Site selectivity in the protonation of a phosphinito bridged Pt I-PtI complex: A combined NMR and density-functional theory mechanistic study

Inorg. Chem. 2008, 47, 9779-9796

Site Selectivity in the Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex: a

Combined NMR and Density-Functional Theory Mechanistic Study^†

Mario Latronico,^‡Flavia Polini,^‡Vito Gallo,^‡Piero Mastrorilli,*^,‡Beatrice Calmuschi-Cula,^§

Ulli Englert,^§Nazzareno Re,^|Timo Repo,^⊥and Minna Ra¨isa¨nen^⊥

Dipartimento di Ingegneria delle Acque e di Chimica del Politecnico di Bari, Via Orabona 4,

I-70125 Bari, Italy, Institut fu¨r Anorganische Chemie der RWTH, Landoltweg 1, D-52074 Aachen,

Germany, Dipartimento di Scienze del Farmaco, UniVersita` “G. d’Annunzio”, Via dei Vestini 31,

06100 Chieti, Italy, and Laboratory of Inorganic Chemistry, Department of Chemistry, UniVersity

of Helsinki, P.O. Box 55, FIN-00014 Helsinki, Finland

Received March 20, 2008

The protonation of the dinuclear phosphinito bridged complex [(PHCy₂)Pt(µ-PCy₂){κ²P,O-µ-P(O)Cy₂}Pt(PHCy₂)] (Pt-Pt)

(1) by Brønsted acids affords hydrido bridged Pt-Pt species the structure of which depends on the nature and on the

amount of the acid used. The addition of 1 equiv of HX (X ) Cl, Br, I) gives products of formal protonation of the Pt-Pt

bond of formula syn-[(PHCy₂)(X)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){κP-P(O)Cy₂}] (Pt-Pt) (5, X ) Cl; 6, X ) Br; 8, X ) I),

containing a Pt-X bond and a dangling κP-P(O)Cy₂ligand. Uptake of a second equivalent of HX results in the protonation

of the P(O)Cy₂ligand with formation of the complexes [(PHCy₂)(X)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){κP-P(OH)Cy₂}]X (Pt-Pt)

(3, X ) Cl; 4, X ) Br; 9, X ) I). Each step of protonation is reversible, thus reactions of 3, 4, with NaOH give, ﬁrst, the

corresponding neutral complexes 5, 6, and then the parent compound 1. While the complexes 3 and 4 are indeﬁnitely

stable, the iodine analogue 9 transforms into anti-[(PHCy₂)(I)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂)(I)] (Pt-Pt) (7) deriving from

substitution of an iodo group for the P(OH)Cy₂ligand. Complexes 3 and 4 are isomorphous crystallizing in the triclinic

¯

space group P1 and show an intramolecular hydrogen bond and an interaction between the halide counteranion and the

POH hydrogen. The occurrence of such an interaction also in solution was ascertained for 3 by ³⁵Cl NMR. Multinuclear

1

NMR spectroscopy (including ³¹P- H HOESY) and density-functional theory calculations indicate that the mechanism of

the reaction starts with a prior protonation of the oxygen with formation of an intermediate (12) endowed with a six

membered Pt¹-X· · ·H-O-P-Pt²ring that evolves into thermodynamically stable products featuring the hydride ligand

bridging the Pt atoms. Energy proﬁles calculated for the various steps of the reaction between 1 and HCl showed very

low barriers for the proton transfer and the subsequent rearrangement to 12, while a barrier of 29 kcal mol^-1was found

for the transformation of 12 into 5.

Introduction

bridged diplatinum complex toward several Brønsted acids

and on the mechanistic study of the consequent protonations.

Dialkylphosphinito bridged homodinuclear complexes are

interesting compounds as the differentiation of the two metal

centers brought about by the combination of a soft donor

(P) and a hard ligand (O) may result in peculiar reactivity.

In this regard we started a project aimed to investigate

the reactivity of [(PHCy₂)Pt(µ-PCy₂){κ²P,O-µ-P(O)Cy₂}-

Pt(PHCy₂)] (Pt-Pt) (1),²the ﬁrst unsymmetrical phosphinito

bridged Pt complex, toward several types of reactants. We

have recently reported that 1 reacts with nucleophiles such

The site selectivity in proton transfer reactions has attracted

considerable interest in the recent literature.¹In this contribu-

tion, we report on the reactivity of a dialkylphosphinito

†

Dedicated to Prof. Cosimo Francesco Nobile on occasion of his 70th

birthday.

*

To whom correspondence should be addressed. E-mail:

p.mastrorilli@poliba.it.

‡

Dipartimento di Ingegneria delle Acque e di Chimica del Politecnico

di Bari.

§

Institut fu¨r Anorganische Chemie der RWTH.

University of Helsinki.

Universita` “G. d’Annunzio”.

⊥

|

(1) Evrard, D.; Cle´ment, S.; Lucas, D.; Hanquet, B.; Knorr, M.; Strohmann,

C.; Decken, A.; Mugnier, Y.; Harvey, P. D. Inorg. Chem. 2006, 45,

1305–1315; and references cited therein.

(2) Gallo, V.; Latronico, M.; Mastrorilli, P.; Nobile, C. F.; Suranna, G. P.;

Ciccarella, G.; Englert, U. Eur. J. Inorg. Chem. 2005, 4607–4616.

10.1021/ic800508t CCC: $40.75  2008 American Chemical Society

Inorganic Chemistry, Vol. 47, No. 21, 2008 9779

Published on Web 10/01/2008

Latronico et al.

as PHCy₂, PCy₃, P(S)HCy₂, and P(O)HCy₂giving substitu-

tion or addition products depending on the nucleophile³

(Scheme 1). It has been underlined that the oxygen end of

the µ-phosphinito ligand can exercise control over the sites

of substitution, as demonstrated in the cases of dinuclear Ru

complexes.⁴In our case such a control resulted in an attack

of the incoming nucleophiles [PHCy₂, PCy₃, P(S)HCy₂] on

1 exclusively to the O-bound Pt atom, which behaves as the

most electrophilic center of the molecule. However, the

reaction of 1 with P(O)HCy₂led selectively to the hydrido

bridged dinuclear complex syn-[(PHCy₂){κP-P(O)Cy₂}Pt(µ-

PCy₂)(µ-H)Pt(PHCy₂){κP-P(O)Cy₂}] (Pt-Pt) (2) which

represents the product of formal protonation of the Pt^I-Pt^I

bond by a relatively weak acid [the P(OH)Cy₂tautomeric

form of the dicyclohexylphosphane oxide]. These ﬁndings

indicated that 1 behaves as an amphiphilic molecule, capable

of reacting with both nucleophiles and electrophiles, and such

view was conﬁrmed by a thorough density-functional theory

(DFT) study which showed that 1 possesses a strongly

electrophilic center (the O-bound Pt¹) and four nucleophilic

centers (in increasing order of nucleophilicity: P⁴, Pt², P²,

and O) as inferred from the Mulliken gross atomic charges

outlined in Figure 1.³

The protonation of the Pt^I-Pt^Ibond that occurred when 1

was reacted with P(O)HCy₂seems to be in contrast with the

DFT predictions, since the order of nucleophilicity indicates

the O (which remains deprotonated) as the most basic site

of 1. This seeming discrepancy prompted us to study the

protonation of 1 by several Brønsted acids and to gain

insights into the mechanism of proton transfer from the acid

to the ﬁnal product.

The elucidation of factors governing the site selectivity

in reactions between polynuclear transition metal complexes

and electrophilic reagents is a matter of long standing interest,

especially when the complexes are phosphanido bridged

dinuclear species featuring a metal-metal bonds.⁵As far as

protonation reactions are concerned, a wealth of synthetic

and mechanistic studies dealing with the reaction of H⁺with

transition metal hydrides showed the formation of “uncon-

ventional” intramolecular and intermolecular hydrogen bonds

involving the hydride ligand as a proton acceptor.⁶

The ﬁrst report on H⁺attack on dinuclear metal complexes

dates back to 1962 and deals with the formation of a series

of homo and heterodinuclear carbonyl cyclopentadienyl

clusters in which the two metals are linked by a metal-metal

bond and are bridged by a hydride ligand.⁷The formation

of a bridging hydride by protonation of the metal-metal

bond is the rule for complexes not bearing bridging phos-

phanido groups as reported in the cases of [Et₄N][Cr₂-

(CO)₁₀],⁸[CpM(µ-CO)(CO)]₂(M

)

Fe⁹or Ru¹⁰),

[µ-(SCH₃)Fe(CO)₂L]₂[L ) P(CH₃)_3-x(C₆H₅)_x],¹¹(µ-CO)-

[CpRh(CO)]₂,¹²(µ-CH₂)[CpRh(CO)]₂,¹³[Cp₂Re₂(CO)₅],¹⁴

[Rh₂Cl₂(µ-CO)(µ-dppm)],¹⁵and [Cp₂Rh₂(µ-CO)(µ-dppm)].¹⁶

On the contrary, a variety of protonation products can be

obtained when the two metals are bridged by a phosphanido

group. Bridging hydrides are formed by protonation of

[Fe₂(µ-A)(µ-A′)(CO)₄L₂] [A ) A′) PPh₂, PMe₂; A ) SPh,

A′ ) PPh₂; L ) P(CH₃)_3-x(C₆H₅)_x],¹⁷[NEt₄][(CO)₄Mn(µ-

PTol₂)Mo(CO)₂Cp] (Mn-Mo),¹⁸[Cp₂Co₂(µ-PR₂)₂] (PR₂)

1

PMe₂, PPh₂, PEt₂, PMePh, /₂Ph₂P(CH₂)_nPPh₂, n ) 2 or

3),¹⁹[CpMo(µ-PPh₂)CO)]₂,²⁰[m(µ-PPh₂)Pt(PPh₃)₂] [m )

W(CO)₂Cp, Mn(CO)₄, Co(CO)₃],²¹[Cp*Rh(µ-PMe₂)]₂,²²or

[Cp(CO)₂Mo(µ-PPh₂)Pt(CO)(PPh₃)].²³Interestingly, the re-

lated complexes [Cp(CO)₂W(µ-PPh₂)Pt(CO)(PPh₃)] and

[Cp(CO)₂W(µ-PCy₂)Pt(CO)(PCy₂H)] give, the ﬁrst proto-

nation directly at the tungsten to give [Cp(CO)₂(H)W(µ-

PPh₂)Pt(CO)(PPh₃)]⁺,²³the second both isomeric hydrides

[Cp(CO)₂W(µ-PCy₂)(µ-H)Pt(CO)(PCy₂H)]⁺and [Cp(H)(CO)₂-

W(µ-PCy₂)Pt(CO) (PCy₂H)]⁺of which the former is the

major product.²⁴

The protonation of the dianion [(CO)₃Fe(µ-PPh₂)₂Fe-

(CO)₃]^2-(Fe-Fe) affords, as main product, [(CO)₂HFe(µ-

PPh₂)₂(µ-CO)Fe(CO)₃]^-in which the hydride is terminally

bonded and the metal-metal bond is broken.²⁵In the case

of the related anions [(CO)₃Fe(µ-PPh₂)(µ-CO)₂Fe(CO)₂-

(PHPh₂)]^-(Fe-Fe) or [(CO)₄W(µ-PPh₂)₂Rh(CO)(PPh₃)]^-

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9780 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

Scheme 1. Reaction of 1 with Nucleophiles

(W-Rh) the attack of H⁺results in the terminal hydride

species [(CO)₃HFe(µ-PPh₂)Fe(PHPh₂)(CO)₃] (Fe-Fe)²⁶and

[(CO)₄W(µ-PPh₂)₂Rh(CO)(H)(PPh₃)] (W-Rh)²⁷without rup-

ture of the metal-metal bond. In the case of [(CO)₄W(µ-

PPh₂)₂Os(CHO)(CO)₂L]^-(L ) PMePh₂, PMe₃) one of the

bridging phosphanides is protonated to the corresponding

phosphane, giving the neutral complex [(CO)₄W(µ-PPh₂)Os-

(PHPh₂)(CHO)(CO)₂L] (L ) PMePh₂, PMe₃).²⁸The disrup-

tion of the dinuclear unit is the result of the protonation

of bridging phosphanides in [(CO)₄M(µ-PPh₂)M(CO)₄-

(PHPh₂)]^-(M ) W or Mo), which gives a mixture of

cis-[M(CO)₄(PHPh₂)₂] and [M(CO)₅(PHPh₂)]²⁹and in

[(PHCy₂)Pd(µ-PCy₂)(µ-η³-C₃H₅)Pd(PHCy₂)] which gives,

upon reaction with PhSH or PhSeH, the mononuclear

complexes trans-[Pd(EPh)₂(PHCy₂)₂] (E ) S or Se, respec-

tively).³⁰It is noteworthy that the dimer [(PH^tBu₂)-

Pd(µ-P^tBu₂)₂Pd(PH^tBu₂)] readily protonates to give the

unusual cationic Pd^Icomplex [(PH^tBu₂)Pd(µ-P^tBu₂)(µ-PH^tBu₂)-

Pd(PH^tBu₂)] containing a Pd-H-P bridging unit.³¹The

related agostic type phosphane bridged complexes [Mo₂Cp₂-

(µ-PR₂)(µ-κ²-HPR₂)(CO)₂]⁺(R ) Cy, Et) were recently

reported by Ruiz and co-workers.^5a

of [(PH^tBu₂)₂Pt(µ-H)(µ-P^tBu₂)Pt(H)(PH^tBu₂)]⁺,³²whereas

the Pt^Idimer [(PH^tBu₂)Pt(µ-P^tBu₂)]₂gives the terminal

hydrido complex [(PH^tBu₂)Pt(µ-P^tBu₂)₂Pt(H)(PH^tBu₂)]⁺by

attack of H⁺on one of the Pt atoms.³³In the case of

[(PH^tBu₂)Pt(µ-P^tBu₂)₂Pt(CO)],thekineticproduct[(PH^tBu₂)Pt(µ-

P^tBu₂)₂Pt(H)(CO)]⁺is converted by an external base into

the thermodynamically favored form [(PH^tBu₂)(H)Pt(µ-

P^tBu₂)₂Pt(CO)]⁺.³³The “mixed bridge” complex [(PPh₃)Pt(µ-

PPh₂)(µ-o-C₆H₄PPh₂)Pt(PPh₃)] reacts with 1 equiv of acid

giving the cation [(PPh₃)Pt(µ-H)(µ-PPh₂)(µ-o-C₆H₄PPh₂)-

Pt(PPh₃)]⁺or with 2 equiv of acid to give [(PPh₃)(solvent)Pt(µ-

H)(µ-PPh₂)Pt(PPh₃)₂]²⁺.^5bFinally, the protonation of [Pt(µ-

P^tBu₂)(η²-C₂H₄)]₂affords [Pt₂(µ-P^tBu₂)(µ-PH^tBu₂)(η²-

C₂H₄)₂]⁺with a P-H-M agostic proton in rapid exchange

with those of the adjacent ethylene molecule.³⁴

In the light of the rich chemistry summarized above,

complex 1, featuring both a bridging phosphanido and

dialkylphosphinito groups, represents an ideal benchmark for

a study of the site selectivity in the electrophilic attack on a

polynuclear complex endowed with metal-metal bonds. In

fact, besides the previously discussed protonation sites (i.e.,

the metal atoms, the metal-metal bond, and the metal-

phosphorus bond) 1 is endowed with a further target site

represented by the phosphinito oxygen.

