Chelating effect as a driving force for the selective formation of heteroligated Pt(II) complexes with bidentate phosphino-chalcoether ligands

Article abstract of DOI:10.1021/ic101973s

The halide-induced ligand rearrangement reaction (HILR) has been employed to provide selective and exclusive in situ formation of heteroligated Rh(I), Pd(II), and Pt(II) complexes with bidentate phosphino-chalcoether ligands. To gain insights on the natur

Full text of DOI:10.1021/ic101973s

Inorg. Chem. 2011, 50, 1411–1419 1411
DOI: 10.1021/ic101973s
Chelating Effect as a Driving Force for the Selective Formation of Heteroligated
Pt(II) Complexes with Bidentate Phosphino-Chalcoether Ligands
Mari S. Rosen,† Alexander M. Spokoyny,† Charles W. Machan, Charlotte Stern, Amy Sarjeant, and Chad A. Mirkin*
Department of Chemistry and International Institute for Nanotechnology, Northwestern University,
2145 Sheridan Road, Evanston, Illinois 60208, United States. †These authors contributed equally to this work.
Received September 27, 2010
The halide-induced ligand rearrangement reaction (HILR) has been employed to provide selective and exclusive in situ
formation of heteroligated Rh(I), Pd(II), and Pt(II) complexes with bidentate phosphino-chalcoether ligands. To gain
insights on the nature of this unique reaction, we explored this process via the stepwise addition of bidentate
phosphino-chalcoether (P, X; X = S or Se) and relevant monodentate phosphine ligands with a Pt(II) metal precursor.
The corresponding monoligated complexes were obtained in quantitative yields by reacting 1 equiv of a P, X bidentate
ligand with Pt(II) and were fully characterized via single crystal X-ray diffraction studies and heteronuclear (31P, 77Se,
and 195Pt) NMR spectroscopy in solution. These species were further reacted with a second equivalent of either a
bidentate ligand or the monodentate ethyl diphenylphosphine ligand, resulting in the clean formation of the
heteroligated species or, in the case of the monodentate ligand with an electron-withdrawing bidentate ligand, a
mixture of products. On the basis of competitive exchange reactions between these heteroligated, homoligated, and
monoligated complexes, we conclude that ligand chelation plays a crucial role in the Pt(II) HILR. The in situ preferable
formation of the stable monoligated complex allows for ligand sorting to occur in these systems. In all cases where the
heteroligated product results, the driving force to these species is ligand chelation.
Introduction
it yields flexible species where the distances between the
chemically active functionalities can be modulated via revers-
ible chemistry on metal centers coordinated to hemilabile
ligands (1-6, Scheme 1).4 Metals that have been explored in
the context of the WLA include Rh(I),5 Ru(II), 6 Pd(II),5a,f,7
Coordination chemistry-based approaches for construct-
ing supramolecular structures are well-established, with three
general substrategies emerging: the directional bonding,1
symmetry interaction,2 and weak-link approaches.3 While
the former two approaches result in rigid structures with well-
defined cavities, the weak-link approach (WLA) is unique as
(4) (a) Gianneschi, N. C.; Bertin, P. A.; Nguyen, S. T.; Mirkin, C. A.;
Zakharov, L. N.; Rheingold, A. L. J. Am. Chem. Soc. 2003, 125, 10508.
(b) Gianneschi, N. C.; Cho, S.-H.; Nguyen, S. T.; Mirkin, C. A. Angew. Chem.,
Int. Ed. 2004, 43, 5503. (c) Gianneschi, N. C.; Nguyen, S. T.; Mirkin, C. A.
J. Am. Chem. Soc. 2005, 127, 1644. (d) Masar, M. S., III; Gianneschi, N. C.;
Oliveri, C. G.; Stern, C. L.; Nguyen, S. T.; Mirkin, C. A. J. Am. Chem. Soc. 2007,
129, 10149. (e) Oliveri, C. G.; Gianneschi, N. C.; Nguyen, S. T.; Mirkin, C. A.;
Stern, C. L.; Wawrzak, Z.; Pink, M. J. Am. Chem. Soc. 2006, 128, 16286.
(f) Yoon, H. J.; Heo, J.; Mirkin, C. A. J. Am. Chem. Soc. 2007, 129, 14182.
(g) Yoon, H. J.; Mirkin, C. A. J. Am. Chem. Soc. 2008, 130, 11590.
(5) (a) Eisenberg, A. H.; Ovchinnikov, M. V.; Mirkin, C. A. J. Am. Chem.
Soc. 2003, 125, 2836. (b) Farrell, J. R.; Eisenberg, A. H.; Mirkin, C. A.; Guzei,
I. A.; Liable-Sands, L. M.; Incarvito, C. D.; Rheingold, A. L.; Stern, C. L.
Organometallics 1999, 18, 4856. (c) Farrell, J. R.; Mirkin, C. A.; Guzei, I. A.;
Liable-Sands, L. M.; Rheingold, A. L. Angew. Chem., Int. Ed. 1998, 37, 465.
(d) Gianneschi, N. C.; Mirkin, C. A.; Zakharov, L. N.; Rheingold, A. L. Inorg.
Chem. 2002, 41, 5326. (e) Jeon, Y.-M.; Heo, J.; Brown, A. M.; Mirkin, C. A.
Organometallics 2006, 25, 2729. (f) Wiester, M. J.; Mirkin, C. A. Inorg. Chem.
2009, 48, 8054.
*To whom correspondence should be addressed. E-mail: chadnano@
northwestern.edu. Fax: (1) 847-467-5123.
