1059 Chem. Soc. A, 1313 (1970). (18) J. N. Francis, A. McAdam, and J. A. Ibers, J. Organometal. Chem., 29, 131 (1971). (19) K. S. Wheelock, J. H. Nelson, L. C. Cusachs, and H. 5 . Jonassen, J. Amer. Chem. Soc.,92, 5110 (1970). (20) J. H. Nelson and H. B. Jonassen, Coord. Chem. Rev.. 6, 27 (1971). (21) B. W. Davies and N. C. Payne, Can. J. Chem., 51, 3477 (1973). (22) M. J. S. Dewar, Bull. SOC.Chim. Fr., 18, C 71 (1951). (23) J. Chatt and L. A. Duncanson, J. Chem. SOC.,2939 (1953).
(24) J. L. Boston. S. 0.Grim, and G. Wilkinson, J. Chem. SOC..3468 (1963). (25) (a) Chem. sdc., Spec. fubl., No. 18 S16s (1965); (b) ibid, p S14s: (c) ibid, p S15s. (26) J. 0.Glanville, J. M. Stewart, and S. 0.Grim, J. Organometal. Chem., 7, P9 (1967). (27) Reference 1, p 1006. (28) J. Dale, ref 1, pp 1-6. (29) J. J. Daly, J. Chem. SOC.,3799 (1964). (30) J. M. Guss and R. Mason, J. Chem. Soc., Dalton Trans., 2193 (1972).
Steric vs. Electronic Effects in Palladium-Thiocyanate Complexes. The Crystal Structures of Dithiocyanato[bis( dipheny lphosphino)methane]palladium( 11), Isothiocyanatothiocyanato[ 1,2-bis(diphenylphosphino)ethane]palladium( 11), and Diisothiocyanato[ 1,3-bis(diphenylphosphino)propane]palladium( 11) Gus J. Palenik,*la M. Mathew,la W. L. Steffen,lb and G . BeranlC Contribution from the Departments of Chemistry, University of Florida, Gainesville, Florida 3261 I , and University of Waterloo, Waterloo, Ontario, Canada. Received July 18, 1974
Abstract: The crystal structures of the series (C6H5)2P(CH2)nP(C6H5)2Pd(cNs)~, CNS represents the thiocyanate ion without specifying the mode of attachment ( n = 1-3), have been determined by X-ray diffraction tethniques. The most important observation is that the thiocyanate coordination changes from S,S when n = 1 to S,N for n = 2 and N,N with n = 3. The conclusion is that the mode of thiocyanate coordination in palladium thiocyanate-phosphine complexes is determined by steric rather than electronic effects. The crystals of ( C ~ H S ) ~ P C H ~ P ( C ~ H ~ ) are~ monoclinic, P ~ ( S C ~space ) ~ group P21/n, with a = 10.426 (8) A, b = 29,353 (10) A, c = 9.884 (6) A, and 13 = 119.86 (4)O. The final R value for the 2814 reflections crystallizes with the orthorhombic used in the analysis was 0.039. The complex (C~HS)P(CH~)~P(C~H~)P~(SCN)(NC~) space group P212121. The cell dimensions are a = 17.773 (6), b = 23.212 (15), and c = 8.502 (4) A. A total of 2249 reflections was used in the analysis and the final R value was 0.056. The last compound (C6H5)2P(CH2),P(C6Hs)2Pd(NCS)2is monoclinic with the space group 12/a and cell dimensions of a = 14.774 (6) A, b = 9.181 (5) A, c = 21.182 (10) A, and /3 = 95.48 (2)O. The molecule has twofold symmetry, as required for four molecules per unit cell. The final R value for the 1781 reflections used in the analysis was 0.025. The Pd-P bond distances are a function of the nature of the trans atom. a u-bond rather than a n-bond effect. The Pd-S distances appear to be independent of the tip of the thiocyanate ion from the coordination plane. A comparison of the angular changes in the three compounds is easily interpreted in terms of increasing steric effects with an increase in the chain length between the phosphorus atoms. The changing mode of the thiocyanate ion is explainable in terms of steric effects without invoking any *-bonding arguments.
