Organometallics 1983,2,585-593 (isomer l),84280-49-9; (BH2CH2SMe)2 (isomer 2), 84280-50-2; (~-BU)~BCH~S 84280-51-3; M~, (MeSCH2I2BH,84280-52-4; LiMe2NCHZBH3,84280-42-2;TMEDA.BBH3,5843-32-3;TMEDA-2BH3,5843-33-4;Me3N.BH3,75-22-9; LiPhCH2BHS,8428043-3; t-BusB, 1113-42-4; (Me2NCH2BH2)2,84280-53-5;
585
LiPhBH3.TMEDA,84280-44-4; LiPhCH2BH3.TMEDA,8428046-6; H3B.SMe2, 13292-87-0; MeLi, 917-54-4; Me3SiCH2Li, 1822-00-0; n-BuLi, 109-72-8;sec-BuLi, 598-30-1;t-BuLi, 594-19-4; i-PrLi, 1888-75-1; Me3SiCH2C1,2344-80-1; BH3, 13283-31-3;B(CH2SiMeJ3,18077-26-4; LiMeSCH2BH3,84280-47-7.
Comparative X-ray Crystallographic and Thermodynamic Studies of Substituted Styrene Complexes of Palladium( II ) Containing the $-Cyclopentadienyl Ligand. Appreciation of Olefin-Palladium( I I ) 7r Interaction in the 18-Electron Complex Kunio Miki, Osamu Shiotani, Yasushi Kai, Nobutami Kasai, Hideki Kanatani,t and Hideo Kurosawagt Department of Applied Chemistry and Department of Petroleum Chem/stry, Faculty of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565, Japan Received November 15, 1982
The molecular structures of the substituted styrene complexes of Pd" with 18-electron configuration
[Pd($-C,H,)(PPh,)(CH2=CHC6H4Y-p)]X (2b, Y = OMe, X = BF4, 2c, Y = H, X = PF6,2d, Y = C1, X
= BF4)have been determined by means of X-ray diffraction. Crystals of 2b-d all belong to the monoclinic system. The crystal data are as follows. 2b: a = 10.538 (1) A, b = 16.333 (2) A, c = 9.680 (1) A, j3 = 100.06 (1)O, 2 = 2, space group El. 2c: a = 15.571 (4) A, b = 11.187 (2) A, c = 17.596 (3) A, j3 = 107.71(2)O,2 = 4, space group P2,/n. 2d: a = 10.359 (2) A, b = 16.474 (3) A, c = 9.654 (2) A, j3 = 100.82 (2)", 2 = 2, space group P2'. The structures of three complexes were solved by the heavy-atom method and refined by the least-squares procedure to R values 0.040,0.048, and 0.050 for 2b, 2c, and 2d, respectively. In each of 2b-d, the palladium atom is surrounded by cyclopentadienyl, triphenylphosphine, and olefinic ligands in the cationic complex. The C=C bond is almost perpendicular to the coordination plane defined by the Pd and P atoms and the centers of the Cp and olefin ligands. The bond length between Pd and the terminal olefin carbon is almost substituent independent, while that between Pd and the aryl-substituted olefin carbon becomes shorter with increasing electron-withdrawing ability of Y. The thermodynamic parameters for the equilibrium pd-NCR' + CH2=CHC6H4Y-p + pd(CH2=CHC6H4Y-p)+ R'CN where (R = Ph, Et, n-Bu; X = C104, BF4; R' = tolyl) have been determined in dilute pd = Pd(qS-C5H5)(PR3)+Xsolutions. The equilibria showing the smaller AGO values for the more donating styrene complexes are controlled mostly by ASo terms, with AHobeing almost substituent independent. The structural and thennod? results mentioned above have been discussed in terms of the nature of the olefm-Pdn bonding in the d ML4(olefin)framework involving more appreciable .rr back-bonding contribution than previously assumed in square-planar (o1efin)Pd" complexes. Much attention has been focused upon both the reactivity and the nature of the bonding of the (o1efin)Pd" complexes.'12 T h e general consensus concerning these subjects seems to be that the Pd" centered in squareplanar complexes primarily acts as an electrophile toward the coordinated olefin, thereby rendering this ligand very susceptible to the attack of nucleophiles.'r2 T h e electrophilic nature of Pd" toward the olefin may in turn be understood in terms of the Dewar-Chatt-Duncanson scheme as olefin-to-Pd u donation overwhelming ?r backbonding. Perhaps the best supporting evidence for this concept was obtained by the observation3 of a good correlation between t h e thermodynamic parameters for equilibrium 1 involving complexes of type 1 and the Hammett u+ constants, suggesting the importance of the bonding mode A. T h e bonding mode of type A was also shown to play a key role in enhancing the nucleophilic attack at the coordinated 0lefinl7~and olefin oligomerization and polymerization with a cationic Pd" catalyst., We have recently isolated some cationic, 18-electron complexes of type 2 and examined their stability in solutions by 'H NMR spectroscopy.6 It was somewhat surprising t o find that, though the more electron-donating styrene complex does exhibit the higher stability as in the Department of Petroleum Chemistry.
0276-7333/83/2302-0585$01.50/0
tb
P d - I
Y
'J
L
Y
1, R = CF,, Ph
2,
R = Ph, Et, ~ - B u ,
A
X = ClO,, BF,, PF,
case of 1, the Hammett relation for eq 1involving 2 holds better by using u rather than u+ constants. Further, the (1) Eisenstein, 0.;Hoffman, R. J. Am. Chem. SOC.1981, 103, 4308 and references therein. (2) Collman, 3. P.; Hegedus, L. S. "Principles and Applications of Organotransition Metal Chemistry"; University Science Books: Mill Valley, CA, 1980; pp 603.
0 1983 American Chemical Society
586 Organometallics, Vol. 2, No. 5, 1983
Miki et al.
Table I. Crystal Data for [Pd ( q 5-C H, )(PPh )( CH, =CHC,H,-Y-p )]X 2b 2c 2d Y X formula
OCH, BF, C,,H,,OPPd. BF,.CH,Cl, fw 739.7 F(000) 748 cryst system monoclinic space group p2 I 10.538 (1) Q, A 16.333 (2) b, A. c, A 9.680 (1) 100.06 (1) P , deg L', A3 1640.5 (3) 1.498 Dcalcd, g 1.49 %easd, g c"3 Z 2 p(Mo Ka), cm-' 8.18
H PFb
C,, H,,PPd*
PF, 682.9 1376 monoclinic P2,In 15.571 (4) 11.187 (2) 17.596 (3) 107.71 (2) 2919.8 (9) 1.553 1.55 4 7.97
c1 BF, C,, H,,ClPPd. BF,*CH,Cl, 744.1 748 monoclinic p2 1 10.359 (2) 16.474 (3) 9.654 (2) 100.82 (2) 1618.3 (5) 1.527 1.52 2 9.06
thermodynamic parameters were counteranion dependent. We tentatively ascribed these findings to the occurrence of tight ion-pair formation under the NMR experimental conditions. In order to gain insight into the more intrinsic nature of the olefin-Pdn bonding, we have undertaken an X-ray crystallographic study of 2. We reported' the X-ray crystal structure analysis of [Pd(q5-C5H,)(PEt3)(CH2=CHC6H5)]BF, (2a) and now extended this to a series of the para-substituted styrene complexes [Pd(05-C5H5)(PPh3)(CH2=CHC6H4Y-p)]X (2b, Y = OMe, X = BF4, 2c, Y = H, X = PF6, and 2d, Y = C1, X = BF4). We further reexamined the stability of 2 in dilute solutions by UV spectroscopy to avoid, as well as possible, complexity arising from the ion-pair formation. Here we describe an intriguing stability trend of 2, attained through both X-ray structural and thermodynamic studies, that suggests a more important role of the T back-bonding than previously assumed in the usual, four-coordinate square-planar (olefin)Pdn complexes. Such unique nature of the olefin-Pd" bond in the 18-electron complexes not only is of theoretical interest1v8but also has bearing on some key steps in synthetic reactions including ligand substitutiongand olefin insertion/ &hydrogen elimination.1°
Experimental Section Materials. A basic method to prepare the styrene complexes of type 2 was described previously? Crystals suitable for X-ray crystallography were grown from CH2C12-n-hexane solutions kept in the refrigerator. Spectroscopic grade of CHpC12was used in UV experiments. o-Tolunitrile and the styrenes were purified by distillation before use in UV measurement. Crystallographic Data. Crystals of 2b-d are all black prisms. Crystal data are summarized in Table I. The accurate unit-cell dimensions were determined by the least-squares fit of 28 values of 25 strong reflections (20' < 28 < 31'). Densities of the crystals were measured by the flotation in carbon tetrachloriden-hexane (or chlorobenzene) mixed solution. Crystals of 2b and 2d, which belong to a noncentrosymmetric space group, are isomorphous (3) Ban, E.; Hughes, R. P.; Powell, J. J. Organomet. Chem. 1974,69,
455. (4) Chang, T. C.; Foxman, B. M.; Rosenblum, M.; Stockman,C. J.Am. Chem. SOC.1981,103,7361. (5)Sen, A,; Lai, T. W. Organometallics 1982,1,415; J.Am. Chem. SOC.
