Pincer hemilabile effect. PCN platinum(II) complexes with different amine arm length

Article abstract of DOI:10.1021/om049182m

The reactivity of the long arm PCN-type pincer ligand C ₆H₄[CH₂P(tBu)₂](CH₂) ₂N(CH₃)₂ (1), which forms complexes bearing a six-member ed amine chelate and a five-membered phosphine chelate, was compared with that of the new normal PCN ligand C₆H ₄[CH₂P-(tBu)₂](CH₂)N(CH ₂CH₃)₂ (2), which leads to formation of complexes bearing two five-membered chelates. The chloride complexes (PCN)PtCl (3, 4) and the unsaturated cationic complexes [(PCN)Pt]⁺X^- (X = BF₄, OTf) (5,6,7), based on both PCN ligands, were prepared and reacted with different reagents to give aqua, [(PCN-1)Pt(H₂O)] ⁺BF₄^- (10); hydroxo, (PCN-1)Pt(OH) (11); carbonyl [(PCN)Pt(CO)]⁺BF₄^- (8, 9); and hydride, (PCN-1)PtH (16) complexes. The structures of complexes 4, 6, 8, 10, 11, and 12 were determined by X-ray crystallography. When both carbonyl complexes were treated with hydrogen gas, the long arm PCN-1-based complex 8 led to formation of a trimeric cluster, [C₆H₆[CH ₂P(tBu)₂]-(CH₂)₂N(CH ₃)₂Pt(CO)]₃ (12), while the normal PCN-based complex 9 remained unchanged under the same conditions. This observation clearly demonstrates the very significant effect of the amine arm length (five- vs six-membered chelate) on the hemilability of the ligand and the reactivity of the corresponding complexes.

Full text of DOI:10.1021/om049182m

1082
Organometallics 2005, 24, 1082-1090
Pincer “Hemilabile” Effect. PCN Platinum(II) Complexes
with Different Amine “Arm Length”
Elena Poverenov,† Mark Gandelman,† Linda J. W. Shimon,‡ Haim Rozenberg,‡
Yehoshoa Ben-David,† and David Milstein*,†
Department of Organic Chemistry and Unit of Chemical Research Support,
The Weizmann Institute of Science, Rehovot, 76100, Israel
Received October 21, 2004
The reactivity of the “long arm” PCN-type pincer ligand C6H4[CH2P(tBu)2](CH2)2N(CH3)2
(1), which forms complexes bearing a six-membered amine chelate and a five-membered
phosphine chelate, was compared with that of the new “normal” PCN ligand C6H4[CH2P-
(tBu)2](CH2)N(CH2CH3)2 (2), which leads to formation of complexes bearing two five-
membered chelates. The chloride complexes (PCN)PtCl (3, 4) and the unsaturated cationic
complexes [(PCN)Pt]+X- (X ) BF4, OTf) (5, 6, 7), based on both PCN ligands, were prepared
and reacted with different reagents to give aqua, [(PCN-1)Pt(H2O)]+BF4 (10); hydroxo,
-
-
(PCN-1)Pt(OH) (11); carbonyl [(PCN)Pt(CO)]+BF4 (8, 9); and hydride, (PCN-1)PtH (16)
complexes. The structures of complexes 4, 6, 8, 10, 11, and 12 were determined by X-ray
crystallography. When both carbonyl complexes were treated with hydrogen gas, the “long
arm” PCN-1-based complex 8 led to formation of a trimeric cluster, [C6H6[CH2P(tBu)2]-
(CH2)2N(CH3)2Pt(CO)]3 (12), while the “normal” PCN-based complex 9 remained unchanged
under the same conditions. This observation clearly demonstrates the very significant effect
of the amine arm length (five- vs six-membered chelate) on the hemilability of the ligand
and the reactivity of the corresponding complexes.
Introduction
utilized in selective C-C and C-H bond activation,3 in
catalytic C-N bond activation,4 and in novel catalytic
azine reactivity.5 Carbene- and diazo-PCN-Rh(I) com-
plexes were reported6 and utilized in mechanistic stud-
ies of carbene formation from diazo compounds.6b Using
PCN-based complexes, medium effects on highly unsat-
urated Rh(III) complexes were investigated and a
dearomatized methylene arenium system was obtained
when stabilizing solvents and/or counteranions were
absent.7 Moreover, a PCN-based system allowed for the
first time the observation of a single-step metal insertion
into a C-C bond and the evaluation of the kinetic
parameters of this process.8 Hemilabile PCO complexes
were also reported to be involved in C-C activation.9
It is expected that the amine “arm” will be involved
in more labile coordination to late transition metals in
Late transition metal pincer-type complexes contain-
ing a T-shaped X-C-X (X ) N, P) ligand core play an
important role in organometallic chemistry. Such trident-
ate ligands enhance the stability of the complexes and
allow the manipulation of steric and electronic param-
eters, which control reactivity at the metal center.1
In NCN (A1) ligand-based complexes, which were
extensively studied by van Koten and co-workers, the
hard, σ-donating amine groups are not always spectator
ligands and can participate in metal-centered reactions,
providing the corresponding NCN complexes with in-
teresting stoichiometric and catalytic properties.1a,2
PCP-ligand-based complexes (A2) exhibit high chelate
stability and were utilized in the activation of strong
bonds, stabilization of unstable elusive compounds, and
various catalytic transformations.1
(1) Recent reviews: (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) (g) Jensen, C. J. 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. Engl. 1999, 38, 870. (g) Milstein, D. Pure Appl.
Chem. 2003, 75, 2003. (h) Milstein, D.; Rybtchinski, B. ACS Symp.
Ser. 2004, 885, 70.
(2) (a) van Koten, G. Pure Appl. Chem. 1989, 62, 1681. (c) Grove,
D. M.; van Koten, G.; Verschuuren, A. H. M. J. Mol. Catal. 1988, 45,
169. (d) van Beek, J. A. M.; van Koten, G.; Smeets, W. J. J.; Spek, A.
L. J. Am. Chem. Soc. 1986, 108, 5010.
(3) (a) Gandelman, M.; Vigalok, A.; Shimon, L. J. W.; Milstein, D.
Organometallics, 1997, 16, 3981. (b) Gandelman, M.; Shimon, L.;
Milstein, D. Chem. Eur. J. 2003, 9, 4295.
Recently, the mixed PCN ligand (A3) was synthesized
in our group, and it was shown that such a ligand could
benefit from advantages of both the NCN and PCP
ligand systems. PCN-based rhodium complexes were
(4) Gandelman, M.; Milstein, D. Chem. Commun. 2000, 1603.
(5) Rybtchinski, B.; Cohen, R.; Gandelman, M.; Shimon. L. J. W.;
Martin, J. M. L.; Milstein, D. Angew. Chem., Int. Ed. 2003, 115, 1993.
(6) (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.; Rozenberg, M.; Martin, J. M. L.;
Milstein, D. J. Am. Chem. Soc. 2003, 125, 6532.
* Corresponding author. Fax: 972-8-9344142. E-mail: david.milstein@
weizmann.ac.il.
† Department of Organic Chemistry.
‡ Unit of Chemical Research Support.