(1) (a) Andres, R. P.; Bein, T.; Dorogi, M.; Feng, S.; Henderson, J. I.;
Kubiak, C. P.; Mahoney, W.; Osifchin, R. G.; Reifenberger, R. Science 1996,
272, 1323. (b) Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1989, 111, 5962.
(c) Klosterman, J. K.; Yamauchi, Y.; Fujita, M. Chem. Soc. Rev. 2009, 38, 1714.
(d) Lee, S. J.; Lin, W. Acc. Chem. Res. 2008, 41, 521. (e) Leininger, S.; Olenyuk,
B.; Stang, P. J. Chem. Rev. 2000, 100, 853. (f) Lu, Z.; Knobler, C. B.; Furukawa,
H.; Wang, B.; Liu, G.; Yaghi, O. M. J. Am. Chem. Soc. 2009, 131, 12532.
(g) Piermattei, A.; Giesbers, M.; Marcelis, A. T. M.; Mendes, E.; Picken, S. J.;
Crego-Calama, M.; Reinhoudt, D. N. Angew. Chem., Int. Ed. 2006, 45, 7543.
(h) Spokoyny, A. M.; Kim, D.; Sumrein, A.; Mirkin, C. A. Chem. Soc. Rev. 2009,
38, 1218. (i) Wurthner, F.; You, C.-C.; Saha-Moller Chantu, R. Chem. Soc. Rev.
2004, 33, 133. (j) Amijs, C. H. M.; van Klink, G. P. M.; van Koten, G. Dalton
Trans. 2006, 308.
(2) (a) Albrecht, M. Chem. Soc. Rev. 1998, 27, 281. (b) Faiz, J. A.; Heitz, V.;
Sauvage, J.-P. Chem. Soc. Rev. 2009, 38, 422. (c) Fiedler, D.; Leung, D. H.;
Bergman, R. G.; Raymond, K. N. Acc. Chem. Res. 2005, 38, 349. (d) Flamigni,
L.; Collin, J.-P.; Sauvage, J.-P. Acc. Chem. Res. 2008, 41, 857. (e) Lehn, J.-M.
Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 4763. (f) Pluth, M. D.; Bergman, R. G.;
Raymond, K. N. J. Am. Chem. Soc. 2008, 130, 11423. (g) Stoddart, J. F. Chem.
Soc. Rev. 2009, 38, 1521.
(6) Kuwabara, J.; Stern, C. L.; Mirkin, C. A. J. Am. Chem. Soc. 2007, 129,
10074.
(7) (a) Eisenberg, A. H.; Dixon, F. M.; Mirkin, C. A.; Stern, C. L.; Incarvito,
C. D.; Rheingold, A. L. Organometallics 2001, 20, 2052. (b) Spokoyny, A. M.;
Reuter, M. G.; Stern, C. L.; Ratner, M. A.; Seideman, T.; Mirkin, C. A. J. Am. Chem.
Soc. 2009, 131, 9482.
(3) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022.
r
2010 American Chemical Society
Published on Web 12/28/2010
pubs.acs.org/IC

1412 Inorganic Chemistry, Vol. 50, No. 4, 2011
Rosen et al.
Scheme 1. Weak-Link Approach (WLA) to Making Heteroligated Structuresa
a (a) The WLA can be used to make heteroligated structures in quantitative yield via a multicomponent assembly process that involves bidentate ligands
and a metal precursor (M). This makes the WLA an ideal method for the construction of a wide variety of coordination complexes including: (b) tweezers 2,
(c) macrocycles 3 and 4, and (d) triple-layer complexes 6. The geometry of the complexes can be further manipulated via reversible chemistry on the metal
regulatory sites coordinated to hemilabile ligands. Here, X represents the “weak-link” moiety (usually a chalcoether or amine) and A and B are functional
groups (e.g., catalytic center,4d-f or recognition site,11 etc.). When A=B the resulting complex is homoligated. When L (an elemental anion or small
molecule) is coordinated to the metal center, the complex is “semi-open” (1 and 5) or “fully open” (3). Conversely, 2, 4, and 6 are “closed” complexes.
Ir(I),8 Cu(I),9 and Pt(II).10 Since Pt(II) often provides struc-
tures that are resistant to degradation in air, it has been the
focus of many recent studies.7b,10 The hemilabile, bidentate
ligands commonly used to synthesize WLA systems employ
strong-binding phosphines and weak-binding sites that in-
corporate chalcoethers (O, S, or Se) and amines. The diverse
toolbox of metals and ligands explored thus far has resulted in
the synthesis of increasingly sophisticated molecular architec-
tures including tweezers (2, Scheme 1b),7a triangular prisms,8
macrocycles (3 and 4, Scheme 1c),5a,d,f and triple-layer com-
plexes (6, Scheme 1d).5e
involving the above-mentioned d8 transition metals and bi-
dentate, hemilabile ligands that is dependent on the presence
of a halide ion and allows for the quantitative formation of
heteroligated structures (Scheme 1).11 This type of multi-
component self-assembly (Scheme 1a) is unusual in Pt(II)
coordination chemistry.10,12 While in Rh(I) systems this
reaction works well with phosphine-ether (P, O) and phosphine-
thioether (P, S) ligands to form exclusively A-Rh(I)-B mixed
ligand structures,5b,c we showed that Pt(II) systems can
employ P, S and/or phosphine-selenoether (P, Se) ligands
to make A-Pt(II)-B heteroligated structures. Further investi-
gation has led us to conclude that the strength of the binding
While studying WLA systems, we discovered the halide-
induced ligand rearrangement reaction (HILR), a process
(11) (a) Brown, A. M.; Ovchinnikov, M. V.; Stern, C. L.; Mirkin, C. A.
