding, and coupling constants
are given in hertz. Microanalyses were performed by Atlantic
Microlab, Inc., Norcross, GA.
All reactions were carried out under an atmosphere of argon
at ambient temperature, unless specified. All solvents were
dried before use. Dichloromethane, methanol, acetonitrile, and
diethylamine were distilled from calcium hydride. THF and
diethyl ether were distilled from sodium benzophenone ketyl.
Complexes 4, 6a , 7, and 9 were prepared by Bruce and co-
workers,26 but different experimental methods were used in
our work.
F igu r e 6. Molecular structure of [Pt(CtCC5H4N)2(dppp)]
(14), with atoms represented by thermal ellipsoids at the
50% level.
P r ep a r a tion of [P t(CtCH)2(d p p e)] (1). A suspension of
[PtCl2(dppe)] (0.10 g, 0.15 mmol) in THF (40 mL) and diethyl-
amine (10 mL) was maintained at 0 °C, and CuI (1.5 mg) was
added. Ethyne gas was bubbled through the mixture for 2 h,
and then the solvent was removed under reduced pressure.
The resulting solid was dissolved in CH2Cl2 and washed
several times with water to remove the metal salts. The
organic phase was dried over MgSO4 and filtered. The filtrate
was passed through a short column of neutral alumina. The
solvent was removed, and the solid was crystallized from
CH2Cl2/ether. The solid was dried in vacuo, leaving a pale
yellow solid (0.080 g, 85%). Anal. Calcd for C30H26P2Pt: C,
56.00; H, 4.10. Found: C, 55.75; H, 4.20. 1H NMR (CDCl3):
δ(H) 2.36 (d, 2J PH ) 18 Hz, 3J PtH ) 21 Hz, PCH2), 2.54 (d, 4J PH
Ta ble 4. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for [P t(CtCC5H4N)2(d p p p )] (14)
Pt(1)-C(1)
Pt(1)-P(1)
C(1)-C(2)
C(8)-C(9)
1.998(2)
2.2917(6)
1.200(3)
1.180(4)
Pt(1)-C(8)
Pt(1)-P(2)
C(2)-C(3)
C(9)-C(10)
2.013(3)
2.2959(6)
1.437(3)
1.442(4)
C(1)-Pt(1)-C(8)
C(1)-Pt(1)-P(2)
C(8)-Pt(1)-P(2)
Pt(1)-C(1)-C(2)
Pt(1)-C(8)-C(9)
86.95(9)
90.67(7)
177.61(7)
179.6(2)
177.5(2)
C(1)-Pt(1)-P(1)
C(8)-Pt(1)-P(1)
P(1)-Pt(1)-P(2)
C(1)-C(2)-C(3)
C(8)-C(9)-C(10)
177.64(7)
90.75(6)
91.64(2)
175.0(3)
173.4(3)
in 14 and 15 appear as doublets of doublets at 114.4
and 112.3 ppm, respectively, but couplings to 195Pt are
not observed. The â-carbon signals appear at 106.7 and
3
) 4 Hz, J PtH ) 43 Hz, CH), 7.95-7.27 (m, PPh2). 13C{1H}
NMR: δ(C) 28.8 (s, 2J PtC ) 26 Hz, PCH2), 97.5 (dd, 2J PC ) 144,
3
2
15 Hz, PtC), 97.5 (d, J PC ) 34 Hz, J PtC ) 311 Hz, PtCtCH),
133.7, 131.4, 130.1, 128.9 (PPh2). 31P{1H} NMR: δ(P) 40.8 (s,
1J PtP ) 2288 Hz). Crystals suitable for an X-ray diffraction
study were obtained by slow diffusion of ether into a CH2Cl2
solution.
2
109.7 ppm, and a value of J PtC of 335 Hz is found in
each case.
The molecular structure of 14 is shown in Figure 6,
and selected bond distances and angles are presented
in Table 4. The geometry at platinum is approximately
square planar, the sum of the angles around the metal
center being 360.0°. The C-Pt-C angle is smaller than
90°, and the other three angles are slightly greater than
90°. The alkynylplatinum units are nearly linear. The
Pt-C(1) and Pt-C(8) distances are 1.998(2) and 2.013(3)
Å, respectively, and the corresponding CtC distances
are 1.200(3) and 1.180(4) Å. The Pt-N distances are
7.44 Å. The Pt‚‚‚N vectors are nearly perpendicular to
one another, so this unit represents a suitable corner
unit for the construction of metal-containing squares.