(7) Gandelman, M.; Konstantinovski, L.; Rozenberg, H.; Milstein,
D. Chem. Eur. J. 2003, 9, 2595.
10.1021/om049182m CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/08/2005

Pincer “Hemilabile” Effect
Scheme 1
Organometallics, Vol. 24, No. 6, 2005 1083
Scheme 2
Table 1. Selected Bond Lengths and Angles of
Complex 4
bond length
Å
angle
deg
Pt(1)-C(1)
Pt(1)-N(1)
Pt(1)-P(2)
Pt(1)-Cl(3)
N(1)-C(14)
N(1)-C(12)
P(2)-C(21)
P(2)-C(23)
1.971(5)
2.192(4)
2.217(13)
2.408(13)
1.500(7)
1.500(7)
1.849(5)
1.870(5)
C(1)-Pt(1)-N(1)
C(1)-Pt(1)-P(2)
C(1)-Pt(1)-Cl(3)
N(1)-Pt(1)-P(2)
N(1)-Pt(1)-Cl(3)
P(2)-Pt(1)-Cl(3)
C(14)-N(1)-C(12)
C(14)-N(1)-Pt(1)
82.84(19)
83.58(15)
174.36(14)
166.25(12)
93.22(12)
100.48(5)
108.3(4)
109.9(3)
Synthesis and Characterization of PCN-Based
Platinum Chloride Complexes. “Long arm” and
“normal arm” PCN-based platinum chloride complexes
were obtained as a result of C-H activation and
methane elimination reactions (Scheme 2). We have
recently reported the synthesis of complex 3.11 Complex
4 was quantitatively prepared by addition of a THF sol-
ution of ligand 2 to (COD)Pt(CH3)Cl (COD ) cyclooc-
tadiene), followed by heating at 100 °C for 30 min. The
31P{1H} NMR spectrum of 4 exhibits a singlet at 64.31
ppm with Pt satellites (JPt-P ) 4294 Hz), and in the
13C{1H} NMR spectrum the ipso carbon shows a doublet
at 149.22 ppm (JP-C ) 29 Hz). Colorless plates of com-
plex 4 suitable for a single-crystal X-ray analysis were
obtained by crystallization of 4 from a benzene/pentane
solution at room temperature (Figure 1). Selected bond
lengths and bond angles are given in Table 1.
comparison with a phosphine,10 particularly when low
oxidation states are involved. Such on/off coordination
could provide the system with additional reactivity pat-
terns, and it was of interest to explore the influence of
the amine “arm” length on the hemilability of the system.
Recently we reported on the synthesis of the “long
arm” PCN ligand 1 bearing a dimethylene unit as a
connector of the aromatic ring and the amine group.11
This ligand enabled the generation and stabilization of
rare anionic dialkyl, diaryl, and dihydride Pt complexes
(which bear no stabilizing π-acceptors) due to the labile
coordination of the amine arm. Here we present our
studies on the chemical properties and reactivity of Pt
complexes based on the PCN ligand 1. To understand
the role of the additional methylene group in the amine
“arm” of ligand 1, the new PCN ligand 2, which bears a
shorter arm, was synthesized and the chemical behavior
of 1 and 2 was compared.
Like in the case of complex 3,11 complex 4 has a
square-planar structure. The main difference between
the two structures is the P-Pt-N angle, which is almost
linear (175.2°) in the case of complex 3, while in complex
4 this angle is 166.2°. These values reflect the lower
Results and Discussion
Synthesis of the PCN Ligand 2. The new PCN
ligand 2 was synthesized from 3-(bromomethyl)benzyl
alcohol, which was obtained by esterification, bromina-
tion, and reduction of 3-(methyl)benzoic acid according
to a literature procedure.12 The resulting 3-(bromom-
ethyl)benzyl alcohol was reacted with a slight excess of
diethylamine at room temperature to give 3-(diethy-
laminomethyl)benzyl alcohol, which was brominated
with an aqueous solution of HBr to yield 3-(diethylami-
nomethyl)benzyl bromide‚HBr salt. Reaction of the
latter with di-tert-butylphosphine at 50 °C for 48 h
yielded the clean ligand 2 (Scheme 1).
(8) Gandelman, M.; Vigalok, A.; Kontantinovski, L.; Milstein, D. J.
Am. Chem. Soc. 2000, 122, 9848.
(9) Rybtchinski, B.; Oevers, S.; Montag, M.; Vigalok, A.; Rogenberg,
H.; Martin, J. M. L.; Milstein, D. J. Am. Chem. Soc. 2001, 123, 9064.
(10) Crabtree, R. H. The Organometallic Chemistry of The Transition
Metals; John Wiley & Sons: New York, 1994.
(11) Poverenov, E.; Gandelman, M.; Shimon, L. J. W.; Rozenberg,
H.; Ben-David, Y.; Milstein, D. Chem. Eur. J. 2004, 10, 4673.
Figure 1. ORTEP view of a molecule of complex 4.
Hydrogen atoms are omitted for clarity.

1084 Organometallics, Vol. 24, No. 6, 2005
Poverenov et al.
Scheme 4
Table 2. Selected Bond Lengths and Angles of
Complex 6
bond length
Å
angle
deg
Figure 2. ORTEP view of a molecule of complex 6.
Pt(1)-C(11)
Pt(1)-N(3)
Pt(1)-P(2)
Pt(1)-O(1)
S(1)-O(1)
N(3)-C(33)
P(2)-C(21)
C(1)-F(1)
2.005(7)
2.168(6)
2.248(17)
2.249(5)
1.468(5)
1.472(9)
1.832(7)
1.345(10)
C(11)-Pt(1)-N(3)
C(11)-Pt(1)-P(2)
N(3)-Pt(1)-P(2)
C(11)-Pt(1)-O(1)
P(2)-Pt(1)-O(1)
O(2)-S(1)-O(3)
C(12)-C(11)-Pt(1)
S(1)-O(1)-Pt(1)
95.1(3)
84.6(2)
Hydrogen atoms are omitted for clarity.
174.4(17)
178.2(3)
94.0(14)
116.1(4)
124.7(6)
144.5(4)
Scheme 3
planar structure, with the triflate anion being coordi-
nated to platinum trans to the aromatic ring. Selected
bond lengths and bond angles of 6 are given in Table 2.
Complex 4, based on the “normal arm” PCN ligand,
also undergoes facile abstraction of the chloride ligand
by silver salts. Reaction of 4 with AgBF4 gave, after 1 h
of stirring at room temperature, the cationic complex 7
(Scheme 3). 7 exhibits a single resonance at 63.91 ppm
(JPt-P ) 4195 Hz) in the 31P{1H} NMR spectrum (in
C6D6), and its ipso carbon appears at 148.41 ppm in the
13C{1H} NMR spectrum. The BF4 counteranion appears
in the 19F NMR spectrum (in CD2Cl2) at -162.14 ppm,
indicating that it is coordinated to the metal center (see
above).
rigidity of the six-membered ring in comparison with
the five-membered one, providing complex 3 with con-
siderable flexibility.
Synthesis and Reactions of Cationic Complexes.
The electron-rich and bulky PCN ligands 1 and 2 can
readily stabilize cationic Pt(II) complexes. When AgX
(X ) BF4-, CF3SO3-) was added to a CH2Cl2 solution
or (in case of CF3SO3-) THF solution of 3, the cationic
complexes 5 and 6 were obtained after 1 h of stirring at
room temperature (Scheme 3). The 31P{1H} NMR spec-
trum of 5 exhibits a singlet at 69.60 ppm with Pt satel-
lites (JPt-P ) 3985 Hz), and in the 13C{1H} NMR spec-
trum the ipso carbon exhibits a doublet at 150.71 ppm
-
Reaction with CO. The weakly coordinated BF4
counteranion is easily displaced by better coordinating
ligands. When a slight excess of CO was added to a
methylene chloride solution of complex 5, the new car-
bonyl complex 8 was immediately formed (Scheme 4).
The 31P{1H} NMR spectrum of 8 shows a singlet at
81.04 ppm with Pt satellites (JPt-P ) 3045 Hz). In the
13C{1H} NMR spectrum the ipso carbon exhibits a
doublet at 150.65 ppm (JP-C ) 9 Hz), and a peak due to
the carbonyl ligand appears at 181.14 ppm as a doublet
(JP-C ) 8 Hz) with Pt satellites (JPt-C ) 981 Hz). In
the IR spectrum, the carbonyl stretch was observed at
2082 cm-1, indicating little back-bonding, and a rela-
tively low electron density at the metal center. In
complex 8 the noncoordinated BF4 anion appears in the
19F NMR spectrum as a singlet at -153.01 ppm.
