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The preparation and NMR spectra of some trimethylphosphite complexes of platinum
J. inorg,nucl.Chem.,1971,Vol.33, pp. 253 to 257. PergamonPress. Printedin Great Britain
THE PREPARATION TRIMETHYLPHOSPHITE
AND
NMR SPECTRA OF SOME COMPLEXES OF PLATINUM
M. J. C H U R C H and M. J. MAYS University Chemical Laboratory, Lensfield Road, Cambridge, England (Received 22 April 1970) Abstraet--A series of complexes, cis-PtX~[P(OMe)3]~ (X = Cl, Br, I, NCO, N:,, Ph), has been prepared and their ~H NMR spectra are reported and discussed. INTRODUCTION
THE 1H NMR spectra of a number of complexes of the type MX2L2 (M = Pt" or PdX~;X = Cl, Br or I" L = Me3P or Me3As) have been studied[l]. This NMR data may be used for the determination of stereochemistry [2] and also yields information on the bonding in these complexes [1]. There is, however, much less information available on the 1H NMR spectra of trimethylphosphite complexes. In this paper we report the preparation and 1H N MR spectra of a series of platinum complexes of the type cis-PtX2L2 (X = C1, Br, I, NCO, N3, Ph; L = P(OMe)3). The ~H NMR spectra of these complexes are examples ofXgAA'X 9 systems (X = ~H, A = 3~p) and, in favourable circumstances, a value of J(AA') can be deduced by the method of Harris [3]. The chloride and bromide complexes have been prepared previously by an alternative but less convenient method[4]. The other complexes in the series, which were established as having a cis-configuration from their i.r. spectra, are being reported for the first time. EXPERIMENTAL ~H NMR spectra were recorded at 100 MHz on a Varian Associates H.A. 100 spectrometer using tetramethylsilane as internal lock signal. Spectra were run at a sweep rate of 0.1 Hz sec -1, and the H1 level kept very low to avoid saturation [5]. Microanalyses were performed by the microanalytical department of this laboratory. All reactions were performed under nitrogen. cis-Dichlorobis(trimethylphosphite)platinum(ll). A solution of K2PtCI4 (1.1 g ) i n water (30 ml) mixed with benzonitrile (4 ml) was stirred vigorously at 70°C for 3 hr. After cooling, the resulting yellow precipitate of trans-PtCl2(PhCN)2 was filtered off and washed with H20, then EtOH and finally Et20. A solution of P(OMe)3 (484 rag, 3-9 m-mole) in acetone (15 ml) was added dropwise to a vigorously stirred suspension of the product (910 mg, 1.93 m-mole) in acetone (40 ml). The resulting pale yellow solution was evaporated under reduced pressure to a volume of ca. l 0 ml, and precipitation of the product completed by addition of 50 ml of diethyl ether. The product was filtered off, and washed with ether to remove all traces of PhCN. It was recrystallised from EtOH by addition of Et~O to give I. D. A. DuddelL J. G. Evans, P. L. Goggin, R. J. Goodfellow, A. J. Rest and J. G. Smith, J. chem. Soc. A, 2134 (1970). 2. J. M. Jenkins and B. L. Shaw, J. chem. Soc. A, 770 (1966). 3. R. K. H a m s , Can.J. Chem. 42, 2275 (1964). 4. A. Rosenheim and W. Loewenstamm, Z. anorg, aUg. Chem. 37, 394 (1903); A. Rosenheim and W. Levy, ibid. 42, 35 (1905). 5. see W. C. Hamilton, Statistics in Physical Science. Ronald Press, New York (1964). 253
254
M.J. C H U R C H and M. J. MAYS
the complex as white needles. Overall yield 700 mg (50 per cent). (Found: C, 13.8; H, 3.5. CrHlsCI2Oe P2Pt requires C, 14.0; H, 3.5%). cis-Dibromobis(trimethylphosphite)platinum(ll). A solution of K2PtCI4 (1.2 g) and KBr (2 g) in water (40 ml) mixed with PhCN (4 ml) was stirred at 70°C for 5 hr. After cooling, the orange-yellow precipitate of trans-PtBr2(PhCN)z was filtered off, and washed with H20, EtOH and EtzO. It was then treated with P(OMe)3 as for the chloride to give the complex as white needles. Overall yield 700 mg, (40 per cent). (Found: C, 12.2; H, 3"2. CrH18BrzO6P2Pt requires C, 11.9; H, 3.0%). cis-Diiodobis(trimethylphosphite)platinum(ll). A