Reaction of 14 or 15 with 1 equiv of AgNO3 in MeOH/
MeCN solution produced a light yellow solid that
exhibits a single resonance in its 31P{1H} NMR spec-
trum. In each case the signal is shifted by about 2 ppm
P r ep a r a tion of [P t(CtCH)2(d p p p )] (2). This complex was
prepared similarly, starting from [PtCl2(dppp)], and obtained
as a pale yellow solid in 87% yield. HRMS (NBA) in FAB
12
mode: calcd for
C
H29P2195Pt+ (MH+), 658.1396; found,
31
658.1394. 1H NMR (CDCl3): δ(H) 2.01 (br, CH2), 2.45 (br,
4
3
PCH2), 2.21 (d, J PH ) 3.6 Hz, J PtH ) 48 Hz, CH), 7.74-7.27
(m, PPh2). 13C{1H} NMR: δ(C) 20.5 (s, CH2), 26.3 (s, J PtC
)
2
36 Hz, PCH2), 95.8 (t, 3J PC ) 17 Hz, 2J PtC ) 305 Hz, 2C, PtCt
2
CH), 97.3 (dd, J PC ) 145, 21 Hz, PtC), 128.3, 130.8, 131.5,
134.0 (PPh2). 31P{1H} NMR: δ(P) -6.4 (s, J PtP ) 2195 Hz).
1
P r ep a r a tion of cis-[P tCtCH)2(P Et3)2)] (3a ). This com-
plex was prepared analogously from cis-[PtCl2(PEt3)2], and
1
isolated as an off-white solid in 93% yield. H NMR (CDCl3):
4
δ(H) 1.04 (m, CH3), 2.03 (m, PCH2), 2.32 (d, J PH ) 3.5 Hz,
3
3J PtH ) 48 Hz, CH). 13C{1H} NMR: δ(C) 8.7 (s, J PtC ) 21 Hz,
3
2
CH3), 17.0 (m, PCH2), 92.7 (t, J PC ) 16 Hz, J PtC ) 297 Hz,
1
to low frequency, and the J PtP value is increased by 22
PtCtCH), 98.7 (dd, 2J PC ) 140 Hz, 2J PC ) 21 Hz, PtC). 31P{1H}
NMR: δ(P) 4.6 (s, J PtP ) 2267 Hz).
or 46 Hz, respectively. The products are clearly sym-
metrical in nature, and we propose that they have the
octametallic structures [{Pt(CtCC5H4N)2(dppp)}4Ag4]-
(NO3)4 (16) and [{Pt(CtCC6H4CN)2-(dppp)}4Ag4](NO3)4
(17). We have been unable to grow crystals of these
materials. Although the entire cation does not survive
electrospray mass spectrometry, fragments correspond-
ing to one Ag+ ligated by two units of 14 or 15 are
observed. Since Ag-N bonds are relatively weak, it is
1
P r ep a r a tion of tr a n s-[P t(CtCH)2(P Et3)2)] (3b). This
complex was prepared analogously from trans-[PtCl2(PEt3)2]
1
and isolated as a yellow solid in 94% yield. H NMR (CDCl3):
δ(H) 1.20 (m, CH3), 2.14 (m, PCH2). The CH signal is obscured
3
by the PCH2 resonance. 13C{1H} NMR: δ(C) 9.2 (s, J PtC ) 25
1
2
Hz, CH3), 16.8 (t, J PC ) 18 Hz, J PtC ) 72 Hz, PCH2), 95.0 (s,
2J PtC ) 271 Hz, PtCtCH), 101.4 (t, J PC ) 143 Hz, J PtC 485
2
1
Hz, PtC). 31P{1H} NMR: δ(P) 11.6 (s, J PtP ) 2368 Hz).
1

4388 Organometallics, Vol. 23, No. 19, 2004
J anka et al.