T h e thiocyanate ion is a n ambidentate ligand that c a n v ~ k e d In . ~fact ~ ~contrary ~ evidence such a s n m r coupling coordinate either through the sulfur or nitrogen atom.2 This constants which suggested that 7r-bonding in Pt(n)-phosambidentate nature can be interpreted in terms of the “softphine complexes was minimal a t best” was ignored. T h e in the h a r d ” concepts developed by P e a r ~ o n .Therefore, ~ presence of both N-bonded and S-bonded thiocyanates in case of class b or “soft” metals, such as Pd(I1) or P t ( I I ) , P d ( d p p n ) ( N C S ) ( S C N ) , dppn is ( C ~ H S ) ~ P C H ~ C H ~ C H ~ N coordination of thiocyanate is expected to occur through t h e (CH3)2,” appeared to support these n-bonding arguments “soft” sulfur a t o m . Indeed, Pd(I1) complexes with m a n y and has also been used as a n example of “antisymbiosis.”6 a m i n e ligands form S-bonded thiocyanates. In contrast, a However, the existence of both N-and S-bonded thiocylimited number of phosphine complexes of Pd(I1) were anates in P d ( d p e ) ( N C S ) ( S C N ) , I 3 d p e is (C6H5)2PCH*found to have N-bonded thiocyanates, a fact which has CH2P(C&s)2, suggested t h a t steric effects were extremely ~ been rationalized on t h e basis of n - b ~ n d i n g ,polyelectronic important and tended to refute the “antisymbiosis” arguperturbation theory,5 and the so-called antisymbiosis efments, a t least for palladium complexes. fects.6 T h e problem in all of the previous studies has been the A study of palladium- and platinum-thiocyanate comdifficulty in separating steric from electronic effects. Thereplexes involving PPh3, AsPh3, a n d SbPh3 was complicated fore, after the completion of our study of by t h e fact that t h e steric and electronic factors operated in P d ( d p e ) ( N C S ) ( S C N ) , we undertook an investigation of the s a m e d i r e ~ t i o n Nevertheless, .~ steric control was used to two other closely related complexes P d ( d p m ) ( S C N ) 2 , d p m prepare the N-bonded complex P ~ [ ( C ~ H S ) ~ N C H ~ C is H ~( -C ~ H S ) ~ P C H ~ P ( C ~and H ~ Pd(dpp)(NCS)z. )~, d p p is N H C H ~ C H ~ N ( C ~ H( N SC ) ~S )] + r a t h e r t h a n t h e usual S( C ~ H S ) ~ P C H ~ C H ~ C H ~ PT(hC e ~ series H ~ )of~ .complexes bonded thiocyanates.8 However, despite this early evidence ( C ~ H ~ ) ~ P ( C H ~ ) , P ( C ~ H S ) ~ PC~N( C SN does S ) ~not, specthat steric effects could explain the changes in thiocyanate ify the mode of attachment, will have approximately equivcoordination, n-bonding arguments continued t o be inalent electronic effects but vastly different steric require-
Palenik, Mathew, Steffen, Beran
/
Palladium- Thiocyanate Complexes
1060 Table I. Crystal Data
Pd(dpm)(SCN)z Monoclinic P2dn 10.426 (8) 29.353 (10) 9.884 (6) 119.86 (4) 2623.5 606.97 4 1.536 1.54 0 . 2 8 X 0.19 X 0 . 1 9 Moving crystal moving counter MO K a 9.9 0-45 3432
Crystal System Space group a, A
b, A c, A
8, deg Volume, A3 Molecular weight Z p(calcd), g/cm3 p(measd), gjcm3 Crystal size, mm3 Method of data collection Radiation used p, cm-'
20 range, deg No. of unique reflections No. of observed reflections
2814
ments for t h e phosphine ligand. Therefore, these effects can be delineated. Our results show a change in thiocyanate coordination from S,S when n = 1 t o S,N for n = 2 a n d t o N , N for n = 3 which parallels t h e increasing steric requirem e n t s of t h e phosphine ligands.I4 Therefore, t h e structural studies presented in this paper suggest t h a t t h e primary mode of coordination of thiocyanate t o Pd(I1) is via t h e sulfur a t o m (an electronic effect) but t h a t steric effects c a n be used t o alter t h e mode of thiocyanate coordination.
