Indian Journal or ChemistryVol. 24A, May 1985, pp. 398-402

Preparation & Characterisation of Some New BisphosphoniumYlides & Their Palladium(II) & Mercury(II) Complexes

RAM SANEHI, R K BANSAL & R C MEHROTRA·Department of Chemistry, University of Rajasthan, Jaipur 302004

Received 17 September 1984; accepted 30 October 1984

Transylidation of alkrl~etriphenylphos~or~s with bisthioesters of dicarboxylic acids affords new bisphosphoniumylides of the type [Ph3P-CRCO(CH~nCOCR-PPh3] [n==I), 2). These ylides behave as chelating ligands and form 1:1adducts with Pd(11)and Hg(11)chlorides in which the metal appears to be coordinated through the ylidic carbon atom.

The ylides, particularly those of phosphorus andsulphur, have been utilized as versatile synthons inorganic chemistry. Another important aspect of cheylides, viz., their potential ligating ability with the lewisacids has been only recently realized 1.

In the phosphorus series, only the monoylides havebeen employed as ligating agents so far and theseusually act as monodentate ligands. However,methylenetrimethylphosphorane, [Me3P - CH2], andthe related ylides (R2MeP+-CHJ, besides functioningas monodentate ligands, also show a tendency togenerate their anions, the phosphonium dimethylides,which act as bidentate ligands forming many novelcomplexes! -3. A new class of monophosphoniumylides, [Ph2P(CH2)nPPh2 -CHCOR], has beenrecently employed as chelating ligands involvingcoordination through ylidic carbon and the phosphinephosphorus". Some z-allylphosphonium ylides havealso been used to obtain 1l3-allylidecomplexes ofPd(II)and other metals". Although a number ofbisphosphonium ylides have been described in theliterature" 7, yet the complexation tendency of none ofthese has been explored so far. In view-of the specialstability of ketostabilized monophosphonium ylidesand their marked complexation ability" -12, we havecarried out the synthesis of a series of new bis-Ii-ketophosphonium ylides and a study of their ligatingbehaviour.

In this paper, we report the synthesis of some newbis-f1-ketophosphonium ylides, [Ph3P-CRCO(CHJnCOCR-PPh3] (I, rr=D, R=H, CH3,C2Hs, COOCH3; II, n=2, R=H, CH3)' The firstseries of the ylides (I, n = 0) has been used to preparePd(II) and Hg(II) chloride complexes which have beencharacterised on the basis of spectral and other studies.

Materials and MethodsThe IR spectra were recorded on a Perkin Elmer 337

spectrophotometer in KBr. The NMR spectra were

398

scanned in CDCI3, chemical shifts (in fJ, ppm) weremeasured from TMS as the internal standard. Themolecular weights were determined ebullioscopicallyon a Gallenkamp ebulliometer and molar con-ductances were measured on a conductivity meter typebridge 302 Sr. No. 471.

The bisthioesters, viz., ethanebis(thioic) acid-S,s'-diethylester and butanebis(thioic) acid-S,s' -diethyl-ester were prepared by standard methods. Thephosphonium salts, viz., methyltriphenyl-phosphonium iodide, ethyltriphenylphosphoniumiodide and carbomethoxytriphenylphosphoniumbromide were also prepared by the standard methods.

Synthesis of the bisphosphoniumylides(la-Id, lIa, lIb)

The general method is illustrated by the synthesis of1,4- bis(triphenylphosphoranylidene)bu tane-2,3-dione.

To a toluene solution of methylenetriphenyl-phosphorane (obtained from methyltriphenylphos-phonium iodide, 12g, 0.03 mol and sodium amide,lOml, 50% toluene suspension) under nitrogen wasadded a toluene solution of ethanebis(thioic) acid-S,s'-diethylester (2,64 g, 0.015 mol) slowly with vigorousstirring at ambient temperature. A pale yellowprecipitate was formed. The reaction mixture wasstirred at ambient temperature for about 5 h followedby refluxing for 3 h; a white solid deposited which wasfiltered and washed with ether. It was recrystallisedfrom a mixture of methanol and chloroform (I: I).

Other ylides were prepared (Table I) following thesame method using appropriate bisthioester andphosphonium salts.