1981,103, 4627. (6)Kurosawa, H.; Majima, T.; Asada, N. J.Am. Chem. SOC.1980,102, 6996. (7)Miki, K.;Yama, M.; Kai, Y.; Kasai, N. J.Organomet. Chem. 1982, 239, 269. (8)Hartley, F. R. J. Organomet. Chem. 1981,216,277. (9)Basolo, F.; Pearson, R. G. "Mechanisms of Inorganic Reactions"; Wiley: New York, 1967;pp 371. (IO) Thorn, D. L.; Hoffmann, R. J . Am. Chem. SOC.1978,100,2079; Ozawa, F.; Ito, T.; Yamamoto, A. Ibid. 1980,102,6457.
with each other. They were found to contain one CH2C12molecule solvated in an asymmetric unit considering from the observed and calculated densities, which were later confirmed by the structures determined. Attempts were made to determine the molecular structure of [Pd(q5-C5H5)(PPh3)(CH2----CHC6H,)]BF, (2e). Crystals of 2e belong to the triclinic space group Pi with unit-cell dimensions of a = 21.34A, b = 26.09 A, c = 10.75 A, (Y = 99.8,p = 91.7,and y = 108.6O. The density calculated for 2 = 8 gives a plausible value of 1.49 g ~ m - which ~ , showed that the asymmetric unit contains four independent molecules in the crystal. Therefore, the structure analysis of 2e was abandoned. Collection a n d Reduction of Intensity Data. Well-shaped crystals with approximate dimensions of 0.30 X 0.35 X 0.40mm (2b), 0.30 X 0.35 X 0.40mm (2c), and 0.25 X 0.40 X 0.40mm (2d) were mounted on a Rigaku automated, four-circle, single-crystal diffractometer. Several strong reflections of each crystal were examined by the w scan, and each crystal was found to give diffraction profiles good enough for the intensity measurement. Integrated intensities were collected by the 8-20 scan technique by using graphite-monochromatized Mo Ka radiation (A = 0.71069 A). The scan speed was 4O min-' in 28,and the scan width was A28 = (2.0 + 0.70 tan 0 ) O . T h e background intensities were measured for 7.5 s at both ends of a scan. The scan was repeated . standard twice in the case of weak reflections ( F < 3 ~ 0 ) Four and 044 for 2b, 12,0,0,080,0,0,10, and reflections (600,080,005, 660 for 212, and 080,005,04~, and 333 for 2d) measured a t regular intervals to monitor the stability and orientation of the crystals showed no s_ignificantdecay throughout the data collection. Both hkl and hkl reflection data were colle_c_tedwithin 28 up to 54.0" ((sin @)/A = 0.639 A-1), and h k t a n d hkl Bijvoet pair reflections were additionally measured for 2b and 2d. Totals of 7188,6376, and 7071 independent reflections were obtained after the symmetry equivalent reflections (e.g., Oklland Okl) were averaged for 2b, 2c, and 2d,respectively. The discrepancy fadors for symmetry - (lfl)l/~(lJl), (IFI),the equivalent reflections (Rep = C (JFJ average value of two or more equivalent reflections) were 0.003, 0.014,and 0.004 for 2b, 2c, and 2d, respectively. These small Rm's indicate the high quality of the reflection data in the present analyses. Corrections for Lorentz and polarization effects were applied to the intensity data, while no absorption corrections were carried out in view of the small crystal sizes and absorption coefficients ( ( p R ) , = 0.25 (2b), 0.25 (2c), and 0.28 (2d)). Determination a n d Refinement of the S t r u c t u r e . The structures of 2c and 2d were solved by the conventional heavyatom method. All the non-hydrogen atoms were reasonably found on the Fourier syntheses that were based on the positions of the P d atom determined from the Patterson map. In 2d, one CH2C12 molecule was found to be solvated in a n asymmetric unit. The structure refinements were carried out by the block-diagonal least-squares procedure (HBLS-v"), the function minimized being Cto(lFoI- lFc1)2. At the first stage of the refinement of the structure of 2b, the atomic positions of non-hydrogen atoms in 2d were used except for the C1 atom in the styrene ligand and the atoms in the BF4 anion and CH2C1, molecule. All of these atoms omitted were reasonably found in the subsequent Fourier maps. The locations of anion and solvent molecule were essentially identical with those in 2d. After anisotropic refinement of the non-hydrogen atoms, all the hydrogen atoms in three complexes were reasonably found in the difference Fourier maps, which were refined isotropically in the subsequent refinement. For the final stage of_t_herefinements of 2b and 2d, the Bijvoet pair (F(hkl)( and IF(hkl)lreflections were treated as independent data including anomalous dispersion effects. The absolute configuration of the molecule in 2d was confirmed by the refinement of both models ( x , y, z and f,9, E ) , including H atom contribution to convergence. The chosen model had finally an R value of 0.0496,while the enantiomeric structure gave an R of 0.0506. The R factor ratio testI2 applied to these R values showed that the alternative model may be rejected a t less than 0.005 significant level. The same procedure as 2d was applied to the refinement of the structure of 2b. However, the final R values of the chosen model and its enantiomer were equal to each other, and there are no significant (11)Ashida, T."The Universal Crystallographic Computing SystemOsaka", 2nd ed.; Computation Center: Osaka University, 1979;pp 53. (12)Hamilton, W.C. Acta Crystallogr. 1965,18, 502.
Organometallics, Vol. 2, No. 5, 1983 587
Substituted Styrene Complexes of Palladium(II) Table 11. Refinement Details 2b 2c 2d no. of reflctns useda 6711 5371 6260 no. of parameters refined 517 474 496 weighting parameter UC 0.0149 0.0657 0.0220 bC 0.0004 0.0001 0.0001 0.040 0.048 0.050 final R valued final weighted R value ( R w ) e 0.047 0.063 0.047 Weighting scheme used: w = a IF, I > 3u( I F, I). (ucsz + u IF, I + b IF, 12)-*, where u,. is the standard deviation obtained from counting statistlcs. Used in the final R = 2 IIF, 1 - IF, ll/z IF, 1. e R , = refinement.
-2
P}’?
n
{ 2 w ( IF, I - IF, 1)2/C w IF,
a 0 c
v)
4
differences in bond lengths and bond angles of the both refined structures. Therefore, the similar model that had the same configuration as 2d was adopted as the final model of 2b. Details of the results on the refinements are s u n u “ d inTableII. The atomic scattering factors and anomalous dispersion corrections for non-hydrogen atoms were obtained from ref 13. Scattering factors of hydrogen atoms were taken from those of Stewart et al.14 Final atomic positional parameters, together with the B,15 for non-hydrogen atoms and B values for hydrogen atoms, are listed in Table 111. Tables of anisotropic temperature factors for non-hydrogen atoms and observed and calculated structure factors are available in Tables S1 and S2, as supplementary material. Computation. All the calculations were done on an ACOS 700s computer at Crystallographic Research Center, Institute for Protein Research, Osaka University. Stability Measurement. The equilibrium constants ( K ) of eq 2 were determined in CH2C12at 0,15, and 30 “C on a Hitachi Model 200-20 spectrophotometer. The equilibrium mixture was
0,5
400
300
r
Wavelength (m)
1
Figure 1. Spectral change corresponding to equilibrium 2 (R = Et, Y = H, X = C104in CH2C12at 15 “C; cell length = 1 cm). To [Pd(v5-C5H5)(PEtJ(CH2=CHC6H5)]C104 (6.00 X lo4 mol/L) was added a mixture of styrene/o-tolunitrile, [mol/L]/ [mol/L]: [4.36 X 10-3]/[0.0] (a); [1.74 X 10-2]/[2.74 X (b); [8.72 X 10-3]/[2.74 X W3] (c); [4.36 X 10-3]/[2.74 X (d); [0.0]/[1.20 x (e).
