Phosphorus-31 nuclear magnetic resonance study of tertiary

Volume 17 Number 7

Inorganic Chemistry

July 1978

0 Copyright 1978 by the American Chemical Society

Contribution from the Departments of Chemistry, The Guelph-Waterloo Centre for Graduate Work in Chemistry, Guelph Campus, Guelph, Ontario, Canada N1G 2W1, and The Ohio State University, Columbus, Ohio 43210

Phosphorus-31 Nuclear Magnetic Resonance Study of Tertiary Phosphine Complexes of Mercury(I1) ELMER C. ALYEA,*2aSHELTON A. DIAS,2aRAM G. GOEL,*2aWILLIAM 0. OGINI,2aPIERRE PILON,2a and DEVON W. MEEK*Zb Received September 29, 1977 Phosphorus-31 NMR results are presented for compounds of the types HgX2(PR3),where, for n = 1, R is o-tolyl, tert-butyl, cyclohexyl, and phenyl and, for n = 2, R is cyclohexyl and phenyl and where X is chloride, bromide, iodide, thiocyanate, acetate, and nitrate. The two-coordinate complex [ H ~ ( P C Y ~ ) ~ ] displays the largest coordination chemical shift and a relatively low coupling constant. Phosphorus-31-mercury199 coupling constants are in the range 3073-10 000 Hz; their correlation with the coordination chemical shift is reported. Factors (e.g., the electronegativityof the anion, the basicity and bulkiness of the phosphine, and the geometry at the mercury atom) affecting the coupling constants and chemical shifts are discussed.

Introduction Relatively few studies of mercury-199 to phosphorus-3 1 nuclear spin-spin coupling in tertiary phosphine complexes of mercury(I1) have been r e p ~ r t e d , ~though - ~ synthetic and other physical studies of such complexes are quite extensive.6 Grim and co-workers3 related the 199Hg-31Pcoupling constants for halide complexes of the types L2HgX2 and L2Hg2X4(L = Bu3P, Bu2PhP, BuPh2P and, for the latter type only, Et2PhP) to the electronegativity of the halogen, the basicity of the phosphine, the type of complex, and the coordination chemical shift. Similar correlations were reported for tri-n-butyl- and trioctylphosphine complexes of the above types as well as some triethyl phosphite and diethylphosphonate complexe~.~ Pidcock and co-workers' had earlier discussed the 199Hg-31Pcoupling constants in the compounds [HgX((EtO),PO]] (X = C1, Br, I, M e C 0 2 , (Et0)2PO) and the crystal structure of the chloro complex. Phosphorus-3 1 N M R data for a limited number of trimethylphosphine complexes of mercury(I1) with different coordination numbers for the mercury are also a ~ a i l a b l e .No ~ 31PN M R spectral data have yet been reported for triarylphosphine complexes of mercury(I1). During investigations8 in our laboratories of the steric effects of sterically demanding phosphines such as tri-tert-butylphosphine, tricyclohexylphosphine, and tri-o-tolylphosphine we have synthesized and characterized several new 1:l and 1:2 adducts with mercury(I1) salts. Their preparation and structural elucidation via vibrational spectral studiesg and several x-ray single-crystal determination are reported elsewhere.1° Herein are presented 31PN M R spectral data for the complexes L,HgX2, where, for n = 1, L = t-Bu3P, (o-tolyl),P, Cy3P, and Ph3P, and for n = 2 , L = Cy3Pand Ph3P, and where X = C1, Br, I, S C N , OAc, and NO3. The N M R results for the two-coordinate complex [ H ~ ( P C Y ~ ) ~ ] are also discussed. Experimental Section The 31PNMR spectra were obtained either with a Bruker HX-90 Fourier transform spectrometer at 36.43 MHz using 10-mm tubes, deuterium lock from the deuterated solvent, and external 85% H3P04 0020-1669/78/13 17-1697$01.OO/O

