Inorganic Chemistry, Vol. 15, No. 12, 1976 3161
Notes (22) A. Pajunen, Ann. Acad. Sci. Fenn., 138,2 (1967);Struct. Rep. B, 32, 379 (1967). (23) Y . Komiyama and E. C. Lingafelter, Acta Crystallogr., 17, 1145 (1964). (24) D. S. Brown, J. D. Lee, and B. G. A. Melsom, Acta Crystallogr., Sect. B, 24, 730 (1968). (25) E. Luukkonen, A. Pajunen, and M. Lehtonen, Suom. Kemistil. B, 43, 160 (1970). (26) J. A. Thich, R. A. Lalancette, J. A. Potenza, and H. J. Schugar, Inorg. Chem.. 15..2731 11976). . . ., ~ , (27) J. A. Thich, D. Ma'stropaolo, J. Potenza, and H. J. Schugar, J. Am. Chem. Soc., 96, 726 (1974). (28) D. Mastropaolo, D. A. Powers, J. A. Potenza, and H.J. Schugar, Inorg. Chem., 15, 1444 (1976). ~
~~
(29) F. A. Cotton and D. L. Weaver, J . Am. Chem. Soc., 87,4189 (1965). (30) W. R. McWhinnie, J . Inorg. Nucl. Chem., 26, 21 (1964). (31) G. A. Rodley and P. W. Smith, J . Chem. SOC.A, 1580 (1967). (32) D. S.Brown, J. D. Lee, B. G. A. Melsom, B. J. Hathaway, I. M. Procter, and A. A. G. Tomlinson, Chem. Commun., 369 (1967). (33) A. W. Downs, S. A. Dias, and W. R. McWhinnie, Spectrochim. Acta, Part A , 29, 1213 (1973). (34) J. Almlof, J.-0. Lundgren, and I. Olovsson, Acta Crystallogr., Sect. B,
27.. 898 11971). (35) D. L. Lewis, W. E. Hatfield, and D. J. Hcdgson, Inorg. Chem., 11,2216 ( 1972). (36) M. Toofan, A. Boushehri, and M. UI-Haque,J. Chem. Sm.,Dalton Trans., 217 (1976). ~
~
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Notes Contribution from the Department of Chemistry, University of Nevada, Reno, Reno, Nevada 89557, and the Life Sciences Division, Stanford Research Institute, Menlo Park. California 94025
Palladium (11)-Cyanide-Phosphine Complexes' Allen W. Verstuyft,2a Lewis W. Cary,Zb and John H. Nelson*Za Received November I O , 1975 AIC50810D
Recent investigation^^-*^ of the geometrical isomerization of complexes of the type L2PdX2 have indicated that the isomerization process is associative, proceeding through pentacoordinate transition states (I and 11) according to eq 1. Each of the three pathways (1, 2, and 3) occurs under g[L,L'yxl+x-
\
L' @
trans-ML,X,
(1)
various conditions and the conditions favoring each have been d e l i ~ ~ e a t e dThe . ~ least studied pathway is fluxional rotation15 (pathway 2) and it should dominate in nonpolar solvents when L and L' are small and have nearly the same basicity, with X being a strongly coordinating anion. In some investigation^^-^ of catalyzed isomerizations the lack of L and L' interchange was taken to imply that any mechanistically important pentacoordinate species cannot have a regular geometry but must be distorted in such a way that L and L' can never become equivalent. It is apparent then that more information is needed regarding the solution behavior of pentacoordinate palladium complexes. To date there have been few pentacoordinate complexes of palladium(I1) with monodentate ligands Except for the ligand21 C6H5CH2P(CH3)2, these all involve the sterically undemanding phosphole type ligands, 16-20 and still, each of these complexes is extensively dissociated in solution. Numerous studies with pentacoordinate nickel complexes have shown that pentacoordination is stabilized by strong field ligands.22 The exact reasons are not yet clear but evidence is emerging which suggests that the relative stabilities of ML2X2 and ML3X2 complexes depend upon a subtle interplay of steric and electronic effects.23 Thus there are two possible approaches in seeking to stabilize pentacoordinate heteroleptic palladium(I1) complexes of the type PdL3X2. One approach is to seek sterically undemanding
J I 1 8 4
400
I1
I I
I
I l l I I I I I I 1 1
300
l
l
2 00
~
l
l
Il I I I I
100
Figure 1. The 100-MHz 'H NMR spectra in the methyl and methoxy regions for a CDCl, solution containing an equimolar (1.25 X M each) mixture of [(CH,),PC,H,],Pd(CN), and (CH,O),P as a function of time. The numbers are chemical shifts in Hz from internalTMS. L', = [(CH,O),P],Pd(CN),, LL' = [ ~(CH30),p~{(CH,),pC,Hs}lPd(CN),, and I-, = I(CH,),PC,H,I,Pd(CN), .