CH
\sf\\
3
/
J
L
Me
2
attained by adding to 2 or 3 ((4-6) X lod M) in CH2C12a mixture of the appropriate styrene and o-blunitrile (R’CN) with a known mole ratio, [R’CN],/ [styrene]@Both ligands were used in sufficiently excess amounts with regard to Pd for simplicityof the calculation and avoidance of the decomposition of the complexes during the measurements. In the case of the complexes with R = Et and n-Bu where no o-tolunitrile complexes could be isolated, the absorbances of the solution containing R’CN and 2 (R = Et, n-Bu; Y = H; X = C104)([R’CN]/[2] 2 200) were used as those of 3 in the calculation K = ([R’CNl~/[styrenel~)(((Abs) - (AbsM/NAbsh - (AWD
A typical spectral change of the equilibrium mixture in the range of 400-300 nm is shown in Figure 1. The change of the absorbances in the range of 340-315 nm was used in the calculation. Each K value was obtained as an average of three to four measurements employing different [R’CN],/ [styrene], ratios. At(13) “InternationalTables for X-ray Crystallography”;Kynoch Press: Birmingham, England, 1974; Vol. IV. (14) Stewart,R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys. 1965,42,3175. (15) Hamilton, W. C. Acta Crystallogr. 1959,12, 609. (16) Johnson, C. K. ORTEP-11, Report ORNL-5138; Oak Ridge National Laboratory: TN.
tempts to determine the K values for eq 2 involving the para-nitro and para-dimethylamino substituents were unsuccessful owing to strong absorptions of the free olefin ligands in the range 1350 nm that prevented reproducible calculations to be obtained. Representative Hammett relations and thermodynamic parameters are shown in Tables IV and V.
Results and Discussion Molecular Structure. The molecular structures of 2b-d are shown in Figure 2. The bond lengths and bond angles are listed in Tables VI and VII, respectively. The structures of three cations are quite similar to each other. In each cationic complex, the P d atom is coordinated by the cyclopentadienyl (Cp) group, the triphenylphosphine (PPh3) ligand, and the olefin bond of styrene. A similar coordination geometry around the metal atom has been found in [Rh(~5-C5Me5)(PPh3)(ethylene)]17 as well as 2a.7 The P d atom, the P atom in the PPh3 ligand, the center of the Cp group (CCP), and the midpoint of the C(l)=C(2) double bond lie on a plane approximately. The equations of the least-squares planes are listed in Table S3. Figure 3 presents perspective views of the cations in 2b-d as well as 2a as viewed along the olefin-metal axis. The atomic numbering scheme of the cation is shown in Figure 4. In 2b-d,the phenyl groups of the styrene ligands are located ~~
(17) Porzio, W.; Zocchi, M. J . Am. Chem. SOC.1978, 100, 2048.
588
atom Pd
P(1) 0
c(i)
C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(11) C(12) C(13) C(14)
C(15) C(21) C(22) C(23) C(24) C(25) C(26) C(31) C(32) C(33) C(34) C(35) C(36) C(41) C(42) C(43) C(44) C(45) C(46) B
Organometallics, Vol. 2, No. 5, 1983
Miki et al.
Table 111. Final Atomic Parameters along with Their Estimated Standard Deviations in Parenthesesa X Y z Be,/B atom X Y z
0.94035 ( 3 ) 0.78509 (10) 0.8847 14) 0.9822 (5j 0.8776 (5) 0.8776 (5) 0.7636 (5) 0.7614 (5) 0.8755 (5) 0.9892 (5) 0.9909 (5) 0.7704 (8) 0.9979 (7) 0.9367 (7) 1.0055 (7) 1.1136 (6) 1.1132 (6) 0.6596 (4) 0.6131 (4) 0.5157 (6) 0.4670 (5) 0.5130 (6) 0.6094 (5) 0.8349 (5) 0.9513 (5) 0.9819 (7) 0.8980 (8) 0.7825 (7) 0.7500 (6) 0.7073 (4) 0.5905 (5) 0.5428 (5) 0.6059 (6) 0.7240 (5) 0.7718 (5) 0.3373 (6)
Pd 0.58112 (2 P ( l ) 0.60003 (7 C ( l ) 0.7069 (4) C(2) 0.7265 (3) C(3) 0.7329 (3) C(4) 0.7384 (4) C(5) 0.7427 (4) C(6) 0.7428 (4) C(7) 0.7380 (4) C(8) 0.7327 (4) C(11) 0.4318 (4) C(12) 0.4623 (5) C(13) 0.5087 (4) C(14) 0.5076 (5) C(15) 0.4555 (5) C(21) 0.5448 (3) C(22) 0.4864 (4) C(23) 0.4436 (4) C(24) 0.4591 (5) C(25) 0.5167 ( 6 ) C(26) 0.5596 (5) C(31) 0.5570 (3) C(32) 0.4934 (3) C(33) 0.4610 (4) C(34) 0.4929 (4) C(35) 0.5552 (5) C(36) 0.5876 (4) C(41) 0.7178 (3) C(42) 0.7608 (4) C(43) 0.8522 (4) (21441 0.9019 14) c(45j 0.8611 j4j ~ ( 4 6 0.7690 ) (4) P(2) 0.22498 (10)
(a) [Pd(s5-C,HS)(PPh,)(CH,=CHC,H40CH,~)IBF4 (2b) 0.75 0.7979 (3) 0.2945 (5) 0.88380 (3) 3.5 F ( l ) 0.82057 (7) 0.6618 (3) 0.97217 110) 3.3 F(2) 0.3119 (5) 0.5316 (3) 0.2881 ( 4 ) 0.2670 14) 0.7302 (3) 6.1 F131 4.8 ~ (j 4 0.4617 (3 j 0.7460 (5j 0.8375 (3) 0.7275 (6) 0.7942 (4) 0.6606 (5) 4.6 CI(1S) 0.3565 (5) 0.8968 (3) 4.2 Cl(2S) 0.3224 (4) 0.99477 (17) 0.7268 (3) 0.5634 (4) 5.0 C(S) 0.3697 (13) 0.9011 (7) 0.6858 (4) 0.5073 (5) 0.4163 (6) 5.6 H(1A) 0.981 (5) 0.898 (4) 0.6213 (4) 1.069 (4j 4.6 0.821 (3) 0.5949 (3) 0.3775 (5) 0.810 (5) 4.6 0.806 (3) 0.6353 (4) 0.4291 (5) 0.707 (3) 0.686 (4) 4.4 0.6998 (3) 0.5193 (5) 0.595 (3) 0.690 (5) 9.5 0.2305 (9) 0.4889 (6) 0.621 (3) 1.060 (5) 6.6 0.6637 (4) 1.0595 (6) 0.728 (3) 0.6108 (4) 1.071 (5) 6.7 0.9509 (7) 0.519 (4) 0.6138 (4) 0.722 (5) 6.7 0.8486 (7) 0.458 (3) 0.781 (5) 7.1 0.6638 (5) 0.8873 (7) 0.472 (4) 0.747 (6) 7.3 1.0282 (7) 0.6916 (5) 1.0011 (4) 0.675 (5) 0.970 (6) 3.7 0.7484 (4) 1.1264 (4) 0.584 (3) 0.850 (5) 4.6 0.7455 (5) 1.1409 (6) 0.590 (4) 0.976 (6) 5.6 0.6894 (4) 1.175 (5) 1.0321 (7) 0.684 (4) 6.0 0.6388 (4) 0.725 (4) 1.169 (6) 6.1 0.9096 (7) 0.6406 (4) 0.777 (3) 0.649 (4) 0.8937 (5) 0.6955 (4) 5.0 0.687 (3) 1.1377 (5) 0.494 (5) 3.8 0.8744 (3) 0.602 (3) 1.2230 (5) 0.392 (4) 5.1 0.8579 (4) 0.607 (4) 1.3534 (6) 0.482 (7) 6.4 0.8962 (4) 0.699 (4) 1.3976 (5) 0.638 (6) 6.9 0.9485 (4) 0.822 (3) 1.3119 (6) 1.014 (5) 6.1 0.9684 (4) 0.880 (4) 1.1813 (6) 1.058 (5) 5.1 0.9311 (4) 0.915 (6) 0.968 (4) 3.4 0.8532 (4) 0.8993 (3) 0.720 (7) 1.004 (4) 4.2 0.7650 (5) 0.8854 (3) 0.665 (5) 0.943 (3) 0.6639 (6) 0.9430 (4) 4.9 0.536 (4) 0.836 (3) 0.6517 (6) 1.0153 (4) 5.3 0.454 (6) 0.927 (4) 0.7440 (5) 4.3 1.0304 (3) 1.054 (4) 0.579 (5) 0.8430 (5) 4.0 0.9726 (3) 0.774 (5) 1.081 (3) 5.7 0.7355 (5) 0.5154 (7) 0.844 (4) 0.979 (3) 0.328 (10) 0.866 (7) 0.904 (6) 0.462 (8)