Experimental Section All three compounds Pd(dpm)(SCN)z, Pd(dpe)(NCS)(SCN), and Pd(dpp)(NCS)z were kindly supplied by Professor D. W. Meek. The relevant crystal data are summarized in Table 1. Pd(dpm)(SCN)2.Preliminary Weissenberg and precession photographs showed the crystals to be monoclinic. The systematic absences of h01 for h I = 2 n + 1 arrd OkO for k = 2n + 1 indicated the space group to be P21/n. The unit cell dimensions were determined from a least-squares fit of 26, o,I p and x values for 15 reflections. The intensity data were collected on a Syntex P i automatic difractometer using graphite monochromatized Mo Kcu radiation ( A = 0.71069 A) and a variable scan rate. The background was measured for a time equal to one-half of the total scan time at a point 1' to each side of the c y ) and a2 peak. Four standard reflections were measured after every 100 reflections and were used to correct for a small variation (maximum 2%) of intensities with time. Reflections with an intensity I > 1.40(1) were used in the structure analysis. The remaining reflections were flagged with a minus sign and not used in the determination. The data were reduced to a set of structure amplitudes in the usual manner.
+
Table 11. Scheme of Refinement
Pd(dpm)- Pd(dpe)- Pd(dpp)(SCN), (NCS)(SCN) (NCS)?
R index with all atoms from Fourier syntheses Refinement with isotropic thermal parameters R index Refinement with anisotropic thermal parameters R index Refinement with hydrogen atoms included, but not refined R index (final) F(10w) for weighting scheme F(high) for weighting scheme
0.20
0.19
0.12
3 cycles
3 cycles
3 cycles
0.089 6 cycles
0 086 6 cycles
3 cycles
0 052
0.062
0.072 0.037
3 cycles
3 cycles
3 cycles
0,039 36 0 72.0
0.056 52.0 104.0
16.8
Journal of the American Chemical Society
0.025 25.2
Pd(dpe)(NCS)(SCN) Orthorhombic p212121 17,773(6) 23.212(15) 8.502 (4) 2718.1 620.99 4 1.517 1.51 0.078 X 0.085 X 0.090 Stationary crystal stationary counter Cu K a
83.1 0-135 2808 2249
Pd(dPP)(NCSh Monoclinic I2/a 14.774 (6) 9.181 ( 5 ) 21.182 (IO) 95.48 (2) 2860.0 635.02 4
1.475 1.48 0.41 X 0.38 X 0 . 3 8 Moving crystal moving counter MO K a 9.1 0-45 1874 1781
Pd(dpeXNCS1SCN).The systematic absences of h0O for h = 2n
+ 1 , OkO for k = 2n + 1, and 001 for I = 2n + 1 indicated the space group to be P212121. The unit cell dimensions were determined from a least-squares fit of 26 values measured using the Cu K P peak (A 1.39217 A). The intensity measurements were made with a General Electric XRD-6 diffractometer, using a wide beam of Cu Kal radiation ( A = 1.54051 A) with 0.35 mil Ni foil in front of the scintillation counter. All reflections with 28 5 135' in the unique quadrant were measured first and then those in the halfhemisphere, thus giving three measurements for each reflection. Measurements of four standard reflections after ever 100 reflections indicated that the change in intensity with time was not significant. An experimental background curve was derived by nieasurement of the background in areas of reciprocal space which were known to be free from reflections and streaking. Those reflections which had intensities greater than 1.3 times the appropriate background were used in the structure analysis. An empirical correction for the al-a2 splitting was made