Preparation of dichloro(bisylide)palla-diurr(Il) complexes (lIla, IlIh & 1I1d)

The following general procedure was adopted forpreparing all the complexes:

RAM SANEHI et al.: COMPLEXES OF BlSPHOSPHONlUM YLlDES

Table I-Physical and Spectral Data of the Ylides

Compd Colour Yield VC=O IH NMR (b, ppm)SI. No. (m.p .. "C) ('~,~) (em -I)

la White 68 1520 7.3-7.8 (m. Aromatic H)(242d)

Ib White 73 1505 1.0 (d, 6H, CHj•

(258d) 3 •Jp -c --C-H'

10Hz) 1.65 (d. 6H. CH3•

3Jp -<:. -c -H' 10Hz) 7.3-7.8 (m, 30H, Aromatic'

lc Pale 58 1520 InsolubleYellow(264d)

Id White 60 1720 V. poor solubility(I36d) 1620

IIa White 68 1540 2.8 (s, 4H, CH2). 3.9(212d) (d, 2H, CH, •Jp -c -H'

26Hz) 7.4-8.0 (m, 30H,Aromatic)

lIb White 63 1540 1.56 (d, 6H, CH3•

(184d) 3J r-c=c=n- 12 Hz)2.65 (s, 4H, CH2),

7.0-7.6 (m. 30H,Aromatic)

To a stirred solution of the bisylide (1.4 mmol) in amixed solvent (CH30H +CHCI3) was added asolution of dichlorobis(benzonitrile)palladium(I1)(0.5412g, 1.4 mmol) in chloroform. The reactionmixture was stirred at ambient temperature for about7-8 h whereupon an orange solution of the complexresulted. It was concentrated upto 5 ml and a smallamount of light petroleum was added. The complexprecipitated out. It was washed with ether and dried invacuo. It was not possible to obtain the complex incrystalline form; however, repeated precipitationafforded a sample of analytical purity.

Preparation of dichloro(bisylide)mer-curyil I) complexes (/Va & IVb)

To a stirred solution of bisylide (1.5 mmol) inchloroform was added a solution of mercuric chloride(0.4195 ~, 1.5 mmol) in ethanol. The reaction mixturewas stirred for about 4-5 h at ambient temperature.The complex precipitated out which was washed withether and dried in vacuo. In some cases, initially asemisolid W1S obtained which on maceration with lightpetroleum afforded the amorphous powder.

Preparation of cationic complexes(Va & Vb)

The following procedure was followed for preparingall the cationic complexes.

To a chloroform solution of the complex, an excessof ethylenediamine was added. The reaction mixturewas stirred for about 30 min at ambient temperatureand then set aside overnight. .\ pale yellow solid

separated, which was filtered, washed with lightpetroleum and dried in vacuo.

Results and DiscussionTransylidation of phosphoniumalkylides with

thioesters provides a facile method for synthesising {3-ketophosphonium ylides 13. The bis-{3-ketophos-phonium ylides (la-d, IIa, lIb) have been preparedaccordingly from the reaction of the bisthioester withan appropriate phosphoniumalkylide under nitrogen(Scheme I).

/CO - S -C2HS + - t /CO-CHR-t>Phj

(~)n + 2Ph3P-Cff'l- (C~)n + 2S~HS

cO-S-C2HS Co-CHR-P~

I-2C2HsSH 1 Heol

/CO-CR-~Ph3(CH2)n

~ - +CO-CR-PPh3

I, n = 00, R = Hb , R z CH3c, R = ~HSd', R = COOC~

II, n = 2a, R = H

b, R = CH3

Sch e m e 1

The yJides are obtained as white to pale yellow highmelting solids which are quite stable in atmosphere.They have poor solubilities but can be dissolved onheating either in CHCI3 or in its mixture withmethanol.

IR spectraThe carbonyl stretching frequencies of the ylides are

observed in the range 1505-1620 em -1 suggesting thatthe resonance form (C) contributes substantially to thefinal structure of the ylides.

A B C

These ylides are expected to show an ambidentatebehaviour like mono-Ji-ketophosphonium ylides.

PMR spectraAlthough the methine proton could be observed in

,;•.: spectrum of lIa, the same could not be detected inthe spectrum of la. This may be attributed to the rapidproton exchange between the ylide and a trace ofparent phosphonium salt 14. The methine proton of theylide I1a is observed asa doublet at 6 3.9 ppm eJp_C.H

399

INDIAN 1. CHEM., VOL. 24A, MAY 1985

26 Hz) due to coupling with phosphorus. Methylprotons of the ylide Ib show a pair of doublets centeredat Ii 1.0 and 1.65 ppm eJp-C-C-H' 10 Hz) whichprobably arise from the existence of two rotamers!".However, the methyl protons of the ylide lIb give onlyone doublet at b 1.56 ppm eJp-C-C-H 12 Hz).