P r ep a r a tion of Bu ta d iyn e.44 KOH (9.0 g, 0.08 mol), water
(20.0 mL), and DMSO (5.0 mL) were heated to 70 °C for 30
min in a three-necked flask equipped with a condenser and a
dropping funnel. The top of the condenser was connected, via
a tube filled with CaCl2, to a trap containing dry THF, which
was cooled to -78 °C. 1,4-Dichloro-2-butyne (4.0 mL, 0.04 mol)
was added dropwise over a period of 30 min, while the
temperature was maintained at 70 °C. A stream of argon was
passed through the apparatus, which forced the butadiyne into
the cold THF trap. The THF solution was stored at -45 °C in
a sealed container. The weight increase of the trap cor-
responded to an 80% yield. The material could be stored for
at least 3 days without significant deterioration.
0.14 mmol) were stirred in THF (50 mL) and diethylamine
(20 mL) in the presence of CuI (2.6 mg) at 55 °C for 2 days. A
yellow suspension formed. The solvent was removed under
reduced pressure. The residue was dissolved in CH2Cl2, and
the resulting solution was washed several times with water.
The organic phase was dried over MgSO4 and filtered. The
filtrate was passed through a short column of neutral alumina.
The solvent was removed, and the solid was crystallized from
CH2Cl2/ether. The solid was dried in vacuo, yielding an off-
white solid (0.14 g, 78%). HRMS (NBA, CsI) in FAB mode:
12
calcd for
C
H104P8195Pt4Cs+ (M + Cs+), 2753.3658; found,
124
2753.3638. 1H NMR (CDCl3): δ(H) 1.93 (br, CH2), 2.37 (br,
PCH2), 7.07-7.62 (m, PPh2). 13C{1H} NMR (DMSO-d6): δ(C)
2
2
18.8 (s, CH2), 24.1 (m, PCH2), 92.0 (dd, J PC ) 146 Hz, J PC
)
P r ep a r a tion of [P t(CtCCtCH)2(d p p p )] (4). To a sus-
pension of [PtCl2(dppp)] (0.10 g, 0.15 mmol) in THF (40 mL)
and diethylamine (10 mL) was added CuI (1.5 mg). The
mixture was maintained at 0 °C, and a cold THF solution (10
mL) of butadiyne was introduced. The reaction mixture was
stirred for 2 h at 0 °C, and the solvent was removed under
reduced pressure. The resulting solid was dissolved in CH2Cl2
and washed several times with water. The organic phase was
dried over MgSO4 and filtered. The filtrate was passed through
a short column of neutral alumina. The solvent was removed,
and the solid was crystallized from CH2Cl2/ether. The solid
was dried in vacuo, yielding a pale yellow-brown solid (0.097
g, 95%). Anal. Calcd for C35H28P2Pt: C, 59.57; H, 4.10. Found:
C, 58.82; H, 4.26.1H NMR (CDCl3): δ(H) 1.6 (s, CH), 2.03 (br,
CH2), 2.50 (br, PCH2), 7.66-7.26 (m, PPh2).13C{1H} NMR
(DMSO-d6): δ(C) 19.8 (s, CH2), 24.4 (m, PCH2), 65.2 (s, δ-C),
2
19 Hz, PtC), 96.1 (br, J PtC ) 316 Hz, PtCtC), 127.6, 130.3,
132.1, 134.5 (PPh2).31P{1H} NMR: δ(P) -8.5 (s, J PtP ) 2202
1
Hz). Crystals suitable for an X-ray diffraction study were
grown from a CHCl3/Et2O/MeCN mixture.
P r ep a r a tion of [P t(µ-CtCCtC)(d cp e)]4 (8). This com-
plex was prepared in a similar manner from [Pt(dcpe)(CtCCt
CH)2] and [PtCl2(dcpe)] and isolated as a brown solid in 86%
12
yield. HRMS (NBA, CsI) in FAB mode: Calcd for
C
H192P8-
120
195Pt4Cs+ (M + Cs+), 2794.0569; found, 2794.0464. 1H NMR
(CDCl3): δ(H) 1.12-2.45 (m, CH and CH2). 31P{1H} NMR: δ-
1
(P) 62.6 (s, J PtP ) 2288 Hz).
