Reactivity of a phosphinito-bridged PtI-PtI complex with nucleophiles: Substitution versus addition

Article abstract of DOI:10.1021/ic800045u

As a result of the strong electrophilic character of the Pt bound to O, the phosphinito-bridged Pt¹ complex [(PHCy₂)R(μ-PCy ₂){κ²P, O-μ-P(O)Cy₂}Pt(PHCy ₂)](Pt-Pt) (1) undergoes attack at the O-bound Pt atom by molecules such as diand tricyclohexylphosphane, dicyclohexylphosphane oxide, and dicyclohexylphosphane sulfide. Thus, reaction of 1 with PHCy₂ gives the symmetric Pt^I dimer [(PHCy₂)Pt(μ-PCy ₂)]₂(Pt-Pt) (2), while the hydrido-bridged complex syn-[(PHCy₂){κP-P(O)Cy₂}Pt(μ-PCy ₂)(μ-H)Pt(PHCy₂){κP-P(O)Cy₂}](Pt-Pt) (4) is obtained from reaction of 1 with P(O)HCy₂; the thiophosphinito complex [(PHCy₂)Pt(μ-PCy₂){κ²P,S- μ-P(S)Cy₂}Pt(PHCy₂)](Pt-Pt) (8) forms selectively in reaction of 1 with P(S)HCy₂. For comparison, the reaction with PCy₃ results only in ligand substitution, affording [(PCy ₃)Pt(μ-PCy₂){κ²P,O-μ-P(O)Cy ₂}Pt(PHCy₂)](Pt-Pt) (5). DFT studies confirmed the remarkable electrophilicity of the oxygen-bound Pt and shed light on the nature of the metal-metal bond in Pt dimers.

Full text of DOI:10.1021/ic800045u

Inorg. Chem. 2008, 47, 4785-4795
Reactivity of a Phosphinito-Bridged PtI-PtI Complex with Nucleophiles:
Substitution versus Addition
Vito Gallo,† Mario Latronico,† Piero Mastrorilli,*,† Cosimo F. Nobile,† Flavia Polini,† Nazzareno Re,‡
and Ulli Englert§
Dipartimento di Ingegneria delle Acque e di Chimica del Politecnico di Bari, Via Orabona 4,
I-70125 Bari, Italy, Dipartimento di Scienze del Farmaco, UniVersità “G. d’Annunzio”, Via dei
Vestini 31, I-06100 Chieti, Italy, and Institut für Anorganische Chemie der RWTH, Landoltweg 1,
D-52074 Aachen, Germany
Received January 15, 2008
As a result of the strong electrophilic character of the Pt bound to O, the phosphinito-bridged PtI complex [(PHCy2)Pt(µ-
PCy2){κ2P,O-µ-P(O)Cy2}Pt(PHCy2)](Pt-Pt) (1) undergoes attack at the O-bound Pt atom by molecules such as di-
and tricyclohexylphosphane, dicyclohexylphosphane oxide, and dicyclohexylphosphane sulfide. Thus, reaction of 1
with PHCy2 gives the symmetric PtI dimer [(PHCy2)Pt(µ-PCy2)]2(Pt-Pt) (2), while the hydrido-bridged complex
syn-[(PHCy2){κP-P(O)Cy2}Pt(µ-PCy2)(µ-H)Pt(PHCy2){κP-P(O)Cy2}](Pt-Pt) (4) is obtained from reaction of 1 with
P(O)HCy2; the thiophosphinito complex [(PHCy2)Pt(µ-PCy2){κ2P,S-µ-P(S)Cy2}Pt(PHCy2)](Pt-Pt) (8) forms selectively
in reaction of 1 with P(S)HCy2. For comparison, the reaction with PCy3 results only in ligand substitution, affording
[(PCy3)Pt(µ-PCy2){κ2P,O-µ-P(O)Cy2}Pt(PHCy2)](Pt-Pt) (5). DFT studies confirmed the remarkable electrophilicity
of the oxygen-bound Pt and shed light on the nature of the metal-metal bond in Pt dimers.
Introduction
pomer having two 195Pt atoms were absent from the 195Pt{1H}
NMR spectrum suggested that the molecule might rather be
considered as a PtII-Pt0 system, with a Pt-Pt bond endowed
with a low s character. Moreover, the 195Pt NMR chemical
shifts [δPt(1) ) -4798, δPt(2) ) -5205] indicated significantly
different electron densities for the two Pt atoms, suggesting
an electrophilic character for Pt1 (the Pt bonded to O).
Intrigued by this view, which paves the way to a wide
and unexplored reactivity, we have studied the electronic
structure of 1 by X-ray diffraction (XRD) and density
functional theory (DFT) and investigated the reactivity of 1
with suitable nucleophiles, such as PHCy2, PCy3, P(O)HCy2,
and P(S)HCy2.
We have recently described the synthesis of [(PHCy2)Pt1(µ-
PCy2){κ2P,O-µ-P(O)Cy2}Pt2(PHCy2)](Pt-Pt) (1), a rare ex-
ample of an asymmetric monophosphido-bridged complex
with Pt atoms in the formal oxidation state +1.1 Although
no solid-state structure was reported, multinuclear NMR
features allowed us to infer a bridging coordination mode
of the P(O)Cy2 ligand. The valence electron count of 30 for
1 indicates the presence of a Pt-Pt bond, in agreement with
the diamagnetic character of the PtI-PtI complex. The
195Pt{1H} NMR spectrum did not show any coupling between
the Pt atoms, which was an odd circumstance in view of the
results obtained for related unsymmetrical PtI-PtI dimers,
where coupling constants of 337,1 512,2 or 1552 Hz3 were
observed. The fact that satellites stemming from the isoto-
Results and Discussion
XRD Structure of 1. The structure of 1 is reported in
Figure 1 and confirms our previous assignments made on
the basis of IR, NMR, high-resolution (HR) electrospray
ionization mass spectrometry (ESI-MS), and elemental
analyses. In particular, the complex features a P(O)Cy2 ligand
bridging two Pt atoms that are joined by a Pt-Pt single bond
[2.5731(16) Å] and further bridged by a dicyclohexylphos-
phide ligand. The coordination sphere of each platinum is
completed by a PHCy2 ligand trans to the Pt-Pt bond. The
* To whom correspondence should be addressed. E-mail: p.mastrorilli@
poliba.it.
†
Politecnico di Bari.
Università “G. d’Annunzio”.
Institut für Anorganische Chemie der RWTH.
‡
§
(1) Gallo, V.; Latronico, M.; Mastrorilli, P.; Nobile, C. F.; Suranna, G. P.;
Ciccarella, G.; Englert, U. Eur. J. Inorg. Chem. 2005, 4607–4616.
(2) Cittadini, V.; Leoni, P.; Marchetti, L.; Pasquali, M.; Albinati, A. Inorg.
Chim. Acta 2002, 330, 25–32.
(3) Bender, R.; Bouaoud, S.-E.; Braunstein, P.; Dusausoy, Y.; Merabet,
N.; Raya, J.; Rouag, D. J. Chem. Soc., Dalton Trans. 1999, 735–741.
10.1021/ic800045u CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 11, 2008 4785
Published on Web 04/16/2008

Gallo et al.
bridge with a phosphido bridge caused the expected strong
deshielding in the 31P NMR signal of µ-PCy2 (from δ 137
in 1 to δ 242 in 2) due to the presence of two phosphides
bridging two Pt atoms linked by a single bond.7
Monitoring the reaction mixture containing 1 and PHCy2
at room temperature using 31P{1H} NMR made possible the
detection in the solution of a large amount of the intermediate
3, which started to form immediately after addition of PHCy2
and progressively transformed into 2 (Scheme 1). The
multinuclear NMR features of 38 indicated the structure syn-
[(PHCy2)2Pt(µ-PCy2)Pt(PHCy2){κP-P(O)Cy2}](Pt-Pt) (3),
the product of attack by PHCy2 at Pt1 of 1 with decoordi-
nation of the phosphinito oxygen. The fact that PHCy2 attacks
at Pt1 was clearly revealed by a 31P{1H} exchange spectros-
copy (EXSY) experiment performed on a C6D6 solution
containing 1 and PHCy2, which showed an exchange cross-
peak between free PHCy2 (δ -27.6) and P3 of 3 (δ 38.1)
(Figure S1 in the Supporting Information). The transforma-
tion of 3 into 2 can be envisaged to occur via proton transfer
from P3H to P4O, followed by ring closure of the resulting
Pt1-PCy2 moiety and elimination of P(O)HCy2.