J. Am. Chem. Soc. 2004, 126, 14316. (b) Oliveri, C. G.; Ulmann, P. A.; Wiester,
M. J.; Mirkin, C. A. Acc. Chem. Res. 2008, 41, 1618.
(12) (a) Baxter, P.; Lehn, J. M.; DeCian, A.; Fischer, J. Angew. Chem.
1993, 105, 92. (b) Baxter, P. N. W.; Lehn, J.-M.; Kneisel, B. O.; Baum, G.; Fenske,
D. Chem.;Eur. J. 1999, 5, 113. (c) Kuil, M.; Goudriaan, P. E.; Van Leeuwen,
P. W. N. M.; Reek, J. N. H. Chem. Commun. 2006, 4679. (d) Schmittel, M.;
Kalsani, V. Top. Curr. Chem. 2005, 245, 1. (e) Yoshizawa, M.; Nagao, M.;
Kumazawa, K.; Fujita, M. J. Organomet. Chem. 2005, 690, 5383.
(8) Ovchinnikov, M. V.; Holliday, B. J.; Mirkin, C. A.; Zakharov, L. N.;
Rheingold, A. L. Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 4927.
(9) Masar, M. S., III; Mirkin, C. A.; Stern, C. L.; Zakharov, L. N.;
Rheingold, A. L. Inorg. Chem. 2004, 43, 4693.
(10) (a) Spokoyny, A. M.; Rosen, M. S.; Ulmann, P. A.; Stern, C.; Mirkin,
C. A. Inorg. Chem. 2010, 49, 1577. (b) Ulmann, P. A.; Brown, A. M.;
Ovchinnikov, M. V.; Mirkin, C. A.; DiPasquale, A. G.; Rheingold, A. L.
Chem.;Eur. J. 2007, 13, 4529.

Article
Inorganic Chemistry, Vol. 50, No. 4, 2011 1413
Scheme 2. Synthesis of Phosphino-Selenoether (P, Se) and Phosphino-
Thioether (P, S) Monoligated Complexes
Scheme 4. Formation of Heteroligated Complexes with the Electron-
Donating XMe Ligand 8 or 12 (X = Se or S)a
Scheme 3. Formation of Heteroligated Complexes with the Electron-
Withdrawing XPh Ligand 7 or 11 (X = Se or S)a
a Addition of 1 equiv of the electron-withdrawing ligand 7 or 11 to the
homoligated, semi-open complex 19 or 20 results in the formation of
the heteroligated semi-open species 17 or 18, and the release of 1 equiv of
the electron-donating ligand 8 or 12, respectively. The experiments with
the thioether ligands were performed in dichloromethane, and those
with the selenoether ligands, in 1,2-dichloroethane.
Figure 1. Crystal structures of complexes 9, 10, and 13, respectively,
drawn with 50% thermal ellipsoid probability. The crystal structure of
complex 14 was previously reported by Yang et al.19 When applicable,
only one stereoisomer in the unit cell is shown. In all cases, hydrogens, sol-
vent molecules, and anions are omitted for clarity. Platinum atoms are
black; sulfur, green; selenium, red; phosphorus, blue; and carbon, gray. See
Table 1 for selected bond lengths and angles. Crystallographic information
can be found in the Supporting Information, Table S1.
a Addition of 1 equiv of the electron-donating ligand 8 or 12 to the
homoligated complex 15 or 16 results in the formation of the hetero-
ligated semi-open species 17 or 18, and the release of 1 equiv of the
electron-withdrawing ligand 7 or 11, respectively.
weaker chalcoether chelate is introduced. If this first chela-
tion is weak, the second bidentate ligand must be a strong
chelator to obtain the desired heteroligated product. Further-
more, when a non-chelating phosphine is introduced to the
monoligated complex, heteroligated structures are not al-
ways observed. Competitive displacement reactions indicate
that the first chelation, forming the monoligated product, has
a significantly larger stabilization on the metal than does the
second ligand. The stability of the monoligated complexes
allows for ligand sorting to occur in the HILR, which we think
is a crucial aspect in approaching the design of more sophis-
ticated structures in this family of complexes. The extent of
stabilization of monoligated complexes is dependent on the
electron-donating or -withdrawing nature of the functionality
appended to the chalcoether. Here we examine how ligand
electronics and overall chelating ability are intimately related,
resulting in the clean assembly of Pt(II) heteroligated WLA
species, providing important fundamental insights into the co-
ordination chemistry of Pt(II) with phosphino-chalcoether li-
gands and the above-mentioned multicomponent self-assembly
processes.
interaction between the Pt(II) and the chalcogen, modulated
via the aryl or alkyl moiety on the chalcoether, is crucial for
the formation of these heteroligated motifs.10,13
We are interested in developing a fundamental under-
standing of the critical factors underlying the formation of
the heteroligated species in Pt(II) WLA complexes, which have
remained unclear until now. In general, controlling the assem-
bly of multicomponent systems remains an underdeveloped
area of research.12,14 Through a stepwise addition of ligands to
a Pt(II) precursor, we now show that the bidentate nature of
these ligands is crucial for the clean formation of the hetero-
ligated species. The ligand’s chelating ability drives the first
step of the ligand addition to the Pt(II) metal toward the clean,
preferential formation of the monoligated Pt(II) chelate. If this
chelation is strong, the desired heteroligated product is ob-
served when a second bidentate ligand (P, Se or P, S) with a
(13) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759.
(14) Bar, A. K.; Mostafa, G.; Mukherjee, P. S. Inorg. Chem. 2010, 49,
7647.

1414 Inorganic Chemistry, Vol. 50, No. 4, 2011
Rosen et al.
