Ram G . Goel and William 6.Ogini
1968 Inorganic Chemistry, Vol. 16, No. 8, 1977
equivalent hydrogen atoms, H( 1l), of neighboring molecules at a distance of 2.91 A. The two hydrogen atoms are related by the molecular mirror plane and form a trans angle at the angle is 136’. nickel atom of 1 5 5 O . The C(ll)-H(ll)-.Ni Acknowledgment. L.F.L. and W.E.M. thank the Australian Research Grants Committee for support and the Australian Institute of Nuclear Science and Engineering for the use of facilities. Registry No. Ni(Etaen), 55519-92-1; Cu(Etaen), 62816-09-5; Ni(i-Praen), 62816-08-4; Cu(i-Praen), 628 16-07-3; Ni(i-Buaen), 555 19-93-2; Cu(i-Buaen), 628 16-06-2; Ni(t-Buaen), 55524-07-7; Cu(t-Buaen), 628 16-05-1; EtaenH2, 628 16-28-8; i-PraenH2, 628 16-27-7; i-BuaenH2, 62796-06-9; f-BuaenH2, 62796-05-8; Ni(Meaen), 36802-27-4; Ni(Meapn), 40792-91-4; ” C , 14762-74-4. Supplementary Material Available: A listing of structure factor amplitudes (5 pages). Ordering information is given on any current masthead page.
References and Notes (1) (a) James Cook University. (b) Australian National University. (2) L F. Lindoy and W. E. Moody, J . Am. Cbem. Sac., 91, 2275 (1975). (3) P. J. McCarthy, R. J. Hovey, K. Ueno, and A. E. Martell, J . Am. Chem. Soc., 77, 5820 (1955). (4) The ligands are abbreviated RaenHl where R represents the alkyl group which replaces one methyl group of each acetylacetone-derived ring in 1.
(5) M. J. Carter, D. P. Pillema, and F. Basolo, J . Am. Cbem. SOC.,96, 392 (1974), and references therein. (6) M. Calligaris, G. Nardin, and L. Randaccio, Courd. Cbem. Reu., 7, 385 (1972). (7) R. H. Holm, G. W. Everett, and A. Chakravorty, Prog. Inorg. Cbem., 7, 83 (1966), and references therein.
(8) R. J . Hover, J. J. OConnell, and A. E. Martell, J . Am. Cbem. Sac.,
81,3189 (i959). (9) R. H. Holm, J . Am. Chem. Sac., 82, 5632 (1960). (10) . . A. E. Martell, R. L. Belford. and M. Calvin. J . Inora. Nucl. Cbem.. 5. 170 (1958). (11) S. H. Chaston, S. E. Livingstone, T. N. Lockyer, and 9. S. Shannon, Aust. J . Cbem., 18, 1539 (1965); S. E. Livingstone and J. H. Mayfield, ibid.,28, 1517 (1975). (12) R. P. Scaringe and D. J. Hodgson, Inorg. Chem., 15, 1193 (1976). (13) Complexes of two of these ligands have been used for gas chromatography studies but details of their isolation and characterization have not appeared, see S. Dilli and E. Patsalides, J. Chromatogr., 130, 251 (1977). (14) Ni(Meapn) represents the 1.2-diaminopropaneanalogue of Ni(Meaen). (15) L. F. Lindoy, H. C. Lip, and W.E. Moody, J . Cbem.Soc., Dalton Trans., 44 (1974). (16) J. T. Adams and C . R. Hauser, J, Am. Cbem. SOC.,66, 1220 (1944); R. Levine, J. A. Conroy, J. T. Adams, and C. R. Hauser, ibid.,67,1510 (1945). (17) “International Tables for X-Ray Crystallography”,Vol. I, Kynoch Press, Birmingham, 1965, (a) p 151; (b) p 119. (18) A. R. Hendrickson, R. L. Martin, and D. Taylor, J . Chem. Soc., Dalton Trans., 2182 (1975). (19) “1:ternational Tables for X-Ray Crystallography”,Vol. IV, Kyncch Press, Birmingham, 1974, (a) p 99; (b) p 148. (20) D. Taylor and P. 0. Whimp, unpublished data. (21) P. J. McCarthy and A. E. Martell, Inorg. Chem., 6, 781 (1967). (22) G. 0. Dudek and R. H. Holm, J . Am. Chem. Soc., 83, 2099 (1961). (23) G. Maki, J. Cbem. Phys., 29, 162, 1129 (1958); R. D. Archer, Inorg. Cbem., 2, 292 (1963). (24) K. Ueno and A. E. Martell, J . Phys. Cbem., 611, 257 (1957). (25) P. H. Howells, J. L. Kenney, J. H. Nelson, and R. A. Henry, Inorg. Cbem., 15, 124 (1976). (26) B. N. Figgis, “Introduction to Ligand Fields”, Interscience, New York, N.Y., 1966. (27) E. M. Bulewiez and T. M. Sugden, Trans. Faraday Soc., 54,1475 (1956). (28) L. F. Lindoy, W. E. Moody, J. Lewis, and T. W. Matheson, J . Chem. Sac., Dalion Trans., 1965 (1976). (29) S. Bruckner, M. Calligaris, G. Nardin, and L. Randaccio, Inurg. Chim. Acta, 2, 386 (1968). (30) F. Cariati, F. Morazzoni, C . Busetto, G. Del Piero, and A. Zazzetta, J . Cbem. SOC.,Dalton Trans., 342 (1976).