ligands L and the other is to study strong-field anions X. The latter approach has been undertaken in this work by utilizing cyanide as the strong-field anion with a variety of phosphorus ligands L.
Experimental Section Chemicals used were reagent grade and used as received. All solvents, when necessary, were dried by standard procedures and stored over Linde 4-A molecular sieves for at least 2 days prior to use. All
reactions involving phosphines were conducted in a prepurified nitrogen
3162 Inorganic Chemistry, Vol. 15, No. 12, 1976
Notes
Table I. Physical Properties of the Complexes L,Pd(CN), Electronic spectraa
’ H NMRb
11 spectra, cm-’
L
Mp. “C
v, pm-’
104€
VCzN
Me,PPh MePPh, BzPPh, Bz,PPh Bz,P MeOPPh, (MeO) ,PPh (MeO),P BzOPPh, (BzO),PPh (BzO) ,P
183 219 24 1 25 2 179 208 172 131 188 168 148
3.55 3.5 1 3.57 3.72 3.85 3.68 3.98 4.02 3.70 4.03 4.00
2.30 2.40 2.67 2.10 4.57 3.67 2.19 2.20 3.85 1.97 2.00
2136 2130 2126 2135 2130 2132 2135 2145 2135 2139 2143
~pdr.
500 507 509 490 474 497 485 5 39 495 544 498
6(CH,
01 CH,)
2.00 t 2.32 t 4.13 t 3.75 qtc 3.46 t 3.79 t 3.33 t 3.88 t 4.99 t 4.91 qtd 4.95 t
J , HZ
,‘P NMR -6(3’P)
7.5 6 8 .0 7.5 6.3 15.6 15 .O 15.2 15.1 10.0 15 .O
-4.5 7.6 21.1 16.4 15.1 116.2 105.9 95.7 110.4 112.3 102.5
a In CHC1, solution, all complexes are colorless. Key. t , triplet; d, doublet; q t , quartet of triplets; J = l n J p ~ + n’-2JpH1. [ABXI, spin system: J ~ ~ = O ; ~ , = 3 . 7 3 6 ; ~ ~ = 63 .. 7 7[ABX], spinsystem: J ~ ~ = 1 2 H. 5z ; v ~ = 5 . 0 3 6 ; v g = 4 . 7 96 .
Table 11.
’
P H } Data for CDC1, Solutions of the Complexes L,Pd(CN),
La
S(CH, or CH,)a J,b Hz
6(CN)
J,c Hz
6(C,)
J,b
6(C,,,)
132.05 s 132.84s 127.44s 131.47 s 132.68s 131.4s 131.4 s 132.70 s 132.96 s 133.16 s 128.96 s 128.96 s
0 0 0 0 0 0 0 0 0 0 0 0
131.1 s 131.27s 130.17s 130.33s 132.88 t 133.59 s 133.84 t 132.18 t 132.34s 132.87 t 128.39s 128.71 t
Me,PPh MePPh, Bz,P Bz,PPh
16.73 t 17.23 t 32.39 t 32.86 t
10.3 16.9 19.6 20.2
132.5 t d 132.9 t 131.0
25 d 22 d
BzPPh,
37.50t
20.2
132.5 t
10
(BzO),P (BzO),PPh
70.40 s 70.60s
0 0
d 135.9 t
9
BzOPPh,
70.89 s
0
132.2
d
Bz Ph Bz Ph Bz Ph Bz Ph
J,b Hz
6(C,,,)
J,b Hz
6(C,)
J
0 0 0 0 12 0 9.2 12.6 0 14.0 0 3.0
129.1 s 128.87s 128.99 s 128.71 s 129.00t 128.32 s 128.56 t 128.10 t 128.43 t 128.71 t 128.07 s 128.07 s
0
d d 127.44s 127.38 s 128.52s 127.13s 128.25 s 127.82 s 127.80 s 128.17 s 127.50 s 127.50 s
0 0 0 0 0 0 0 0 0 0
a Key: Me, CH,; Ph, C,H,; Bz, C,H,CH,; BzO, C,H,CH,O; t , triplet; s, singlet. J = PJpc J for first-order triplet. Not observed due t o limited solubility and/or long relaxation time.
