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Reactions of metal complexes
.L inorg, nucl. Chem., 1977, Vol. 39, pp. 1003-10~6. Pergamon Press. Printed in Great Britain
REACTIONS OF METAL COMPLEXES THE EFFECT OF TRANS LIGAND ON '~'F RESONANCE SPECTRA OF SUBSTITUTED TRANS-BIS (TRIP HENYLP HOSP HINE)-P ERFLUOROVIN YL-P LATINUM(II) V. A. MUKHEDKAR National Chemical Laboratory, Poona, India 411 008 and B. J. KAVATHEKAR and A. J. MUKHEDKAR* University Department of Chemistry, Poona, India 411 007
(First received 29 December 1975; in revised form 12 May 1976) Abstraet--A series of compounds with formula trans-(Ph3P):Pt(CF:CF2)X were synthesized to study the effect of a trans group on the 19F resonance spectra of perttuorovinyl group. The reactions of (Ph3P)2Pt(C2F3Br) with potassium salts, silver salts, mercuric chloride and sulfur dioxide substantiated the SN2 mechanism for the vinyl rearrangement. The reaction of carbon monoxide with (Ph2MeP)2Pt(C:F~CI) in the presence of sodium perchlorate led to the formation of trans-(Ph2MeP)2Pt(CF:CFz)(CO)CI04. The characteristic spectroscopic properties of perfluorovinyl group (FJF2C :C(F3)Pt, F 2 and F 3 trans) such as 6v~,~,6F~3~and Uc_-cwere found to be related with the relative softness of ligands trans to the perfluorovinyl group. INTRODUCTION
spectrum was measured on CHCI3 solution with reference to CFCI3; the 'H NMR spectrum was measured on CDCL solutions with reference to TMS; IR spectra were measured by using Nujol and hexachlorobutadiene mull.
The chemical and physical properties of ligands are modified by the metal ion and depend on the nature of the other ligands present in the metal complex[l]. The variations in the properties are mainly associated with the transmission of the polarization effects of the various groups present in the complex on the group of interest through the metal ion. It is possible to study the influence of a group in a trans position to perfluorovinyl group on its ~gF N M R spectra as a series of complexes with a formula trans-(Ph3P)2Pt(CF--CF2)L, can be synthesized from (Ph3P)2Pt(C2F3Br)(I) by using the methods reported previously[2]. It was suggested that the vinyl rearrangement of (I) was an SN2 type reaction[3]. The additional reactions are reported in the present work to substantiate the proposed mechanism.
Reactions of bromotrifluoroethylene-bis (triphenylphosphine)platinum (a) With potassium trifluoroacetate. A mixture of
,L
CF2 (Ph~P)2Pt/[ ~'CFBr
+L
~Ph3P)2i.~.C F21
(i)
Ph~P CF:CE~ ~pt / Br PPh~
~,
IPh3P)2it--CF:CF21
;r
(fi)
J
[H
EXPERIMENTAL
The 'H and '9F NMR spectra were measured on a Varian Associates HA 100 spectrometer at 100 and 94.1 MHz respectively. The IR spectra were recorded on a Perkin-Elmer 257 and Beckman IR 4 spectrophotometers. The microanalyses were done at the microanalytical laboratory of National Chemical Laboratory, Poona and A. Bernhardt, Miilheim. All the reactions were carried under the nitrogen atmosphere. The JgF NMR
(PhsP)2Pt(C2F3Br) (0.44g, 0.5 mmole) and CF3CO2K (1.52g, 10mmole) in acetone (50ml) was stirred for 10h at the room temperature. After the vacuum concentration the mixture was extracted with methylenechloride and the extract was chromatographed on Florisil-packed column. Elution with methylenechloride-acetone (10:1 v/v) gave white crystals of III (0.24 g, 50%), m.p. 215-217 ° d.c., from methylenechloride--diethyl ether (2:1 v/v) (Found: C, 52.7; H, 3.4; F, 12.6; P, 7.2. C4oH3oO2P~F~Pt requires C, 52.5:; H, 3.3; F, 12.5; P, 6.8%). l/max 3065(W), 3055(m), 1726(m), 1690(m), 1585(w), 1570(w), 1480(m), 1435(s), 1320(w), 1306(w), 1230(s), 1182(m), 1155(w), ll15(w), 1095(s), 1065(m), 1035(m), 1025(m), 995(w), 978(s), 965(w), 842(w), 742(s), 720(w). 705(m), 690(s) cm -~. (b) With potassium acetylacetonate. A mixture of (Ph3P)2Pt(C2FsBr) (0.44g, 0.5mmole) and CsHTO2K (l.4g, 10mmoles) in acetone (50ml) was refluxed for l hr. After the vacuum concentration the mixture was washed with water and the residue was chromatographed on Florisil-packed column. Elution with methylene chloride gave the white crystals of IV (0.12g, 25%), m.p. 213-215 °, from methylenechloride-diethyl ether (l:lv/v) (Found: C, 56.9; H, 3.8: F, 6.1; P, 7.1. C43Hs7OzP2F3Pt requires C, 57.3; H, 4.1; F, 6.3: P, 6.9%). Vm,x 3065(W), 3055(W), 2968(W), 2870(W), 1735(W), 1724(W), 1640(S), 1605(m), 1588(w), 1572(w), 1482(m), 1440(s), 1432(s), 1375(m), 1358(m), 1316(m), 1241(s), 1182(m), ll60(w), 1096(s), 1065(m), 1053(m), 1025(w), 995(w), 982(s), 970(w), 920(w), 870(w), 750(m), 742(s), 718(w), 707(m), 690(s), cm 1. The ~H NMR spectrum showed the resonances on the r scale at 7.95 (~'CH3, 6H; two triplets; Jcn3~:~, 12.2 Hz; J p t ~ a s , 4.2 Hz) and 4.80 (r,:,, triplet: Jp,-n, 101 Hz). (c) With silver cyanide. A mixture of (Ph~P)zPt(C2F3Br) (0.44 g, 0.5 mmole) and AgCN (1.34 g, 10 mmole) in acetone (50 roll was stirred for 20 hr at the room temperature. The mixture was filtered through a short silica column and was vacuum concentrated. The residue was dissolved in a small volume of methy-
1003
1004
V.A. MUKHEDKAR et al.
