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Boletín de la Sociedad Chilena de Química

versión impresa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.44 n.3 Concepción set. 1999

http://dx.doi.org/10.4067/S0366-16441999000300006 

DI AND TRIMETALLIC PtII, PtIV COMPLEXES CONTAINING
DIMETHYLPHOSPHONATE GROUPS S BRIDGING LIGANDS.

RAUL CONTRERAS*, MAURICIO VALDERRAMA, ALEXIS NETTLE AND
VERONICA ARANCIBIA

Departamento de Química Inorgánica, Facultad de Química, Pontificia Universidad Católica
de Chile, Casilla 306, Santiago-22, Chile. E-mail: rcontrer@puc.cl
(Received: April 5, 1999 - Accepted: June 9, 1999).

ABSTRACT

The complexes [Pt{(P(O)(OMe)2)2H}2 ] and [PtCl(PPh3){(P(O)(OMe)2) 2H}] react with Tl(acac) in chloroform or with KOH in methanol solution to yield the trinuclear and binuclear complexes, [Pt{µ-P)O)(OMe)2}4M 2] and [PtCl(PPh3){µ-P(O)(OMe)2 }2M] (M = Tl, K), respectively. These derivatives react with (PtMe3)2SO4·4H 2O or [{Me3PtI}4] with formation of the solvated complexes [Pt{µ-P(O))OMe)2}4{PtMe 3(MeOH)}2] and [PtCl(PPh3){µ-P(O)(OMe)2 }2{PtMe3(MeOH)}]. Addition of donor ligands displaces the coordinated methanol to afford the corresponding adducts [Pt{µ-P(O)(OMe)2}4{PtMe 3L}2] (L = py, 3,5-Me2py, P(p-MeOPh)3} and [PtCl(PPh3){µ-P(O)(OMe)2 }2{PtMe3L}] (L = py, PPh3). The complexes are characterized by elemental analysis, and IR and NMR spectroscopy.

KEY WORDS: Platinum(II), trimethylplatinum(IV), bimetallic, trimetallic, phosphonate, synthesis.

RESUMEN

Los complejos Pt{(P(O)(OMe)2)2H}2 ] y[PtCl(PPh3){(P(O)(OMe)2) 2H}] reaccionan con Tl(acac) en disolución de cloroformo o con KOH en metanol generando los compuestos trinucleares y dinucleares, Pt{µ-P)O)(OMe)2}4M2 ] y[PtCl(PPh3){µ-P(O)(OMe)2 }2M] (M = Tl, K), respectivamente. Estos derivados reaccionan con (PtMe3)2SO4·4H 2O o [{Me3PtI}4] con formación de las especies solvatadas [Pt{µ-P(O))OMe)2}4{PtMe 3(MeOH)}2] y [PtCl(PPh3){µ-P(O)(OMe)2 }2{PtMe3(MeOH)}]. La adición de ligandos dadores producen el desplazamiento del metanol coordinado formando los correspondientes aductos [Pt{µ-P(O)(OMe)2}4{PtMe 3L}2] (L = py, 3,5-Me2py, P(p-MeOPh)3} y[PtCl(PPh3){µ-P(O)(OMe)2 }2{PtMe3L}] (L = py, PPh3). Los complejos obtenidos fueron caracterizados mediante análisis elemental y espectroscopías IR y de RMN.

PALABRAS CLAVES: Platino(II), trimetilplatino(IV), bimetálico, trimetálico, fosfonato, síntesis.

INTRODUCTION

Transition metal complexes containing a secondary phosphinite or phosphonate and a secondary phosphinous acid or phosphite as ligands in a cis arrangement have been the subject of increasing interst due to the presence of a symmetrical hydrogen system [LnM{PR2O· ·H· ·OPR2}](R=OMe, OEt, Ph), where the hydrogen-bonded proton can easily be removed to form a bis(phosphinite) or bis(phosphonate) complex which can act as a bidentate chelating ligand through the oxygen atoms1-6). A variety of bimetallic derivatives have been reported and the formation of the heterometallocycle was confirmed by X-ray diffraction studies4,7).