Reaction with P(O)HCy2. When equimolar amounts of
1 and P(O)HCy2 in toluene were mixed, no reaction occurred
even after 10 days at 50 °C. However, using an excess of
P(O)HCy2 (>5 eq) caused the transformation of 1 into the
hydrido-bridged complex syn-[(PHCy2){κP-P(O)Cy2}Pt(µ-
PCy2)(µ-H)Pt(PHCy2){κP-P(O)Cy2}](Pt-Pt) (4) (Scheme 2).
Although 31P and 1H NMR spectra of the reaction mixtures
after 2 h at 50 °C showed the quantitative conversion of 1
into 4, the purification of the product from excess P(O)HCy2
required particular care. The reason for this was found in
the formation of adducts of 4 with free P(O)HCy2, as
suggested by NMR spectroscopy. In particular, all of the
signals in the 31P{1H} NMR spectrum of the mixture after
reaction [which contained an excess of P(O)HCy2] were very
broad except for that of the bridging phosphide. The broadness
of the free P(O)HCy2 signal was due to an exchange process
involving formation and rupture of the hydrogen bonds between
free P(O)HCy2 and coordinated P(O)Cy2 in the adducts of 4
with free P(O)HCy2; the broadness of the signals from the
coordinated P(O)Cy2 and PHCy2 ligands had to be attributed
to hindered rotation about the Pt-P bonds.6,9 Exchange between
free P(O)HCy2 and coordinated P(O)Cy2 could be ruled out on
Figure 1. PLATON5 drawing of 1. Displacement ellipsoids are scaled to
50% probability; H atoms bonded to C and an alternative conformation in
the disordered cyclohexyl ring (C19-C24) have been omitted for clarity.
Interatomic distances (Å) and angles (deg): Pt(1)-O(1) 2.180(4), Pt(1)-P(2)
2.2117(19), Pt(1)-P(4) 2.2365(18), Pt(1)-Pt(2) 2.5731(16), Pt(2)-P(3)
2.2513(19), Pt(2)-P(1) 2.2860(17), Pt(2)-P(2) 2.292(2), P(1)-O(1) 1.556(4),
O(1)-Pt(1)-P(2) 139.83(10), O(1)-Pt(1)-P(4) 102.47(10), P(2)-Pt(1)-P(4)
117.68(7), O(1)-Pt(1)-Pt(2) 83.26(9), P(2)-Pt(1)-Pt(2) 56.63(6), P(4)-
Pt(1)-Pt(2) 174.15(4), P(3)-Pt(2)-P(1) 117.45(6), P(3)-Pt(2)-P(2)
118.73(5), P(1)-Pt(2)-P(2) 123.80(6), P(3)-Pt(2)-Pt(1) 169.59(3),
Pt(1)-P(2)-Pt(2) 69.67(6).
steric requirements of the bridging phosphide force the
coordination geometry of the platinum atoms to become a
very distorted square planar arrangement [the angles between
two adjacent atoms around the platinum centers range from
53.71(4) to 118.73(5)°]. The P-H bonds of the two PHCy2
ligands are almost antiperiplanar in order to fulfill steric
requirements generated by the cyclohexyl groups. The
distances P(2)-Pt(1) [2.2117(19) Å] and P(2)-Pt(2) [2.292(2)
Å] are different, the latter being longer as expected on the
basis of the different trans influences exerted by the oxygen
and phosphorus atoms. The sum of the angles at Pt indicates
a perfect planarity of the Pt2P4O core. An analogous
Pt-Pt-P-O trapezoid is found in [(PMePh2)Pt{κ2P,O-µ-
P(O)Ph2}]2(Pt-Pt),4 in which the two Pt atoms are bridged
by two diphenylphosphinito ligands. Comparison of the two
complexes shows that the bond distances of the Pt-Pt-P-O
core in complex 1 are all slightly longer {for instance, the
Pt-O distance is 2.180(4) Å in 1 vs 2.167(3) Å in
[(PMePh2)Pt{κ2P,O-µ-P(O)Ph2}]2(Pt-Pt)}. It is interesting
to note that replacing one four-membered ring in [(PMePh2)-
Pt{κ2P,O-µ-P(O)Ph2}]2(Pt-Pt) with a three-membered ring
in 1 results in a longer Pt-Pt bond {2.5731(16) Å for 1 vs
2.554(1) Å for [(PMePh2)Pt{κ2P,O-µ-P(O)Ph2}]2(Pt-Pt)}.
Reaction with PHCy2. The addition of one equivalent of
PHCy2 to a toluene solution of 1 caused its transformation,
after 3 h at 50 °C, into the symmetric PtI dimer [(PHCy2)Pt(µ-
PCy2)]2(Pt-Pt) (2) with contemporary elimination of P(O)-
HCy2. Complex 2 was previously obtained by us, and its
spectroscopic features have been discussed elsewhere.6 Here
it is sufficient to note that substitution of the phosphinito
(6) Mastrorilli, P.; Nobile, C. F.; Fanizzi, F. P.; Latronico, M.; Hu, C.;
Englert, U. Eur. J. Inorg. Chem. 2002, 1210–1218.
(7) PtI dinuclear complexes having a planar Pt2P2 core are described in
ref 1 and in: (a) Leoni, P.; Chiaradonna, G.; Pasquali, M.; Marchetti,
F. Inorg. Chem. 1999, 38, 253–259. (b) Cristofani, S.; Leoni, P.;
Pasquali, M.; Eisentraeger, F.; Albinati, A. Organometallics 2000, 19,
4589–4595.
(8) δP(1) 182.9, δP(2) 29.3, δP(3) 38.1, δP(4) 84.1, δP(5) 8.7, 2JP(1),P(3) ) 228
2
2
1
Hz, JP(1),P(4) ) 255 Hz, JP(2),P(5) ) 210 Hz, JP(1),Pt(1) ) 2020 Hz,
1JP(1),Pt(2) ) 2578 Hz, JP(2),Pt(1) ) 2692 Hz, JP(3),Pt(1) ) 2990 Hz,
1
1
1JP(4),Pt(2) ) 3460 Hz, 1JP(5),Pt(2) ) 2571 Hz; δH-P(2) 4.31, δH-P(3) 4.28,
1
1
1
(4) Alcock, N. W.; Bergamini, P.; Gomes-Carniero, T. M.; Jackson, R. D.;
Nicholls, J.; Orpen, A. G.; Pringle, P. G.; Sostero, S.; Traverso, O.
J. Chem. Soc., Chem. Commun. 1990, 980–982.
δH-P(5) 4.54, JH,P(2) ) 318 Hz, JH,P(3) ) 284 Hz, JH,P(5) ) 313 Hz;
δPt(1) –5030, δPt(2) –5211.
(9) Mastrorilli, P.; Nobile, C. F.; Latronico, M.; Gallo, V.; Englert, U.;
Fanizzi, F. P.; Sciacovelli, O. Inorg. Chem. 2005, 44, 9097–9104.
(5) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.
4786 Inorganic Chemistry, Vol. 47, No. 11, 2008

ReactiWity of a Phosphinito-Bridged PtI-PtI Complex
Scheme 1. Reaction of 1 with PHCy2
Scheme 2. Reaction of 1 with P(O)HCy2
analogous Pt dinuclear complexes having a bridging phos-
phide and a bridging hydride.13
An interesting structural feature in the solid is the
formation of an extended one-dimensional chain in which
complexes and water molecules interact via hydrogen bonds
(Figure 5), a feature recently found in the related phosphinito
platinum complexes [Pt(L){(PPh2O)2H}(PPh2OH)] (L )
C6F5, Ct CBut).14 Each phosphinito oxygen atom of 4
participates in hydrogen bonds to two water molecules in
general positions, thus forming an alternating sequence of
one complex and two water molecules that has an overall
stoichiometry of 4 · 2H2O.
Since dicyclohexylphosphane oxide is in tautomeric equi-
librium with dicyclohexylphosphinic acid,15 its reaction with
1 can in principle occur by attack of either the oxygen of
the tetrahedral P(O)HCy2 form or the phosphorus of the
pyramidal P(OH)Cy2 form at Pt1. However, given that
coordination to a metal stabilizes the pyramidal phosphinic
acid form,16 attack at Pt1 by the phosphorus of the Cy2P(OH)
seems more likely.