-
(JP-C ) 10 Hz). In the 19F NMR spectrum, the BF4
anion gives rise to a broad singlet at -162.27 ppm. Since
this value is significantly different from the chemical
shift of noncoordinated BF4- (-151.23 ppm, narrow peak,
in CD2Cl2), and based on previously reported coordinat-
ed and noncoordinated BF4- unsaturated complexes,7 it
is clear that in this case BF4- is coordinated to the metal.
Complex 6 was also characterized by multinuclear
NMR techniques. In the 31P{1H} NMR spectrum it gives
rise to a singlet at 66.52 ppm with Pt satellites (JPt-P
) 4005 Hz). In the 19F NMR spectrum the coordinated
OTf group was observed as a singlet at -77.61 ppm.
Crystallization of 6 from a THF/pentane mixture re-
sulted in colorless needles, which were suitable for X-ray
single-crystal analysis (Figure 2). The platinum atom
is located in the center of a slightly distorted square-
Complex 8 was crystallized by slow evaporation of a
CH2Cl2 solution to give pale yellow prisms, which were
appropriate for a single-crystal X-ray analysis. It ex-
hibits a square-planar structure, the carbonyl ligand
being coordinated trans to the aromatic ring (Figure 3).
The counteranion BF4- is located out of the coordination
sphere. Selected bond lengths and bond angles of
complex 8 are given in Table 3. In a similar mode,
reaction of complex 7 (“normal arm” PCN-based cationic
(12) O’Hanlon, P. J.; Rogers, N. H. Eur. Pat. Appl. AN 406065, 1982.

Pincer “Hemilabile” Effect
Organometallics, Vol. 24, No. 6, 2005 1085
Scheme 5
Figure 3. ORTEP view of a molecule of complex 8.
Table 3. Selected Bond Lengths and Angles of
Complex 8
bond length
Å
angle
deg
Pt(1)-C(2)
Pt(1)-C(5)
Pt(1)-N(4)
Pt(1)-P(3)
O(1)-C(2)
N(4)-C(17)
P(3)-C(35)
C(5)-C(15)
1.923(4)
2.063(4)
2.158(3)
2.272(11)
1.143(5)
1.494(5)
1.872(4)
1.411(5)
C(2)-Pt(1)-C(5)
C(2)-Pt(1)-N(4)
C(5)-Pt(1)-N(4)
C(2)-Pt(1)-P(3)
C(5)-Pt(1)-P(3)
N(4)-Pt(1)-P(3)
O(1)-C(2)-Pt(1)
C(10)-P(3)-Pt(1)
172.3(18)
88.9(15)
94.4(13)
94.4(12)
83.1(11)
172.9(9)
175.2(5)
102.9(1)
Table 4. Selected Bond Lengths and Angles of
Complex 10
bond length
Å
angle
deg
Pt(1)-C(1)
Pt(1)-N(1)
Pt(1)-O(1)
Pt(1)-P(2)
O(1)-H(1A)
O(1)-H(2A)
N(1)-C(11)
H(2A)-F(1)
P(2)-C(21)
1.99(4)
2.16(3)
2.18(3)
2.23(10)
0.86(6)
0.86(8)
1.48(5)
2.04
C(11)-Pt(1)-N(1)
C(1)-Pt(1)-O(1)
N(1)-Pt(1)-O(1)
C(1)-Pt(1)-P(2)
N(1)-Pt(1)-P(2)
O(1)-Pt(1)-P(2)
Pt(1)-O(1)-H(1A)
O(1)-H(2A)-F(1)
Pt(1)-O(1)-H(2A)
95.9(14)
172.6(14)
88.0(14)
84.0(11)
174.0(8)
92.7(9)
130(3)
complex) with CO resulted in the expected carbonyl
complex 9 (Scheme 4). This complex exhibits a signal
at 80.16 ppm (JPt-P ) 3264 Hz) in the 31P{1H} NMR
spectrum, and the coordinated carbonyl ligand appears
at 185.19 ppm (d, JP-C ) 6 Hz) in the 13C{1H} NMR
spectrum and gives rise to an absorption at 2085 cm-1
in the IR spectrum.
Coordination of Water. Protonation and Depro-
tonation Reactions. Chemistry of aqua and hydroxo
complexes is of significant current interest. With late
metal complexes, the water ligand is expected to bind
to the metal fairly weakly, and the hydroxo ligand is
expected to undergo heterolysis readily.13 Such com-
plexes may be relevant to catalytic hydration of olefins
to form alcohols, under neutral conditions, which is an
attractive industrial goal.14 Aqua complexes of Pt(II) are
well known.15 Stable monomeric Pt(II) hydroxides are
less common, because of their high reactivity and
tendency to dimerize, and very few of them have been
structurally characterized.16
165
1.82(3)
113(5)
of 5, quantitative coordination of water was observed
to give complex 10 (Scheme 5). The 31P{1H} NMR
spectrum of 10 exhibits a single resonance at 67.52 ppm
with Pt-P satellites (JPt-P ) 3950 Hz), and the protons
of the coordinated water molecule appear in the 1H
NMR spectrum as a broad singlet at 5.12 ppm. Recrys-
tallization of 10 from a THF/pentane solution resulted
in colorless prismatic crystals, which were subjected to
a single-crystal X-ray analysis (Figure 4). Complex 10
exhibits a square-planar structure with a practically
symmetrical arrangement of the four ligands around the
Pt center and an outer-sphere BF4- counteranion. The
metal-oxygen (2.18 Å) and H-O (0.86 Å) bond lengths
are similar to those observed in other known late
transition metal aqua complexes. According to the X-ray
data, there are hydrogen-bonding interactions between
protons of the coordinated water molecule and the
fluorine atoms of the BF4 counteranion, the shortest
distance being observed between the H(2A) and F1
atoms (2.04 Å). These data are in good agreement with
other known organometallic complexes that exhibit
Utilizing the PCN ligands, we prepared monomeric
aqua and hydroxo Pt complexes. Thus, when a slight
excess of H2O was added to a dichloromethane solution
(13) (a) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G.
Acc. Chem. Res. 2002, 35, 44. (b) Bryndza, H. E.; Tam, W. Chem. Rev.
1988, 88, 1163.
(14) Lukehart, C. M. Fundamental Transition Metal Organometallic
Chemistry; Wadsworth Inc.: California, 1985.
(15) Recent examples of Pt(II)(OH2) complexes: (a) van den Broeke,
J.; Heeringa, J. J. H.; Chuchuryukin, A. V.; Kooijman, H.; Mills, A.
M.; Spek, A. L.; van Lenthe, J. H.; Ruttink, P. J. A.; Deelman, B.-J.;
van Koten, G. Organometallics 2004, 23, 2287. (b) Bera, P. S.;
Sengupta, P. S.; De, G. S. Inorg. Reac. Mech. 2003, 5, 65. (c) Sun, X.
J.; Jin, C.; Mei, Y. H.; Yang, G. S.; Guo, Z. J.; Zhu, L. G. Inorg. Chem.
2004, 43, 290. (d) Bera, P. S.; Chandra, S. K.; De, G. S. Int. J. Chem.
Kinet. 2003, 53, 252. (e) Gerdes, G.; Chen, P. Organometallics 2003,
22, 2217. (f) Anandhi, U.; Holbert, T.; Lueng, D.; Sharp, P. R. Inorg.
Chem. 2003, 42, 1282
(16) Structurally characterized terminal-hydroxo platinum com-
plexes: (a) Flint, B.; Li, J. J.; Sharp, P. R. Organometallics 2002, 21,
997. (b) Straub, B. F.; Rominger, F.; Hoffman, P. Inorg. Chem. Comm.