Table 1. Selected Bond Lengths and 31P{1H} and 77Se{1H}Chemical Shifts for Complexes 9 through 14
a
a
31P{1H} (ppm)
77Se{1H} (ppm)
˚
˚
˚
˚
compound
Pt-P (A)
Pt-X (A)
Pt-Cl1 (A)
Pt-Cl2 (A)
9
2.205(2)
2.212 (1)
2.2175(5)
2.210(4)
2.3727(7)
2.3726(4)
2.2600(6)
2.256(4)
2.319(2)
2.3309(8)
2.3229(6)
2.325(3)
2.352(2)
2.372(1)
2.3665(4)
2.367(4)
39.6
39.6
39.5
39.6
499 (d)
352 (d)
10
13
14
a Cl1 is trans to the chalcogen (X) and Cl2 is cis to X (X = Se or S).
Figure 2. (a) 31P{1H} NMR spectra of complex 15 at room temperature. (b) 31P{1H} NMR spectra of complex 16 at room temperature.
Figure 3. 31P{1H} NMR spectrum of the products formed by adding ligand 12 to complex 16. The main resonances of interest are marked with a star, and
the associated 195Pt satellite resonances are located about 10 ppm upfield and downfield of the main resonance.
Results and Discussion
195Pt satellites (JSe-Pt = 588 Hz).10a,17 The singlet in the
31P{1H} NMR spectrum for monoligated complex 10 has a
similar chemical shift of δ 39.6 (JP-Pt=3650 Hz), while the
Monoligated Complexes. A general synthesis for all
monoligated complexes entails mixing 1 equiv of the desired
hemilabile ligand 7, 8, 11, or 12, prepared via literature
methods,10a,15 with the Pt(II) precursor (Pt(cod)Cl2, cod =
cyclooctadiene, 1 equiv) in dichloromethane (CH2Cl2),
resulting in quantitative formation of complexes 9, 10, 13,
and 14 within a few minutes (Scheme 2). 31P{1H} NMR
and, where appropriate, 77Se{1H} NMR spectroscopies
were used to probe the environment of the strong- and
weak-binding moieties, respectively. Monoligated com-
plex 9 exhibits a singlet in the 31P{1H} NMR spectrum at
δ 39.6 with characteristic Pt satellites (JP-Pt = 3580 Hz)10a,16
and a doublet in the 77Se{1H} NMR spectrum at δ 499
(JSe-P = 10 Hz) also with characteristic and well-resolved
doublet in the 77Se{1H} NMR spectrum at δ 352 (JSe-P
=
13 Hz, JSe-Pt=477 Hz) is quite different, consistent with
the significantly larger electron-donating ability of the
SeMe group compared to the SePh group. Consistent
with this hypothesis, the Pt-P coupling constant for
complex 10 is greater than that of complex 9.18 Similarly,
the thioether analogues of 9 and 10, 13 and 14, respec-
tively, exhibit 31P{1H} NMR chemical shifts of δ 39.5
(JPt-P=3590 Hz) and δ 39.6 (JPt-P=3590 Hz), consis-
tent with the conclusion that the electronic environment
of the phosphine is not greatly affected by the electron-
donating ability of the substituent on the chalcoether
(15) Cunningham, T. J.; Elsegood, M. R. J.; Kelly, P. F.; Smith, M. B.;
Staniland, P. M. Dalton Trans. 2010, 39, 5216.
(16) White, S.; Kalberer, E. W.; Bennett, B. L.; Roddick, D. M. Organo-
metallics 2001, 20, 5731.
(17) (a) Hassan, F. S. M.; McEwan, D. M.; Pringle, P. G.; Shaw, B. L.
J. Chem. Soc., Dalton Trans. 1985, 1501. (b) Briggs, J. R.; Crocker, C.;
McDonald, W. S.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1981, 575.
(18) Garrou, P. E. Chem. Rev. 1981, 81, 229.

Article
Inorganic Chemistry, Vol. 50, No. 4, 2011 1415
Figure 4. (a) 31P{1H} NMR spectra of complex 18. (b) Upon addition of 1 equiv of Pt(cod)Cl2 to complex 18, the monoligated complexes 13 and 14 form.
Scheme 5. Upon Addition of a Second Equivalent of Pt(cod)Cl2 to the Heteroligated Complex 17 or 18, the Monoligated Complexes 9 and 10 or 13 and
14 Form, Respectively
Scheme 6. Upon Addition of a Second Equivalent of Pt(cod)Cl2 to the Fully-Open Complex 21, No Reaction Occurs
˚
moiety. Electrospray ionization mass spectroscopy, single
crystal X-ray diffraction studies, and elemental analyses of
complexes 9, 10, 13, and 14 confirmed their composition.
It is noteworthy that only species 9, 10, 13, and 14 form
under the reaction conditions outlined above; there are no
observable quantities of the diligated species, which sug-
gests that the formation of the monoligated complexes is
preferential over a mixture of the homoligated analogues
15, 16, 19, and20 (Schemes3and4) andthePt(II)precursor
under these conditions (note that the term homoligated is
used to designate that 2 equiv of the same P, X ligands are
coordinated to one metal center). This clean formation of
the monoligated product is driven by the chelating ability of
ligands 7, 8, 11, and 12, respectively (Scheme 2).
2.319(2) A, respectively (Table 1). This is consistent with
the conclusion that the Pt-Se interaction in 10 is stronger
than in 9.
A similar conclusion can be made for the analogous
thioether complexes 13 and 14, where the Pt-Cl1 bond in
13 is shorter than that in 14, 2.3229(6) A and 2.325(3) A,
respectively. The corresponding Pt-S bond lengths re-
flect this trend, with the Pt-S bond being longer in com-
˚
˚
˚
˚
plex 13, at 2.2600(6) A, than in 14, at 2.256(4) A. The dif-
ference in Pt-X bond strengths between complexes with
an electron-donating or withdrawing ligand proves to be
important when constructing diligated complexes, as
described below.