0.31990 (3) 0.16556 (10) 0.4140 (6) 0.3394 (4) 0.3733 (4) 0.2838 (5) 0.3138 (6) 0.4309 (7) 0.5192 (6) 0.4920 (5) 0.3216 (8) 0.2791 ( 7 ) 0.3668 (8) 0.4655 (7) 0.4423 (8) 0.0320 (4) -0.0340 (5) - 0 . 1 3 4 ~(6) -0.1683 (6) -0.1041 (7) -0.0020 (6) 0.1900 (4) 0.2764 (5) 0.2936 (5j 0.2247 17) 0.1382 (7 j 0.1186 (6) 0.1274 (4) 0.0405 (5) 0.0218 (7) 0.887 (8) 0.1764 (6) 0.1973 (5) 0.09229 (14)
(b) [Pd(qs-C,H5)(PPh,)(CH,=CHC,H,)]PF, (2c) 0.0432 (7 0.345776 (18) 3.6 F(1) 0.3197 (4) 0.0123 (5 0.26704 (6) ’ 3.1 0.2196 (5j
0.3562 (3) 0.4202 (3) 0.5034 (3) 0.5592 (3) 0.6372 (4) 0.6596 (3) 0.6055 (4) 0.5271 (3) 0.3147 (4) 0.3943 (5) 0.4399 (4) 0.3912 (5) 0.3151 (4) 0.2872 (3) 0.2264 (4) 0.2464 (5) 0.3219 (6) 0.3831 ( 5 ) 0.3665 (4) 0.1602 (3) 0.1280 (3) 0.0464 (3) -0.0034 (4) 0.0274 (4) 0.1086 (3) 0.2839 (3) 0.3379 (3) 0.3557 (4) 0.3199 (5) 0.2659 (5) 0.2477 j4j 0.41317 (9)
4.3 3.6 3.6 4.5 5.6 5.9 5.5 4.4 8.3 7.2 7.1 7.1 7.7 4.0 5.3 7.2 8.0 8.5
6.2 3.7 4.1 5.0 6.1 6.5 5.3 3.6 4.8 6.9 8.2 7.3 5.1 5.3
0.1334 (5) 0.2366 (5) 0.1912 (6) 0.2622 (6) 0.724 (3) 0.694 (3) 0.756 (3) 0.738 (3) 0.747 (4) 0.745 (4) 0.736 (4) 0.733 (3) 0.404 (5) 0.458 (4) 0.534 (4) 0.533 (5) 0.444 (5) 0.481 (3) 0.411 (4) 0.432 (5) 0.527 (5) 0.594 (4) 0.478 (4) 0.421 (4) 0.471 (4) 0.575 (4) 0.626 (4) 0.730 (3) 0.877 (4) 0.962 (4) 0.889 (4) 0.739 (4)
0.1462 (9 0.1700 (4 -0.0125 (5 0.1943 (5 0.392 (5) 0.490 (4) 0.267 (4) 0.203 (4) 0.258 (6) 0.447 (5) 0.601 (5) 0.556 (4) 0.280 (7) 0.205 (5) 0.361 (6) 0.541 (6) 0.498 (7) -0.009 (4) -0.177 (5) -0.243 (6) -0.126 (7) 0.054 (5) 0.320 (4) 0.352 (5) 0.237 (6) 0.093 (5) 0.058 (5) -0.000 (5) -0.033 (5) 0.073 (5) 0.217 (6) 0.255 ( 5 )
0.5863 (6) 0.5790 (5) 0.3829 (41 0.5108 (5j 0.0873 (4) 0.3235 (3) 0.2576 (10) 0.757 (5) 0.715 (5) 0.659 (5) 0.529 (4) 0.382 (5) 0.400 (5) 0.554 (5) 0.165 (6) 0.174 (6) 0.317 (7) 1.142 (7) 0.949 (5) 0.757 (7) 0.831 (5) 1.085 (6) 1.201 (5) 1.231 (5) 1.047 (4) 0.845 (7) 0.807 (5) 1.190 (5) 1.410 (6) 1.488 (6) 1.342 (7) 1.121 (5) 0.774 (5) 0.598 (6) 0.582 (5) 0.739 (5) 0.899 (4) 0.301 (10) 0.301 (9) 0.4308 (5) 0.4838 (3) 0.3991 (6) 0.3430 (3) 0.3573 (3) 0.4704 (4) 0.311 (3) 0.360 (3) 0.414 (3) 0.542 (3) 0.675 (4) 0.714 (3) 0.619 (3) 0.489 (3) 0.273 (4) 0.411 (3) 0.496 (4) 0.404 (4) 0.270 (4) 0.172 (3) 0.205 (4) 0.333 (4) 0.441 (4) 0.409 (3) 0.159 (3) 0.027 (3) -0.062 (4) -0.004 (4) 0.129 (3) 0.363 (3) 0.392 (3) 0.335 (4) 0.242 (4) 0.209 (3)
Be, lB
10.2 9.6 8.3 10.9 17.1 12.2 11.9 5.5 (12) 3.8 (9) 4.4 (10) 3.9 (9) 4.4 (10) 5.0 (11) 4.8 (11) 6.5 (13) 5.5 (11) 8.4 (16) 8.4 (16) 5.1 (11) 8.2 (16) 5.7 (12) 7.1 (14) 4.3 (10) 4.6 (10) 3.2 (8) 7.8 (16) 6.1 (12) 4.6 (10) 5.9 (12) 6.7 (14) 8.5 (16) 4.7 (10) 4.2 (10) 6.8 (14) 5.3 (11) 4.5 (10) 3.2 (8) 15.6 (32) 12.0 (23) 14.9 12.5 19.6 10.6 17.8 15.2 4.8 (11) 3.7 (9) 3.6 (9) 3.8 (10) 7.1 (15) 5.8 (13) 4.9 (11) 4.4 (10) 9.6 (19) 6.2 (13) 7.1 (15) 9.3 (19) 10.2 (20) 4.3 (10) 7.1 (15) 8.8 (17) 9.8 (19) 6.1 (13) 5.2 (12) 5.4 (12) 7.4 (15) 6.5 (14) 5.5 (12) 4.7 (11) 6.3 (13) 6.4 (14) 8.0 (16) 5.8 (12)
Substituted Styrene Complexes of Palladium(IZ)
Organometallics, Vol. 2, No. 5, 1983 589 Table I11 (Continued)
(c) [Pd(q '-C,H,)(PPh3)(CH,=CHC,H,Cl-p)]BF4 (2d) 0.2831 (5) 0.7921(4) 0.89122(4) 3.2 F(1) 0.93728(4) 0.75 Pd 0.3061(8) 0.6620(4) 7.7 F(2) 0.51742(13) 0.2764(3) Cl(1) 0.8223 (3) P(l) 0.77824 (13) 0.82142(9) 0.97504 (13) 3.2 F(3) 0.2430(5) 0.7334 (4)
atom X C(l) 0.9947(7) C(2) 0.8821(6) C( 3) 0.8701(5) C(4) 0.7456(6) C(5) 0.7307(7) C(6) 0.8411(7) C(7) 0.9627(6) C(8) 0.9760(6) C(11) 0.9931(8) C(12) 0.9252( 8 ) C(13) 0.9957(8) C(14) 1.1107(7) C(15) 1.1103(7) C(21) 0.6501(4) C(22) 0.5996(5) C(23) 0.5033 (6) C(24) 0.4557(6) C(25) 0.5057 ( 8 ) C(26) 0.6022(6) C(31) 0.8282(6) C(32) 0.9469(6) C(33) 0.9764(7) C(34) 0.8930( 8 ) C(35) 0.7757( 8 ) C(36) 0.7431(7) C(41) 0.7015(5) C(42) 0.5789(6) C(43) 0.5329 (6) C(44) 0.6019(6) C(45) 0.7239(6) C(46) 0.7724 (5) B 0.3233(7)
z
Y
B,,/B
atom
Y
X
0.5859(7) 10.6 0.5599(7) 13.0 0.3743(5) 9.0 Beg l B
z