solution of K2PtCI4 (1.04g) and KI (2"0g) in water (40 ml) mixed with PhCN (4 ml) was stirred at 70°C for 5 hr. After cooling, the solution was filtered to give a brown solid. This solid was shaken with ethanol and filtered. Most of the'brown impurity goes through the filter, and the rest collects on the surface below the orange-brown crystals of transPtI2(PhCN)2, which were separated from the impurity, filtered once more from ethanol, and finally washed with ether. Treatment with P(OMe)a as before gave the complex as pale yellow needles. Overall yield 780 mg, (45 per cent). (Found: C, 10.6; H, 2.6. CsHIsi206P2Pt requires C, 10.3; H, 2.6%). cis-Diisocyanatobis(trimethylphosphite)platinum(ll), cis-PtCl2[P(OMe)a]2 (257 mg) and K N C O (81 mg) were refluxed in acetone (35 ml) for 1 hr. The solution was evaporated to dryness and the solid residue extracted with CH2C!2. Addition of ether caused precipitation of the complex as white needles. Yield 150 mg, (60 per cent). The complex has Vcs 2212 cm-l(s) and 2236 cm-l(sh) (CHCI3). (Found: C, 18.7; H, 3.4; N, 5.6. CsH~sNzOsPzPt requires C, 18.2; H, 3.4; N, 5.3%) cis-Diazidobis(trimethylphosphite)platinum(ll). A solution of cis-PtCl~[P(OMe)3]2 (257 mg) and NaNa (65 mg) in acetone (15 ml) was heated to 50°C for 15 min. The solution was evaporated to dryness and the residue extracted with CH2Clz. Addition of ether and cooling to 0°C caused precipitation of the complex as white plates, vNs 2068 cm-~(s) and 2056 cm-~(sh) (CHCIa). Yield 160 mg, (60 per cent). (Found: C, 14.0; H, 3.4; N, 15.9. C6HlsNrOrP~Pt requires C, 13.7; H, 3.4; N, 15.9%). cis-Diphenylbis(trimethylphosphite)platinum(ll). A benzene suspension of cis-PtCl2[P(OMe)3]~ (1 m-mole) was added to the Grignard solution prepared from 4 m-mole. PhBr and 4-1 g atoms of Mg in ether ( 10 ml). The solution was stirred for I hr at r.t. and dioxane ( 10 ml) was then added. The precipitated magnesium salts were removed by centrifugation, and the solution evaporated to a volume of ca. 3 ml. Addition of 10 ml of 30/40 ligroin caused precipitation of the complex as white crystals, which were recrystallised from acetone/hexane. Yield 360 mg, (60 per cent). (Found: C, 36.7; H, 4.6. ClsHzsOrP2Pt requires C, 36.2; H, 4.7%). cis-Dichloro(trimethylphosphite)(triethylphosphine)platinum(ll). A solution of P(OMe)3 ( 124 mg) in acetone (10 ml) was added dropwise to a stirred solution of Pt2CI4(PEt3)z (384 mg) (384 mg) in acetone (40 ml). The resulting pale yellow solution was evaporated to dryness, and the residue recrystallised from ethanol by addition of ether to give the complex as white needles. Yield 240 mg, (60 per cent). (Found: C, 21.7; H, 4.9; Ci, 14.6. CaH24C1203P~Pt requires C, 21 "3; H, 4.7; CI, 14.0%). RESULTS A N D
DISCUSSION
The 1H N M R spectrum ofcis-PtClz[P(OMe)z]2 is shown in Fig. 1. All four X = 1 lines (using the nomenclature of Ref. [1]) are visible, and the analysis is trivial. The spectrum is, however, complicated by the presence of 19~Pt satellites. Since calculation based on the X = 1 lines shows that no fundamental line of significant intensity lies close outside the N doublet, the peak which is resolved on the outside of each component of the doublet must be a satellite, with ]4j(PtPOCH)I = 2.5 Hz. That this is a reasonable value is confirmed by the ~H N M R spectrum of cis-PtCI2[P(OMe)z]PEtz, where the methoxyl resonance is not complicated by second order effects, and is observed as a pair of 1 : 4 : 1 triplets; (IzJ(POCH)I = 12.6, and 14j(PtPOCH)I = 2.4 Hz). The theoretical lines shown in Fig. 1 were calculated using the coupling constants in Table 1. 195pt satellites are shown only for the six most intense fundamental lines. The spectrum of cis-PtBr2[P(OMe)z]2 is similar to that of the chloride, while for cis-PtI2[P(OMe)3]2 the fact that none of the X = 1 lines is resolved from the N doublet indicates that [zJ(PMP')[ is less than 5Hz.