Reaction with PCy3. The reactions of 1 with PHCy2 and
P(O)HCy2 involve proton transfer: from PHCy2 to the
coordinated P(O)Cy2 to release P(O)HCy2 in the synthesis
of 2 and from P(O)HCy2 to the Pt-Pt bond to give 4. In
order to assess the reactivity of 1 with a nucleophile that
does not contain an easily transferable H atom, we reacted
1 with 1 eq of PCy3. The reaction led to nearly complete
conversion of 1 into 5 (Scheme 3) after 6 h at 295 K in
THF. In this case, in contrast to the reaction with PHCy2,
the monobridged intermediate 617 shown in Scheme 3 cannot
undergo proton transfer from the incoming nucleophile to
the vicinal P(O)Cy2. Therefore, reclosing of the phosphinito
the basis of the relative sharpness of the phosphide signal along
1
with the absence of cross-peaks in 31P{1H} and H EXSY
experiments.10
Addition of water to the mixture after reaction caused 4
to precipitate as a mixture of H2O and P(O)HCy2 solvates,
but use of aqueous NaOH instead of pure water afforded
pure 4 (as the water adduct) devoid of P(O)HCy2.
The 31P{1H} spectrum (Figure 2) of 4 showed the
resonance of the bridging phosphide as a triplet [with 195Pt
2
1
satellites; JP(1),P(2) ) 254 Hz, JP(1),Pt ) 1173 Hz] due to
coupling with the phosphinito ligands in the trans positions.11
The H NMR spectrum showed only a signal attributed to
1
1
the H atoms of the coordinated PHCy2 ligands (δ 5.0, JH,P
) 330 Hz, 2JH,Pt ) 60 Hz) and a multiplet (with two sets of
195Pt satellites arising from isotopomers containing one or
two NMR-active Pt atoms) attributable to the bridging
hydride (Figure 3a). Comparison with the H{31P} NMR
1
spectrum (Figure 3b) showed that the multiplicity of the
1
hydride signal was due only to H-31P couplings. The
195Pt{1H} NMR spectrum showed a very broad signal (δ
-5467) that confirmed the presence of slowly rotating P
ligands bound to Pt.
The crystal structure of 4·2H2O is shown in Figure 4. The
molecule is located on a crystallographic C2 axis passing
through the bridging phosphide and hydride ligands; it
has a uniformly distributed arrangement of ten cyclohexyl
groups around the Pt2P5 core. The dicyclohexylphosphinite
ligands are oriented with both oxygens pointing out from
the molecule and forming hydrogen bonds with two H2O
molecules clathrated in the crystal.12 The Pt-Pt distance of
2.8502(6) Å is compatible with a single bond between the
metal atoms (the Pt-Pt distance in platinum metal is 2.77
Å). Such a distance compares well with those found in
(13) (a) Jans, J.; Naegeli, R.; Venanzi, L. M.; Albinati, A. J. Organomet.
Chem. 1983, 247, C37–C41. (b) Siedle, A. R.; Newmark, R. A.;
Gleason, W. B. J. Am. Chem. Soc. 1986, 108, 767–773. (c) Alonso,
E.; Forniés, J.; Fortuño, C.; Martin, A.; Orpen, A. G. Organometallics
2001, 20, 850–859. (d) Reference 11.
(14) Dìez, A.; Forniés, J.; Gòmez, J.; Lalinde, E.; Martìn, A.; Moreno,
M. T.; Sànchez, S. Dalton Trans. 2007, 3653–3660.
(15) The prototropic equilibrium of phosphane oxides has been reported
to depend on the medium of the samples (see, for instance: Magiera,
D.; Szmigielska, A.; Pietrusiewicz, K. M.; Duddeck, H. Chirality 2004,
16, 57–64. ). We have found that in the case of dicyclohexylphosphane
oxide, the phosphinic acid form is the predominant one in aromatic
solvents.
(16) (a) Algarra, A. G.; Basallote, M. G.; Fernandez-Trujillo, M. J.;
Hernandez-Molina, R.; Safont, V. S. Chem. Commun. 2007, 3071–
3073. (b) Akbayeva, D. N.; Di Vaira, M.; Costantini, S. S.; Peruzzini,
M.; Stoppioni, P. Dalton Trans. 2006, 389–395. (c) Nagaraja, C. M.;
Nethaji, M.; Jagirdar, B. R. Inorg. Chem. 2005, 44, 4145–4147.
(10) The mixing time was varied in the 10–200 ms range for both 1H and
31P{1H} EXSY experiments performed at 295 and 323 K.
(11) In these systems, the coupling constant between the phosphide and
the PHCy2 ligands in mutually cis positions is often negligible. See,
for instance: Van Leeuwen, P. W. N. M.; Roobeek, V. F.; Frijns,
J. H. G.; Orpen, A. G. Organometallics 1990, 9, 1211–1222.
(12) A dimethylphosphinito complex featuring hydrogen bonds with water
molecules in the solid state has recently been reported in: Ruiz, J.;
Garcia-Granda, S.; Diaz, M. R.; Quesada, R. Dalton Trans. 2006,
4371–4376.
(17) Signals at δ 183.6 (dd, 2Jµ-P,PCy ) 233 Hz, 2Jµ-P,PO ) 260 Hz, µ-PCy2),
3
2
2
δ 85.4 [m, Jµ-P,PO ) 260 Hz, P(O)Cy2], δ 37.5 (m, Jµ-P,PCy ) 233
3
Hz, PCy3), δ 47.1 (m, PHCy2), and δ 11.8 (m, PHCy2) observed by
monitoring the reaction solution using 31P{1H} NMR were attributed
to this monobridged intermediate by comparison with the spectroscopic
features of 3.
Inorganic Chemistry, Vol. 47, No. 11, 2008 4787

Gallo et al.
Figure 5. One-dimensional chain of complexes and water molecules in
j
4·2H2O. The chain extends along [101]; the view direction is [111].
Figure 2. 31P{1H} NMR spectrum of 4 (CDCl3, 295 K).
by an 20% yield of [(PCy3)Pt(µ-PCy2)]2(Pt-Pt) (7), the
PCy3 analogue of 2. The formation of 7, which precipitates
from the reaction mixture as a yellow powder, is not
unexpected. In fact, the released PHCy2 molecule can trigger
the formation of diphosphido compounds by attacking the
phosphinito-bridged species 1 and 5, after which replacement
of the residual coordinated PHCy2 ligand(s) with PCy3
occurs.
Reaction with P(S)HCy2. We completed this study by
investigating the reactivity of 1 toward dicyclohexylphos-
phane sulfide, P(S)HCy2, a molecule possessing two atoms
(P and S) that potentially can ligate to the metal. The reaction,
carried out in toluene at 50 °C, selectively gave complex 8,
in which the bridging P(O)Cy2 ligand was replaced by a
bridging P(S)Cy2 ligand (Scheme 4).
Figure 3. (a) 1H and (b) 1H{31P} NMR spectra of 4 in the hydride region
(CDCl3, 295 K).
The 31P{1H} NMR spectrum of 8 (Figure 6) was very
similar to those of 1 and 5, the main differences being the
highfield shift of the resonance and the remarkably large
2
value of the JP,Pt coupling constant of the P(S)Cy2 ligand
compared with those of P(O)Cy2 in 1. The sharpness of all
of the 31P{1H} NMR signals can be taken as an indicator of
the bridging coordination mode of the P(S)Cy2 ligand. In
fact, as in the case of 1, the doubly bridged structure assures
free rotation of the coordinated dicyclohexylphosphanes and,
at the same time, a unique conformation for the P(S)Cy2
ligand; both of these circumstances are compatible with sharp
31P{1H} NMR signals. As a result of the decreased PdS bond
order, and analogous to results for other known κ2P,S-
thiophosphinito-bridged PtI-PtI compounds,18 the PdS IR
stretching band of 8 (545 cm-1) was red-shifted with respect
to that of the free phosphane sulfide (615 cm-1).