The only previous examples dealing with protonation of

dinuclear phosphanido bridged diplatinum complexes with

strong acids have been reported by Leoni et al. and by

Braunstein et al. It has been found that addition of triﬂic

acid to [Pt(µ-P^tBu₂)(H)(P^tBu₂H)]₂results in the formation

Results and Discussion

Synthesis of Cationic Complexes by Reactions with

HX (X ) Cl, Br). The reactions between 1 and excess HCl

(gaseous or aqueous) or HBr (gaseous or aqueous) in

n-hexane led to the new hydrido bridged complexes 3 and 4

in isolated yields higher than 90% (Scheme 2). As the

products 3 and 4 share the same spectroscopic features, we

will only discuss those of 3 in the following section.

The ³¹P{¹H} NMR spectrum of 3 (Figure 2) resembles

that of the parent complex 1, consisting of four mutually

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Inorganic Chemistry, Vol. 47, No. 21, 2008 9781

Latronico et al.

Figure 1. Mulliken gross atomic charges for the Pt₂P₂O core of complex

1.

Scheme 2. Protonation of 1 with HCl or HBr

Figure 2. ³¹P{¹H} NMR spectrum of 3 (CD₂Cl₂, 295 K).

Figure 3. ¹⁹⁵Pt{¹H} NMR spectrum of 3 (CD₂Cl₂, 295 K).

coupled signals (all ﬂanked by ¹⁹⁵Pt satellites) at δ 155.3

(P²), δ 118.8 (P⁴), δ 10.8 (P¹), and δ 5.2 (P³).

The ¹⁹⁵Pt signals were found at δ -5379 (Pt¹) and δ

-5621 (Pt²) (Figure 3). Differently from the parent com-

pound 1, which did not show any ¹⁹⁵Pt-¹⁹⁵Pt coupling, a

J_Pt,Ptof 845 Hz was directly extracted from the ¹⁹⁵Pt{¹H}

NMR spectrum.

The presence of the bridging hydride is unequivocally

demonstrated by the ¹H NMR spectrum showing a multiplet

centered at δ -5.61 ﬂanked by three sets of ¹⁹⁵Pt satellites,

while a broad signal at δ 10.8³⁵is diagnostic for the presence

of the POH moiety. The attribution of the hydride NMR

features was made using the data directly extractable from

the H-¹⁹⁵Pt HMQC spectrum of 3 (Figure 4). The hydro-

1

Figure 4. H-¹⁹⁵Pt HMQC spectrum of 3 (hydride region, CD₂Cl₂, 295

gens directly bound to P fall at δ 4.58 (P¹H) and δ 5.12

K).

1

(P³H) and were attributed by the H-³¹P HMQC spectrum

attributed to Pt²compared to that of Pt¹(Figure 3). A possible

interaction between the cationic complex and the chloride

counteranion should be also taken into account. We have

previously demonstrated that the chloride counteranion

strongly interacts with the H-P of cationic Pt^IIcomplexes

such as [Pt(PHCy₂)₃Cl]Cl³⁶and [Pt(PHCy₂)₂(κ²S,S′-

PS₂Cy₂)]Cl³⁷and that ³⁵Cl NMR spectroscopy is a useful

tool to detect the presence of “free” chlorides in solution.³⁸

Interestingly, the ³⁵Cl NMR spectrum of 3 in CD₂Cl₂gave

no signal even in the presence of methanol, thus suggesting

that complex 3 behaves as an intimate ion couple not only

in solvents with low dielectric constant (CD₂Cl₂) but also in

the presence of a classic hydrogen bond breaker such as

methanol. Given that PH · · · Cl^-interactions are easily

(Supporting Information, Figure S1). Of these signals, that

at δ 4.58 is sharper (∆ν_1/2are 46 Hz for P¹H and 92 Hz for

P³H) and shows a signiﬁcantly higher coupling constant with

2

the vicinal Pt atom (²J_H(1),Pt(1)) 158 Hz vs J_H(2),Pt(2)) 29

Hz). Similar features were found for the complexes described

hereafter having the same scaffold (compounds 4, 5, 6, 8, 9,

11, 15, 16, 19).

The broadness of the signals attributed to P³and P⁴might

be explainable in terms of hindered rotation about the P-Pt

bonds because of the steric hindrance brought about by the

cyclohexyl groups.³⁶The dynamic behavior alleged for 3

can be held responsible also for the broadness of the multiplet

(35) The chemical shift of this signal was found sensitive to the presence

of traces of moisture in the deuterated solvent.

(36) Broadening of ³¹P NMR signals due to hindered rotation occurs in

the related phosphanido bridged complexes [(Cy₂PH)(Cl)Pt(µ-

PCy₂)Pt(Cy₂PH)₂] (Pt-Pt) [(a) Mastrorilli, P.; Nobile, C. F.; Fanizzi,

F. P.; Latronico, M.; Hu, C.; Englert, U. Eur. J. Inorg. Chem. 2002,

1210–1218.]andsyn-[(Cy₂PH)(kP-POCy₂)Pt(µ-PCy₂)(µ-H)Pt(Cy₂PH)(kP-

POCy₂)] (Pt-Pt) [(b) Ref 3]. The hindered rotation about the P-Pt bonds

of dicyclohexylphosphane derivatives is discussed in (c) Mastrorilli,

P.; Nobile, C. F.; Latronico, M.; Gallo, V.; Englert, U.; Fanizzi, F. P.;

Sciacovelli, O. Inorg. Chem. 2005, 44, 9097–9104.

(37) Gallo, V.; Latronico, M.; Mastrorilli, P.; Nobile, C. F.; Ciccarella,

G.; Englert, U. Eur. J. Inorg. Chem., 2006, 2634–2641.

(38) NMR signals of quadrupolar nuclei such as ³⁵Cl are strongly affected

by the symmetry of the surrounding electronic cloud. Thus, when a

chloride counteranion of a metal complex forms an intimate ion couple,

the ³⁵Cl NMR signal usually does not emerge from the baseline unless

a solvent able to disrupt the ion couple and to form a nearly symmetric

solvation sphere is added.

9782 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

Table 1. Interatomic Distances (Å) and Angles (deg) for D-H· · ·A

Hydrogen Bonds

D-H· · ·A moiety

D-H H· · ·A D· · ·A D-H· · ·A

O1-H1a^a· · ·Cl2 for 3·3CH₂Cl₂0.98

2.12 2.961(8)

2.28 3.266(8)

2.27 3.100(5)

2.22 3.190(6)

143

128

141

127

P3-H3· · ·O1 for 3·3CH₂Cl₂1.32

O1-H1a^a· · ·Br2 for 4·3CH₂Cl₂0.98

1.32

P3-H3· · ·O1 for 4·3CH₂Cl₂

^aH1a is related to H1 by the symmetry operation x, -1 + y, z.

0.0625(3) [0.0629(3)] Å for Pt¹and 0.0350(4) [0.0108(3)]

Å for Pt². The coordination planes around each platinum are

almost coplanar with a dihedral angle of 8.70(9) [7.61(7)]°.

The P-H bond of the P¹HCy₂points toward the bridging

phosphanide, while the P-H bond of the P³HCy₂points

toward the P⁴(OH)Cy₂, forming an intramolecular hydrogen

bond (see Figures 5 and Supporting Information, Figure S24)

with the oxygen. A hydrogen bond is present also between

the Cy₂P⁴OH hydrogen and the neighboring symmetry

equivalent Cl^-[Br^-] counteranion, thus corroborating our

deductions on POH · · ·Cl^-interactions in solution stemming

from ³⁵Cl NMR experiments. Table 1 shows the main

features of the hydrogen bonds for both structures. Passing

from chloride to bromide acceptors the hydrogen-bond

distance increases by 0.15 Å.⁴²The O · · · Cl and H · · ·Cl

distances found for 3 · 3CH₂Cl₂are comparable to those

found in the crystal structure of [Pt(COMe)(PPh₃){(R,S)-

Ph(HO)PCH₂CH₂P(OH)Ph}]Cl.⁴³

Figure 5. PLATON drawing of 3·3CH₂Cl₂; displacement ellipsoids are

scaled to 30% probability; the solvent molecules and H atoms bonded to

carbon have been omitted for clarity. Interatomic distances (Å) and angles

(deg) [values for 4 · 3CH₂Cl₂in square brackets]: Pt1-P2 2.243(2)

[2.2173(17)]; Pt1-P1 2.280(3) [2.2509(17)]; Pt1-Cl1 2.412(2) [Pt1-Br1

2.4949(8)]; Pt1-H 1.71 [1.70]; Pt2-P3 2.306(3) [2.2764(18)]; Pt2-P4

2.328(3) [2.2915(18)]; Pt2-P2 2.337(3) [2.3050(18)]; Pt2-H 1.69 [1.64];

Pt1-Pt2 2.8778(15) [2.8379(4)]; P2-Pt1-P1 101.63(10) [101.71(6)];

P2-Pt1-Cl1 166.37(9) [P2-Pt1-Br1 165.49(5)]; P1-Pt1-Cl1 91.48(9)

[P1-Pt1-Br1 92.09(5)]; P2-Pt1-Pt2 52.56(7) [52.52(4)]; P1-Pt1-Pt2

153.98(6) [154.07(4)]; Cl1-Pt1-Pt2 114.09(7) [Br1-Pt1-Pt2 113.39(2)];

P2-Pt1-H 84.4 [83.8]; P1-Pt1-H 173.0 [173.9]; Cl1-Pt1-H 82.3

[Br1-Pt1-H 82.2]; P3-Pt2-P4 93.23(9) [92.94(7)]; P3-Pt2-P2 108.01(9)

[107.69(7)]; P4-Pt2-P2 158.60(9) [159.03(6)]; P3-Pt2-Pt1 156.39(7)

[156.55(6)]; P4-Pt2-Pt1 109.64(7) [110.10(4)]; P2-Pt2-Pt1 49.62(6)

[49.76(4)]; P3-Pt2-H 166.9 [168.0]; P4-Pt2-H 77.4 [77.6]; P2-Pt2-H

82.0 [82.3].

Synthesis of Neutral Complexes by Reactions with

HX (X ) Cl, Br). When exactly 1 equiv of HCl or HBr

was taken up by complex 1, the neutral hydrido bridged

complexes 5 or 6 containing the POCy₂ligand instead of

the P(OH)Cy₂formed (Scheme 2). Passing from P(OH)Cy₂

cleaved by methanol,³⁶this result suggests the presence of

a strong interaction of the type POH · · · Cl^-.

in 3-4 to POCy₂in 5-6 caused a high-ﬁeld shift of the ³¹

P

Crystal Structures of 3 and 4. Crystals of 3 and 4 suitable

for X-ray diffraction were obtained from CH₂Cl₂/n-hexane.

Complexes 3 · 3CH₂Cl₂and 4 · 3CH₂Cl₂are isomorphous

NMR signal of about 40 ppm. (Supporting Information,

1

Figures S6 and S9). The hydride H NMR signals of the

neutral complexes 5 and 6 (Supporting Information, Figures

S7 and S10) are low-ﬁeld shifted with respect to those of

their cationic analogues 3 and 4.

In the IR spectrum the bands of Pt-µH, P-H and PdO

stretchings are located at ν ) 1611, 2322, 1088 +1019 cm^-1

for 5 and ν ) 1589, 2324, 1086 +1020 cm^-1for 6. The

Pt-Cl band of 5 was found at 285 cm^-1.

Complexes 5-6 always coexist with variable amounts of

3-4 present when reactions are carried out with less than 2

equiv of hydrohalic acid. In these cases an equilibrium

between the neutral and the cationic forms was ascertained

by ³¹P{¹H} exchange spectroscopy (EXSY) experiments.

Figure 6 shows the ³¹P{¹H} EXSY spectrum of a mixture

of the chloro species 3 and 5. A similar equilibrium between

the neutral dimethylphosphinito complex [(CO)₃Mn(CNR)-

(PMe₃)(POMe₂)] and its protonated form has been recently

described.⁴⁴

j

crystallizing in the triclinic space group P1; the following

discussion of the molecular geometry refers to 3 · 3CH₂Cl₂,

with values for 4 · 3CH₂Cl₂appended in square brackets for

comparison. Each asymmetric unit consists of a complex

molecule and three molecules of CH₂Cl₂, the solvent of

crystallization. The molecular structure of 3 is depicted in

Figure 5; a displacement ellipsoid plot of 4 is provided in

the Supporting Information, Figure S24.

In complex 3 · 3CH₂Cl₂[complex 4 · 3CH₂Cl₂] the two Pt

atoms are linked by a metal-metal bond of 2.8778(15)

[2.8379(4)] Å and bridged by a phosphanide subtending a

Pt-P-Pt angle of 77.82(8) [77.71(6)]°. The elongation of

the Pt-Pt distance caused by protonation [the Pt-Pt

interatomic distance for 1 is 2.5731(16) Å] is consistent with

the transformation of the 2e-2c into a weaker 2e-3c M-M

bond.⁴⁰The presence of the Pt-Pt bond is in line with a

valence electron count of 30 and of a Framework Electron

Count of 6.⁴¹The coordination around the Pt atoms is planar

with a deviation of the metal from the coordination plane of

Pure 5-6 could be obtained by deprotonation of the

cationic counterparts 3-4 with aqueous NaOH in CH₂Cl₂

(or, alternatively, with NaH in toluene). Interestingly, excess

(39) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.

(40) See ref 3 and refs therein.

(41) Aullon, G.; Alemany, P.; Alvarez, S. J. Organomet. Chem. 1994, 478,

75–82.

(42) Steiner, T. Acta Crystallogr. 1998, B54, 456–463.

(43) Powell, J.; Horvath, M. J.; Lough, A. J. Chem. Soc., Dalton Trans.