Some trimethylphosphite complexes of platinum
255
-,---12.6 cps
Fig. 1. Slow passage ~H NMR spectrum ofcis-PtCl2[P(OMeh]e. Table I. Methoxyl NMR data*
cis-PtCl2[P(OMe):d2
cis-PtBr2[P(OMe)3]2 cis-Ptl2[P(OMe)3]2 cis-Pt(NCO)2lP(OMe):d2 cis-Pt(N3).z[P(OMe):d2 cis-PtPh2[P(OMe)3].z
N (Hz)
JPt-H (Hz)
12.6 12-7 12-8 12-6 12.4
2.5 2.4 2-4 2-4 2-4
11.7
2.5
±0.I
±0.1
JPH (Hz)
JPH' (Hz)
± 12.85 ~0"25 ± 13-0~ T-0-3~
±0-3
±0.3
JPP' (Hz) 18.3 8.8 5
±0.1
*In CDC13solution at 35°C. Values of Jpp, given directly by separation of first inner and first outer lines. JPHand Jpw calculated using equations of Ref. [1]. The spectra of cis-Pt(NCO)2[P(OMe)~]2 and cis-PtPh2[P(OMe),~]2 are shown in Fig. 2. (The spectrum of the azide complex is similar to that of the isocyanate.) N o outside lines are visible and, as may be seen from the figure, the inner lines are not resolved. H e n c e these spectra are not susceptible to straightforward analysis. In an attempt to extract coupling constants from the line-shape, the computer program L H A S A was written by Dr. G. M. Sheldrick of this department. The program calculates a theoretical spectrum using the equations of Ref. [3], and then constructs a line-shape assuming all transitions to be Lorentzian. It then performs a least-squares analysis using the standard N e w t o n - R a p h s o n procedure [5], and the parameters are refined until the line shape fits the observed spectrum. It has been possible to obtain a close fit in all cases, but the final standard deviations on
256
M.J. C H U R C H and M. J. MAYS ~11'7 cps--~ ~ 1 2 - 6 cps --.'-
J
Fig. 2. ~H N M R spectra of(a) cis-Pt(NCO)2[P(OMe)z]2; (b) cis-PtPh~[P(OMe)3]2.