P r ep a r a tion of [P t(µ-CtCCtC)(P Et3)2]4 (9). This com-
plex was prepared in a similar manner from cis-[Pt(PEt3)2-
(CtCCtCH)2] and cis-[PtCl2(PEt3)2] and obtained as an off-
white solid in 77% yield. LRMS in ESI+ mode, m/z (relative
intensity calculated, observed) for C64H120P8Pt4Cs+ (MCs+):
2046 (20, 24), 2047 (47, 49), 2048 (77, 79), 2049 (98, 96), 2050
(100, 100), 2051 (87, 92), 2052 (66, 72), 2053 (46, 50), 2054
(28, 33). 1H NMR (CDCl3): δ(H) 1.14 (m, CH3), 2.06 (m, PCH2).
3
2
72.8 (s, γ-C), 91.2 (t, J PC ) 16 Hz, J PtC ) 431 Hz, â-C), 98.9
(dd, 2J PC ) 146, 21 Hz, R-C), 129.1, 131.2, 131.7, 134.2 (PPh2).
31P{1H} NMR (CDCl3): δ(P) -7.1 (s, J PtP ) 2200 Hz).
1
P r ep a r a tion of [P t(CtCCtCH)2(d cp e)] (5). This com-
plex was prepared in a similar manner from [PtCl2(dcpe)] and
obtained as a pale yellow solid in 80% yield. Anal. Calcd for
1
31P{1H} NMR: δ(P) 6.4 (s, J PtP ) 2318 Hz).
P r ep a r a tion of [P t4(µ-CtCCtC)4(d p p p )2(P Et3)4] (10).
This complex was prepared in a similar manner from cis-[Pt-
(PEt3)2(CtCCtCH)2] and [PtCl2(dppp)]. It was obtained as a
C
34H50P2Pt‚0.25CH2Cl2: C, 55.81; H, 6.91. Found: C, 55.70;
1
H, 6.95. H NMR (CDCl3): δ(H) 1.12-2.45 (m, CH and CH2).
13C{1H} NMR: δ(C) 23.4 (dd, 1J PC ) 31 Hz, 1J PC ) 10 Hz, 2J PtC
1
light yellow solid in 82% yield. H NMR (CDCl3): δ(H) 1.12-
4
) 45 Hz, PCH), 26.1 (s, CH2), 27.0 (s, J PtC ) 22 Hz, CH2),
2.41 (m, CH2 and CH3), 7.02-7.68 (m, PPh2). 31P{1H} NMR:
3
2
1
28.9 (d, J PtC ) 22 Hz, J PC ) 20 Hz, CH2), 34.7 (d, J PC ) 31
1
1
δ(P) 6.3 (s, J PtP ) 2284 Hz, PEt3), -6.7 (s, J PtP ) 2208 Hz,
2
3
Hz, J PtC ) 24 Hz, PCH2), 60.9 (s, δ-C), 72.8 (s, J PtC ) 36 Hz,
dppp).
γ-C), 93.4 (d, 3J PC ) 32 Hz, 2J PtC ) 311 Hz, â-C), 99.2 (dd, 2J PC
) 136, 15 Hz, J PtC ) 1130 Hz, R-C). 31P{1H} NMR: δ(P) 62.9
1
P r ep a r a tion of [P t 4(µ-CtCCtC)4(d cp e)2(P Et 3)4] (11).
This complex was prepared in a similar manner from cis-[Pt-
(PEt3)2(CtCCtCH)2] and [PtCl2(dcpe)]. It was obtained as a
light yellow solid in 82% yield. LRMS in ESI+ mode, m/z
(relative intensity calculated, observed) for C92H156P8Pt4Cs+
(MCs+): 2420 (69, 70), 2421 (92, 90), 2422 (100, 100) 2423 (92,
90), 2424 (73, 80), 2425 (52,59). 1H NMR (CDCl3): δ(H) 1.07-
1
(s, J PtP ) 2273 Hz).