The 195Pt{1H} NMR spectrum of 8 (Figure 7) showed two
dddd signals, one centered at δ -5218 (S-bound Pt1) and
the other at δ -5376 (P-bound Pt2). These values compare
well to those obtained for related Pt2{κ2P,S-µ-P(S)R2}L2
complexes (R ) Me, Ph, Cy, OEt; L ) P(OMe)3, P(OPh)3,
PPh3, PMePh2),18c,d,19 which range from δ -5128 to -5216
and are compatible with both Pt atoms being in the +1
oxidation state.18 In contrast to the results for 1, each 195Pt
Figure 4. PLATON5 drawing of 4 · 2H2O. Displacement ellipsoids are
scaled to 50% probability; only the shortest hydrogen bonds have been
shown. H atoms bonded to C have been omitted for clarity. Primed atoms
are related to unprimed ones by the symmetry operation 1 - x, y,
1
/
- z. Interatomic distances (Å) and angles (deg): Pt(1)-P(3)
2
2.2428(10), Pt(1)-P(1) 2.3065(11), Pt(1)-P(2) 2.3322(11), Pt(1)-Pt(1)′
2.8502(6), P(1)-C(1) 1.850(4), P(2)-O(1) 1.526(3), Pt(1)-H(1) 1.74(4),
P(3)-Pt(1)-P(1) 101.16(3), P(3)-Pt(1)-P(2) 91.46(4), P(1)-Pt(1)-P(2)
164.47(3), P(3)-Pt(1)-Pt(1)′ 151.88(3), P(1)-Pt(1)-Pt(1)′ 51.83(2),
P(2)-Pt(1)-Pt(1)′116.52(2),P(3)-Pt(1)-H(1)168.2(12),P(1)-Pt(1)-H(1)
86.8(18), P(2)-Pt(1)-H(1) 82.2(17), Pt(1)-Pt(1)′-H(1) 35.0(18).
(18) (a) Wagner, K. P.; Hess, R. W.; Treichel, P. M.; Calabrese, J. C. Inorg.
Chem. 1975, 14, 1121–1127. (b) Walther, B.; Messbauer, B.; Meyer,
H. Inorg. Chim. Acta 1979, 37, L525–L527. (c) Boag, N. M.;
Browning, J.; Crocker, C.; Goggin, P. L.; Goodfellow, R. J.; Murray,
M.; Spencer, J. L. J. Chem. Res., Miniprint 1978, 2962–2983. (d)
Messbauer, B.; Meyer, H.; Walther, B.; Heeg, M. J.; Rahman,
A. F. M. M.; Oliver, J. P. Inorg. Chem. 1983, 22, 272–277.
bridge accompanied by release of the PHCy2 molecule
(which is less basic than PCy3) becomes favored.
When the reaction was carried out in toluene at 50 °C
with an excess of PCy3, formation of 5 was accompanied
(19) Zschunke, A.; Meyer, H.; Heidlas, I.; Messbauer, B.; Walther, B.;
Schädler, H.-D. Z. Anorg. Allg. Chem. 1983, 504, 117–127.
4788 Inorganic Chemistry, Vol. 47, No. 11, 2008

ReactiWity of a Phosphinito-Bridged PtI-PtI Complex
Scheme 3. Reaction of 1 with PCy3
Scheme 4. Reaction of 1 with Dicyclohexylphosphane Sulfide
phosphanes. Thus, geometry optimizations of the two simpli-
fied model complexes 1-Methyl and 1-Isopropyl and the
actual complex 1 were performed. Table 1 compares the main
geometrical parameters of the Pt2P4O core obtained from
these calculations with those from the X-ray data for the
actual complex.
The results showed that the geometrical parameters of the
simplest model, having the small methyl substituents, were
already in good agreement with the X-ray results, suggesting
that inclusion of the full cyclohexyl groups on the phosphane
ligands was not necessary to reproduce the electronic
structure and the main geometrical features of the Pt2P2O
core of complex 1. Indeed, the calculated interatomic
distances within the Pt2P4O core were only slightly (0.03–0.07
Å) larger than the X-ray values (with the greatest discrep-
ancy, 0.07 Å, being observed only for the Pt-Pt bond),
probably as a result of incomplete inclusion of the relativistic
effects, which is known to lead to overestimates of metal–
ligand and metal-metal bond distances. Therefore, in
subsequent calculations we used only the simplified models
having methyl substituents on the phosphane ligands; for the
sake of simplicity, we will not distinguish between the actual
cyclohexyl-substituted complexes and their methyl-substi-
tuted models in the discussion that follows.
Next we performed a Mulliken analysis of the charge
distribution in complex 1 in order to align the atoms of the
Pt2P2O core in order of increasing electron density. We found
the following Mulliken gross atomic charges: Q(Pt1) )
+0.18, Q(Pt2) ) -0.20, Q(P1) ) -0.18, Q(P2) ) -0.29,
and Q(O) ) -0.82 (Figure 8). It is apparent from these
values that the most electron-poor center within the Pt2P2O
core is the O-bound Pt1 atom while the most electron-rich
center is the O atom. It is worth noting that the asymmetry
of the bridging phosphinito ligand leads to an asymmetric
charge distribution on the two platinum atoms, with phos-
phane-bound Pt2 being significantly more electron-rich than
peak was flanked by 195Pt satellites (1JPt,Pt ) 190 Hz, Figure
7), suggesting that replacing O with S has a pronounced
effect on the types of orbitals involved in the metal-metal
bond (see below).
In light of the results obtained with PHCy2 and P(O)HCy2,
it can be presumed that P(S)HCy2 attacks the Pt1 atom,
forming either intermediate A (S attack at Pt1, path a) or
intermediate C (P attack at Pt1, path b).20 Both intermediates
could evolve into the final product 8 by hydrogen transfer
to the dangling P(O)Cy2 ligand (forming intermediates B and
D, respectively) followed by ring closure (Scheme 5).
NMR monitoring of the reaction between 1 and P(S)HCy2
did not detect any species other than reactants and 8. Thus,
we tried to distinguish between these two reaction paths by
studying the reaction of 5 with P(S)HCy2 (in this case,
products deriving from paths a and b become distinguishable
in view of the different phosphanes borne by Pt1 and Pt2),
but the expected substitution product did not form. With the
experimental data collected to this point, no definitive choice
between paths a and b could be made. Thus, a DFT study
aimed at elucidating the relative stabilities of the proposed
intermediates was carried out.
DFT Study. Density functional theory calculations were
first performed in order to study the electronic structure of
complex 1 and its reactivity toward nucleophiles. Because
of the large size of this complex and the computational load
necessary to perform high-level calculations on several
compounds, we performed preliminary calculations on three
models that included increasing sizes of the substituents on
the phosphane ligands. In particular, we considered ligands
having (i) methyl, (ii) isopropyl, and (iii) the full cyclohexyl
substituents on the four (two terminal and two bridging)
(20) P- or S-bound thiophosphinito complexes with several metals have
been reported. Complexes with Pt: (a) Rahman, A. F. M. M.;
Ceccarelli, C.; Oliver, J. P.; Messbauer, B.; Meyer, H. Inorg. Chem.
1985, 24, 2355–2359. (b) Anderson, D. M.; Ebsworth, E. A. V.;
Stephenson, T. A.; Walkinshaw, M. D. Angew. Chem., Int. Ed. Engl.
1981, 20, 290–291. Complexes with W, Mo, or Cr: (c) Lindner, E.;
Meier, W.-P. J. Organomet. Chem. 1976, 114, 67–87. Complexes with
Mn or Re: (d) Lindner, E.; Schilling, B. Chem. Ber. 1977, 110, 3725–
3732. Complexes with Mn: (e) Lindner, E.; Dreher, H. J. Organomet.
Chem. 1976, 104, 331–346. (f) Lindner, E.; Dreher, H. J. Organomet.
Chem. 1973, 55, 347–356. (g) Lindner, E.; Dreher, H. Angew. Chem.,
Int. Ed. Engl. 1975, 14, 416–417. Complexes with Cr, Mn, or Mo:
(h) Lindner, E.; Meier, W.-P. J. Organomet. Chem. 1973, 51, C14–
C16. Complexes with Cr or Mo: (i) Lindner, E.; Meier, W.-P. J.
Organomet. Chem. 1974, 67, 277–285. Complexes with Ir: (j) Marsala,
V.; Faraone, F.; Piraino, P. J. Organomet. Chem. 1977, 133, 301–
305.
Figure 6. 31P{1H} NMR spectrum of 8 (C6D6, 295 K).
Inorganic Chemistry, Vol. 47, No. 11, 2008 4789

Gallo et al.
Table 1. Comparison of the Main Interatomic Separations (Å)
Calculated for the Three Models of 1 with the Values Obtained from the
X-ray Data for the Actual Complex
Pt1-Pt2 Pt1-µ-P Pt2-µ-P Pt1-O
P-O Pt2-P(O)
1-Methyl
1-Isopropyl 2.64
1
2.64
2.26
2.26
2.25
2.34
2.35
2.35
2.21
2.21
2.21
1.59
1.60
1.60
2.33
2.34
2.34
2.64
1 from
X-ray data
2.573(2) 2.212(2) 2.292(2) 2.180(4) 1.556(4) 2.286(2)
Figure 7. 195Pt{1H} NMR spectrum of 8 (C6D6, 295 K).