12J(PMP')I are so large as to make the values obtained of little significance. The reason for this is probably that, as has been previously pointed out [6, 7] the halfwidths of all the lines in a system such as this need not be the same. Indeed, when the line shape analysis is applied to the chloride, where the coupling constants are known, it is found that the half-width of the inner lines must be approximately twice that of the N doublet lines (assuming that all inner lines have the same halfwidth, which is not necessarily true). This observation parallels that made by McFarlane for the X A A ' X ' system H2P2Os where the half-widths of the lines were found to differ by a factor of 2-3 [8]. For the platinum complexes, it is evident that ligand exchange is not responsible for the line-broadening since this should result in a relaxation of the P t - H coupling [9]. Some form of intramolecular motion may, however, result in incomplete averaging of more than one value of 2J(PMP) and produce the observed effect. The values of 12J(PMP')I obtained for the chloride and bromide, 18.3 Hz and 8.8 Hz respectively, may be compared with the values obtained by Goodfellow et al. [1] for the corresponding trimethylphosphine complexes, viz. 18.9 Hz and 16.2 Hz. Direct measurement of IzJ(PMP')I in several t r a n s phosphine and phosphite complexes [10] has shown that substituting a phosphite for a phosphine increases the magnitude of the coupling constant by a factor of ca. 1.5. The same is true of 12J(HMP)I in t r a n s hydrido-phosphine complexes [11]. The explanation 6. 7. 8. 9. 10. 11.
A.J. Rest, J. chem. Soc. A, 2212 (1968). E. G. Finer and R. K. Harris, Molec. Phys. 12, 457 (1967). W. McFarlane, J. chem. Soc. A, 1715 (1968). see J. P. Fackler, Jr., J. A. Fetchin and W. C. Seidel, J. Am. chem. Soc. 91, 1217 (1969). A. Pidcock, Chem. Comm. 92 (1968). M.J. Church and M. J. Mays, J. chem. Soc. A, 3074 (1968).
Some trimethylphosphite complexes of platinum
25 7
of this[10] in terms of a change in (at,)" (t01,(:~s)(0))2 implies that these coupling constants are dominated by the contact term, and predicts that 12j(PMP')I between two phosphites should be ca. 2.25 times larger than that between two phosphines in a closely related compound. This may be true for t r a n s complexes; it is certainly not true for the cis compounds discussed here and it is possible that the reason for the small values normally obtained for 12(pMP')] in cis complexes is that the contact contribution is very small. Acknowledgements-We thank Messrs Johnson-Matthey Ltd. for a loan of platinum salts and one of us (M.J.C.) thanks the S.R.C. for a maintenance grant. We acknowledge also the invaluable assistance given by Dr. G. M. Sheldrick in the computer work.
THE PREPARATION TRIMETHYLPHOSPHITE
AND
NMR SPECTRA OF SOME COMPLEXES OF PLATINUM
M. J. C H U R C H and M. J. MAYS University Chemical Laboratory, Lensfield Road, Cambridge, England (Received 22 April 1970) Abstraet--A series of complexes, cis-PtX~[P(OMe)3]~ (X = Cl, Br, I, NCO, N:,, Ph), has been prepared and their ~H NMR spectra are reported and discussed. INTRODUCTION