P r ep a r a tion of cis-[P t(CtCCtCH)2(P Et3)2] (6a ). This
complex was prepared analogously from cis-[PtCl2(PEt3)2] and
isolated as an off-white solid in 83% yield. Anal. Calcd for
C
20H32P2Pt: C, 45.73; H, 6.09. Found: C, 45.03; H, 5.80. 1H
5
NMR (CDCl3): δ(H) 1.13 (m, CH3), 1.86 (s, J PtH ) 9 Hz, CH),
1
2.45 (m, CH, CH2 and CH3). 31P{1H} NMR: δ(P) 5.3 (s, J PtP
2.03 (m, PCH2). 13C{1H} NMR: δ(C) 8.5 (s, 3J PtC ) 21 Hz, CH3),
1
) 2282 Hz, PEt3), 62.4 (s, J PtP ) 2292 Hz, dcpe).
1
2
17.1 (t, J PC ) 18 Hz, J PtC ) 52 Hz, PCH2), 61.1 (s, δ-C), 72.3
3
3
2
P r ep a r a tion of [P t 2(µ-CtCCtC)2(d cp e)(P Et 3)2]4 (12).
[PtCl2(dcpe)] (0.10 g, 0.15 mmol) and trans-[Pt(PEt3)2(CtCCt
CH)2] (0.076 g, 0.15 mmol) were stirred in THF (50 mL) and
diethylamine (20 mL) in the presence of CuI (2.6 mg) at 55 °C
for 2 days. A yellow suspension formed. The solvent was
removed under reduced pressure. The residue was dissolved
in CH2Cl2 and washed several times with water. The organic
phase was dried over MgSO4 and filtered. The filtrate was
passed through a short column of neutral alumina. The solvent
was removed, and the solid was crystallized from CH2Cl2/ether,
(s, J PtC ) 38 Hz, γ-C), 88.9 (t, J PC ) 17 Hz, J PtC ) 307 Hz,
â-C), 96.7 (dd, 2J PC ) 142, 22 Hz, 1J PtC ) 1083 Hz, R-C). 31P{1H}
1
NMR: δ(P) 5.7 (s, J PtP ) 2270 Hz).
P r epar ation of tr a n s-[P t(CtCCtCH)2(P Et3)2] (6b). This
complex was prepared similarly from trans-[PtCl2(PEt3)2] and
obtained as a yellow solid in 87% yield. Anal. Calcd for
C
20H32P2Pt: C, 45.73; H, 6.09. Found: C, 45.41; H, 6.17. 1H
5
NMR (CDCl3): δ(H) 1.17 (m, CH3), 1.82 (s, J PtH ) 9 Hz, CH),
2.10 (m, PCH2). 13C{1H} NMR: δ(C) 8.4 (s, 3J PtC ) 23 Hz, CH3),
1
2
16.4 (t, J PC ) 18 Hz, J PtC ) 70 Hz, PCH2), 59.8 (s, δ-C), 72.3
1
3
2
yielding a yellow solid (0.146 g, 87%). H NMR (CDCl3): δ(H)
(s, J PtC ) 36 Hz, γ-C), 91.0 (s, J PtC ) 287 Hz, â-C), 100.1 (t,
1.13-2.35 (m, CH, CH2, and CH3). 31P{1H} NMR: δ(P) 12.3
2J PC ) 15 Hz, J PtC ) 1002 Hz, R-C). 31P{1H} NMR: δ(P) 13.8
1
1
1
1
(s, J PtP ) 2338 Hz, PEt3), 62.0 (s, J PtP ) 2329 Hz, dcpe).
(s, J PtP ) 2299 Hz). Crystals suitable for an X-ray diffraction
study were obtained by slow diffusion of pentane into a CH2Cl2
solution.
P r ep a r a tion of [P t(µ-CtCCtC)(d p p p )]4 (7). [Pt(dppp)-
(CtCCtCH)2] (0.10 g, 0.14 mmol) and [PtCl2(dppp)] (0.096 g,
P r ep a r a tion of [P t2(µ-CtCCtC)2(d p p p )(P Et3)2]4 (13).
This complex was prepared in a similar manner from trans-
[Pt(PEt3)2(CtCCtCH)2] and [PtCl2(dppp)]. The product was
obtained as a light yellow solid (0.19 g, 82%). 1H NMR
(CDCl3): δ(H) 1.07-2.45 (m, CH2 and CH3). 31P{1H} NMR:
1
1
δ(P) 13.7 (s, J PtP ) 2368 Hz, PEt3), -6.7 (s, J PtP ) 2212 Hz,
(44) Brandsma, L. Preparative Acetylenic Chemistry, 2nd ed.; Elsevi-
er: New York, 1988; p 179.
dppp).