as the reference or with a Bruker WP-60 FT spectrometer at 24.3 MHz using the sideband technique with 85% H3P04as reference in a concentric capillary. Chemical shifts are considered accurate to rlrO.1 ppm and coupling constants to =k2 Hz. Acetone-d6 was used as a lock in some instances. Low-temperature measurements were made on dichloromethane solutions when necessary to observe the satellite peaks due to mercury- 199; several complexes undergo phosphine dissociation and rapid exchange at room temperature. Dimethylformamide and dimethyl-d6sulfoxide were used as solvents for some complexes, with the tri-o-tolylphosphinecomplexes having the least solubility even in these polar solvents. Preparation of the complexes followed the general which normally involves stirring the phosphine and the mercuric salt in an appropriate molar ratio (usually in ethanol). Only 1:l adducts were isolated with tri-tert-butylphosphine and tri-o-tolylphosphine. The synthesis of one new complex Hg(N03)2(Cy3P)2is given as a representative example; satisfactory elemental analyses were obtained for all the complexes. A mixture of Hg(N03)2(0.65 g, 2.0 mmol) and PCy, (1.12 g, 4.0 mmol) was stirred in 40 mL of dichloromethane for 5 h. The white solid obtained after filtration and concentration of the filtrate was recrystallized from dichloromethane-ether; yield 59%; mp 203-208 OC dec. Anal. Calcd for Hg(N03)2(Cy3P)2:C, 48.83; H, 7.51;N, 3.16. Found: C, 48.80; H, 7.65; N, 2.94. Discussion Phosphorus-3 1 nuclear magnetic resonance data are given in Tables 1-111. Plots of coordination chemical shift, bcomplex - Bllgand (As), against 1J(*99Hg-31P),the separation between satellite peaks, are shown in Figures 1 and 2. In those cases which showed only the relatively intense central peak a t ambient temperature, the two small satellite peaks arising from those molecules containing mercury-199 (1 6.84% natural abundance, I = '/J were observable a t lower temperatures. All complexes showed positive coordination chemical shifts (downfield relative to 85% H3P04 at 0.0 ppm), corresponding to a decrease in electron density upon coordination of the phosphorus atom. The data are discussed below according to the type of complex and the particular phosphine ligand. Previous attempts3 to observe 31P signals for triphenylphosphine complexes of mercury were thwarted by solubility 0 1978 American Chemical Society

1698 Inorganic Chemistry, Vol. 17, No. 7, 1978

Alyea et al.

Table I. "P NMR Data for (Ph,P),HgX,

X n=2

I SCN Br c1 OAc

n=l

I SCN Br c1 OAc

A 6 , ppma

1.T(199Hg-31P),Hz

13.1 37.4 21.5 33.9 39.9 12.2 (24.1)b 43.2 (40.9)b (36.l)& (38.8)b 35.1 (3 3 .2)b

3073 3716 4178 4740 5 024 4673 (4 7 0 0) 6159 (6366)b (6464)b (7431)b 8640

a A6 is the change of chemical shift o n coordination in CH,Cl, solution, a t 243 K (n = 1) or a t 230 K (n = 2); free PPh, has 6 at -5.8 ppm with reference to 85% H,PO,; the 31PIesonance of t h e ligand shifts downfield o n Coordination to a metal. In DMF solution a t 243 K.

Table 11. 31PNMR Data for (Cy,P),HgX, X

n=2

I SCN

Br c1

NO,

OAc c10, n=l

I SCN

Br c1 OAc

NO,

A 6 , ppma

1J(199Hg-3'P), Hz

19.5 49.1 36.0 41.3 56.5 46.1 67.8 30.4 63.0 44.5 52.1 51.9 (58.3)b

3970 4326 4561 4815 4805 5 156 3755 4439 5640 6201 6992 7461 (85 4 0)

i s the change of chemical shift o n coordination in CH,Cl, solution. Free PCy, has 6 a t 8.6 ppm with reference to 85% H,PO,; the 31P resonance of the ligand shifts downfield on coordiMeasured in Ne,SO-d,; A6 a t 60.0 ppm for nation to a metal. CH,Cl, solution.

4

2

6 lJisHB - Z I P

8

IO

kHz

Figure 1. Phosphorus-31 NMR data for the HgX2(PPh3), complexes. T h e lines are drawn through the halide points only, as those complexes have known structure^.^^'^

SCN

60

-

50

-

-A8 ppm 40

-

30

-

20

-

a A6

t-Bu,P

I CN SCN Br

c1

OAc (0-tolyl),P

I Br c1 SCN OAc

15.8 21.6 41.4 30.5 37.8 36.1 16.6 (44.5)b (41.7)' (4 2 .O)c (42.2)C 46.1 (47.8)d (48.1)c