Scheme 5. Possible Mechanisms for Formation of 8
Figure 8. Mulliken gross atomic charges in the Pt2P2O core of complex 1.
were also performed in order to study the effect of the
different bridging ligands on the metal-metal bonding and
charge distribution. The calculated values of the main
interatomic distances in the Pt2P2S core of 8, which are
reported in Table 2, show that changing the bridging ligands
does not significantly affect the metal-metal distance. In
particular, the metal-metal distances slightly increased in
the order 1 < 2 ≈ 8, with all of the values being within the
range of a PtI-PtI single bond. It is worth noting that the
Pt-Pt bond length in 8 was only slightly (0.03 Å) longer
than that in 1 in spite of the fact that the Pt-S and P-S
bonds were significantly longer (by 0.2–0.5 Å) than the Pt-O
and P-O bonds (see Tables 1 and 2); this indicates that a
net strengthening of the Pt-Pt bond occurs upon replacement
of the bridging phosphinito ligand by a thiophosphinito
ligand. Moreover, the Pt-Pt bond length was slightly shorter
in 1 than in 2 in spite of the presence of the longer bridging
ligand κ2P,O-µ-Cy2PO instead of µ-PCy2, indicating a net
weakening of the Pt-Pt bond in 2. A significantly longer
Pt-Pt bond distance of 2.93 Å was calculated for 4, in
agreement with the X-ray value of 2.85 Å (in view of the
expected elongation of 0.07 Å due to incomplete inclusion
of relativistic effects, as also observed for 1) and consistent
with the lengthening expected upon protonation.
O-bound Pt1. On the one hand, this result corroborates our
starting hypothesis (based on 195Pt NMR features) concerning
the electrophilic character of Pt1, while on the other hand, it
predicts an amphiphilic character for 1, suggesting that Pt1
is the target of nucleophilic attack while O is the preferred
site of electrophilic attack.21 Indeed, the reactivity with
nucleophiles discussed above (Schemes 1–4) is characterized
by initial attack of the incoming nucleophile at the Pt1 atom,
leading to cleavage of the Pt1-O bond and formation of a
singly PCy2-bridged intermediate that subsequently evolves
to the thermodynamically most stable product, the nature of
which depends on the nucleophile used.
Energy-level diagrams for the frontier molecular orbitals
(MOs) of 1, 2, and 8 are displayed in Figure 9. The energy-
level diagram for the MOs of 2 shows the expected pattern
for a dinuclear PtI-PtI complex with a metal-metal single
bond.22 Indeed, for this species, which has C2h symmetry,
nine of the highest-occupied MOs have predominant con-
tributions from the metal orbitals, and each is classified
according to its irreducible representation in the C2h point
group and the bonding character (σ, π, etc.) of the combina-
tion of metal orbitals that form it. In the coordinate system
used in our calculations (see Chart 1), in which the Pt2P4
core lies in the xy plane and the two platinum atoms are
DFT calculations of the structural and electronic properties
of complexes 2, 4, and 8 (using methyl-substituted models)
2
2
located along the y axis, combining the two Pt 5dx –y orbitals
(21) The reactivity of 1 toward electrophiles is currently under investigation
(22) Mealli, C.; Ienco, A.; Galindo, A.; Carreño, E. P. Inorg. Chem. 1999,
38, 4620–4625.
in our laboratories.
4790 Inorganic Chemistry, Vol. 47, No. 11, 2008

ReactiWity of a Phosphinito-Bridged PtI-PtI Complex
Table 2. Interatomic Separations (Å) Obtained from DFT Calculations
or X-ray Data for Complexes 2, 4, and 8
thus suggest a slightly stronger Pt-Pt bond, in agreement
with the structural evidence discussed above.
Pt-Pt
Pt-µ-P
Pt-P(H)
A detailed orbital analysis of the frontier orbitals of 4 has
also been carried out in order to study the effect of
protonation of the Pt-Pt bond on its electronic structure.
The small but significant decrease of the Pt-Pt bond order
upon protonation is consistent with the transformation of the
two-electron, two-center (2-e, 2-c) metal-metal bond into
a weaker two-electron, three-center (2-e, 3-c) bond that has
been experimentally14,16a–c and theoretically23 investigated.
Figure 10 shows the perturbation of the frontier MOs of the
symmetric [(PHMe2){P(O)Me2}Pt(µ-PMe2)Pt{P(O)Me2}-
(PMe2H)]- fragment, 4′, by the empty 1s orbital of the
bridging proton fragment. The frontier MOs of this dinuclear
fragment are similar to those of 2, except for the C2V
symmetry and the smaller difference in the energies of MOs
with bonding and antibonding character that results from the
longer Pt-Pt bond. In a coordinate system similar to that
used for 2, having the Pt2P5 core in the xy plane and the two
Pt atoms along the y axis, only the MOs with σ and π|
character have the appropriate symmetries and sufficient
overlap to interact with the empty 1s orbital of the H
fragment. The in-phase combination gives rise to a 3-c
Pt-H-Pt bonding orbital (1a1) at low energy, while the
occupied nonbonding (2a1) and empty out-of-phase (3a1)
combinations have significantly higher energies. The result-
ing transfer of electron density from the metal-metal-based
σ and π| orbitals to the bridging H ligand, supported by a
Mulliken charge of -0.21 on the hydrogen, leads to
weakening and elongation of the metal-metal bond. The
slightly negative charge on the bridging hydrogen suggests
behavior intermediate between those of a proton and a
hydride ligand, in agreement with the relatively short Pt-Pt
bond (2.850 Å), which is not completely broken as would
be expected for a “true” PtII-PtII dimer.
2-Methyl
2.66
2.35
2.24
Pt1-Pt2 Pt1-µ-P Pt1-H Pt1-P(H) Pt1-P(O)
2.93 2.34 1.79 2.27 2.38
2.8502(6) 2.3065(11) 2.2428(10) 2.3322(11)
4-Methyl
4 from
X-ray data
Pt1-Pt2 Pt1-µ-P Pt2-µ-P P-S
2.67 2.27 2.33 2.10
Pt2-P(S) Pt1-S
2.33 2.42
8-Methyl
leads to ag and bu MOs having σ and σ* character,
respectively. Combination of the two 5dyz orbitals produces
au and bg MOs having π⊥ and π⊥* character, respectively
(⊥ ) perpendicular to the xy plane), while combination of
the two 5dxy orbitals yields ag and bu MOs having π| and
π|* character, respectively (| ) parallel to the xy plane).
Combining the two 5dxz orbitals leads to bg and au MOs
having δ and δ* character, respectively, and combination
2
of the two 5dz orbitals generates set of ag and bu MOs having
δ and δ* character, respectively. Within the same coordinate
system, the Pt-P bonds are described by orbitals having ag
2
2
and bu symmetry that involve 5dxy, 5dx –y , 6s, and 6p metal
orbitals. Among the nine occupied MOs, the four fully
occupied orbitals having δ or δ* character (13bg, 14au, 21ag,
and 20bu) are nearly pure metal-based orbitals (>80% 5dxz
2
or 5dz ) with bonding and antibonding counterparts close in
energy. These four MOs are responsible for the δ-type Pt-Pt
interaction; however, they are fully occupied, and there is
no net δ bonding. A substantial metal contribution (70% 5dyz)
is also observed for the 13au and 14bg orbitals, which have
π⊥ and π⊥* character, respectively, and together yield no
net π bonding. The 19ag and 21bu MOs, which have π| and
π|* character, respectively, show a smaller 5dxy contribution
(30–60%), since they also involve platinum 6s and 6p and
phosphorus 3p orbitals and describe the bonding between
the Pt and bridging P atoms. They combine to give no net
contribution to Pt-Pt bonding as well. The MO responsible
for metal-metal bonding is 18ag (not shown in Figure 9),
which is located at lower energy (–7.7 eV) and has Pt-Pt σ
character; the corresponding MO with σ* character, 22bu, is
empty. This picture shows that the Pt-Pt bond in 2 arises
DFT calculations were eventually performed in order to
elucidate the relative stabilities of the possible intermediates
involved in the reaction of 1 with P(S)HCy2 to give 8 (A-D
in Scheme 5) and make a definitive choice between paths a
and b.
Geometry optimizations of A and C, which result from
the initial attack of P(S)HCy2 through the S and P atoms,
respectively, led to two local minima on the potential energy
surface only when a conformation having the hydrogen of
the P(S)HCy2 ligand on Pt1 in the anti position with respect
to the oxygen atom of the P(O)Cy2 ligand on Pt2 was
considered. In this case, C was 10.4 kcal mol-1 more stable
in energy than A.