2000, 3, 214. (c) Klein, A.; Klinkhammer, K.-W.; Scheiring, T. J.
Organomet. Chem. 1999, 592, 128. (d) Navaro, J. A. R.; Romero, M.
A.; Salas, J. M.; Quiros, M. Inorg. Chem. 1997, 36, 3277. (e) Miyamoto,
T. K. Chem. Lett. 1994, 1971. (f) Britten, J. F.; Lippert, B.; Lock, C. J.
L.; Pilon, P. Inorg. Chem. 1982, 21, 1936.
Figure 4. ORTEP view of a molecule of complex 10.

1086 Organometallics, Vol. 24, No. 6, 2005
Poverenov et al.
Scheme 6
Figure 5. ORTEP view of a molecule of complex 11.
Table 5. Selected Bond Lengths and Angles of
Complex 11
bond length
Å
angle
deg
Pt(1)-C(1)
Pt(1)-N(3)
Pt(1)-O(1)
Pt(1)-P(2)
O(1)-H(1)
P(2)-C(21)
N(3)-C(33)
C(15)-C(16)
2.02(5)
2.17(4)
2.09(3)
2.21(13)
0.82
1.82(5)
1.49(6)
1.34(7)
C(11)-Pt(1)-N(3)
C(11)-Pt(1)-O(1)
N(3)-Pt(1)-O(1)
C(11)-Pt(1)-P(2)
N(3)-Pt(1)-P(2)
O(1)-Pt(1)-P(2)
Pt(1)-O(1)-H(1)
C(21)-P(2)-Pt(1)
95.6(16)
177.8(15)
83.6(14)
83.7(13)
175.6(10)
97.3(10)
109.5
Scheme 7
103.4(16)
hydrogen bonds between coordinated H2O and outer-
sphere BF4. It was shown by van Koten and co-workers
that these coordinated water-counteranion interactions
have important contribution to the stability of mono-
meric monocationic aqua complexes.15a Additional bond
lengths and angles of complex 10 are given in Table 4.
Due to coordination to the metal center, the water
molecule becomes more acidic. While no deprotonation
was observed by the internal amine base, treatment of
10 with 1 equiv of (Me3Si)2N-K+ resulted in formation
of the neutral hydroxo complex 11. The deprotonation
reaction of 10 is reversible, and treatment of 11 with
HBF4 or CF3SO3H regenerated the starting aqua com-
plex (Scheme 5).
NMR spectrum, four aromatic protons were found, while
a new proton appears as a singlet at 6.55 ppm. In
addition, in the 13C{1H} NMR spectrum the ipso carbon
was not detected, and in a C-H correlation spectrum
an additional C-H cross-peak in the aromatic area was
found. The NMR data indicate demetalation of the
aromatic ring during the reaction (Scheme 7). To verify
this suggestion, we performed the same experiment with
D2 gas. As expected, the signal of the additional aro-
The 31P{1H} NMR spectrum of 11 shows a singlet at
65.15 ppm (JPt-P ) 4185 Hz). The signal due to the
1
hydroxyl ligand appears in the H NMR spectrum at
-1.15 ppm as a broad singlet.
Complex 11 was crystallized from a benzene/pentane
mixture to give orange-brown prisms suitable for a
single-crystal X-ray analysis (Figure 5), which shows the
expected square-planar structure. The Pt-O bond length
of 2.09(3) Å falls within the range (2.02-2.19 Å) of the
few other structurally characterized terminal hydroxo
Pt(II) complexes.16 Other selected bond lengths and
bond angles of 11 are given in Table 5.
1
matic proton at 6.55 ppm disappeared in the H NMR
2
spectrum, while in the H NMR spectrum in CH2Cl2 a
signal of an aromatic proton at 6.35 ppm was observed.
In addition, the signal due to N(CH3)2 appeared at 1.78
1
ppm as a singlet without Pt satellites in the H NMR
spectrum and at 44.39 ppm in the 13C{1H} NMR
spectrum. The fact that the two methyl groups of the
N(CH3)2 unit have the same chemical shifts and the
platinum satellites are not observed indicates that the
amine arm is not coordinated to the metal center and
that there is free rotation. Finally, a signal compatible
with bridging CO was found at 247.29 ppm (JPt-C ) 724
Hz) in the 13C{1H} NMR spectrum and in the IR a µ-CO
stretch appeared at 1759 cm-1. Thus, on the basis of
NMR data we predicted an approximate configuration
of the cluster, while the exact structure was obtained
by an X-ray diffraction study. Complex 12 was crystal-
Formation of a Trimeric Cluster. When an ac-
etone solution of 8 was reacted with 5 atm of H2 gas in
a Fischer Porter tube at 65 °C, the novel complex 12
was quantitatively formed after 12 h (Scheme 6). This
complex exhibits one resonance at 79.49 ppm in the 31P-
{1H} NMR spectrum with three sets of Pt satellites
(JPt1-P ) 4742 Hz, JPt2-P ) 460 Hz, JPt3-P ) 357 Hz).
Such an unusual NMR pattern led us to consider the
possibility of cluster formation, where each phosphorus
1
atom is coupled to three different Pt atoms. In the H

Pincer “Hemilabile” Effect
Organometallics, Vol. 24, No. 6, 2005 1087
In striking difference to the reactivity of complex 8,
the “normal arm” PCN-based carbonyl complex 9 did
not react with dihydrogen under the same conditions
and remained unchanged (Scheme 6). This result vividly
reflects the influence of the amine “arm” length on its
hemilability and, as a consequence, on the accessible
reactivity patterns.
Summary
The reactivity of complexes based on mixed phos-
phino-amine (PCN) ligands with different amine “arm”
lengths was studied. The new “long arm” PCN-based
Pt(II) unsaturated cationic complex (5) exhibits inter-
esting reactivity, including coordination of a water
molecule to generate an aqua complex (10), which was
deprotonated to yield a rare monomeric hydroxy com-
plex (11). Treatment of the cationic complex (5) with
carbon monoxide resulted in a stable carbonyl complex
(8), which reacted with H2 to form a trimeric cluster
(12). Parallel investigation of the reactivity of the
“normal arm”′ PCN-based complexes showed that the
longer amine “arm” provides additional reactivity pos-
sibilities, since, as expected, it enhances the hemilability
effect of the amine ligand. We are currently exploring
the effect of this reversible coordination on the activa-
tion of various strong bonds and catalysis.
Figure 6. Complex 12.
Table 6. Selected Bond Lengths and Angles of
Complex 12
bond length
Å
angle
deg
Pt(1)-C(3)
Pt(1)-P(1)
Pt(1)-Pt(2)
Pt(2)-P(2)
C(1)-O(1)
P(3)-C(30)
Pt(2)-Pt(3)
C(11)-C(14)
2.03(17)
2.29(4)
2.67(12)
2.30(4)
1.16(19)
1.86(18)
2.67(12)
1.52(3)
C(3)-Pt(1)-C(1)
C(3)-Pt(1)-P(1)
Pt(1)-Pt(2)-Pt(3)
O(1)-C(1)-Pt(1)
0(2)-C(2)-Pt(3)
Pt(1)-Pt(3)-Pt(2)
P(2)-Pt(2)-Pt(3)
C(1)-Pt(2)-Pt(3)
154.0(7)
102.9(5)
60.05(4)
138.9(13)
141.8(14)
59.9(3)
Experimental Section
146.3(11)
107.5(5)
General Procedures. All experiments with metal com-
plexes 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 used as received. The precursor Pt(COD)(CH3)-
Cl was prepared according to a literature procedure.18 1H, 13C,
lized by slow evaporation of a CH2Cl2 solution to give
red crystals, the X-ray structure of which (Figure 6)
confirmed our spectroscopic structural prediction. Three
Pt atoms are connected by metal-metal bonds and by
three bridging carbonyl ligands, forming a rigid cluster.