Contribution from the Guelph-Waterloo Centre for Graduate Work in Chemistry, University of Guelph, Guelph, Ontario, N I G 2W1 Canada
aration, Characterization, and Spectral Studies of Neutral Tri- ~ Complexes of Zinc(I1) and Cadmium(I1)
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R A M G. GQEL’ and WILLIAM 0. QGINI Received January 29, 1977
AIC700796
Complexes having the empirical formula (t-Bu),PMX2 are formed from the reaction of tri-terf-butylphosphine with anhydrous zinc(I1) or cadmium(I1) salts, in an aprotic solvent. The complexes (r-Bu)3PZnX2 (X = C1, Br, and I) and ( ~ - B U ) ~ P C ~ X ~ ( X = C1, Br, I, and SCN) have been isolated and characterized by elemental analyses, conductance, and molecular weight measurements and by infrared, Raman, and ’H and 31PNMR spectral studies. The complexes (t-Bu),PZnBr2 and (t-Bu),PZn12 are about 10% ionized in acetonitrile or nitromethane; other complexes are not appreciably ionized in these solvents. All the complexes behave as dimeric species in 1,2-dichloroethane. The far-infrared and Raman data for all the complexes indicate a dimeric tetrahedral structure (C2*skeletal symmetry) in the solid state. The terminal as well as the bridging M-X stretching frequencies and the M-P stretching frequencies for all the complexes have been assigned. The M-P stretching frequencies for these complexes decrease in the order C1 N S C N > Br > I. ‘H N M R spectral measurements show that the complexes do not undergo a rapid phosphine exchange a t room temperature. The ”P N M R spectra of cadmium(I1) complexes, at ambient temperatures, show sharp satellites due to the coupling of the 31P nucleus with the ‘“Cd and ‘I3Cd S C N > Br > I. nuclei. The ‘J(P-Cd) values for the complexes vary in the order CI N
Introduction Recent studies’ demonstrate that the chemical reactivity and the stereochemistry of metal complexes of phosphorus ligands are markedly affected by the steric interactions involving the substituents on phosphorus. For example, platinum(I1) and palladium(I1) complexes of tertiary phosphines containing bulky substituents on phosphorus undergo intramolecular m e t a l a t i ~ n . ~Bulky - ~ phosphines also stabilize unusual coordination geometries of metals as exemplified by the for-
mation of two-coordinate 14-electron ~omplexes~-~ of the type ML2 where M = Pt or Pd and L = tricylcohexylphosphine. In this laboratory we initiated a systematic study of metal complexes of the little studied but very bulky and basic ligand tri-tert-b~tylphosphine.**~ In a previous studyg it was found that the reaction of tri-tert-butylphosphine with cobalt(II), nickel(II), or zinc(I1) halides in 1-butanol results in the formation of the anionic complexes ((t-Bu),PH) [ ( t B u ) ~ P M X ~instead ], of the expected neutral complexes of the
~
~
Inorganic Chemlstry, Vol. 16, No. 8, 1977 1969
Tri-tert-butylphosphine Complexes of Zn" and Cd"
Table I. Analytical, Molecular, Weight, and Conductance Data for (t-Bu,PMX,) Complexes Analytical data Molecular weight dataQ Calcd Found Calcd for Complex %C %H %C %H Found (t-Bu,PMX,), 9 ;
d
!
