Structural Isomers of Bis(diphenylarsino)methane-dichloroplatinum(II)

Arash Babaia,b, Glen B. Deacon*,a, and Gerd Meyerb

a Clayton, Victoria/Australia, Monash University, School of Chemistryb Köln, Institut für Anorganische Chemie der Universität

Received November 6th, 2003.

Abstract. From a range of preparative methods, three geometricisomers of bis(diphenylarsino)methane-dichloroplatinum(II) havebeen isolated, viz. cis-PtCl2(dpam), trans, trans-Pt2Cl4(dpam)2 and

Strukturisomere von Bis(diphenylarsino)methan-dichloroplatin(II)

Inhaltsübersicht. Mit Hilfe einer Reihe präparativer Verfahren wur-den drei geometrische Isomere von Bis(diphenylarsino)methan-dichloroplatin(II) isoliert: cis-PtCl2(dpam), trans, trans-

Introduction

The complex bis(diphenylarsino)methane-dichloroplati-num(II) [PtCl2(dpam)] is a necessary reagent for the syn-thesis of Pt(dpam) organometallic compounds. From at-tempting the reported synthesis stated to give monomeric[PtCl2(dpam)] [1, 2], as well as alternative methods, we haveisolated monomeric cis-[PtCl2(dpam)], trans, trans-[PtCl2(dpam)]2, and cis, trans-[PtCl2(dpam)]2 and charac-terized them by X-ray crystallography, thus establishing therange of geometric isomers.

Results and Discussion

The reported synthesis [1, 2] gave a product mixture of cis-[PtCl2(dpam)] (1) and trans, trans-[PtCl2(dpam)]2 (2):

As the products 1 and 2 are distinguishable by 1H-NMRspectroscopy, a ratio of 3:1 (1:2) was determined for thecomposition of the mixture. A similar route using only thecis-[PtCl2(MeCN)2] isomer, synthesised by Belluco’s method[3], and milder reaction conditions gave a mixture with adifferent composition 3:5 (1:2).

* Prof. Glen B. DeaconMonash UniversityDepartment of ChemistryWellington RoadClayton, Victoria, Australia 3800Fax: �61 39 90 54 59 7e-mail: g.deacon@sci.monash.edu.au

Z. Anorg. Allg. Chem. 2004, 630, 399�402 DOI: 10.1002/zaac.200300358 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 399

cis, trans-Pt2Cl4(dpam)2. Their structures were determined bysingle-crystal X-ray diffraction.Keywords: Crystal Structure; Platinum; Arsine ligands; Geometricisomers

Pt2Cl4(dpam)2 und cis, trans-Pt2Cl4(dpam)2, und ihre Strukturendurch Einkristall-Röntgenstrukturanalyse bestimmt.

By recrystallising the product mixture from DMF/ether,colourless (1) and bright yellow (2) single crystals were iso-lated. The structures were determined by X-Ray diffractionand are displayed in Fig. 1 and 2. An alternative synthesisyielded a 2:1 mixture of 1 and cis, trans-[PtCl2(dpam)]2 (3).

By recrystallisation from CH2Cl2/acetone 3 was isolated.The molecular structure of 3 is shown in Fig. 3. Althoughisolated as a CH2Cl2 and acetone solvate, the former waslost before microanalysis. In order to synthesise 1 in absenceof the other isomers, a ligand exchange reaction (4) success-fully yielded the pure product.

The products were all distinguishable by the CH2-resonancein the 1H NMR spectra (see Experimental). 1 showed asimple aromatic region, 2 a more complex region with over-lapping features and 3 a highly complex pattern with 12different resonances, located on 4 different phenyl-groups.The AB system for the CH2 resonance of 3 indicates a lackof symmetry in the proton-environment, which results inthe phenyl group differences.

A. Babai, G. B. Deacon, G. Meyer

Table 1 Selected distances/A and angles/deg for 1�3

1 2 3

Pt(1)1)-Cl(1) 2.3420(11) 2.317(3) 2.3061(12)Pt(1)1)-Cl(2) 2.3482(11) 2.307(3) 2.3009(12)

Pt(2)2)-Cl(3) 2.3248(13)Pt(2)2)-Cl(4) 2.3527(13)

Pt(1)1)-As(1) 2.3334(7) 2.400(2) 2.4090(7)Pt(1)1)-As(2) 2.3261(6) 2.392(2) 2.3928(7)

Pt(2)2)-As(3) 2.3616(7)Pt(2)2)-As(4) 2.3606(7)

Cl(1)-Pt(1)1)-As(1) 95.12(3) 91.69(12) 97.61(4)Cl(1)-Pt(1)1)-As(2) 87.05(12) 93.71(4)Cl(2)-Pt(1)1)-As(1) 90.85(12) 83.44(4)Cl(2)-Pt(1)1)-As(2) 95.68(4) 90.86(12) 85.30(4)

