Heterobimetallic MIr (M=Pt or Pd) dithiolato bridge complexes

Inorganic Chemistry Communications 2 (1999) 89–92

Heterobimetallic MIr (MsPt or Pd) dithiolato bridge complexes ´ ´ Jorge Fornies-Camer, Anna M. Masdeu-Bulto´ *, Carmen Claver ´ ´ ` Departament de Quımica Fısica i Inorganica, Universitat Rovira i Virgili, Pl. Imperial Tarraco 1, 43005 Tarragona, Spain Received 18 December 1998

Abstract New palladium–iridium and platinum–iridium heterobimetallic bridged dithiolato complexes of general formula [(P-P)M(m-S-S)Ir(COD)]PF6 (CODs1,5-cyclooctadiene; MsPt; P-Ps(PPh3)2 and S-SsEDT (1,2-ethanedithiolato) (1), PDT (1,3-propanedithiolato) (2) and BDT (1,4-buthanedithiolato) (3); MsPd; P-Psdppb and S-SsEDT (4), P-Psdppp and S-SsEDT (5) have been prepared. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Platinum complexes; Palladium complexes; Iridium complexes; Dithiolato bridge complexes; Heterobimetallic complexes

1. Introduction In the last few years the study of homo- and heterobimetallic complexes has increased remarkably because the properties and reactivity of one metal can be modified by another metallic centre in close proximity in the same molecule. Most studies of heterobimetallic complexes have focused on the preparation, physical properties and reactivity of such compounds [1] and some catalytic applications have also been reported [2]. Heterobimetallic complexes have mainly been prepared by reacting two monometallic complexes and by using monoor bidentate bridge ligands which favour metal–metal interaction. Most of the bidentate ligands studied have been diphosphines, in particular Ph2PCH2PPh2 [3–5]. In the case of S-donor ligands, dithiolates have been scarcely used [6] in comparison with thiolato bridge ligands [7–9]. Alkyl dithiolates with few methylenic units produce only the syn conformers and bent structures [10], thus making the systems less flexible than monothiolate ones. More rigid systems might decrease the conformational mobility of the intermediates producing a different reactivity. This characteristic is interesting, for instance, when applying this type of complex as catalyst in homogeneous catalysis. The selectivity of a catalytic process is often determined by reducing the number of transition states which lead to the desired isomer. Another interesting feature of heterobimetallic complexes for homogeneous catalysis is that they allow a wider range of modifi* Corresponding author. Tel.: q34-977-55 81 37; Fax: q34-977-66 95 63

cations than other species, since different metals, bridge or terminal ligands can be introduced in the same system. In a previous paper we reported the preparation and X-ray determination of the first examples of heterobimetallic PtRh and PdRh complexes of general formula [(phosphine)M(m-dithiolato)Rh(COD)]ClO4 (MsPd, Pt) with the alkyl dithiolato bridge ligands yS(CH2)nSy (ns2, 3 and 4) [11]. The synthetic pathway to preparing these compounds was shown to be an efficient method for obtaining heterobimetallic complexes. It consisted of the reaction between the corresponding mononuclear palladium or platinum phosphino-dithiolato complex and the rhodium mononuclear [Rh(COD)2]ClO4 [11]. These complexes have been applied in the hydroformylation of alkenes [12]. We now report the syntheses of new MIr heterobimetallic complexes of general formulation [(P-P)M(m-S-S)Ir(COD)]PF6. Extending this preparation method to the synthesis of these complexes is a good example of its versatility.

2. Experimental All reactions were carried out under nitrogen atmosphere using Schlenk techniques. Solvents were dried by standard methods and distilled before to use. Starting materials [Pd(EDT)(PPh3)2] [13], [Pd(PDT)(PPh3)2] [14] and [Pd(BDT)(PPh3)2] [15] were prepared using already described procedures and the new complexes [Pd(EDT)(dppb)] and [Pd(EDT)(dppp)] were prepared by a similar method. The 1H and 31P-{1H} NMR spectra were recorded on a Varian Gemini 300 spectrometer. Chemical shifts are

1387-7003/99/$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII S 1 3 8 7 - 7 0 0 3 ( 9 9 ) 0 0 0 1 7 - 9