-
!
Conductance data
(t-Bu),PZnCl,b
250
42.60
7.99
42.88
7.78
686
676
(t-Bu),PZnBr,
225
33.72
6.32
33.84
6.82
861
854
(t-Bu),PZnI, (t-Bu),PCdClZC (t-Bu),PCdBr,
230 300 244
27.64 37.40 30.38
5.18 7.03 5.70
27.32 37.64 30.02
5.32 7.00 5.87
1039 772 952
1042 770 948
Solvent CH,Cl, CH,CN CH,Cl, CHCN CH~CN CH ,NO , CH,Cl,
(t-Bu) ,PCdI , (t-Bu),PCd(SCN),
252 205
35.35 39.07
4.75 6.28
35.38 38.93
4.66 6.51
1139 859
1136 860
CH,CN CH ,NO
In 1.2-dichloroethane:. concentration range 10" to lo-' M. In s t i cmz mol-'.
% C l calcd, 21.01; found, 20.99.
,
Concn X 1 0 3 , M 1.24 1.01 1.19 1.054 1.094 1.04 1.05 1.25 1.00 1.09
AMd
0.02 8.00 5.30 21.12 27.72 6.56 1.31 8.39 8.96 3.55
% C l calcd, 18.44;found, 18.19.
type ( ( ~ - B u ) ~ P ) ~ MFurther X ~ . investigationson the reactions of tri-tert-butylphosphine with zinc(I1) halides showed that the formation of the anionic complexes in the previous work was due to the protonation of the phosphine by the solvent. Neutral tri-tert-butylphosphine complexes of zinc(I1) and cadmium(I1) have been isolated in the present work by using Figure 1. Structure of [ ( ( t - B ~ ) ~ P ) c d B r ~ ] ~ . aprotic solvents. The preparation, structural characterization, Table 11. Infrared and Raman Spectral Dataa for and spectral studies on these complexes are reported herein. (t-Bu),PZnX, Complexes Results and Discussion (t-Bu),PZnCl, (t-Bu),PZnBr, (t-Bu),PZnI, Reaction of tri-tert-butylphosphine with anhydrous zinc(I1) IR R IR R IR R Assignment or cadmium(I1) halides, in an aprotic solvent such as an380 vw 386vw b hydrous ether or dichloromethane, afforded moisture-sensitive 374w 376vw 375 w b complexes of the empirical formula (Z-BU)~PMX~. Attempts 318s 320m ut(ZnC1) to isolate complexes containing more than 1 mol of phos295 vs 292 vw 294 vs b 294 s phine/mol of metal were not successful, and the unreacted 272 sh 266 w 268mw b phosphine was recovered unchanged. The reaction of the 250 w b 230 s vb(Zn-C1) phosphine and zinc(I1) iodide initially yielded a mixture of 225 s, b 232m ut(Zn-Br) from which pure ( ~ - B U ) ~ Pand Z ~((~-Bu),PH)[(~-Bu)~PZ~I~] I~ 206 m 203 m 204m b ( ~ - B U ) ~ Pwas Z ~ obtained I~ by treatment with benzene. The 188 s 188 s vt(Zn-I) reaction of the phosphine and cadmium(I1) thiocyanate gave 185 s )v,,(Zn-Br) the complex ( ~ - B U ) , P C ~ ( S C N )However, ~. the analogous 1 5 2 s 160s u (Zn-I) zinc(I1) complex could not be isolated; an impure anionic 152 w 137 s 116 vs v$n-P) complex ((t-Bu)3PH) [ ( ~ - B u ) ~ P Z ~ ( S Cwas N ) ~obtained ] in114vs 116 m stead. The reaction of the phosphine and hydrated zinc(I1) 91 s 105 m 96 s An impure 1:l nitrate gave ((~-Bu)~PH)~[Z~(NO,),OH]. 