Cationic, neutral, and anionic platinum(II) complexes based on an electron-rich PNN ligand. New modes of reactivity based on pincer hemilability and dearomatization

Article abstract of DOI:10.1021/om8001069

The synthesis and reactivity of new Pt(II) complexes, including anionic d⁸ complexes, based on the electron-rich, hemilabile PNN-type pincer ligand C₅H₃N-2-(CH₂P^tBu ₂)(CH₂NEt₂) are described. Formation of these complexes involves dearomatization/aromatization processes of the ligand. The chloride complex [(PNN)PtCl]⁺Cl^- (1) was prepared and reacted with the base ^tBuOK to give the deprotonated, neutral chloride complex (PNN*)PtCl (2) (PNN* = C₅H ₃N-2-(CHP^tBu₂)(CH₂NEt₂)). Reaction of 2 with ⁿBuLi gave the corresponding neutral hydride complex (PNN*)PtH (3), which was readily protonated by triflic acid to give the cationic hydride complex [(PNN)PtH]⁺OTf^- (4). Unexpectedly, reaction of complex 2 with 1 equiv of RLi resulted in opening of the chelate ring, to give the corresponding anionic, dearomatized complexes Li⁺[(PNN*)Pt(Cl)(R)]^- (R = methyl, 5; phenyl, 6). Notably, these complexes are relatively stable although they bear no stabilizing π acceptors that can lower the electron density at the metal center. Complexes 5 and 6 readily undergo protonation by HCl to form the corresponding neutral, aromatic complexes (PNN)Pt(Cl)(R) (R = methyl, 7; phenyl, 8), in which the hemilabile amine "arm" remains decoordinated and does not undergo protonation. Minor amounts of the dearomatized chloride complex 2 are also formed as a result of elimination of RH. Reaction of complexes 5 and 6 with water results in selective protonation-aromatization to give the corresponding complexes 7 and 8.

Full text of DOI:10.1021/om8001069

Organometallics 2008, 27, 2627–2634
2627
Cationic, Neutral, and Anionic Platinum(II) Complexes Based on an
Electron-Rich PNN Ligand. New Modes of Reactivity Based on
Pincer Hemilability and Dearomatization
Dana Vuzman,† Elena Poverenov,† Linda J. W. Shimon,‡ Yael Diskin-Posner,‡ and
David Milstein*,†
Department of Organic Chemistry and Unit of Chemical Research Support, The Weizmann Institute of
Science, RehoVot, 76100, Israel
ReceiVed February 6, 2008
The synthesis and reactivity of new Pt(II) complexes, including anionic d8 complexes, based on the
electron-rich, hemilabile PNN-type pincer ligand C5H3N-2-(CH2PtBu2)(CH2NEt2) are described. Formation
of these complexes involves dearomatization/aromatization processes of the ligand. The chloride complex
t
[(PNN)PtCl]+Cl- (1) was prepared and reacted with the base BuOK to give the deprotonated, neutral
n
chloride complex (PNN*)PtCl (2) (PNN* ) C5H3N-2-(CHPtBu2)(CH2NEt2)). Reaction of 2 with BuLi
gave the corresponding neutral hydride complex (PNN*)PtH (3), which was readily protonated by triflic
acid to give the cationic hydride complex [(PNN)PtH]+OTf- (4). Unexpectedly, reaction of complex 2
with 1 equiv of RLi resulted in opening of the chelate ring, to give the corresponding anionic, dearomatized
complexes Li+[(PNN*)Pt(Cl)(R)]- (R ) methyl, 5; phenyl, 6). Notably, these complexes are relatively
stable although they bear no stabilizing π acceptors that can lower the electron density at the metal
center. Complexes 5 and 6 readily undergo protonation by HCl to form the corresponding neutral, aromatic
complexes (PNN)Pt(Cl)(R) (R ) methyl, 7; phenyl, 8), in which the hemilabile amine “arm” remains
decoordinated and does not undergo protonation. Minor amounts of the dearomatized chloride complex
2 are also formed as a result of elimination of RH. Reaction of complexes 5 and 6 with water results in
selective protonation-aromatization to give the corresponding complexes 7 and 8.
coordination of the latter in the case of late transition metal
complexes7 can play important roles in catalytic and stochio-
metric reactions, as shown for complexes based on PCN8,9
C6HR3(CH2PtBu2)[(CH2)xNR′2] (x ) 1, 2; R ) H, Me; R′ )
Me, Et) and PNN-type ligands. A PNN-based Ru(II) hydride
Introduction
Transition metal complexes of bulky pincer-type ligands1
have found significant applications in synthesis, bond activation,
and catalysis. Among those, complexes of the pyridine-based
bulky ligand tBuPNP (tBuPNP ) 2,6-(di-tert-butylphosphino-
methyl)pyridine) have been explored in recent years,2–5 and
recently the hemilabile6 PNN ligand (PNN ) (2-(di-tert-
butylphosphinomethyl)-6-diethylaminomethyl)pyridine)) was
synthesized in our group.5 The different electronic properties
of the phosphine and amine ligands and the more labile
(4) (a) Hermann, D.; Gandelman, M.; Rozenberg, H.; Shimon, L. J. W.;
Milstein, D. Organometallics 2002, 21, 812. (b) Ben-Ari, E.; Gandelman,
M.; Rozenberg, H.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 2003,
125, 4714. (c) Zhang, J.; Gandelman, M.; Shimon, L. J. W.; Rozenberg,
H.; Milstein, D. Organometallics 2004, 23, 4026. (d) Ben-Ari, E.; Cohen,
R.; Gandelman, M.; Shimon, L. J. W.; Martin, J. M. L.; Milstein, D.
Organometallics 2006, 25, 3190. (f) Feller, M.; Karton, A.; Leitus, G.;
Martin, J. M. L.; Milstein, D. J. Am. Chem. Soc. 2006, 128, 15390. (g)
Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc.
2006, 128, 15390. (h) Feller, M.; Ben-Ari, E.; Gupta, T,; Shimon, L. J. W.;
Leitus, G.; Diskin-Posner, Y.; Weiner, L.; Milstein, D. Inorg. Chem. 2007,
46, 10479.
* Corresponding author. E-mail: david.milstein@weizmann.ac.il. Fax:
972-8-9344142.
† Department of Organic Chemistry.
‡ Unit of Chemical Research Support.
(1) For recent reviews on pincer-type complexes, see:(a) Albrecht, M.;
van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750. (b) van der Boom,
M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759. (c) Jensen, C. M. Chem.
Commun. 1999, 2443. (d) Singleton, J. T. Tetrahedron 2003, 59, 1837. (e)
Vigalok, A.; Milstein, D. Acc. Chem. Res. 2001, 34, 798. (f) Rybtchinski,
B.; Milstein, D. Angew. Chem., Int. Ed. 1999, 38, 870. (g) Milstein, D.
Pure Appl. Chem. 2003, 75, 445. (h) Rybtchinski, B.; Milstein, D. ACS
Symp. Ser. 2004, 885, 70.
(5) (a) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J. Am. Chem.
Soc. 2005, 127, 12429. (b) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein,
D. Angew. Chem., Int. Ed. 2006, 45, 1113. (e) Zhang, J.; Gandelman, M.;
Herrman, D.; Leitus, G.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D.
Inorg. Chim. Acta 2006, 359, 1955.
(6) Examples of hemilabile pincer complexes: (a) Choualeb, A.; Lough,
A. J.; Gusev, D. G. Organometallics 2007, 26, 5224. (b) Gomez-Benitez,
V.; Toscano, R. A.; Morales-Morales, D. Inorg. Chem. Commun. 2007,
10, 1. (c) Poverenov, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D.
Organometallics 2005, 24, 5937. (d) Rybtchinski, B.; Oevers, S.; Montag,
M.; Vigalok, A.; Rozenberg, H.; Martin, J. M. L.; Milstein, D. J. Am. Chem.
Soc. 2001, 123, 9064. (e) Van Koten, G. Pure Appl. Chem. 1989, 61, 1681.
(7) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. 1994, 33, 497.