1996, 1679–1685.

Inorganic Chemistry, Vol. 47, No. 21, 2008 9783

Latronico et al.

Scheme 3. Reaction of 1 with Excess HI

product which was isolated in 70% yield and characterized

as the neutral diiodo hydrido-bridged diplatinum complex 7

(see Scheme 3).

The ³¹P{¹H} spectrum of complex 7 shows three signals

centered at δ 185.7, δ 16.4, and δ 0.9 (Supporting Informa-

tion, Figure S12). The low ﬁeld signal is a dd because of a

phosphanide bridging two unequivalent Pt atoms (¹J_P(2),Pt(1)

1

) 2510 Hz, J_P(2),Pt(2)) 1919 Hz) having a PHCy₂in cis

position (²J_P(2),Pt(1)) 6 Hz) and another PHCy₂in trans

position (²J_P(2),Pt(3)) 321 Hz). Accordingly, 7 shows in the

¹H NMR spectrum a ddd in the hydride region centered at δ

-7.29 ﬂanked by three sets of ¹⁹⁵Pt satellites from which

the J_H,Ptof 361 (with Pt¹) and 799 Hz (with Pt²) were

1

Figure 6. ³¹P{¹H} EXSY spectrum (C₆D₆, 295 K) of the mixture of 3 and

5.

extracted (Supporting Information, Figure S13). The values

of the ¹H-³¹P coupling constants (60, 12, and 9 Hz) conﬁrm

that only one position trans to the hydride is occupied by a

P atom (²J_H,P) 60 Hz).

The iodine analogues of complexes 5 and 3 (complexes 8

and 9, respectively, Scheme 4) were detected by adding

gradually HI_(aq)to a CD₂Cl₂solution of 1 in an NMR tube

and monitoring the reaction course at 295 K with multi-

nuclear NMR (Supporting Information, Figures S15, S16,

S18 and S19).

of base and prolonged reaction times caused a further

dehydrohalogenation that eventually led to complex 1

(Scheme 2).

Although deprotonation of bridging hydrido complexes has

been reported for Co₂,⁴⁵Rh₂,⁴⁶Mo₂,⁴⁷Mo-Mn,⁴⁸Os₃,⁴⁹

Mo-Pt or W-Pt⁵⁰systems, to the best of our knowledge

no example is known to date of a reversible protonation of

a Pt-Pt bond.⁵¹Such a behavior may be favored in the

present case by the possibility of the phosphinite to rebind

the Pt¹restoring the κ²-P,O bridge. The acidity of 5-6

corroborates the view of the Pt-H-Pt moiety as a protonated

Pt^I-Pt^Ifragment rather than a “true” Pt^II-Pt^IIµ-hydride.⁵²

Reaction with HI. The reactivity of 1 toward HI differs

from that observed with HBr or HCl. Carrying out the

reaction of 1 with excess aqueous HI in toluene at 25 °C

results, after 30 min, in the formation of an unexpected

On standing, complex 9 transforms spontaneously into 10⁵³

which, within a few hours, isomerizes completely into the

thermodynamically stable complex 7, namely, the end

product found when the reaction between 1 and excess HI

was carried out in one pot. The retention of stereochemistry

observed in the step 9f10 corresponds to the expected

outcome for a substitution reaction on a square-planar

complex following an associative mechanism.⁵⁴Complex 8

could be isolated in the pure state after reaction of 1 with

exactly an equimolar amount of hydroiodic acid. On the other

hand, pure 9 was obtained by carrying out the reaction of 1

with 2 equiv of HI in dichloromethane and stopping the

reaction as soon as NMR monitoring showed the complete

consumption of 8.

(44) Ruiz, J.; Garcia-Granda, S.; Diaz, M. R.; Quesada, R. Dalton Trans.

2006, 4371–4376.

(45) Werner, H.; Hofmann, W.; Zolk, R.; Dahl, L. F.; Kocal, J.; Ku¨hn, A.

J. Organomet. Chem. 1985, 289, 173–188.

(46) (a) Hermann, W. A.; Plank, J.; Ziegler, M. L.; Balbach, B. J. Am.

Chem. Soc. 1980, 102, 5906–5908. (b) Hermann, W. A.; Plank, J.;

Riedel, D. J. Organomet. Chem. 1980, 190, C47–C50. (c) Hermann,

W. A.; Plank, J.; Guggolz, M. E.; Ziegler, M. L. Angew. Chem., Int.

Ed. Engl. 1980, 19, 651–653. (d) Hermann, W. A.; Plank, J.; Riedel,

D.; Ziegler, M. L.; Weidenhammer, K.; Balbach, B. J. Am. Chem.

Soc. 1981, 103, 63–75.

(47) (a) Petersen, J. L., Jr. Inorg. Chem. 1980, 19, 186–191. (b) Adatia,

T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby, P. R. J. Chem.

Soc., Dalton Trans. 1989, 1555–1564.

Mechanism of the Reaction. The results presented up to

here reveal that the protonation of 1 by HX (X ) Cl, Br, I)

causes the opening of the phosphinito bridge giving rise to

hydrido bridged complexes in which the dicyclohexylphos-

phinito behaves as monodentate ligand on Pt²and the anion

of the acid binds to Pt¹.

Knowing that Pt¹of 1 is susceptible to nucleophilic attack,³

we have ﬁrst tried to determine whether the ﬁrst step of the

(48) Casey, C. P.; Bullock, R. M. Organometallics 1984, 3, 1100–1104.

(49) Colbran, S. B.; Johnson, B. F. G.; Lewis, J.; Sorrell, R. M. J.

Organomet. Chem. 1985, 296, C1–C5.

(50) Powell, J.; Sawyer, J. F.; Smith, S. J. J. Chem. Soc., Chem. Commun.,

1985, 1312–1313.

(51) A spontaneous dehydrochlorination of the bridging hydrido complex

stemming from protonation of [PtCl(dppm)]₂] has been described in

Brown, M. P.; Puddephatt, R. J.; Rashidi, M.; Seddon, K. R. J. Chem.

Soc., Dalton Trans. 1978, 516–522.

(53) Spectroscopic features of 10: ¹H NMR (CDCl₃, δ): 4.71 (m, H(1),

2

¹J_H(1),P(1)) 345 Hz, J_H(1),Pt(1)) 126 Hz), -4.35 (td, H(2), J_H(2),P(2)

) 9 Hz, ²J_H(2),P(1)) 80 Hz, ¹J_H(2),Pt(1)) 436 Hz) ppm. ³¹P{¹H} NMR

1

(CDCl₃, δ): 171.0 (s, P(2), J_P(2),Pt(1)) 2663 Hz), -2.4 (s, P(1),

2

3

¹J_P(1),Pt(1)) 3640 Hz, J_{P(1),Pt(1′)}) 248 Hz, J_P(1),P(1′)) 63 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CDCl₃, δ): -5711 (ddd, Pt(1), ¹J_Pt(1),P(2)) 3981 Hz,

¹J_Pt(1),P(1)) 4334 Hz) ppm.

(52) Similar conclusions were drawn by a DFT study on the related complex

2. See ref 3.

9784 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

Scheme 4. Reaction Course of 1 with HI

Scheme 5. Possible Pathways for the Protonation of 1

reaction with HX was the attack of the halide on 1, with

opening of the phosphinito bridge and thus rendering the

molecule susceptible of proton attack (Scheme 5, path i) or

whether, alternatively, the reaction started with a proton

attack on 1 that results in the formation of the bridging

hydride, followed by coordination of the halide to Pt¹

(Scheme 5, path ii). The contemporary attack of H⁺and X^-

from molecular HX has to be discarded in the light of the

effective reaction that occurs when aqueous HX were used.

To discriminate between paths i and ii we have carried

out the following experiments:

(a) an equimolar mixture of 1 and [Bu₄N]Cl (chosen to

consider the interaction of the chloride with the Pt complex)

was stirred in tetrahydrofuran (THF) at room temperature

but no changes in the multinuclear NMR spectra of the

solution was observed during the 3 days of monitoring. The

same result was obtained using a saturated THF solution of

NaCl;

allowed us to isolate the complex [(PHCy₂)(CH₃CN)Pt(µ-

PCy₂)(µ-H)Pt(PHCy₂){κP-P(OH)Cy₂}](BF₄)₂(Pt-Pt) (11).⁵⁵

Although the ﬁndings described in point a do not allow

the possibility of discriminating between the incapacity of

chloride to open the phosphinito bridge and the establishment

of an energetically unfavorable pre-equilibrium between 1

and its (undetected) chloro adduct, the ﬁndings reported in

point b unequivocally indicate path ii as operative. In fact

the formation of the bridging hydride upon reaction of 1 with

HBF₄demonstrates that the proton can attack 1 without the

prior opening of the phosphinito bridge by a nucleophile.

Once it was ascertained that the ﬁrst act of the reaction is

the proton attack on 1, it remained to establish the site where

(b) etherate HBF₄(having a poorly nucleophilic anion and

therefore chosen to consider the interaction of the H⁺with

the Pt complex) was added to a n-hexane solution of 1 at

room temperature causing the immediate transformation into

a hydrido bridged dinuclear Pt species characterized by a

¹H NMR signal at δ -5.4 (¹H-¹⁹⁵Pt HMQC experiment).

The addition of few drops of acetonitrile to the solution

(55) Main spectroscopic features for 11: ¹H NMR (CD₃CN, δ): -6.48 (m,

²J_H(1),P(1)) 65 Hz, ²J_H(1),P(3)) 63 Hz, ²J_H(1),P(4)) 16 Hz, ²J_H(1),P(2)

)

11 Hz, ¹J_H(1),Pt(2)) 516 Hz, ¹J_H(1),Pt(1)) 392 Hz, µ-H) ppm. ³¹P{¹H}

NMR (CD₃CN, δ): 155.2 (dd, P(2), ¹J_P(2),Pt(1)) 2674 Hz, ¹J_P(2),Pt(2)

)

2

1485 Hz, J_P(2),P(4)) 290 Hz, J_P(2),P(3)) 12 Hz), 126.7 (dd, P(4),

¹J_P(4),Pt(2)) 2764 Hz, ²J_P(4),Pt(1)) 48 Hz, ²J_P(4),P(2)) 290 Hz, ²J_P(4),P(3)

1

2

) 25 Hz), 0.6 (d, P(1), J_P(1),Pt(1)) 3822 Hz, J_P(1),Pt(2)) 175

Hz,³J_P(1),P(3)) 41 Hz), -2.2 (m, P(3), ¹J_P(3),Pt(2)) 3444 Hz, ²J_P(3),Pt(1)

2

3

) 179 Hz, J_P(3),P(2)) 12 Hz, J_P(3),P(4)) 25 Hz, J_P(3),P(1)) 41 Hz)

ppm. More details on the reactivity of 1 with HBF₄will be reported

elsewhere.

(54) Henderson, R. A. The Mechanisms of Reactions at Transition Metal

Sites, Oxford UniVersity Press 1993, p. 13.

Inorganic Chemistry, Vol. 47, No. 21, 2008 9785

Latronico et al.

Table 2. NMR Parameters for the Intermediate 12 (C₆D₆, 295 K)^a

P²

P¹

40

P⁴

P³

Pt¹

Pt²

P²

187.3

251

22

117.5

6

195

8

3897

3330

48

2727

520

3690

2500

P¹

19.3

P⁴

P³

19.0

428

Pt¹

Pt²

-4856

-5194

^aChemical shifts (bold typeface) are in ppm; coupling constants (normal

type) are in Hz. The drawing represents the skeleton of 12 as inferable

from NMR data.

Figure 7. Portion of the ³¹P{¹H} NMR spectrum of 12: (a) experimental;

(b) calculated.

H⁺binds. As already mentioned, the incoming proton may

ﬁrst attack (a) the Pt-Pt bond or one of the Pt atoms; (b) a

P-Pt bond; and (c) the oxygen atom of the coordinated

POCy₂. The latter protonation site is that favored by DFT

calculations on 1 that indicated the phosphinito oxygen as

the most nucleophilic center of the molecule.³Moreover, it

is known that the small intrinsic barrier typical for proto-

nation at the oxygen often causes protonation of an oxygen

ligand to be more facile than protonation of the metal even

if the latter (as in the system at hand) is thermodynamically

favored.⁵⁶A relevant example of proton attack onto an

oxygen atom of a Pt complex has been recently described

for the reaction of triﬂic acid with the triangulo cluster [Pt₃(µ-

P^tBu₂)₃(H)(CO)₂]⁵⁷which proceeds through the formation

of a CO-hydrogen bonded (or protonated) intermediate giving

a bridging hydride complex as the ﬁnal thermodynamic

product.

Monitoring the reaction between 1 and aqueous HCl (<1

1

equiv) with ³¹P and H NMR spectroscopy allowed us to

Figure 8. Low ﬁeld portion of the ¹H-¹⁹⁵Pt HMQC spectrum of 12 (C₆D₆,

detect, along with unreacted 1 and small amounts of 5, the

formation of an intermediate 12, which slowly transforms

into 5, and that was found relatively stable at low temperature

in toluene (1 week at -10 °C).

295 K).

the parent compound 1, the main difference being the

signiﬁcant deshielding of both the phosphanide P²and the

phosphinito P⁴.

The ³¹P{¹H} NMR spectrum of intermediate 12 shows four

mutually coupled signals, all ﬂanked by ¹⁹⁵Pt satellites: a

low-ﬁeld ddd centered at δ 186.9 attributable to a phos-

phanide bridging two non equivalent Pt atoms, a doublet of

pseudotriplets centered at δ 117.1 attributable to a dicyclo-

hexylphosphinito moiety, and a second order set of signals

near δ 19 belonging to the two coordinated PHCy₂. These

latter signals constitute the AB part of the ABXY spin system

where A and B are the PHCy₂, X is the µ-PCy₂, and Y is

the POH. The whole spectrum was calculated (Figure 7),

and the spectroscopic features reported in Table 2 were

obtained.

The most interesting feature of the ¹H NMR spectrum of

the intermediate 12 (that does not show high-ﬁeld resonances

attributable to hydrides) is a low-ﬁeld signal centered at δ

10.0 (295 K, C₆D₆). Such a signal refers to a proton which

is scalar coupled to both of the Pt atoms, as ascertained by

¹H-¹⁹⁵Pt HMQC experiment (Figure 8), but to none of the

P atoms, a circumstance that suggests the presence of a

PCy₂(OH) ligand involved in a cyclic structure.⁵⁸This is in

accordance with the remarkable sharpness of the P⁴signal

1

in the ³¹P{¹H} NMR and the H¹signal in the H NMR

spectrum of 12.⁵⁹

The NMR data reported above indicate a structure for 12

in which the position of the P atoms is the same as that in

The presence of the P(OH)Cy₂moiety in 12 was deﬁnitely

ascertained by heteronuclear Overhauser enhancement spec-

(56) Kristjansdottir, S. S.; Norton, J. R. Transition Metal Hydrides; Dedieu,

A. , Ed.; VCH: New York, 1992; pp 309-359; and references cited

therein.