2
2
from the bonding σ interaction between the two 5dx –y
orbitals (with the corresponding antibonding combination σ*
being empty), which means that the bond between the two
metal atoms may be qualitatively described as a single σ
bond.
Similar energy-level diagrams are observed for 1 and 8
(Figure 9), even though the lower Cs symmetry of the latter
compounds changes the labels of the MOs and allows a larger
mixing among different d-type orbitals. The main differences
are observed for MOs having σ, π|, or π|* character, which
show a more extensive mixing of the 5dxy and 5dx –y orbitals,
particularly those on Pt1, with the 2p orbitals of oxygen or
3p orbitals of sulfur. The same is also observed for the MOs
of δ* character in which the 5dxz orbital of Pt1 mixes with
the 2pz orbital of oxygen (3pz of sulfur) to describe Pt-O
(Pt-S) π bonding. These effects lead to a decrease in the
Pt-Pt antibonding character of the π|* and δ*(dxz) MOs and
When the conformation having the hydrogen on P(S)HCy2
in the syn position with respect to the oxygen atom on
P(O)Cy2 was considered, a barrierless proton transfer (rather
than just the expected formation of a P-H · · · O hydrogen
bond) between the two ligands occurred, and the geometry
2
2
(23) (a) Baik, M.-H.; Friesner, R. A.; Parkin, G. Polyhedron 2004, 23,
2879–2900, and references therein. (b) Bo, C.; Poblet, J.-M.; Costas,
M.; Sarasa, J.-P. J. Mol. Struct. 1996, 371, 37–43. (c) Bo, C.; Costas,
M.; Poblet, J. M.; Rohmer, M.-M.; Benard, M. Inorg. Chem. 1996,
35, 3298–3306.
Inorganic Chemistry, Vol. 47, No. 11, 2008 4791

Gallo et al.
Figure 9. Energy-level diagrams for the frontier molecular orbitals of 1, 2, and 8.
Chart 1. Coordinate System Used in the DFT Calculations
optimizations led directly to B and D. These intermediates
are thus the global minima on potential energy surface for
the attack of P(S)HCy2 through S and P, respectively, with
D more stable by 9.0 kcal mol-1. Since B and D were 12.0
and 10.6 kcal mol-1 below A and C, respectively, and the
only barriers for the A f B and C f D interconversions
(the barriers for rotation around the Pt-P and Pt-S bonds,
respectively) were negligible, B and D can be considered
the only real possible intermediates (both of which rapidly
evolve into 8) in the reaction of 1 with P(S)HCy2. This result
indicates that attack by P(S)HCy2 through the P atom is
thermodynamically favored over attack through the S atom,
thus suggesting that the reaction of 1 with P(S)HCy2 occurs
preferentially through path b.
Figure 10. MO interaction diagram for 4 built from 4′ and H+ fragments.
phosphido or thiophosphinito ligand, respectively. In the case
of PCy3, substitution of the Pt1-bound PHCy2 ligand with
retention of the phosphinito bridge takes place. Finally, in
the reaction with P(O)HCy2, which contains an acidic proton
in its P(OH)Cy2 tautomeric form, formal protonation of the
Pt-Pt bond occurs, yielding the hydrido-bridged dinuclear
complex 4.
Conclusions
This study revealed that the reactivity of complex 1 with
molecules such as PHCy2, PCy3, P(O)HCy2, and P(S)HCy2
is governed by the electrophilicity of the O-bound Pt1 atom,
at which the incoming nucleophile attacks. In the case of
PHCy2 or P(S)HCy2, the reaction leads to a product in which
the bridging phosphinito ligand is substituted with a bridging
In every case, the starting 30-electron structure is pre-
served. In particular: (i) the 2-e donor molecule PCy3 replaces
4792 Inorganic Chemistry, Vol. 47, No. 11, 2008

ReactiWity of a Phosphinito-Bridged PtI-PtI Complex
Table 3. Crystallographic Data and Structural Refinement Details for 1
and 4·2H2O
(Bruker micrOTOF). All of analyses were carried out in positive-
ion mode. The sample solutions were introduced by continuous
infusion at a flow rate of 180 µL min-1 with the aid of a syringe
pump. The instrument was operated with end-plate offset and
capillary voltages set to -500 and -4500 V, respectively. The
nebulizer pressure was 0.8 bar (N2), and the drying gas (N2) flow
rate was 7.0 L min-1. The capillary exit and skimmer 1 voltages
were 90 and 30 V, respectively. The drying gas temperature was
set at 220 °C. The software used for the simulations was Bruker
Daltonics DataAnalysis (version 3.3).
1
4·2H2O
empirical formula
formula mass
temperature (K)
wavelength (Å)
crystal system
space group
unit cell dimensions
a (Å)
C48H90OP4Pt2
1197.26
130(2)
0.71073
Monoclinic
P21/c
C60H117O4P5Pt2
1447.59
110(2)
0.71073
Monoclinic
C2/c
14.548(10)
19.811(14)
21.225(12)
125.31(3)
4992(6)
4
13.536(4)
23.754(6)
20.066(5)
91.154(4)
6451(3)
4
b (Å)
c (Å)
NMR spectra were recorded using a BRUKER Avance DRX400
spectrometer; frequencies are referenced to Me4Si (1H and 13C),
(
85% H3PO4 (31P), and H2PtCl6 195Pt). Signal attributions and
ꢁ (deg)
V (Å3)
coupling-constant assessments were made on the basis of a
multinuclear NMR analysis that included 1H-31P HMQC, 1H-195Pt
HMQC, and 31P{1H} long-range COSY experiments. Coupling
constants not directly extractable from the monodimensional
spectra were obtained and attributed on the basis of the tilts of the
multiplets due to the “passive” nuclei26 in the aforementioned 2D
spectra.
All of the calculations were performed using the Amsterdam
Density Functional (ADF) package.27–29 The inner-shell cores (1s
for C and O, 1s and 2p for P, and 1s-4f for Pt) were kept frozen.
Valence orbitals based on Slater-type orbitals (STOs) were ex-
panded within a triple-ꢀ basis set augmented with a polarization
function. The MOs for all of the main group atoms were expanded
in an uncontracted triple-ꢀ STO basis set. For platinum orbitals,
we used a double-ꢀ STO basis set for 5s and 5p and a triple-ꢀ
STO basis set for 5d and 6s. As polarization functions, we used
one 6p function for Pt, one 4d for P, one 3d for C, N, and O, and
one 2p for H.
The local density approximation exchange correlation potential
and energy were used along with the Vosko-Wilk-Nusair pa-
rametrization30 for homogeneous electron-gas correlation, including
Becke’s nonlocal correction31 to the local exchange expression and
Perdew’s nonlocal correction32 to the local expression for the
correlation energy. Molecular structures of all of the considered
complexes were optimized at this gradient-corrected level. Since
the relativistic effect is important in these Pt-containing dimers,
the zero-order regular approximation (ZORA) formalism without
spin–orbit coupling was included.33,34 Previous calculations have
indicated that use of gradient-corrected functionals with the ZORA
approximation can reliably predict properties of metal dimers in
comparison with Dirac four-component MP2 calculations.35,36 Since
the properties and reactivities of the considered complexes were
investigated in the solid state or in apolar solvents, only gas-phase
calculations without inclusion of any solvation effects were
performed.
Z
Dcalcd (mg m-3
)
1.593
5.760
1.490
4.498
absorption coeffient (mm-1
)
θ range for data collection (deg)
total reflections
2.00–29.16
67284
1.71–27.45
41737
independent reflections
data/parameters
13077
13077/541
1.027
0.0396
0.0938
7385
7385/321
1.052
0.0293
0.0781
2.287, –0.515
2
goodness of fit on F2
R1a [I > 2σ(I)]
wR2b (all data)
largest diff. peak, hole (e Å-3
)
4.936, –3.938
2
a R1 ) ∑||Fo| – |Fc||/∑|Fo|. b wR2 ) [∑w(Fo – Fc )2/∑w(Fo )2]1/2
.
2
the 2-e donor PHCy2 coordinated to the electrophilic Pt atom;
(ii) the potentially 3-e donor molecules PHCy2 and P(S)HCy2
replace only one of the two 3-e donor ligands originally
present in 1, namely, P(O)Cy2; (iii) the potentially 3-e donor
P(O)HCy2 fragments into two 1-e donor ligands, giving the
bridging hydride addition product 4. In this case, the κ2P,O-
µ-P(O)Cy2 group is not released by the complex, but its
coordination mode is changed from bidentate (a 3-e donor
ligand) in 1 to monodentate (a 1-e donor ligand) in 4.