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reported in parts per million relative to external standards (TMS for 1H and H3PO4 for 31P-{1H}). Elemental analyses were carried out with a Carlo-Erba microanalyser. Mass spectra were recorded on a V.G. Autospec spectrometer. 2.1. [(P-P)M(m-S-S)Ir(COD)]PF6 (MsPt, Pd; S-SsEDT (S(CH2)2S), PDT (S(CH2)3S) and BDT (S(CH2)4S); P-Ps(PPh3)2, dppb (Ph2P(CH2)4PPh2) and dppp (Ph2P(CH2)3PPh2). General procedure for complexes 1–5 A stoichiometric amount of [Ir(COD)(py)2]PF6 was added to a solution of the corresponding mononuclear compound [M(S-S)(P-P)] in dichloromethane (5 ml) and the mixture was stirred at room temperature for 30 min. The reaction was controlled by TLC. The red solutions were concentrated to 2 ml and the complexes were isolated as microcrystalline solids by adding cold hexane. [(PPh3)2Pt(m-EDT)Ir(COD)]PF6P1/2CH2Cl2 (1). cis[Pt(EDT)(PPh3)2] (0.0300 g, 0.0370 mmol) and [Ir(COD)(py)2]PF6 (0.0223 g, 0.0370 mmol), red solid (74% yield). 1H NMR (CDCl3) at 208C: d 4.22 (m, 2 H, –CH_, COD), 3.68 (m, 2 H, –CH_, COD), 2.20 (m, 4 H, –CH2–, COD), 2.00 (m, 2 H, –CH2–, COD), 1.75 (m, 2 H, –CH2–, COD), 3.08 (m, 2 H, –CH2–, EDT), 2.35 (m, 2 H, –CH2–, EDT), 7.2–7.5 (m, 30 H, Ph, PPh3). Anal. Calc. for PtIrS2P3F6C46H46P1/2CH2Cl2: C, 42.96; H, 3.62; S, 4.93. Found: C, 42.79; H, 3.61; S, 4.95%. FAB mass: m/z 1111 [MyPF6]q. [(PPh3)2Pt(m-PDT)Ir(COD)]PF6P1/2CH2Cl2 (2). cis[Pt(PDT)(PPh3)2] (0.0300 g, 0.0362 mmol) and [Ir(COD)(py)2]PF6 (0.0218 g, 0.0362 mmol), red solid, (79% yield). 1H NMR (CDCl3) at 208C: d 4.15 (m, 2 H, –CH_, COD), 3.65 (m, 2 H, –CH_, COD), 2.35 (m, 4 H, –CH2–, COD), 2.00 (m, 2 H, –CH2–, COD), 1.80 (m, 2 H, –CH2–, COD), 2.95 (m, 2 H, –SCH2–, PDT), 2.52 (ov, 2 H, –SCH2–, PDT), 2.50 (ov, 2 H, –CH2–, PDT), 7.3–7.6 (m, 30 H, Ph, PPh3). Anal. Calc. for PtIrS2P3F6C47H48P 1/2CH2Cl2: C, 43.42; H, 3.73; S, 4.87. Found: C, 43.53; H, 3.78; S, 4.86%. FAB mass: m/z 1125 [MyPF6]q. [(PPh3)2Pt(m-BDT)Ir(COD)]PF6P1/2CH2Cl2 (3). cis[Pt(BDT)(PPh3)2] (0.0300 g, 0.0358 mmol) and [Ir(COD)(py)2]PF6 (0.0216 g, 0.0358 mmol), red solid (69% yield). 1H NMR (CDCl3) at 208C: d 3.95 (m, 2 H, –CH_, COD), 3.78 (m, 2 H, –CH_COD), 2.65 (m, 2 H, –CH2–, COD), 2.10–2.30 (w, 4 H, –CH2–, COD), 1.98 (m, 2 H, –CH2–, COD), 2.35 (m, 4 H, –SCH2–, BDT), 1.40 (m, 4 H, –CH2–, BDT), 7.2–7.6 (m, 30 H, Ph, PPh3). Anal. Calc. for PtIrS2P3F6C48H50P1/2CH2Cl2: C, 43.86; H, 3.84; S, 4.82. Found: C, 43.77; H, 3.83; S, 4.82%. FAB mass: m/z 1139 [MyPF6]q. [(dppb)Pd(m-EDT)Ir(COD)]PF6P1/2CH2Cl2 (4). cis[Pd(EDT)(dppb)] (0.0300 g, 0.0478 mmol) and [Ir(COD)(py)2]PF6 (0.0288 g, 0.0478 mmol), red solid (76% yield). 1H NMR (CDCl3) at 208C: d 4.02 (m, 2 H, –CH_, COD), 2.48 (m, 2 H, –CH_, COD), 2.05 (m, 2 H, –CH2–, COD), 1.90 (m, 2 H, –CH2–, COD), 1.63 (m, 2 H, –CH2–,