(57) Fortunelli, A.; Leoni, P.; Marchetti, L.; Pasquali, M.; Sbrana, F.; Selmi,

M. Inorg. Chem. 2001, 40, 3055–3060.

(58) In the case of [PtCl(PHCy₂){(PCy₂O)₂H}], the proton bound to the

phosphinito groups showed a scalar coupling with Pt through

Pt-P-O-H bonds but not with the P atoms. See: Mastrorilli, P.;

Latronico, M.; Nobile, C. F.; Suranna, G. P.; Fanizzi, F. P.; Englert,

U.; Ciccarella, G. Dalton Trans. 2004, 1117–1119.

9786 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

Figure 9. ³¹P^-1H HOESY spectrum of a mixture of 12, 1, and 5 (C₆D₆, 295 K). The inset shows cross peaks a and b in a 3D view.

Table 3. NMR Parameters for the Intermediates from the First Attack

of HX (X ) Cl, Br, I or PhS) on 1^a

Chart 1

HX

δ P¹δ P²δ P³δ P⁴δ H¹

δ Pt¹

δ Pt²

12 HCl_(g)19.4 186.9 18.1 117.0 9.9

13 HBr_(aq)20.1 193.2 18.3 117.5 9.2

-4856

-5194

-4984^b-5179^b

20.1 187.4 19.4 117.4 10.2 -4059 -5195

14 HI_(aq)

18^cPhSH

17.2 188.0 16.9 109.4 11.7 -5000

-5180

^aSee Table 2 for atom numbering. Solvent C₆D₆; T ) 295 K. ^bIn

CD₂Cl₂. ^c283 K.

amounts of complexes 3 or 3a (Chart 1) as protonating

agents. Those complexes have the same cation, featuring an

acidic proton bound to the PO, and differ only for the

counteranion which is a chloride for 3 and a tetraﬂuoroborate

for 3a. The detection of 12 by monitoring the reaction was

possible using 3 but not using 3a (Table 4) thus deﬁnitively

pointing out the role played by the chloride in stabilizing

the intermediate 12.

The absence of any signal in the ³⁵Cl NMR spectrum of

12 (see above)³⁶rules out structures in which the chloride

is purely the counteranion of the protonated form of complex

1. In other words, the chloride must be either covalently

bound or involved in an intimate ion couple.

With the data collected on intermediate 12 the three

structures depicted in Scheme 6 can be put forward.

Structure A is an ion couple in which the chloride interacts

with the acidic proton of the POH ligand; structure B features

a covalent chloride and the POH ligand involved in a

6-membered metallacycle; structure C features a covalently

bound chloride and the POH ligand involved in a 4-mem-

bered ring.

troscopy (HOESY) experiments which showed through space

correlations between H and P. The presence of the cross-

peak a between the signals of H¹(δ 10.0) and P⁴(δ 117.1)

in the ³¹P-¹H HOESY (Figure 9) suggests that the acidic

proton belongs to a P(OH)Cy₂ligand and that its permanence

on the phosphinito group is relatively long (i.e., its involve-

ment in exchange processes, typical for protic species, is slow

in the NMR time scale). Moreover, as it is apparent from

the box in Figure 9, the comparable volumes of the cross-

peaks a (between P⁴and H¹) and b (between P⁴and the

methinic protons of the cyclohexyl groups) indicate that the

P⁴· · ·H¹distance is compatible with a P-O-H moiety, even

though an accurate determination of such distance was not

possible.⁶⁰

Intermediates similar to 12 were detected by monitoring

at 295 K the protonation of 1 by HBr_(aq)(intermediate 13)

or by HI_(aq)(14) but not when the Brønsted acid was HBF₄

(either aqueous, or etherate,⁶¹Table 3). This suggests a role

of the halide in the formation of intermediates 12-14. To

conﬁrm such a role, we have reacted 1 with equimolar

(59) The ∆ν_1/2of the ³¹P{¹H} NMR signal of the coordinated P(OH)Cy₂

in complexes 3 and 4 (with the P(OH)Cy₂exhibiting a monodentate

behavior) are 52 and 54 Hz respectively, to be compared with the

∆ν_1/2of the ³¹P{¹H} NMR signal of the coordinated P(OH)Cy₂in

intermediate 12 of 4 Hz. Analogously, in the ¹H NMR spectra, the

∆ν_1/2of POH for the coordinated P(OH)Cy₂in complexes 3 and 4

are 126 and 112 Hz, respectively, to be compared with the ∆ν_1/2) 6

Hz for intermediate 12.

Structure A differs from B and C in that the halide is not

covalently bound to Pt¹. To gain insights into the possible

coordination of the X residue of the Brønsted acid HX on

Pt¹, we have carried out the reaction of 1 with Brønsted acids

having a residue containing NMR informative nuclei. The

ﬁrst two molecules tested for this purpose were HF_(aq)and

2,2,2-triﬂuoroethanol, both having a moderate acidity and

the ﬂuorine atoms suitable for NMR studies. The addition

of an equimolar amount of 2,2,2-triﬂuoroethanol to 1 in

n-hexane gave no reaction after 1 week at room temperature.

(60) An accurate determination of the P⁴· · ·H¹distance needs preliminary

experiments for the evaluation of T₁values and kinetic NOE proﬁles.

Such experiments are dramatically time-consuming and incompatible

with the relatively short lifetime of 12 at 295 K.

(61) Intermediate 12 was detected also by monitoring the reaction of 1

with gaseous HCl.

Inorganic Chemistry, Vol. 47, No. 21, 2008 9787

Latronico et al.

Table 4. Role of the Counteranion of the Protonating Agent in the Stabilization of the Intermediate of the First Protonation

protonating agent

detection of intermediates similar to 12

HCl_(g)

yes

HCl_(aq)

yes

HBr_(g)

yes

HBr_(aq)

yes

HI_(aq)

yes

HBF_4(aq)

no

HBF₄·Et₂O

no

3

yes

3a

no

Scheme 6. Three Possible Structures for Intermediate 12

intermediate collapses into 19 (the thiophenoxide analogues

of 5 and 6), which is present in solution always in small

amount. The circumstance that the NMR signals of 19 are

broad throughout the reaction indicates that it is involved in

a further reaction. In fact, 19 reacts faster than 1 with PhSH

giving the neutral hydrido bridged complex 17 containing

two coordinated thiophenoxides.⁶⁵As a consequence, even

when equimolar amounts of 1 and PhSH were reacted at 0

°C, the ﬁnal mixture contained mainly 17 with unreacted 1.

The ³¹P-¹H HOESY spectrum of the reaction mixture

containing 18 (along with residual 1) showed, as in the case

of HCl as protonating agent, the cross peak due to the dipolar

coupling between the acidic H¹and the phosphinite P⁴.

Scheme 7. Reactions of 1 with Phenol and 2,2,2-Triﬂuoroethanol

1

Moreover the H-¹⁹⁵Pt HMQC spectrum of the reaction

Scheme 8. Reaction Course of 1 with Thiophenol

mixture containing 18 (Figure 10) showed correlations

between (i) the H¹proton at δ 11.7 (C₆D₆) with both Pt

atoms, according to what was found for 12, 13, and 14; (ii)

the ortho protons of the thiophenyl group with the Pt¹atom.

The latter result permits to rule out a structure of type A for

intermediate 18 and, extending this result to the other

protonating agents giving observable intermediates, to 12,

13, and 14. The discrimination between structures B and C

was made on the basis of DFT calculations.

DFT Study. Density functional calculations were per-

formed on several of the considered complexes and the

proposed intermediates to study the energetics of the pro-

tonation reactions of 1 and to shed light on their mechanism.

This study was carried out using models with methyl groups

in place of cyclohexyl groups, an approximation previously

validated.³

Geometrical parameters calculated for complexes 1 and

3, for which X-ray structures are available, are in good

agreement with the experimental data, with bond lengths

within 0.1 Å and bond angles within 5°. As to complex 3,

However, using a 10-fold excess of the alcohol resulted in

the nearly quantitative formation of 15⁶²after 2 days at room

temperature in toluene (Scheme 7). Unfortunately, no

intermediates were detected during the monitoring of the

reaction. In the case of HF, no reaction occurred even when

a strong excess of the acid was used.⁶³

The third molecule chosen was phenol, having a residue

with aromatic protons for which the scalar coupling with

Pt¹could be easily proven by ¹H-¹⁹⁵Pt HMQC experiments.

However, results similar to those obtained with 2,2,2-

triﬂuoroethanol were obtained: no intermediates were de-

tected,⁶⁴and the transformation of 1 into 16 (Scheme 7) was

achieved after 3 days at room temperature using a 10-fold

excess of phenol.

The detection of the intermediate coming from the ﬁrst

attack of the acidic molecule on 1 was possible using PhSH.

The reaction of 1 with PhSH led to 17 as the ﬁnal product,

and its course is shown in Scheme 8. The ﬁrst species

detected in solution is intermediate 18 which shows spec-

troscopic features similar to those of 12 (Table 3). This

(62) The isolation of 15 was hampered by its decomposition during work-

up procedures.

(63) The addition of aqueous HF resulted only in the broadening of the

³¹P NMR signals of 1.

(64) The addition of excess phenol (2,2,2-triﬂuoroethanol) resulted in the

broadening of the ³¹P NMR signals of 1, which progressively decrease

with the appearance of the peaks attributed to 16 (15).

Figure 10. Portion of the ¹H-¹⁹⁵Pt HMQC spectrum of the reaction mixture

obtained immediately after mixing 1 with PhSH (283 K, C₆D₆). The cross

peaks refer to intermediate 18.

9788 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

Figure 11. Energy diagram for the protonation reaction of 1 with HCl in n-hexane solution.

and 9, respectively. Moreover, complexes 10 and 7, featuring

two covalently bound I atoms, are slightly lower in energy

than 9, by 2 and 3 kcal mol^-1, respectively (Figure 12), in

agreement with the experimental evidence indicating that 9

evolves spontaneously, ﬁrst to 10 and eventually to 7. On

the contrary, the ion pair 3 was found more stable than the

neutral complex 3′ or 3′′ by 18 and 16 kcal mol^-1,

respectively (Figure 11), giving the rationale for why neither

3′ nor 3′′ were ever experimentally observed. The lower

stability of symmetric compounds 10 and 3′ with respect to

the corresponding unsymmetrical ones 7 and 3′′ is due to

unfavorable steric interactions between the alkyl substituents

of the P ligands, as shown by the calculated geometries.

Reaction Mechanism and Intermediates. Theoretical

calculations have been carried out to shed light on the

detailed mechanism of the protonation reaction of 1 with

HCl and to ﬁnd the energy barriers for all its steps. Several

sites of complex 1 can in principle undergo protonation, such

as the two platinum atoms, the phosphinito oxygen, the

metal-metal bond, and the Pt-P bonds. We ﬁrst addressed

the preliminary approach of HCl to 1 and investigated the

formation of hydrogen bond adducts with each of these sites.

Geometry optimizations allowed us to locate six stable

adducts corresponding to the formation of a hydrogen bond

of HCl with the phosphinito oxygen, with each of the two

platinum atoms (the HCl molecule lying perpendicular to

the platinum coordination planes), with two Pt-P bonds (the

HCl molecule lying in the Pt coordination plane and

interacting with both the bridging and one of the terminal

phosphanido ligands), and with the Pt¹-P (terminal) bond

(the HCl molecule lying in the Pt coordination plane trans

to the bridging phosphanido ligand). Among them, the

thermodynamically most stable adduct is that with a hydro-

gen bond between HCl and the phosphinito oxygen, 1 · HCl,

with a binding energy of 13.5 kcal mol^-1. The formation of

the hydrogen bond between the oxygen and the proton is

reﬂected by a lengthening of the H-Cl bond, from 1.31 to

1.53 Å, and the short O · · · Cl distance of 2.79 Å in the ﬁnal

adduct. Slightly higher in energy are the adducts with a

hydrogen bond between HCl and the Pt¹or Pt²atoms, 1·HCl′

and 1·HCl′′, with bonding energies of 9 and 9.5 kcal mol^-1,

Figure 12. Energy diagram for the protonation reaction of 1 with HI in

n-hexane solution.

DFT calculations were performed considering explicitly the

complex as an ion pair, as indicated by NMR and diffraction

results.

Thermodynamics. The protonation reactions of 1 with

one and two HCl and HI molecules (considered as repre-

sentative of Brønsted acids with a hard and a soft anion

respectively) were addressed, and the energetics of these

reactions are illustrated by the energy proﬁles reported in

Figures 11 and 12.

In both cases all possible products experimentally observed

upon protonation by each of the two acids were considered,

that is, 8, 9, 10, and 7 for HI and 5, 3, and the Cl analogues

of 10 and 7 (hereafter 3′ and 3′′) for HCl.

Figure 11 shows an energy gain of 34 kcal mol^-1for the

protonation of 1 by one HCl molecule, leading to 5, and of

48 kcal mol^-1for the protonation by two HCl molecules,

leading to 3. Slightly more favorable values, -44 and -52

kcal mol^-1, are shown in Figure 12 for the protonation

energies of the ﬁrst and second HI molecules leading to 8

(65) The similar behavior exhibited by HI and PhSH towards 1 [i.e., the

formation of neutral complexes featuring a double incorporation of

the residues I (to give 7) and PhS (to give 17)] can be rationalized

with the high afﬁnity to platinum of the “soft” I and PhS residues

which replace the “harder” P(OH)Cy₂ligand on Pt².

Inorganic Chemistry, Vol. 47, No. 21, 2008 9789

Latronico et al.

Scheme 9. Possible Ion Pairs D-I for the Reaction of 1 with HCl^a

protonated structures, the formation of the complexes with

protonated O ligand requires the smallest structural

changes relative to the parent species 1.⁵⁶

According to our calculations, the most stable ion couple

formed by proton transfer from HCl to 1 corresponds to the

structure A, one of those initially proposed for intermediate

12 and ruled out on the basis of the experiments with

thiophenol (vide supra); combination of experimental and

computational data suggests that A is an early intermediate

of the reaction which rapidly evolves to 12, in which the

Pt-Cl bond has already formed. To assign the structure to

the intermediate 12, detectable in solution by spectroscopic

methods, we then carried out geometry optimizations for

structures B and C. While optimization of structure B led to

a local minimum on the potential energy surface, structure

C collapsed to B when optimized, conceivably because of

the instability of the pentacoordination of Pt¹and the small

bonding energy of the protonated phosphinito oxygen to

platinum. Structure B was found 19 kcal mol^-1lower than

A and lies 31 kcal mol^-1below the reactants 1 and HCl and

only 3 kcal mol^-1above 5 (Figure 11).