Some mono and binuclear complexes which contain a pair of symmetrical hydrogen system, [Pt{(P(O)R2)2H}2] (R = Ph, OMe)1) and [M(µ-Cl){(P(O)R2)2H}] 2 (M = Pt, Pd; R = Ph, OMe)1,8), have been described. The mononuclear platinum complex reacts with BF3 to form the trinuclear complex [Pt{(P(O)R2)2BF2} 2] in which the anionic complex acts as a dianionic bridging9). Interestingly, in the reaction of the binuclear complex [Pd(µ-Cl){(P(O)R2)2H}] 2 (R = OMe) with [{Rh(OMe)cod}2] or [Rh(acac)cod], the palladium complex shows a different behavior and the reaction gives an unexpected trimetallic complex that contain a mixed phosphonate-chlorine bridge10).

In this article we report the synthesis and characterization of new homotrimetallic and bimetallic platinum complexes of the types [Pt{µ-P(O)(OMe)2}4{PtMe 3L}2] (L = MeOH, py, 3,5-Me2py, P(p-MeOPh)3} and [PtCl(PPh3){µ-P(O)(OMe)2 }2{PtMe3L}] (L = MeOH, py, PPh3) using the thallium or potassium derivatives, [Pt{µ-P(O)(OMe)2}4M 2] and [PtCl(PPh3{µ-P(O)(OMe)2} 2M], as starting complexes.

EXPERIMENTAL

Elemental analyses were made with a Heraeus Midro Standard microanalyzer. Infrared spectra were recorded on a Perkin-Elmer 567 spectrophotometer (over the range 4000-200 cm-1) using KBr pellets. 1H and 31P{1H} NMR spectra were recorded on a Varian XL-100 (complexes 2-9) and a Bruker AC-200P spectrometers and the chemical shifts are reported in ppm relative to Me4Si and 85% H3PO4 (positive shifts downfield), respectively. The TG/DTA measurements were performed with a Perkin-Elmer system composed by a TGS-1 thermobalance and a UU-1 temperature module.

All reactions were carried out in air at room temperature, except where otherwise stated. Reagent grade solvents were dried, distilled, and stored under a nitrogen atmosphere. The starting complexes [{PtMe3I}4]11), [(PtMe3)2SO4·4H 2O]12), [PtCl(PPh3){(P(O)(OMe)2) 2H}]13), [{PtMe3(OH)}4]14) and [Pd(h3-Me-allyl)(acac)]15) were prepared by published procedures.

Synthesis of complexes

Prreparation of [Pt{(P(O)(OMe)2)2H}2 ] (1).

This compound was prepared by a modification of the reported method1a). To a solution of K2PtCl4 (2.0 g; 4.8 mmol) in methaol-water NaHCO3 solid was added until pH = 9-10, and then an excess of P(OMe)3 (3.2 mL, 24.5 mmol). After the mixture was stired at 45°C in a water-bath for one hour, the excess of NaHCO3 was neutralized with aqueous HCl. The acidic solution was concentrated to half volume and cooled to -20°C, to give white crystals which were washed with methanol-water and diethyl ether. Yield 2.5 g (81%). Calc. for C8H26O12P4 Pt: C, 15.2; H, 4.1; found: C, 15.2; H, 4.2%. IR(KBr): n(P-OCH3) = 1010; n(P=O)= = 1100; d(P-O) = 600 cm-1. 31P{1H} NMR (CDCl3): d 90.15 ppm [s, 1J(Pt-P) = 3458 Hz].