Cl(1)-Pt(1)1)-Cl(2) 93.21(4) 173.02(5)Cl(3)-Pt(2)2)-Cl(4) 89.38(5)

Cl(3)-Pt(2)2)-As(3) 82.49(4)Cl(4)-Pt(2)2)-As(4) 82.83(4)

As(1)-Pt(1)1)-As(2) 75.98(3) 175.83(2)As(4)-Pt(2)2)-As(3) 105.43(2)

As(1)-C(1)-As(3) 118.4(3)As(2)-C(2)-As(4) 119.8(3)As(1)-C(1)-As(2)3) 92.86(19) 117.9(3)

1) For compound 3 trans configurated Pt2) For compound 3 cis configurated Pt3) Symmetry transformation for equivalent atoms in compound 2: �x�1,

�y�1, �z�2

X-Ray Crystal Structures

All isomers (Fig. 1�3) crystallise in the space group P21/n;selected bond distances and angles are given in Table 1.

In compound 1 the ligand forms a 4-membered chelatering around Pt(1) in a planar arrangement with the atomsPt(1), As(1), C(1), As(2), Cl(1) and Cl(2) in one plane. TheAs(1)-Pt(1)-As(2) (75.98(3)°) angle (Table 1) is identicalwith the P-Pt-P (75.96(3)°) angle in the structure of cis-[PtCl2(dppm)] (dppm � bis(di(o-iso-propylphenyl)phosphi-no)methane) [5], the platinum environment deviates fromsquare planar towards rhombohedral. The bridge headangle of dpam is smaller than that of dppm in cis-[PtCl2(dppm)]; As(1)-C(1)-As(2) (92.86(13)°), (P-C-P94.54(13)°). The Pt-Cl distances (2.342(1), 2.348(1)) are inthe same range as cis-[PtCl2(dppm)] (2.3627(9), 2.3456(9))and cis-[PtCl2(Ph3Sb)2] (2.354(3), 2.326(4)) [6]. The As-Ptdistances (2.3334(7), 2.3261(6)) are greater than P-Pt(2.2301(9), 2.2202(9)) and lower than Sb-Pt (2.491(1),2.510(1)) which is consistent with the ionic radii of the do-nor atoms [7].

The -1 symmetry of 2 ensures a square planar arrange-ment for both platinum atoms, As(1)-Pt(1)-(As2) and thesymmetry generated equivalents form a plane whilst C(1) istilted 41.08° out of this plane. The view along the Pt---Ptaxis (Fig. 2) shows an eclipsed conformation of atoms coor-dinated to platinum, the torsion angle along Cl(1)-Pt(1)-Pt(1)’-Cl(2) is 2.5°. The Pt-Cl distances (2.317(3), 2.307(3))are shorter than in 1 attributable to the weaker trans influ-ence of Cl than As [8] and similar to those of trans-[PtCl2(PPh3)2] (2.2997(11) A) [9]. The As(1)-C(1)-As(2)

2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2004, 630, 399�402400

Figure 1 Structure of cis-[PtCl2(dpam)]

Figure 2 Structure of trans, trans-[(PtCl2(dpam))2]

bridge head angle is 117.9(3)°, much bigger than in the freeligand (105.64(13)°) [10] and in cis, trans-[PtCl2(dpsm)]2(dpsm � bis(diphenylstibino)methane) (114.5(7)°,112.5(7)°) [11] but comparable with compound 3 (118.4(3)°,119.8(3)°). The Pt-As distances are 2.400(2) and 2.392(2) Awhich are similar to the corresponding distances of Pt(1)in (3).

3 is only the second compound reported with this ge-ometry, the other being the distibine analogue mentionedabove [11]. The molecule is built up by two metal centerswith identical donor atoms, each platinum atom has asquare planar stereochemistry, two arsenic atoms from dif-ferent ligand molecules and two chlorine atoms are coordi-nated, but Pt(1) has a trans and Pt(2) a cis arrangement.

Geometric Isomers of Bis(diphenylarsino)methane-dichloroplatinum(II)

Figure 3 Structure of cis, trans-[(PtCl2(dpam))2]

The staggered arrangement along the Pt---Pt axis shows atorsion angle (Cl(1)-Pt(1)-Pt(2)-Cl(4) (�34.2°)) which is inthe same range as that of the distibine analogue (�36.6°).The Pt-Cl bond lengths of Pt(1) are in the expected rangefor a trans Cl-Pt-Cl arrangement (2) (see Table 1) and ofPt(2) for a cis Cl-Pt-Cl arrangement (1) (see Table 1).Longer Pt-As distances are observed for Pt(1) compared toPt(2) due to the stronger trans influence of As than Cl [8].