Neutral Molecular Squares
Organometallics, Vol. 23, No. 19, 2004 4389
Ta ble 5. Cr ysta l Da ta a n d Str u ctu r e Refin em en t Deta ils for [P t(CtCH)2(d p p e)] (1),
tr a n s-[P t(CtCCtCH)2(P Et3)2] (6b), [P t4(CtCCtC)4(d p p p )4] (7), a n d [P t(CtCC5H4N)2(d p p p )] (14)
Pt(CtCH)2(dppe)
(1)
Pt(CtCCtCH)2(PEt3)2
(6b)
Pt4(CtCCtC)4(dppp)4
(7)
Pt(CtCC5H4N)2(dppp)
(14)
cryst syst
space group, Z
a, Å
b, Å
monoclinic
P21/n, 4
9.2339(1)
13.7662(2)
19.8834(3)
90
93.027(1)
90
2523.97(6)
1.694
orthorhombic
Pna21, 4
16.6199(5)
7.2620(2)
17.6231(5)
90
orthorhombic
Ibca, 8
19.9283(3)
33.6486(5)
43.7364(8)
90
triclinic
P1h, 2
10.5896(2)
13.0367(2)
14.1702(3)
67.352(1)
75.040(1)
79.537(1)
1736.78(6)
1.552
c, Å
R, deg
â, deg
90
90
90
90
γ, deg
V, Å3
2127.00(11)
1.653
170(2)
6.746
1040
29 327.9(8)
1.411
120(2)
3.946
12 400
density (calcd), Mg/m3
temp, K
218(2)
5.702
1256
223(2)
4.163
804
abs coeff, mm-1
F(000)
θ range, deg
2.05-27.00
2.31-30.01
1.86-26.00
1.70-28.00
no. of rflns collected
no. of indep rflns
abs cor
57 794
50 454
201 666
3 270
5516 (Rint ) 0.031)
empirical
5516/3/310
1.239
5879 (Rint ) 0.0252)
empirical
5879/1/208
0.928
14 413 (Rint ) 0.1005)
empirical
14 413/0/760
1.144
8288 (Rint ) 0.022)
empirical
8288/0/415
1.129
no. of data/restraints/params
goodness of fit on F2
final R indices (F2 > 2.0σ(F2)):
R(F), Rw(F2)
0.026, 0.072
0.022, 0.054
0.062, 0.187
0.022, 0.043
largest diff peak and hole, e Å-3
0.94, -0.87
3.74, -1.15
2.96, -1.57
0.82, -0.75
2
2
P r ep a r a tion of 4-HCtCC5H4N. 4-Bromopyridine hydro-
chloride (2.0 g, 10.3 mmol) and diethylamine (20 mL) were
stirred overnight in THF (50 mL) in the absence of light to
obtain free 4-bromopyridine. HCtCSi(CH3)3 (1.5 mL, 10.6
mmol), CuI (0.04 g), and [PdCl2(PPh3)2] (0.14 g) were added,
and the reaction mixture was stirred overnight in the absence
of light. The solvent was removed under reduced pressure. The
residue was extracted several times with diethyl ether, and
the ether extracts were passed through neutral alumina. The
solvent was removed to afford 4-((trimethylsilyl)ethynyl)-
pyridine. Desilylation of this material was achieved by treat-
ment with 2.0 N NaOH (2.0 mL) in methanol (30 mL) at room
temperature for 2 h. Removal of the solvent under reduced
pressure and purification by chromatography on alumina, with
hexane/benzene as eluent (3/2), resulted in isolation of a light
yellow solid (0.52 g, 50% overall yield). 4-(CH3)3SiCtCC5H4N:
1H NMR (CDCl3) δ(H) 0.25 (s, CH3) 7.04 (d, 3J HH ) 6 Hz, CH),
(s, CH2), 26.3 (m, PCH2), 114.4 (dd, J PC ) 124 Hz, J PC ) 21
Hz, PtC), 106.7 (t, 3J PC ) 17 Hz, 2J PtC ) 335 Hz, PtCtC), 125.7,
129.0, 131.2, 131.6, 134.0, 135.7, 149.4 (C5H4N, PPh2).31P{1H}
1
NMR: δ(P) -5.6 (s, J PtP ) 2198 Hz). Crystals suitable for an
X-ray diffraction study were obtained by slow evaporation of
a CH2Cl2/Et2O solution.