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COD), 1.40 (m, 2 H, –CH2–, COD), 2.95 (m, 2 H, –CH2–, EDT), 2.60 (m, 2 H, –CH2–, EDT), 7.4–7.8 (m, 20 H, Ph, dppb), 2.80 (m, 4 H, –PCH2–, dppb), 1.70 (ov, 4 H, –CH2–, dppb). Anal. Calc. for PdIrS2P3F6C38H44P 1/2CH2Cl2: C, 41.55; H, 4.04; S, 5.75. Found: C, 41.53; H, 3.95; S, 5.72%. FAB mass: m/z 925 [MHyPF6]q. [(dppp)Pd(m-EDT)Ir(COD)]PF6P1/2CH2Cl2 (5). cis[Pd(EDT)(dppp)] (0.0300 g. 0.0491 mmol) and [Ir(COD)(py)2]PF6 (0.0278 g, 0.0491 mmol), brown solid (82% yield). 1H NMR (CDCl3) at 208C: d 4.10 (m, 2 H, –CH_, COD), 3.15 (m, 2 H, –CH_, COD), 2.18 (m, 2 H, –CH2–, COD), 2.00 (m, 4 H, –CH2–, COD), 1.55 (m, 2 H –CH2–, COD), 2.95 (m, 2 H, –CH2–, EDT), 2.75 (m, 2 H, –CH2–, EDT), 7.4–7.7 (m, 20 H, Ph, dppp), 2.50 (m, 4 H, –PCH2–, dppp), 2.10 (m, 2 H, –CH2–, dppp). Anal. Calc. for PdRhS2P3F6C37H42P1/2CH2Cl2: C, 40.99; H, 3.92; S, 5.83. Found: C, 40.87; H, 4.01; S, 5.85%. FAB mass: m/z 911 [MHyPF6]q.

3. Results and discussion The most efficient method for preparing heterobimetallic complexes M1M19 described in the literature is the direct reaction between the two mononuclear fragments M1qM19 [1]. Previous studies reported the preparation of mononuclear platinum and palladium complexes containing dithiolates with general formula [M(S-S)(P-P)] (MsPt, Pd; S-SsEDT, PDT, BDT; P-Ps(PPh3)2, dppb and dppp [13– 15]. Because of the non-bonding electrons in the dithiolato ligand, these complexes act as metalloligands which coordinate a second metal to form heterobimetallic complexes. We recently reported the preparation of MRh complexes [(P-P)M(m-S-S)Rh(COD)]ClO4 by reacting the mononuclear complexes [M(S-S)(P-P)] with [Rh(COD)2]ClO4, in which it is known that the diolefin can be easily displaced [11]. To prepare related MIr complexes we initially used several Ir(I) cationic complexes with different counteranions. When [Ir(COD)2]BF4 was used as the starting material, the heterobimetallic complexes were rather unstable. More stable complexes were formed with the counteranion PF6y when the complex [Ir(COD)(py)2]PF6 was used as the starting material (Scheme 1). This method was applied to the synthesis of PtIr complexes with triphenylphosphine 1–3. With PdIr complexes only EDT and diphosphine complexes were prepared. In all cases, the desired heterobimetallic species were isolated in high yields. There were no other species either in solid state or in solution. The heterobinuclear nature of the related PtRh and PdRh complexes was shown by X-ray analysis in a previous study [11]. Unfortunately, in this case it was not possible to obtain suitable crystals for X-ray characterisation. Nevertheless,elemental analysis agreed with the proposed stoichiometry and FAB mass spectra had signals at m/z which corresponded to the cationic species [(P-P)M(S-S)Ir(COD)]q.