lenechloride and was chromatographed on Florisil-packed column. Elusion with methylenechlofide gave the white crystals of V (0.29g, 70%), m.p. 215-2200 d.c., from methylenechloridediethyl ether (2:1 v/v) (Found: C, 56.4; H, 3.9; N, 1.5; F, 7.1; P, 8.0. C39H3oNFsP2Pt requires C, 56.6; H, 3.6; N, 1.7; F, 6.9; P, 7.5%). Um,x 3060(W), 2145(S), (2086cm-1 in CCL), 1719(m), 1587(w), 1570(w), 1487(m), 1442(s), 1310(w), 1238(s), 1185(m), l160(m), l120(m), 1098(s), 1065(s), 1030(w), 1002(w), 987(s), 748(s), 726(m), 713(m), 698(s) cm 1. (d) With silver thiocyanate. A reaction between (PhsP):Pt(C:F~Br) (0.44g, 0.5mmole) and silver thiocyanate (1.66g, 10mmole) was carried out by following a procedure similar to that summarized in (c) to give the white crystals of VI (0.26 g, 60%), m.p. 245-248°, from benzene-n-hexane (3:1 v/v) (Found: C, 54.6; H, 4.0; N, 1.5; F, 6.2; P, 7.6; S, 3.8. C39H3oF3NSP2Pt requires C, 54.5; H, 3.5; N, 1.6; F, 6.6; P, 7.2; S, 3.7%). U~x 3058(w), 2096(s), 1732(m), 1588(w), 1573(w), 1482(m), 1438(s), 1310(w), 1246(s), l180(m), ll18(m), 1095(s), 1050(m), 1025(w), 993(s), 865(w), 852(w), 752(s), 748(s), 725(s), 710(m), 695(s) cm 1 (e) With sulfur dioxide. A solution of (Ph~P)2Pt(C2F3Br) (0.44g, 0.5 mmole) in benzene (40 ml) was introduced into a Carius tube (200ml). An excess of sulfur dioxide (0.64g, 10 mmole) was condensed (-196 °) into the tube and the reaction mixture was allowed to warm to room temperature. After three days pale yellow crystals of VII (0.12g, 30%) separated, m.p. 251-253°, from methylenechloride-petroleum ether (40-50°) under nitrogen (Found: C, 48.7; H, 3.5; F, 5.6; P, 6.5; S, 3.4; Br, 8. CssH3oO2FsP2SBrPt requires C; 48.3; H, 3.2; F, 6.0; P, 6.6; S, 3.4; Br, 8.5%). Vm~x3060(W), 1725(m), 1588(w), 1572(w), 1483(s), 1438(s), 1531(w), 1332(w), 1310(m), 1243(m), 1185(s), 1158(s), 1147(s), 1095(s), 1075(m), 1070(s), 1060(s), 1029(m), 998(m), 987(s), 855(w), 812(w), 748(s), 710(s), 696(s) cm-1. Solvent from the mother liquor was removed in vacuo to give the white crystals of IX (0.28g, 60%), m.p. 275-276°. IR was identical with the literature[4]. Reaction of chlorotrifluoroethylene-bis(triphenylphosphine)-platinum with mercuric chloride
A mixture of (Ph~P)~Pt(C2F~CI) (0.34g, 0.4 mmole) and HgCl~ (1.36 g, 5 mmole) in acetone (40 ml) was stirred for 48 hr at the room temperature under nitrogen. After the vacuum concentration the residue was extracted with methylene chloride. The solvent from the extract was removed in vacuo and the residue was extracted with a minimum amount of methylene chloride. After the repetition of this procedure for three times, the white crystals of X (0.29g, 70%), obtained from methylenechloridediethyl ether (4:1 v/v), m.p. 264-267°, (Found: C, 54.5; H, 3.7; F, 7.0; P, 7.4: C1, 4.1, C3,HsoFsP2CIrequires C, 54.6; H, 3.6; F, 6.8; P, 7.4; C1, 4.3%). ~,~ax3078(w), 3050(w), 1720(s), 1590(w), 1480(s), 1440(s), 1432(s), 1310(w), 1282(w), 1235(s), 1182(w), 1152(w), l102(w), 1090(s), I068(m), 1028(w), 1000(w), 982(s), 760(m), 745(s), 720(w), 705(s), 690(s) cm ~. Reaction o[ chlorotrifluoroethylene-bis -(methyl diphenylphosphine)-platinum with carbonmonoxide in the presence of sodium perchlorate
A mixture of bromotrittuoroethylene-bis-(methyl diphenylphosphine)-platinum (0.36 g, 0.5 mmole) and NaCIO4.H20 (0.28 g, 2 mmole) in anhydrous acetone (80 ml) contained in a glass liner (100ml) in a stainless steel autoclave was stirred at room temperature under carbonmonoxide (300 atm). After three days the reaction mixture was filtered and the solvent was removed in vacuo. The residue was dissolved in benzene-acetone (4:1 v/v) and the insoluble sodium perchlorate was filtered off. The solvent from the filtrate was removed in vacuo and the above procedure was repeated four times to remove any contamination of free sodium perchlorate. The compounds XI and XII were separated from the residue by taking the advantage that the compound XII was comparatively less soluble in benzene. Compound XI was crystallized from benzene-acetone-n-hexane to give the white crystals (0.20g, 50%), m.p. 152-1530 (Found: C, 43.1; H, 3.2; O, 10.1; F, 7.1; P, 7.8; C1, 4.6. C29H26OsFsP2CIPtrequires C, 43.3; H, 3.2; O, 10.0; F, 7.1; P, 7.7; C1, 4.4%). t'max3062(m), 2914(w),
2118(s), 1725(w), 1718(m), 1588(w), 1573(w), 1482(s), 1440(s), 1415(w), 1336(m), 1314(w), 1293(w), 1265(s), 1192(w), l108(w), 1090(s, broad), 1080(s), 1070(m), 995(s), 905(s), 898(s), 808(w), 749(s), 713(m), 690(s). The IH NMR spectrum showed the resonances at r 2.2-2.7 (20 H (m), C6H~P) and 7.9 (6H (t), CH3P, Jp-H 7.6 Hz, JP~ns 31 Hz). Compound XII was crystallized from acetone-diethylether to give the white crystals (0.05 g, 25%), m.p. 168-1720 d.c. (Found: C, 43.1; H, 3.3; P, 9.0; Cl, 8.9%. C27H26OsPzCI2Pt requires C, 42.7; H, 3.4; P, 8.9; CI, 9.2%). vm~x3060(w), 2925(w) 2120(s), 1482(s), 1412(w), 1340(s), 1092(s, broad), 996(w), 894(s), 807(w), 742(s), 735(s), 695(s). The 1H NMR spectrum showed the resonances at r 2.2-2.7 (20H (m), C6HsP) and 7.4 (6H (t), CH3P, JP-r~ 7.0 Hz, Jet-on3 30 Hz). RESULTS AND DISCUSSION By following the reactions previously reported using the potassium salts[3], the complexes with trifluoroacetate and acetylacetonate as L in the perfluorovinyl complex given in eqn (I) were synthesized. The product obtained in a reaction using potassium cyanide, however, could not be characterized. F(3).~ /F(1) Ph3 P~. / . C ~ C . ~ jCF Pt I L / P t ~ p p h ~ F(2) L/ ~'CFX I L = PPh3 III L = CF3COOII L = PMePh2 IV L = acetylacetonate (Ia,IIa: X = CI; Ib,IIb: X = Br) V L=CNVI L = NCSIX L = B r L.x.