Preparation of [Pt{P(O)(OMe)2}4Tl2 ] (2)

To a solution of 1 (200 mg; 0.31 mmol) in chloroform (20 mL) was added a solution of Tl(acac) (192 mg; 0.63 mmol) in chloroform (40 mL). The mixture was stirred for 24 h. The solution obtained was filtered, evaporated to dryness and the solid residue dissolved in chloroform (10 mL). Careful addition of n-hexane and cooling to -20°C, caused the formation of white crystals, which were washed with diethylether and dried in vacuo. Yield: 264 mg (80%). Calc. for C8H24O12P4 PtTl2: C, 9.2; H, 2.3; found: C, 9.2; H, 2.5%. IR(KBr): n(P-OCH3) = 1020; n(P=O) = 1080; d(P-O) = 564 cm-1.

The similar potassium derivative was obtained using KOH in methanol instead of Tl(acac).

Preparation of [Pt{µ-P(O)(OMe)2}4{PtMe 3(MeOH)}2] (3)

A methanol solution of complex (PtMe3)2SO4·4H 2O (61.4 mg; 0.095 mmol) was added to a methanol solution of [Pt{P(O)(OMe)2}4K2 ] prepared in situ [complex 1 (60 mg; 0.095 mmol) in 15 mL of methanol was neutralized with KOH (10.6 mg; 0.19 mmol) in 10 mL of methanol]. The solid K2SO4 formed was filtered off and the filtrate evaporated to dryness. The solid residue was extracted with the minimal amount of methanol and the complex was precipitated as a white solid by addition of n-hexane as a white solid. Yield: 67 mg (60%). Calc. for C16H50O14P4 Pt3: C, 16.4; H, 4.3: found: C, 16.5; H, 4.4%. IR(KBr): n(P-OCH3) = 1010; n(P=O) = 1070; n(OH) = 3395 cm-1.

This complex can be altrnatively prepared by reaction of complex 1 with [{PtMe3(OH)}4] in a mixture of chloroform-methanol (1:1).

Preparation of [PtCl(PPh3){µ-P(O)(OMe)2 }2{PtMe3(MeOH)}] (4)

A methanol solution of complex (PtMe3)2SO4·4H 2O (100 mg; 0.154 mmol) was added to a methanol solution of PtCl(PPh3){P(O)(OMe)2}2 K] prepared in situ [complex [PtCl(PPh3){(P(O)(OMe)2) 2H}] (219.5 mg; 0.308 mmol) in 20 mL of methanol was neutralized with KOH (17.31 mg; 0.308 mmol) in 10 mL of methanol]. The solid K2SO4 formed was filtered off and the filtrate evaporated to dryness. The solid residue was extracted with the minimal amount of methanol and the complex was precipitated as a white solid by addition of n-hexane. Yield: 186 mg (61%). Calc. for C26H40O7P3 Pt2: C, 31.8; H, 4.1; found: C, 31.9; H, 3.9%. IR(KBr): n(P-OMe) = 1010; n(P=O) = 1070; n(OH) = 3412 cm-1.

This complex can be alternatively prepared by reaction of complex [PtCl(PPh3){(P()(OMe)2)2 H}] with [{PtMe3(OH)}4] in a mixture of chloroform-methanol (1:1).

Preparation of [Pt{µ-P(O)(OMe)2}4{PtMe 3L}2] [L = py(5); 3,5-Me2py(6); P(p-MeOC6H5)3(7 )]

The complexes were prepared by two altenative routes.

a) To a solution of [Pt{P(O)(OMe)2}4Tl2 ], prepared in situ by reaction of 1 (43 mg; 0.068 mmol) with Tl(acac) (41 mg; .136 mmol) in 25 mL of chloroform, was added [{PtMe3I}4] (50 mg; 0.136 mmol) and an excess of the ligand L [pyridine, 0.5 mL; 3,4-lutidine, 0.3 mL]. The resulting mixture was boiled under reflux for 2 h. The thallium iodide formed was filterd off, the solution obtained was concentrated under reduced pressure to a small volume and slow addition of n-hexane gave a microcrystalline white solid.

b) To a solution of complex 3 (120 mg; 0.1 mmol) in methanol (25 mL) was added the stoichiometric amount of P(p-MeOPh)3 (72 mg, 0.2 mmol). The obtained solution was evaporated to dryness, extracted with the minimal amount of dichloromethane and complex 7 crystallized by addition of diethyl ether.