(8) (a) Gandelman, M.; Rybtchinski, B.; Ashkenazi, N.; Gauvin, R.;
Milstein, D. J. Am. Chem. Soc. 2001, 123, 5372. (b) Cohen, R.; Rybtchinski,
B.; Gandelman, M.; Martin, J. M. L; Milstein, D. J. Am. Chem. Soc. 2003,
125, 6532. (c) Gandelman, M.; Vigalok, A.; Shimon, L. J. W.; Milstein, D.
Organometallics 1997, 16, 3981. (d) Gandelman, M.; Shimon, L. J. W.;
Milstein, D. Chem. Eur. J. 2003, 9, 4295. (e) Gandelman, M.; Milstein, D.
Chem. Commun. 2000, 1603. (f) Gandelman, M.; Vigalok, A.; Kontanti-
novski, L.; Milstein, D. J. Am. Chem. Soc. 2000, 122, 9848.
(2) (a) Kawatsura, M.; Hartwig, J. F. Organometallics 2001, 20, 1960.
(b) Stambuli, J. P.; Stauffer, S. R.; Shaughnessy, K. H.; Hartwig, J. F. J. Am.
Chem. Soc. 2001, 123, 2677. (c) Gibson, D. H.; Pariya, C.; Mashuta, M. S.
Organometallics 2004, 23, 2510. (d) Kloek, S. M.; Heinekey, D. M.;
Goldberg, K. I. Organometallics 2006, 25, 3007. (e) Benito-Garagori, D.;
Becker, E.; Wiederman, J.; Lackner, W.; Pollak, M.; Mereiter, K.; Kisala,
J.; Kirchner, K. Organometallics 2006, 25, 1900. (f) Kloek, S. M.; Heinekey,
D. M.; Goldberg, K. I. Angew. Chem., Int. Ed. 2007, 46, 4736. (g) Benito-
Garagorri, D.; Wiederman, J.; Pollak, M.; Mereiter, K.; Kirchner, K.
Organometallics 2007, 26, 217.
(3) Pyridine-based iPrPNP: (a) Jansen, A.; Pitter, S. Monatsch. Chem.
1999, 130, 783. (b) Trovitch, R. J.; Lobkovsky, E.; Chirik, P. J. Inorg.
Chem. 2006, 45, 7252. (c) Ref 5e.
10.1021/om8001069 CCC: $40.75
2008 American Chemical Society
Publication on Web 05/09/2008

2628 Organometallics, Vol. 27, No. 11, 2008
Vuzman et al.
Scheme 1
complex is a highly effective catalyst for the acceptorless
dehydrogenation of primary alcohols to esters under neutral
conditions in high yields and high turnover numbers,5a for the
hydrogenation of esters to alcohols under mild conditions,5b and
for the new reaction of alcohols with amines to form amides
and H2, leading to a variety of amides.10 The corresponding
PNP Ru complexes, which are also catalytically quite active,
are less efficient.4c,5
Herein we report the synthesis and reactivity of cationic,
neutral, and anionic complexes of Pt(II) based on a hemilabile
PNN system. Two major processes affect the reactivity of this
system, namely, hemilability of the amine “arm” and dearo-
matization of the pyridine core following benzylic deprotonation.
Unexpectedly, direct nucleophilic attack of organolithium
reagents on a Pt-Cl center results in formation of anionic
complexes without chloride substitution.
Table 1. Selected Bond Lengths (Å) and Angles (deg) of Complex 1
Bond Lengths
Pt(1)-Cl(24)
Pt(1)-N(2)
Pt(1)-N(3)
Pt(1)-P(4)
2.296(1)
1.997(4)
2.148(4)
2.236(1)
P(4)-C(5)
1.841(5)
1.864(5)
1.496(6)
1.513(6)
P(4)-C(12)
N(3)-C(11)
N(3)-C(20)
Bond Angles
Cl(24)-Pt(1)-P(4)
Cl(24)-Pt(1)-N(3)
N(2)-Pt(1)-P(4)
N(3)-Pt(1)-N(2)
98.47(4)
92.5(1)
85.5(1)
83.4(1)
N(3)-Pt(1)-P(4)
N(2)-Pt(1)-Cl(24)
C(11)-N(3)-Pt(1)
C(5)-P(4)-Pt(1)
168.0(1)
176.0(1)
107.5(3)
100.2(2)
Hz). Signals at 5.15, 6.25, and 6.47 ppm in the 1H NMR
spectrum, corresponding to three protons, indicate dearomati-
zation of the pyridine ring. A one-proton doublet at 3.36 ppm
(JP-H ) 7 Hz, JPt-H ) 51 Hz) in the 1H NMR spectrum and a
doublet at 60.26 ppm (JP-C ) 70 Hz) in the 13C{1H} NMR
spectrum indicate that deprotonation at the benzylic phosphine
“arm” took place. Dearomatization following deprotonation of
one methylene position in pincer ligands was reported in a few
cases.3b,4g,5,13 Deprotonation of the two methylene positions in
pincer ligands is also known.14
Results and Discussion
Synthesis and Characterization of PNN-Pt(II) Complexes.
Upon addition of the PNN ligand to (COD)PtCl2 (COD )
cyclooctadiene) in methylene chloride, complex 1 was obtained
in 90% yield (Scheme 1). The 31P{1H} NMR spectrum of this
complex shows a singlet at 49.25 ppm with Pt satellites (JPt-P
) 3409 Hz). The 1H NMR spectrum of 1 exhibits two multiplets
at 3.01 and 3.39 ppm for the diastereotopic methylene protons
of the diethylamine unit, indicating that the amine is coordinated
to the metal center. Complex 1 was identified as the cationic
[(PNN)PtCl]+Cl- with one chloride coordinated to the metal
center and the second chloride in the outer sphere.11
The neutral (PNN*)Pt(II) (PNN* ) dearomatized PNN)
hydride complex 3 was prepared by chloride substitution of 2
n
with BuLi in THF at -20 °C, followed by ꢀ-H elimination
(Scheme 2). The 31P{1H} NMR spectrum of 3 shows a singlet
at 59.64 ppm with Pt satellites (JPt-P ) 3874 Hz), and in the
1H NMR spectrum it exhibits the hydride as a doublet at -12.46
ppm (JP-H ) 17 Hz) with Pt satellites (JPt-H ) 1156 Hz).
Upon reaction of complex 3 with 1 equiv of triflic acid, the
cationic hydride Pt(II) complex 4 was formed and fully
characterized by multinuclear NMR techniques (Scheme 3). The
31P{1H} NMR spectrum of 4 exhibits a singlet with Pt satellites
at 65.23 ppm (JPt-P ) 3744 Hz). In the 1H NMR spectrum the
hydride ligand gives rise to a doublet with Pt satellites at -14.59
Colorless crystals of complex 1 suitable for X-ray diffraction
analysis were obtained from a saturated benzene solution at
room temperature. The platinum atom is located in the center
of a square-planar structure in which the chloride ligand is
located trans to the pyridine ring and the amine “arm” is
coordinated to the metal center (Figure 1). The Pt-P and
Pt-N(“arm”) bond lengths are comparable to the corresponding
bond distances in (PCN)PtCl.9b However, the Pt-Cl bond length
(2.296(1) Å) is significantly shorter than the corresponding bond
in the PCN-based complex (2.41(1) Å)9b due to the stronger
trans influence of the aryl ligand as compared to pyridine.12
Additional bond lengths and angles are given in Table 1.
t
Upon treatment of complex 1 with 1.05 equiv of BuOK at
room temperature, deprotonation of the benzylic phosphine
“arm” took place, resulting in the orange neutral Pt(II) complex
2 in 95% yield (Scheme 2). The 31P{1H} NMR spectrum of 2
shows a singlet at 47.83 ppm with Pt satellites (JPt-P ) 3658
(9) (a) Poverenov, E.; Gandelman, M.; Shimon, L. J. W.; Rozenberg,
H.; Ben-David, Y.; Milstein, D. Chem. Eur. J. 2004, 10, 4673. (b)
Poverenov, E.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.; Ben-
David, Y.; Milstein, D. Organometallics 2005, 24, 1082.