for reflections with 20 > 80'. N o absorption corrections were applied. The data were reduced to a set of structure amplitudes in the usual manner. Pd(dpp)(NCS)z.The crystals belong to the monoclinic system. The systematic absences of hkl for h + k + I = 2n + 1 and h01 for h = 2n 1 indicated the possible space group to be l a or I 2 / a . I n tensity statistics indicated that the most probable space group was /2/a and was confirmed by the successful structure analysis. A spherical shape was obtained by dissolving a large crystal slowly in CHzClz with a rotary motion. This crystal was used in the measurement of cell constants and intensity data. The procedure was similar to those given in the case of Pd(dpm)(SCN)z. The relevant data are summarized in Table I. Structure Determination and Refinement. All three structures were solved by the heavy atom method and refined by least-squares techniques. The scheme of refinement and R index at various stages are summarized in Table 11. Three cycles of full-matrix leastsquares calculations using individual isotropic thermal parameters were carried out on each compound. In the case of Pd(dpe)(NCS)(SCN), the imaginary part of the anomalous dispersion correction15 was applied and the present enantiomorph was selected on the basis of Hamilton R-test.Ih Refinements using anisotropic thermal parameters were carried out by block-diagonal approximation for Pd(dpm)(SCN)? and Pd(dpe)(NCS)(SCN) and full-matrix calculation for Pd(dpp)(NCS)z. At this stage a difference Fourier synthesis was computed, and the positions of hydrogen atoms were located in all three compounds. Their positions were included in subsequent least-squares calculations but were not refined. Refinement was terminated when the indicated shifts in parameters were less than one-third of the corresponding estimated standard deviation. The quantity minimized by the least-squares calculations was Xw(lF4 where v'w = F,,/F(low) if F, < F(low), d w = 1 if F(low) 5 F, I F(high) and v'w = F(high)/Fo if F(high) < Fo. The values of F(1ow) and F(high) in each case are listed in Table 11. The atomic scattering factor for Pd was from Cromer, Larson,
/' 97.5 / March 5, I975
+
1061 Table 111. The Final Parameters of Nonhydrogen Atoms in Pd(dpm)(SCN)2a
Atom
Y
X
12,774 (1) 1,218 (1) 1,196 (1) 1,294(1) 1,372 (1) 1,633 (5) 1,208 (2) 1,456 (3) 1,200 (2) 1,454 (2) 1,714 (2) 1,541 (2) 1,921 (3) 2,371 (3) 2.503 (2) 2,167 (2) 750 (2) 705 (2) 281 (3) -70 (2) -28 (2) 391 (2) 1,858 (2) 1,795 (2) 2,171 (2) 2,608 (2) 2,665 (2) 2,299 (2) 881 (2) 580 (3) 204 (3) 146 (3) 445 (3) 824 (2)
1952 (4) - 2259 (2)
-530 (2) 2609 (1) 1523 (1) -2516 (9) -3630 (6) -2347 (8) - 2379 (6) 3317 (6) 3223 (6) 3809 (7) 4286 (8) 4143 (8) 3516 (9) 3043 (8) 3376 (6) 4901 (7) 5469 (8) 4511 (9) 3018 (9) 2451 (7) 1241 (5) 673 (7) 453 (8) 794 (8) 1331 (7) 1531 (7) 1693 (6) 526 (9) 643 (12) 1904 (11) 3043 (10)
z
P11
24,269 (4) 338 (2) 4,333 (2) 4,301 (1) 1,181 (1) -2,298 (10) 2,844 (8) - 1,202 (8) 3,420 (7) 3 ,OOO (6) 5,832 (6) 7,366 (7) 8,526 (7) 8,121 (9) 6,593 (9) 5,435 (8) 5,183 (6) 6,100 (7) 6,840 (7) 6,612 (8) 5,668 (9) 4,990 (7) -52 (6) - 1 .655 (7) - 2,587 (8) - 1,976 (8) -408 (8) 550 (7) 170 (6) -519 (9) -1,320 (11) -1,431 (10) -769 (9) 44 (7)