Diligated (Homoligated or Heteroligated) Complexes.
The stepwise addition of hemilabile ligands (P, S or P, Se)
to either the monoligated complexes with an electron-
withdrawing XPh (X = Se or S) group, 9 or 13, or an
electron-donating XMe (X=Se or S) group, 10 or 14, as
depicted in Schemes 3 and 4, ultimately leads to clean
formation of the heteroligated species in all cases.
The species formed upon the addition of a second P, X
ligand to complex 9 was characterized by NMR spectros-
copy (Figure 2a). For example, the addition of a second
Complexes 9, 10, 13, and 14 were further characterized
by single-crystal X-ray diffraction studies (Figure 1). A
comparison between the Pt-Cl1 bond for the Cl trans to
the chalcoether moiety in complexes 9 and 10 reveals that
the chalcoether with the more electron-donating substit-
uent exhibits a larger trans influence than its electron-
withdrawing analogue as evidenced by the elongation
of the Pt-Cl1 bond in complex 10 as compared with the
˚
analogous Pt-Cl1 bond in complex 9, 2.3309(8) A and

1416 Inorganic Chemistry, Vol. 50, No. 4, 2011
Rosen et al.
Figure 5. Upon the addition of 1 equiv of Pt(cod)Cl2 to complex 21, no rearrangement occurs as shown in the (a) 195Pt NMR spectra of complex 21 where
the resonance for the Pt(II) precursor is observed at ∼ -3350 ppm and that of complex 21 is observed at ∼ -4400 ppm, and (b) 31P{1H} NMR spectra of
complex 21. (c) Crystal structure of complex 21, drawn with 50% thermal ellipsoid probability. Hydrogens and solvent molecules are omitted for clarity.
Platinum atoms are black; sulfur, green; phosphorus, blue; and carbon, gray. Crystallographic information can be found in the Supporting Information,
Table S1.
Scheme 7. Upon Addition of 1 equiv of the Monodentate Ligand
Ethyl Diphenylphosphine (EDP) to Either Complex 10 or 14, the Hetero-
ligated Complex 22 or 23 Forms, Respectively; However, When EDP Is
Added to Either Complex 9 or 13, the Result Is a Mixture of Products
Figure 6. Crystal structures of 19 and 20, respectively, drawn with 50%
thermal ellipsoid probability. In all cases, hydrogens, solvent molecules,
and anions are omitted for clarity. Only one stereoisomer in the unit cell is
shown. Platinum atoms are black; sulfur, green; selenium, red; phosphorus,
blue; and carbon, gray. Crystallographic information can be found in the
Supporting Information, Table S1.
releasing at the Pt(II) center.20 Cooling a solution of com-
plex 15 or 16 to -60 °C in dichloromethane-d2 freezes out
various species, as observed via 31P{1H} NMR spectrosco-
py, although many resonances are still broad. In the case of
the selenoether complex 15 (Scheme 3), the semiopen com-
plex appears as two broad resonances at -60 °C, with the
chelating ligand 7 at δ 43.7 (JP-Pt = 3500 Hz) and the non-
equivalent of the electron-withdrawing ligand 7 to a stir-
ring solution of complex 9 in dichloromethane results in
the formation of a complex that exhibits a broad reso-
=
nance in the 31P{1H} NMR spectrum at δ 24.8 (JP-Pt
chelating ligand 7at δ9.17 (JP-Pt = 3160 Hz), and the single
resonance at δ50.1 (JP-Pt = 3190 Hz) can be assigned to the
fully closed complex. In the case of the thioether complex 16
(Figure 3) at -60 °C, only the semiopen species is observed
as two broad resonances in the 31P{1H} NMR spectrum,
with the chelating ligand 11 at δ 45.2 (JP-Pt=3500 Hz)
and the non-chelating ligand 11 at δ 8.08 (JP-Pt =3130
Hz). The presence of the closed complex at -60 °C in the
31P{1H} NMR spectrum of complex 15 but not for com-
plex 16, coupled with the differences in their room tem-
perature 31P{1H} NMR spectra (Figure 2), suggests that
3430 Hz). This resonance has been assigned to the homo-
ligated complex 15 (Figure 2a) and compares well with
isolectronic and isostructural model complexes.10b The
analogous thioether complex 16 also exhibits a broad
resonance in the 31P{1H} NMR spectrum, significantly
upfield of the resonance for 15 (Figure 2b), observed at
δ 14.36 (JP-Pt = 3530 Hz) (Figure 2b).
This chemical shift for complex 15 roughly lies between
the 31P{1H} NMR resonance of the closed, homoligated
SePh-Pt(II)-SePh complex (Supporting Information,
Figures 1 and 2), in which the selenoethers in both P, Se
hemilabile ligands are chelating to the Pt(II) center, that
occurs at δ 49.7 (JP-Pt = 4180 Hz) and the resonance at δ
12.3 assigned to the unbound chalcoether in the semiopen
complex 17 (Figure 2). This indicates that the interaction
of the selenoether moiety with the Pt center in complex 15
is dynamic, where one chalcoether is coordinating and
(19) Yang, J.; Huang, D.; Li, G.; Zhang, L. Huaxue Xuebao 1993, 51,
1145.
(20) (a) Barthel-Rosa, L. P.; Maitra, K.; Nelson, J. H. Inorg. Chem. 1998,
37, 633. (b) Liu, J.; Jacob, C.; Sheridan, K. J.; Al-Mosule, F.; Heaton, B. T.; Iggo,
J. A.; Matthews, M.; Pelletier, J.; Whyman, R.; Bickley, J. F.; Steiner, A. Dalton
Trans. 2010, 39, 7921.