THE 1H NMR spectra of a number of complexes of the type MX2L2 (M = Pt" or PdX~;X = Cl, Br or I" L = Me3P or Me3As) have been studied[l]. This NMR data may be used for the determination of stereochemistry [2] and also yields information on the bonding in these complexes [1]. There is, however, much less information available on the 1H NMR spectra of trimethylphosphite complexes. In this paper we report the preparation and 1H N MR spectra of a series of platinum complexes of the type cis-PtX2L2 (X = C1, Br, I, NCO, N3, Ph; L = P(OMe)3). The ~H NMR spectra of these complexes are examples ofXgAA'X 9 systems (X = ~H, A = 3~p) and, in favourable circumstances, a value of J(AA') can be deduced by the method of Harris [3]. The chloride and bromide complexes have been prepared previously by an alternative but less convenient method[4]. The other complexes in the series, which were established as having a cis-configuration from their i.r. spectra, are being reported for the first time. EXPERIMENTAL ~H NMR spectra were recorded at 100 MHz on a Varian Associates H.A. 100 spectrometer using tetramethylsilane as internal lock signal. Spectra were run at a sweep rate of 0.1 Hz sec -1, and the H1 level kept very low to avoid saturation [5]. Microanalyses were performed by the microanalytical department of this laboratory. All reactions were performed under nitrogen. cis-Dichlorobis(trimethylphosphite)platinum(ll). A solution of K2PtCI4 (1.1 g ) i n water (30 ml) mixed with benzonitrile (4 ml) was stirred vigorously at 70°C for 3 hr. After cooling, the resulting yellow precipitate of trans-PtCl2(PhCN)2 was filtered off and washed with H20, then EtOH and finally Et20. A solution of P(OMe)3 (484 rag, 3-9 m-mole) in acetone (15 ml) was added dropwise to a vigorously stirred suspension of the product (910 mg, 1.93 m-mole) in acetone (40 ml). The resulting pale yellow solution was evaporated under reduced pressure to a volume of ca. l 0 ml, and precipitation of the product completed by addition of 50 ml of diethyl ether. The product was filtered off, and washed with ether to remove all traces of PhCN. It was recrystallised from EtOH by addition of Et~O to give I. D. A. DuddelL J. G. Evans, P. L. Goggin, R. J. Goodfellow, A. J. Rest and J. G. Smith, J. chem. Soc. A, 2134 (1970). 2. J. M. Jenkins and B. L. Shaw, J. chem. Soc. A, 770 (1966). 3. R. K. H a m s , Can.J. Chem. 42, 2275 (1964). 4. A. Rosenheim and W. Loewenstamm, Z. anorg, aUg. Chem. 37, 394 (1903); A. Rosenheim and W. Levy, ibid. 42, 35 (1905). 5. see W. C. Hamilton, Statistics in Physical Science. Ronald Press, New York (1964). 253
254
M.J. C H U R C H and M. J. MAYS
the complex as white needles. Overall yield 700 mg (50 per cent). (Found: C, 13.8; H, 3.5. CrHlsCI2Oe P2Pt requires C, 14.0; H, 3.5%). cis-Dibromobis(trimethylphosphite)platinum(ll). A solution of K2PtCI4 (1.2 g) and KBr (2 g) in water (40 ml) mixed with PhCN (4 ml) was stirred at 70°C for 5 hr. After cooling, the orange-yellow precipitate of trans-PtBr2(PhCN)z was filtered off, and washed with H20, EtOH and EtzO. It was then treated with P(OMe)3 as for the chloride to give the complex as white needles. Overall yield 700 mg, (40 per cent). (Found: C, 12.2; H, 3"2. CrH18BrzO6P2Pt requires C, 11.9; H, 3.0%). cis-Diiodobis(trimethylphosphite)platinum(ll). A solution of K2PtCI4 (1.04g) and KI (2"0g) in water (40 ml) mixed with PhCN (4 ml) was stirred at 70°C for 5 hr. After cooling, the solution was filtered to give a brown solid. This solid was shaken with ethanol and filtered. Most of the'brown impurity goes through the filter, and the rest collects on the surface below the orange-brown crystals of transPtI2(PhCN)2, which were separated from the impurity, filtered once more from ethanol, and finally washed