Complexes of palladium, platinum and rhodium with potentially tetradentate ligands containing nitrogen and tellurium donor atoms (N2Te2)

Polyhedron Vol. 8, No. 23, pp. Printed in Great Britain

2769-2776,

0277-5387/89 S3.00+ .Jl Pergamon Press plc

1989

COMPLEXES OF PALLADIUM, PLATINUM AND RHODIUM WITH POTENTIALLY TETRADENTATE LIGANDS CONTAINING NITROGEN AND TELLURIUM DONOR ATOMS (N,Te,) N. I. AL-SALIM

and W. R. McWHINNIE”

Department of Chemical Engineering and Applied Chemistry, Aston University, Aston Triangle, Birmingham B4 7ET, U.K. (Received 7 February 1989 ; accepted 20 July 1989) Abstract-Complexes of the ligands 1,6-bis-2-butyltellurophenyl-2,5-diazahexa1,5-diene (I) and 1,4-bis-2-butyltellurophenyl-2,3-diazabuta1,3-diene (II) with palladium, platinum, and rhodium are described. [PdCl(I)(H,O)]Cl is an electrolyte and has the chloro-ligand tram to water; the implications for the mode of coordination of I are discussed. For [PdCl,(II)] evidence for both “cis” and “trans” isomers is obtained ; since, as in the above case, no evidence for N-coordination is obtained, the nature of the “tram” isomer is debated. [PtCl(I)(H,O)]Cl, an electrolyte, decomposes in polar solvents to give [PtCl,(I’-)], where (12-) donotes ligand I which has lost two butyl groups, the complex being a platinum(IV) derivative. Ligand I coordinates only via tellurium in the platinum(I1) complex, but some evidence of N-coordination to platinum(IV) is obtained. The early stages of the de-alkylation reaction are monitored by “‘Te and ‘95Pt NMR spectroscopy. By contrast, [PtCl,(II)] - H20 is a cis complex in which II coordinates via tellurium only and does not undergo de-alkylation. Some complexes of both rhodium(II1) and rhodium(I) are reported. The most interesting observation being that I may function as a terdentate ligand (Te, N, Te) in [RhCl(I)].

We have recently published papers describing the syntheses of potentially bidentate Te, Te ligands’ of the type RTe(CH,),TeR, and of ligands containing both tellurium and nitrogen as potential donor atoms, e.g. derivatives of tellurated 2-phenylpyridine2 and 1,6-bis-2-butyltellurophenyl-2,5diazahexa-1,5-diene (I),3 together with l,Cbis2-butyltellurophenyl-2,3-diazabuta1,3-diene (II). n-Bu I Te &by:I a

-0

\ ’ ’

(X)/7= Te

I /7-E%

I

(I[)n=O

Some investigations on the coordination chemistry of these materials have been reported. For example, *Author to whom correspondence should be addressed.

the reactions of (p-Et0 - C,H,)Te(CH,),Te (CsH40Et-p) (n = 5-10) with palladium(II), platinum(I1) and mercury(I1) have been described.4 The complexes were poorly crystalline and tended to have a limited range of thermal stability which limited the information obtainable from multinuclear NMR studies. The crystal structure of compound I has been reported together with that of the complex with HgC125 in which only the two tellurium atoms coordinated mercury(I1). In this paper we attempt to extend studies of I in complexes with palladium, platinum and rhodium. The literature contains a paucity of reports on biand multidentate tellurium ligands, although many sulphur systems are known. Of relevance is the report by Bertini et al6 on Schiff base ligands having donor sets S, N and S2N2, including an analogue of I in which -SH replaces -TeBu. Blum et al.’ have also produced a related sulphur ligand which forms square-planar complexes with a range

2769

N. I. AL-SALIM

2770

and W. R. McWHINNIE

of divalent metals, e.g. ligand III. An interesting feature of the crystal structure of I5 was a weak Te-- -N interaction. One objective of this paper is to ascertain to what extent this interaction limits the availability of the nitrogen for coordination to the added transition metal salt.