(10) Gunanathan, C.; Ben-David, Y.; Milstein, D. Science 2007, 317,
790.
(11) The outer-sphere chloride is disordered and appears in a few
different positions.
(12) Crabtree, R. H. The Organometalic Chemistry of the Transition
Metals; Wiley: New York, 2005.
Figure 1. ORTEP view of a molecule of complex 1 at the 50%
probability level. Hydrogen atoms, counteranion, and benzene were
omitted for clarity.

Pt(II) Complexes Based on an Electron-Rich PNN Ligand
Organometallics, Vol. 27, No. 11, 2008 2629
Scheme 2
Scheme 3
ppm (JP-H ) 18 Hz, JPt-H ) 1258 Hz). Downfield-shifted
signals at 7.54, 7.61, and 8.04 ppm and the two benzylic protons
at 3.62 ppm (JP-H ) 9 Hz) indicate rearomatization of the PNN
ligand.
Interestingly, addition of methyllithium to a THF-d8 solution
of complex 2 at -20 °C resulted in an immediate color change
from orange to red with formation of the anionic complex 5
(Scheme 3), which was characterized by multinuclear NMR
techniques. The 31P{1H} NMR spectrum of 5 gives rise to a
singlet at 56.94 ppm with Pt satellites (JPt-P ) 2043 Hz). This
relatively small Pt-P coupling constant, as compared to
characteristic coupling of the (PNN)Pt system (about 3600 Hz),
indicates substitution of the amine ligand trans to phosphorus
by a strong σ donor.12 The value of 2043 Hz is in line with
reported values of Pt-P coupling of a phosphine located trans
to a CH3 ligand in an anionic PCN Pt complex.9a The methyl
Formation of Anionic Pt(II) Complexes Based on a
Deprotonated PNN Ligand. The chemistry of anionic transition
metal complexes is of significant interest due to their nucleo-
philic reactivity toward organic molecules,15 their utilization in
the preparation of homo- and heteronuclear transition metal
clusters,16 and their reactivity as alkylating reagents with various
electrophiles17,18 and as reducing hydride donors with polar
molecules.19–22 Formation of relatively stable anionic complexes
in the absence of strong π-accepting ligands, capable of lowering
the electron density at the metal center by enhancing back-
bonding, is generally difficult, and relatively few examples of
such compounds are known.9a,18,20,21,23–25
group gives rise to a three-proton doublet at 0.29 ppm (JP-H
)
8 Hz) with Pt satellites (JPt-H ) 56 Hz) in the 1H NMR spectrum
and to a doublet at 5.59 ppm (JP-C ) 111 Hz) in the 13C{1H}
NMR spectrum. The 1H NMR spectrum indicates that the amine
“arm” of the PNN ligand is not coordinated to the metal, since
the methylene groups of the NEt2 moiety exhibit a single quartet
at 2.41 ppm (JH-H ) 7 Hz) without Pt satellites. Both 1H NMR
and 13C{1H} NMR spectra exhibit high-field signals of the
dearomatized pyridine ring. A heteronuclear 2D 15N-1H
correlation spectrum shows two 15N cross-peaks, a singlet at
160.62 ppm of the pyridine nitrogen, and a singlet at 49.08 ppm
of the amine nitrogen.
(13) Sacco, A.; Vasapollo, G.; Nobile, C. F.; Piergiovanni, A.; Pelling-
helli, M. A.; Lanfranchi, A. J. Organomet. Chem. 1988, 356, 397.
(14) (a) Gorla, F.; Venanzi, L. M.; Albinati, A. Organometallics 1994,
13, 43. (b) Hahn, C.; Spiegler, M.; Herdtweck, E.; Taube, R. Eur. J. Inorg.
Chem. 1998, 1425.
(15) (a) King, R. B. AdV. Organometal. Chem. 1964, 2, 157. (b)
Theopold, K. H.; Bergman, R. G. J. Am. Chem. Soc. 1981, 103, 2489. (c)
Theopold, K. H.; Bergman, R. G. Organometallics 1982, 1, 219. (d) Krause,
M. J.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107, 2972.
(16) (a) Anders, U.; Graham, W. A. G. Chem. Commun. 1966, 291. (b)
Tachikawa, M.; Sievert, A. C.; Muetterties, E. L.; Thompson, M. R.; Day,
C. S.; Day, V. W. J. Am. Chem. Soc. 1980, 102, 1725. (c) Tachikawa, M.;
Geerts, R. L.; Muetterties, E. L. J. Organomet. Chem. 1981, 213, 11.
(17) (a) Kraus, M. J.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107,
2972. (b) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G.
Principles and Application of Organotransition Metal Chemistry; Univerity
Science Books: Mill Valley, CA, 1987.
The Li+ counterion probably stabilizes the anionic complex
5 by coordination to the amine opened “arm”. In line with that,
no reaction took place when MeLi was added to 2 in the
presence of 12-crown-4, due to Li+ complexation by the latter.
Coordination of Li+ might also assist in the opening of the
hemilabile “arm” of complex 2, thus providing a vacant
coordination site and making possible the nucleophilic attack
at the Pt center. The 7Li NMR spectrum of complex 5 exhibits
a broad singlet at 2.67 ppm, which suggests coordinated Li+.
For comparison, LiCl in THF gives rise to a narrow peak at 0
ppm. Crystallographic indication for Li+ coordination was
reported for the complex [(PCN)Pt(H)2]-Li+.9a
A similar reactivity pattern was observed when 1 equiv of
phenyllithium was added to a THF solution of complex 2 at
room temperature. Rapid color change to red took place with
formation of the anionic complex 6 (Scheme 4). The 31P{1H}
NMR spectrum of 6 exhibits a singlet at 53.88 ppm with small
(18) (a) Rice, G. W.; Tobias, R. S. J. Am. Chem. Soc. 1977, 99, 2141.
(b) Nakazawa, H.; Ozawa, F.; Yamamoto, A. Organometallics 1983, 2,
241. (c) Garcia, M. P.; Oro, L. A.; Lahoz, F. J. Angew. Chem. 1988, 100,
1766. Angew. Chem., Int. Ed. Engl. 1988, 27, 1700. (d) Brunet, J. J.;
Commenges, G.; Neibecker, D.; Rosenberg, L. J. Organomet. Chem. 1996,
522, 117. (e) Gusev, D. G.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc.
1998, 120, 13138.
(19) Dedieu, A. Transition Metal Hydrides; VCH: Weinheim, 1991; p
361.
(20) (a) Benfield, F. W. S.; Fonder, R. A.; Green, M. L. H.; Moser,
G. A.; Prout, K. J. Chem. Soc., Chem. Commun. 1973, 759. (b) Francis,
B. R.; Green, M. L. H.; Tuyet, L.; Moser, G. A. J. Chem. Soc., Dalton
Trans. 1976, 1339.
(21) (a) Pez, G. P.; Grey, R. A.; Corsi, J. J. Am. Chem. Soc. 1981, 103,
7528. (b) Grey, R. A.; Pez, G. P.; Wallo, A. J. Am. Chem. Soc. 1981, 103,
7536. (c) Grey, R. A.; Pez, G. P.; Wallo, A. J. Am. Chem. Soc. 1980, 102,
5949.
(24) (a) Ferna´ndez, S.; Fornie′s, J.; Gil, B.; Gomez, J.; Lalinde, E. Dalton
Trans. 2003, 822. (b) Berenguer, J. R.; Lalinde, E.; Torroba, J. Inorg. Chem.
2007, 46, 9919.
(22) Gaus, P. L.; Kao, S. C.; Youngdahl, K.; Darensbourg, M. Y. J. Am.
Chem. Soc. 1985, 107, 2428.
(23) (a) Bruno, J. W.; Huffman, J. C.; Green, M. A.; Caulton, K. G.
J. Am. Chem. Soc. 1984, 106, 8310. (b) Del Paggio, A. A.; Andersen, R. A.;
Muetterties, E. L. Organometallics 1987, 6, 1260.