DFT calculations confirmed the remarkable electrophilicity
of Pt1 and allowed us to clarify the nature of the metal-metal
bond in several of the considered dinuclear complexes and
elucidate some of their reaction pathways.
Experimental Section
Complex 1 was prepared using a slight modification of the
literature procedure.1 A solution of cis-[PtCl2(PHCy2)2] (100 mg)
in CH2Cl2 (7.0 mL) was added to a solution containing 1.0 g of
NaOH, 2.0 mL of H2O, and 7.0 mL of acetone; the resulting
biphasic system was vigorously stirred at room temperature for 2 h.
The yellow organic phase was separated and dried on Na2SO4. After
filtration, the solvent was evaporated to dryness and the residue
redissolved in n-hexane. The resulting suspension was filtered, and
the filtrate was dried under vacuum, yielding 76 mg of pure 1 (85%).
Dicyclohexylphosphane and tricyclohexylphosphane were pur-
chased from Strem and used as received. Dicyclohexylphosphine
oxide24 and dicyclohexylphosphine sulfide25 were synthesized using
literature procedures. All of the manipulations were carried out
under a pure dinitrogen atmosphere using freshly distilled, oxygen-
free solvents. C, H, N elemental analyses were performed using a
Carlo Erba EA1108 CHNS-O elemental analyzer. Infrared spectra
were recorded on a Bruker Vector 22 spectrometer.
(26) Carlton, L. Bruker Rep. 2000, 148, 28–29.
(27) Amsterdam Density Functional (ADF) 2004; Scientific Computing
& Modelling NV: Amsterdam, 2004; available from http://www.scm.
com.
(28) Boerrigter, P. M.; te Velde, G.; Baerends, E. Int. J. Quantum Chem.
1988, 33, 87–113.
(29) te Velde, G.; Baerends, E. J. J. Chem. Phys. 1992, 99, 84–98.
(30) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200–
1211.
(31) Becke, A. D. Phys. ReV. A 1988, 38, 3098–3100.
(32) Perdew, J. P. Phys. ReV. B 1986, 33, 8822–8824.
(33) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1993,
99, 4597–4610.
Mass spectrometry analyses were performed using a time-of-
flight mass spectrometer equipped with an electrospray ion source
(34) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1994,
101, 9783–9792.
(24) Klaui, W.; Song, C.-E. Inorg. Chem. 1989, 28, 3845–3849.
(25) Rauhut, M. M.; Currier, H. A.; Wystrach, V. P. J. Org. Chem. 1961,
26, 5133–5135.
(35) Minori, A.; Sayaka, M.; Takahito, N.; Kimihiko, H. Chem. Phys. 2005,
311, 129–137.
(36) Xia, F.; Chen, J.; Cao, Z. X. Chem. Phys. Lett. 2006, 418, 386–391.
Inorganic Chemistry, Vol. 47, No. 11, 2008 4793

Gallo et al.
[(PHCy2)Pt(µ-PCy2)]2(Pt-Pt) (2).6 A solution of dicyclohexyl-
phosphane (14.4 mg, 0.73 mmol) in toluene (2 mL) was added to
a yellow-orange solution of 1 (87.0 mg, 0.073 mmol) in toluene (3
mL), and the mixture was stirred at 50 °C for 3 h. After the solution
was cooled to room temperature and concentrated to 2 mL, it was
stored at -18 °C for 1 month in order to precipitate the desired
product as an orange solid. The solid was filtered off at -20 °C,
washed with ice-cold n-pentane, and dried in vacuo. The yield (15
mg, 17%) is believed to be limited by isolation and not by conversion.
Attempts to purify 2 by selective extraction of P(O)HCy2 with methanol
(other solvents, such as toluene, THF, and even alkanes, were
unsuitable) were unsuccessful because addition of methanol caused
the decomposition of 2.
195Pt{1H} NMR (C6D6, δ): -4765 [dddd, Pt(1), 1JPt(1),P(1) ) 4349
1
2
2
Hz, JPt(1),P(2) ) 4243 Hz, JPt(1),P(3) ) 63 Hz, JPt(1),P(4) ) 102
Hz, 1JPt(1),Pt(2) ) 72 Hz], -5246 [dddd, Pt(2), 1JPt(2),P(1) ) 2989 Hz,
1
1
2JPt(2),P(2) ) 120 Hz, JPt(2),P(3) ) 3013 Hz, JPt(2),P(4) ) 3682 Hz,
1JPt(1),Pt(2) ) 72 Hz].
When the reaction was carried out in toluene at 50 °C for 2 h
using a 2-fold excess of PCy3, in addition to 5 the resulting mixture
contained PHCy2, PCy3, P(O)HCy2, and a significant amount (20%
yield) of 7, which was selectively precipitated upon cooling of the
concentrated toluene solution at -20 °C. The following spectro-
scopic data were obtained for 7:
syn-[(PHCy2){KP-P(O)Cy2}Pt(µ-PCy2)(µ-H)Pt(PHCy2){KP-
P(O)Cy2}](Pt-Pt)·2H2O (4·2H2O). Solid 1 (90 mg, 0.075 mmol)
was added to a solution of dicyclohexylphosphane oxide (90 mg,
0.42 mmol) in toluene (0.5 mL), and the mixture was stirred at 50
°C. After 2 h of reaction, the mixture was cooled to room
temperature, and aqueous NaOH (7 mg in 3 mL) was added; this
sequestrated the excess P(OH)Cy2, causing the precipitation of a
pale-yellow solid. The product was isolated by filtration, washed
with n-hexane, redissolved in CH2Cl2, and dried over Na2SO4.
Filtration and evaporation of the solvent under high vacuum yielded
76 mg of pure 4·2H2O (70% yield) as an off-white solid. The
complex is stable in air, soluble in halogenated solvents and
methanol, and insoluble in toluene and n-hexane. Anal. Calcd for
C60H117O4P5Pt2 (4·2H2O): C, 49.78; H, 8.15. Found: C, 50.11; H,
8.22.
HRMS(+) (toluene/CH3CN): exact mass for 7, 1344.6853 Da;
found for [M + H]+, m/z 1345.6889.
IR (KBr) νj (cm-1): 2924 vs, 2848 vs, 1447 vs, 1328 w, 1263 m,
1175 m, 1109 m, 1004 s, 916 w, 888 w, 849 m, 817 m, 733 m, 521 m.
1
2
31P{1H} NMR (C6D6, δ): 234.8 (t, JP,Pt ) 2603 Hz, JP,P ) 52
1
2
3
Hz, µ-PCy2,), 57.8 (t, JP,Pt ) 4850 Hz, JP,P ) 52 Hz, JP,P ) 65
Hz, PCy3).
1
195Pt{1H} NMR (C6D6, δ): -5554 (dt, JPt,PCy ) 4850 Hz,
3
1JPt,µ-PCy ) 2603 Hz).
2
HRMS(+) (CHCl3/CH3CN): exact mass for 4, 1410.6724 Da;
found for [M + H]+, m/z 1411.6851.
IR (KBr) νj (cm-1): 2924 s, 2848 s, 2310 w (P-H), 1636 w
(Pt-H-Pt), 1447 s, 1348 w, 1328 w, 1292 w, 1262 s, 1191 w,
1178 w, 1104 s, 1041 s (PdO), 917 w, 886 w, 849 m, 802 m,
733 m, 575 w, 541 m, 519 m, 462 m, 407 w, 380 w, 302 w, 254 m.
1H NMR (CDCl3, δ): 5.01 [m, H(3), 1JH,P ) 330 Hz, 2JH,Pt ) 60
Hz], -5.06 [m, H(1), 2JH(1),P(3) ) 68 Hz, 2JH(1),P(1) ) 14 Hz, 2JH(1),P(2)
[(PHCy2)Pt(µ-PCy2){K2P,S-µ-P(S)Cy2}Pt(PHCy2)](Pt-Pt) (8).
Solid 1 (72 mg, 0.060 mmol) was added to a solution of
dicyclohexylphosphane sulfide (14 mg, 0.060 mmol) in toluene (2.0
mL), and the mixture was stirred at 50 °C for 3 h. After reaction,
the solvent was removed under reduced pressure, and the residue
was washed with methanol (3 × 1 mL) and dried under vacuum to
give 64 mg of 8 (88% yield). The complex is stable in air in the
solid state, very soluble in dichloromethane, toluene, and n-hexane,
and scarcely soluble in methanol. Anal. Calcd for C48H90P4SPt2:
C, 47.51; H, 7.48; S, 2.64. Found: C, 47.11; H, 7.59; S, 2.60.