atmosphere. Melting points were determined on a Meltemp melting point apparatus and are uncorrected. Elemental analyses were performed by chemalytics, Inc., Tempe, Ariz. 85282, and satisfactory C, H, and N analyses were obtained for all complexes. Infrared, electronic, and NMR spectra were obtained a s described previously.12 Proton and 13C(1H) chemical shifts are relative to internal TMS. The 31P(1H) chemical shifts are relative to external 85% H3P04 (capillary) with signals downfield of H3P04 being reported with negative shifts. T h e ligands were prepared24 by standard Grignard or solvolysis reactions and purified by vacuum distillation. T h e chloride complexes L2PdC12 were prepared by standard methods24 and each of the cyano complexes was prepared from these by metathesis reactions with sodium cyanide. T h e physical properties of the complexes are listed in Table I.
Results and Discussion All (R3P)2Pd(CN)2 complexes exhibit single Upd-C vibrations in the solid state and the single V-N vibrations both in the solid state and in chloroform solutions (both of) which are required of a D 2 h trans geometry (Table I). Each of the complexes except [ ( C ~ H S C H ~ ) Z P C ~ H ~ ] P and ~ ( [(c6CN)~ H5CH20)2PC6H5]2Pd(CN)2 exhibits 1:2:1 triplets for the methyl or methylene resonances in its ‘H N M R spectrum, typical of the trans geometry13 for the [XnA]2 spin systems. Both [(CsHsCH2)2PCsHsl 2Pd(CN)2 and [(CsHsCHz0)2PCsHs]2Pd(CN)2 exhibit quartets of triplets for the methylene resonances in their ‘H NMR spectra, typical of the trans geometry for [ABX]2 spin system^.^^,^^ All phosphine complexes exhibited 1:2:1 triplets for their l3C(IH)CH3 or CH2 resonances typical of the trans geometry for [A]2X spin systems.27 In four cases (Table 11) a 1:2:1 triplet was observed for the 13C11H)resonance of the cyanide carbon, consistent with the trans geometry and an A2X (A = 31P,X = 13C) spin system. The cis geometry should exhibit a doublet of doublets for the associated [A]2X spin system of the 13C(IH)cyanide
0 0 0 10 0 10.2 4.0 4.0 13.2 0 0
+ n + 2 J p ~for1 “virtually
coupled” multiplet.