EXPERIMENTAL The details of the preparations of I and II appear elsewhere. 3,5 (a) Palladium complexes With ligand I. Bis(benzonitrile)dichloropalladiurn( (0.38 g, 0.001 mol) in a&on&rile (15 cm3) was added to an acetonitrile (15 cm3) solution of I (0.60 g, 0.001 mol), and the mixture was stirred at room temperature, under dinitrogen, for 2 h. The volume was reduced to 5 cm3 in a stream of dinitrogen gas and benzene was added to precipitate a brown compound, which was filtered, washed with benzene and diethyl ether and dried in uacuo. The yield of the blackish-brown material was 0.67 g, m.p. 131-132°C (dec.). With ligand II. Two methods were used: (i) Bis(benzonitrile)dichloropalladium(II) (0.38 g, 0.001 mol) in a 1 : 1 benzene-acetonitrile mixture (15 cm’) was treated with a warm acetonitrile solution (I 5 cm3) of II (0.58 g, 0.001 mol). The mixture was stirred at 50°C under dinitrogen for 5 h to give a brown precipitate which was collected by filtration and washed several times with benzene. Recrystallization from toluene gave a brownish-red compound, m.p. 183-185°C (dec.). (ii) A solution of [Ph,As][PdCl,] (prepared by metathesis of Ph,AsCl and K,PtCl,) (0.20 g, 0.0002 mol) in dichloromethane (15 cm3) was added slowly, with stirring, to a solution of II (0.115 g, 0.0002 mol) in dichloromethane (10 cm3). On setting aside for 2 h the solution deposited an orange-brown compound which was separated, washed with dichloromethane and air-dried (yield : 0.136 g) ; m.p. 185°C (dec.).

(b) Platinum complexes With ligand I. Two methods were used: (i) A solution of [Ph,As] ,[PtCI,] (1.103 g, 0.001 mol) in

dichloromethane (20 cm3) was added to I (0.60 g, 0.001 mol) in dichloromethane (15 cm’) and refluxed for 1 h, during which time a pale cream suspension formed. The compound was collected by filtration, washed with dichloromethane and airdried. During the melting point determination the compound darkened at 80°C became black, but failed to melt under 300°C. (ii) The same experiment was carried out in refluxing acetonitrile. The cream suspension was visible for the first 15 min, but when reflux was continued beyond that point the product became brownish. After 2 h, a dark brown solution and solid were present, the solid was filtered, washed with acetonitrile and dried in vacua. The material failed to melt under 300°C. With 1igandII. A solution of [Ph,As],[PtCl.,] (0.22 g, 0.0002 mol) in dichloromethane (15 cm’) was added slowly, with stirring, to a solution of II (0.115 g, 0.002 mol) in dichloromethane (10 cm3). The resulting solution was stirred and heated under reflux for 5 h. The orange precipitate so formed was filtered, washed with dichloromethane and air-dried (Yield : 0.10 g) ; m.p. 170°C (dec.). (c) Rhodium complexes With ligand I. (i) Thodium(II1): Dipotassium pentachloroaquorhodate(III), KdWH,Wl,l (supplied) (0.38 g, 0.001 mol), in a mixture of methanol (20 cm3) and DMSO (10 cm3) was reacted with a warm solution of I(O.60 g, 0.001 mol) in methanol (10 cm3). The mixture was stirred for 2 h under dinitrogen, after which the methanol was removed in uacuo ; the remaining solution was allowed to evaporate slowly at room temperature. The resulting solid was dissolved in dichloromethane (20 cm3) and filtered, the filtrate, after evaporation at room temperature, afforded a brown solid, m.p. 122°C. (ii) Rhodium(I) : Method A. Di-p-chloro-bis(q41,5-cyclooctadiene)dirhodium(I)’ (0.15 g, 0.0003 mol) in dichloromethane (10 cm’) was added to a solution of I (0.36 g, 0.0006 mol) in dichloromethane (15 cm’). The colour changed immediately to brown. Following reflux (4 h) the colour of the solution became red-brown and some precipitate deposited. Filtration afforded a red-violet solid (product A) which was washed with dichloromethane and air-dried (yield : 0.02 g) ; m.p. 243°C (dec.). Dry diethyl ether was added to the filtrate to give a brown material which was redissolved in ethanol, filtered and recovered by evaporation at room temperature: product B, yield: 0.26 g, m.p. 185°C (dec.). Method B. Di-~-chloro-bis(~4-1,5-cyclooctadiene)dirhodium(I) (0.15 g, 0.0003 mol) was dis-