0.4455(4) 0.7472(7) 0.4891(7) 14.1 0.3241(4) 0.99317(18) 0.3078(3) 11.5 0.0473 (4) 15.3 0.3215(5) 0.9064(3) 0.3437(15) 0.9042 (7) 0.2238(14) 13.0 0.779(7) 0.881(5) 7.9(18) 0.989(7) 0.712(6) 1.072(5) 0.818(4) 4.7(12) 0.824(3) 0.673(5) 2.5(9) 0.824(4) 0.726(3) 0.557(5) 3.5(11) 0.667(5) 0.609(4) 0.408(6) 0.654(6) 6.0(15) 0.403(4) 1.023(4) 0.612(3) 1.4( 8 ) 0.720 (3) 0.543(5) 4.1 (12) 1.049(5) 0.677(4) 1.147(6) 0.961(6) 6.3(15) 0.591(4) 0.967(6) 0.839(6) 6.0(15) 0.593(4) 0.772(6) 0.986(6) 6.0(15) 0.835(7) 1.161(6) 0.667(5) 7.2(17) 1.167 (6) 0.721(3) 1.081(6) 5.6(15) 0.777 (3) 0.631 (5) 1.188(6) 4.7(13) 0.473(6) 0.688 (4) 1.232(6) 5.3(13) 0.367(5) 0.592(3) 1.050(5) 3.8(11) 0.619(4) 0.475(7) 0.865(7) 7.4(17) 0.696(3) 0.811(5) 2.9(10) 0.631(5) 1.013(5) 0.816(3) 1.201(5) 3.1 (10) 1.054(7) 0.880 (5) 1.403( 8 ) 8.3(19) 0.909 (6) 0.969(4) 1.505(7) 6.7(16) 1.001(4) 1.339(7) 6.5(16) 0.730(6) 0.947 (4) 1.131 (6) 0.670(5) 4.2(12) 0.839(3) 0.769(5) 3.2 (10) 0.527(5) 0.938 (5) 0.455(7) 0.624 (7) 7.8 (18) 1.055 (3) 0.574(5) 3.6(11) 0.574 (5) 1.067(3) 0.768(4) 0.730(4) 1.6( 8 ) 0.846(5) 0.970(3) 0.893(5) 3.1(10) 0.410(10) 0.896(7) 0.249(11) 14.9(33) 0.303( 8 ) 0.256( 8 ) 0.883(5) 9.4(21) Positional parameters in fraction of cell edges and thermal parameters (Beq for non-hydrogen atoms and B for hydrogen atoms) in the form of exp{-B((sin e ) / k y } , where B , is the equivalent isotropic temperature factor calculated from the corresponding anisotropic factors.lS 0.8345(4) 0.7985(4) 0.7313(3) 0.6977(4) 0.6324(5) 0.6001(4) 0.6335 (4) 0.6983 (4) 0.6653(4) 0.6120(4) 0.6115(4) 0.6614(5) 0.6884(5) 0.7516(5) 0.7478(7) 0.6907 (5) 0.6397(5) 0.6427(5) 0.6976(4) 0.8747 (4) 0.8580(4) 0.8962(5) 0.9502(4) 0.9679(5) 0.9321 (4) 0.8994(3) 0.8883(4) 0.9456(5) 1.0135 (4) 1.0257(4) 0.9698(4) 0.7369(7)
0.7389(7) 0.6718(6) 0.5724 (5) 0.5231(6) 0.4318(7) 0.3896(6) 0.4350(6) 0.5237(6) 1.0701(7) 0.9600( 8 ) 0.8571(7) 0.8991( 8 ) 1.0345( 8 ) 1.0008(5) 1.1240(5) 1.1380(7) 1.0302( 8 ) 0.9094( 8 ) 0.8931(7) 1.1410(5) 1.2303 (6) 1.3614(7) 1.4018(6) 1.3137(7) 1.1841 (7) 0.8548(5) 0.7682(6) 0.6644(7) 0.6466(7) 0.7361(7) 0.8392(6) 0.5032(9)
4.8 4.1 3.6 4.5 5.2 4.7 4.6 4.2 6.1 5.7 5.9 6.3 6.4 3.6 4.6 5.3 5.7 6.4 5.0 3.6 4.4 5.5 5.8 6.2 5.1 3.2 4.0 5.4 4.9 4.1 3.7 5.8
Table IV. Equilibrium Constants (K) and Hammett Correlations' for Equilibrium 2 at 15 "C R Ph
X c10,
Y
c1 H Me OMe
BF,
Et
ClO,
c1
H Me OMe
c1
H Me OMe
n-Bu
c10,
c1 H
Me OMe log K = P O
K
-P
0.048 t 0.002 0.13?r 0.01 0.27 ?r 0.03 0.45?r 0.04 0.050* 0.002 0.14r 0.01 0.28r 0.03 0.40* 0.04 0.095 * 0.009 0.27 * 0.02 0.52* 0.04 1.01 * 0.06 0.092r 0.008 0.27* 0.02 0.47* 0.05 0.88
0.1
-P+
(r)
0.97(0.920)
1 t
1.83(0.999)
0.89(0.891)
2.01 (0.996)
1.02(0.931)
0.96(0,919)
* 0.08
+ C o r p+o+ + C'
a t the Cp side, while a t the P E t Bside in 2a.' This is due to the difference of the steric hindrance between the PPh, and PEt, ligands. The C(l)=C(2) olefin bonds are almost perpendicular to the coordination plane of Pd in agreement with the theoretical prediction (see later). However, there are slight twists of the C-C bond about the olefin-Pd bond. The angles between the C(l)=C(2) bond and the P-Pd-CCP plane are 83.0,89.9, and 78.1O for 2b, 2c, and 2d, respectively (cf. 77.3O for 2a'). In the previous paper, we suggestedthat the twist of the C = C bond has probably
resulted from intramolecular contacts between the styrene and the other ligands in 2a. Also in the present complexes, the styrene ligands contact with both the Cp and PPh, ligands: C(l)-.C(14) = 3.408 (8), 3.391 (91, and 3.358 (10) A, C ( 1 ) 4 ( 4 6 ) = 3.449 (7), 3.403 (€0, and 3.471 (8) A, C ( 2 ) 4 ( 4 1 ) = 3.288 (6), 3.347 (6), and 3.260 (7) A, C(3). -C(13) = 3.397 (8),3.327 (91, and 3.435 (9) A, C(8)-.C(13) = 3.462 (9), 3.637 (lo), and 3.493 (9) 8, for 2b, 2c, and 2d, respectively. The slight differences of the twist angles in 2b, 2c, and 2d are probably caused by both these intra-
590 Organometallics, Vol. 2, No. 5, 1983
Miki et al.
0
a
b
Figure 2. The molecular structure of 2b, 2c, and 2d (ORTEP drawing16). Non-hydrogen atoms are represented by thermal ellipsoids at 30% probability levels, whereas temperature factors of hydrogens are arbitrarily reduced for clarity: (a) 2 b (b) 2c; (c) 2d.
d
C
Figure 3. Perspective views of the cations viewed along the olefin-metal axis. Representations of atoms are same as those in the cation).' Figure 2 (ORTEP drawing16): (a) 2b; (b) 2c; (c) 2 d (d) 2a ([Pd(~s-C,Hs)(PEt,)(CH,=CHC6Hs)]
Table V. Thermodynamic Data for Equilibrium 2
R Ph
X
Y
ClO,
Cl H Me OMe C1 H Me OMe C1 H Me OMe C1 H Me OMe
BF,
Et
C10,
n-Bu
C10,
AG"(288 K), KJ/mol 7.3 i 0.1 4.9 * 0.2 3.1 i 0.3 1.9 k 0.2 7.2 + 0.1 4.7 * 0.2 3.0 r 0.3 2.2 * 0.3 5.6 i 0.3 3.1 + 0.2 1.6 k 0.2 O . O * 0.2 5.7 + 0.2 3.1 0.2 1.8 * 0.3 0.3 i 0.2
c (33 1-34)
-AS"( 288 K), J/
-AH", KJ/mol (mol deg) 9.3 + 0.9 58 2 4 9.9 i: 1.0 51 k 4 10.4 * 1.0 47 + 5 11.0 4 1.0 45 k 4 8.9 i 0.9 56 4 9.5 k 0.9 49 * 4 10.2 + 1.0 46 k 5 11.1 k 1.0 46 i 5 12.7 1.3 6 3 i 6 13.7 * 1.3 58 + 6 13.8 i 1.4 53 i 6 1 3 . 3 k 1.3 4 6 + 6 12.9 * 1.3 65 * 6 13.5 ~f:1.3 58 + 6 12.6 i 1.3 50 6 12.6 * 1.3 45 6
moleculqr Contacts and the intermolecular contacts in crystal structures. Olefin-Palladium Bonding. The Pd-C( 1) distances in 2b, 2c, and 2d are significantly shorter than the Pd-C(2) ones, as in the other styrene complexes of Pd and Pt7s1*% [M-C(1) = 2.14-2.19, M-C(2) = 2.20-2.26 A]. Such asymmetrical coordination of two carbon atoms in asymmetrically substituted olefins to the metal atom has been (18)Ball,R. G.; Payne, N. C. Znorg. Chem. 1976,15,2494. Nyburg, S. C.; Simpson, K.; Wong-Ng, W.J. Chem.SOC.,Dalton Tram. 1976,1865. (20) van der Poel, H.; van Koten, G.; Kokkes, M.; Stam, C. H. Inorg. Chem. 1981,20,2941.