P r ep a r a tion of [P t(CtCC6H4CN)2(d p p p )] (15). This
complex was prepared similarly from [PtCl2(dppp)] and 4-HCt
CC6H4CN and obtained as a yellow solid (0.122 g, 95%). Anal.
Calcd for C45H34P2NPt‚CH2Cl2: C, 58.48; H, 3.84. Found: C,
58.47; H, 3.64. 1H NMR (CDCl3): δ(H) 2.11 (br, CH2), 2.56 (br,
PCH2), 6.82-7.74 (m, C5H4N, PPh2). 13C{1H} NMR: δ(C) 20.2
2
2
(s, CH2), 26.1 (m, PCH2), 112.3 (dd, J PC ) 146 Hz, J PC ) 21
Hz, PtC), 109.7 (t, 3J PC ) 17 Hz, 2J PtC ) 335 Hz, PtCtC), 108.1
(CN), 119.7, 128.6, 130.6, 131.0, 131.2, 131.9, 133.0, 133.7
(C6H4, PPh2). 31P{1H} NMR: δ(P) -5.5 (s, J PtP ) 2192 Hz).
1
P r ep a r a t ion of [P t4(µ-CtCC5H 4N)8(d p p p )4Ag4](NO3)4
(16). [Pt(CtCC5H4N)2(dppp)] (0.10 g, 0.12 mmol) and AgNO3
(0.02 g, 0.12 mmol) were dissolved in MeOH/CH3CN (1:1, 20
mL) and stirred overnight in the absence of light. The solvents
were removed, and the resulting solid was crystallized from
CH2Cl2/ether, yielding a light yellow solid, which was dried
in vacuo (0.098 g, 81%). LRMS in ESI+ mode, m/z (relative
intensity calculated, observed) for C82H68P4N4Pt2Ag: 1728 (37,
35), 1729 (70, 67), 1730 (92, 92), 1731 (100, 100), 1732 (84,
3
8.28 (d, J HH ) 6 Hz, CH); 13C{1H} NMR δ(C) -0.2 (s, CH3),
100.2, 102.0 (CtC), 126.0 (CH), 149.8 (CH), 131.4 (s, ipso C).
4-HCtCC5H4N: 1H NMR (CDCl3) δ(H) 3.31 (s, CtCH), 7.37
(d, 3J HH ) 6 Hz, CH), 8.61 (d, 3J HH ) 6 Hz, CH); 13C{1H} NMR
δ(C) 81.3 (CtCH), 82.3 (CtCH), 130.7 (s, ipso C), 126.5 (CH),
150.2 (CH).
P r ep a r a tion of 4-HCtCC6H4CN. This ligand was pre-
pared in a similar manner from 4-bromobenzonitrile, HCtCSi-
(CH3)3, CuI, and [PdCl2(PPh3)2], followed by desilylation with
NaOH in methanol, and isolated in a 75% overall yield.
4-(CH3)3SiCtCC6H4CN: 1H NMR (CDCl3) δ(H) 0.07 (s, CH3),
7.37 (CH); 13C{1H} NMR δ(C) 0.1 (s, CH3), 100.0, 103.4 (Ct
C), 112.1 (CN), 118.8 (CH), 128.4 (ipso C), 132.3 (ipso C), 132.8
(CH). 4-HCtCC6H4CN: 1H NMR (CDCl3) δ(H) 3.9 (s, CH) 7.51
(CH); 13C{1H} NMR δ(C) 79.4 (CtCH), 81.7 (CtCH), 112.4
(CN), 118.4 (ipso C), 127.1 (CH), 132.1 (ipso C), 132.8 (CH).