AIass spectraA detailed mass spectral study of two ylides (Ia & Ib)

corroborates the structures indicated on the basis ofother spectroscopic studies. It appears that in theseylides the elimination of CO moiety is very facile, somuch so that in Ia no molecular ion peak is obtained;Instead an intense peak is observed at m]: 578 whichcorresponds to [M - COr· ion. However, in the caseor ~b, molecular ion peak is observed at m]z 634. In thelatter, the formation of an appreciably intense M-I ion), also observed, which is in conformity with the resultsreported earlier 16.17. An intense ion at m]z 303, whichforms the base peak in the mass spectrum of la, can beassigned the structure b. A doubly charged molecularion can also give rise to a peak at this mass number, butit can be excluded on the basis of the fact that this ionforms the base peak in the spectrum. The molecularion of Ib splits off a Ph radical to give an ion b' of m]z557. The latter loses CO to yield the ion c' (m/z 529)which subsequently leads to the ion d' (m/z 317). Theion d', as in the first case, forms the base peak in thespectrum. The other ions commonly observed in themass spectra of the triphenylphosphonium ylides 16.17

are also observed in the present two cases.The mass fragmentation patterns of the ylides Ia &

Ib have been shown in Scheme 2.

la,

lb,

0, M+-CO, Mil 578(78%)

lrr-~~~Ph3 J T ~

CO-y=PPh3CH3

a', M+, M/l634(25%)

b, Mil 303000%)

~

CH3 ~ +COot =PPh2I ~CO-?=PPh3

CH3

b, Mil 557(64 %)

d' , Mil 317(100%)

The yields, physical characteristics and spectral dataof the ylides are given in Table I.

The reaction of yhde(L) with dichlorobis(benzo-nitrilelpalladiumrl l) in an appropriate solvent atambient temperature ( ~ 30°C) afforded the complexes,L. PdCI2 (IlIa, IIIb, IlId). Mercury(II) chloridecomplexes, L.HgOz OVa and IVb) were prepared bysimilar reactions.

The complexes are obtained as dark coloured solidswhich are quite stable in atmosphere. They are solublein CHCl3 except IVa which has poor solubility in thissolvent.The yields, physical characteristics, metal analyses andspectral data of the complexes are given in Table 2. Themetal analyses and ebullioscopic determination of

c', Mil 529 (2 %)Scheme 2

Table 2-Physical, Analytical and Spectral Data of the Complexes

SI. Compound Colour Yield Found(Ca\c.) vC=O 1H NMR (b, ppm)No. (m.p.,°C) (%) (MC=O)

Molec. Metal in cm :'wt. %

ilia PdClrIa Orange 75 a 13.30 1650 7.1-8.0 (m, Aromatic H)yellow (13.53) (130)(l1l5)

IIIb PdClrlb Yellow 68 804 12.50 1520 1.50 (d, 6H, CH3, 3Jp-c-C-H' 18 Hz)

(138) (81\) (13.07) (15) 7.1-8.0 (m, 30H, Arornanc)

IIId PdC12-ld Orange 56 843 11.79 1720 3.52 (s, 6H, OCH3)

(165) (899) ( 11.86) 1660 7.3-7.8 (m, 30H, Aromatic)(40)

IVa HgClrla Yellow 94 a 22.50 1660 7.4-7.8 (m, Aromatic H)

(\34) (22.80) (140)

IVa HgCI2-Ib Pink 74 934 21.80 1520 1.03 id, 6H, CH3, 3Jp --CCH' 1.7 Hz)

(\64) (905.6) (22.10) (15) 7.0-7.8 (m, 30H, Aromatic)

'not determined due to low solubility: brOr - \0 -0 \f solutions at 30"C.

400

RAM SANEHI et al.: COMPLEXES OF BISPHOSPHONIUM YLIDES

molecular weights of the complexes in chloroformindicate the complexes to be 1:1 adducts. The molarconductance values of( < 2.6 for all adducts, except 6.5ohm -1 em? mol "" for PdClz-Ia in chloroform) thecomplexes clearly indicate them to be nonelectrolytes.

A blue shift in the vC = 0 frequencies in the IRspectra of the ketostabilized ylides has been used as themain evidence for the coordination of the ylidic carbonto the metal in the complexes8-1Z• 18-Z0. In thepresent studies also, the carbonyl stretching frequencyof the ylide shifted to higher frequency on itscomplexation with metal. This clearly indicates thatthe coordination of the ylides occurs to the metalsthrough the ylidic carbon; this can be expected on thebasis of 'softness' of Pd(II) and Hg(II) as lewis acids,which prefer coordination with softer carbanions tothe possible alternative donor site 'enolic oxygen'. Infact, it is only in the case of organotin moieties forwhich a facile conversion of Sn - C to Sn - 0 bond hasbeen demonstrated recently21.Z2 that coordinationthrough enolate oxygen has been suggested+' -25.