Complexes of Pd, Pt and Rh with potentially tridentate ligands solved in dichloromethane (10 cm3) and added to I (0.54 g, 0.0009 mol) in dichloromethane (10 cm3) at room temperature. The mixture was refrigerated at 4°C for 4 h, after which the solution was filtered to give a red-violet crystalline compound (product A) which was washed with dichloromethane (yield :0.1 g); m.p. 243°C (dec.). The filtrate was treated with diethyl ether as described above to give a further quantity (0.28 g) of product B, m.p. 186°C (dec.). The elemental analytical data for A and B were independent of the method of preparation. With ligund II. (i) Rhodium(II1): K,[Rh(H,O)Cl,] (0.19 g, 0.0005 mol) was dissolved in ethanolDMSO (1 : 1, 20 cm’) and treated with a solution of II(0.29 g,0.0005 mol) in ethanol (10 cm’). The mixture was stirred at 80°C under dinitrogen for 2 h, during which time the colour changed from orange to dark brown. The solution was taken to 5 cm3 in Z~QCUO and left to evaporate at room temperature. The resulting solid was dissolved in chloroform, recovered by removal of solvent in uacuo and washed with methanol followed by diethyl ether, m.p. 160°C (dec.). (ii) Rhodium(I) : Di-p-chloro-bis(q4- 1,5-cyclooctadiene)dirhodium(I) (0.25 g, 0.0005 mol) in dichloromethane (15 cm’) was added slowly to a solution of II(0.58 g,0.001 mol) and refluxed for 7 h under dinitrogen. The colour changed from orange to deep brown, the solution was cooled and treated with diethyl ether to give a brown compound which was filtered, washed with diethyl ether and air-dried (yield : 0.51 g) ; m.p. 220°C (dec.).

2771

Physical measurements

Elemental analyses were carried out by the Analytical Services Unit, Aston University. NMR spectra (‘H, 90 MHz; 13C, 22.5 MHz; 125Te, 28.2 MHz ; 19’Pt, 21.46 MHz) were obtained with a JEOL FX 90Q spectrometer. Conductivities were measured using a standard Mullard bridge and an immersion-type bright platinum electrode cell (E 7591/B). IR spectra were determined as KBr pellets or Nujol mulls with a Perkin-Elmer 599B instrument (range 400&200 cm- I). UV-vis spectra were recorded with a Unicam SP8-100 instrument. DISCUSSION Table 1 gives the stoichiometries of the complexes. Where the presence of water is involved, IR support for this is available. Although precautions were taken to exclude air from the preparations, no particular precautions were taken for the exclusion of moisture. Of importance to this work is the complex of mercury(I1) chloride and 1,6-bis-2-butyltellurophenyl-2,5-diazahexa-1,5-d&e (I), the structure of which has been reported. 5Only the tellurium atoms coordinate mercury, the weak but significant Te---N contact remains almost unaltered in the complex (Te---N, 2.773 A-free ligand; 2.752, 2.786 A--complex). Formally, the mercury(I1) complex contains a 13-membered chelate ring, but if the Te---N interaction is taken as a bond then

Table 1. Analytical data for new complexes Complex F'dWI)l

- Hz0 (1)

FdCl,(II)I” (2) l?dWIW (3) [PtClx(I)1- H D (4) [PtCl,(I’-)I-2H,0d (5)

Ptcl,W)l - Hz0 (6)

[=C~,O)l* 2H20 (7 [RhCl,(II)] - H,O (8) lRhCl(I)P (9)

[~CW%o* 00) NaWI

(11)

C

Found (%) H

N

C

35.8 35.4 35.2 32.1 24.7 30.3 34.1 32.8 38.5 39.4 36.7

4.3 3.8 3.7 3.5 2.3 3.2 4.0 3.4 4.4 4.6 3.9

3.4 3.7 3.5 3.1 3.3 3.0 3.8 3.5 3.5 3.8 3.8

36.1 35.1 35.1 32.5 24.3 30.7 34.0 32.9 38.8 39.4 37.0

Required (%) H N 4.3 3.7 3.7 3.9 2.3 3.5 4.3 3.7 4.3 4.4 4.0

“Method (i). bMethod (ii). ‘From [Ph,As],[PtCl,] in CH,C12. ‘From [Ph4As12[PtC1,] in CH,CN; I*- is derived from I by loss of butyl groups. e “Product ’ “Product

A”. B”.