Article
Inorganic Chemistry, Vol. 50, No. 4, 2011 1417
Scheme 8. Comprehensive Scheme Summarizing the Reactions of Hemilabile Phosphino-Chalcoether Ligands with Pt(II)
the selenoether-Pt(II) interaction is slightly stronger than
the analogous thioether-Pt(II) interaction.
of the heteroligated product. In support of this, a hetero-
ligated semiopen complex will form the corresponding
monoligated complexes if a second equivalent of Pt(cod)-
Cl2 is introduced (Figure 4, Scheme 5). This qualitatively
indicates that the stabilization energy is higher for the
binding of the first ligand to the Pt(II) metal center than
for the second. It should be noted that when 1 equiv of
Pt(cod)Cl2 is added to solutions of 15, 16, 19, or 20, that
the corresponding monoligated complexes form, 9, 13,
10, or 14, respectively.
Further evidence of the chelating effect’s role in hetero-
ligated complex formation comes from experiments with
complex 21, which is synthesized from the addition of ligand
7a to Pt(cod)Cl2 in dichloromethane (Scheme 6). The addi-
tion of a second equivalent of the Pt(II) precursor to com-
plex 21 does not result in the formation of two monoligated
complexes from this diligated species (Figure 5). Here, both
of the thioethers do not coordinate to the Pt(II) center be-
cause of the electron-withdrawing perfluorinated substitu-
ent, thus precluding rearrangement from occurring.
To directly examine the role of the bidentate ligand, ethyl
diphenylphosphine (EDP) was employed as a monodentate,
non-chelating analogue. When 1 equiv of EDP was added to
the monoligated complex 10 or 14, the expected heteroligated
complex formed in quantitative yield (Scheme 7). Complexes
22 and 23 were characterized by 31P{1H} NMR and, where
appropriate, 77Se{1H} NMR spectroscopy; single-crystal
X-ray diffraction studies (Figure 6); and electrospray ioniza-
tion mass spectrometry.
When ligand 8 is added to complex 15, it chelates to the
Pt(II) center, displacing 1 equiv of ligand 7 to form 17,
which can be unequivocally confirmed by 31P{1H} NMR
spectroscopy as evidenced by a singlet at δ -15.7. Complex
17 does not undergo exchange in solution like complex15, a
consequence of the significantly stronger chelating ability
of ligand 8 as compared with its aryl analogue, 7. Indeed
this chelation is a significant driving force for the formation
of the heteroligated complex 17. This provides a means of
rearrangement, or ligand sorting in this process. Note that
it is known that complex 9 will react with ligand 8 directly to
form the heteroligated product 17.10a
The monoligated complex 10 reacts with 1 equiv of
electron-donating ligand 8 to form the homoligated com-
plex 19, which exhibits a broad resonance at δ 44.1 (JPt-P
=
3300 Hz) in its 31P{1H} NMR spectrum. With complex
19, one chalcoether is under dynamic exchange between
metal bound and unbound states,10 which is character-
istic of isolectronic and isostructural model complexes.10b
Upon addition of 1 equiv of ligand 7 to complex 19, the
heteroligated, semiopen complex 17 is formed, releasing
1 equiv of the SeMe ligand as evidenced by a diagnostic
resonance for ligand 8 at δ -15.7 in the 31P{1H} NMR
spectrum (Scheme 4). Consequently, it is only when
ligands of different chelating abilities are present that
the heteroligated species is formed.
Chelating Effect. The results of the competition experi-
ments discussed thus far (Schemes 3 and 4) indicate that
the chelating ability of the ligand is crucial for the formation
However, if the EDP was added to complex 9 or 13, a
mixture of products was observed (Scheme 7); that is,

1418 Inorganic Chemistry, Vol. 50, No. 4, 2011
Rosen et al.
heteroligation did not occur in the same manner as in
the previous cases. This reinforces the idea that a chelate
comprising a strongly electron-donating moiety stabilizes
the Pt(II) center and is a required element for the HILR
reaction.
LC/MS MSD1100 mass spectrometer. Elemental analyses were
performed by Quantitative Technologies, Whitehouse, NJ. [The
inability to obtain accurate EA results is not unknown in
Pt-containing complexes. Likely, this is due to incomplete com-
bustion and formation of platinum hydroxide and/or platinum
carbides as byproducts, which would decrease the experimental
values of the carbon and hydrogen content in some samples, as
observed.23] Single crystals suitable for X-ray diffraction studies
were obtained by layering diethyl ether over a dichloromethane
solution of the relevant complex.
Heteroligated complex formation via the WLA with
Pt(II) is summarized in Scheme 8.
Conclusion
General Procedure for Formation of Monoligated Complexes.
A solution of the ligand (7, 8, 11, or 12) (0.33 mmol, 1 equiv) in
dichloromethane (5 mL) was added dropwise to a solution of the
platinum precursor [Pt(cod)Cl2] (125 mg, 0.33 mmol, 1 equiv) in
dichloromethane (5 mL) at room temperature. After 20 min, the
solvent was reduced to about 1 mL in vacuo, and 10 mL of dieth-
yl ether was added, precipitating a white solid. The solid was
filtered and washed with an additional amount of ether (5 mL)
to afford the analytically pure monoligated complex (in situ
31P{1H} NMR yields = 100%, isolated yields >95%).
While controlled heteroligated species formation has
been described as a “challenging design job,”21 our system
employsrelatively simple design parameters for thesuccessful
synthesis of heteroligated structures in quantitative yield.