(5) Yield: 67 mg (78%). Calc. for C24H52N2O12 P4Pt3: C, 22.7; H, 4.1; found: C, 22.7; H, 4.1%. IR(KBr): n(P-OCH3) = 1015; n(P=O) = 1080 cm-1. (6) Yield: 57 mg (63%). Calc. for C28H60N2O11 P4Pt3: C, 25.4; H, 2.7; found: C, 25.7; H, 3.0%. IR(KBr): n(P-OCH3) = 1024; n(P=O) = 1088 cm-1. (7) Yield: 102 mg (86%). Calc. for C56H84O18P6 Pt3: C, 37.0; H, 4.6; found: C, 37.0; H, 4.5%. IR(KBr): n(P-OCH3) = 1020; n(P=O) = 1090 cm-1.

Preparation of [PtCl(PPh3){µ-P(O)OMe)2} 2{PtMe3(L)}] [L = py (8); PPh3 (9)]

The complexes were prepared by the alternative routes:

a) To a solution of [PtCl(PPh3){P(O)(OMe)2}2 Tl], prepared in situ by reaction of [PtCl(PPh3){(P(O)(OMe)2) 2H}] (71.3 mg; 0.1 mmol) with Tl(acac) (30.2 mg; 0.1 mmol) in 25 mL of chloroform, was added [{PtMe3I}4] (36.8 mg; 0.1 mmol) and an excess of the ligand L [pyridine, 0.2 mL; PPh3 (31.5 mg; 0.12 mmol)}]. The resulting mixture was boiled under reflux for 2 h. The thallium iodide formed was filtered off, and the solution obtained was concentrated under reduced pressure to a small volume. Addition of n-hexane gave a white solid, which was washed with diethyl ether and dried in vacuo.

b) To a solution of complex 4 (98.4 mg; 0.1 mmol) in methanol (20 mL) was added the stoichiometric amount of PPh3 (26.2 mg; 0.1 mmol). The obtained solution was concentrated under reduced pressure to a small volume. The addition of n-hexane gave the complex 9 as a white solid, which was filtered off, washed with diethyl ether and dried in vacuo.

(8) Yield: 85.6 mg (83%). Calc. for C30H41O6NP3 ClPt2: C, 35.0; H, 4.1; found: C, 35.4; H, 3.9%. IR(KBr): n(P-OCH3) = 1015; n(P=O) = 1080 cm-1. (9) Yield: 72.9 mg (60%). Calc. for C43H51O6P4 ClPt2: C, 42.6; H, 4.2; found: C, 42.5; H, 4.3%. IR(KBr): n(P.OCH3) = 1020; n(P=O) = 1096 cm-1.

Preparation of [PtI2{(P(O)(OMe)2)2 H}2] (10)

To a solution of complex 1 (100 mg; 0.16 mmol) in chloroform (15 mL) was added to a chloroform solution of I2 (40 mg; 0.16 mmol). The mixture was stirred for one hour, while the color changed from yellow to orange. The solution was evaporated to dryness, the solid residue extracted with chloroform and orange crystals were obtained by addition of n-hexane and cooling to -20°C. Yield: 123 mg (88%). Calc. for C8H26I2O12 P4Pt: C, 10.8; H, 3.0; found: C, 10.3; H, 3.2%. IR(KBr): n(P-OCH3) = 1028; n(P=O) = 1096; d(P-O) = 608 cm-1. 31P{1H} n.m.r. (CDCl3: d 31.70 [t, P trans P, 1J(Pt-P) = 2574 Hz]; 2.12 ppm [t, P trans I, 1J(Pt-P) = 3250 Hz].

Reaction between [PtCl(PPh3){P(O)(OMe)2)2 H}] and [Pd(h3-Me-allyl)(acac)].