(25) (a) Amatore, C.; Jutand, A. Acc. Chem. Res. 2000, 33, 314. (b)
Ingleson, M. J.; Pink, M.; Caulton, K. G. J. Am. Chem. Soc. 2006, 128,
4248.

2630 Organometallics, Vol. 27, No. 11, 2008
Vuzman et al.
Scheme 4
Pt satellites (JPt-P ) 1977 Hz). The 1H NMR spectrum reveals
one proton of the benzylic phosphine “arm” as a broad singlet
at 3.17 ppm, and the equivalent methylene groups of the free
amine “arm” appear as a quartet at 2.06 ppm (JH-H ) 7 Hz).
The 13C{1H} NMR spectrum shows the ipso carbon of the
amine “arm”.27 This can be explained by the stronger and
kinetically less labile Pt-Cl bond in the latter complexes due
to the weaker trans effect and trans influence of the pyridine-
type ligand as compared with the aryl ligand.12
The PNN* ligand enables direct coordination of the nucleo-
phile due to dissociation of the hemilabile amine “arm”, which
leads to a decrease of electron density at the metal center and
generation of a vacant site. The corresponding PCN ligand, in
which the amine “arm” forms a five-membered amine chelate,
showed no dissociation of the amine “arm” from the Pt
center.9b,28
1
phenyl ligand at 166.23 ppm (JP-C ) 127 Hz). Both H NMR
and 13C{1H} NMR spectra reveal a dearomatized pyridine ring.
The heteronuclear 2D 15N-1H correlation spectrum exhibits the
pyridine nitrogen as a singlet at 147.33 ppm and the amine
“arm” nitrogen at 49.84 ppm. The 7Li NMR spectrum of
complex 6 shows a broad singlet at 1.16 ppm, which apparently
corresponds to Li+ coordinated to the nitrogen of the opened
amine “arm”.
Reactions of the Anionic Complexes with Acid and
with Water. (a) Reaction with Acid. Anionic complexes show
diverse behavior when treated with acidic reagents.14,18e,21a,23b,29
There are a number of possible outcomes to protonation of the
anionic complexes 5 and 6. It could conceivably regenerate
complex 2 with formation CH4 or C6H6 or regenerate the
aromatic system by attacking the deprotonated benzylic phos-
phine “arm”. Protonation at the nitrogen of the decoordinated
amine “arm” is also a possibility. Interestingly, reaction of a
THF solution of 5 with 1 equiv of HCl resulted mostly in
protonation at the benzylic position to form the neutral complex
7a, with only minor amounts of complex 2 being formed as a
result of CH4 elimination, 7a:2 ) 10:1 (Scheme 4). The 31P{1H}
NMR spectrum of 7a gives rise to a singlet at 73.68 ppm with
Pt satellites (JPt-P ) 1737 Hz). The coordinated methyl group
appears as a doublet at 1.49 ppm (JP-H ) 8 Hz) with Pt satellites
The small Pt-P coupling in the 31P{1H} NMR spectrum and
the large C-P coupling of the ipso carbon in the 13C{1H} NMR
spectrum point to coordination of the phenyl ligand trans to
phosphorus. Crystallographic evidence for this geometry was
obtained for the analogous neutral phenyl chloride complex 8
(vide infra).
Complex 6 is expected to be more stable than complex 5,
because of the possibility of participation of the phenyl group
in delocalization of the negative charge of the Pt complex. In
addition, the Pt-phenyl bond is stronger than Pt-methyl.12
Indeed, 6 can be isolated by evaporation of the solvent and
extraction with benzene, which could not be applied to complex
5. Moreover, 6 is thermally stable, whereas 5 decomposes to
the starting chloride complex 2 and methane during 2-3 days.26
1
(JPt-H ) 64 Hz) in the H NMR and as a doublet at 7.05 ppm
(JP-C ) 112 Hz) in the 13C{1H} NMR. The benzylic phosphine
“arm” exhibits a doublet at 2.72 ppm (JP-H ) 7 Hz) corre-
sponding to two protons, and the methylene groups of the
decoordinated amine “arm” give rise to a quartet at 2.28 ppm
Formation of anionic complexes based on pincer type ligands
as a result of nucleophilic attack was observed before with PCN-
based9a and CNC-based23b Pt(II) neutral complexes. In the PCN
system, which contains a six-membered (long “arm”) chelate,
the first equivalent of RLi (R ) methyl, aryl) caused substitution
of the chloride ligand, and the second equivalent led to
coordination of the nucleophile to the Pt center, resulting in
chelate-ring opening and formation of stable dialkyl and diaryl
anionic complexes. In contrast, surprisingly, no chloride dis-
placement was observed in the reaction of RLi with the PNN*
system; rather, attack at the metal center resulted in formation
of anionic (PNN*)Pt(Cl)(R) complexes with a decoordinated
1
1
(JH-H ) 7 Hz) in the H NMR. Both H NMR and 13C{1H}
NMR spectra reveal downfield signals of the rearomatized
pyridine ring. The heteronuclear 2D 15N-1H correlation spec-
trum gives rise to a singlet at 231.54 ppm attributed to the
(27) The fact that in the reaction of nBuLi with complex 2 substitution
of the chloride to form the hydride complex 3 took place (rather than
formation of an anionic product) might be a result of the ꢀ-elimination
process. Thus, an anionic butyl complex, analogous to 5, might be formed
first, followed by a ꢀ-H elimination process that involves chloride loss.
(28) Five-membered chelate-ring opening in a PNP Co complex was
described.25b
(29) (a) Ellis, J. E.; Faltynek, R. A. J. Am. Chem. Soc. 1977, 99, 1801.
(b) Reinartz, S.; Brookhart, M.; Templeton, J. L. Organometallics 2002,
21, 247.
(26) Formation of methane was detected by GC/MS. Its origin is not
clear.

Pt(II) Complexes Based on an Electron-Rich PNN Ligand
Organometallics, Vol. 27, No. 11, 2008 2631
Scheme 5
Scheme 6
Pt-P distance (2.338(1) Å) is much longer than the correspond-
ing bond in 1 (2.236(1) Å), as expected from the larger trans
influence of the phenyl ligand as compared with that of the
amine moiety. Additional bond distances and bond angles of 8
are given in Table 2.
It is noteworthy that reaction of the protonated complex 7a
with MeLi regenerates the anionic, dearomatized system. Thus,
upon reaction of 7a with MeLi at -20 °C, an immediate color
change to red took place and the anionic complex 5 was obtained
(Scheme 5). No substitution of the chloride ligand to give a
dimethyl complex was observed.
Figure 2. ORTEP view of a molecule of complex 8 at the 50%
probability level.
Table 2. Selected Bond Lengths (Å) and Angles (deg) of Complex 8
Bond Lengths
Pt(1)-Cl(24)
Pt(1)-N(2)
Pt(1)-P(4)
Pt(1)-C(25)
2.305(1) C(5)-C(6)
2.054(3) P(4)-C(5)
2.338(1) N(3)-C(11)
2.049(4) N(3)-C(20)
Bond Angles
1.497(6)
1.854(4)
1.470(5)
1.477(5)
(b) Reaction with Water. Reaction of the anionic complexes
5 and 6 with water in a THF solution at room temperature
resulted in immediate color change to orange with quantitative
formation of complexes 7a and 8, respectively (Scheme 4).
Protonation of the phosphine “arm” by water was confirmed
by reaction of 5 with D2O. The 1H NMR of the product exhibits
the benzylic group of the phosphine “arm” as a broad doublet
at 2.69 ppm (JP-H ) 7 Hz) corresponding to one proton.
This reactivity pattern of the anionic complexes with acid
and water suggests that the negative charge is not concentrated
on the metal center or on the R ligand (R ) aryl, methyl), but
rather on the deprotonated benzylic phosphine “arm”.
Significantly, although complexes 7a and 8 are thermally
stable,30 they cannot be produced by treating the aromatized
complex 1 with RLi (R ) aryl, methyl). Instead, the deproto-
nated complex 2 was formed after addition of 1 equiv of RLi
to a THF solution of complex 1 (Scheme 6). Thus, the
organolithium reagents act as bases rather than as nucleophiles.