with ether. Treatment with P(OMe)a as before gave the complex as pale yellow needles. Overall yield 780 mg, (45 per cent). (Found: C, 10.6; H, 2.6. CsHIsi206P2Pt requires C, 10.3; H, 2.6%). cis-Diisocyanatobis(trimethylphosphite)platinum(ll), cis-PtCl2[P(OMe)a]2 (257 mg) and K N C O (81 mg) were refluxed in acetone (35 ml) for 1 hr. The solution was evaporated to dryness and the solid residue extracted with CH2C!2. Addition of ether caused precipitation of the complex as white needles. Yield 150 mg, (60 per cent). The complex has Vcs 2212 cm-l(s) and 2236 cm-l(sh) (CHCI3). (Found: C, 18.7; H, 3.4; N, 5.6. CsH~sNzOsPzPt requires C, 18.2; H, 3.4; N, 5.3%) cis-Diazidobis(trimethylphosphite)platinum(ll). A solution of cis-PtCl~[P(OMe)3]2 (257 mg) and NaNa (65 mg) in acetone (15 ml) was heated to 50°C for 15 min. The solution was evaporated to dryness and the residue extracted with CH2Clz. Addition of ether and cooling to 0°C caused precipitation of the complex as white plates, vNs 2068 cm-~(s) and 2056 cm-~(sh) (CHCIa). Yield 160 mg, (60 per cent). (Found: C, 14.0; H, 3.4; N, 15.9. C6HlsNrOrP~Pt requires C, 13.7; H, 3.4; N, 15.9%). cis-Diphenylbis(trimethylphosphite)platinum(ll). A benzene suspension of cis-PtCl2[P(OMe)3]~ (1 m-mole) was added to the Grignard solution prepared from 4 m-mole. PhBr and 4-1 g atoms of Mg in ether ( 10 ml). The solution was stirred for I hr at r.t. and dioxane ( 10 ml) was then added. The precipitated magnesium salts were removed by centrifugation, and the solution evaporated to a volume of ca. 3 ml. Addition of 10 ml of 30/40 ligroin caused precipitation of the complex as white crystals, which were recrystallised from acetone/hexane. Yield 360 mg, (60 per cent). (Found: C, 36.7; H, 4.6. ClsHzsOrP2Pt requires C, 36.2; H, 4.7%). cis-Dichloro(trimethylphosphite)(triethylphosphine)platinum(ll). A solution of P(OMe)3 ( 124 mg) in acetone (10 ml) was added dropwise to a stirred solution of Pt2CI4(PEt3)z (384 mg) (384 mg) in acetone (40 ml). The resulting pale yellow solution was evaporated to dryness, and the residue recrystallised from ethanol by addition of ether to give the complex as white needles. Yield 240 mg, (60 per cent). (Found: C, 21.7; H, 4.9; Ci, 14.6. CaH24C1203P~Pt requires C, 21 "3; H, 4.7; CI, 14.0%). RESULTS A N D
DISCUSSION
The 1H N M R spectrum ofcis-PtClz[P(OMe)z]2 is shown in Fig. 1. All four X = 1 lines (using the nomenclature of Ref. [1]) are visible, and the analysis is trivial. The spectrum is, however, complicated by the presence of 19~Pt satellites. Since calculation based on the X = 1 lines shows that no fundamental line of significant intensity lies close outside the N doublet, the peak which is resolved on the outside of each component of the doublet must be a satellite, with ]4j(PtPOCH)I = 2.5 Hz. That this is a reasonable value is confirmed by the ~H N M R spectrum of cis-PtCI2[P(OMe)z]PEtz, where the methoxyl resonance is not complicated by second order effects, and is observed as a pair of 1 : 4 : 1 triplets; (IzJ(POCH)I = 12.6, and 14j(PtPOCH)I = 2.4 Hz). The theoretical lines shown in Fig. 1 were calculated using the coupling constants in Table 1. 195pt satellites are shown only for the six most intense fundamental lines. The spectrum of cis-PtBr2[P(OMe)z]2 is similar to that of the chloride, while for cis-PtI2[P(OMe)3]2 the fact that none of the X = 1 lines is resolved from the N doublet indicates that [zJ(PMP')[ is less than 5Hz.