4419 485 8 5810 5 941 6755 7220

8299 (8255)d (10000)d

NO3 Change of chemical shift on coordination in CH,Cl, solution; free P-t-Bu, at -60.9 ppm; free P(o-tolyl), at +32.2 ppm in CH,Cl, solution, a t +32.4 ppm in Me,SO solution with reference to 85% H,PO, at S = 0 ppm. The 31P resonance of t h e ligand shifts downfield o n coordination t o a metal. In DMF solution In Me,SO solution, In CDC1, solution. a t 218 K. a

problems. Our Fourier transform data collection capability has allowed us to obtain spectra for dichloromethane solutions for both the (Ph3P)2HgX2 and [(Ph,P)HgX2J2 series of compounds (Table I, Figure 1). The former 1:2 halide and thiocyanate adducts are known to be pseudotetrahedral on the basis of vibrational spectral assignment^'^-'^ and the x-ray

I

499H9-31p

kHz

Figure 2. Phosphorus-31 NMK data for the HgX2(PPR3),series of complexes. T h e lines a r e drawn through the halide points only, a s those complexes have known s t r u c t ~ r e s . ~ ~ ' ~

analysis of (Ph3P)2Hg(SCN)2.'7 Similarly, vibrational data14-16 for the 1:l complexes are consistent with a transcentrosymmetrical dimer, recently proved by x-ray crystallography for the chloride,'* The structures of the (R3P)2Hg(OAc)2complexes are unknown, although it has been establishedIod that ( ~ - B U , P ) H ~ ( O A C is ) monomeric ~ with unsymmetrically chelated acetato groups. Other studies indicate that L2Hg(OAc), complexes undergo dissociation and rapid ligand exchange in ~ o l u t i o n . ' ~In the present study the temperature was lowered sufficiently to permit observance of the satellite peaks; Le., phosphine exchange is then slow on the NMR time scale. The various trends observed by Grim and co-workers3 are also found for the present triphenylphosphine complexes: the magnitude of 1J('99Hg-31P)increases in the order of the electronegativity of the halogen ligand, is larger for the 1:l dimeric species than the corresponding 1:2 adducts, and generally increases with the coordination chemical shift. (The best straight lines in Figures 1 and 2 are drawn from the data

Tertiary Phosphine Complexes of Mercury(I1)