As described before, decoordination of the amine “arm” and
nucleophilic attack at the metal center by RLi can occur when
the starting material is a complex based on the deprotonated
PNN* ligand (Scheme 3). It may very well be that formation
of complexes 7a and 8 is thermodynamically more favorable
than the deprotonation process of 1, but the need to open the
chelate “arm” to allow attack at the metal center may make
this process kinetically unfavorable.
Cl(24)-Pt(1)-P(4)
99.78(4)
C(25)-Pt(1)-P(4)
164.06(11)
179.44(10)
C(25)-Pt(1)-Cl(24) 87.58(11) N(2)-Pt(1)-Cl(24)
N(2)-Pt(1)-P(4)
C(25)-Pt(1)-N(2)
80.71(9)
92.02(14) C(5)-P(4)-Pt(1)
C(30)-C(25)-Pt(1) 120.2(3)
90.43(13)
pyridine nitrogen and a singlet at 47.54 ppm attributed to the
amine nitrogen.
The same mode of reactivity was observed for the phenyl
complex 6. Thus, reaction of a THF solution of complex 6 with
1 equiv of HCl at room temperature resulted in formation of
complexes 8 and 2 in a 25:1 ratio, respectively (Scheme 4).
Complex 8 exhibits a singlet at 66.86 ppm with Pt satellites
(JPt-P ) 1694 Hz) in the 31P{1H} NMR spectrum. The two
methylene groups of the amine “arm” give rise to a quartet at
2.15 ppm (JH-H ) 7 Hz) in the 1H NMR spectra with no
coupling to Pt. In the 13C{1H} spectrum the ipso signal at 157.99
ppm (d, JP-C ) 130 Hz) was found, indicating coordination of
the phenyl group trans to the phosphine ligand. Both 1H NMR
and 13C{1H} NMR spectra reveal downfield signals of the
rearomatized pyridine ring. In the heteronuclear 2D 15N-1H
correlation spectrum the pyridine nitrogen appears as a singlet
at 233.06 ppm, and the amine “arm” nitrogen gives rise to a
singlet at 47.40 ppm.
Single crystals of complex 8 suitable for an X-ray diffraction
study were obtained by slow evaporation of the solvent from a
saturated benzene solution at room temperature. Complex 8 has
a slightly distorted square-planar structure around the Pt(II)
center, with the phenyl ligand located trans to the phosphorus
atom and the chloride ligand coordinated trans to the pyridine
ring (Figure 2). As shown by multinuclear NMR spectroscopy
in solution, the amine “arm” is disconnected from the metal
center, allowing coordination of the phenyl in its place. The
Summary
New cationic, neutral, and anionic Pt(II) complexes of the
PNN system are reported. The PNN ligand takes an active role
in the formation and reactivity of the complexes, by virtue of
(30) While complexes 7 and 8 are highly stable at room temperature,
they completely decompose during 72 h at 60 °C (complex 7) and 72 h at
90 °C (complex 8).

2632 Organometallics, Vol. 27, No. 11, 2008
Vuzman et al.
color change to yellowish. The 31P{1H} NMR spectrum of the
solution revealed formation of complex 1. The solvent was removed
under vacuum, and the residue was washed with pentane and
extracted with methylene chloride. Solvent evaporation yielded 471
mg (0.80 mmol, 90% yield) of cream-colored complex 1.
dearomatization/aromatization processes (as a result of ligand
deprotonation) and hemilability. Treatment of the cationic
chloride complex 1 with BuOK resulted in deprotonation,
t
leading to the dearomatized, neutral chloride complex 2.
Nucleophilic attack on this complex by 1 equiv of RLi did not
lead to chloride substitution; rather, facile formation of the
corresponding anionic complexes Li+[(PNN*)Pt(Cl)(R)]- (R )
methyl (5), phenyl (6)) took place, in which the amine “arm”
underwent decoordination. Formation of these highly electron-
rich d8 complexes in the absence of stabilizing π acceptors is
possibly assisted by coordination of Li+ to the amine group,
allowing the opening of the chelate ring followed by nucleophilic
attack on Pt. Reaction of the anionic complexes 5 and 6 with
HCl resulted mainly in aromatization to form the neutral
complexes (PNN)Pt(Cl)(R) (R ) methyl (7), phenyl (8)), RH
elimination playing a minor role. This aromatization reaction
was completely selective when water was used.
31P{1H} NMR (CD2Cl2): 49.25 (s, JPt-P )3409 Hz). H NMR
1
(CD2Cl2): 8.13 (dt, JH-H ) 8 Hz, JP-H)8 Hz,1H, pyridine-H4),
7.97 (d, JH-H ) 8 Hz, 1H, pyridine-H5), 7.84 (d, JH-H ) 8 Hz,
1H, pyridine-H3), 4.70 (s, 2H, CH2N), 3.93 (d, JP-H ) 10 Hz, JPt-H
) 26 Hz, 2H, CH2P), 3.39 (m, 2H, NCHHCH3), 3.01 (m, 2H,
NCHHCH3), 1.48 (t, JH-H ) 7 Hz, N(CH2CH3)2 1.46 (d, JP-H
)
16 Hz, P(C(CH3)3)2; the last two reported signals are overlapped,
and their integral corresponds to 24H. 13C{1H} NMR (CD2Cl2):
162.20 (bs, Py-C2), 161.95 (bs, Py-C6), 140.47 (s, Py-C4), 128.62
(s, Py-C5), 121.64 (s, Py-C3), 65.75 (s, Py-CH2N), 55.97 (s,
N(CH2Me)2), 36.19 (d, JPC ) 27 Hz, P(C(CH3)3)2), 36.11 (d, JPC
) 32 Hz, PCH2), 28.69 (s, P(C(CH3)3)2),12.28 (s, N(CH2CH3)2
(assignment of 13C{1H} NMR signals was confirmed by 13C
DEPT). Anal. Found (calcd for C19H35P1N2Pt1Cl2+0.5(CH2Cl2)):
C, 37.36 (37.12); H, 6.49 (5.75); N, 4.46 (4.44).
Experimental Section
X-ray Structural Analysis of 1. Complex 1 was crystallized
from a saturated benzene solution at room temperature to give
colorless crystals. Crystal data: C19H35Cl2N2P1Pt1 + C6H6, 0.3 ×
General Procedures. All experiments with metal complexes and
phosphine ligands were carried out under an atmosphere of purified
nitrogen in a Vacuum Atmospheres glovebox equipped with an MO
40-2 inert gas purifier or using standard Schlenk techniques. All
solvents were reagent grade or better. All nondeuterated solvents
were refluxed over sodium/benzophenone ketyl and distilled under
an argon atmosphere. Deuterated solvents were used as received.
All the solvents were degassed with argon and kept in the glovebox
over 4 Å molecular sieves. Commercially available reagents were
3
j
0.2 × 0.05 mm , triclinic, space group P1, a ) 9.1580(2) Å, b )
10.9628(2) Å, c ) 16.0184(2) Å, R ) 77.293(1)°, ꢀ ) 76.973(1)°,
γ ) 69.110(1)° from 25 degrees of data, V ) 1446.51(4) Å3, Z )
2, fw ) 666.56, Dc ) 1.530 Mg/m3, µ ) 5.104 mm-1. Data
collection and treatment: 28 500 reflections collected, -11 e h e
11, -13 e k e 14, 0 e l e 20, 6593 independent reflections (Rint
) 0.080); 293 parameters refined with no restraints, final R1 )
0.0326 for data with I > 2σ(I) and R1 ) 0.0365 on 6592 reflections,
wR2 ) 0.0911, goodness-of-fit on F2 ) 1.086, largest electron
density peak ) 2.576 e/Å3.