Unlike other motifs that heavily rely on steric constraints or
the coordination preferences of the metal center(s) to achieve
heteroligated structures,21 we have demonstrated that the
chelating effect in combination with rationally designed P,
X-type hemilabile ligands provides a driving force for hetero-
ligated complex formation. This was established by a series of
competitive exchange reactions between heteroligated, homo-
ligated, and monoligated complexes, which are either prod-
ucts or intermediates in the Pt(II) HILR reaction. The pref-
erential formation of the monoligated species is a critical
factor for ligand rearrangement, which provides stable inter-
mediates. Clean formation of heteroligated complexes with
one bidentate and one monodentate ligand occurs only if the
bidentate ligand strongly chelates to the Pt(II) metal center.
Consequently, attempts to make heteroligated complexes re-
sult in a mixture of products when a monodentate ligand is
combined with a weakly chelating bidentate ligand in the
same complex. Overall, this understanding may help in con-
structing supramolecular assemblies based on the weak-link
approach (WLA) and design other ligands that can, with the
right metals, lead to similar processes. Finally, the rationale
presented here suggests that the influence of the chelating
effect in this system should be applicable not only to P,
X-type ligands, but to other hemilabile ligands with a variety
of metals.
General Procedure for Formation of Heteroligated Semiopen
Complexes. A solution of ligand A (7 or 11) (0.33 mmol, 1 equiv)
in dichloromethane (5 mL) was added dropwise to a solution
of the platinum precursor [Pt(COD)Cl2] (125 mg, 0.33 mmol,
1 equiv) in dichloromethane (5 mL) at room temperature. The
solution was allowed to stir for 5 min before ligand B (8 or 12),
dissolved in dichloromethane (5 mL), was added dropwise.
After 20 min, the solvent was reduced to about 1 mL in vacuo
and 10 mL of diethyl ether was added, precipitating a white solid.
The solid was filtered and washed with an additional amount of
ether (5 mL) to afford the analytically pure heteroligated complex
(in situ 31P{1H} NMR yields = 100%, isolated yields >95%).
General Procedure for Formation of Heteroligated Complexes
with One Monodentate Ligand. A solution of the bidentate
ligand (8 or 12) (0.33 mmol, 1 equiv) in dichloromethane (5 mL)
was added dropwise to a solution of the platinum precursor
[Pt(cod)Cl2] (125 mg, 0.33 mmol, 1 equiv) in dichloromethane
(5 mL) at room temperature. The solution was allowed to stir for
5 min before the monodentate ligand, ethyl diphenylphosphine
(EDP), dissolved in dichloromethane (5 mL), was added drop-
wise. After 20 min, the solvent was reduced to about 1 mL in
vacuo and 10 mL of diethyl ether was added, precipitating a
white solid. The solid was filtered and washed with an additional
amount of ether (5 mL) to afford the analytically pure hetero-
ligated complex (in situ 31P{1H} NMR yields = 100%, isolated
yields >95%).
Experimental Section
General Methods/Instrument Details. All phosphine-based
ligands were prepared and stored using standard Schlenk tech-
niques under an inert nitrogen atmosphere. The syntheses of
Pt(II) complexes and all manipulations were done at ambient
conditions. Dichloromethane (DCM), diethyl ether, ethanol,
and hexanes were purchased as anhydrous grade from Sigma-
Aldrich and used as received. Deuterated solvents were pur-
chased from Cambridge Isotope Laboratories and used as
received. All other chemicals were used as received from Aldrich
Chemical Co. or prepared according to literature procedures.
Ligands 7,10a 7a,22 8,10a 11,10b and 12,10b were synthesized ac-
cording to previously described procedures. All NMR spectra
were recorded on a Bruker Advance 400 MHz NMR spectrom-
eter. 1H spectra were referenced to residual proton and carbon
resonances in the deuterated solvents. 31P{1H}, 77Se{1H}, and
195Pt NMR spectra were referenced to H3PO4, Me2Se, and
Na2PtCl6 standards, respectively. For 77Se acquisition, relaxa-
tion delays of 0.01 s or less were usually sufficient because of the
fast relaxation of the Pt(II) complexes studied. Electrospray
ionization (ESI) mass spectra were recorded on a Micromass
Quatro II triple quadrupole mass spectrometer or an Agilent
General Procedure for Conversion of Heteroligated Semiopen
Complexes to Monoligated Complexes. A solution of the semi-
open heteroligated complex in dichloromethane was prepared as
described above. A solution of the platinum precursor [Pt(cod)Cl2]
(125 mg, 0.33 mmol, 1 equiv) in dichloromethane (5 mL) at room
temperature was added dropwise. After 20 min, the solvent was
reduced to about 1 mL in vacuo and 10 mL of diethyl ether was
added, precipitating a white solid. The solid was filtered and
washed with an additional amount of ether (5 mL) to afford the
monoligated complexes (in situ 31P{1H} NMR yields = 100%,
isolated yields >95%).
Characterization. 9. 1H NMR (400.13 MHz, CD2Cl2, 25 °C,
TMS): δ 8.10-7.40 (m, 15 Ar H), δ 3.09-2.70 (m, 3 Aliph H); δ
2.53-2.35 (m, 1 Aliph H); 31P{1H} NMR (161.98 MHz, CD2Cl2,
25 °C): δ 39.6, JP-Pt = 3580 Hz; HRMS (ESI): m/z calcd for
C20H19Cl2PPtSe [M-Cl]þ: 600.9804; found: 600.9736; Anal.
Calcd for C20H19Cl2PPtSe 1/2CH2Cl2: C, 36.33; H, 2.97. Found:
3
C, 36.72; H, 2.82.