The aromatic rings of the ligands underwent demeta-
lation and the amine “arms” were detached from the
metal center, the phosphine groups remaining the only
coordinated part of the PCN moiety. Selected bond
lengths and bond angles of 12 are given in Table 6.
Comparable platinum clusters were obtained by Wong
as part of an investigation of the reactivity of trans-
PtH2L2 complexes (L ) PR3) with carbon monoxide.
These dihydrido complexes react to give different cluster
compounds as a result of reductive elimination reac-
tions.17 Significantly, reaction of the (PCN)PtH complex
16 (which was formed by reaction of 3 with Et3BHNa
at room temperature) with 5 atm of CO under identical
conditions resulted in the same complex 12 (Scheme 6).
A plausible mechanism for the cluster-forming reac-
tion is presented in Scheme 7. Coordination of dihydro-
gen may lead to the five-coordinated intermediate 13
in which the dihydrogen ligand protons become acidic
and undergo deprotonation by the internal amine base.
Deprotonation of a strong C-H bond by an intramo-
lecular amine base as a result of its coordination to a
cationic Rh atom was recently reported.3b The opening
of the electron-donating amine-“arm” decreases the
electron density on the metal center and promotes C-H
reductive elimination of the aromatic ring. The resulting
coordinatively unsaturated intermediate 15 undergoes
trimerization to form the cluster 12.
2
and 31P, 19F, and H NMR spectra were recorded at 400, 100,
162, 376, and 61 MHz, respectively, using a Bruker AMX-400
NMR spectrometer and 250 (1H), 101 (31P), and 235 (19F) using
Bruker DPX 250 spectrometer. All spectra were recorded at
23 °C. 1H NMR and 13C{1H} NMR chemical shifts are reported
in parts per million downfield from tetramethylsilane. 1H NMR
chemical shifts were referenced to the residual hydrogen signal
of the deuterated solvents (7.15 ppm, benzene; 7.24 ppm,
chloroform; 5.32 ppm, dichloromethane; 3.58 ppm, tetrahy-
drofuran). In 13C{1H} NMR measurements the signals of C6D6
(128.0 ppm), CDCl3 (77.0 ppm), CD2Cl2 (53.8 ppm), and d8-
THF (67.5 ppm.) were used as a reference. 31P NMR chemical
shifts are reported in ppm downfield from H3PO4 and refer-
enced to an external 85% solution of phosphoric acid in D2O.
19F NMR chemical shifts were referenced to C6F6 (-163 ppm),
and 2H NMR chemical shifts were referenced to CD2Cl2 (3.58
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: b, broad; s, singlet; d, doublet; t,
triplet; q, quartet; m, multiplet.
Preparation of the PCN Ligand 2. 3-(Bromomethyl)-
benzyl alcohol, which served as the starting material for the
preparation of ligand 2, was obtained by esterification, bro-
mination, and reduction of 3-(methyl)benzoic acid according
to a literature procedure.12
(17) Clark, H. C.; Goel, A. B.; Wong, C. S. Inorg. Chim. Acta 1979,
159, 34.
(18) Clark. H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411.

1088 Organometallics, Vol. 24, No. 6, 2005
Poverenov et al.
(a) Preparation of 3-(Diethylaminomethyl)benzyl Al-
cohol. In an oven-heated, argon-flushed 100 mL Schlenk flask,
equipped with a dropping funnel and a magnetic stirring bar,
was dissolved 5.2 mL (0.0050 mol) of degassed Et2NH in 10
mL of dry THF, and the reaction mixture was cooled to 0 °C.
A solution of 3-(bromomethyl)benzyl alcohol (4.6 g, 0.023 mol)
in 8 mL of dry THF was added dropwise during 30 min and
stirred for a further 24 h. TLC analysis of the solution showed
complete conversion to a product. The solvents were removed
under vacuum, the residue was treated with 100 mL of diethyl
ether, and the organic phase was washed with 10% aqueous
KOH solution (2 × 20 mL), dried with Na2SO4, filtered, and
concentrated in a vacuum. The crude yield was 96%. Distil-
lation (110-120 °C at 0.4 mmHg) resulted in the clean
3-(diethylaminomethyl)benzyl alcohol in 55% yield.
tion of 4. The solvent was evaporated, and the complex was
washed with pentane and dissolved in benzene. Benzene
evaporation yielded 145 mg (0.264 mmol, yield 90%) of 4. X-ray
quality colorless crystals were obtained from a benzene/
pentane two-phase mixture at room temperature.
1
31P{1H} NMR (C6D6): 64.31 (s, JP-Pt ) 4294 Hz). H NMR
(C6D6): 7.05 (t, JH-H ) 8 Hz, 1H, Ar), 6.93 (d, JH-H ) 8 Hz,
1H, Ar), 6.71(d, JH-H ) 8 Hz, 1H, Ar), 3.59 (s, JPt-H ) 22 Hz,
2H, Ar-CH2-N), 3.44 (m, 2H, N-CH2-CH3), 2.76 (d, JP-H
)
11 Hz, JPt-H ) 40 Hz, 2H, Ar-CH2-P), 2.41 (m, 2H, N-CH2-
CH3), 1.31 (s, JPt-H ) 15 Hz, 6H, N-CH2-CH3), 1.29 (d, JP-H
) 14 Hz, 18 H, P-t-Bu). 13C{1H} NMR (C6D6): 149.22 (d, JP-C
) 29 Hz, ipso), 148.91 (d, JP-C ) 10 Hz, JPt-C ) 31 Hz, Ar),
146.30 (d, JP-C ) 10 Hz, Ar), 123.62 (s, Ar), 121.71 (d, JP-C
)
17 Hz, JPt-C ) 80 Hz, Ar), 118.85 (s, JPt-C ) 30 Hz, Ar), 67.15
(d, JPt-C ) 59 Hz, JP-C ) 3 Hz, Ar-CH2-P), 56.20 (s, N-CH2-
CH3), 56.18 (s, N-CH2-CH3), 35.15 (d, JP-C ) 61 Hz, P-C-
1H NMR (CDCl3): 7.35-7.22 (4H, Ar), 4.63(s, 2H, CH2-
OH), 3.57 (s, 2H, CH2-N), 3.14 (bs, 1H, CH2-OH), 2.53 (q,
4H, N-(CH2-CH3)2), 1.06 (t, 6H, N-(CH2-CH3)2). 13C{1H}
NMR (CDCl3): 141.10 (s, Ar), 139.33 (s, Ar), 128.25 (s, Ar),
128.22 (s, Ar), 127.65(s, Ar), 125.52 (s, Ar), 64.89 (s, CH2-
OH), 57.25 (s, CH2-N), 46.45 (s, N-(CH2-CH3)2), 11.22 (s,
N-(CH2-CH3)2) (assignment of 13C{1H} NMR was confirmed
by 13C DEPT).
(CH3) 3), 35.11 (s, Ar-CH2-N), 29.14 (d, JP-C ) 4 Hz, JPt-C
)
22 Hz, P-C-(CH3) 3), 12.86 (s, JPt-C ) 23 Hz, N-CH2-CH3 ).
ES-MS: m/z+ 573.55 [calc 574.02] (M + Na+), 515.62 [calc
515.58] (M - Cl).
Synthesis of [(PCN)Pt]+BF4 (5). To a CH2Cl2 solution
-
(1 mL) of (PCN)PtCl 3 (20 mg, 0.037 mmol) was added 7 mg
(0.037 mmol) of AgBF4, resulting in immediate formation of a
white precipitate. After stirring the reaction mixture at room
temperature for 1 h, the 31P {1H} NMR spectrum revealed
formation of a new complex. The suspension was filtered
through Celite, and the solvent was evaporated. The resulting
white solid was washed with pentane and benzene and
dissolved in THF. After evaporation of THF 24 mg (0.035
mmol, 95% yield) of the white complex 5 was obtained.