643 (4) 71 (2) 102 (2) 57 (1) 78 (2) 186 (13) 120 (8) 105 (10) 109 (8) 80 (7) 71 (7) 133 (9) 173 (12) 158 (11) 256 (15) 206 (12) 100 (8) 124 (10) 158 (11) 259 (14) 241 (14) 151 (10) 71 (7) 133 (9) 180 (12) 150 (10) 130 (9) 133 (9) 132 (9) 224 (13) 398 (22) 377 (20) 276 (15) 165 (11)
P2Z
P33
812
PIS
780 (5) 122 (2) 125 (2) 60 (2) 63 (2) 233 (15) 317 (14) 148 (12) 186 (11) 66 (7) 83 (8) 90 (9) 101 (11) 190 (13) 219 (14) 137 (11) 78 (8) 125 (10) 107 (10) 158 (12) 183 (13) 138 (10) 81 (8) 90 (9) 109 (10) 145 (11) 174 (12) 122 (10) 76 (8) 190 (13) 271 (18) 214 (15) 173 (13) 134 (10)
-40 (3) -13 (1) -5 (1) -1 (1) -7 (1) -75 (10) -19 (5) -38 (6) -13 (5) - 10 (4) -3 (4) 14 (5) 17 (7) -20 (6) -17 (6) -3 ( 5 ) 14 (4) 26 (5) 57 (6) 38 (6) 17 (6) 4 (5) 5 (4) -4 (5) 14 (6) 13 (5) 8 (5) 12 (4) -8 (4) -41 (6) -75 (9) -14 (8) 38 (7) 13 (5)
530 (7) 9 (3) 135 (4) 38 (3) 56 (3) 40 (23) 235 (18) 15 (18) 168 (16) 57 (12) 73 (12) 80 (15) 97 (19) 164 (20) 288 (24) 173 (19) 79 (13) 91 (17) 69 (18) 218 (22) 260 (23) 152 (17) 77 (12) 97 (15) 148 (18) 168 (17) 138 (17) 127 (16) 103 (14) 255 (23) 451 (35) 397 (31) 301 (24) 159 (18)
P23
a All values are X I O 4 except for Pd which is X 105. The estimated standard deviations are given in parentheses. The temperature factor is of the form exp[-(Pllh2 P 2 k 2 P 3 d 2 Plzhk PI3hl P ~ ~ k l ) l .
+
+
+
+
+
and Waber's compilation,17 the scattering factors for P, S, N, and C were from Hanson, Herman, Lea, and Skillman18and the hydrogen curve was from Stewart, Davidson, and Simpson.19 The scattering factors were corrected for the real part of the anomalous dispersion. The final atomic parameters for the nonhydrogen atoms are given in Tables 111, IV, and V. The hydrogen atom parameters are given i n Tables VI, VII, and VIII. A table of observed and calculated structure factor amplitudes is available.20
Results and Discussion In all three compounds t h e crystal consists of discrete complexes, with no unusual intermolecular interactions between the molecules. A view approximately normal t o t h e coordination plane, giving t h e atomic numbering, bond distances, and angles, is given in Figures 1-3. T h e distances and angles in t h e ten phenyl rings a r e normal.20 Similarly, t h e P-C (of C H 2 ) distances in t h e three compounds range from 1.820 (12) to 1.855 (6) A, a r e not significantly different, and a r e consistent with the available d a t a . T h e average P-CH2 distance of 1.832 8, is slightly longer t h a n the P-C (of phenyl ring) distance of 1.801 8, although t h e difference is not significant. T h e difference'in P-C (of C H 2 ) vs. P-C (of phenyl ring) is not unexpected since t h e hybridization of the carbon atoms is different in t h e two cases. T h e dimensions of t h e thiocyanate groups in t h e three compounds a r e similar t o those found in other thiocyanates. Distances and angles not included in Figures 1-3 a r e given in Table IX. T h e estimated standard deviations for distances and angles a r e given in T a b l e X . There is a n approximately square-planar arrangement of donor atoms around t h e palladium a t o m in each case. T h e deviations from t h e least-squares plane for P d ( d p m ) ( S C N ) z a r e Pd 0.023, S ( 1 ) -0.041, S ( 2 ) 0.032, P ( l ) -0.053, and P(2) 0.038 A. In t h e case of P d ( d p e ) ( S C N ) ( N C S ) t h e de-