A solution of complex [Pd(h3-Me-allyl)(acac)] (60 mg; 0.24 mmol) in chloroform (20 mL) was treated with the complex [PtCl(PPh3){(P(O)(OMe)2) 2H}] (171.2 mg; 0.24 mmol). The mixture was stirred at room temperature for 3 h. The white solid formed was filtered off, washed with chloroform and dried in vacuo. This solid was characterized as the polymeric compound [Pt{P(O)(OMe)2}2]n (11). On the other hand the filtrate was evaporated to dryness, the residue extracted with dichloromethane and the solution obtained concentrated under reduced pressure to a small volume. The addition of diethyl eter gave a yellow precipitate, which was filtred off, washed with diethyl ether and dried in vacuo. The yellow complex corresponds to the mononuclear palladium(II) complex [PdCl(PPh3)(h3-Me-allyl)] (12).

(11) Yield: 86,7 mg (79%). Calc. for C4H12O6P2 Pt: C, 11.6; H, 2.9; found: C, 11.5; H, 3.1%. (12) Yield: 74.4 mg (75%). Calc. for C22H22ClPPd: C, 57.5; H, 4.8; found: C, 57.7; H, 4.7%.

RESULTS AND DISCUSSION

The neutral platinum(II) complex [Pt{(P(O)(OMe)2)2H}2 ] (1) reacts with the stoichiometric amount thallium acetylacetonate in chloroform solution to give the trimetallic complex [Pt{P(O)(OMe)2}4Tl2 ] (2). The potassium derivative [Pt{P(O)(OMe)2}4K2 ] was obtained by neutralization of 1 with KOH in methanol solution.

Similarly, the complex [PtCl(PPh3){(P(O)(OMe)2) 2H}] reacts with Tl(acac) in chloroform solution and with KOH inmethanol solution to form "in situ" the corresponding bimetallic complexes [PtCl(PPh3){P(O)(OMe)2}2 M] (M = Tl, K).

Both types of complex, [Pt{P(O)(OMe)2}4M2 ] and [PtCl(PPh3){P(O)OMe)2} 2M}], can be used as starting material to prepare organometallic homotri- and homobinuclear complexes in which the anions [Pt{P(O)(OMe)2}4]2- and [PtCl(PPh3){P(O)(OMe)2}2 ]1- are acting as tetradentate and bidentate bridging ligands, respectively. The utility of the thallium or potassium derivatives for further synthetic purposes is demonstrated by their clean reactions with the complex [(PtMe3)2SO4·4H 2O] in methanol solution or with the tetramer complex [{Me3PtI}4] in a mixture of chloroform-methanol (1:1) solution, with formation of the corresponding trinuclear and binuclear solvated complexes, [Pt{µ-P(O)(OMe)2}4{PtMe 3(MeOH)}2] (3), [PtCl(PPh3){µ-P(O)(OMe)2 }2{PtMe3(MeOH)}] (4), in which the phosphonate groups are acting as bridging ligands between the Pt(II) and Pt(IV) metal centers.

Thermogravimetric measurements of these complexes show the loss of two mol of metahnol by mol of complex 3, in the range 30-165°C, and the loss of one mol of methanol by mol of complex 4, in the range 20-160°C.

The complexes 3 and 4, rapidly react in methanol solution with N- or P-donor ligands by displacement of the coordinated methanol to form the corresponding adducts [Pt{µ-P(O)(OMe)2}4{PtMe 3L}2] [L = py (5), 3,5-Me2py (6), P(p-MeOPh)3 (7)] (Scheme 1), and [PtCl(PPh3{µ-P(O)(OMe)2} 2{PtMe3L}] [L = py (8), PPh3 (9)] (Scheme 2). All reactions are summarized in the Schemes 1 and 2. Their thermogravimetric analyses show the loss of the ligand L in the range 20-270°C, and a gradual loss of mass in the range 270-680°C.