Y
Figure 4. Numbering systems of non-hydrogen atoms in the cation. For numberings of hydrogen atoms, the same numbers as the carbon atoms are used. Y is O-C(9), H(6), and C1 for 2b, 2c, and 2d, respectively.
pointed out and discussed in terms of the nature of the olefin-metal bond.lgS1 Useful informations for the nature of the olefin-Pd bond may be obtained from comparison of Pd-C(o1efin) distances in the substituted styrene complexes, particularly those in 2b and 2d that are isomorphous with each other as mentioned before. In 2b-d,there is no significant difference in the Pd-C(l) distance, while the Pd-C(Z) distance tends to shorten with increase of the electron-withdrawing ability of Y; the difference of the
(19)
(21) Albright, T. A.;
Hoffmann, R.; Thibeault, J. C.; Thorn, D. L. J.
Am. Chem. SOC.1979,101,3801.
Organometallics, Vol. 2, No. 5, 1983 591
Substituted Styrene Complexes of Palladium(Il)
Table VI, Selected Bond Lengths (A) along with Their Estimated Standard Deviations in Parentheses ~
Pd-C( 1) Pd-C( 2) Pd-CET" Pd-C( 11) Pd-C( 12) Pd-C( 13) Pd-C( 14) Pd-C(15 j Pd-C( Cp) [av] Pd-CCPC
2b
2c
2d
2.182 (5) 2.264 ( 5 j 2.115 2.210 (7) 2.367 (7) 2.370 (7) 2.301 (7) 2.300 (7) 2.310 1.983 2.286 (1) 1.373 (7) 1.448 (7) 1.400 (7) 1.371 (8) 1.389 (8) 1.383 ( 7 ) 1.366 ( 7 ) 1.407 (6) 1.362 (6) 1.419 (9)
2.182 (5) 2.255 (5j 2.112 2.221 (9) 2.306 (8) 2.329 (8) 2.271 (7) 2.313 (8) 2.288 1.964 2.288 (1) 1.361 (7) 1.485 (6) 1.386 (7) 1.395 (8) 1.368 (9) 1.357 (9) 1.389 (8) 1.392 (7)
2.187 (6) 2.235 (6) 2.104 2.211 (8) 2.378 (8) 2.399 (8) 2.305 (7) 2.286 (8) 2.316 1.988 2.292 (1) 1.360 (9) 1.456 ( 7 ) 1.402 (8) 1.381 (9) 1.389 (9) 1.369 (9) 1.360 (8) 1.383 (7)
1.425 (10) 1.327 (10) 1.399 (10) 1.437 (10) 1.380 110) 1.394 ' ' 1.830 (6) 1.386 (9) 1.401 (9) 1.366 (8) 1.358 (9) 1.383 (8) 1.384 (8) 1.823 (5) 1.380 (7) 1.396 (8) 1,351 (10) 1.387 (10) 1.392 (9) 1.403 ( 7 ) 1.822 (4) 1.388 (6) 1.387 (7) 1.370 (8) 1.420 ( 7 ) 1.377 (6) 1.389 (6) 1.349 (9) 1.399 (9) 1.368 (8) 1.331 (10)
1.418 (11) 1.332 (11) 1.396 (11) 1.363 (11) 1.399 (12) . , 1.382 1.812 (5) 1.387 (8) 1.405 (10) 1.331 (12) 1.377 (13) 1.398 (11) 1.396 (8) 1.815 (5) 1.376 (7) 1.383 ( 7 ) 1.368 (9) 1.360 (10) 1.381 (9) 1.396 (7) 1.818 (4) 1.381 (7) 1.378 (9) 1.361 (10) 1.378 (11) 1.391 (10) 1.401 ( 7 )
1.735 ( 7 ) 1.454 (11) 1.339 (11) 1.441 (11) 1.382 (11) 1.377 (11) . , 1.399 1.808 (8) 1.388 (13) 1.396 (12) 1.356 (10) 1.363 (10) 1.378 (10) 1.388(10) 1.815 (6) 1.391 (8) 1.395 (9) 1.348(10) 1.377 (11) 1.367 (10) 1.408 (9) 1.812 (5) 1.395 (7) 1.394 (9) 1.357 (9) 1.405 (9) 1.379 (8) 1.397 (7) 1.327 (12) 1.376 (13) 1.361 (12) 1.309 (15)
C( 15)-C( 11) C(Cp)-C(Cp)b[av] P( 1)-C( 21) C( 21)-C( 22) C( 22)-C( 23) C( 23)-C( 24) C( 24)-C( 25) C( 25)-C( 26) C( 26)-C( 21) P( 1)-C( 31) C( 31)-C( 32) C(32)-C(33) C( 33)-C( 34) C( 34)-C(35) C(35)-C(36) C( 36)-C( 31) P( l)-C( 41) C( 41)-C( 42) C( 4 2)-C( 4 3) C( 43)-C(44) C(44)-C( 45) C( 45)-C( 46) C(46)-C(41) B-F( 1) B-F( 2) B-F( 3) B-F( 4) 1.514 (8) P( 2)-F( 1) 1.554 (7) P(2)-F(2) P ( ~ ) - F (3) 1.498 (10) ~(2)-~(4) 1.566 ( 7 ) P( 2)-F( 5) 1.517 (9) P( 2)-F(6) 1.516 (9) a(1S)-C( S) 1.632 (14) 1.706 (15) 1.762 (13) 1.676 (16) C1( 2S)-C( S) C(l)-H(lA) 1.03 (5) 0.94 ( 5 ) 0.86 (7) C(l)-H(lB) 0.98 (5) 0.88 (5) 0.93 (6) C( 21-w 2) 0.74 (5) 0.96 (5) 0.73 (5) CET is the midpoint of the olefinic C( l)=C( 2) bond in styrene. C(Cp) is the carbon of the cyclopentadienyl CCP is the center of the cyclopentadienyl ring. ring.
Pd-C(2) distances in 2b and 2d is 0.029 (8) A. The former trend is somewhat surprising in view of the fact that in the square-planar complexes, trans-PtC12(Me-pyridine)(CH2=CHC6H4Y-p)l9the Pt-C(l) distance in the more donating styrene (Y = W e 2 ) complex is shorter than that in the less donating styrene (Y = H) complex by 0.043 (21)
a
b
Figure 5. Crystal structures viewed along the c* axis for 2b and along the b axis for 2c (ORW drawings'% Atom are represented by 30% probability ellipsoids. Hydrogen atoms are omitted for clarity: (a) 2b; (b) 2c.
A, and the Pt-C(2) distance in the former is somewhat longer than that in the latter by 0.026 (19) A. This observation was a part of the bases for the significant contribution of form A.l9 By contrast, the present trend can be understood if the K back-bonding plays some role in the olefin-Pd bonding of 2 (see later). Another point of interest lies in the fact that the PdC(2) distance of 2c is longer than that of 2a7by 0.021 (7) A though the Pd-C(l) distances are much the same in 2c and 2a [Pd-C(l) = 2.176 (6) A]. On the other hand, the Pd-C(Cp) distances in 2c are almost the same as or rather a little shorter than those in 2a (see below). This would be understood if the olefin-Pd bond, but not the Cp-Pd bond, in 2a effectively accepted, through ?r interaction, the more electron density donated by PEt, as compared to PPhp CyclopentadienylLigand. The complexes 2b and 2d exhibit the marked asymmetric coordination of and the electron localization around the Cp ring, as in the other (cyclopentadienyl)transition-metal complexes22including those that should be symmetric in nature (e.g., M($C5H5)(C0),, M = Re, Mn).22cpdIn the present case examination of intra- and intermolecular contacts to the Cp carbons did not reveal any correlation with the observed asymmetry, and we cannot present any reasonable explanation for it. The Pd-C(Cp) distances of 2a and 2c show somewhat narrower variations, and those of the latter are almost the same as or slightly shorter than those of the former (2.251-2.353 A, average 2.292 A). Crystal Structure. The crystal structures of 2b and 2c are presented in Figure 5. All the intermolecular atomic contacts are considered to be normal van der Waals distances, the shortest contact between non-hydrogen (22) (a) Bennett, M. J.; Churchill, M. R.; Gerloch, M.; Mason,R. Nature (London) 1964,201, 1318. (b) Byers, L. R.; Dahl,L. F. Inorg. Chem. 1980,19,892. (c) Fitzpatrick, P. J.; Page, Y.L.; Butler, I. S. Acta Crystallogr., Sect. B 1981, B37, 1052. (d) Fitzpatrick, P. J.; Page, Y. L.; Sedman, J.; Butler, I. S. Inorg. Chem. 1981, 20, 2852.