Inorganic Chemistry, Vola17, No. 7 , 1978 1699

electronegativity, with the values for the 1:l complexes being of the halide complexes, whose similar structures are ensured approximately 40% greater than for the analogous 1:2 complex. by other physical methods; see text and ref 9 and 18.) These This compares with a 55% increase between the two tritrends are consistent with the more electronegative anions and phenylphosphine series. The magnitude of the coordination the dimeric cases leading to greater r~ P-Hg interaction and chemical shift also generally increases in the same order as larger couplings. The explanation of these observations asthe coupling constant, though the acetate value in the 1:l series sumes that little or no R bonding7 occurs between mercury(I1) is unexpectedly low and both thiocyanate values are unusually and phosphorus and that other factors such as stereochemistry high. The change in structure in the 1:l series from a trans and bond angles remain constant.zOizl Thus, while the corsymmetrical dimer assumed for the halides', to a monomer relation between anion electronegativityZ2and J( 199Hg-31P) for the acetatelg and a polymer for the thiocyanatez3 is is extended in the present (Ph3P),HgX2 (n = 1, 2) series, it probably a major factor contributing to the anomalous is to be noted that the coordination chemical shift does not chemical shifts. As expected for the more basic tricycloincrease in the same order; Le., I < S C N < Br < C1< OAc. hexylphosphine (pKa of 9.70),26the coordination chemical The magnitude of the coordination chemical shift for shifts are substantially greater for each complex as compared (Ph3P)Hg(OAc)2is substantially less than might be anticipated to the corresponding triphenylphosphine complex. It is inand is undoubtedly related to the monomeric nature of the teresting to note that the J(199Hg-31P) values for the 1:l complex, whereas the other (Ph3P)HgX2complexes are ditricyclohexylphosphine complexes are slightly lower than those meric. The coordination chemical shifts of the (Ph3P),Hgobserved for the 1:1 triphenylphosphine adducts: however, the (SCN)2 (n = 1, 2) complexes are considerably higher than opposite trend is found for the 1:2 series. Whereas the more expected on electronegativity considerations and this anomaly basic phosphine is expected to lead to a larger coupling also occurs for ( B u , P ) ~ H ~ ( S C Nand ) ~ ~LHg(SCN)2 [L = c o n ~ t a n t ,the ~ larger steric requirements of tricyclohexylCy,P, t-Bu,P, (o-tolyl),P] (vide infra). Although a change in stereochemistry as compared to that of the halide p h o ~ p h i n e may ~ ~ , ~reduce ~ its ability to form a strong v bond with mercury and thus give reduced J(199Hg-31P)values. It c ~ m p l e x e s ' ~ - ' may ~ J ~ be a factor for the present 1:l comseems unlikely that J(199Hg-31P)for the 1: 1 tricyclohexylplexe~,~, the LHg(SCN)2 (L = t-Bu3P, (o-tolyl),P) complexes phosphine complexes could be markedly affected by slower are of the same geometry as the corresponding halide adligand exchange (i.e., increase by several hundred hertz) and, d u c t ~ . ' ~ -The ' ~ n-bonding ability of the thiocyanato ligand24 is not an important factor in mercury(I1) complexes;' thus, thus, the steric effect appears to be an important factor. The a determination of which of the other factors20,21affecting bulkiness of tricyclohexylphosphine can be directly related30 to the low chemical shift of the free phosphine (8.6 ppm in chemical shift becomes dominating for the thiocyanato complexes cannot be made at the present time. CH2C12)even though its basicity (pK, of 9.70) is the greatest known for any tertiary phosphine. The steric effect on the Grim3 also observed that the mercury-phosphorus coupling magnitude of the coordination chemical shift is demonstrated constant decreases as the number of phenyl groups attached by comparing the values for the (Cy3P),HgX2 complexes with to the phosphorus atom is increased for the complexes those known for (Bu3P),HgX2,, where tributylphosphine is (PhnR3-nP)2HgX2(n = 0, 1, 2). This trend, which was also much less bulky27but of similar basicity (pKa of 8.43);26those reported by Mann for some cadmium25aand tinZSbcomplexes, for the latter phosphine series are considerably higher. is the opposite of the general relationship found for metalphosphorus coupling constants in which n interactions may The J( 199Hg-31P)values and coordination chemical shifts be invoked.21 The observed decrease for the mercury series again generally increase with increasing anion electronegativity of complexes was related, to the decreasing basicity of the for the 1 :1 series of tri-tert-butylphosphine complexes. Since tertiary phosphine (Bu3P has pKa of 8.43; Ph3P, a pK, of (t-Bu,P)Hg(SCN)* is dimeric in dichloroethane ~ o l u t i o n the ,~ 2.73)26and cited as evidence for the dominating importance anomalously high A6 value is inexplicable in terms of a of a-bond strength on the value of J('99Hg-31P). Our results structural change from the halides; however, the low A6 value show that both the coordination chemical shifts and the for the acetate can be explained by the change to a monomeric coupling constants for the (Ph3P)zHgXzcomplexes are lower, complex in that case.lod The position of the cyanide, as exas predicted, than for ( P ~ , R U P ) ~ H ~The X ~ greatest . decrease pected from electronegativity considerations,22is in agreement for both parameters occurred between the ( P ~ B U ~ P ) ~and H ~ X ~ with earlier contention^^,^' that n bonding is not important in mercury(I1)-phosphine complexes. The similarity in (Ph2BuP)2HgX2complexes. Though less marked, decreases of both coordination chemical shift and J( 199Hg-31P)occur J( 199Hg-31P)values in the corresponding tricyclohexylin the dimeric [(Ph3P)HgX2I2series relative to the alkylphosphine and tri-tert-butylphosphine is as expected for two substituted phosphine series. P i d ~ o c khas ~ ~suggested that phosphines of similar basicity26and bulkiness.27 However, the dissociation and phosphine exchange may invalidate Grim's much lower A6 values for the tri-tert-butylphosphine complexes conclusions concerning the basicity-coupling constant trends. reflect the fact that steric interactions are more important than An inve~tigation'~ of a wide range of the more soluble acetate in the corresponding tricyclohexylphosphine complexes. The complexes has indeed shown that LzHgX2complexes may be failure to isolate any 1 :2 tri-tert-butylphosphine complexesg extensively dissociated and that, as observed for the triand comparisons of x-ray crystallographic datal0 for complexes phenylphosphine complexes in this study, ligand exchange is of both phosphines support this conclusion. The similarity in too fast on the NMR time scale to permit observation of the slope of the plot of A6 against 1J(199Hg-31P)for the three coupling at ambient temperature. Nevertheless, the difference series of complexes LHgX2 (L = Ph3P, Cy,P, tert-Bu3P) between J('99Hg-3'P) in (Ph3P)2Hg12 (3073 Hz) and supports our conclusionsgbased on vibrational spectra that the ( B u , P ) ~ H ~(4100 I ~ Hz) is too great, in our estimation, to be structures are the same for each anion. accounted for by this phenomenon. Measurements at lower The [(o-tolyl),P]HgX2 complexes are much less soluble and temperatures to minimize ligand exchange would probably only A6 could only be measured in dichloromethane for X = I, OAc, increase slightly the magnitude of J('99Hg-31P) in each case.19 and NO,; although 1J(199Hg-31P)values were obtained for the Our results for the triphenylphosphine complexes thus sublatter two cases, the broadness of the central peaks signified stantiate and extend Grim's conclusions. that phosphine exchange was taking place. No coupling was Similar trends are observed for the J('99Hg-31P) values for observed for the iodide complex (even at 218 K in dithe two series of tricyclohexylphosphine derivatives (Table 11, methylformamide) or for the other complexes in the series. Figure 2). The coupling constants increase with greater anion Except for the acetate case, the low solubility of all of the