It is noteworthy that A shows a signiﬁcant elongation of

the Pt-O bond upon oxygen protonation, from 2.18 Å (for

1) to 2.46 Å, indicative of a high degree of bond weakening.

This bond weakening is conﬁrmed by the energy calculation

on the structure obtained from A upon complete breaking

of the Pt-O bond, which showed a negligible (<1 kcal

mol^-1) energy increase with respect to A and indicates a

low-energy pathway for the transformation of A into B. This

is conﬁrmed by the energy proﬁle calculated for this step

(vide infra) and explains why the early intermediate A is

not detectable in solution by spectroscopic methods, allowing

us, at the same time, to assign structure B to intermediate

12 (Figure 11).

Thus far we have considered only the thermodynamics of

the proton transfer from HCl to 1. We will now focus on

the kinetic aspects of the proposed mechanism with the aim

at ﬁnding the energy barrier of the various steps. No barrier

is expected for the preliminary formation of the hydrogen

bond adduct 1-HCl, a step whose rate is therefore deter-

mined only by diffusion. We then addressed the proton

transfer from 1-HCl to A. To estimate the energy barrier

we computed the energy proﬁle for this process taking the

O-H distance as the reaction coordinate. The O-H distance

was varied from 1.26 Å, the value in 1-HCl, to 1.01 Å, the

value found in A, optimizing all the remaining geometrical

parameters at each ﬁxed value of the O-H distance. The

resulting energy proﬁle (Figure 13) indicates that the proton

transfer is endothermic by 1.5 kcal mol^-1with a low barrier,

2.0 kcal mol^-1, showing a maximum only 0.5 kcal mol^-1

above A. We then considered the energy proﬁle for the

rearrangement from the initially formed ion pair A to the

metastable intermediate 12, taking the Pt-Cl distance as a

reaction coordinate. This distance was varied from 3.51 Å,

the value in A, to 2.42 Å, the value in 12, optimizing all the

remaining geometrical parameters at each ﬁxed value of the

reaction coordinate. The energy proﬁle found (Figure 13)

indicates for this exothermic process a very low barrier, less

a

Reaction energies in n-hexane solution with respect to 1 + HCl are

reported. Structure D corresponds to A.

respectively, while the adducts in which HCl interacts with

the Pt-P bonds are signiﬁcantly less stable, with binding

energies of 4-5 kcal mol^-1.

Starting from the calculated hydrogen-bonded adducts, we

have studied the thermodynamics of the proton transfer

process by optimizing the geometries of the ﬁnal products.

A correct evaluation of the proton transfer from HCl to 1 in

the non- or slightly polar solvents employed in the syntheses

required to take explicitly into account the formation of an

intimate ion couple between the resulting [1-H]⁺adduct

and Cl^-.

We thus explicitly considered the most stable ion couples

resulting from the proton transfer in each of the above

adducts, performing geometry optimizations starting from

several Cl^-orientations and evaluating their energies relative

to 1 + HCl. Geometry optimizations led only to six minima

on the potential energy surface for 1 plus H⁺(Scheme 9)

corresponding to the protonation of the oxygen atom (D),

one platinum atom (E, F, G, and H), and to the metal-metal

bond (I). The protonation of one platinum atom or of

bridging and terminal Pt-P bonds leads to the terminal

hydrido species, E-H, with the H atom lying in the

coordination plane. Among them, the thermodynamically

most stable ion couple is that with the protonated phosphinito

oxygen, D, with an energy gain of 12 kcal mol^-1with respect

to 1 and HCl inﬁnitely apart, while the remaining ion couples

are signiﬁcantly higher in energy, by 4 kcal mol^-1or more

(Scheme 9).

That the oxygen atom is the most probable site of the

initial proton attack can be also rationalized with the

concurrence of the following aspects: (i) the O atom has

a high negative atomic charge and it is surrounded by the

extended region with the most negative electrostatic

potential;³(ii) the proton approach to O is less hampered

by steric hindrance of the large cyclohexyl groups than

to the Pt atoms; (iii) there is a signiﬁcant contribution of

p(O) orbitals to the highest occupied molecular orbital

(HOMO) of 1; and (iv) compared with the other mono-

9790 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

Figure 13. Overall energy proﬁle for the reaction of 1 and HCl to 5. Reaction energies are reported with respect to 1 + HCl in n-hexane solution.

than 1 kcal mol^-1, suggesting that A is a highly unstable

species which evolves immediately to 12. The formation of

the intermediate 12 from 1 + HCl is therefore an extremely

fast process with an overall energy barrier of 2 kcal mol^-1.

Eventually, we considered the energy proﬁle of the intramo-

lecular rearrangement from 12 to 5 (the ﬁnal product of

reaction of 1 with 1 equiv of HCl). In this case, the distance

between the oxygen-bound hydrogen and the midpoint of

the Pt-Pt bond was taken as the reaction coordinate, which

was varied from 3.11 Å, the value in 12, to 1.08 Å, the ﬁnal

value in 5, obtaining a maximum in the energy proﬁle about

32 kcal mol^-1above B. Because the chosen reaction

coordinate is only approximate, and the corresponding

maximum is quite high, we performed a transition state (TS)

search starting from the structure of the maximum. This

procedure led to a TS with an energy 29 kcal mol^-1above

12 (Figure 13); its structure shows an almost broken O-H

Figure 14. Overall energy proﬁle for the reaction of 5 with HCl to give 3.

Reaction energies are reported with respect to 1 + HCl in n-hexane solution.

bond (1.509 Å), an almost formed Pt¹-H bond (1.829 Å)

and a still large Pt²-H distance of 2.247 Å, and suggests

that the high barrier is due to the almost complete breaking

of the O-H bond.

protonation product 5. In principle, the protonation sites

in 5 are represented by the platinum atoms, the bridging

hydride, the Pt-µP bonds, the oxygen, and the chlorine.

By considering the interaction of 5 with an HCl molecule,

only two stable hydrogen bonded adducts could be found

by energy optimization of several starting geometries with

all possible orientations of the attacking HCl molecule.

These stable hydrogen bound adducts were those having

the hydrogen bound to the chlorine or to the oxygen. Their

The frequency analysis gave an imaginary frequency of

1009 cm^-1corresponding to the expected normal mode.

Moreover, the energy proﬁle indicates that this transition state

is connected to a conformer of 5 with the phosphinito ligand

oriented with the oxygen atom directed toward the bridging

hydride, 5′, 12 kcal mol^-1above 5. These results show that

the proton transfer from the phosphinito oxygen to the Pt-Pt

bond occurs with an energy barrier of 29 kcal mol^-1and

leads to 5′, a high energy conformer of 5, which then relaxes

to 5 through a facile rotation around the Pt-P bond. The

calculated energy for the intramolecular conversion of the

intermediate 12 to 5, 29 kcal mol^-1, is compatible with the

experimental evidence of relative stability of this species,

that is, 1 week at -10 °C.

computed bonding energies are 6 and 12 kcal mol^-1

,

respectively, indicating that the hydrogen bond formation

to the phosphinito ligand is favored, leading to 5-HCl

(Figure 14). To estimate the energy barrier for the proton

transfer from 5-HCl to the ﬁnal product 3, we computed

the energy proﬁle taking the O-H distance as the reaction

coordinate. The O-H distance was varied from 1.25 Å,

the value in 5-HCl, to 1.01 Å, the value in 3, optimizing

all the remaining geometrical parameters. The energy

Finally, we addressed the second protonation step of 1,

that is, the uptake of an HCl molecule by the ﬁrst

Inorganic Chemistry, Vol. 47, No. 21, 2008 9791

Latronico et al.

(Bruker microTOF). All analyses were carried out in a positive

ion mode. The sample solutions were introduced by continuous

infusion with the aid of a syringe pump at a ﬂow-rate of 180 µL/

min. The instrument was operated at end plate offset -500 V and

capillary -4500 V. Nebulizer pressure was 0.8 bar (N₂) and the

drying gas (N₂) ﬂow 7 L/min. Capillary exit and skimmer 1 were

90 and 30 V, respectively. Drying gas temperature was set at 220

°C. The software used for the simulations is Bruker Daltonics

DataAnalysis (version 3.3).

proﬁle for the reaction of 5 with HCl to give 3 shown in

Figure 14 indicates that the proton transfer step is slightly

exothermic, by 2 kcal mol^-1, and with a very low barrier,

1.0 kcal mol^-1, showing that this is a very easy process,

in agreement with the experimental ﬁndings.

Conclusions

The amphiphilic character of 1 is demonstrated by its

ability to react with both nucleophiles³and electrophiles.

Reactions of 1 with protic species invariably result in the

protonation of the Pt-Pt bond to give unsymmetrical hydrido

bridged species. In the case of strong halohydric acids such

as HCl or HBr, the products 3-6 contain the halide bound

to the electrophilic Pt atom. When HI was used as proto-

nating agent, loss of P(OH)Cy₂and incorporation of two iodo

ligands in anti position led to complex 7. In the case of weak

HX Brønsted acid such as HF, PhOH, CF₃CH₂OH, or PhSH,

the feasibility of the protonation of 1 is regulated by the

afﬁnity of the conjugated base X^-to the platinum rather than

by the strength of the acid. Thus, whereas no reaction

occurred with HF, sluggish reactions were observed with

PhOH, CF₃CH₂OH, and a fast and complete conversion was

obtained with PhSH. The product of the latter reaction (17)

is the analogue of the diiodo-species 7, as a result of the

high afﬁnity of S and I toward Pt, in view of their “soft”

character.

NMR spectra were recorded on a BRUKER Avance 400

spectrometer; frequencies are referenced to Me₄Si (¹H and ¹³C),

85% H₃PO₄(³¹P), H₂PtCl₆(¹⁹⁵Pt), CFCl₃(¹⁹F), and BF₃·Et₂O (¹¹B).

The signal attributions and coupling constant assessment was made

on the basis of a multinuclear NMR analysis of each compound

1

including, beside 1D spectra, H-³¹P HMQC, H-¹⁹⁵Pt HMQC,

³¹P{¹H} COSY, ³¹P{¹H} long-range COSY. The coupling constants

not directly extractable from the one-dimensional spectra were

obtained and attributed by the tilts of the multiplets due to the

“passive” nuclei⁶⁶in the aforementioned 2D spectra. Computer

simulation of the ³¹P{¹H} NMR spectrum for 12 was performed

by using the program WINDAISY (Version 4.0.5.0).

Computational Details. DFT calculations were performed using

the Amsterdam density-functional (ADF) package.⁶⁷The 1s orbital

for C and O, 1s-2p orbitals for P and Cl, and 1s-4f orbitals for

Pt, are kept frozen, respectively. For all main group atoms the

valence orbitals were expanded in an uncontracted triple-ꢀ Slater-

type orbitals (STO) basis set augmented with a polarization function.

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 and Cl,

one 3d for C and O and one 2p for H.

The LDA exchange correlation potential was used, together with

the Vosko-Wilk-Nusair parametrization⁶⁸for homogeneous elec-

tron gas correlation, including the Becke’s nonlocal correction⁶⁹

to the local exchange expression and Perdew’s nonlocal correction⁷⁰

to the local expression of correlation energy. Because the relativistic

effect is important in these Pt-containing dimers, the zero-order

regular approximation formalism (ZORA) without the spin-orbit

coupling has been included.⁷¹Previous calculations indicate that

gradient-corrected functionals together with the ZORA approxima-

tion can predict reliable properties of metal dimers in comparison

with the Dirac four-component-MP2 calculations.⁷²Molecular

structures of all considered complexes were optimized at this

gradient-corrected relativistic level with the above basis set. Single

point calculations were subsequently performed on the optimized

geometries with a larger basis set obtained from the above one

through the addition of a second polarization function, a 5f for Pt,

a 4f for P, Cl, C, and O, and one 3d for H. Solvent effects were

taken into account employing the COSMO continuum solvent

The apparent contrast between the strong nucleophilicity

of the phosphinito oxygen indicated by the Mulliken gross

atomic charges in 1 and the site selectivity observed in the

protonation of 1 (i.e., the addition of the proton to the Pt^I-Pt^I

bond) was clariﬁed by a mechanistic study which combined

NMR, diffraction methods and theoretical calculations. In

fact, it was ascertained that the oxygen atom is indeed the

ﬁrst site of proton attack, provided that a suitable coordinat-

ing anion X^-is present in the reaction medium, giving

intermediates featuring

a

six membered Pt¹-X · · ·

H-O-P-Pt²ring. Multinuclear NMR has allowed us to

detect such intermediates in solution for derivatives with X

) Cl, Br, I, and PhS. The relative stability of the six

membered ring intermediates is explainable in terms of a

signiﬁcant energy barrier (29 kcal mol^-1for X ) Cl) for

the proton transfer from the oxygen to the metal-metal bond.

Experimental Section

Complex 1²was prepared as described in ref 3. Gaseous HCl

was obtained from NaCl plus concentrated sulfuric acid whereas

gaseous HBr was obtained by heating a mixture of NaBr and

metaphosphoric acid. All the other reagents were commercial and

used as received.

Although the starting complex 1, as well as all the hydrido

bridged products, were found air stable, all manipulations were

carried out under a pure dinitrogen atmosphere, using freshly

distilled and oxygen-free solvents. C, H, and S elemental analyses

were carried out on a Carlo Erba EA1108 CHNS-O Elemental

Analyzer. Infrared spectra were recorded on a Bruker Vector 22

spectrometer.

(66) Carlton, L. Bruker Report 2000, 148, 28–29.

(67) (a) Amsterdam Density Functional (ADF); SCM, Theoretical Chem-

istry, Vrije Universiteit: Amsterdam, Netherlands, 2004; www.scm-

.com. (b) Boerrigter, P. M.; te Velde, G.; Baerends, E. J. Int. Quantum

Chem. 1988, 33, 87–113. (c) te Velde, G.; Baerends, E. J. J. Chem.

Phys. 1992, 99, 84–98.

(68) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200–

1211.

(69) Becke, A. D. Phys. ReV. A 1988, 38, 3098–3100.

(70) Perdew, J. P. Phys. ReV. B 1986, 33, 8822–8824.