31
used as received. The ligand PNN5 and the complex Pt(COD)Cl2
were prepared according to literature procedures. The NMR spectra
were recorded at 250 (1H), 101 (31P), and 235 MHz (19F) using a
Bruker DPX 250 spectrometer, at 400 (1H), 100 (13C), 162 (31P),
and 155 MHz (7Li) using a Bruker AMX-400 NMR spectrometer,
and at 500 (1H), 126 (13C), 202 MHz (31P), and 50.7 MHz (15N in
2D 15N-1H correlation) using a Bruker DPX 500 spectrometer.
All spectra were recorded at 23 °C (if not specified otherwise).
The long-range 2D15N-1H correlation spectrum was measured
using the Bruker standard microprogram GHMBC by an inverse
gradient selected experiment using a 5 mm Bruker inverse multi-
nuclear resonance probe with a single-axis (z) gradient coil. 1H
NMR and 13C{1H} NMR chemical shifts are reported in parts per
million downfield from tetramethylsilane. 1H NMR chemical shifts
are referenced to the residual hydrogen signal of the deuterated
solvents, and in 13C{1H} NMR the 13C signal of the deuterated
solvents was used as a reference. 31P NMR chemical shifts are
reported in ppm downfield from H3PO4 and referenced to an
external 85% solution of phosphoric acid in D2O. 19F NMR
chemical shifts were referenced to C6F6 (-163 ppm). 15N NMR
chemical shifts are reported as referenced downfield to liquid
ammonia. In 7Li NMR measurements LiCl was used as a standard
(LiCl in THF ) 0 ppm). Screw-cap 5 mm NMR tubes were used
in the NMR follow-up experiments. Abbreviations used in the
description of NMR data are as follows: Ar aryl, br broad, s singlet,
d doublet, t triplet, q quartet, m multiplet, v virtual. Elemental
analyses were performed by H. Kolbe, Microanalytisches Labora-
torium, Germany. The X-ray data were collected on a Nonius
KappaCCD diffractometer, Mo KR (λ ) 0.71073 Å) with a graphite
monochromator at T ) 120(2) K. The data were processed with
Denzo-Scalepack. The structures were solved by direct methods
with SHELXS and were refined by full matrix least-squares based
on F2 with SHELXL-97.
Preparation of (PNN*)PtCl (2). To a THF (5 mL) suspension
of complex 1 (53.4 mg, 0.091 mmol) was added tBuOK (11.2 mg,
0.095 mmol), resulting in a color change from yellowish to orange.
The solvent was removed under vacuum, and the complex was
extracted with benzene. Solvent evaporation yielded 47.9 mg (0.087
mmol, 95% yield) of complex 2 as an orange solid.
1
31P{1H} NMR (C6D6): 47.83 (s, JPt-P ) 3658 Hz). H NMR
(C6D6): 6.47 (ddd, JH-H ) 9 Hz, JH-H ) 6 Hz, JP-H ) 2 Hz, 1H,
pyridine-H4), 6.25 (d, JH-H ) 9 Hz, 1H, pyridine-H5), 5.15 (d,
JH-H ) 6 Hz, 1H, pyridine-H3), 3.36 (d, JP-H ) 7 Hz, JPt-H ) 51
Hz, 1H, )CHP), 2.98 (s, 2H, CH2N), 2.95 (m, 2H, NCHHCH3),
2.17 (m, 2H, NCHHCH3), 1.47 (d, JP-H ) 14 Hz, 18H, P(C(CH3)3)2,
1.17 (t, JH-H ) 7 Hz, 6H, N(CH2CH3)2. 13C{1H} NMR (C6D6):
169.29 (d, JPC ) 10 Hz, Py-C2), 156.81 (s, Py-C6), 131.98 (s, Py-
C4), 112.81 (d, JP-C ) 12 Hz, Py-C3), 95.85 (s, Py-C5), 64.12 (s,
Py-CH2N), 60.26 (d, JP-C ) 70 Hz, dCHP), 54.25 (s, N(CH2CH3)2),
36.91 (d, JPC ) 33 Hz, P(C(CH3)3)2), 29.08 (d, JPC ) 3 Hz,
P(C(CH3)3)2), 11.60 (s, N(CH2CH3)2) (assignment of 13C{1H} NMR
signals was confirmed by 13C DEPT). Anal. Found (calcd for
C19H34P1N2Pt1Cl1+0.5(C6H6)): C, 44.91 (44.71); H, 6.65 (6.31);
N, 5.20 (4.73).
Preparation of (PNN*)PtH (3). To a THF solution (4 mL) of
complex 2 (167 mg, 0.302 mmol) was added 212 µL of a THF
n
solution of BuLi (1.5 M, 0.109 mmol) at -20 °C. The solution
was warmed to room temperature, and the solvent was removed
under vacuum. Complex 3 was extracted with benzene, and the
benzene was removed under vacuum to yield 152 mg (0.294 mmol,
97% yield) of complex 3 as a dark orange solid.
1
31P{1H} NMR (C6D6): 59.64 (s, JPt-P ) 3874 Hz). H NMR
Preparation of [(PNN)PtCl]+Cl- (1). To a methylene chloride
solution (8 mL) of (COD)PtCl2 (308 mg, 0.89 mmol) was added
the PNN ligand (300 mg, 0.93 mmol), resulting in an immediate
(C6D6): 6.65 (ddd, JH-H ) 9 Hz, JH-H ) 8 Hz, JP-H ) 2 Hz, 1H,
pyridine-H4), 6.45 (d, JH-H ) 9 Hz, 1H, pyridine-H5), 5.38 (d,
JH-H ) 7 Hz, 1H, pyridine-H3), 3.49 (d, JP-H ) 7 Hz, 2H, dCHP),
3.15 (s, 2H, CH2N), 2.51 (m, 4H, NCH2CH3), 1.46 (d, JH-H ) 14
Hz, 18H, P(C(CH3)3)2, 1.16 (t, JH-H ) 7 Hz, 6H, N(CH2CH3)2,
(31) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411.

Pt(II) Complexes Based on an Electron-Rich PNN Ligand
Organometallics, Vol. 27, No. 11, 2008 2633
-12.46 (t, JP-H ) 17 Hz, JPt-H ) 1156 Hz, 1H, Pt-H). 13C{1H}
31P{1H} NMR (d8-THF): 53.88 (s, JPt-P ) 1977 Hz). 1H NMR
(d8-THF): 7.33 (m, 2H, Ar) 6.71 (t, JH-H ) 7 Hz, 2H, Ar), 6.58 (t,
JH-H ) 7 Hz, 1H, Ar), 6.16 (bt, JH-H ) 7 Hz, 1H, pyridine-H4),
5.73 (d, JH-H ) 8 Hz, 1H, pyridine-H5), 5.41 (d, JH-H ) 6 Hz,
1H, pyridine-H3), 3.54 (s, 2H, CH2N), 3.17 (bs, 1H, CHP), 2.06
(q, JH-H ) 7 Hz, 2H, NCHHCH3), 1.33 (d, JP-H ) 12 Hz, 18H,
P(C(CH3)3)2, 0.63 (t, JH-H) 7 Hz, 6H, N(CH2CH3)2. 13C{1H} NMR
NMR (C6D6): 167.73 (d, JP-C ) 11 Hz, Py-C2), 156.74 (d, JPC
3 Hz, Py-C6), 132.6 (d, JP-C ) 2 Hz, Py-C4), 112.43 (d, JP-C
)
)
16 Hz, Py-C3), 95.88 (s, Py-C5), 67.46 (d, JP-C ) 2 Hz, JPy-
CH2N), 59.21 (d, JP-C ) 69 Hz, dCHP), 55.77 (d, JP-C ) 2 Hz,
N(CH2CH3)2), 35.94 (d, JPC ) 35 Hz, P(C(CH3)3)2), 29.61 (d, JP-C
) 4 Hz, JPt-C ) 32 Hz, P(C(CH3)3)2), 13.25 (s, JPt-C ) 36 Hz,
N(CH2CH3)2) (assignment of 13C{1H} NMR signals was confirmed
by 13C DEPT). Anal. Found (calcd for C19H35P1N2Pt1+0.5(C6H6)):
C, 46.77 (47.47); H, 7.11 (6.88); N, 4.86 (5.03).