Ph,P,,, p t / C F i : C F ,
[Ph:MeP~.
Ph3Pj
~X
Xa: X=C1-; Xb: X = B r
L
L Pt
/
OC /
/CIO. ~'PMePhJ
XI L = - C F : : C F 2 XII L = CI-
It was reported that the vinyl rearrangement could also be effected by using the appropriate silver salts [2]. The desired product with cyanide as L was synthesized by carrying out the reaction of (Ph3P)2Pt(C2FsBr) with silver cyanide. A similar reaction with silver thiocyanate gave the compound VI; the strong bands observed at 2096 and 725cm -~ indicated the thiocyanate ion was bonded to platinum(II) by its nitrogen donor atom[5]. The product obtained from the reaction with potassium thiocyanate had bonding through the sulfur donor atom of thiocyanate[3] as it did not show any characteristic band in the region 720-860 cm -l. The IR spectra of compound IV showed a strong band at 1640 cm -~ which indicated that the carbonyl group of acetyl-acetonate did not take part in coordination[6]. The band at 2968 cm -1 was associated with 3-CH bonded through platinum(II). The absence of medium to strong intensity bands at 1570 and 1520dcm -1 also indicated that the bonding was not through the carbonyl groups. The tH NMR spectrum showed a multiplet structure centered at r 7.95 associated with two methyl groups and a triplet centered at ~"4.80 with a large coupling constant (JPt-n) of 101 Hz associated with 3-CH proton[7]. Thus IH NMR spectrum also indicated that the bonding between platinum(II) and acetylacetonate was through 3-CH carbon. The analysis of 19F NMR spectra was based on the previous studies of perfluorovinyl metal complexes [8]. A hyperfine structure in the form of a I : 2: 1 triplet both for
Reactions of metal complexes
1005
Table 1. ~F chemical shifts (ppm)t and coupling constants (Hz) for complex F'FC :C(F~)Pt(PR~)~X (F: and P trans) Compounds:k
By,}
8F{2)
3F(~}
JL~,
JL~
J2.3
J(p.F')
J{P.F2, J(P.i ,s, Ref.
I. I"rans-(Ph3P)2Pt(CF:CF2)(OCOCF3)§(III) 2. Trans-(Ph3P)aPt(CF:CF2)(acac) II (IV) 3. Trans-(PGP)2Pt(CF:CFz)(CN) (V) 4, Trans-(Ph3P)2Pt(CF:CF~)(NCS) (VI) 5 (Ph~P)2Pt(CF:CF2)(SO:)Brt~(VII) 6 Cis-(Ph3P)2Pt(CF:CFz)CI'P~ (X) 7, (Ph2MePhPt(CF:CF2)(CO}(CIO4) (XI) 8. Trans-(Pb~P)2Pt(CF:CF,)CI 9. Trans-(Ph3P)2Pt(CF:CF:)Br 10, Trans-(Ph3P)~Pt(CF:CF~)I 11. Trans-(Ph3PhPt(CF:CF2)(SCN) 12. Trans-(Ph3P)~Pt(CF:CF~)(N02) 13. Trans-(Ph3P)2Pt(CF:CF2)(N03) 14 Frans-{Ph3P)2Pt(CF:CF,)IOCOCH3)
100.2 99.8 96.3 101.0 100.2 100.1 93.1 101.2 101.4 100.6 100.4 %.6 100.2 97.5
130.1 128.0 126.0 128.7 128.6 127.4 120.8 128.7 128.3 129.2 128.7 126.4 127.8 128.1
148,5 149.2 154.3 147.0 149.0 152.3 162.3 147.0 145.6 147.5 148.2 154.1 148.4 147.8
90.1 98.0 96.0 98.5 93.2 95.2 92.{I 98 101 102 97 97 99 96
28.9 32.2 30.8 31.0 30,8 29,7 29.0 31 32 31 30 31 32 31
106.2 106.8 107.4 105.5 109.7 101.5 107.5 105 105 104 105 107 107 108
5.0 6.1 5.9 . . 6.0 18.0 6.5 5,6 5,8 6.0 6 6 6 7
4.0 4.0 4.6 . . 3.8 0.5 5.5 3.5 3.8 3.5 4 4.5 4 4
2.11 1,8 2.{1 15 26,0 2,8 15 2 25 25 2
$:~ J/,~ $~ $~ $; $,+ ;t§§ §§ §§ §§ §§ §§ rHi
+Studied in chloroform. Chemical shifts (-+1ppm) are relative to CCI~F increasing to high field; isotopes are '~F. "P and '~'Pt; :~ Roman number corresponds to the compound number reported in the present work; §~(CF3), 75.5 ppm; ¶acac =acetylacetonate, spectrum taken at -50°; u(Pt,F): F(1) 70.2, F(2) 65.0, F(3) 549.0 Hz. tt8 accumulations. :~:present work; §§M. Green, R. B. L. Osborn, A. J. Rest and F. G. A. Stone, J. Chem. Soc. (A), 2525 (1%8); ¶¶(Mrs) V. A. Mukhedkar, (Miss) B. J. Kavathekar and A. 1. Mukhedkar. J. Inorg. Nucl. Chem. 37, 483 (1975); hA. J. Mukhedkar, M. Green and F. G. A. Stone, J. Chem. Soc. (A), 947(1970).
each main and satellite peaks, apparently due to a virtual spin-spin coupling of the two phosphorus atoms [9] with the fluorine atoms, indicated a trans configuration of the triphenylphosphine ligands in this series of complexes (Table 1). It was interesting to note that the reaction of (Ph3P)2Pt(C:F~CI) with HgC12 gave a product which was characterized as a cis-isomer of trans(Ph3P)2Pt(CF=CF2)CI previously reported[4]. A cisconfiguration for the compound X was suggested as a hyperfine structure in the form of a 1:1 doublet was observed in the 19F NMR spectrum for each main and satellite peak; the coupling constants, JPm} and JPv{3)for X were also much higher than those observed for its trans isomer[4]. The order of the 31p-19F coupling constants for these two isomeric complexes were comparable[10] with that for cis and trans(Et~PhPt(CF:CF2)Br. The vinyl rearrangement of I (a) with HgC12 can be explained in terms of SN2 mechanism involving an intermediate containing a halide bridge with mercury (II). This experiment carried out using I (b) in place of 1 (a) gave a mixture of Xa (40%) and Xb (60%) supporting the proposed mechanism. The vinyl rearrangements of I carried out using silver cyanide and silver thiocyanate gave a trans isomer probably due to a large trans-directing influence of the soft ligands like cyanide and isothiocyanate groups[l 1]. The compound obtained by the reaction of I with SO2 showed the strong bands at 1185, 1147 and 1060cm t in the IR spectrum. The comparison of these observations with that reported for MCI(SO2)(CO)(PPh3) (M = Rh(I), Ir(I))[12] indicated that SO2 in VII was coordinated
t}h~P,,,, ..