(71) (a) Lenthe, E. V.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1993,

99, 4597–4610. (b) Lenthe, E. V.; Baerends, E. J.; Snijders, J. G.

J. Chem. Phys. 1994, 101, 9783–9792.

(72) (a) Minori, A.; Sayaka, M.; Takahito, N.; Kimihiko, H. Chem. Phys.

2005, 311, 129–137. (b) Xia, F.; Chen, J.; Cao, Z. X. Chem. Phys.

Lett. 2006, 418, 386–391.

Mass spectrometry analyses were performed using a time-of-

ﬂight mass spectrometer equipped with an electrospray ion source

9792 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

model, ⁷³in the standard parametrization implemented in the ADF

program.⁷⁴Free energies of solvation in n-hexane (ε ) 2.0) were

calculated with the largest basis set on the optimized geometries

of all considered molecules.

IR (KBr, cm^-1): νj ) 3418 broad w (P-O-H), 3228 broad w,

2926 s, 2850 s, 2661 w, 2336 w (P-H); 1621 w (µ H-Pt); 1447 s;

1349 w; 1327 w, 1300 m; 1179 m; 1077 broad s (BF₄

+ PO);

915 s; 886 m; 849 m; 826 w; 771 w; 736 m; 534 s, 522 s; 489 w,

474 m, 409 w, 388 m.

Syn-[(PHCy₂)(Cl)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){P(OH)Cy₂}]Cl

(Pt-Pt) (3). Gaseous HCl was bubbled at room temperature in a

toluene solution of 1 (286 mg, 0.239 mmol in 15 mL) causing the

progressive discoloration of the initially yellow solution and the

contemporary precipitation of 3 as a white solid. The solid was

ﬁltered off, washed with n-hexane (3 × 4 mL) and dried under

reduced pressure.

Yield 278 mg (91%).

The complex is soluble in halogenated solvents, insoluble in

toluene and n-hexane.

Anal. Calcd for C₄₈H₉₂Cl₂OP₄Pt₂: C 45.4, H 7.30; Found C 45.5,

H 7.57. HR ESI-MS, exact mass for C₄₈H₉₂ClOP₄Pt₂[M-Cl]⁺:

1233.5077; measured: m/z: 1233.5074. The error between simulated

and observed isotopic patterns is +0.26 ppm.

1

¹H NMR (CD₂Cl₂, δ): 4.63 (m, H(1), J_H(1),P(1)) 357 Hz,

²J_H(1),Pt(1)) 156 Hz), 5.00 (m, H(2), J_H(2),P(3)) 370 Hz, ²J_H(2),Pt(2)

1

2

) 21 Hz), -5.75 (m, H(3), J_H(3),P(1)) 75 Hz, J_H(3),P(3)) 66 Hz,

²J_H(3),P(2)) 19 Hz, ²J_H(3),P(4)) 14 Hz, ¹J_H(3),Pt(2)) 561 Hz, ¹J_H(3),Pt(1)

) 373 Hz), 9.5 (s, H(4)) ppm.

³¹P{¹H} NMR (CD₂Cl₂, δ): 156.9 (dd, P(2), ²J_P(2),P(4)) 286 Hz,

²J_P(2),P(3)) 12 Hz, ¹J_P(2),Pt(1)) 2630 Hz, ¹J_P(2),Pt(2)) 1538 Hz), 125.1

(dd, P(4), ¹J_P(4),Pt(2)) 2704 Hz, ²J_P(4),Pt(1)) 44 Hz, ²J_P(4),P(2)) 286

Hz, ²J_P(4),P(3)) 24 Hz), 9.0 (d, P(1), ¹J_P(1),Pt(1)) 4025 Hz, ²J_P(1),Pt(2)

3

1

) 230 Hz, J_P(1),P(3)) 50 Hz), 2.6 (br, P(3), J_P(3),Pt(2)) 3447 Hz,

²J_P(3),Pt(1)) 190 Hz, ²J_P(3),P(4)) 24 Hz, ²J_P(3),P(2)) 12 Hz, ³J_P(3),P(1)

) 50 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5375 (dddd, Pt(1), J_Pt(1),P(1)

)

1

IR (KBr, cm^-1): νj ) 3440 broad w (P-O-H), 2924 s, 2850 s,

2520 m (P-O-H), 2358 w (P-H), 2161 m (P-O-H), 1546 w

(Pt-H-Pt), 1495 w, 1447 s, 1340 w, 1324 w, 1294 m, 1263 s,

1206 w, 1179 m, 1106 m, 1005 s, 917 s (P-O-H), 888 m, 847 m,

818 m, 800 m, 734 m, 696 w, 538 w, 523 m, 474 m, 457 w, 407 w,

389 m, 286 m (Pt-Cl).

4025 Hz, ¹J_Pt(1),P(2)) 2630 Hz, ²J_Pt(1),P(3)) 190 Hz, ²J_Pt(1),P(4)) 44

1

Hz), -5624 (dddd, Pt(2), J_Pt(2),P(3)) 3447 Hz, J_Pt(2),P(4)) 2704

1

2

Hz, J_Pt(2),P(2)) 1538 Hz, J_Pt(2),P(1)) 230 Hz) ppm.

¹¹B{¹H} NMR (CD₂Cl₂, δ): -1.0 (br, BF₄^-).

¹⁹F NMR (CD₂Cl₂, δ): -151.6 (br, BF₄^-).

1

¹H NMR (CD₂Cl₂, δ): 4.58 (m, H(1), J_H(1),P(1)) 356 Hz,

1

²J_H(1),Pt(1)) 158 Hz), 5.12 (m, H(2), J_H(2),P(3)) 375 Hz, ²J_H(2),Pt(2)

2

) 29 Hz), -5.61 (m, H(3), J_H(3),P(3)) 74 Hz, J_H(3),P(1)) 69 Hz,

²J_H(3),P(4)) 18 Hz, ²J_H(3),P(2)) 14 Hz, ¹J_H(3),Pt(2)) 568 Hz, ¹J_H(3),Pt(1)

) 389 Hz,), 10.54 (s, H(4)) ppm.³¹P{¹H} NMR (CD₂Cl₂, δ): 155.3

(dd, P(2), ²J_P(2),P(4)) 285 Hz, ²J_P(2),P(3)) 13 Hz, ¹J_P(2),Pt(1)) 2597

1

2

Hz, J_P(2),Pt(2)) 1527 Hz), 118.8 (dd, P(4), J_P(4),P(2)) 285 Hz,

Syn-[(PHCy₂)(Br)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){P(OH)Cy₂}]-

Br (Pt-Pt) (4). An aqueous 1.0 M HBr solution (3 mL) was added

at room temperature under vigorous stirring to a n-hexane solution

of 1 (91 mg, 0.08 mmol in 4 mL). After 2 h the organic phase was

extracted with n-hexane, dried over Na₂SO₄and ﬁltered to give,

after evaporation of the solvent, 4 as a white solid.

Yield 92 mg (91%).

The complex is soluble in halogenated solvents, insoluble in

toluene, n-hexane.

Anal. Calcd for C₄₈H₉₂Br₂OP₄Pt₂: C 42.4, H 6.82; Found C 42.1,

H 6.91. HR ESI-MS, exact mass for C₄₈H₉₂BrOP₄Pt₂[M-Br]⁺:

1277.4572; measured: m/z: 1277.4517 (Supporting Information,

Figure S5).

²J_P(4),P(3)) 25 Hz, J_P(4),Pt(2)) 2652 Hz, J_P(4),Pt(1)) 42 Hz), 10.8

1

2

3

1

2

(d, P(1), J_P(1),P(3)) 50 Hz, J_P(1),Pt(1)) 4016 Hz, J_P(1),Pt(2)) 206

Hz), 5.2 (br, P(3), ³J_P(3),P(1)) 50 Hz, ²J_P(3),P(4)) 25 Hz, ²J_P(3),P(2)

)

1

2

13 Hz, J_P(3),Pt(2)) 3508 Hz, J_P(3),Pt(1)) 180 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5379 (dddd, Pt(1), J_Pt(1),P(1)

)

1

4016 Hz, ¹J_Pt(1),P(2)) 2597 Hz, ²J_Pt(1),P(3)) 180 Hz, ²J_Pt(1),P(4)) 42

1

Hz, J_Pt(1),Pt(2)) 845 Hz), -5621 (dddd, Pt(2), J_Pt(2),P(3)) 3508

1

2

Hz, J_Pt(2),P(4)) 2652 Hz, J_Pt(2),P(2)) 1527 Hz, J_Pt(2),P(1)) 206

1

Hz, J_Pt(2),Pt(1)) 845 Hz) ppm.

IR (KBr, cm^-1): νj ) 3435 broad w (P-O-H), 2923 s, 2850 s,

2655 w, 2580 m (P-O-H), 2360 w (P-H), 2240 w (P-O-H),

1620 w (Pt-H-Pt), 1447 s, 1342 w, 1323 w, 1292 w, 1267 m,

1205 w, 1117 m, 1176 w, 1108 w, 1004 s, 917 s, 898 m, 887 m,

846 m, 816 m, 736 m, 534 w, 522 m, 473 m, 384 w.

Syn-[(PHCy₂)(Cl)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){P(OH)Cy₂}]-

BF₄(Pt-Pt) (3a). Etherate HBF₄(51÷57%, 38 µL) was added at

room temperature under vigorous stirring to a dichloromethane

solution of 5 (216 mg, 0.17 mmol in 10 mL). After 10 min the

colorless solution was evaporated to dryness, the residue was

washed with Et₂O (3 × 4 mL) and n-hexane (3 × 4 mL), and dried

under reduced pressure. Yield 217 mg (95%).

The complex is soluble in halogenated solvents, insoluble in

toluene and n-hexane.

Anal. Calcd for C₄₆H₉₂BClF₄OP₄Pt₂: C 43.6, H 7.02; Found C

44.1, H 7.15. HR ESI-MS, exact mass for C₄₈H₉₂ClOP₄Pt₂

[M-BF₄]⁺: 1233.5077; measured: m/z: 1233.5065. (Supporting

Information, Figure S2)

1

¹H NMR (CD₂Cl₂, δ): 4.66 (m, H(1), J_H(1),P(1)) 355 Hz,

1

²J_H(1),Pt(1)) 155 Hz), 5.18 (m, H(2), J_H(2),P(3)) 374 Hz, ²J_H(2),Pt(2)

2

) 37 Hz), -5.51 (m, H(3), J_H(3),P(3)) 74 Hz, J_H(3),P(1)) 68 Hz,

2

1

²J_H(3),P(4)) 16 Hz, J

) 15 Hz, J

) 568 Hz, J

H(3),P(2)

H(3),Pt(2)

) 382 Hz), 8.90 (s, H(4)) ppm.

H(3),Pt(1)

³¹P{¹H} NMR (CD₂Cl₂, δ): 161.7 (dd, P(2), ²J_P(2),P(4)) 285 Hz,

²J_P(2),P(3)) 13 Hz, ¹J_P(2),Pt(1)) 2575 Hz, ¹J_P(2),Pt(2)) 1565 Hz), 120.6

(dd, P(4), ²J_P(4),P(2)) 285 Hz, ²J_P(4),P(3)) 25 Hz, ¹J_P(4),Pt(2)) 2675

Hz, ²J_P(4),Pt(1)) 43 Hz), 9.6 (d, P(1), ¹J_P(1),Pt(1)) 3984 Hz, ²J_P(1),Pt(2)

3

2

) 224 Hz, J_P(1),P(3)) 50 Hz), 4.2 (broad, P(3), J_P(3),Pt(2)) 3479

2

3

2

Hz, J_P(3),Pt(1)) 174 Hz, J_P(3),P(1)) 50 Hz, J_P(3),P(4)) 25 Hz,

²J_P(3),P(2)) 13 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5522 (dddd, Pt(1), J_Pt(1),P(1)

)

1

(73) Klamt, A.; Schu¨u¨rmann, G. J. Chem. Soc., Perkin Trans. 1993, 2,

799–805.

(74) Pye, C. C.; Ziegler, T. Theor. Chem. Acc. 1999, 101, 396–408.

3984 Hz, ¹J_Pt(1),P(2)) 2575 Hz, ²J_Pt(1),P(3)) 174 Hz, ²J_Pt(1),P(4)) 43

Hz, ¹J_Pt(1),Pt(2)) 806 Hz), -5638 (dddd, Pt(2), ²J_Pt(2),P(1)) 224 Hz,

Inorganic Chemistry, Vol. 47, No. 21, 2008 9793

Latronico et al.

1

2

¹J_Pt(2),P(2)) 1565 Hz, J_Pt(2),P(3)) 3479 Hz, J_Pt(2),P(4)) 2675 Hz,

) 40 Hz), -4.63 (m, H(3), J_H(3),P(1)) 77 Hz, J_H(3),P(3)) 70 Hz,

²J_H(3),P(2)) 16 Hz, ²J_H(3),P(4)) 7 Hz, ¹J_H(3),Pt(2)) 520 Hz, ¹J_H(3),Pt(1)

) 441 Hz), ppm.

¹J_Pt(2),Pt(1)) 806 Hz) ppm.

³¹P{¹H} NMR (CD₂Cl₂, δ): 151.1 (dd, P(2), J_P(2),Pt(1)) 2465

1

2

Hz, J_P(2),Pt(2)) 1264 Hz, J_P(2),P(4)) 270 Hz, J_P(2),P(3)) 13 Hz),

80.3 (dd, P(4), ¹J_P(4),Pt(2)) 2365 Hz, ²J_P(4),Pt(1)) 55 Hz, ²J_P(4),P(2)

)

2

1

270 Hz, J_P(4),P(3)) 25 Hz), 16.4 (broad, P(3), J_P(3),Pt(2)) 3808

2

3

2

Hz, J_P(3),Pt(1)) 225 Hz, J_P(3),P(1)) 55 Hz, J_P(3),P(4)) 25 Hz,

²J_P(3),P(2)) 13 Hz), 12.7 (d, P(1), ¹J_P(1),Pt(1)) 3955 Hz, ²J_P(1),Pt(2)

)

Syn-[(PHCy₂)(Cl)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){P(O)Cy₂}](Pt-Pt)

(5). An aqueous 1.5 M NaOH solution (10 mL) was added at room

temperature under vigorous stirring to a dichloromethane solution

of 3 (222 mg, 0.17 mmol in 15 mL) giving a yellow biphasic

system. After 30 min the organic phase was extracted with CH₂Cl₂,

dried over Na₂SO₄, and ﬁltered to give, after evaporation of the

solvent, 5 as a yellow powder.