(d8-THF): 177.13 (d, JP-C ) 20 Hz, Py-C6), 166.23 (d, JP-C
)
127 Hz, ipso of phenyl, coordinated trans to P), 159.96 (s, Py-
C2), 138.28 (s, Ar), 131.16 (d, JP-C ) 15 Hz, Ar), 129.47 (s, Ar),
127.69 (s, Ar), 125.56 (bs, Ar), 121.48 (s, Py-C3), 112.18 (bs, Ar),
102.92 (d, Py-C5), 63.82 (s, Py-CH2N), 47.81 (s, N(CH2CH3)2),
35.53 (d, JP-C ) 19 Hz, CH2P), 34.61 (d, JP-C ) 10 Hz,
P(C(CH3)3)2), 29.05 (bs, P(C(CH3)3)2), 12.27 (s, N(CH2CH3)2),
(assignment of 13C{1H} NMR signals was confirmed by 13C
DEPT). 15N NMR from 15N-1H correlation (d8-THF): 147.33 (s,
Py-N), 49.84 (s, Py-CH2N). 7Li NMR (d8-THF): 1.16 (bs). ES-
MS: m/z 629.98 (M + H) (calcd 630.10), 666.97 (M + 2H + Cl)
(calcd 666.56), m/z+ 595.20 (M + H - Cl) (calcd 594.65) (major),
554.09 (M + 2H - C6H5) (calcd 554.01).
Preparation of [(PNN)PtH]+OTf- (4). To a toluene solution
(1 mL) of complex 3 (16 mg, 0.031 mmol) was added 1 equiv of
HOTf (2.7 µL, 0.031 mmol) at -20 °C. An immediate color change
from orange to yellowish took place. The solution was warmed to
room temperature, and the solvent was removed under vacuum.
Complex 4 was washed with pentane and extracted with THF.
Solvent removal under vacuum yielded 21.3 mg (0.03 mmol, 98%
yield) of complex 4 as a light yellowish solid.
31P{1H} NMR (CD2Cl2): 65.23 (s, JPt-P ) 3744 Hz). 1H NMR
(CD2Cl2): 8.04 (t, JH-H ) 8 Hz, 1H, pyridine-H4), 7.61 (d, JH-H
)
Reactivity of Anionic Complexes. Reaction of [(PNN*)Pt(Cl)
(CH3)]-Li+ (5) with HCl. To a THF solution (1.5 mL) of complex
2 (20 mg, 0.036 mmol) at -20 °C was added 38.4 µL of a THF
solution of MeLi (1 M, 0.039 mmol), resulting in the formation of
complex 5. This was followed immediately by addition of 9 µL of
dioxane solution of HCl (4 M, 0.036 mmol) at room temperature,
resulting in a color change to orange light. The 31P{1H} NMR
spectrum at room temperature revealed formation of complex 7a
as a major product and 2 as a minor product, in a 10:1 ratio,
respectively. The solvent was removed under vacuum, and complex
7a was extracted with benzene. Benzene evaporation yielded 19
mg (0.025 mmol, 93% yield) of complex 7 as an orange solid.
8 Hz, 1H, pyridine-H5), 7.54 (d, JH-H ) 8 Hz, 1H, pyridine-H3),
4.47 (s, 2H, CH2N), 3.62 (d, JP-H ) 9 Hz, 2H, CH2P), 3.29 (m,
2H, NCHHCH3), 3.21 (m, 2H, NCHHCH3), 1.48 (t, JH-H ) 7 Hz,
6H, N(CH2CH3)2), 1.35 (d, JP-H ) 15 Hz, 18H, P(C(CH3)3)2),
-14.59 (d, JP-H ) 18 Hz, JPt-H ) 1258 Hz, 1H, Pt-H). 13C{1H}
NMR (CD2Cl2): 159.91 (bs, Py-C2), 159.41 (bs, Py-C6), 138.98
(s, Py-C4), 128.62 (s, Py-C5), 120.96 (s, Py-C3), 68.09 (s, Py-
CH2N), 57.72 (s, N(CH2Me)2), 35.70 (d, JP-C ) 30 Hz, PCH2),
35.14 (d, JP-C ) 29 Hz, P(C(CH3)3)2), 28.76 (d, JP-C ) 4 Hz,
P(C(CH3)3)2),13.75 (s, N(CH2CH3)2 (assignment of 13C{1H} NMR
signals was confirmed by 13C DEPT). 19F{1H} NMR (CD2Cl2):
-79.68 (s, free SO3CF3). Anal. Found (calcd for C20H36P1N2Pt1
SO3F3): C, 36.53 (35.98); H, 6.11 (5.44); N, 4.01 (4.20).
Complex 7a. 31P{1H} NMR (C6D6): 73.68 (s, JPt-P ) 1737 Hz).
1H NMR (C6D6): 7.49 (d, JH-H ) 7 Hz,1H, pyridine-H5), 6.98 (t,
JH-H ) 7 Hz, 1H, pyridine-H4), 6.47 (d, JH-H ) 7 Hz, 1H, pyridine-
H3), 4.30 (s, 2H, CH2N), 2.72 (d, 2H, JP-H ) 7 Hz, CH2P), 2.28
Preparation of [(PNN*)Pt(Cl)(CH3)]-Li+ (5). To a d8-THF
solution (0.5 mL) of complex 2 (20 mg, 0.036 mmol) at -20 °C
was added 38 µL of a diethyl ether solution of MeLi (1 M, 0.038
mmol), resulting in a color change from orange to red. Formation
of complex 5 was immediately revealed by 31P{1H} NMR.
Complex 5 was converted to complex 2 during 3-4 days at room
temperature. GC/MS analysis of a 10 µL sample of the gas phase
from the screw-cap tube revealed formation of CH4.
31P{1H} NMR (d8-THF): 56.94 (s, JPt-P ) 2043 Hz). 1H NMR
(d8-THF): 6.18 (ddd, JH-H ) 9 Hz, JH-H ) 7 Hz, JP-H ) 2 Hz,
1H, pyridine-H4), 5.72 (d, JH-H ) 9 Hz, 1H, pyridine-H5), 5.60
(d, JH-H ) 7 Hz, 1H, pyridine-H3), 3.60 (s, 2H, CH2N), 3.26 (bs,
2H, dCHP), 2.41 (q, JH-H ) 7 Hz, 2H, NCHHCH3), 1.32 (d, JP-H
) 12 Hz, 18H, P(C(CH3)3)2, 0.95 (t, JH-H ) 7 Hz, 6H, N(CH2CH3)2,
0.29 (d, JP-H ) 8 Hz, JPt-H ) 56 Hz, 3H, Pt-CH3). 13C{1H} NMR
(C6D6): 177.14 (d, JP-C ) 20 Hz, Py-C2), 159.68 (s, Py-C6), 132.59
(s, Py-C4), 112.69 (d, JP-C ) 15 Hz, Py-C3), 96.37 (s, Py-C5),
65.56 (d, JP-C ) 56 Hz, dCHP), 62.78 (s, Py-CH2N), 48.17 (s,
N(CH2CH3)2), 36.55 (d, JP-C ) 17 Hz, P(C(CH3)3)2), 29.89 (d, JP-C
(q, JH-H ) 7 Hz, 2H, NCHHCH3), 1.49 (d, JP-H ) 8 Hz, JPt-H
)
64 Hz, 3H, Pt-CH3), 1.17 (d, JP-H ) 13 Hz, 18H, P(C(CH3)3)2,
0.86 (t, JH-H ) 7 Hz, 6H, N(CH2CH3)2. 13C{1H} NMR (C6D6):
166.26 (Py-C6), 164.40 (d, JP-C ) 7 Hz, Py-C2), 136.34 (s, Py-
C4), 123.82 (s, Py-C5), 120.89 (d, JP-C ) 7 Hz, Py-C3), 61.89 (s,
Py-CH2N), 47.37 (s, N(CH2CH3)2), 35.55 (d, JP-C ) 21 Hz, CH2P),
34.54 (d, JP-C ) 8 Hz, P(C(CH3)3)2), 29.02 (d, JP-C ) 5 Hz,
P(C(CH3)3)2), 12.26 (s, N(CH2CH3)2), 7.05 (d, JP-C ) 112 Hz, Pt-
CH3) (assignment of 13C{1H} NMR signals was confirmed by 13
C
DEPT). 15N NMR from 15N-1H correlation (C6D6): 231.54 (s, Py-
N), 47.54 (s, Py-CH2N). ES-MS: m/z- 567.98 (M - H) (calcd
567.20), 603.99 (M + Cl) (calcd 603.66), m/z+ 533.21 (M - Cl)
(calcd 532.75) (major), 553.19 (M - CH3) (calcd 554.17). Anal.