1700 Inorganic Chemistry, Vol. 17, No. 7 , I978 (0-tolyl),P complexes, even in dimethyl sulfoxide or dimethylformamide, precluded other attempts to observe the satellite peaks. Although [ ( ~ - t o l y l ) ~ P ] H g ( N Omay ~ ) ~ be recovered from dimethyl sulfoxide and A6 is nearly unchanged for [ ( ~ - t o l y l ) ~Hg(SCN), P] in dimethyl sulfoxide as compared to dichloromethane, it appears that solvation and/or solvolysis may be extensive for the [ ( ~ - t o l y l ) ~ P ] H g complex I, in dimethylformamide. The greater value of A6 in the more polar solvent (44.5 ppm) is in better agreement with the presence of monomeric [ (o-tolyl),P] Hg12.DMF than the trans symmetrical dimer. Similarly, [(Ph3P)HgI2I2has a A6 of 24.1 ppm in dimethylformamide a t 243 K (12.2 ppm in dichloromethane at 243 K), the downfield shift in A6 without a change in 1J(’99Hg-31P)(4700 Hz) being consistent with solvation of the dimer to form monomeric (Ph3P)Hg12-DMF. It is probable that dimethyl sulfoxide also solvates the complexes [(o-tolyl),P]HgX, (X = Br, C1, S C N ) because A6 is near 42 ppm in each case; all of these complexes are nonelectrolytes in dimethyl sulfoxide’ so that species such as ([(~-tolyl)~P]Hg(Me~SO),]X, are not involved. The relative position of the A6 and 1J(199Hg-31P)values for [(o-tolyl),P]HgX2 (X = OAc, NO3) (Table 111, Figure 2) is a t first somewhat surprising since the basicity of (o-tolyl),P would be much less than that for Cy3P and t-Bu3P26and the bulkiness, as given by Tolman’s cone angle estimate^,,^ is significantly greater. However, the chemical shift for (otolyl),P is anomalously high and the effect, attributable to an interaction of the ortho methyl group with the phosphorus lone pair of electron^,^^,^^ would be lost on coordination. Thus, a direct comparison of A6 for the (0-tolyl),P compounds with the magnitude of A6 for other phosphines is impossible. Nevertheless, the larger ‘ J (199Hg-31P)values correspond to smaller C-P-C bond angles,30 implying that the steric requirements of (0-tolyl),P are actually less than those of t-Bu,P. That the rings of (0-tolyl),P and Cy3P can mesh together in a cog-like fashion has been verified by x-ray structural data for several complexes.’O The phosphorus-3 1 N M R investigation of a series of (R,P),Hg(OAc), ( n = 1, 2) complexes confirms that lower basicity and greater bulkiness lead to lower A6 and 1J(199Hg-31P)values.’’ has been characterized The complex [ (Cy3P),Hg] by conductivity, infrared, and single-crystal x-ray diffraction analysis as a two-coordinate species.19 The high A6 and low 1J(199Hg-31P)values relative to the other ( C Y , P ) ~ H ~ X species , deserves some comment. Schmidbaur’s results for [(Me3P),HgI2’ ( n = 2, 3, 4) species led him to suggest that the greatest coupling occurs for the linear two-coordinate cation [1J(199Hg-31P)= 5550 Hz], consistent with greater s character in the Hg-P bond.s However, the ,‘P N M R study by Pidcock and co-workers7 of the diethylphosphonate complexes ((Et0)2PO)HgX [X = C1, Br, I, OAc, (EtO),PO] showed that the coupling constant is considerably reduced and that A6 is increased when X is the (EtO),PO moiety. The trans influence of phosphorus thus also explains the current data, with the value of 1J(’99Hg-31P)for [(Cy,P),Hg]’+ (3755 Hz) being lower than that reported for [(Me3P)2Hg]2+5 due to the greater bulkiness of Cy,P. Attempts to prepare other [(R3P)2Hg]2+species32for phosphorus-3 1 N M R studies are currently in progress. Acknowledgment. This work was supported primarily by operating grants from the National Research Council of Canada (to E.C.A. and R.G.G.). We gratefully acknowledge Professor G. Ferguson’s interest in this work. We also acknowledge the NSF instrument grant that aided in the purchase of the Bruker HX-90 N M R instrument a t OSU. Registry No. (Ph3P)2Hg12, 14494-95-2; (Ph3P)2Hg(SCN)2, 27290-69-3; (Ph3P)2HgBr2,14586-76-6;(Ph3P)2HgC12,14494-85-0; (Ph,P)zHg(OAc)?, 661 19-73-1; (Ph3P)HgI2, 22573-17-7; (Ph3P)-