O
I/O ~, _ O ~ S VII
°2 )
CF
CI @ 1
vn~c";t/O " F,C:FC / 1 Br
PPh~
VIII A ~2F3Br
Ph~P~. Pt ph~p/
/O. x /O S x()/ "o
Vlll B
Ph~P /CF::CF /Pt Ph~P 61 CI "'-,12ig "XCI
I(a) + HgCI2 Ph~P
through sulfur[13]. It was observed that the addition of SO2 did show an appreciable shift in vc_-c,;the ' T NMR spectrum also showed a decrease in 6v(1). These results indicated that SO2 being a soft ligand would be trans to perfluorovinyl group. It was interesting to observe that the exposure of VII to the normal atmosphere for about an hour gave a white compound VIII which did not show any bands associated with SO:; instead the new strong bands appeared at 1285, 1152, 880 and 658 cm ' in the IR spectrum. These bands would be assigned to the bidentate SO42 group[14]. After a long exposure the intensity of the bands associated with perfluorovinyl group also became of negligible intensity. The elemental analysis of VIII indicated that it might be a mixture of two or more compounds. These observations would be explained on the basis of the reaction of VII with 02 leading to the oxidative addition followed by the reductive elimination of C2GBr:
[31
PhJ P ~ . p t / C F : : C F ' + Ph~P /
HgCI~
~CI (Xa)
CI (iii)
(iv)
[2]
1006
V.A. MUKHEDKAR et al. I
1
I
I
I
I
104
~O4
I00 T
96
96
#e7 I 1720
I 1730
I 146
I 152
I 156
t 160
°coc -'~3 " Fig. 1. Relation between C--C stretching frequency and the 'gF chemical shifts of F(1) and F(3) in perttuorovinyl group present in complexes (F'F2C:CF3) Pt(PR3)2X. (The numbers given to the points correspond to the compounds given in Table 1). It was reported that the reaction of carbonmonoxide with II led to an interesting ligand isomerism[2]. MePh2P~ (
CF:CF2
H~PPh~Me II
CO; 300 atmosphere benzene
) [41
From the experience of the reaction with sulfur dioxide one would expect that this reaction might be proceeding through an addition product with a configuration similar to VII. It was noteworthy that the reaction of II with carbon monoxide carried out in the presence of sodium perchlorate led to the compounds XI and XII. An appreciable solubility of XI and XII in benzene suggested that the bonding between platinum(II) and perchlorate ion would be mainly covalent. These compounds would have square pyramidal configuration with C104- bonding along the axial axis as CO being a soft ligand would prefer a trans position to the perfluorovinyl group; a large lowering in the chemical shift 8Ftl) also suggested the trans orientation of CO with respect to the perfluorovinyl group. The dependence of 8F,~ and Vc--con a group trans to the perfluorovinyl group follows roughly the trans series[15]. From the results of a large number of chemical reactions, it is suggested that the perfluorovinyl group has a high trans-effect. The reaction of I with HgCI2 indicated that the trans-effect of perfluorovinyl group is higher than that of triphenylphosphine. The relations between 8F(:) and Vc=c, and between 8F(1) and 8F~3~are shown graphically (Fig. 1). Both the relations give a uniform curve. The difference between the coordination of thiocyanate ion through the hard nitrogen end and forming an isothiocyanate complex and through the soft sulfur and forming a thiocyanate complex is clearly shown in the change in vc=c; no appreciable change is
observed in 8F,). The very soft ligands which contain the appropriate empty antibonding orbitals available for metal-ligand back donation of electrons show an appreciable effect on 8F,) and 8Ft3). These observations clearly show the transmition of the polarization of trans ligands through platinum(II). Acknowledgements--We thank Prof. F. G. A. Stone, Department of Inorganic Chemistry, Bristol, England, for the chemicals he has kindly supplied and the facilities provided for a part of the work. Our thanks are also due to the authorities of National Chemical Laboratory, Poona, India, for the facilities provided for a part of the work and to Poona University for a research assistantship (BJK). REFERENCES
1. D. H. Busch, Reaction of Coordinated Ligands and Homogeneous Catalysis, p. 1. Am. Chem. Soc., Washington (1%3). 2. A. J. Mukhedkar, M. Green and F. G. A. Stone, 7. Chem. Soc. (A), 947 (1970). 3. V. A. Mukhedkar, B. J. Kavathekar and A. J. Mukhedkar, J. lnorg. Nucl. Chem. 37, 483 (1975). 4. M. Green, R. B. L. Osborn, A. J. Rest and F. G. A. Stone, J. Chem. Soc. (A), 2525 (1968). 5. J. L. Burmeister and F. Basolo, Inorg. Chem. 3, 1587 (1%3). 6. J. Lewis, R. F. Long and C. Oldham, J. Chem. Soc. 6740 (1965). 7. D. Gibson, J. Lewis and C. Oldham, J. Chem. Soc. (A), 1453 (1%6). 8. T. D. Coyle, S. L. Stafford and F. G. A. Stone, Spectrochim. Acta 17, 968 (1961); H. C. Clark and W. S. Tsang, J. Am. Chem. Soc. 89, 533 (1%7). 9. J. M. Jenkins and B. L. Shaw, Proc. Chem. Soc. 279 (1963); R. K. harris, Inorg. Chem. 5, 701 (1966);J. P. Fackler, Jr., J, A. Fetchin, J. Mayhew, W. C. Seidel, T. J. Swift and M. Weeks, 7. Am. Chem. Soc. 91, 1941 (1%9). 10. A. J. Rest, D. T. Rosevear and F. G. A. Stone, J. Chem. Soc, A, 66 (1967). 11. S. Ahrland, Structure and Bonding 1, 207 (1%6). 12. L. Vaska and S. S. Bath, J. Am. Chem. Soc. 88, 1333(1966). 13. S. J. Laplaca and J. A. Ibers, lnorg. Chem. 5, 405 (1%6). 14. J. J. Levison and S. D. Robinson, Chem. Comm., 198 (1%7). 15. J. Chatt and B. L. Shaw, 3". Chem. Soc. 5075 (1%2).