Found (calcd for C20H38P1N2Pt1Cl+0.5(C6H6)): C, 45.31 (45.50);
H, 6.62 (6.81); N, 5.14 (4.61).
Reaction of [(PNN*)Pt(Cl)(CH3)]-Li+ (5) with Water. To a
THF solution (1.5 mL) of complex 2 (20 mg, 0.036 mmol) at -20
°C was added 38.4 µL of a THF solution of MeLi (1 M, 0.039
mmol), resulting in the formation of complex 5. Upon injection of
excess H2O (1 µL, 0.056 mmol) into a THF solution of 5 in a 5
mm screw-cap tube equipped with a septum, a color change to
yellow took place and formation of the neutral complex 7 was
immediately revealed by 31P{1H} NMR spectroscopy. The solvent
was removed under vacuum, and complex 7a was extracted with
benzene. Benzene evaporation yielded 15.5 mg (0.027 mmol, 76%
yield) of complex 7a as an orange solid.
) 5 Hz, P(C(CH3)3)2), 13.33 (s, N(CH2CH3)2), 5.59 (d, JP-C
)
111 Hz, Pt-CH3) (assignment of 13C{1H} NMR signals was
confirmed by 13C DEPT). 15N NMR from 15N-1H correlation (d8-
THF): 160.62 (s, Py-N), 49.08 (s, Py-CH2N). 7Li NMR (d8-THF):
2.67 (bs). ES-MS: m/z- 567.80 (M) (calcd 567.20), 603.81 (M +
H + Cl) (calcd 603.66), m/z+ 533.08 (M + H - Cl) (calcd 532.75).
Preparation of [(PNN*)Pt(Cl)(C6H5)]-Li+ (6). To a THF
solution (1.5 mL) of complex 2 (20 mg, 0.036 mmol) was added
30.6 µL of a THF solution of PhLi (1.3 M, 0.040 mmol), resulting
in a color change from orange to red. Formation of complex 6 was
immediately revealed by 31P{1H} NMR. The solvent was removed
under vacuum for 1 h, and the residual solid was extracted with
benzene. Benzene evaporation yielded 19 mg (0.030 mmol, 83%
yield) of complex 6 as a bourdeaux solid.
Reaction of [(PNN*)Pt(Cl)(C6H5)]-Li+ (6) with HCl. To a
THF solution (1.5 mL) of complex 6 (23 mg, 0.036 mmol) was
added 9 µL of a dioxane solution of HCl (4 M, 0.036 mmol) at
room temperature, resulting in a color change to light orange. The
31P{1H}NMR spectrum revealed formation of complex 8 as a major

2634 Organometallics, Vol. 27, No. 11, 2008
Vuzman et al.
product and 2 as a minor product, in a 25:1 ratio, respectively.
The solvent was removed under vacuum, and complex 8 was
extracted with 20 mL of pentane (complex 2 was extracted from
the residue with benzene). Pentane evaporation yielded 16 mg
(0.025 mmol, 71% yield) of complex 8 as an orange solid.
Complex 8. 31P{1H} NMR (C6D6): 66.86 (s, JPt-P ) 1694 Hz).
1H NMR (C6D6): 7.65 (t, JH-H ) 7 Hz, 2H, Ar), 7.44 (m, 2H, Ar),
P21/n, a ) 12.6781(3) Å, b ) 10.0244(2) Å, c ) 20.8930(6) Å, ꢀ
) 102.328(1)° from 20 degrees of data, V ) 2594.07(11) Å3, Z )
4, fw ) 630.10, Dc )1.613 Mg/m3, µ ) 5.588 mm-1. Data
collection and treatment: 17 274 reflections collected, -16 e h e
16, 0 e k e 13, 0 e l e 27, 6235 independent reflections (Rint
)
0.052). Solution and refinement: 279 parameters refined with no
restraints, final R1 ) 0.0317 for data with I > 2σ(I) and R1 ) 0.0534
on 5891 reflections, wR2 ) 0.0583, goodness-of-fit on F2 ) 0.978,
largest electron density peak ) 2.635 e/Å3.
7.20 (t, JH-H ) 8 Hz, 1H, Ar), 7.02 (m, 2H, Ar), 6.49 (d, JH-H
)
8 Hz, 1H, Ar), 3.50 (s, 2H, CH2N), 2.83 (d, JP-H ) 7 Hz, 2H,
CH2P), 2.15 (q, JH-H ) 7 Hz, 2H, NCHHCH3), 1.16 (d, JP-H ) 13
Hz, 18H, P(C(CH3)3)2, 0.73 (t, JH-H ) 7 Hz, 6H, N(CH2CH3)2.
13C{1H} NMR (C6D6): 167.61 (s, Py-C6), 163.94 (d, JP-C ) 7
Hz, Py-C2), 157.99 (d, JP-C ) 130 Hz, ipso of phenyl, coordinated
trans to P), 136.93 (s, Ar), 136.7 (s, Py-C4), 128.97 (s, Py-C5),
127.43 (d, JP-C ) 9 Hz, Ar), 126.78 (d, JP-C ) 8 Hz, Ar), 124.31
(s, Ar), 123.58 (s, Ar), 120.51 (d, JP-C ) 4 Hz, Py-C3), 63.82 (s,
Py-CH2N), 47.81 (s, N(CH2CH3)2), 35.53 (d, JP-C ) 19 Hz, CH2P),
34.61 (d, JP-C ) 10 Hz, P(C(CH3)3)2), 29.05 (bs, P(C(CH3)3)2),
12.27 (s, N(CH2CH3)2), (assignment of 13C{1H} NMR signals was
confirmed by 13C DEPT). 15N NMR from 15N-1H correlation
(C6D6): 233.06 (s, Py-N), 47.40 (s, Py-CH2N). ES-MS: m/z- 629.98
(M) (calcd 630.10), 666.97 (M + H + Cl) (calcd 666.56), m/z +
554.09 (M + H - C6H5) (calcd 554.00) (major), 595.20 (M + H
- Cl) (calcd 595.65). Anal. Found (calcd for C25H40P1N2Pt1Cl+
C6H6): C, 52.23 (52.57); H, 6.88 (6.55); N, 4.26 (3.96).
Reaction of [(PNN*)Pt(Cl)(C6H5)]-Li+ (6) with Water. To a
NMR tube equipped with a septum containing a THF solution (1.5
mL) of complex 6 (20 mg, 0.031 mmol) was injected 2 µL (0.112
mmol) of H2O. A color change from red to orange took place, and
formation of complex 8 was revealed by 31P{1H} NMR. The solvent
was removed under vacuum, and the complex was extracted with
benzene. Benzene evaporation yielded 17 mg (0.027 mmol, 87%
yield) of complex 8 as an orange solid.
Acknowledgment. This research was supported by the
Israel Science Foundation, by the DIP program for German-
Israeli Cooperation, and by the Helen and Martin Kimmel
Center for Molecular Design. D.M. is the holder of the Israel
Matz Professorial Chair of Organic Chemistry.
Supporting Information Available: CIF files containing X-ray
crystallographic data for complexes 1 and 8. This material is
available free of charge via the Internet at http://pubs.acs.org.
X-ray Structural Analysis of 8. Complex 8 was crystallized
from a saturated benzene solution by slow evaporation of the solvent
at room temperature to give colorless needles. Crystal data:
C25H40ClN2PPt, 0.10 × 0.03 × 0.01 mm3, monoclinic, space group
OM8001069