SCHEME 1

SCHEME 2

All complexes were isolated as stable microcrystalline solids. In all cases the solid state infrared spectra show the presence of a strong absorption band characteristic of the n(P=O) stretching vibration. This band is shifted to lower frequencies (1070-1100 cm-1) respect to the n(P=O) band of HP(O)(OMe)2 (1260 cm-1), due to decrease of bond strength caused by coordination. Moreover, the spectra show absorptions in the range 1010-1030 cm-1 characteristic of the P-O-Me unit13b). Complexes 3 and 4 show a broad band centered at 3395 and 3412 cm-1, respectively, assigned to the stretching n(OH) of othe coordinated methenol.

The 1H-NMR spectra of complexes 1-7 in deuterated chloroform exhibit in the range d 3.10-3.70 ppm a multiplet resonance for complexes 1-3,7 and two multiplets resonances for complexes 5 and 6, assigned to the protons of the methoxy groups of the phosphonate ligands. The splitting of the multiplet signal appears in complexes 5 and 6 indicating a non equivalence of the methoxy protons and is probably due to a decrease of the angle between the basal plane of the square geometry of the coordinate group {{Pt{P(O)(OMe)2}4} and the equatorial plane of the octahedral geometry of the organometallic moiety {PtMe3}. The decreases of this angle produce a decrease of the distance between the ligand L (py, 3,5-Me2py) and the phosphonate groups, which in turn causes a differentiation of these methoxy groups6,16).

The platinum-methyl regions of the 1H-NMR spectra of complexes 3 and 4 show a broad singlet signal at d 1.18 [2J(Pt-H)=76 Hz] and 1.41 ppm [2J(Pt-H)=77 Hz], respectively. The broadness of these signals are probably due to a fluxional behavior and, consequently, a middle broad signal is observed for the resonance of protons of the three methyl groups coordinated to platinum(IV). However, for the complexes 5-7 the spectra show two singlet signals with an intensity relation 2:1, and the corresponding satellites due to 195Pt-1H coupling. The more intense signals in these derivatives, that appear at d 0.99 [2J(Pt-H)=77 Hz], 0.96 [2J(Pt-H)=76 Hz] and 1.26 ppm [2J(Pt-H)=78 Hz], respectively, are assigned to the methyl groups trans to the oxygen atoms of the phosphonate ligands6,17). The lower intense signals of these derivatives can be attributed to methyl group trans to N(pyridine), N(3,4-dimethylpyridine) and P(p-methoxytriphenylphosphine), on the basis of their coupling constants values18) (see Table I).

TABLE I. 1H-NMR chemical shifts (d, ppm)a and coupling constants (Hz) of platinum complexes.

aMeasured in CDCl3 at room temperature. Chemical shifts relative to Me4Si a standard; s=singlet, d=doublet, q=quartet, m=multiplet. The complexes 4, 7-10 show multiplets in the region d 7.2-7.8 ppm corresponding to phenyl groups of the ligands.

bThe signal of the MeOH group is masked by the multiplet resonance of the phosphonate group.

c 3J(P-OMe) = 12 Hz. Chemical shifts of [PtCl(PPh3){(P(O)(OMe)2} 2H}: d 3.24 (d, 3J(P-Me) = 12 Hz), 3.28 (d, 3J(P-OMe) = 12 Hz) and 11.8 ppm (s, POH).

On the other hand, the 1H-NMR spectra of the complexes 8 and 9 exhibit two pairs of singlet resonances in 2:1 intensity ratio assigned to the platinum-methyl groups and four doublet resonances attributed to the methoxy protons of the phosphonate groups. These results suggest the existence of a mixture of isomers in chloroform solution.

The methyl resonances present the corresponding satellites due to 195Pt-1H coupling. The largest 2J(195Pt-1H) values (78 Hz) correspond to the methyl groups trans to the oxygen atoms of the phosphonate groups and the lowest values are attributed to the methyl groups trans to nitrogen (70 Hz) or phosphorus atoms (66 Hz) of the ancillary ligands. The percentage relation of the isomers was estabished by integration of the methyl resonances, showing an approach population of 52% and 48% for complex 8, and 51% and 49% for complex 9 (Figure 1).