592 Organometallics, Vol. 2, No. 5, 1983
Miki et al.
Table VII. Selected Bond Angles (deg) along with Their Estimated Standard Deviations in Parentheses ~
2b
2c
2d
97.84 129.29 132.30 35.91 (18) 75.3 ( 3 ) 115 ( 3 ) 102 ( 3 ) 111 ( 4 ) 126 ( 3 ) 119 ( 3 ) 68.8 ( 3 ) 110.1 ( 4 ) 103 ( 4 ) 127.4 ( 5 ) 124 (4) 108 ( 4 ) 121.2 ( 5 ) 122.1 ( 5 ) 116.7 ( 5 ) 122.2 ( 6 ) 119.6 ( 6 ) 119.4 ( 5 ) 120.8 ( 5 ) 121.2 ( 5 ) 124.7 ( 5 ) 116.0 ( 5 ) 118.2 ( 5 )
98.18 130.58 131.13 35.68 (17) 75.1 ( 3 106 ( 3 ) 105 (3) 116 ( 5 ) 119 (3) 122 ( 3 ) 69.2 ( 3 110.6 ( 3 106 (3) 126.2 ( 5 115 ( 3 ) 116 ( 3 ) 119.0 ( 5 ) 122.2 ( 5 ) 118.8 ( 5 ) 119.8 ( 5 ) 120.6 ( 6 ) 120.0 ( 7 ) 120.7 ( 6 ) 120.1 ( 5 )
98.81 128.99 131.77 35.8 ( 3 74.1 ( 4 102 ( 5 ) 111 ( 4 ) 122 ( 6 ) 118 ( 5 ) 116 ( 4 ) 70.2 (4 109.1 ( 4 104 ( 4 ) 127.3 (6 112 ( 4 ) 118 ( 4 ) 118.9 ( 5 ) 123.2 ( 5 ) 117.9 ( 5 ) 120.6 (6) 119.1 ( 6 ) 120.8 ( 6 ) 119.6 ( 6 ) 122.0 ( 6 )
2b
2c
2d
119.1 ( 6 ) 120.1 ( 6 ) 121.1 ( 6 ) 119.5 ( 6 ) 120.8 ( 6 ) 121.4 ( 4 ) 118.8 (4) 119.7 ( 5 ) 119.7 ( 5 ) 120.6 ( 7 ) 120.9 ( 7 ) 119.5 ( 7 ) 119.6 ( 6 ) 121.8 ( 4 ) 118.8 ( 3 ) 119.3 ( 4 ) 119.8 ( 5 ) 121.6 ( 5 ) 118.7 ( 5 ) 119.6 ( 5 ) 121.1 ( 4 ) 108.6 ( 6 ) 110.6 ( 6 ) 109.8 ( 7 ) 104.1 ( 6 ) 113.0 ( 7 ) 110.6 ( 7 )
118.9 ( 6 ) 121.4 (8) 120.7 ( 9 ) 120.1 (8) 119.2 ( 7 ) 121.6 ( 4 ) 119.7 ( 4 ) 118.7 ( 5 ) 120.9 ( 5 ) 119.8 ( 6 ) 120.0 ( 7 ) 121.1 ( 7 ) 119.5 ( 6 ) 122.1 ( 4 ) 118.7 ( 4 ) 118.9 ( 5 ) 120.9 ( 6 ) 120.3 ( 7 ) 120.2 (8) 120.3 ( 7 ) 119.4 ( 6 )
120.3 ( 9 ) 120.5 (8) 119.4 ( 7 ) 121.5 ( 7 ) 120.0 ( 7 ) 121.6 ( 5 ) 119.7 ( 5 ) 118.6 ( 6 ) 119.4 ( 6 ) 121.2 ( 7 ) 120.0 (8) 120.8 (8) 120.0 ( 7 ) 122.1 ( 4 ) 118.8 ( 4 ) 118.8 ( 5 ) 119.5 ( 6 ) 122.1 ( 7 ) 118.3 ( 6 ) 120.8 ( 6 ) 120.3 ( 5 ) 107.2 ( 9 ) 111.8 ( 9 ) 113.1 (10) 102.9 ( 9 ) 111.0 (10) 110.3 ( 1 0 )
~~
P( l)-PdrCETa P( 1)-Pd-CCP' CET"-Pd-CCP' C( l)-Pd-C( 2) Pd-C( 1)-C( 2) Pd-C( 1)-H( 1A) Pd-C( 1)-H( 1B) H( 1A)-C(1)-H( 1B) C( 2)-C( 1)-H( 1A) C( 2)-C( 1)-H( 1B) Pd-C( 2)-C( 1) Pd-C( 2)-C( 3) Pd-C( 2)-H( 2) C( l)-C( 2)-C( 3) C( 1)-C( 2)-H( 2) C( 3)-C( 2)-H( 2) C( 2)-C( 3)-C( 4) C( 2)-C( 3)-C(8) C( 4)-C( 3)-C( 8) C( 3)-C( 4)-C( 5) C( 4)-C( 5)-C( 6 ) C( 5)-C(6)-C(7) C( 6)-C( 7)-C( 8) C(7)-C( 8)-C( 3 ) C( 5)-C( 6 ) - 0 C( 7)-C( 6 ) - 0 C( 6)-0-C( 9) C( 5)-C( 6)-C1 C( 7)-C( 6)-C1 C( 15)-C( 11)-C( 1 2 ) C(ll)-C(12)-C(l3) C(12)-C(13)-C(14) C(13)-C(14)-C(15) C(14)-C(l5)-C(ll) Pd-P( 1)-C( 21) Pd-P( 1)-C( 31) Pd-P( 1)-C( 41) C(Bl)-P(l)-C(31) C( 21)-P( 1)-c(41) C( 3 1)-P( 1)-C( 41) P( 1)-C( 21)-C( 22) P( 1)-C( 21)-C( 26) C( 26)-C( 21)-C( 22)
118.9 ( 5 ) 120.3 ( 5 ) 108.0 (8) 108.2 ( 7 ) 109.9 ( 7 ) 107.8 (8) 106.9 ( 7 ) 107.0 ( 7 ) 110.3 ( 7 ) 109.0 ( 7 ) 108.1 (8) 107.5 ( 6 ) 110.1 ( 7 ) 107.5 ( 7 ) 104.7 ( 6 ) 107.9 ( 7 ) 105.5 ( 7 ) 108.42 (19) 110.33 (16) 108.5 ( 3 ) 117.19 (15) 116.02 ( 1 5 ) 117.1 ( 2 ) 113.06 (13) 112.80 (15) 113.3 ( 2 ) 106.3 ( 3 ) 106.3 ( 4 ) 106.2 ( 3 ) 106.9 ( 3 ) 107.1 ( 3 ) 107.1 ( 4 ) 104.1 ( 2 ) 104.0 ( 2 ) 104.0 ( 3 ) 122.1 ( 5 ) 121.8 ( 4 ) 123.4 ( 7 ) 118.6 ( 5 ) 118.3 ( 6 ) 118.4 ( 5 ) 118.3 ( 8 ) 119.8 ( 5 ) 119.3 ( 6 )
a Abbreviations: see the footnote to the Table
C( 21)-C( 22)-C( 23) C( 22)-C( 23)-c( 24) C( 23)-c( 24)-c( 25) C( 24)-C( 25)-C( 26) C( 25)-C( 26)-C( 21) P( 1)-C( 31)-C( 32) P(l)-C(31)-C(36) C( 36)-C( 31)-C( 32) C( 31)-C( 32)-C( 33) C( 32)-C( 33)-C( 34) C( 33)-C( 34)-C( 35) C( 34)-C( 35)-C( 36) C( 35)-C( 36)-C( 31) P( 1)-c(41)-c(42) P( 1)-C( 41)-C( 46) C(46)-C(41)-C(42) C(41)-C(42)-C(43) C(42)-C(43)-C(44) C(43)-C(44)-C(45) C(44)-C( 45)-C( 46) C( 4 5)-C( 46)-C( 4 1) F( 1)-B-F( 2) F( 1)-B-F( 3) F( 1)-B-F( 4) F( 2)-B-F( 3) F( 2)-B-F( 4) F( 3)-B-F( 4) F(1)-P( 2)-F( 3) F( 2)-P( 2)-F( 4) F( 5)-P( 2)-F( 6 ) F( l)-P( 2)-F( 2) F( l)-P( 2)-F(4) F( 1)-P( 2)-F( 5) F( l)-P( 2)-F( 6) F( 2)-P( 2)-F( 3) F( 2)-P( 2)-F( 5) F( 2)-P( 2)-F( 6 ) F( 3)-P( 2)-F(4) F( 3)-P( 2)-F( 5) F( 3)-P( 2)-F( 6 ) F( 4)-P( 2)-F( 5) F( 4)-P( 2)-F( 6) Cl( 1s)-C(S)-C1( 2 s )
176.8 ( 5 ) 176.4 ( 4 ) 177.7 ( 6 ) 85.1 ( 4 ) 91.4 ( 4 ) 88.7 ( 5 ) 89.2 ( 5 ) 94.8 ( 5 ) 88.9 ( 5 ) 90.3 ( 5 ) 88.8 ( 5 ) 94.5 ( 6 ) 87.7 ( 6 ) 91.1 ( 5 ) 89.6 ( 5 ) 115.1 (8)
117.3 ( 9 )
VI.