10. 1H NMR (400.13 MHz, CD2Cl2, 25 °C, TMS): δ
7.95-7.21 (m, 10 Ar H), δ 2.91-2.36 (m, 7 Aliph H); 31P{1H}
(21) De, S.; Mahata, K.; Schmittel, M. Chem. Soc. Rev. 2010, 39, 1555.
(22) Brown, A. M.; Ovchinnikov, M. V.; Mirkin, C. A. Angew. Chem., Int.
Ed. 2005, 44, 4207.
(23) Bennett, M. A.; Canty, A. J.; Felixberger, J. K.; Rendina, L. M.;
Sunderland, C.; Willis, A. C. Inorg. Chem. 1993, 32, 1951.

Article
Inorganic Chemistry, Vol. 50, No. 4, 2011 1419
NMR (161.98 MHz, CD2Cl2, 25 °C): δ 39.6, JP-Pt = 3650 Hz;
HRMS (ESI): m/z calcd for C15H17Cl2PPtSe [M-Cl]þ: 538.9648;
23. 1H NMR (400.13 MHz, CD2Cl2, 25 °C, TMS): δ 7.76-
7.17 (m, 20 Ar H), δ 4.01-2.05 (m, 12 Aliph H); 31P{1H} NMR
(161.98 MHz, CD2Cl2, 25 °C): δ 43.4, JP-P = 15.2, JP-Pt = 3540
Hz; δ 12.9, JP-P = 15.4, JP-Pt = 3130 Hz; HRMS (ESI): m/z
calcd for C29H32Cl2P2PtS [M-Cl]þ: 705.1114; found: 705.1042;
found: 538.9543; Anal. Calcd for C15H17Cl2PPtS 3/2CH2Cl2: C,
28.29; H, 2.88. Found: C, 28.80; H, 2.49.
3
1
13. H NMR (400.13 MHz, CD2Cl2, 25 °C, TMS): δ 8.10-
Anal. Calcd for C29H32Cl2P2PtS 1/3CH2Cl2: C, 46.54; H, 4.35.
7.43 (m, 15 Ar H), δ 3.11-2.78 (m, 2 Aliph H), δ 2.59-2.33 (m, 2
3
Aliph H); 31P{1H} NMR (161.98 MHz, CD2Cl2, 25 °C): δ 39.5,
Found: C, 46.12; H, 4.37.
J
P-Pt = 3590 Hz; HRMS (ESI): m/z calcd for C20H19Cl2PPtS [M-
X-ray Crystallography. Crystallographic data are collected in
the Supporting Information, Table S1. Single crystals were mounted
using oil (Infineum V8512) on a glass fiber. All measurements were
made on a CCD area detector with graphite monochromated Mo
KR or Cu KR radiation. Data were collected using Bruker APEXII
detector and processed using APEX2 from Bruker. All structures
were solved by direct methods and expanded using Fourier
techniques. The non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were included in idealized positions, but
not refined. Their positions were constrained relative to their
parent atom using the appropriate HFIX command in SHELXL-97.
Cl]þ: 553.0360; found: 553.0374; Anal. Calcd for C20H19Cl2PPtS
3
1/2CH2Cl2: C, 39.03; H, 3.20. Found: C, 39.98; H, 2.94.
1
14. H NMR (400.13 MHz, CD2Cl2, 25 °C, TMS): δ 7.96-
7.10 (m, 10 Ar H), δ 2.99-2.36 (m, 7 Aliph H); 31P{1H} NMR
(161.98 MHz, CD2Cl2, 25 °C): δ 39.6, JP-Pt = 3590 Hz; HRMS
(ESI): m/z calcd for C15H17Cl2PPtS [M-Cl]þ: 491.0203; found:
491.0117; Anal. Calcd for C15H17Cl2PPtS: C, 34.23; H, 3.26.
Found: C, 34.56; H, 3.21.
1
21. H NMR (400.13 MHz, CD2Cl2, 25 °C, TMS): δ 7.48-
7.03 (m, 22 Ar H), δ 3.13-2.30 (m, 8 Aliph H); 31P{1H} NMR
(161.98 MHz, CD2Cl2, 25 °C): δ 4.99, JP-Pt = 3620 Hz; HRMS
(ESI): m/z calcd for C40H30Cl2F8P2PtS2 [M-Cl]þ: 1018.0473;
found: 1018.0527; Anal. Calcd for C42H44Cl2F8P2PtS2: C, 45.55;
H, 2.87. Found: C, 45.04; H, 2.86.
Acknowledgment. We thank Dr. Michael Wiester for help
with NMR spectroscopy and Saman Shafie and Dr. Jennifer
Seymour for mass spectrometry assistance. C.A.M. acknowledges
NSF, ARO, DTRA, and AFOSR for financial support. A.M.S.
thanks Northwestern University for a Presidential Fellowship.
22. 1H NMR (400.13 MHz, CD2Cl2, 25 °C, TMS): δ
7.79-7.15 (m, 22 Ar H), δ 3.74-2.00 (m, 12 Aliph H); 31P{1H}
NMR (161.98 MHz, CD2Cl2, 25 °C): δ 41.9, JP-P = 13.0, JP-Pt
=
3550 Hz; δ 12.8, JP-P = 13.5, JP-Pt = 3150 Hz; HRMS (ESI):
Supporting Information Available: Crystallographic data for
complexes 9-10, 13-14, 21-23 in cif file format. Further details
are given in supporting Figures 1 and 2 and Table S1. This material
is available free of charge via the Internet at http://pubs.acs.org.
m/z calcd for C29H32Cl2P2PtSe [M-Cl]þ: 753.0559; found:
753.0494; Anal. Calcd for C29H32Cl2P2PtSe CH2Cl2: C, 41.30;
H, 3.93. Found: C, 41.45; H, 3.74.
3