FIG. 1. Proposed structures for the two isomers of complexes 8 and 9.

All the attempts to realize an oxidative reaction with I2 on the Pt(II) center in the above described tri or binuclear complexes were unsuccessful. In all cases the reactions give rise to uncharacterized solids. However, the starting mononuclear complex 1 reacts with I2 in chloroform solution to give the complex [PtI2{(P(P)(OMe)2)2 H}2] (10). The 1H-NMR spectrum shows a broad signal at d 9.59 ppm assigned to the acidic P-OH proton and the expected multiplet at d 3.92 ppm for the methoxy groups of the phosphonate ligand. This signal is shifted to lower field respect to those in complex 1, due to the modification of the coordination number of the platinum center which causes a large inductive effect of the methoxy groups to the phosphorus atoms. Simultaneously, an increase of the electron density on the Pt(IV) center was produced even though this effect does not cause an increase of the s character of the Pt-P bond. For analogous Pt(II) and Pt(IV) complexes that contain tertiary phosphines, secondary phosphonito or phosphonate and secondary phosphinous acid or phosphite as ligands, some studies show that the s character decreases when the coordination number of the metal center was increased19-21).

The 31P{1H} NMR spectra of complexes 1 and 10 are shown in Figure 2. Complex 1 shows a singlet signal at d 90.14 ppm corresponding to four equivalent phosphorus atoms, with the satellite peaks due to platinum-phosphorus coupling [1J(Pt-P) = 3458 Hz] (spin system A4X), in agreement with the spectral data reported by Roundhill et al.22). The 31P{1H} NMR spectrum of complex 10 shows two triplets resonances corresponding of two pairs of non equivalent phosphorus atoms with a cis PA-PB coupling of 34 Hz(spin system A2B2), together with the satellites due to the Pt-P coupling (spin system A2B2X). This result indicates that the iodine atomes are coordinated to the metal center in a cis arrangement, and the signals that appear at d 31.70 [1J(Pt-P) = 2574 Hz] and 2.12 ppm [1J(Pt-P) = 3250 Hz], are assigned to PA and PB (trans I), respectively. The assignments of the 31P chemical shifts for this complex are on the basis of those reported for similar cis-diiodoplatinum(II) and trans-diiodoplatinum(IV) compounds20,23).

FIG. 2. 31P{1H} NMR spectra for complexes a and 10.

On the other hand, all attempts to prepare heterotri or binuclear Pt-Pd complexes by reactions of starting complexes 1 or [PtCl(PPh3){(P(O)(OMe)2) 2H}] with the compound [Pd(h3-Me-allyl)(acac)] were unsuccessful. In both cases we isolated only decomposition products. Thus, the reaction of the complex [PtCl(PPh3){(P(O)OMe)2)2 H]}] in chloroform solution shows a migration of the Cl and PPh3 ligands from the platinum(II) to the palladium(II) metal center to yield the polymeric compound [{Pt(P(O)(OMe)2)2}n ] (11) and the neutral mononuclear complex [PdCl(PPh3)(h3-Me-allyl)] (12). These compounds were characterized mainly by comparison of their IR and NMR spectra with pure samples obtained by reported methods24,25). As previously reported25), the 1H-NMR spectrum of complex 12 in deuteriochloroform shows two broad doublets, two broad overlapping singlets and a sharp singlet resonances assigned to the protons of the methylallyl ligand, centered at d 4.50 (H1, syn)[3J(P-H1) = 6 Hz]; 3.58 (H2, anti)[3J(P-H2) = 10 Hz], 2.91 (H4, syn), 2.82 (H3, anti) and 1.94 (CH3) ppm. With the aid of double irradiation techniques the broad signals were resolved and all the H-H and P-H couplings can be determined: 3J(H1-H4) = 3.2 Hz; 3J(P-H4) = 1.5 Hz; 2J(H3-H4) = 1.5 Hz and 3J(P-H3) = 2.0 Hz.

ACKNOWLEDGEMENTS
_____________________________
*To whom correspondence should be addressed.

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