82 s 78 s complex was obtained from the reaction of the phosphine with 74 s 63 vs 60 vs C ~ ( O A C ) ~ ( H ~but O ) ~no, reaction was observed when triIn cm-' in the solid state. Description of abbreviations: IR, tert-butylphosphine was allowed to react with Zn(0infrared; R, Raman; ut, terminal metal-halogen stretching freAC)2(H20)2. quency; ub, bridged metal-halogen stretching frequenc b, broad; The formation of only 1:l complexes in the present work m, medium; s, strong; sh, shoulder; v, very; w, weak. lkands is in marked contrast with the behavior of less bulky phosdue to (t-Bu),P. phines such as triphenylphosphine" and tricyclohexylphosphine," both of which form stable 2:l complexes with both Structural Characterization and Spectral Studies. The zinc(I1) and cadmium(I1). Although neutral 1:l complexes melting points and analytical, conductance, and molecular of cadmium halides and tertiary phosphines are k n o ~ n , ' ~ - ' ~ weight data for the (t-Bu)jPMX2complexes prepared in this analogous zinc(I1) complexes have hitherto not been isolated. work are recorded in Table I. The conductance data show In the present work, the failure to isolate complexes containing that all the cadmium complexes as well as the zinc(I1) chloride more than 1 mol of tri-tert-butylphosphinelmol of metal is complex are nonelectrolytes in acetonitrile or nitromethane. undoubtedly due to very large steric requirements of triThe molar conductancesfor the complexes ( t - B ~ ) ~ P z n B and r~ tert-butylphosphine. Crystallographicdata show that the Ni-P ( ~ - B u ) ~ P in Z~ acetonitrile I~ are 21.12 and 28.82 Q-' an2mol-', bond in the anion (~-Bu)~pNiBr,-~ is considerably longer than respectively. Since the molar conductances for the 1:2 that in Ph3PNiI3-.I4 The elongation of the Ni-P bond in electrolytes in acetonitrile occur in the range of 200-300 Q-' (t-B~)~pNiBr;is clearly due to the inability of the bulky cm2 mol-', the degree of ionization for the zinc(I1) bromide phosphine to approach within a normal bonding distance and the zinc(I1) iodide complexes. is about 10%. The molecular because of steric repulsion between the bromines and the weight data listed in Table I clearly show that all the (ttert-butyl groups. T ~ l r n a n ' ~has ' ~ proposed the use of metB U ) ~ P M Xcomplexes ~ exist as dimeric species in 1,2-dial-ligand cone angles to measure the steric requirements of chloroethane. Previously reported 1:1 cadmium(I1) complexes phosphorus ligands. The Ni-p(t-B~)~ cone angle in the anion of tertiarr phosphines have also been shown to be dimeric in (t-Bu)3PNiBr< is found to be 180 f 2'. The cone angles for A dimeric tetrahedral structure as shown in solution. triphenylphosphine and tricyclohexylphosphine have been Figure 1 has been established for the complex Et3PCdBrzby reported','' to be 145 and 170°, respectively. a preliminary crystallographic study.12 A similar structure
ii;i
23
1970 Inorganic Chemistry, Vol. 16, No. 8, 1977
Ram G. Goel and William 0. Ogini
Table 111. Infrared and Raman Spectral Dataa for (t-Bu),PCdX, Complexes (t-Bu),PCdCl, (t-B U) ,PCdBr, (t-B U) ,PCd12 IR
R
R
296 s 285 s
298 vw
314 w 299 s
R
IR 380 vw
290 vw
383 sh 312 w 296 vs
R
Assignment
306 s
270 w 242 sh 234 vw
270 w 248 vw 228 vw
236 mw
(t-B U) ,PCd( SCN)
IR
390 vw
388 vw 374 vw 285 s
IR
12, 210 m, b
198 s
208 s 206 vw
202 vw 198 s
200 vs
146 s
158 ms
159 s 128 ms 9 0 vs 66 m
118 ms 84 s