carbon resonance since the two phosphorus-carbon coupling constants, 2 J p c and 2Jp,c, should be considerably different12J4 and 2Jppf should be small for the cis g e ~ m e t r y . ~All ~,~~ complexes exhibited single 31Presonances, demonstrating the existence of a single species in solution. The 31Pchemical shifts are consistent with those anticipated for the trans geometry.29 All of the phosphorus ester complexes exhibited singlets in their l3Ci1H}NMR spectra except for the cyanide carbon resonance of [(Bz0)2PPh]2Pd(CN)2. These singlets are typical for the trans geometry in which algebraic cancelation of “ J p c and n + 2 J p ~has occurred in the [A]2X I3C spin systems.30 Whenever the solutions contained even the slightest trace of excess phosphine, the ‘H N M R resonance of the methyl or methylene groups collapsed to a singlet indicative of rapid phosphine e ~ c h a n g e . ~ l This - ~ ~ occurred for samples with excellent chemical analyses. Multiple recrystallizations, Pd(CN)2, or reactions36with CHC13 or CDC13 were necessary to remove this trace of excess phosphine. This is much more critical than for analogous chloride, azide, or bromide complexes. Similar behavior has been noted34 for [(CH3)3P]2Ni(CN)2 and excess ligand has been utilized to catalyze isomerizations in other system^.^-^^"^^^ Addition of a trace of (CH3)2PC& to a CDCl3 solution of trans[(CH3)2PC6H5] 2Pd(CN)2 collapsed the triplet methyl resonance to a singlet which remained a singlet even at -50 OC. Addition of more (CH3)2PC&5 to this solution caused the singlet to change to a doublet indicating that the exchange rate increases as the concentration of excess phosphine increases.33 This is suggestive of an associative mode of exchange. When a trace of (CH30)3P was added to a CDC13 solution of [(CH3)2PC6Hs] 2Pd(CN)2, geometric isomerization occurred with the concomitant formation of cis- [(CH30)3P][ (CH3)2PC6H5]Pd(C N ) 2.28,37 T h e complex cis[(CH30)2P][(CH3)2PC6H5]Pd(CN)2 was also prepared by
Notes the redistribution reaction which occurs upon mixing solutions of trans-[(CH30)3P]2Pd(CN)2 and trans[ (CH3)2PC6H5]2Pd(CN)2 in equimolar amount^.^^,^^ When a 1:l mole ratio of (CH30)3P was added to a solution of [(CH3)2PC6H5]2Pd(CN)2 in CDCl3 (Figure I), the NMR spectra were consistent with the occurrence of the reactions
Inorganic Chemistry, Vol. 15,No. 12, 1976 3163 upon addition of excess ligand to solutions of L2Pd(CN)2. Thus, as anticipated, cyanide does stabilize the pentacoordinate complexes relative to chloride and azide but the pentacoordinate L3Pd(CN)2 species are not detectable in solution.
Acknowledgment. The financial support of the University of Nevada, Reno, Research Advisory Board, and the donors of the Petroleum Research Fund, administered by the American Chemical Society, is gratefully acknowledged.
where L = (CH3)2PC& and L’ = (CH30)3P. Thus, at the Registry No. (MezPPh)zPd(CN)z, 60488-88-2;(MePPh2)zPd(CN)2, 60488-89-3; (BzPPhz)2Pd(CN)z, 60488-90-6; instant at which (CH30)3P was added, ligand substitution of (BzzPPh)2Pd(CN)z, 60488-91-1;(Bz3P)zPd(CN)z, 60488-92-8; (CH3)2PC& by (CH30)3P occurred in a stepwise manner. (MeOPPh2)2Pd(CN)z, 60488-93-9;((MeO)zPPh)2Pd(CN)2, Initially, there is a small concentration of free (CH3)2PC6H5 ((Me0)3P)zPd(CN)2,60488-951; (BzOPPh2)2Pd(CN)2, 60488-94-0; and ligand exchange occurs at an intermediate rate between 60488-96-2; ((BzO)zPPh)2Pd(CN)2, 60488-97-3; ((BzO)~P)~P~(CH3)9C6H5 and [(CH3)2PC6H5]2Pd(CN)2 