REACTIONS OF METAL COMPLEXES THE EFFECT OF TRANS LIGAND ON '~'F RESONANCE SPECTRA OF SUBSTITUTED TRANS-BIS (TRIP HENYLP HOSP HINE)-P ERFLUOROVIN YL-P LATINUM(II) V. A. MUKHEDKAR National Chemical Laboratory, Poona, India 411 008 and B. J. KAVATHEKAR and A. J. MUKHEDKAR* University Department of Chemistry, Poona, India 411 007
(First received 29 December 1975; in revised form 12 May 1976) Abstraet--A series of compounds with formula trans-(Ph3P):Pt(CF:CF2)X were synthesized to study the effect of a trans group on the 19F resonance spectra of perttuorovinyl group. The reactions of (Ph3P)2Pt(C2F3Br) with potassium salts, silver salts, mercuric chloride and sulfur dioxide substantiated the SN2 mechanism for the vinyl rearrangement. The reaction of carbon monoxide with (Ph2MeP)2Pt(C:F~CI) in the presence of sodium perchlorate led to the formation of trans-(Ph2MeP)2Pt(CF:CFz)(CO)CI04. The characteristic spectroscopic properties of perfluorovinyl group (FJF2C :C(F3)Pt, F 2 and F 3 trans) such as 6v~,~,6F~3~and Uc_-cwere found to be related with the relative softness of ligands trans to the perfluorovinyl group. INTRODUCTION
spectrum was measured on CHCI3 solution with reference to CFCI3; the 'H NMR spectrum was measured on CDCL solutions with reference to TMS; IR spectra were measured by using Nujol and hexachlorobutadiene mull.
The chemical and physical properties of ligands are modified by the metal ion and depend on the nature of the other ligands present in the metal complex[l]. The variations in the properties are mainly associated with the transmission of the polarization effects of the various groups present in the complex on the group of interest through the metal ion. It is possible to study the influence of a group in a trans position to perfluorovinyl group on its ~gF N M R spectra as a series of complexes with a formula trans-(Ph3P)2Pt(CF--CF2)L, can be synthesized from (Ph3P)2Pt(C2F3Br)(I) by using the methods reported previously[2]. It was suggested that the vinyl rearrangement of (I) was an SN2 type reaction[3]. The additional reactions are reported in the present work to substantiate the proposed mechanism.
Reactions of bromotrifluoroethylene-bis (triphenylphosphine)platinum (a) With potassium trifluoroacetate. A mixture of
,L
CF2 (Ph~P)2Pt/[ ~'CFBr
+L
~Ph3P)2i.~.C F21
(i)
Ph~P CF:CE~ ~pt / Br PPh~
~,
IPh3P)2it--CF:CF21
;r
(fi)
J
[H
EXPERIMENTAL
The 'H and '9F NMR spectra were measured on a Varian Associates HA 100 spectrometer at 100 and 94.1 MHz respectively. The IR spectra were recorded on a Perkin-Elmer 257 and Beckman IR 4 spectrophotometers. The microanalyses were done at the microanalytical laboratory of National Chemical Laboratory, Poona and A. Bernhardt, Miilheim. All the reactions were carried under the nitrogen atmosphere. The JgF NMR
(PhsP)2Pt(C2F3Br) (0.44g, 0.5 mmole) and CF3CO2K (1.52g, 10mmole) in acetone (50ml) was stirred for 10h at the room temperature. After the vacuum concentration the mixture was extracted with methylenechloride and the extract was chromatographed on Florisil-packed column. Elution with methylenechloride-acetone (10:1 v/v) gave white crystals of III (0.24 g, 50%), m.p. 215-217 ° d.c., from methylenechloride--diethyl ether (2:1 v/v) (Found: C, 52.7; H, 3.4; F, 12.6; P, 7.2. C4oH3oO2P~F~Pt requires C, 52.5:; H, 3.3; F, 12.5; P, 6.8%). l/max 3065(W), 3055(m), 1726(m), 1690(m), 1585(w), 1570(w), 1480(m), 1435(s), 1320(w), 1306(w), 1230(s), 1182(m), 1155(w), ll15(w), 1095(s), 1065(m), 1035(m), 1025(m), 995(w), 978(s), 965(w), 842(w), 742(s), 720(w). 705(m), 690(s) cm -~. (b) With potassium acetylacetonate. A mixture of (Ph3P)2Pt(C2FsBr) (0.44g, 0.5mmole) and CsHTO2K (l.4g, 10mmoles) in acetone (50ml) was refluxed for l hr. After the vacuum concentration the mixture was washed with water and the residue was chromatographed on Florisil-packed column. Elution with methylene chloride gave the white crystals of IV (0.12g, 25%), m.p. 213-215 °, from methylenechloride-diethyl ether (l:lv/v) (Found: C, 56.9; H, 3.8: F, 6.1; P, 7.1. C43Hs7OzP2F3Pt requires C, 57.3; H, 4.1; F, 6.3: P, 6.9%). Vm,x 3065(W), 3055(W), 2968(W), 2870(W), 1735(W), 1724(W), 1640(S), 1605(m), 1588(w), 1572(w), 1482(m), 1440(s), 1432(s), 1375(m), 1358(m), 1316(m), 1241(s), 1182(m), ll60(w), 1096(s), 1065(m), 1053(m), 1025(w), 995(w), 982(s), 970(w), 920(w), 870(w), 750(m), 742(s), 718(w), 707(m), 690(s), cm 1. The ~H NMR spectrum showed the resonances on the r scale at 7.95 (~'CH3, 6H; two triplets; Jcn3~:~, 12.2 Hz; J p t ~ a s , 4.2 Hz) and 4.80 (r,:,, triplet: Jp,-n, 101 Hz). (c) With silver cyanide. A mixture of (Ph~P)zPt(C2F3Br) (0.44 g, 0.5 mmole) and AgCN (1.34 g, 10 mmole) in acetone (50 roll was stirred for 20 hr at the room temperature. The mixture was filtered through a short silica column and was vacuum concentrated. The residue was dissolved in a small volume of methy-
1003
1004
V.A. MUKHEDKAR et al.