The downfield shift of the ylidic methine proton in1H NMR spectra of the complexes has been found tobe an additional proof of the coordination through theylidic carbon. But in the present studies neither theylide Ia nor its complexes IlIa & IVa showed any signalfor the me thine protons. This may be due to fastproton exchange'" or very low ratio of methineprotons as compared to that of aromatic protons+",The other protons showed signals in the expectedregions (Table 2). On the basis of the aboveobservations and in view of the very low molarconductance values of the complexes in chloroform,the following chelate structure (0) can be proposed forthe complexes:

The square planar chelate structure suggests a cis-geometry for these complexes. This is furtherconfirmed by conversion of IlIa & llIb into thecationic complexes of the type (E) on treatment withethylenediamine at ambient temperature:

The physical characteristics of the cationiccomplexes have been given in Table 3. The molarconductance values of the complexes clearly indicatethem to be strong electrolytes.

2CI

++

(E)

M=PdVa: R = HVb:R=CH3

Table 3-Physical Data of Cationic ComplexesCompd Colour Yield AMSI. No. (m.p., 0q (%)

Va Pale 90yellow(182d)Pale

yellow(I 93d)

425(water)

Vb 76(Dioxane +water)

91

The elemental analyses of the complexes gave aslightly low value of the carbon percentage. The TGAstudy of one of the complexes (IlIa) shows that a littleamount of carbon is retained by the metal even at1045DC. Similar results regarding low values of carbonanalyses have been reported earlier'", The thermalfragmentation of the complex (IlIa) is suggested tooccur as shown in Scheme 3.

C27H220PPdC[ 140°C, C 38 H 3 2 P 2 P d-He[-COC[+ PPh2HCl

290°C-1045DC• C2 H202Pd

- PPh 2

+ ° 2Scheme 3

ReferencesI (a) Schmidbaur H, Acc chem Res. 8 (1975) 62 & references cited

therein; (b) Schmidbaur H, Pure Appl Chern, 50(1978) 19; 52(1980) 1057; (c) Weber L The chemistry of metal-carbonbond, Chapter 3, edited by F R Hartley & S Patai (JohnWiley, New York) 1982.

401

INDIAN J. CHEM .• VOL. 24A. MAY 1985

2 Kurras E & Rosenthal 0, J organometal Chern, 160(1978) 35 &references cited therein.

3 Gell K I & Schwartz J, Inorg Chern, 19(1980) 3207 & referencescited therein.

4 Oosawa Y. Saito T. Sasaki Y & Urabe H, J organometal Chern,122 (1976) 113 & referei.ces cited therein.

5 Hirai M F, Miyasaka M, Iton K & Ishii Y, J chem Soc, DaltonTrans. (1979) 1200.

6 Johnson A W, Ylide chemistry (Academic Press, New York).7 Bestmann H J, Organic phosphorus compounds, volume 3, edited

by G M Kosolapoff & L Mayer (Wiley Interscience, NewYork) 1972.

8 Arnup P A & Baird M C, Inorg nucl chem u«. 5 (1969) 65.9 Nishiyama H, Itoh K & Ishii Y, J organometal Chern, 87 (1975)

129.10 Weleski E T, Silver J L, Jansson M D & Burmeister J L, J

organometal Chern, 102 (1975) 365.11 Koezuka H, Matsubayashi G & Tanaka T, lnorg Chern,15(1976)

417.12 Okunaka M, Matsubayashi G & Tanaka T,fnorg nucl chem Leu,

12 (1976) 813.13 Bestmann H J & Arnason B, Tetrahedron Leu, (\ 961) 445; Chern

Ber. 95 (1962) 1513.14 Randall F J & Johnson A W, Tetrahedron Lett, (1968) 21141.

402

15 Bestmann H J & Snyder J p, J Arn chem Soc, 89 (1967) 3936.

16 Williams D H, Ward R S & Cooks R G, J chem Soc B, (1968)2841.

17 Cooks R G, Ward R S, Williams D H, Shaw M A & Tebby J C.Tetrahedron, 24 (1968) 3289.

18 Koezuka H, Matsubayashi G & Tanaka T, Tetrahedron Leu,(1961) 455; Chern Ber, 95 (1962) 1513.

19. Bravo P, Fronza G & Ticozzi C, J organometal Chern, 111(1976)361.

20 Bravo P, Fronza G & Ticozzi C, J organometal Chern, 79 (1974)143.

21 Sawer A K & Fray C, Synth React inorg met-org Chern, 13(1983)143.

22 Shandilya P R, Srivastava G & Mehrotra R C, Synth React inorgmet-org Chern, 13(7)(1983) 899.

23 Kato S, Kato T, Mizutta M Itoh K Ishii v, J organometal Chern,51 (1973) 167.

24 Buckle J, Harrison PG, KingT J & RichardsJ A, Chern Commun(1972) 1104.

25 Buckle J & Harrison P G, J organometal Chern, 49 (1973 C'7'26 Kato M, Urabe H, Oosawa Y, Saito T & Saski Y, J organometal

Chern, 121 (1976) 81.27 Molnar S P & Orchin M, J organometal Chern, 16 (1969) 196.