as shown by the (CN)z,60488-98-4; ((MeO)3P)(MezPPh)Pd(CN)z, 60488-99-5; I3C, singlet ‘H resonance in the methyl region. Slow exchange is 14162-14-4;31P,1123-14-0. observed between (CH30)3P and [(CH30)3P]2Pd(CN)2 since there is loss of 1H-31P coupling in the (CH30)3P methyl References and Notes resonance and the line shape for the [(CH30)3P]2Pd(CN)2 Presented in part at the 30th Annual Northwest Regional Meeting of methyl resonance has changed. No exchange occurs with the the American Chemical Society, Honolulu, Hawaii, June 12-13, 1975; “mixed-ligand” complex as doublets are observed in both the see Abstracts, No. 152. methoxy and methyl regions with the same coupling constants (a) University of Nevada, Reno. (b) Stanford Research Institute. and chemical shifts as a solution containing only cisP. Haake and R. M. Pfeiffer, Chem. Commun., 1330 (1969). P. Haake and R. M. Pfeiffer, J . Am. Chem. Soc., 92, 4996 (1970). [(CH30)3P][(CH3)2PC6H5]Pd(CN)2. Over a period of time P. Haake and R. M. Pfeiffer, J . Am. Chem. Soc., 92, 5243 (1970). (30 min) the concentrations of the “mixed-ligand’’ complex, D. G. Cooper and J. Powell, J. Am. Chem. SOC.,95, 1102 (1973). free (CH3)2PC6H5, and trans-[(CH30)3P]2Pd(CN)2 increase D. G. Cooper and J. Powell, Can. J . Chem., 51, 1634 (1973). J. Powell and D. G. Cooper, J . Chem. SOC.,Chem. Commun., 749 (1974). at the expense of [(CH3)2PCsH5]2Pd(CN)2. As this occurs, D. A. Redfield and J. H. Nelson, J . Am. Chem. SOC.,96,6219 (1974). the rate of ligand exchange of [(CH3)2PC6H5]2Pd(CN)2 D. A. Redfield, J. H. Nelson, R. A. Henry, D. W. Moore, and H. B. increases as seen by the transition of the singlet ‘H methyl Jonassen, J . Am. Chem. SOC.,96, 6298 (1974). W. J. Louw, J. Chem. Soc., Chem. Commun., 353 (1974). resonance into a doublet. Others16-21,31,34,38 have isolated D. A. Redfield, L. W. Cary, and J. H. Nelson, Inorg. Chem., 14,50 (1975). pentacoordinate complexes of the type L3MX2 (M = Ni, Pd, D. A. Redfield and J. H. Nelson, Inorg. Chem., 12, 15 (1973). Pt) and found that in each case extensive dissociation of either A. W. Verstuyft and J. H. Nelson, Inorg. Chem., 14, 1501 (1975). P. Meakin, E. L. Muetterties, and J. P. Jesson, J . Am. Chem. Soc., 94, the neutral ligand L or the ionic ligand X occurs in solution. 5271 J. P. Jesson and P. Meakin, ibid., 96, 5760 (1974). In some cases this dissociation is temperature d e p e n d e ~ ~ t . ~ ~ , ~ ~ D. , ~W. ~(1972); Allen, I. T. Millar, and F. G. Mann, J . Chem. SOC. A, 1101 (1969). For example, at -50 OC the IH NMR spectrum of [(CD. W. Allen, F. G. Mann, and I. T. Millar, Chem. Ind. (London),2096 (1966). H3)2P&H5] sPtBr3 possesses a doublet and triplet (both of J. W. Collier, F. G. Mann, D. G. Watson, and H. R. Watson, J . Chem. which have platinum satellites) with 1:2 relative integrated SOC.,1803 (1964). i n t e n ~ i t i e s . ~This ~ is consistent with the pentacoordinate J. W. Collier and F. G. Mann, J . Chem. Soc., 18 I5 (1 964). square-pyramidal geometry established by x-ray crystallogD. W. Allen, F. G. Mann, and I. T. Millar, J . Chem. SOC.C, 3937 (1971). R. L. Bennett, M. I. Bruce, and F. G. A. Stone, J . Organomet. Chem., raphy for PdL3Br2, L = 5-ethyl-5H-diben~ophosphole~~ and 38, 325 (1972). L = 2-phenyli~ophosphindoline.