lenechloride and was chromatographed on Florisil-packed column. Elusion with methylenechlofide gave the white crystals of V (0.29g, 70%), m.p. 215-2200 d.c., from methylenechloridediethyl ether (2:1 v/v) (Found: C, 56.4; H, 3.9; N, 1.5; F, 7.1; P, 8.0. C39H3oNFsP2Pt requires C, 56.6; H, 3.6; N, 1.7; F, 6.9; P, 7.5%). Um,x 3060(W), 2145(S), (2086cm-1 in CCL), 1719(m), 1587(w), 1570(w), 1487(m), 1442(s), 1310(w), 1238(s), 1185(m), l160(m), l120(m), 1098(s), 1065(s), 1030(w), 1002(w), 987(s), 748(s), 726(m), 713(m), 698(s) cm 1. (d) With silver thiocyanate. A reaction between (PhsP):Pt(C:F~Br) (0.44g, 0.5mmole) and silver thiocyanate (1.66g, 10mmole) was carried out by following a procedure similar to that summarized in (c) to give the white crystals of VI (0.26 g, 60%), m.p. 245-248°, from benzene-n-hexane (3:1 v/v) (Found: C, 54.6; H, 4.0; N, 1.5; F, 6.2; P, 7.6; S, 3.8. C39H3oF3NSP2Pt requires C, 54.5; H, 3.5; N, 1.6; F, 6.6; P, 7.2; S, 3.7%). U~x 3058(w), 2096(s), 1732(m), 1588(w), 1573(w), 1482(m), 1438(s), 1310(w), 1246(s), l180(m), ll18(m), 1095(s), 1050(m), 1025(w), 993(s), 865(w), 852(w), 752(s), 748(s), 725(s), 710(m), 695(s) cm 1 (e) With sulfur dioxide. A solution of (Ph~P)2Pt(C2F3Br) (0.44g, 0.5 mmole) in benzene (40 ml) was introduced into a Carius tube (200ml). An excess of sulfur dioxide (0.64g, 10 mmole) was condensed (-196 °) into the tube and the reaction mixture was allowed to warm to room temperature. After three days pale yellow crystals of VII (0.12g, 30%) separated, m.p. 251-253°, from methylenechloride-petroleum ether (40-50°) under nitrogen (Found: C, 48.7; H, 3.5; F, 5.6; P, 6.5; S, 3.4; Br, 8. CssH3oO2FsP2SBrPt requires C; 48.3; H, 3.2; F, 6.0; P, 6.6; S, 3.4; Br, 8.5%). Vm~x3060(W), 1725(m), 1588(w), 1572(w), 1483(s), 1438(s), 1531(w), 1332(w), 1310(m), 1243(m), 1185(s), 1158(s), 1147(s), 1095(s), 1075(m), 1070(s), 1060(s), 1029(m), 998(m), 987(s), 855(w), 812(w), 748(s), 710(s), 696(s) cm-1. Solvent from the mother liquor was removed in vacuo to give the white crystals of IX (0.28g, 60%), m.p. 275-276°. IR was identical with the literature[4]. Reaction of chlorotrifluoroethylene-bis(triphenylphosphine)-platinum with mercuric chloride
A mixture of (Ph~P)~Pt(C2F~CI) (0.34g, 0.4 mmole) and HgCl~ (1.36 g, 5 mmole) in acetone (40 ml) was stirred for 48 hr at the room temperature under nitrogen. After the vacuum concentration the residue was extracted with methylene chloride. The solvent from the extract was removed in vacuo and the residue was extracted with a minimum amount of methylene chloride. After the repetition of this procedure for three times, the white crystals of X (0.29g, 70%), obtained from methylenechloridediethyl ether (4:1 v/v), m.p. 264-267°, (Found: C, 54.5; H, 3.7; F, 7.0; P, 7.4: C1, 4.1, C3,HsoFsP2CIrequires C, 54.6; H, 3.6; F, 6.8; P, 7.4; C1, 4.3%). ~,~ax3078(w), 3050(w), 1720(s), 1590(w), 1480(s), 1440(s), 1432(s), 1310(w), 1282(w), 1235(s), 1182(w), 1152(w), l102(w), 1090(s), I068(m), 1028(w), 1000(w), 982(s), 760(m), 745(s), 720(w), 705(s), 690(s) cm ~. Reaction o[ chlorotrifluoroethylene-bis -(methyl diphenylphosphine)-platinum with carbonmonoxide in the presence of sodium perchlorate
A mixture of bromotrittuoroethylene-bis-(methyl diphenylphosphine)-platinum (0.36 g, 0.5 mmole) and NaCIO4.H20 (0.28 g, 2 mmole) in anhydrous acetone (80 ml) contained in a glass liner (100ml) in a stainless steel autoclave was stirred at room temperature under carbonmonoxide (300 atm). After three days the reaction mixture was filtered and the solvent was removed in vacuo. The residue was dissolved in benzene-acetone (4:1 v/v) and the insoluble sodium perchlorate was filtered off. The solvent from the filtrate was removed in vacuo and the above procedure was repeated four times to remove any contamination of free sodium perchlorate. The compounds XI and XII were separated from the residue by taking the advantage that the compound XII was comparatively less soluble in benzene. Compound XI was crystallized from benzene-acetone-n-hexane to give the white crystals (0.20g, 50%), m.p. 152-1530 (Found: C, 43.1; H, 3.2; O, 10.1; F, 7.1; P, 7.8; C1, 4.6. C29H26OsFsP2CIPtrequires C, 43.3; H, 3.2; O, 10.0; F, 7.1; P, 7.7; C1, 4.4%). t'max3062(m), 2914(w),
2118(s), 1725(w), 1718(m), 1588(w), 1573(w), 1482(s), 1440(s), 1415(w), 1336(m), 1314(w), 1293(w), 1265(s), 1192(w), l108(w), 1090(s, broad), 1080(s), 1070(m), 995(s), 905(s), 898(s), 808(w), 749(s), 713(m), 690(s). The IH NMR spectrum showed the resonances at r 2.2-2.7 (20 H (m), C6H~P) and 7.9 (6H (t), CH3P, Jp-H 7.6 Hz, JP~ns 31 Hz). Compound XII was crystallized from acetone-diethylether to give the white crystals (0.05 g, 25%), m.p. 168-1720 d.c. (Found: C, 43.1; H, 3.3; P, 9.0; Cl, 8.9%. C27H26OsPzCI2Pt requires C, 42.7; H, 3.4; P, 8.9; CI, 9.2%). vm~x3060(w), 2925(w) 2120(s), 1482(s), 1412(w), 1340(s), 1092(s, broad), 996(w), 894(s), 807(w), 742(s), 735(s), 695(s). The 1H NMR spectrum showed the resonances at r 2.2-2.7 (20H (m), C6HsP) and 7.4 (6H (t), CH3P, JP-r~ 7.0 Hz, Jet-on3 30 Hz). RESULTS AND DISCUSSION By following the reactions previously reported using the potassium salts[3], the complexes with trifluoroacetate and acetylacetonate as L in the perfluorovinyl complex given in eqn (I) were synthesized. The product obtained in a reaction using potassium cyanide, however, could not be characterized. F(3).~ /F(1) Ph3 P~. / . C ~ C . ~ jCF Pt I L / P t ~ p p h ~ F(2) L/ ~'CFX I L = PPh3 III L = CF3COOII L = PMePh2 IV L = acetylacetonate (Ia,IIa: X = CI; Ib,IIb: X = Br) V L=CNVI L = NCSIX L = B r L.x.