3

218 Hz, J_P(1),P(3)) 55 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5507 (dddd, Pt(1), J_Pt(1),P(1)

)

1

3955 Hz, ¹J_Pt(1),P(2)) 2465 Hz, ²J_Pt(1),P(3)) 225 Hz, ²J_Pt(1),P(4)) 55

1

Hz, J_Pt(1),Pt(2)) 950 Hz), -5568 (dddd, Pt(2), J_Pt(2),P(3)) 3808

Hz, J_Pt(2),P(4)) 2365 Hz, J_Pt(2),P(2)) 1264 Hz, J_Pt(2),P(1)) 218

Hz, J_Pt(2),Pt(1)) 950 Hz) ppm.

1

2

1

Yield 188 mg (87%).

The complex is soluble in halogenated solvents, in toluene, and

in n-hexane.

Anal. Calcd for C₄₈H₉₁ClOP₄Pt₂: C 46.7, H 7.43; Found C 46.6, H

7.28. HR ESI-MS, exact mass for C₄₈H₉₂ClOP₄Pt₂: 1233.5082;

measured: m/z: 1233.5078 [M+H]⁺(Supporting Information, Figure

S8).

Anti-[(PHCy₂)(I)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂)(I)](Pt-Pt) (7).

An aqueous 0.50 M HI solution (0.35 mL) was added at room

temperature under vigorous stirring to a toluene solution of 1 (100

mg, 0.084 mmol in 8 mL). After 2 h the organic phase was extracted

with toluene, dried over Na₂SO₄, and dried under reduced pressure.

The yellow solid was washed with MeOH (3 × 4 mL), n-hexane

(3 × 4 mL) and dried under reduced pressure.

IR (Nujol, cm^-1): νj ) 2924 s, 2851 s, 2322 w (P-H), 1611 w

(Pt-H-Pt), 1447 s, 1377 w, 1343 w, 1261 s, 1177 m, 1088 s (P

) O), 1019 s (P ) O), 917 w, 849 m, 803 s, 735 w, 540 w, 520 m,

471 m, 388 m, 285 m (Pt-Cl).

1

¹H NMR (CD₂Cl₂, δ): 4.37 (m, H(1), J_H(1),P(1)) 349 Hz,

1

²J_H(1),Pt(1)) 160 Hz), 5.12 (m, H(2), J_H(2),P(3)) 387 Hz, ²J_H(2),Pt(2)

Yield 82 mg (70%).

2

) 42 Hz), -4.73 (m, H(3), J_H(3),P(1)) 80 Hz, J_H(3),P(3)) 70 Hz,

²J_H(3),P(2)) 17 Hz, ²J_H(3),P(4)) 8 Hz, ¹J_H(3),Pt(2)) 616 Hz, ¹J_H(3),Pt(1)

) 430 Hz) ppm.

The complex is soluble in halogenated solvents and toluene,

insoluble in n-hexane.

Anal. Calcd for C₃₆H₆₉I₂P₃Pt₂: C 34.9, H 5.61; Found C 34.7, H

5.64. HR ESI-MS, exact mass for C₃₆H₆₉I₂P₃Pt₂Na: 1261.1889;

measured: m/z: 1261.1935 [M+Na]⁺(Supporting Information,

Figure S14).

³¹P{¹H} NMR (CD₂Cl₂, δ):145.2 (dd, P(2), ¹J_P(2),Pt(1)) 2484 Hz,

¹J_P(2),Pt(2)) 1242 Hz, ²J_P(2),P(4)) 268 Hz, ²J_P(2),P(3)) 13 Hz), 78.6

(dd, P(4), ¹J_P(4),Pt(2)) 2328 Hz, ²J_P(4),Pt(1)) 56 Hz, ²J_P(4),P(2)) 268

2

1

IR (KBr, cm^-1): νj ) 2925 s, 2849 s, 2323 w (P-H), 1626 w

(Pt-H-Pt), 1462 w, 1448 s, 1341 w, 1329 w, 1290 w, 1262 s,

1195 w, 1175 m, 1106 s, 1023 s, 918 w, 889 w, 854 m, 816 s,

801 s, 731 m, 517 w, 474 m, 391 w.

Hz, J_P(4),P(3)) 27 Hz), 16.4 (broad, P(3), J_P(3),Pt(2)) 3846 Hz,

²J_P(3),Pt(1)) 198 Hz, ³J_P(3),P(1)) 54 Hz, ²J_P(3),P(4)) 27 Hz, ²J_P(3),P(2)

) 13 Hz), 13.8 (d, P(1), ¹J_P(1),Pt(1)) 3996 Hz, ²J_P(1),Pt(2)) 219 Hz,

³J_P(1),P(3)) 54 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5365 (dddd, Pt(1), J_Pt(1),P(1)

)

1

¹H NMR (C₆D₆, δ): 4.64 (m, H(1), ¹J_H(1),P(1)) 352 Hz, ³J_H(1),P(2)

3996 Hz, ¹J_Pt(1),P(2)) 2484 Hz, ²J_Pt(1),P(3)) 198 Hz, ²J_Pt(1),P(4)) 56

2

1

) 7 Hz, J_H(1),Pt(1)) 142 Hz), 5.13 (m, H(2), J_H(2),P(3)) 347 Hz,

1

²J_H(2),Pt(2)) 10 Hz), -7.29 (m, H(3), J_H(3),P(1)) 60 Hz, J_H(3),P(3)

2

Hz), -5547 (dddd, Pt(2), J_Pt(2),P(3)) 3846 Hz, J_Pt(2),P(4)) 2328

1

2

1

Hz, J_Pt(2),P(2)) 1242 Hz, J_Pt(2),P(1)) 219 Hz) ppm.

) 9 Hz, J_H(3),P(2)) 12 Hz, J_H(3),Pt(2)) 799 Hz, J_H(3),Pt(1)) 361

Hz) ppm.

2

³¹P{¹H} NMR (C₆D₆, δ): 185.7 (dd, P(2), J_P(2),P(3)) 321 Hz,

²J_P(2),P(1)) 7 Hz, J_P(2),Pt(1)) 2510 Hz, J_P(2),Pt(2)) 1919 Hz), 0.6

(broad s, P(1), J_P(1),Pt(1)) 4255 Hz, J_P(1),Pt(2)) 447 Hz, J_P(1),P(2)

1

2

1

2

) 7 Hz), 16.4 (d, P(3), J_P(3),Pt(2)) 2463 Hz, J_P(3),Pt(1)) 41 Hz,

²J_P(3),P(2)) 321, Hz) ppm.

Syn-[(PHCy₂)(Br)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){P(O)Cy₂}](Pt-Pt)

(6). Complex 6 was obtained in 79% yield by reaction of 4 with

NaOH, following the procedure used for the synthesis of 5.

The complex is soluble in halogenated solvents, toluene, and

n-hexane.

Anal. Calcd for C₄₈H₉₁BrOP₄Pt₂: C 45.1, H 7.18; Found C 45.0, H

7.21. HR ESI-MS, exact mass for C₄₈H₉₂BrOP₄Pt₂1277.4577;

measured: m/z: 1277.4484 [M+H]⁺(Supporting Information, Figure

S11).

¹⁹⁵Pt{¹H} NMR (C₆D₆, δ): -5723 (ddd, Pt(1), ¹J_Pt(1),P(1)) 4255

Hz, ¹J_Pt(1),P(2)) 2510 Hz, ²J_Pt(1),P(3)) 41 Hz, ¹J_Pt(1),Pt(2)) 1365 Hz),

1

-5550 (ddd, Pt(2), J_Pt(2),P(3)) 2463 Hz, J_Pt(2),P(2)) 1919 Hz,

²J_Pt(2),P(1)) 447 Hz, J_Pt(2),Pt(1)) 1365 Hz) ppm.

1

IR (KBr, cm^-1): νj ) 2924 s, 2848 s, 2656 w, 2347 w, 2324 w

(P-H), 1589 w (Pt-H-Pt), 1446 s, 1343 w, 1326 w, 1292 w,

1262 s, 1178 m, 1167 m, 1086 s (P ) O), 1020 s (P ) O), 916 w,

901 w, 888 m, 863 m, 848 m, 800 s, 734 w, 539 m, 522 m, 497 w,

454 m, 442 m, 388 m, 285 w.

Reaction of 1 with CF₃CH₂OH and PhOH. Solid 1 (100 mg,

0.084 mmol) was added to a toluene solution of CF₃CH₂OH (65

µL, 0.84 mmol in 5 mL) and stirred at room temperature for 2

days, a time after which ³¹P{¹H} NMR monitoring showed the

nearly complete conversion of 1 into 15. An analogous procedure

was followed for the reaction of 1 with PhOH that gave >95%

1

¹H NMR (CD₂Cl₂, δ): 4.61 (m, H(1), J_H(1),P(1)) 349 Hz,

1

²J_H(1),Pt(1)) 153 Hz), 5.22 (m, H(2), J_H(2),P(3)) 385 Hz, ²J_H(2),Pt(2)

9794 Inorganic Chemistry, Vol. 47, No. 21, 2008

Protonation of a Phosphinito Bridged Pt^I-Pt^IComplex

yield of 16 (based on ³¹P NMR integrals) after 1 day. Attempts to

isolate 15 and 16 in pure state were unsuccessful mainly because

of the formation of undesired products during the removal of excess

CF₃CH₂OH (or phenol).

1468 m,1446 s, 1343 w, 1293 w, 1264 m, 1193 w, 1179 m, 1121 m,

1108 s, 1084 w, 1023 s, 1002 s, 906 m, 861 m, 848 m, 838 m,

817 m, 747 s, 733 s, 697 s, 514 m, 473 s.

¹H NMR (CD₂Cl₂, δ): 7.42/6.86 (m, 10 H, aromatic), 4.79 (m,

H(1), ¹J_H(1),P(1)) 355 Hz, ³J_H(1),P(2)) 10 Hz, ²J_H(1),Pt(1)) 110 Hz),

3.09 (m, H(2), ¹J_H(2),P(3)) 346 Hz, ²J_H(2),Pt(2)) 13 Hz), -8.81 (m,

Spectroscopic Features of 15:

¹H NMR (C₆D₆, δ): 4.32 (m, H(1), ¹J_H(1),P(1)) 335 Hz, ²J_H(1),Pt(1)

1

2

) 156 Hz), 5.21 (m, H(2), J_H(2),P(3)) 362 Hz), -4.32 (m, H(3),

H(3), J_H(3),P(1)) 69 Hz, J_H(3),P(3)) 13 Hz, J_H(3),P(2)) 11 Hz,

2

1

²J_H(3),P(1)) 79 Hz, J_H(3),P(3)) 73 Hz, J_H(3),P(2)) 16 Hz, J_H(3),P(4)

¹J_H(3),Pt(2)) 595 Hz, J_H(3),Pt(1)) 440 Hz) ppm.

1

) 8 Hz, J_H(3),Pt(2)) 602 Hz, J_H(3),Pt(1)) 431 Hz) ppm.

³¹P{¹H} NMR (CD₂Cl₂, Supporting Information, Figure S20, δ):

³¹P{¹H} NMR (C₆D₆, δ): 143.2 (dd, P(2), J_P(2),P(4)) 271 Hz,

154.1 (d, P(2), J_P(2),P(3)) 298 Hz, J_P(2),Pt(1)) 2050 Hz, J_P(2),Pt(2)

2

1

²J_P(2),P(3)) 11 Hz, ¹J_P(2),Pt(1)) 2520 Hz, ¹J_P(2),Pt(2)) 1248 Hz), 83.9

(dd, P(4), ¹J_P(4),Pt(2)) 2410 Hz, ²J_P(4),Pt(1)) 64 Hz, ²J_P(4),P(2)) 271

Hz, ²J_P(4),P(3)) 25 Hz), 12.5 (d, P(1), ¹J_P(1),Pt(1)) 4004 Hz, ²J_P(1),Pt(2)

) 214 Hz, ³J_P(1),P(3)) 51 Hz), 13.8 (broad, P(3), ¹J_P(3),Pt(2)) 3687

) 1975 Hz), 4.5 (d, P(1), J_P(1),Pt(1)) 4046 Hz, J_P(1),Pt(2)) 275

1

2

Hz, ³J_P(1),P(3)) 8 Hz), 20.8 (d, P(3), ¹J_P(3),Pt(2)) 2528 Hz, ²J_P(3),Pt(1)

2

3

) 32 Hz, J_P(3),P(2)) 298 Hz, J_P(3),P(1)) 8 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5432 (ddd, Pt(1), ¹J_Pt(1),P(1)) 4046

2

3

2

1

2

Hz, J_P(3),Pt(1)) 206 Hz, J_P(3),P(1)) 54 Hz, J_P(3),P(4)) 25 Hz,

Hz, J_Pt(1),P(2)) 2050 Hz, J_Pt(1),P(3)) 32 Hz), -5465 (ddd, Pt(2),

²J_P(3),P(2)) 11 Hz) ppm.

¹J_Pt(2),P(3)) 2528 Hz, J_Pt(2),P(2)) 1975 Hz, J_Pt(2),P(1)) 275 Hz)

1

2

¹⁹⁵Pt{¹H} NMR (C₆D₆, δ): -5358 (dddd, Pt(1), ¹J_Pt(1),P(1)) 4004

Hz, ¹J_Pt(1),P(2)) 2520 Hz, ²J_Pt(1),P(3)) 206 Hz, ²J_Pt(1),P(4)) 64 Hz),

ppm.

1

-5585 (dddd, Pt(2), J_Pt(2),P(3)) 3687 Hz, J_Pt(2),P(4)) 2410 Hz,

¹J_Pt(2),P(2)) 1248 Hz, J_Pt(2),P(1)) 214 Hz) ppm.

2

Syn-[(PHCy₂)(I)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){P(O)Cy₂}] (Pt-Pt)

(8). Strictly equimolar amounts of HI and 1 were used in this

preparation. An aqueous 0.10 M HI solution (0.84 mL) was added

at room temperature under vigorous stirring to a dichloromethane

solution of 1 (100 mg, 0.084 mmol in 8 mL). After 12 h the organic

phase was separated, dried over Na₂SO₄and ﬁltered. Pure 8 was

obtained as a pale yellow powder after evaporation of the solvent.

Yield 86 mg (78%).

Spectroscopic Features of 16:

2

¹H NMR (CDCl₃, δ): 7.09 (t, H-meta, J_H,H) 8 Hz), 6.83 (d,

2

H-ortho, J_H,H) 8 Hz), 6.57 (t, H-para, J_H,H) 7 Hz); 4.63 (m,

1

2

3

H(1), J_H(1),P(1)) 356 Hz, J_H(1),Pt(1)) 156 Hz, J_H(1),P(2)) 5 Hz),

5.03 (m, H(2), ¹J_H(2),P(3)) 368 Hz, ²J_H(2),Pt(2)) 58 Hz), -4.97 (m,

H(3), ²J_H(3),P(1)) ²J_H(3),P(3)) 74 Hz, ²J_H(3),P(2)) 16 Hz, ²J_H(3),P(4)

)

The complex is soluble in toluene and halogenated solvents.