~~ It is also consistent with J. S. Wood, Prog. Inorg. Chem., 16, 227 (1972). a trigonal-bipyramidal geometry with equatorial bromines. B. B. Chastain, E. A. Rick, R. L. Pruett, and H. B. Gray, J . Am. Chem. Soc., 90, 3994 (1968); M. Bressan and P. Rigo, Inorg. Chem., 14, 38 Decreasing the temperature to as low as -120 “C failed to slow (1975); G. Favero and P. Rigo, Gazz. Chim. Ital., 102, 597 (1972). ligand exchange to the point where any pentacoordinate G. Kosolapoff and L. Maier, Ed., “Organophosphorus Compounds”, Vol. palladium(I1) cyanide species could be observed. On the 1-111, Wiley-Interscience, New York, N.Y., 1972. J. H. Nelson and D. A. Redfield, Inorg. Nucl. Chem. Lett., 9,807 (1973). contrary, we find, for example, that upon heating a solution D. A. Couch, S. D. Robinson, and J. N. Wingfield, J . Chem. SOC.,Dalton of [ ( C H ~ ) ~ P C ~ H S ] ~ P in ~ (nitrobenzene, CN)~ its triplet ‘H Trans., 1309 (1974). methyl resonance observed at 25 OC begins to broaden at 39 D. A. Redfield, J. H. Nelson, and L. W. Cary, Inorg. Nucl. Chem. Lett., 10. 727 OC, collapses to a singlet at 57 OC, becomes a sharp singlet - (1974). A. W. Verstuift, D. A. Redfield, L. W. Cary, and J. H. Nelson, Inorg. at 75 OC, and returns to the triplet upon returning to 25 OC. Chem., 15, 1128 (1976). Similar behavior occurs for the other cyanide complexes. For A. W. Verstuyft, J. H. Nelson, and L. W. Cary, Inorg. Nucl. Chem. the analogous complexes [(CH3)2PC6H5]2PdX2(X = C1, N3) Lett., 12, 53 (1976). P. S. Pregosin and R. Kunz, Helu. Chim. Acta, 58 423 (1975); A. W. exchange could not be initiated even at 140 OC in nitroVerstuyft, J. H. Nelson, and L. W. Cary, Inorg. Chem., 15, 732 (1976). benzene.l23l3 C. G. Grimes and R. G. Pearson, Inorg. Chem., 13, 970 (1974). We have found that generally9,10s12-14 the cis isomer of K. J. Coskran, J. M. Jenkins, and J. G. Verkade, J . Am. Chem. Soc., 90, 5437 (1968). L2PdX2 (X = C1-, N3-) complexes is thermodynamically more J. P. Fackler, Jr., J. A. Fetchin, J. Mayhew, W. C. Seidel, T. J. Swift, stable than the trans isomer and in numerous cases both and M. Weeks, J . Am. Chem. Soc., 91, 1941 (1969). isomers are present in equilibrium in solution. For the 1 1 E. J. Lukosius and K. J. Coskran, Inorg. Chem., 14, 1926 (1975). S. 0. Grim and R. L. Keiter, Inorg. Chim. Acta, 4, 56 (1970). complexes investigated herein the trans isomer is the therPhosphines react very slowly with CHC13: A. J. Burns and J. I. G. modynamically more stable isomer and the cis isomer could Cadogan, J . Chem. Soc., 5788 (1963). Traces of excess phosphine could not be detected in solution. The two platinum complexes be removed from solutions of LzPd(CN)z in CDC13 or CHC13 by simply allowing the solutions to stand at room temperature for several days and (CH3P(C6H5)2)2Pt(CN)2 and ((CH3)2PC6H5)2Pt(CN)2, filtering them. prepared by metathesis from the cis chloride complexes, are A. W. Verstuyft and J. H. Nelson, Synth. React. Inorg. Met.-Org. Chem., also trans in solution as shown by ‘H, l3C(’H),and 31P(1H) 5, 69 (1975), and references contained therein. R. G. Pearson, W. Louw, and J. Rajaram, Inorg. Chim. Acta, 9, 251 NMR. (1974). These authors have demonstrated that [PtBr[P(CH3)zCsHs]3]+ The cyanide complexes undergo phosphine exchange much exchanges phosphine at a slower rate than P ~ B ~ z [ P ( C H ~ ) Z C ~ H S ] ~ . more rapidly than the chloride or azide complexes and conK. M. Chui and H. M. Powell, J . Chem. Soc.,Dalton Trans., 1879 (1974). ductance titrations indicate that no ionic species are formed K. M. Chui and H. M. Powell, J. Chem. Soc.,Dalton Trans., 21 17 (1 974). - - 7
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