3.5 3.7 3.7 3.1 3.5 3.2 3.3 3.5 3.7 3.8 3.9

N. I. AL-SALIM

2772

and W. R. McWHINNIE

the mercury(I1) ion “sees” a seven-membered ring. The change in the ligand v(C=N) frequency on complexing mercury(I1) is + 5 cm- ‘, thus changes of this order are likely to imply that the Te---N interaction in the coordinated ligand remains intact and that the ligand functions as a Te, Te bidentate. It is not unreasonable to apply similar reasoning to ligand II. Thus, inspection of Table 2 suggests that only in the cases of complexes 9 and 10 need the question of nitrogen coordination be considered. Complex 5 comes into this category, but is clearly a complex of a derived ligand (aide infru). Palludium(I1) complexes

[PdCl,(I)] - Hz0 (compound 1, Tables 1 and 2) is a 1: 1 electrolyte in both DMSO and acetonitrile, thus the formulation [Pd(I)Cl(H,O)]Cl is suggested. In the IR spectrum v(OH) is noted at 3400 cn- ’ and the position of v(C=N) (Table 2) implies Te,Te coordination only ; v(PdC1) may be assigned at 345 cm- ‘. It is known that v(PdC1) for [PdC1L’L2]+, where L’ = neutral ligand and L = phosphine, is a function of L’ in the trans isomer. lo It is also known that the tram influence decreases in the order: Cdonors (sp3 > sp2 > sp) > P-donors > As-donors > S-donors > N-donors > halide > O-donors; also Te-donors > Se-donors > S-donors. ” Thus in the present complex the value of 345 cm-’ suggests that the chloro-ligand is truns to oxygen. We also note that for I2 truns-{Pd[Te(CH2

SiMe3)2]nC12}, v(PdC1) = 348 cm- ’ and for-l3 trans-

{Pd[Te(C6H4-OEt-p)2]2C12}, v(PdC1) = 351 cm-‘. The above data suggest that the structure of the complex may be more complex than at first imagined. One model would have the ligand spanning tram coordination sites, however, given that the Te-- -N interaction is retained we feel that the ligand is too inflexible for this to be realistic (the TeHgTe angle is 109.1”).5 An alternative model is given in Fig. 1. This type of dimer has been suggested for complexes of RTe(CH2)sTeR.4 The conductivities would now be 228 (MeCN) and 70 (DMSO) Q- ’ cm2 mol- ‘, values not inconsistent with 2 : 1 electrolytes. Geometric isomers are possible but the available data would make differentiation difficult. Unfortunately, limited solubility prevented a comprehensive NMR study. [PdCl,(II)] (compound 2, Tables 1 and 2) is a non-electrolyte in benzonitrile and is insoluble in more polar solvents. We argue that the position of v(C=N) suggests that the ligand is bidentate (Te,Te), in which case the metal “sees” a five-membered chelate ring if the Te---N interactions remain intact. Two v(PdC1) frequencies are seen at 332 and 288 cm-’ suggestive of a cis complex, although the v,,(PdCl) frequency at 332 cm-’ is rather higher than the range normally associated with this mode (3053 12 err- ‘), however, v,(PdCl) is usually assigned between 285-292 cm- ‘. 14*’5 Attempts to recrystallize this complex from chloroform led to the recovery of material having the same

Table 2. Physical data for new complexes UV-vis spectra maxima Complex” Ligand I Ligand II 1 2 3 2’b 4 5 6 7 8 9 10 11

v(C=N)

(cm- ‘)

1637 1616 1635 1622 1622 1620 1625 1615 1626 1640 1620 1632, 1595 1660,1595 1610

Av(C=N)

-2 +6 +6 +4 -12 -22 +10 +3 +4 -5, -42 +23, -42 -6

r?See Table 1. bCompound 2 after digestion in CHCl,. Note : the complex [HgCl,(I)ls gives v(C=N)

v(M-Cl)

345 332,288 335,290 332,289,345 315 325,295 322 340,365 300

(cm- ‘)

(nm) 366 410 464,384 435,355,320

AM (a- ’ cm’ mol- ‘)

114 (MeCN) 35 (DMSO)

464,384

35 (DMSO) 12 (DMSO)

425,360 395 412

20 (DMSO) 6 (DMSO) 11 (CH,CN)

660,555,390,315,295 7 (CH,CN)

at 1642 cm- ‘, i.e. Av(C=N)

= + 5

cm- ‘.