Ph,P,,, p t / C F i : C F ,
[Ph:MeP~.
Ph3Pj
~X
Xa: X=C1-; Xb: X = B r
L
L Pt
/
OC /
/CIO. ~'PMePhJ
XI L = - C F : : C F 2 XII L = CI-
It was reported that the vinyl rearrangement could also be effected by using the appropriate silver salts [2]. The desired product with cyanide as L was synthesized by carrying out the reaction of (Ph3P)2Pt(C2FsBr) with silver cyanide. A similar reaction with silver thiocyanate gave the compound VI; the strong bands observed at 2096 and 725cm -~ indicated the thiocyanate ion was bonded to platinum(II) by its nitrogen donor atom[5]. The product obtained from the reaction with potassium thiocyanate had bonding through the sulfur donor atom of thiocyanate[3] as it did not show any characteristic band in the region 720-860 cm -l. The IR spectra of compound IV showed a strong band at 1640 cm -~ which indicated that the carbonyl group of acetyl-acetonate did not take part in coordination[6]. The band at 2968 cm -1 was associated with 3-CH bonded through platinum(II). The absence of medium to strong intensity bands at 1570 and 1520dcm -1 also indicated that the bonding was not through the carbonyl groups. The tH NMR spectrum showed a multiplet structure centered at r 7.95 associated with two methyl groups and a triplet centered at ~"4.80 with a large coupling constant (JPt-n) of 101 Hz associated with 3-CH proton[7]. Thus IH NMR spectrum also indicated that the bonding between platinum(II) and acetylacetonate was through 3-CH carbon. The analysis of 19F NMR spectra was based on the previous studies of perfluorovinyl metal complexes [8]. A hyperfine structure in the form of a I : 2: 1 triplet both for
Reactions of metal complexes
1005
Table 1. ~F chemical shifts (ppm)t and coupling constants (Hz) for complex F'FC :C(F~)Pt(PR~)~X (F: and P trans) Compounds:k
By,}
8F{2)
3F(~}
JL~,
JL~
J2.3
J(p.F')
J{P.F2, J(P.i ,s, Ref.
I. I"rans-(Ph3P)2Pt(CF:CF2)(OCOCF3)§(III) 2. Trans-(Ph3P)aPt(CF:CF2)(acac) II (IV) 3. Trans-(PGP)2Pt(CF:CFz)(CN) (V) 4, Trans-(Ph3P)2Pt(CF:CF~)(NCS) (VI) 5 (Ph~P)2Pt(CF:CF2)(SO:)Brt~(VII) 6 Cis-(Ph3P)2Pt(CF:CFz)CI'P~ (X) 7, (Ph2MePhPt(CF:CF2)(CO}(CIO4) (XI) 8. Trans-(Pb~P)2Pt(CF:CF,)CI 9. Trans-(Ph3P)2Pt(CF:CF:)Br 10, Trans-(Ph3P)~Pt(CF:CF~)I 11. Trans-(Ph3PhPt(CF:CF2)(SCN) 12. Trans-(Ph3P)~Pt(CF:CF~)(N02) 13. Trans-(Ph3P)2Pt(CF:CF2)(N03) 14 Frans-{Ph3P)2Pt(CF:CF,)IOCOCH3)
100.2 99.8 96.3 101.0 100.2 100.1 93.1 101.2 101.4 100.6 100.4 %.6 100.2 97.5
130.1 128.0 126.0 128.7 128.6 127.4 120.8 128.7 128.3 129.2 128.7 126.4 127.8 128.1
148,5 149.2 154.3 147.0 149.0 152.3 162.3 147.0 145.6 147.5 148.2 154.1 148.4 147.8
90.1 98.0 96.0 98.5 93.2 95.2 92.{I 98 101 102 97 97 99 96
28.9 32.2 30.8 31.0 30,8 29,7 29.0 31 32 31 30 31 32 31
106.2 106.8 107.4 105.5 109.7 101.5 107.5 105 105 104 105 107 107 108
5.0 6.1 5.9 . . 6.0 18.0 6.5 5,6 5,8 6.0 6 6 6 7
4.0 4.0 4.6 . . 3.8 0.5 5.5 3.5 3.8 3.5 4 4.5 4 4
2.11 1,8 2.{1 15 26,0 2,8 15 2 25 25 2
$:~ J/,~ $~ $~ $; $,+ ;t§§ §§ §§ §§ §§ §§ rHi
+Studied in chloroform. Chemical shifts (-+1ppm) are relative to CCI~F increasing to high field; isotopes are '~F. "P and '~'Pt; :~ Roman number corresponds to the compound number reported in the present work; §~(CF3), 75.5 ppm; ¶acac =acetylacetonate, spectrum taken at -50°; u(Pt,F): F(1) 70.2, F(2) 65.0, F(3) 549.0 Hz. tt8 accumulations. :~:present work; §§M. Green, R. B. L. Osborn, A. J. Rest and F. G. A. Stone, J. Chem. Soc. (A), 2525 (1%8); ¶¶(Mrs) V. A. Mukhedkar, (Miss) B. J. Kavathekar and A. 1. Mukhedkar. J. Inorg. Nucl. Chem. 37, 483 (1975); hA. J. Mukhedkar, M. Green and F. G. A. Stone, J. Chem. Soc. (A), 947(1970).
each main and satellite peaks, apparently due to a virtual spin-spin coupling of the two phosphorus atoms [9] with the fluorine atoms, indicated a trans configuration of the triphenylphosphine ligands in this series of complexes (Table 1). It was interesting to note that the reaction of (Ph3P)2Pt(C:F~CI) with HgC12 gave a product which was characterized as a cis-isomer of trans(Ph3P)2Pt(CF=CF2)CI previously reported[4]. A cisconfiguration for the compound X was suggested as a hyperfine structure in the form of a 1:1 doublet was observed in the 19F NMR spectrum for each main and satellite peak; the coupling constants, JPm} and JPv{3)for X were also much higher than those observed for its trans isomer[4]. The order of the 31p-19F coupling constants for these two isomeric complexes were comparable[10] with that for cis and trans(Et~PhPt(CF:CF2)Br. The vinyl rearrangement of I (a) with HgC12 can be explained in terms of SN2 mechanism involving an intermediate containing a halide bridge with mercury (II). This experiment carried out using I (b) in place of 1 (a) gave a mixture of Xa (40%) and Xb (60%) supporting the proposed mechanism. The vinyl rearrangements of I carried out using silver cyanide and silver thiocyanate gave a trans isomer probably due to a large trans-directing influence of the soft ligands like cyanide and isothiocyanate groups[l 1]. The compound obtained by the reaction of I with SO2 showed the strong bands at 1185, 1147 and 1060cm t in the IR spectrum. The comparison of these observations with that reported for MCI(SO2)(CO)(PPh3) (M = Rh(I), Ir(I))[12] indicated that SO2 in VII was coordinated
t}h~P,,,, ..