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91

Scheme 1.

The spectroscopic data (1H NMR in Section 2 and 31P{ H} NMR in Table 1) show that there are no redistribution reactions in solution. The 31P-{1H} NMR spectra show only one signal for all the complexes as expected for equivalent phosphorus atoms. For platinum compounds 1–3 the satellites attributed to the 31P–195Pt coupling of the coordinated phosphino ligand were observed. The palladium complexes 4 and 5 show the singlet signal that is to be expected when the diphosphine ligands coordinate to the palladium centre. For platinum complexes 1–3, the coupling constants 1JPt–P have higher values in the heterobimetallic complexes than in the mononuclear ones (for example, 1JPt–P is 3313 Hz for complex 1 and 2884 Hz for the complex [Pt(EDT)(PPh3)2] [15]. This indicates that the M–P bond is stronger in the heterobinuclear complexes. This, in turn, may be related to the weakening of the M–S bond due to bridge coordination. If we compare these coupling constants with those of the corresponding MRh complexes [11], the 1JPt–P values are higher in the MIr complexes (Table 1) probably due to the higher electronic density of the Ir centres. The signals of the 1H NMR spectra were assigned by comparing them with analogous MRh complexes. In all species the olefinic protons corresponding to the coordinated COD appear in the 1H NMR spectra as two multiplet signals. This is expected for a bent structure with a different environment for each of the two different faces of the coordination plane [10,11]. Because of the bent structure and the endo and exo positions of methylenic COD protons, four non-equivalent 1

Table 1 P-{1H} NMR data (d ppm) for complexes 1–5 in CDCl3 solutions with H3PO4 as external standard

sites should be expected for methylenic COD protons. However, not all the non-equivalencies are resolved and the spectra show only 3 signals for all the complexes, except for complex 4 for which the four signals can be seen. As far as the dithiolato protons for complexes 1, 4 and 5 with EDT are concerned, the resonances attributed to the methylenic groups of the dithiolato bridging ligands, which should be equivalent in a homometallic environment, clearly split into two signals around 3.0 and 2.5 ppm. This behaviour was also observed in the analogous PtRh complexes, but not in the PDT and BDT complexes 2 and 3, whose spectra have wide or overlapped signals. This is probably due to conformational exchange of the condensed 6 and 7 membered metalocycles formed by coordination to both metals. This conformational exchange is more difficult in the more rigid complexes with the EDT dithiolato ligand, which forms a five membered ring.

4. Conclusions In conclusion, we set up a new series of heterobimetallic complexes with bridging dithiolato ligands [(P-P)M(mS-S)Ir(COD)]PF6. Combining different dithiolato ligands in the bridge position with different terminal ligands (phosphines or diolefins) may allow the structural and electronic parameters of these complexes to be finely tuned. The catalytic activity in homogeneous processes and the reactivity of these complexes is currently being investigated.

31

Complex

d (ppm)

1 J (Hz)

[(PPh3)2Pt(m-EDT)Ir(COD)]PF6 (1) [(PPh3)2Pt(m-EDT)Rh(COD)]ClO4 [(PPh3)2Pt(m-PDT)Ir(COD)]PF6 (2) [(PPh3)2Pt(m-PDT)Rh(COD)]ClO4 [(PPh3)2Pt(m-BDT)Ir(COD)]PF6 (3) [(PPh3)2Pt(m-BDT)Rh(COD)]ClO4 [(dppb)Pd(m-EDT)Ir(COD)]PF6 (4) [(dppp)Pd(m-EDT)Ir(COD)]PF6 (5)

14.02 15.98 16.45 15.33 19.13 17.69 22.46 6.02

3313 3220 3197 3128 2915 2910

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Ref.

Acknowledgements ´ y Ciencia and the We thank the Ministerio de Educacion Generalitat de Catalunya for financial support (QFN-954725-C03-2; CICYT-CIRIT).

[11] [11]

References

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