HRMS(+) (toluene/CH3CN): exact mass for C48H90P4SPt2,
1212.5009 Da; found for [M + H]+, m/z 1213.4830.
1
) 7 Hz, JH,Pt ) 571 Hz].
1
31P{1H} NMR (CDCl3, δ): 125.0 [t, P(1), JP,Pt ) 1173 Hz,
2JP(1),P(2) ) 254 Hz], 79.6 [d, P(2), JP,Pt ) 2619 Hz, JP(2),P(1)
)
1
2
1
254 Hz], 4.2 [br, P(3), JP,Pt ) 3952 Hz].
195Pt{1H} NMR (CDCl3, δ): -5464 (m, br).
Reaction of 1 with PCy3. A solution of tricyclohexylphosphane
(25 mg, 0.089 mmol) in THF (4 mL) was added to a solution of 1
(100 mg, 0.083 mmol) in THF (4 mL) at room temperature, and
the mixture was stirred for 6 h. The resulting orange reaction
mixture contained 5, PHCy2, and a small amount of PCy3, as
ascertained by multinuclear NMR spectroscopy. An HRMS(+)
analysis performed on the orange solid obtained after evaporation
of the solvent under vacuum showed a peak at m/z 1279.6074
that was ascribable to [5 + H]+ (the exact mass calculated for
C54H100OP4Pt2 is 1278.6020 Da). All attempts to separate 5 from
the phosphanes were unsuccessful (Figure S5 in the Supporting
Information). The following spectroscopic data were obtained
for 5:
IR (nujol) νj (cm-1): 2246 w (P-H), 2310 w (P-H), 545 s (PdS).
1H NMR (400 MHz, C6D6, 295 K): δ ) 5.45 [m, H(2), 1JH(2),P(4)
) 305 Hz, 2JH(2),Pt(2) ) 24 Hz], 4.91 [m, H(1), 1JH(1),P(2) ) 318 Hz,
2JH(1),Pt(1) ) 89 Hz].
31P{1H} NMR (161 MHz, C6D6, 295 K): δ ) 140.8 [ddd, P(1),
2JP(1),P(2) ) 44 Hz, 2JP(1),P(3) ) 246 Hz, 2JP(1),P(4) ) 50 Hz, 1JP(1),Pt(1)
1
2
) 3794 Hz, JP(1),Pt(2) ) 3234 Hz], 38.8 [d, P(3), JP(3),P(1) ) 246,
1JP(3),Pt(2) ) 2626 Hz, 2JP(3),Pt(1) ) 255 Hz], 13.7 [dd, P(4), 2JP(4),P(1)
) 50 Hz, JP(4),P(2) ) 133 Hz, JP(4),Pt(2) ) 3503 Hz, JP(4),Pt(1)
3
1
2
)
1
2
2
3
1H NMR (C6D6, δ): 5.64 [m, H(1), JH,P ) 303 Hz, JH,Pt ) 43
100 Hz], 8.9 [dd, P(2), JP(2),P(1) ) 44 Hz, JP(2),P(4) ) 133 Hz,
2
Hz].
1JP(2),Pt(1) ) 3922 Hz, JP(2),Pt(2) ) 124 Hz].
2
31P{1H} NMR (C6D6, δ): 126.7 [ddd, P(1), JP(1),P(2) ) 52 Hz,
195Pt{1H} NMR (86 MHz, C6D6, 295 K, δ): -5218 [dddd, Pt(1),
2JP(1),P(3) ) 225 Hz, 2JP(1),P(4) ) 50 Hz, 1JP(1),Pt(1) ) 4349 Hz, 1JP(1),Pt(2)
) 2989 Hz], 97.7 [dd, P(3), 2JP(3),P(1) ) 225 Hz, 2JP(3),P(2) ) 27 Hz,
1JP(3),Pt(2) ) 3013 Hz, 2JP(3),Pt(1) ) 63 Hz], 41.9 [ddd, P(2), 2JP(2),P(1)
1JPt(1),P(1) ) 3794 Hz, JPt(1),P(2) ) 3922 Hz, JPt(1),P(3) ) 255 Hz,
1
2
2JPt(1),P(4) ) 100 Hz, JPt(1),Pt(2) ) 190 Hz], -5376 [dddd, Pt(2),
1
1JPt(2),P(1) ) 3234 Hz, JPt(2),P(2) ) 124 Hz, JPt(2),P(3) ) 2626 Hz,
2
1
2
3
1
1
) 52 Hz, JP(2),P(3) ) 27 Hz, JP(2),P(4) ) 111 Hz, JP(2),Pt(1) ) 4243
1JPt(2),P(4) ) 3503 Hz, JPt(1),Pt(2) ) 190 Hz].
Hz, 2JP(2),Pt(2) ) 120 Hz], 15.4 [dd, P(4), 2JP(4),P(1) ) 50 Hz, 3JP(4),P(2)
X-ray Crystallography. Crystal data, parameters for intensity
data collection, and convergence results for 1 and 4·2H2O are
1
2
) 111 Hz, JP(4),Pt(2) ) 3682 Hz, JP(4),Pt(1) ) 102 Hz].
4794 Inorganic Chemistry, Vol. 47, No. 11, 2008

ReactiWity of a Phosphinito-Bridged PtI-PtI Complex
1, split positions for the atoms in the C19-C24 cyclohexyl ring
were refined. In 4·2H2O, the hydride H and the hydrogen atoms
associated with the water molecules were located using difference
Fourier maps; the former was refined isotropically, whereas the
latter were treated as riding on the water oxygens. All of the other
hydrogen atoms were calculated in idealized positions and treated
as riding on the closest non-hydrogen atom.
compiled in Table 3.37 Diffraction-quality crystals were grown from
slow evaporation of THF/n-hexane (1) and C6D6/n-hexane (4·2H2O)
mixtures. Data were collected using Mo KR radiation (graphite
monochromator, λ ) 0.71073 Å) on a Bruker D8 goniometer with
SMART CCD area detector on crystals having approximate
dimensions of 0.27 × 0.23 × 0.17 mm (1) and 0.36 × 0.19 ×
0.14 mm (4·2H2O). Multiscan absorption corrections38 (minimum
and maximum transmissions, respectively, of 0.30 and 0.44 for 1
and 0.30 and 0.57 for 4·2H2O) were applied before averaging of
symmetry-equivalent data (Rint ) 0.0596 and 0.0493 for 1 and
4·2H2O, respectively). The structures were solved using direct
methods39 and refined using full-matrix least-squares on F2.40 In
Acknowledgment. We thank Dr. T. Repo and Dr. M.
Räisänen (University of Helsinki) for the HR ESI-MS
analyses and a referee for valuable comments. The Italian
MiUR is gratefully acknowledged for financial support.
Supporting Information Available: 31P{1H} EXSY spectrum
of the mixture obtained after stirring of equimolar amounts of 1
and PHCy2 for 1 h (Figure S1), 31P{1H} NMR spectrum of 2 (Figure
S2), 1H-195Pt HMQC and HRMS(+) spectra of 4 (Figures S3 and
S4, respectively), 31P{1H} NMR spectrum of the reaction mixture
after 6 h of reaction of 1 with PCy3 (Figure S5), 1H-195Pt HMQC,
195Pt{1H} NMR, and HRMS(+) spectra of 5 (Figures S6-S9,
respectively), 31P{1H} NMR and HRMS(+) spectra of 7 (Figures
S10 and S11, respectively), 1H-195Pt HMQC and HRMS(+) spectra
of 8 (Figures S12 and S13, respectively), and crystallographic data
in CIF format for the structural analyses of 1 and 4·2H2O. This
materialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.
(37) Crystallographic data (excluding structure factors) for 1 and 4·2H2O
have been deposited with the Cambridge Crystallographic Data Centre
as supplementary publications CCDC 657269 (1) and CCDC 657270
(4·2H2O). Copies of the data can be obtained free of charge upon
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K.
[Fax: int. code +44(1223)336–033. E-mail: deposit@ccdc.cam.
ac.uk.].
(38) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Göttingen: Göttingen,
Germany, 1996.
(39) Sheldrick, G. M. SHELXS97, Program for Crystal Structure Solution;
University of Göttingen: Göttingen, Germany, 1997.
(40) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Göttingen: Göttingen, Germany, 1997.
IC800045U
Inorganic Chemistry, Vol. 47, No. 11, 2008 4795