Experimental1H-NMR spectra were recorded on a 400 MHz Bruker Avancespectrometer at 30°C. IR data (4000�650 cm�1) were obtainedfrom Nujol and hexachlorobutadiene mulls between NaCl plates

Table 2 Selected crystallographic data and refinement parameters

1 2·2DMF 3·Me2CO·CH2Cl2

Empirical formula C25H22As2Cl2Pt C56H58As4Cl4N2O2Pt2 C54H52As4Cl6OPt2

Formula weight 738.26 1622.70 1619.52Crystal system monoclinic monoclinic monoclinicSpace group P21/n P21/n P21/nUnit cell dimensions a � 13.876(3) A a � 18.444(4) A a � 11.380(2) A

b � 13.227(3) A b � 13.727(3) A b � 27.798(6) Ac � 14.340(3) A c � 11.11(2) A c � 16.973(3) Ab � 116.86(3)° b � 90.88(3)° b � 92.04(3)°

Volume 2348.00(11) A3 2813(5) A3 5366.00(19) A3

Z 4 2 4Density (calculated) 2.088 g cm�3 1.916 g cm�3 2.005 g cm�3

Absorption coefficient 9.011 mm�1 7.535 mm�1 7.994 mm�1

Reflections collected 35657 30997 75679Independent reflections / Rint 5675 / 0.0837 6909 / 0.0940 12628 / 0.0823Absorption correction numerical numerical numericalTmax / Tmin 0.3375 / 0.2220 0.3938 / 0.2813 0.5843 / 0.3595Parameters 271 318 607GooF on F 2 1.098 0.979 1.046Final R indices [I>2σ(I)] R1 � 0.0293, wR2 � 0.0663 R1 � 0.0440, wR2 � 0.0982 R1 � 0.0355, wR2 � 0.0613R indices (all data) R1 � 0.0416, wR2 � 0.0765 R1 � 0.0662, wR2 � 0.1064 R1 � 0.0712, wR2 � 0.0733

Z. Anorg. Allg. Chem. 2004, 630, 399�402 zaac.wiley-vch.de 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 401

with a Perkin Elmer 1600 FT-IR spectrometer. Elemental analyses(C, H) were determined by the Campbell Microanalytical Service,University of Otago, New Zealand. The ratio of the product mix-tures was determined by 1H-NMR spectra. This included for anattempt to repeat the reported synthesis [1, 2] of 1 when a 3:1 ratioof 1:2 was obtained. Analytical data for 2 and 3 were obtained forsingle crystals. It was not possible to separate the products chroma-tographically, so the mixtures were separated by handpicking withthe aid of a microscope. Suitable single crystals for X-Ray studiesof 1 and 2 were obtained by recrystallisation from DMF/ether, sin-gle crystals of 3 were grown by recrystallisation from CH2Cl2/ace-tone. K2PtCl4 was supplied by IDT, bis(diphenylarsino)methanewas obtained from Strem Chemicals Inc., dichloro-1,5-hexadien-eplatinum(II) was synthesised by the standard method of Jensen[12], and cis-bis(acetonitrile)dichloroplatinum(II) was synthesisedby the method of Belluco [3].

trans, trans-di-µ-bis(diphenylarsino)methanetetrachlorodiplatinum(II)(2)cis-Bis(acetonitrile)dichloroplatinum(II) (0.42 g, 1.27 mmol) andbis(diphenylarsino)methane (0.60 g, 1.27 mmol) were dissolved inCH2Cl2 (100 ml) and stirred for 24 h at room temperature. Afterremoving the solvent, the product mixture of 1 and 2 (3:5) waswashed with ethanol (20 ml) and dried in high vacuum. Yield: 0.63g (55%). The 1H-NMR data for the main product 2 were derivedfrom the spectrum of the mixture. For elemental analysis, hand-picked crystals of 2 recrystallised from CH2Cl2/ethanol were used.Anal. data [C50H44As4Cl4Pt2 (1476,52)]: C 40.37 (calc. 40.67); H2.80 (3.00)%.