Selected NMR data: 31P{1H} NMR (CD2Cl2): 69.60 (s, JP-Pt
) 3985 Hz). 1H NMR (CD2Cl2): 6.96 (d, JH-H ) 8 Hz, 1H, Ar),
6.85 (dt, JH-H ) 8 Hz, JP-H ) 1 Hz, 1H, Ar), 6.62 (d, JH-H ) 8
Hz, 1H, Ar), 2.89 (s, 3H, N-CH3), 2.88 (s, 3H, N-CH3), 2.84
(m, 2H, CH2-CH2-N), 2.72 (m, 2H, CH2-CH2-N), 1.35 (d,
JP-H ) 15 Hz, 18 H, P-t-Bu). 13C{1H} NMR (CD2Cl2): 150.71
(d, JP-C ) 10 Hz, ipso), 142.34 (s, Ar), 125.79 (s, Ar), 125.63
(s, Ar), 122.72 (s, Ar), 122.56 (s, Ar), 64.24 (s, CH2-CH2-N),
64.23 (s, CH2-CH2-N), 48.71 (s, N-CH3), 48.70 (s, N-CH3),
(b) Preparation of 3-(Diethylaminomethyl)benzyl
Bromide‚HBr Salt. In a 250 mL flask under argon was dis-
solved 5.48 g (0.028 mol) of 3-(diethylaminemethyl)benzyl alco-
hol in 55 mL of 48% HBr aqueous solution. The mixture was
stirred overnight, and the resulting slightly brown solution
was evaporated to dryness under high vacuum. The resulting
sticky solid was washed with a copious amount of diethyl ether
and stirred overnight, whereupon it became a slightly brown
granular solid, which was filtered, washed with diethyl ether,
and dried under high vacuum, resulting in 9.14 g (97.2%) of
product.
1H NMR (CD3OD): 7.53-7.37 (4H, Ar), 4.54(s, 2H, CH2-
Br), 4.27 (s, 2H, CH2-N), 3.14 (q, 4H, N-(CH2-CH3)2), 1.22
(t, 6H, N-(CH2-CH3)2).
(c) Preparation of Ligand 2. In a 100 mL vessel in the
glovebox was dissolved 5.04 g (0.015 mol) of 3-(diethylami-
nomethyl)benzyl bromide‚HBr salt in 45 mL of pure MeOH.
A solution of 4.82 g (0.033 mol) of di-tert-butyl phosphine in
15 mL of pure MeOH was added, resulting in a colorless
solution. The vessel was closed tightly, taken outside the
glovebox, and heated with stirring for 48 h under argon. The
mixture was cooled to room temperature and reintroduced into
the glovebox. Then 9 mL of triethylamine was added, followed
by stirring for 30 min. The organic solvent was removed under
vacuum, giving a mixture of a white solid and a viscous oil.
The residue was treated with a copious amount of diethyl
ether, filtered, and dried under vacuum. The resulting snow-
white crystals were analyzed by NMR showing some impuri-
ties. The product was distilled (bp 140 °C at 0.1 mmHg),
yielding 3.85 g (81%) of pure ligand 2.
34.85 (d, JP-C ) 27 Hz, P-C-(CH3) ), 30.61(d, JP-C ) 35 Hz,
3
Ar-CH2-P), 28.82 (d, JP-C ) 3 Hz, P-C-(CH3)3). 19F NMR
(CD2Cl2): -162.27 (bs). Anal. Found (Calcd for C22H45BF4-
NOPPt): C, 40.34 (40.50); H, 7.12 (6.95).
Synthesis of (PCN)Pt(OTf) (6). To a THF (1 mL) solution
of (PCN)PtCl 3 (20 mg, 0.037 mmol) was added 10 mg (0.037
mmol) of silver triflate. The mixture was stirred at room
temperature for 1 h, resulting in a pink-brown solution. The
suspension was filtered through Celite, and the solvent was
evaporated. The resulting brown solid was washed with
pentane and benzene and dissolved in THF. After evaporation
of THF 22 mg (0.033 mmol, 90.2% yield) of (PCN)Pt-OTf 6 was
obtained. X-ray quality colorless crystals of complex 6 were
obtained from a THF/pentane two-phase mixture at room
temperature.
31P{1H} NMR (C6D6): 35.66 (s). 1H NMR (C6D6): 7.55 (s,
1H, Ar), 7.30 (d, JH-H ) 7 Hz, 1H, Ar), 7.18 (d, JH-H ) 7 Hz,
1H, Ar), 7.12 (d, JH-H ) 7 Hz, 1H, Ar), 3.44 (s, 2H, Ar-CH2-
N), 2.74 (d, JP-H ) 3 Hz, 2H, Ar-CH2-P), 2.39 (q, JH-H ) 7
Hz, 4H, N-(CH2-CH3)2), 1.02 (d, JP-H ) 11 Hz, 18H, P(t-
Bu)2), 0.92 (t, JH-H ) 7 Hz, 6H, N-(CH2-CH3)2). 13C{1H} NMR
(CDCl3): 141.82 (d, JP-C ) 12 Hz, Ar), 140.72 (s, Ar), 130.41
(s, Ar), 130.33 (s, Ar), 128.46 (d, JP-C ) 8 Hz, Ar), 126.15 (d,
JP-C ) 2 Hz, Ar). 58.30 (s, Ar-CH2-N), 47.06 (s, N-(CH2-
31P{1H} NMR (CD2Cl2): 66.52 (s, JPt-P ) 4005 Hz). 1H NMR
(CD2Cl2): 6.79 (d, JHH ) 7 Hz, 1H, Ar), 6.78 (d, JHH ) 7 Hz,
1H, Ar), 6.47 (d, JHH ) 7 Hz, 1H, Ar), 2.59 (s, JPtH ) 20 Hz,
3H, N-CH3), 2.58 (s, JPtH ) 20 Hz, 3H, N-CH3), 2.55 (d, JPH
) 10 Hz, JPtH ) 44 Hz, 2H, Ar-CH2-P), 2.34 (m, 2H, CH2-
CH2-N), 1.92 (m, 2H, CH2-CH2-N), 1.15 (d, JPH ) 14 Hz, 18
H, P-t-Bu). 13C{1H } NMR (CD2Cl2): 150.33 (d, JPH ) 10 Hz,
ipso), 142.72 (s, Ar), 125.30 (s, Ar), 125.24 (s, Ar), 122.07 (s,
Ar), 122.91 (s, Ar), 64.14 (s, Ar-CH2-CH2-N), 64.12 (s, Ar-
CH2-CH2-N), 49.18 (s, N-CH3), 49.17 (s, N-CH3), 34.42 (d,
JPC ) 36 Hz, P-C-(CH3)3), 32.55 (d, JPC ) 26 Hz, Ar-CH2-
P), 35.32 (s, Pt-O-SO2-CF3), 28.89 (d, JPC ) 3 Hz, P-C-
CH3)2), 31.77 (d, JP-C ) 25 Hz, Ar-CH2-P), 29.87 (d, JP-C
)
13 Hz, P(C(CH3)3)2), 29.15 (d, JP-C ) 26 Hz, P(C(CH3)3)2), 12.25
(s, N-(CH2-CH3)2).
Reaction of the PCN Ligand 2 with (COD)Pt(Cl)Me.
Formation of (PCN)PtCl (4). To a THF solution (4 mL) of
(COD)Pt(Cl)CH3 (COD ) cyclooctadiene; 104 mg, 0.294 mmol)
was added 95 mg (0.294 mmol) of ligand 2 in THF (4 mL).
The mixture was stirred at 100 °C for 30 min, resulting in a
colorless solution. The 31P{1H} NMR spectrum revealed forma-
(CH3) ), 19F NMR (CD2Cl2): -77.61 (s). ES-MS: m/z+ 501.32
3
[calc 501.59] (M - OTf), m/z- 148.82 [calc 149.07] (OTf -).