O
I/O ~, _ O ~ S VII
°2 )
CF
CI @ 1
vn~c";t/O " F,C:FC / 1 Br
PPh~
VIII A ~2F3Br
Ph~P~. Pt ph~p/
/O. x /O S x()/ "o
Vlll B
Ph~P /CF::CF /Pt Ph~P 61 CI "'-,12ig "XCI
I(a) + HgCI2 Ph~P
through sulfur[13]. It was observed that the addition of SO2 did show an appreciable shift in vc_-c,;the ' T NMR spectrum also showed a decrease in 6v(1). These results indicated that SO2 being a soft ligand would be trans to perfluorovinyl group. It was interesting to observe that the exposure of VII to the normal atmosphere for about an hour gave a white compound VIII which did not show any bands associated with SO:; instead the new strong bands appeared at 1285, 1152, 880 and 658 cm ' in the IR spectrum. These bands would be assigned to the bidentate SO42 group[14]. After a long exposure the intensity of the bands associated with perfluorovinyl group also became of negligible intensity. The elemental analysis of VIII indicated that it might be a mixture of two or more compounds. These observations would be explained on the basis of the reaction of VII with 02 leading to the oxidative addition followed by the reductive elimination of C2GBr:
[31
PhJ P ~ . p t / C F : : C F ' + Ph~P /
HgCI~
~CI (Xa)
CI (iii)
(iv)
[2]
1006
V.A. MUKHEDKAR et al. I
1
I
I
I
I
104
~O4
I00 T
96
96
#e7 I 1720
I 1730
I 146
I 152
I 156
t 160
°coc -'~3 " Fig. 1. Relation between C--C stretching frequency and the 'gF chemical shifts of F(1) and F(3) in perttuorovinyl group present in complexes (F'F2C:CF3) Pt(PR3)2X. (The numbers given to the points correspond to the compounds given in Table 1). It was reported that the reaction of carbonmonoxide with II led to an interesting ligand isomerism[2]. MePh2P~ (
CF:CF2
H~PPh~Me II
CO; 300 atmosphere benzene
) [41
From the experience of the reaction with sulfur dioxide one would expect that this reaction might be proceeding through an addition product with a configuration similar to VII. It was noteworthy that the reaction of II with carbon monoxide carried out in the presence of sodium perchlorate led to the compounds XI and XII. An appreciable solubility of XI and XII in benzene suggested that the bonding between platinum(II) and perchlorate ion would be mainly covalent. These compounds would have square pyramidal configuration with C104- bonding along the axial axis as CO being a soft ligand would prefer a trans position to the perfluorovinyl group; a large lowering in the chemical shift 8Ftl) also suggested the trans orientation of CO with respect to the perfluorovinyl group. The dependence of 8F,~ and Vc--con a group trans to the perfluorovinyl group follows roughly the trans series[15]. From the results of a large number of chemical reactions, it is suggested that the perfluorovinyl group has a high trans-effect. The reaction of I with HgCI2 indicated that the trans-effect of perfluorovinyl group is higher than that of triphenylphosphine. The relations between 8F(:) and Vc=c, and between 8F(1) and 8F~3~are shown graphically (Fig. 1). Both the relations give a uniform curve. The difference between the coordination of thiocyanate ion through the hard nitrogen end and forming an isothiocyanate complex and through the soft sulfur and forming a thiocyanate complex is clearly shown in the change in vc=c; no appreciable change is
observed in 8F,). The very soft ligands which contain the appropriate empty antibonding orbitals available for metal-ligand back donation of electrons show an appreciable effect on 8F,) and 8Ft3). These observations clearly show the transmition of the polarization of trans ligands through platinum(II). Acknowledgements--We thank Prof. F. G. A. Stone, Department of Inorganic Chemistry, Bristol, England, for the chemicals he has kindly supplied and the facilities provided for a part of the work. Our thanks are also due to the authorities of National Chemical Laboratory, Poona, India, for the facilities provided for a part of the work and to Poona University for a research assistantship (BJK). REFERENCES
1. D. H. Busch, Reaction of Coordinated Ligands and Homogeneous Catalysis, p. 1. Am. Chem. Soc., Washington (1%3). 2. A. J. Mukhedkar, M. Green and F. G. A. Stone, 7. Chem. Soc. (A), 947 (1970). 3. V. A. Mukhedkar, B. J. Kavathekar and A. J. Mukhedkar, J. lnorg. Nucl. Chem. 37, 483 (1975). 4. M. Green, R. B. L. Osborn, A. J. Rest and F. G. A. Stone, J. Chem. Soc. (A), 2525 (1968). 5. J. L. Burmeister and F. Basolo, Inorg. Chem. 3, 1587 (1%3). 6. J. Lewis, R. F. Long and C. Oldham, J. Chem. Soc. 6740 (1965). 7. D. Gibson, J. Lewis and C. Oldham, J. Chem. Soc. (A), 1453 (1%6). 8. T. D. Coyle, S. L. Stafford and F. G. A. Stone, Spectrochim. Acta 17, 968 (1961); H. C. Clark and W. S. Tsang, J. Am. Chem. Soc. 89, 533 (1%7). 9. J. M. Jenkins and B. L. Shaw, Proc. Chem. Soc. 279 (1963); R. K. harris, Inorg. Chem. 5, 701 (1966);J. P. Fackler, Jr., J, A. Fetchin, J. Mayhew, W. C. Seidel, T. J. Swift and M. Weeks, 7. Am. Chem. Soc. 91, 1941 (1%9). 10. A. J. Rest, D. T. Rosevear and F. G. A. Stone, J. Chem. Soc, A, 66 (1967). 11. S. Ahrland, Structure and Bonding 1, 207 (1%6). 12. L. Vaska and S. S. Bath, J. Am. Chem. Soc. 88, 1333(1966). 13. S. J. Laplaca and J. A. Ibers, lnorg. Chem. 5, 405 (1%6). 14. J. J. Levison and S. D. Robinson, Chem. Comm., 198 (1%7). 15. J. Chatt and B. L. Shaw, 3". Chem. Soc. 5075 (1%2).