Anal. Calcd for C₄₈H₉₁IOP₄Pt₂: C 43.5, H 6.92; Found C 43.4,

H 6.84.

1

9 Hz, J_H(3),Pt(2)) 599 Hz, J_H(3),Pt(1)) 459 Hz) ppm.

³¹P{¹H} NMR (CDCl₃, δ): 124.9 (dd, P(2), ²J_P(2),P(4)) 276 Hz,

²J_P(2),P(3)) 16 Hz, ¹J_P(2),Pt(1)) 2470 Hz, ¹J_P(2),Pt(2)) 1205 Hz), 88.4

HR ESI-MS, exact mass for C₄₈H₉₁IOP₄Pt₂: 1324.4360; mea-

sured: m/z: 1324.4429 [M]⁺(Supporting Information, Figure S17).

IR (KBr, cm^-1): νj ) 2924 s, 2849 s, 2660 w, 2321 w (P-H),

1624 w (Pt-H-Pt), 1447 s, 1345 w, 1327 w, 1292 w, 1263 s,

1194 w, 1178 m, 1089 s (P ) O), 1023 s (P ) O), 915 w, 886 w,

849 s, 817 s, 801 s, 734 m, 540 w, 521 m, 468 m, 385 m.

1

2

(broad d, P(4), J_P(4),Pt(2)) 2497 Hz, J_P(4),P(2)) 276 Hz), 9.5 (d,

1

2

P(1), J_P(1),Pt(1)) 4176 Hz, J_P(1),Pt(2)) 227 Hz), 9.8 (m, P(3),

¹J_P(3),Pt(2)) 3678 Hz, J_P(3),P(2)) 16 Hz) ppm.

2

¹⁹⁵Pt{¹H} NMR (CDCl₃, δ): -5177 (dd, Pt(1), ¹J_Pt(1),P(1)) 4176

1

2

Hz, J_Pt(1),P(2)) 2470 Hz), -5497 (dddd, Pt(2), J_Pt(2),P(1)) 227

Hz, J_Pt(2),P(2)) 1205 Hz, J_Pt(2),P(3)) 3678 Hz, J_Pt(2),P(4)) 2497

1

¹H NMR (CD₂Cl₂, δ): 4.50 (m, H(1), J_H(1),P(1)) 362 Hz,

1

²J_H(1),Pt(1)) 133 Hz), 5.11 (m, H(2), J_H(2),P(3)) 384 Hz), -4.89

Hz) ppm.

(m, H(3), ²J_H(3),P(3)) 76 Hz, ²J_H(3),P(1)) 69 Hz, ²J_H(3),P(2)) 15 Hz,

1

²J_H(3),P(4)) 8 Hz, J_H(3),Pt(2)) 671 Hz, J_H(3),Pt(1)) 506 Hz) ppm.

³¹P{¹H} NMR (CD₂Cl₂, δ): 157.38 (dd, P(2), J_P(2),P(4)) 272

Hz, J_P(2),P(3)) 9 Hz, J_P(2),Pt(1)) 2381 Hz, J_P(2),Pt(2)) 1291 Hz),

81.24 (dd, P(4), J_P(4),Pt(2)) 2421 Hz, J_P(4),Pt(1)) 52 Hz, J_P(4),P(2)

) 272 Hz, ²J_P(4),P(3)) 25 Hz), 9.95 (d, P(1), ¹J_P(1),Pt(1)) 3904 Hz,

²J_P(1),Pt(2)) 295 Hz, ³J_P(1),P(3)) 53 Hz), 13.88 (broad, P(3), ¹J_P(3),Pt(2)

2

1

2

Anti-[(PHCy₂)(PhS)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂)(SPh)] (Pt-Pt)

(17). A toluene solution of PhSH (22.1 mg, 0.20 mmol in 4 mL)

was added dropwise at room temperature to a stirred toluene

solution of 1 (120 mg, 0.10 mmol in 10 mL) giving an orange

solution. After 2 h the solvent was removed under reduce pressure,

and the obtained solid was treated with MeOH (3 mL). The resulting

suspension was ﬁltered, and the yellow-orange solid was washed

with MeOH and dried under vacuum. Yield 95 mg (79%).

The complex is soluble in toluene and halogenated solvents,

insoluble in methanol.

2

3

2

) 3626 Hz, J_P(3),Pt(1)) 201 Hz, J_P(3),P(1)) 53 Hz, J_P(3),P(4)) 25

2

Hz, J_P(3),P(2)) 9 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5745 (dddd, Pt(1), J_Pt(1),P(1)

)

1

3904 Hz, ¹J_Pt(1),P(2)) 2381 Hz, ²J_Pt(1),P(3)) 201 Hz, ²J_Pt(1),P(4)) 52

1

Hz), -5582 (dddd, Pt(2), J_Pt(2),P(3)) 3626 Hz, J_Pt(2),P(4)) 2421

Hz, J_Pt(2),P(2)) 1291 Hz, J_Pt(2),P(1)) 295 Hz) ppm.

1

2

Anal. Calcd for C₄₈H₇₉P₃Pt₂S₂: C 47.9, H 6.62, S 5.33; Found C

47.7, H 6.76, S 5.28.

HR ESI-MS, exact mass for C₄₈H₇₉P₃Pt₂S₂: 1202.4131; mea-

sured: m/z: 1202.4132 [M]⁺(Supporting Information, Figure S23)

and 1093.4087 [M-PhS]⁺.

Syn-[(PHCy₂)(I)Pt(µ-PCy₂)(µ-H)Pt(PHCy₂){P(OH)Cy₂}]I(Pt-Pt)

(9). An aqueous 0.5 M HI solution (0.35 mL) was added at room

temperature under vigorous stirring to a dichloromethane solution

of 1 (103 mg, 0.09 mmol in 5 mL) giving a pale yellow solution.

IR (KBr, cm^-1): νj ) 3057 m (aromatic CH), 2923 s, 2847 s,

2331 m (P-H), 2324 m (P-H), 1619 w (Pt-H-Pt), 1576 s,

Inorganic Chemistry, Vol. 47, No. 21, 2008 9795

Latronico et al.

After 30 min, the time required for the ³¹P{¹H} NMR to show the

complete disappearance of 8, the organic phase was separated, dried

over Na₂SO₄, and ﬁltered. The solvent was evaporated, and the

crude was treated with toluene. The solid obtained after ﬁltration

was washed with toluene (3 × 4 mL) and n-hexane (3 × 4 mL)

and dried with a gentle stream of dinitrogen. Yield about 40 mg

(ca. 32%).

Complex 9 is unstable at room temperature both in the solid

state and in solution because it transforms spontaneously into 7.

The transformation in the solid state is faster under reduced pressure

thus hampering elemental and HR-MS analyses. The IR spectrum

was recorded immediately after the isolation.

Table 5. Crystal Data and Structural Reﬁnement Details for 3·3CH₂Cl₂

and 4·3CH₂Cl₂

3·3CH₂Cl₂

4·3CH₂Cl₂

empirical formula

formula mass

temperature [K]

wavelength [Å]

crystal system

space group

a [Å]

C₅₁H₉₈OCl₈P₄Pt₂C₅₁H₉₈OBr₂Cl₆P₄Pt₂

1524.95

110(2)

1613.75

110(2)

0.71073

triclinic

P1

0.71073

triclinic

P1

j

14.019(10)

15.335(11)

16.746(12)

105.574(12)

91.827(13)

107.446(12)

3284(4)

2

13.8510(18)

15.2389(19)

16.563(2)

104.614(2)

92.913(2)

107.145(2)

3202.9(7)

2

b [Å]

c [Å]

R [°]

ꢁ [°]

Complex 9 is soluble in halogenated solvents, insoluble in toluene

and n-hexane.

γ [°]

V [Å³]

IR (KBr, cm^-1): νj ) 3446 broad w (P-O-H), 2925 s, 2850 s,

2658 w, 2335 w (P-H), 1632 w (Pt-H-Pt), 1495 w, 1447 s,

1346 w, 1329 w, 1296 w, 1267 m, 1204 w, 1179 m, 1107 m, 1004 s,

917 s (P-O-H), 877 s, 848 m, 818 m, 800 w, 735 m, 530 w,

521 m, 471 m, 457 w, 413 w, 385 w.

Z

D_calcd.[Mg m^-3

]

1.542

1.673

absorption coeff. [mm^-1

]

4.711

5.994

θ range for data coll. [deg]

total reﬂections

2.01-26.00

37106

1.28-26.00

55997

independent reﬂections

data/parameters

9073

12890/586

1.050

0.0546

0.1564

9583

12574/606

1.027

0.0443

0.1145

1

¹H NMR (CD₂Cl₂, δ): 4.80 (m, H(1), J_H(1),P(1)) 354 Hz,

goodness-of-ﬁt on F²

1

²J_H(1),Pt(1)) 136 Hz), 5.19 (m, H(2), J_H(2),P(3)) 372 Hz), -5.52

R^a(I > 2σ(I))

(m, H(3), ²J_H(3),P(2)) 13 Hz, ²J_H(3),P(1)) 68 Hz, ²J_H(3),P(4)) 15 Hz,

²J_H(3),P(3)) 72 Hz, ¹J_H(3),Pt(1)) 379 Hz, ¹J_H(3),Pt(2)) 539 Hz), 7.58

(s, H(4)) ppm.

b

wR₂(all data)

largest diff. peak/hole [e · Å^-3

]

2.37/-2.47

2.61/-2.25

2

^aR ) ∑||F_o| - |F_c||/∑|F_o|. ^bwR₂) [∑w(F_o- F_c)²/∑w(F_o)²]^1/2

.

2

1

³¹P{¹H} NMR (CD₂Cl₂, δ): 169.0 (dd, P(2), J_P(2),Pt(1)) 2470

1

2

Hz, J_P(2),Pt(2)) 1582 Hz, J_P(2),P(4)) 283 Hz, J_P(2),P(3)) 11 Hz),

D8 goniometer with SMART CCD area detector on crystals of

approximate dimensions 0.14 × 0.02 × 0.02 mm (3·3CH₂Cl₂) and

0.14 × 0.33 × 0.40 mm (4·3CH₂Cl₂). Multiscan absorption

corrections with SADABS⁷⁶(for 3·3CH₂Cl₂) and PLATON³⁹(for

4·3CH₂Cl₂) were applied before averaging symmetry equivalent

data. The structures were solved by direct methods⁷⁷and reﬁned

with full-matrix least-squares on F².⁷⁸All non-hydrogen atoms were

reﬁned anisotropically. Hydrogen atoms (except for the bridging

one) were introduced in their idealized positions [d(CH) ) 0.98

Å, d(CH) ) 0.98 Å, d(PH) ) 1.32 Å)] and reﬁned using a riding

model. The bridging hydrogen was treated as riding on Pt1 in a

calculated position (on the plane formed by Pt1, Pt2 and P2, at a

distance of ca. 1.7 Å from the metal atoms).

1

2

122.7 (dd, P(4), J_P(4),Pt(2)) 2691 Hz, J_P(4),Pt(1)) 40 Hz, J_P(4),P(2)

2

1

) 283 Hz, J_P(4),P(3)) 21 Hz), 6.6 (d, P(1), J_P(1),Pt(1)) 3918 Hz,

²J_P(1),Pt(2)) 221 Hz, ³J_P(1),P(3)) 49 Hz), 1.9 (broad, P(3), ²J_P(3),Pt(2)

2

3

2

) 3464 Hz, J_P(3),Pt(1)) 180 Hz, J_P(3),P(1)) 49 Hz, J_P(3),P(4)) 21

2

Hz, J_P(3),P(2)) 11 Hz) ppm.

¹⁹⁵Pt{¹H} NMR (CD₂Cl₂, δ): -5778 (dddd, Pt(1), J_Pt(1),P(1)

)

1

3918 Hz, ¹J_Pt(1),P(2)) 2470 Hz, ²J_Pt(1),P(3)) 180 Hz, ²J_Pt(1),P(4)) 40

1

Hz, J_Pt(1),Pt(2)) 721 Hz), -5668 (dddd, Pt(2), J_Pt(2),P(3)) 3464

1

2

Hz, J_Pt(2),P(4)) 2691 Hz, J_Pt(2),P(2)) 1582 Hz, J_Pt(2),P(1)) 221

1

Hz, J_Pt(2),Pt(1)) 721 Hz) ppm.

Supporting Information Available: ¹H-³¹P HMQC spectrum

of complex 3, ³¹P{¹H} NMR and ¹H-¹⁹⁵Pt HMQC spectra of

complexes 4, 5, 6, 7, 8, 9, 17, HR-MS spectrograms of complexes

3a, 4, 5, 6, 7, 8, 17 and a displacement ellipsoid plot of 4. This

materialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.

X-ray Crystallography⁷⁵. Crystal data, parameters for intensity

data collection and convergence results for 3 · 3CH₂Cl₂and

4·3CH₂Cl₂are compiled in Table 5. Diffraction quality crystals

were grown from CH₂Cl₂/n-hexane. Data were collected with Mo

KR radiation (graphite monochromator, λ ) 0.71073 Å) on a Bruker

IC800508T

(75) Crystallographic data (excluding structure factors) for 3·3CH₂Cl₂and

4·3CH₂Cl₂have been deposited with the Cambridge Crystallographic

Data Centre (CCDC) as supplementary publications no. CCDC 664298

(3·3CH₂Cl₂) and CCDC 664299 (4·3CH₂Cl₂). Copies of the data can

be obtained free of charge on 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].

(76) Sheldrick, G. M. SADABS, Program for Empirical Absorption

Correction of Area Detector Data; University of Go¨ttingen: Go¨ttingen,

Germany, 1996.

(77) Sheldrick, G. M. SHELXS97, Program for Crystal Structure Solution;

University of Go¨ttingen: Go¨ttingen, Germany, 1997.

(78) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Reﬁne-

ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.

9796 Inorganic Chemistry, Vol. 47, No. 21, 2008

Article Doi

Site selectivity in the protonation of a phosphinito bridged Pt I-PtI complex: A combined NMR and density-functional theory mechanistic study

DOI: 10.1021/ic800508t

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Article abstract of DOI:10.1021/ic800508t

Full text of DOI:10.1021/ic800508t

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