P r ep a r a tion of [P t(CtCC5H4N)2(d p p p )] (14).41 A sus-
pension of [PtCl2(dppp)] (0.10 g, 0.15 mmol) and 4-HCt
CC5H4N (0.031 g, 0.30 mmol) in THF (40 mL) and diethyl-
amine (10 mL) was maintained at 0 °C, and CuI (1.5 mg) was
added. The reaction mixture was stirred for 2 h at 0 °C, and
the solvent was removed under reduced pressure. The residue
was dissolved in CH2Cl2 and washed several times with water.
The organic phase was dried over MgSO4 and filtered. The
filtrate was passed through a short column of neutral alumina.
The solvent was removed, and the solid was crystallized from
1
89), 1733 (60, 64), 1734 (36, 38). H NMR (CDCl3): δ(H) 2.07
(br, CH2), 2.67 (br, PCH2), 6.60-7.63 (m, C5H4, PPh2). 31P{1H}
1
NMR: δ(P) -7.5 (s, J PtP ) 2320 Hz).
P r ep a r a tion of [P t4(µ-CtCC6H4CN)8(d p p p )4Ag4](NO3)4
(17). This complex was prepared similarly from [Pt(CtCC6H4-
CN)2(dppp)] and AgNO3 and obtained as a light yellow solid
in 78% yield. LRMS in ESI+ mode, m/z (relative intensity
calculated, observed) for C90H68P4N4Pt2Ag: 1824 (35, 34), 1825
(68, 68), 1826 (91, 94), 1827 (100, 100), 1828 (86, 90), 1829
1
(63, 66), 1830 (38, 42). H NMR (CDCl3): δ(H) 2.25 (br, CH2),
2.68 (br, PCH2), 6.67-7.63 (m, C6H4, PPh2). 31P{1H} NMR: δ(P)
1
-8.2 (s, J PtP ) 2338 Hz).
X-r a y Str u ctu r e Deter m in a tion s. Preliminary examina-
tion and data collection were performed using a Bruker
SMART CCD detector system single-crystal X-ray diffracto-
meter equipped with a sealed-tube X-ray source (40 kV × 50
mA) using graphite-monochromated Mo KR radiation (λ )
0.710 73 Å). Preliminary unit cell constants were determined
with a set of 45 narrow-frame (0.3° in ω) scans. The double-
pass method of scanning was used to exclude any noise. The
collected frames were integrated using an orientation matrix
1
CH2Cl2/ether, yielding a yellow solid (0.116 g, 96%). H NMR
(CDCl3): δ(H) 2.09 (m, CH2), 2.56 (m, PCH2), 6.67 (br, C5H4N),
7.27-7.73 (m, PPh2), 8.23 (br, C5H4N). 13C{1H} NMR: δ(C) 19.2

4390 Organometallics, Vol. 23, No. 19, 2004
J anka et al.
determined from the narrow-frame scans. The SMART soft-
ware package was used for data collection, and SAINT was
used for frame integration.45 Final cell constants were deter-
mined by a global refinement of xyz centroids of reflections
harvested from the entire data set. An empirical absorption
correction was applied using equivalent reflections (SAD-
ABS).46 Structure solution and refinement were carried out
using the SHELXTL-PLUS software package.47 The absolute
structure of 6b was determined using the Flack parameter x
) 0.1(1). Crystallographic data are collected in Table 5.
Ack n ow led gm en t. Thanks are expressed to the
University of MissourisSt. Louis for a Research Award
for support of this work and to the NSF (Grant Nos.
CHE-9318696, 9309690, and 9974801), the U.S. Depart-
ment of Energy (Grant No. DE-FG02-92CH10499), and
the University of Missouri Research Board for instru-
mentation grants. We thank Dr. R. Winter and Mr. J .
Kramer for help with the mass spectra.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates and displacement parameters, and
all bond distances and angles. This material is available free
of charge via the Internet at http://pubs.acs.org.
(45) SMART and SAINT; Bruker Analytical X-ray Division, Madi-
son, WI, 2002.
(46) SADABS: Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51,
33.
(47) Sheldrick, G. M. SHELXTL-PLUS Software Package; Bruker
Analytical X-ray Division, Madison, WI, 2002.
OM049690W