Some trimethylphosphite complexes of platinum
255
-,---12.6 cps
Fig. 1. Slow passage ~H NMR spectrum ofcis-PtCl2[P(OMeh]e. Table I. Methoxyl NMR data*
cis-PtCl2[P(OMe):d2
cis-PtBr2[P(OMe)3]2 cis-Ptl2[P(OMe)3]2 cis-Pt(NCO)2lP(OMe):d2 cis-Pt(N3).z[P(OMe):d2 cis-PtPh2[P(OMe)3].z
N (Hz)
JPt-H (Hz)
12.6 12-7 12-8 12-6 12.4
2.5 2.4 2-4 2-4 2-4
11.7
2.5
±0.I
±0.1
JPH (Hz)
JPH' (Hz)
± 12.85 ~0"25 ± 13-0~ T-0-3~
±0-3
±0.3
JPP' (Hz) 18.3 8.8 5
±0.1
*In CDC13solution at 35°C. Values of Jpp, given directly by separation of first inner and first outer lines. JPHand Jpw calculated using equations of Ref. [1]. The spectra of cis-Pt(NCO)2[P(OMe)~]2 and cis-PtPh2[P(OMe),~]2 are shown in Fig. 2. (The spectrum of the azide complex is similar to that of the isocyanate.) N o outside lines are visible and, as may be seen from the figure, the inner lines are not resolved. H e n c e these spectra are not susceptible to straightforward analysis. In an attempt to extract coupling constants from the line-shape, the computer program L H A S A was written by Dr. G. M. Sheldrick of this department. The program calculates a theoretical spectrum using the equations of Ref. [3], and then constructs a line-shape assuming all transitions to be Lorentzian. It then performs a least-squares analysis using the standard N e w t o n - R a p h s o n procedure [5], and the parameters are refined until the line shape fits the observed spectrum. It has been possible to obtain a close fit in all cases, but the final standard deviations on
256
M.J. C H U R C H and M. J. MAYS ~11'7 cps--~ ~ 1 2 - 6 cps --.'-
J
Fig. 2. ~H N M R spectra of(a) cis-Pt(NCO)2[P(OMe)z]2; (b) cis-PtPh~[P(OMe)3]2.
12J(PMP')I are so large as to make the values obtained of little significance. The reason for this is probably that, as has been previously pointed out [6, 7] the halfwidths of all the lines in a system such as this need not be the same. Indeed, when the line shape analysis is applied to the chloride, where the coupling constants are known, it is found that the half-width of the inner lines must be approximately twice that of the N doublet lines (assuming that all inner lines have the same halfwidth, which is not necessarily true). This observation parallels that made by McFarlane for the X A A ' X ' system H2P2Os where the half-widths of the lines were found to differ by a factor of 2-3 [8]. For the platinum complexes, it is evident that ligand exchange is not responsible for the line-broadening since this should result in a relaxation of the P t - H coupling [9]. Some form of intramolecular motion may, however, result in incomplete averaging of more than one value of 2J(PMP) and produce the observed effect. The values of 12J(PMP')I obtained for the chloride and bromide, 18.3 Hz and 8.8 Hz respectively, may be compared with the values obtained by Goodfellow et al. [1] for the corresponding trimethylphosphine complexes, viz. 18.9 Hz and 16.2 Hz. Direct measurement of IzJ(PMP')I in several t r a n s phosphine and phosphite complexes [10] has shown that substituting a phosphite for a phosphine increases the magnitude of the coupling constant by a factor of ca. 1.5. The same is true of 12J(HMP)I in t r a n s hydrido-phosphine complexes [11]. The explanation 6. 7. 8. 9. 10. 11.
A.J. Rest, J. chem. Soc. A, 2212 (1968). E. G. Finer and R. K. Harris, Molec. Phys. 12, 457 (1967). W. McFarlane, J. chem. Soc. A, 1715 (1968). see J. P. Fackler, Jr., J. A. Fetchin and W. C. Seidel, J. Am. chem. Soc. 91, 1217 (1969). A. Pidcock, Chem. Comm. 92 (1968). M.J. Church and M. J. Mays, J. chem. Soc. A, 3074 (1968).
Some trimethylphosphite complexes of platinum
25 7
of this[10] in terms of a change in (at,)" (t01,(:~s)(0))2 implies that these coupling constants are dominated by the contact term, and predicts that 12j(PMP')I between two phosphites should be ca. 2.25 times larger than that between two phosphines in a closely related compound. This may be true for t r a n s complexes; it is certainly not true for the cis compounds discussed here and it is possible that the reason for the small values normally obtained for 12(pMP')] in cis complexes is that the contact contribution is very small. Acknowledgements-We thank Messrs Johnson-Matthey Ltd. for a loan of platinum salts and one of us (M.J.C.) thanks the S.R.C. for a maintenance grant. We acknowledge also the invaluable assistance given by Dr. G. M. Sheldrick in the computer work.