atoms being 3.388 (7) A (C(B)(x,y, z)-F(2)(1 + x:, y, z ) ) for 2b, 3.114 (9) A (C(42)(x,y, z)--F(2)(1- f, 9 , l - Z ) ) for 2c, and 3.392 (10) A (C(15)(x,y,z)--F(3)(1+ x , y, 1 + z ) ) for 2d, respectively. Relative Stability in Dilute Solutions. Conductivity measurement in CH,Cl, suggested that 1:l ion pair formation constants for 2 (R = n-Bu, X = C104and BF4) lie in the range of 10L4 X 103 L/equive6 On the basis of these values more than 80% of the complexes are calculated to exist as free ions under the UV experimental conditions. In accord with this assumption the thermodynamic parameters for eq 2 involving 2 (R = Ph) were found to be almost counteranion independent, unlike the corresponding parameters determined in the concentrated solution (5 X lo-, M) by 'H NMR spectra.6 Under the latter condition the amount of the complexes existing as free ions would be very small. Of particular note in Table V is that the change of AGO as a function of Y is primarily controlled by the change of AS", with AHo for 2 (R = Et, n-Bu) being almost independent of Y. In addition, competition between the nitrile and the styrene ligands in coordinating with palladium (eq 2) is also entropy controlled. The negative values of ASo for eq 2 would partly be a reflection of the smaller degree of solvent orientation in the vicinity of the palladium atom of the nitrile complex than that of 2. The reduced solvent orientation in the former could be at-
tributed to the reduced effective nuclear charge on the palladium arising from the more effective delocalization of the positive charge over the coordinated ligands and the much smaller contribution of the K back-bonding effect. Similarly, the change of AS" as a function of Y may be ascribed to the more positive charge residing on the palladium of the more electron-withdrawing styrene complexes as a result of the decreasing u donation and increasing K back-donation effects (see later). The range of the variation of AH" for 2 (R = Ph) is well within the experimental error. However, its trend, if assumed to be real and compared with that for 2 (R = Et, n-Bu), suggests a slightly more electrophilic nature of the (s5-C5H5)(PPh3)Pd+moiety than the ( T ~ - C ~ H ~ ) ( P R ~ ) P ~ + (R = Et, n-Bu) ones. In any case, by far the smaller sensitivity of AH" of 2 to the change of Y than that of 1 (e.g., AHoYaH= 5.2 K J / ~ o is~ remarkable. ) ~ Of further remark is that the Hammett relation for eq 2 holds better with u than u+ constants (Table IV). These results are now understandable= in terms of the difference in the intrinsic nature of the olefin-Pd bond in 1 and 2. The Nature of the Olefin-Palladium Bond. The most significant difference in the electronic effects of 1 and (23) In the absence of knowledge about structures of ion pairs or ion aggregates, it is difficult to rationalize the observed trend in AH" and AS" of 2 in the concentrated solutions.
Substituted Styrene Complexes of Palladium(Il)
2 on the olefin-Pd bond is clearly the number of the valence shell electrons or, in other words, the effective coordination number. Thus, 2 may be regarded as an analogue of ML,(olefin) complexes, for a small distortion of the ML4 fragment and substitution of the Cp group for three L's cis to each other lead to a rough representation of the M(q6-C6Hs)Lfragment. The configuration of 2 determined crystallographically is essentially the one predicted by the MO considerationst21of d6 ML4(olefin) complexes. That is, the olefin ?r* interacts well with the filled metal orbital (b,) in configuration B rather than in
L
B the one in which the olefin has rotated about the olefin-M axis by 90°. Moreover, the b2 orbital used in B is more favorably situated in ita energy and shape in overlapping with the olefin ?r* than the metal orbitals used in the ?r interaction in the square-planar olefin complexes. We propose that it is the enhanced role of the ?r backbonding in the l&electron complexes as shown above that is responsible for the different trends in the thermodynamic parameters of 2 than those of 1. In 1the substituent effect was suggested to be transferred to the interaction center pPedominantly through the form A. On the other hand, in 2 an increase in the ?r interaction energy in the more electron-withdrawing styrene complex must have compensated for a decrease in the u interaction energy to some extent. Also, if the ?r interaction were not important in 2,the Pd-C( 1)length of the more electron-withdrawing styrene complex would have become longer than that of the more donating styrene complex to an experimentally appreciable extent, as was the case in the square-planar complexes tram-PtC1,(Me-pyridine)(CH2=CHC6H4Y-p) (Y= NMe,, H).l9 9 The observed difference in the PdC(o1efin) lengths of 2a and 2c is also consistent with the palladium atom in the former complex bearing the more donating phosphine acting as a better ?r base.
Organometallics, Vol. 2, No. 5, 1983 593
Finally, however, it should be stressed that the almost constant AHo values in 2 do not necessarily imply that the ?r interaction makes almost the same contribution as the u interaction does, for the observed AHo values are well expected to include in addition to the contributions from the intrinsic olefin-Pd bond strength those from the solvation effects. It seems rather unreasonable to believe that the ?r interaction is as important as the u interaction, particularly in the cationic Pdn complexes. The C(l)-C(2) lengths observed in 2a-d are well within the range of the carbon-carbon double bond. Also, the barrier to the rotation of ethylene in [Pd(q6-C6H5)(PPh3)(CzH4)]C104 is small6and is estimated to be less than 35 KJ/mol at -90 "C on the assumption that the chemical shift difference in the nonequivalent ethylene proton resonances is almost the same as that of [Pt(q6-C6Hs)(PPh3)(C2H4)]C104.6 In conclusion,the ?r interaction energy in the olefin-Pdn bond may not be very large in nature, as has been pointed out previously,' but the relative contribution of this interaction with regard to that of the u interaction can be increased in the lselectron complexes to such a point as to influence the structural and thermodynamic parameters to an experimentally observable extent. Registry No. 2 (R = Ph, X = BF4, Y = OMe), 84432-87-1; 2 (R = Ph, X = PFe, Y = H), 84432-88-2;2 (R = Ph, X = BF4, Y = CI), 84432-89-3;2 (R = Ph, X = C104,Y = Cl), 75346-33-7; 2 (R= Ph, X = C104,Y = H), 75346-35-9;2 (R = Ph, X = ClO,, Y = Me), 75346-37-1; 2 (R= Ph, X = ClO,, Y = OMe), 75346-39-3; 2 (R= Ph, X = BF4, X = Me), 84432-90-6;2 (R = Et, X = CIO,, Y = Cl), 84432-92-8; 2 (R = Et, X = C104, Y = H), 75345-58-3; 2 (R= Et, X = C104,Y = Me), 84432-94-0;2 (R = Et, X = C104, Y = OMe), 84454-18-2; 2 (R = Bu, X = C104,Y = Cl), 75346-43-9; 2 (R = Bu, X = C104,Y = H), 75346-45-1;2 (R = Bu, X = ClO,, Y = Me), 75346-47-3; 2 (R = Bu, X = C104,Y = OMe), 75346-49-5; 2 (R Ph, X = BF4, Y = H), 84432-97-3;3 (R = Ph), 75346-64-4; 3 (R = Et), 84432-95-1;3 (R= Bu), 84432-96-2;2-methylbenzonitrile, 529-19-1; 4-chlorostyrene, 1073-67-2;styrene, 100-42-5; 4-methylstyrene, 622-97-9; 4-methoxystyrene, 637-69-4.
Supplementary Material Available: A table of anisotropic temperature factora (Table Sl), a listing of structure factors (Table S2), and least-squares planes and atomic deviations from the plane (Table S3) for 2b-d (51 pages). Ordering information is given on any current masthead page.