Synthesis of [(PCN)Pt]+BF4 (7). To a CH2Cl2 solution
-
(1 mL) of (PCN)PtCl 4 (20 mg. 0.036 mmol) was added 7 mg

Pincer “Hemilabile” Effect
Organometallics, Vol. 24, No. 6, 2005 1089
(0.036 mmol) of AgBF4, resulting in immediate formation of a
yellow precipitate. After stirring the reaction mixture at room
temperature for 1 h, the 31P{1H} NMR spectrum revealed
formation of a new complex. The suspension was filtered
through Celite, and the solvent was evaporated. The resulting
yellow solid was washed with pentane and benzene and
dissolved in THF. After evaporation of THF 21 mg (0.035
mmol, 96% yield) of complex 7 was obtained.
1
31P{1H} NMR (C6D6): 63.91 (s, JPPt ) 4195 Hz). H NMR
(C6D6): 6.88 (t, JHH ) 7 Hz, 1H, Ar), 6.67 (d, JHH ) 7 Hz, 1H,
Ar), 6.42 (d, JHH ) 7 Hz, 1H, Ar), 3.38 (m, 2H, N-CH2-CH3),
3.34 (s, JPtH ) 24 Hz, 2H, Ar-CH2-N), 2.57 (m, 2H, N-CH2-
CH3), 2.47 (d, JPH ) 9 Hz, 2H, Ar-CH2-P), 1.26 (t, JPH ) 7
Hz, 6H, N-CH2-CH3), 1.15 (d, JPH ) 14 Hz, 18H, P-t-Bu).
13C{1H} NMR (C6D6): 148.41 (d, JPC ) 1, ipso), 146.68 (d, JPC
) 9 Hz, Ar), 124.83 (s, Ar), 123.57 (s, Ar), 121.78 (d, JPC ) 14
Hz, Ar), 119.09 (s, Ar), 67.78 (s, N-CH2-CH3), 65.30 (s, Ar-
CH2-N), 55.70 (s, N-CH2-CH3), 34.74 (d, JPC ) 26 Hz, P-C-
(CH ) 3), 32.84 (d, JPC ) 36 Hz, Ar-CH2-P), 28.68 (d, JPC ) 4
Hz, 3P-C-(CH3) ), 13.97 (s, N-CH2-CH3 ). 19F NMR (CD2-
3
Cl2): -162.14 (bs). Anal. Found (Calcd for C24H49BF4NOPPt):
C, 42.46 (42.36); H, 7.18 (7.26).
Synthesis of (PCN)Pt(CO) Complex (8). To a CH2Cl2
solution (0.7 mL) of [(PCN)Pt]+BF4 (5) (20 mg, 0.034 mmol)
-
in a screw up NMR tube was injected 2.4 mL (0.080 mmol) of
CO gas. The 31P{1H} NMR spectrum revealed the immediate
formation of (PCN)PtCO complex 8. The solvent was evapo-
rated, and the resulting white solid was washed with pentane,
benzene, and THF and dissolved in CH2Cl2. The solvent was
evaporated, yielding 19 mg (0.032 mmol, 88.2% yield) of 8 as
white crystals. X-ray quality pale yellow crystals of 8 were
obtained by slow evaporation of a CH2Cl2 solution at room
temperature.
1
31P{1H} NMR (CDCl3): 81.04 ppm (s, JPtP ) 3045 Hz). H
NMR (CDCl3): 7.16 (d, JHH ) 7 Hz, 1H, Ar), 6.98 (dt, JHH )7
Hz, JPH ) 2 Hz, 1H, Ar), 6.85 (d, JHH ) 7 Hz, 1H, Ar), 3.39 (d,
JPH ) 7 Hz, JPtH ) 44 Hz, 2H, Ar-CH2-P), 3.19 (s, JPtH ) 28
Hz, 3H, N-CH3), 3.19 (s, JPtH ) 18 Hz, 3H, N-CH3), 2.93 (m,
2H, CH2-CH2-N), 2.76 (m, 2H, CH2-CH2-N), 1.27 (d, JPH
) 15 Hz, 18 H, P-t-Bu). 13C{1H } NMR (CDCl3): 181.14 (d,
JPC ) 8 Hz, JPt ) 981 Hz, Pt-CO), 150.65 (d, JPC ) 9 Hz,
C
ipso), 142.41 (d, JPC ) 1 Hz, Ar), 128.77 (s, Ar), 126.53 (s, Ar),
122.64 (s, Ar), 122.46 (s, Ar), 63.09 (s, Ar-CH2-CH2-N), 63.07
(s, Ar-CH2-CH2-N), 55.12 (s, N-CH3), 55.10 (s, N-CH3),
36.19 (d, JPC ) 22 Hz, P-C-(CH3)3), 33.82 (d, JPC ) 23 Hz,
Ar-CH2-P), 29.01 (d, JPC ) 3 Hz, P-C-(CH3)3). 19F NMR
(CDCl3): -153.01 (s). IR (film): (Pt-CO) 2082 cm-1. ES-MS:
m/z+ 501.57 [calc 501.59] (M - CO), m/z- 87.05 [calc 86.80]
(BF4-).
Synthesis of (PCN)Pt(CO) (9). To a CH2Cl2 solution (0.7
mL) of [(PCN)Pt]+BF4 7 (20 mg, 0.033 mmol) in a screw up
-
NMR tube was injected 2.4 mL (0.08 mmol) of CO gas. The
31P{1H} NMR spectrum revealed the immediate formation of
a new complex. After evaporation, the resulting white solid
was washed with pentane, benzene, and THF and dissolved
in dichloromethane, which was evaporated to yield 19 mg (0.0
29 mmol) of 9 as white crystals in 87.2% yield.
31P{1H} NMR (CDCl3): 80.16 (s, JP-Pt ) 3264 Hz). 1H NMR
(CDCl3): 7.19 (d, JH-H ) 7 Hz, 1H, Ar), 7.15 (t, JH-H ) 7 Hz,
1H, Ar), 7.11 (d, JH-H ) 7 Hz, 1H, Ar), 4.52 (s, JPt-H )16 Hz,
2H, Ar-CH2-N), 3.67 (d, JP-H ) 15 Hz, 2H, Ar-CH2-P), 3.65
(m, 2H, N-CH2-CH3), 3.58 (m, 2H, N-CH2-CH3), 1.48 (t,
JH-H ) 14 Hz, 6H, N-CH2-CH3), 1.40 (d, JP-H ) 15 Hz, 18
H, P-t-Bu). 13C{1H} NMR (CDCl3): 185.19 (d, JP-C ) 6 Hz,
Pt-CO), 160.56 (d, JP-C ) 1 Hz, ipso), 153.82 (s, Ar), 148.98
(d, JP-C ) 8 Hz, Ar), 129.61 (s, Ar), 123.10 (d, JP-C ) 18 Hz,
Ar), 121.16 (s, JPt-C ) 16 Hz, Ar), 70.76 (d, JP-C ) 2 Hz, JPt-C
) 37.5 Hz, Ar-CH2-N), 69.78 (s, N-CH2-CH3), 60.64 (s,
N-CH2-CH3), 37.3 (d, JP-C ) 37 Hz, Ar-CH2-P), 38.35 (d,
JP-C ) 26 Hz, P-C-(CH3) 3), 30.73 (d, JP-C ) 3 Hz, P-C-
(CH3)3), 15.16 (s, JPt-C ) 23 Hz, N-CH2-CH3 ). 19F NMR

1090 Organometallics, Vol. 24, No. 6, 2005
Poverenov et al.
(CDCl3): -154.29 (s). IR (film): 2085 cm-1 (Pt-CO). ES-MS:
m/z+ 515.36 [calc 515.58] (M - CO), m/z- 86.87 [calc 86.80]
(BF4-).