Alyea et al. Hg(SCN)2, 29050-70-2; (Ph3P)HgBrz,22573-16-6; (Ph3P)HgCI2, 22573-15-5; (Ph,P)Hg(OAc)z, 66119-74-2;(Cy,P)ZHgI2, 50725-85-4; ( C Y , P ) ~ H ~ ( S C N50725-94-5; )~, (Cy3P),HgBr2, 50725-84-3; (Cy,P)2HgC12, 50725-83-2; (Cy3P)2Hg(N03)2, 661 19-61-7; ( C ~ ~ P ) ~ H ~ ( O66161-25-9; A C ) ~ , (Cy3P),Hg(C104)2, 661 19-63-9; (Cy3P)HgI2, 50725-93-4; (Cy3P)Hg(SCN)2, 50725-74-1; (Cy3P)HgBr,, 50725-92-3; (Cy3P)HgC12,50725-91-2; (Cy,P)Hg(OAc),, 66119-64-0;(Cy,P)Hg(N03)2, 66119-65-1; (t-Bu3P)HgIz, 661 19-66-2; ( ~ - B u ~ P ) H ~ ( C661 N )19-67-3; ~, ( ~ - B u ~ P ) H ~ ( S C 661 N ) ~19-68-4; , (t-Bu3P)HgBr2, 661 19-69-5; (t-Bu3P)HgC12, 661 19-70-8; ( t Bu~P)H~(OAC),, 661 19-71-9; [(o-t0lyl)3P]HgI2, 661 19-55-9; [(ot ~ l y l ) ~ P ] H g B661 r ~ 19-56-0; , [(o-t~lyl)~P]HgCl~, 66119-57-1; [(otolyl)3P]Hg(SCN)2,66119-58-2; [ (o-tolyl),P] Hg(OAc),, 66 1 19-59-3; [ (o-t0ly1)3P]Hg(N03)2, 66 1 19-60-6. References and Notes Presented in part at the 173rd National Meeting of the American Chemical Society, New Orleans, La., 1977; see Abstracts, No. INOR 60. (a) The Guelph-Waterloo Centre for Graduate Work in Chemistry. (b) The Ohio State University. (a) S. 0.Grim, P. J. Lui, and R. L. Keiter, Inorg. Chem., 13,342 (1974); (b) R. L. Keiter and S. 0. Grim, J . Chem. Soc., Chem. Commun., 521 (1968). A. Yamasaki and E. Fluck, 2. Anorg. Allg. Chem., 396, 297 (1973). H. Schmidbaur and K.-H. Rathlein, Chem. Ber., 106, 2491 (1973). K. K. Chow, W. Levason, and C. A. McAuliffe in “Transition Metal Complexes of Phosphorus, Arsenic, and Antimony Ligands”, C. A. McAuliffe, Ed., Macmillan, London, 1973, p 33, and references therein. (a) J. Bennett, A. Pidcock, C. R. Waterhouse, P. Coggon, and A. T. McPhail, J. Chem. Soc. A , 2094 (1970); (b) A. Pidcock in “Transition Metal Complexes of Phosphorus, Arsenic, and Antimony Ligands”, C. A. McAuliffe, Ed., Macmillan, London, 1973, p 1. (a) E. C. Alyea, A. 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