Complexes of Pd, Pt and Rh with potentidly tridentate ligands I

I

Te

Te

1

+

1 2+

p/clnp/w~c~ t

t

Te

Te

I

I

Fig. 1.

elemental analysis but with a new v(PdC1) frequency at 345 cm-‘, in addition to those already noted. This appears to indicate the presence of a “trans” isomer which, for reasons given above, would have to be modelled on Fig. 1. Thus the available data suggest that either of the two equilibria (A) or (B) (see Scheme 1) could provide an explanation of the observations. The UV-vis spectra (Table 2) of 1 and 2 are consistent with square-planar palladium ; for example bands around 420 nm have been reported for other ditellurium complexes4 Platinum complexes Compounds 4 and 6 (Tables 1 and 2) have the stoichiometry [PtCl,(L)] *(H,O) (L = I or II). In neither case does the shift in v(C=N) from the free ligand value seem large enough to invoke nitrogen coordination. Compound 4 has a AM value consistent with that for a 1 : 1 electrolyte (but see below). The single v(PtC1) frequency at 315 cm- ’ suggests that the chloro-ligand is trans to groups with moderate trans influence ;” of particular interest is a comparison with the complex [Pt(bmsp)C1]PF6,‘6 where bmsp = (Me SeCH,CH,),Se, which has v(PtC1) at 320 cm-‘. Thus the probability is that chlorine is trans to tellurium rather than to HzO. The lz5Te NMR of complex 4 was measured in DMSO, but not without gentle heating to obtain a clear solution of the appropriate concentration. It was noted that the colour of the solution had become slightly brown during the dissolution process. The observed spectrum (Fig. 2) shows two resonances centred at 6 469.5 and 512.2 ppm down-

field from dimethyltelluride. Both resonances have associated satellites arising from spin-spin coupling to 19’Pt (6 469.5 ppm J(PtTe) = 1014 Hz; 6 512.2 ppm J(PtTe) = 1035 Hz), thus demonstrating that both signals originate from tellurium bound to platinum. The observed coupling constants support the IR implication of cis-tellurium atoms, since for trans-TePtTe, J(PtTe) is generally of the order of 600 Hz.~’ I5 Further, the lz5Te chemical shift of the resonance at 512.2 ppm also supports a cis configuration since A(6) (the coordination shift) for tram complexes is generally greater than the 47.8 ppm observed here. 4,’5 The second tellurium resonance is, however, at 469.5 ppm, close to the free ligand value of 464.4 ppm, but it cannot arise from uncoordinated tellurium since J(PtTe) is clearly seen. No evidence for the coupling of inequivalent tellurium atoms is seen (however, J(TeTe) may be small or apparently zero due to multiple transmission paths), also the resonances are of unequal intensity ; we believe this to imply that the resonances arise from different solution species. Cistrans isomers are eliminated by the similar values of J(PtTe). A common phenomenon in group 16 ligand chemistry is the observation of meso and DL isomers which may arise due to inversion at the coordinated S, Se, or Te ligand atoms of the bidentate ligands. “7 ’ 7 It is anticipated that the barrier to inversion at tellurium will be greater than for selenium and sulphur, ’ ’ thus distinct signals from the meso and DL invertomers may well be seen at ambient temperature. Although it had been suggested previously that chemical shift differences between meso and DL invertomers may be small,4 a recent paper I9demonstrates, for platinum(I1) complexes of [RTeCH&H,CH$H,TeR] (R = Me, Ph), that chemical shift differences of 63 ppm {for [Pt(MeTe(CH,),TeMe)Cl,]} and 26 ppm {for [Pt(PhTe(CH,),TePh)Cl,]} are possible for the invertomers ; however both invertomers show large coordination shifts.” Thus we believe that the species observed may not be accounted for in terms of invertomers. The reaction of [Ph,As],[PtCl,] with I in refluxing acetonitrile gives complex 5 (Table l), which analyses as a complex of de-butylated I. IR data

Te -Te

Te-Te *\ Te/

p/c1 ‘Cl

2773

(A)

e

Cl’

Scheme 1.