1H NMR ([D6]acetone) δ � 2.99 (s, 4H, CH2); 7.09 (m, 4H(Ph)); 7.23 (m,16H(Ph)); 7.38 (m, 10H(Ph)): 7.47 (m, 10H(Ph))IR: 1578 w, 1481 s, 1434 s, 1338 w, 1302 w, 1184 w, 1080 m, 1023 m, 997 m,913 w, 845 w, 733 s, 709 m, 692 s, 644 s cm�1.

cis, trans-di-µ-bis(diphenylarsino)methanetetrachlorodiplatinum(II)(3)K2PtCl4 (0.95 g, 2.30 mmol) dissolved in 20 ml water was addedto bis(diphenylarsino)methane (1.08 g, 2.30 mmol) dissolved inCH2Cl2 (20 ml), and the mixture was stirred for 2 h at room tem-perature giving a colourless aqueous phase. After separating theaqueous phase, ether was added to the orange CH2Cl2 layer tocrystallise a product mixture of 1 and 3 (2:1). Yield: 1.69 g � 89%

A. Babai, G. B. Deacon, G. Meyer

The 1H-NMR data for 3 are derived from single crystals. For el-emental analysis, handpicked crystals recrystallised from CH2Cl2/acetone were used.Anal. data [C50H44As4Cl4Pt2(CH3)2CO (1534.62)]: C 41.72 (calc.41.48); H 3.35 (3.28)%.1H NMR ([D6]acetone) δ � 3.86/3.98 (AB doublet, J(A,B) � 12.8 Hz, 4H,CHAHB); 6.61 (m, 4H, m-H(Ph)); 6.81 (m, 4H, o-H(Ph)); 6.89 (m, 2H, p-H(Ph)); 7.27 (m, 4H, m-H(Ph)); 7.31(m, 2H, p-H(Ph)); 7.45 (m, 6H, o, p-H(Ph)); 7.64 (m, 6H, m, p-H(Ph)); 7.86 (m, 4H, o-H(Ph)); 8.08 (m, 4H, m-H(Ph)); 8.37 (m, 4H, o-H(Ph))IR: 1580 w, 1483 s, 1436 s, 1308 w,1251 w, 1186 w, 1091 m, 1078 m, 1026 m,997 m, 750 s, 740 s, 734 s, 690 s, 658 s cm�1.

cis-bis(diphenylarsino)methanedichloroplatinum(II) (1)Bis(diphenylarsino)methane (0.20 g, 0.42 mmol) and dichloro-1,5-hexadieneplatinum(II) (0.15 g, 0.42 mmol) were treated with di-chloromethane (15 ml). The mixture was stirred for 1 h, and theresulting white precipitate was filtered off, washed with ethanol anddried in high vacuum giving a white powder. Yield 0.20 g (64%)Anal. data [C25H22As2Cl2Pt(738.26)]: C 40.83 (calc. 40.67); H2.96 (3.00)%.1H NMR ([D6]acetone) δ � 5.29 (s with 195Pt satellites, J(Pt, H) � 50 Hz,2H, CH2); 7.55 (m, 8H, m-H(Ph)); 7.57 (m, 4H, p-H(Ph)); 7.97 (m, 8H,o-H(Ph))IR: 1581 w, 1573 w, 1548 w, 1478 s, 1436 s, 1438 s, 1309 w, 1164 w, 1081 m,1024 m, 997 m, 971 w, 846 w, 736 s, 722 m, 690 s, 682 w, 657 m, 643 m cm�1.

X-Ray-structure determination

For all compounds a hemisphere of data (1° frames in phi andomega) were collected at 123(1) K using an Enraf-Nonius CCDarea-detector diffractometer (monochromatic Mo-Kα radiation,λ � 0.71073 A), yielding Ntotal collected reflections after inte-gration and scaling using the DENZO SMN software package [13].Each data set was merged to N unique reflections (N0 (I>2σ(I))‘observed’). The structures were solved using Direct Methods andrefined with anisotropic thermal parameters for the non-hydrogenatoms by full matrix least-squares on all F 2 data using theSHELX97 [14] and XSEED [15] software packages. For all com-pounds hydrogen atoms were placed geometrically and refined iso-tropically using the riding model. Absorption corrections were per-formed using the program X-Red [16] (compound 1 and 2) andWinGX [17] (compound 3). Crystal and refinement details for eachcompound are listed in Table 2. Compound 2 crystallised with twoDMF molecules per molecule of dimer, 3 with one molecule ofdichloromethane and one molecule of acetone per dimer molecule.

2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2004, 630, 399�402402

For clarity reasons the solvent molecules in Figure 2 and 3 areomitted. For compound 3, an attempt to model carbon atomsC(31), C(32), C(34) and C(35) as part of a disordered phenyl group(the two components related by a rotation of approximately 20 degabout the C(30), C(33) axis) gave unsatisfactory refinement charac-teristics. Details of the structures have been deposited with theCambridge Crystallographic Data Centre of which the depositionnumbers CCDC 222269 (1), CCDC 222270 (2), and CCDC 222271(3) were allocated.

This work has been supported by the DAAD (Bonn) through astipend to A.B. for which we are grateful.

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