b b b vt(Cd-C1) b
160 vs 158 s 136 s 104 s 82 s
131 s 100 m 80 m
V,(Cd-SCN) Vb(Cd-C1) b vt(Cd-Br) u+(Cd-I) vi(Cd-X) u (Cd-I) &d-P)
In cm-' in the solid state. Description of abbreviations: IR, infrared; R, Raman; ut, terminal Cd-X stretching frequency; ub, bridged Bands due to (t-Bu),P. Cd-X stretching frequency: m, medium; s, strong; sh, shoulder; v, very; w, weak. Table IV. Metal-Halogen Stretching Frequency Ratiosa for the Halide Complexes Ratios M=Zn M=Cd ut(M-Br)/v (M-CI) vt(M-I)/vt (L-Cl) ub(M-Cl)/vt( M-C1) vb(M-Br)/v (M-Br) Ub(M-1)h'th-I)
0.71 0.70 0.59 0.56 0.7 2 0.73 0.76 0.76 0.83 0.85 Description of abbreviations: vt(M-X), terminal metalhalogen stretching frequency: v,,(M-X), bridged metal-halogen stretching frequency.
*
is indicated for the tri-tert-butylphosphine complexes of both zinc(I1) and cadmium(I1) on the basis of their infrared and Raman spectral studies, in the solid state. The observed infrared and Raman spectral frequencies for the complexes, in the solid state, in the region below 400 cm-', together with their proposed assignments are given in Tables I1 and 111. The basic features of the infrared and Raman spectra for the ( t - B ~ ) ~ P c d complex Br~ are shown in Figure 2. As shown by the data in Tables I1 and 111, the infrared spectra for the complexes of zinc(I1) and cadmium(I1) halides show two strong bands below the 400-cm-' region. Both of these bands progressively shift to lower frequencies as X is changed from C1 to Br to I. Thus, there can be little doubt that these bands are associated with the vibrations of the metal-halogen bonds. For each complex, the higher frequency is comparable to the metal-halogen antisymmetric stretching frequency reported" for the tetrahedral complexes (Ph3P)2ZnXzor (Ph3P)2CdX2.The lower frequency in each case is markedly lower than the corresponding symmetric metal-halogen stretching frequency, but it is much higher than the metal-halogen bending Therefore, the higher frequency band can be assigned to a stretching mode of the terminal metal-halogen bonds and the lower frequency band can be assigned to a stretching mode of the metalhalogen bridge bonds. As shown in Table IV, frequency ratios vt(M-Br)/vt(M-C1) and vt(M-I)/vt(M-Cl) for the terminal metal-halogen frequencies for the zinc as well as for the cadmium complexes are in excellent agreement with the reported frequency ratios for the (Ph3P)2ZnXzand (Ph3P)CdX2 complexes. Little information is available in the literature on the bridged metal-halogen stretching frequencies for zinc or cadmium complexes. For the binuclear anion Zn2C162-,the infrared bands at 238 and 225 cm-' have been assignedi3to the bridged Zn-C1 stretchin frequencies. The vb(M-X)/vt(M-X) for Zn2Cl)-, AlzX6, and the
250
300
Br > I, it is reasonable to assign this band to the zinc-phosphorus or cadmium-phosphorus stretching frequency. There are no reports on metal-phosphorus stretching frequencies for zinc(I1) or cadmium(I1) complexes except for the complexes (R3P)2MX2103" (R = phenyl or cyclohexyl), Ph3PZnX