Synthesis of the Trimeric Cluster 12. An acetone solu-
tion (3 mL) of complex 8 (20 mg, 0.32 mmol) in a Fischer Porter
tube was charged with 5 atm of H2. The solution was stirred
at 65 °C for 12 h, and an orange-red color appeared. The 31P-
{1H} NMR spectrum of the solution revealed formation of a
new complex. The solution was evaporated, resulting in a red
solid, which was washed with pentane and THF and dissolved
in methylene chloride. Evaporation of the solvent resulted in
red crystals of complex 12 (12.4 mg, 0.01 mmol of trimeric
cluster, 93.7% yield).
31P{1H} NMR (CD2Cl2): 79.49 (s, JPt1-P ) 4742 Hz, JPt2-P
) 460 Hz, JPt3-P ) 357 Hz). 1H NMR (CD2Cl2): 6.55 (s, 1H,
Ar), 6.47 (d, JHH ) 8 Hz, 1H, Ar), 6.25 (d, JHH ) 8 Hz, 1H, Ar),
6.14 (d, JHH ) 8 Hz, 1H, Ar), 3.21 (d, JPH ) 2 Hz, JPtH ) 44
Hz, 2H, Ar-CH2-P), 2.21 (m, 2H, CH2-CH2-N), 1.90 (m, 2H,
CH2-CH2-N), 1.78 (s, 6H, N-(CH3)2), 0.32 (d, JPH ) 13 Hz,
18 H, P-t-Bu). 13C{1H } NMR (CD2Cl2): 247.29 (s, JPtC ) 724
Hz, µ-CO), 137.9 (s, Ar), 135.8 (s, Ar), 131.74 (bs, Ar), 129.71
(bs, Ar), 128.80 (s, Ar), 126.92 (s, Ar), 68.11 (s, Ar-CH2-CH2-
Preparation of the Aqua Complex 10. To a CH2Cl2
solution (1 mL) of the cationic complex 5 (20 mg, 0.034 mmol)
was added (0.63 µL, 0.034mol) of H2O, and the 31P{1H} NMR
spectrum revealed formation of a new complex. The solvent
was evaporated, and the resulting white solid was washed with
pentane and benzene and dissolved in THF. The THF solvent
was evaporated to yield 19.5 mg (0.032 mmol, 94.7% yield) of
complex 10. X-ray quality colorless prismatic crystals of 10
were obtained from a concentrated THF solution, after slow
addition of pentane at room temperature.
31P{1H} NMR (CD2Cl2): 67.52 ppm, JPt-P ) 3950 Hz. 1H
NMR (CD2Cl2): 6.88 (t, JHH ) 7 Hz, 1H, Ar), 6.78 (d, JHH ) 7
Hz, 1H, Ar), 6.50 (d, JHH ) 7 Hz, 1H, Ar), 5.12 (bs, 2H, Pt-
OH2), 2.23 (m, 2H, CH2-CH2-N), 1.85 (m, 2H, CH2-CH2-
N), 1.11 (d, JPH ) 14 Hz, 18 H, P-t-Bu). 13C{1H } NMR
(C6D6): 150.70 (d, JPC ) 10 Hz, ipso), 142.81 (s, JPtC ) 90 Hz,
Ar), 125.43 (s, Ar), 125.35 (s, Ar), 121.70 (s, Ar), 121.54 (s, Ar),
64.01 (s, Ar-CH2-CH2-N), 64.03 (s, Ar-CH2-CH2-N), 48.78
(s, N-CH3), 48.75 (s, N-CH3), 34.71 (d, JPC ) 26 Hz, P-C-
(CH3)3), 32.27 (d, JPC ) 25 Hz, Ar-CH2-P), 28.97 (d, JPC ) 2
Hz, P-C-(CH3)3). 19F NMR (CD2Cl2): -150.72 (s). Anal. Found
(Calcd for C20H43BF4NOPPt): C, 38.49 (38.35); H, 7.08 (6.92).
Preparation of the (PCN)Pt(OH) (11). To a THF solution
(1.5 mL) of the aqua complex 10 (20 mg, 0.033 mmol) was
added 7.1 mg (0.033 mmol) of (Me3Si)2NK. Deprotonation of
the coordinated water molecule and formation of the neutral
hydroxo 11 complex were revealed by the 31P{1H} NMR
spectrum. The solvent was evaporated, and the resulting
orange solid was washed with pentane and dissolved in
benzene. The benzene was evaporated to yield 16 mg (0.031
mmol, 93.6% yield) of complex 11. Complex 11 was crystallized
by careful pentane addition to a concentrated benzene solution,
leading after 3 days at room temperature to orange-brown
crystals.
N), 59.80 (s, Ar-CH2-CH2-N), 44.39 (s, N-(CH3 ) ), 38.55
2
(d, JPC ) 10 Hz, P-C-(CH3) 3), 38.25 (d, JPC ) 12 Hz, P-C-
(CH3) 3), 30.13 (bs, Ar-CH2-P). IR: (µ-CO) 1759 cm-1. Anal.
Found (Calcd for C60H124N3O3P3Pt3): C, 44.73 (44.65); H, 7.78
(7.74).
X-ray Structure Determination and Refinement of
Complexes 4, 6, 8, 10, 11, and 12. The crystals were mounted
in a nylon loop and flash frozen in a cold nitrogen stream (120
K) on a Nonius Kappa CCD with Mo KR radiation (λ ) 0.71071
Å). Accurate unit cell dimensions were obtained from 20° of
data. The data were processed with the Denzo-Scalepack
package. The structure was solved by direct methods (SHELXS-
97) and refined by full-matrix least-squares (SHELXL-97).
Idealized hydrogen atoms were placed and refined in the riding
mode. Crystal data are given in Table 7.
1
31P{1H} NMR (C6D6): 65.15 (s, JPPt ) 4185 Hz). H NMR
(C6D6): 7.03 (dd, JP-H ) 2 Hz, JH-H ) 7 Hz, 1H, Ar), 6.83 (t,
JH-H ) 7 Hz, 1H, Ar), 6.74 (d, JH-H ) 7 Hz, 1H, Ar), 2.74 (s,
JPt-H ) 23 Hz, 3H, N-CH3), 2.73 (s, JPt-H ) 22 Hz, 3H,
N-CH3), 2.55 (m, 2H, CH2-CH2-N), 2.23 (m, 2H, CH2-CH2-
N), 1.20 (d, JPH ) 14 Hz, 18 H, P-t-Bu), -1.15 (bs, 1H, Pt-
OH). 13C{1H} NMR (C6D6): 150.61 (d, JP-C ) 10 Hz, ipso),
143.29 (s, Ar), 124.67 (d, JPC ) 2 Hz, Ar), 122.66 (s, Ar), 121.50
(s, Ar), 121.34 (s, Ar), 62.84 (s, CH2-CH2-N), 62.82 (s, CH2-
Acknowledgment. This work was supported by the
Israel Science Foundation and by the Helen and Martin
Kimmel Center for Molecular Design. D.M. is the holder
of the Israel Matz Professorial Chair of Organic Chem-
istry.
Supporting Information Available: Tables giving X-ray
crystallographic data for complexes 4, 6, 8, and 10-12. This
material is available free of charge via the Internet at
http://pubs.acs.org.
CH2-N), 47.45 (s, N-CH3), 47.43 (s, N-CH3), 34.77 (d, JPC
)
35 Hz, Ar-CH2-P), 33.82 (d, JP-C ) 27 Hz, P-C-(CH3)3),
29.09 (d, JP-C ) 3 Hz, JPt-C ) 20 Hz, P-C-(CH3)3). Anal.
Found (Calcd for C13H22NOPPt): C, 36.15 (36.95); H, 5.04
(5.11).
OM049182M