2774

N. I. AL-SALIM and W. R. McWHINNIE 469.5 ppm from MezTe 5. I ppm from ligand

Ligand = 28283163.9 (L)

=

464.4

from Me,Te

512.2 ppm from Me,Te 47.8 ppm from ligond (Ll

J (ls’Pt

-‘z5Te)

- 1034.6

J (‘95Pt -“‘Te

Hz

1 = 1014

Hz

Fig. 2.

support the postulate of de-butylation and complex 5 is therefore, by implication, a complex of platinum(IV) (see Fig. 3). The shift of v(C=N) for de-butylated I is also greater than for other palladium and platinum complexes in Table 1, and this must raise the possibility of Pt’” c N coordination in complex 5. The final formation of complex 5 does then raise the possibility that the species giving a chemical shift of 6 469.5 ppm in the “‘Te NMR spectrum is a complex of de-butylated I. It is improbable that the species seen is a complex of platinum(IV), since if similar platinum(II~platinum(IV) complexes are compared Jpoc(Pt’“) N 0.67 JptX(Pt”)20 (where X = ligand atom), whereas J(PtTe) for the two species are virtually identical. Thus, if the species with 6(‘25Te) at 469.5 ppm is

a:I

-N?

‘PP

Te’

Alkyl aryl telluride complex of Pt”

Aryl tellurate complex of Pt’“. Fig. 3.

a complex of the de-butylated ligand, the solvent DMSO must be implicated [eq. (I)] : I Te\ Te, c

7 Pt

\C~

+

4 DMSO

I 8 =512.2

=

ppm

*\ Te, c

JDMSO Pt ,DMso

6=469.5

+ 2 [DMSO.Bul+Cl

(1)

ppm

Rainville and Zingaro2’ have demonstrated that lomethylphenoxatelluronium iodide will readily form [(CD,),SO(Me)]+Iin (CDJ2SO; since there is Mijssbauer evidence that, electronically, tellurium experiences similar environments in R3Te+ and R,Te + Pt,22*23the postulate of facile de-butylation of coordinated I in DMSO is reasonable. The model of tellurium de-butylation mirrors a phenomenon well known for organosulphur24 and organoselenium25 ligands. Further NMR and conductivity work was then carried out. Thus the ‘H NMR spectrum of a solu-

Complexes of Pd, Pt and Rh with potentially tridentate ligands

2775

tion of complex 4 in DMSO was determined. The n-Bu most interesting feature was a doubling of the -CH=Nresonance (6 = 9.12, 9.15 ppm vs TMS) one component of which shows J(PtH) = 92 Hz. This coupling constant is higher than some O-hTe values of J(PtH) reported for various organoselenium complexes 17*26(41 Hz) ; it seems improbable that the coupling should occur through five bonds, but if the nitrogen was coordinated in the Fig. 4. de-butyl case, as implied by IR evidence, a more convincing explanation for the magnitude of this in CH3CN. These values are significant, but less coupling becomes available. The implication from compound 5 that the final than values usually associated with 1 : 1 electrolytes de-butylated species must be a complex of pla- in these solvents ; thus a dimeric formulation may tinum(IV) was explored by measurement of ‘95Pt be implied. At least one v(RhC1) was assigned in NMR spectrum in DMSO. These spectra were the terminal region (322 cm-‘, Table 2) but no monitored over 15 h. After 1 h, three signals were bridging rhodium
The rhodium complexes were less well-defined than their palladium and platinum counterparts. Thus the rhodium(II1) species (compounds 7 and 8, Table 1) are both hydrates (analysis, IR). The complex of I (compound 7) gives values of AM of 20 R- ’ cm2 mol- ’ in DMSO and 65 R- ’ cm2 mole 1

Acknowledgements-N. I. Al-S. thanks the University of Basrah, Iraq for study leave. We thank Johnson and Matthey for a generous loan of palladium, platinum and rhodium salts. REFERENCES 1. H. M. K. K. Pathirana and W. R. McWhinnie, J. Chem. Sot., Dalton Trans. 1986, 2003.

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and W. R. McWHINNIE

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