viations from planarity a r e Pd 0.004, S ( l ) -0.033, N ( 2 ) 0.036, P(1) -0.037, and P ( 2 ) 0.030 8,. T h e thiocyanate groups a r e required to be cis because of the constraints imposed by t h e chelating phosphine ligands PhzP(CH2),,PPh2. T h e number of C H 2 groups between t h e phosphorus atoms is the only difference between t h e ligands in the three complexes. Therefore, these three ligands should have approximately the s a m e u-donor a n d *-acceptor properties. However, t h e steric requirements of the three ligands will not be identical. A n increase in steric requirements with a n increase in t h e alkyl chain length is nicely illustrated by t h e change in P-Pd-P angle from 73.2' for n = 1, to 85.1' for n = 2 and to 89.1' for n = 3. Concomitant with the increasing P-Pd-P angle is a decrease in the P-Pd-S or N (other atom in coordination sphere) angle. For example, P(1)Pd-S(2) is 90.94 (6)' when n = 1 and P(I)-Pd-N2) is 90.2 (3)' when n = 2 and 89.82 (8)' for n = 3. T h e P(2)-PdS ( 1 ) angle goes from 102.79 (6)' for n = 1 to 100.3 ( 1 ) O for n = 2 to the P(2)-Pd-N of 89.82 (3)' when n = 3. T h e increasing steric effects a r e also illustrated in the increase of the Pd-S(1)-N(1) angle from 108.5 (3)' when n = 1 to 115.5' for n = 2. There is also a n increase in t h e Pd-P-C (chelate ring) angles from 95.9 and 94.7' in the d p m case to 110.8 and 107.0' in the dpe complex to 114.4' in d p p ring. However, in spite of large angular changes involving the phosphorus atom and the chelate ring system, the angle between the phenyl rings is almost constant. T h e angles C ( l a ) - P ( I)-C( 1b) and C ( lc)-P(2)-C( I d ) show a maxim u m difference of 2.6'. Presumably, there is less flexibility for the angles involving t h e phenyl rings than in the chelating system. T h e net result of the various angular changes is to move the phenyl rings toward the other two coordination sites in the square-planar arrangement. Therefore, although
Palenik, Mathew, Steffen, Beran
/ Palladium- Thiocyanate Complexes
1062 Table IV.
The Final Parameters of Nonhydrogen Atoms in Pd(dpe)(SCN)(NCS)a
Atom
X
Y
-10,431 (6) - 520 (3) -3,217 (3) - 1,674 (2) -171 (2) 303 (9) 1 ,864 (7) -23 (9) -2,397 (9) - 1 ,220 (8) -134 (7) -2,959 (9) -3,558 (9) -4,524 (9) -4,947 (10) - 4,424 (9) - 3,438 (9) - 1,359 (8) -640 (10) -318 (11) -732 (13) -1,423 (12) - 1,753 (10) 1,040 (10) 1,550 (10) 2,552 (11) 3,017 (11) 2,534 (11) 1,556 (10) -771 (8) -1,409 (9) -1,878 (10) -1,697 (10) -1.058 (12) -592 (10)
-15,313 (3) -1,029 (2) -2,311 (3) -2.039 (1) -1,080 (1) 49 ( 5 ) -2,003 (4) -403 (5) -2,132 (5) -1,772 (4) -1,556 (5) -1,995 ( 5 ) -2,438 (5) - 2,399 (7) -1,895 (6) -1,447 (6) -1,499 (6) -2,793 ( 5 ) -2,971 (6) -3,541 (6) -3.892 (7) -3,738 (5) -3,173 (5) -923 (5) - 1 ,252 (6) -1,175 (7) -717 (7) -342 (6) -447 (7) -420 (4) -151 (6) 343 (6) 555 (5) 278 ( 5 ) -214 (5)
T
z
PI1
822
-8114 (10) 1453 (4) 2934 (6) -2833 (4) -2667 (4) 753 (19) 756 (14) 992 (16) 1614 (15) -4706 (12) -4379 (12) -2865 (14) -2271 (16) -2307 (19) - 2847 (19) -3391 (17) -3387 (15) -2761 (15) -1691 (18) -1658 (19) - 2806 (22) - 3876 (20) -3888 (20) -2211 (13) -1175 (17) - 876 (25) -1532 (19) -2519 (22) -2847 (20) -3361 (13) -2378 (18) -2928 (20) -4432 (20) -5345 (15) -4882 (15)
Psi 655 (8) 76 ( 5 ) 139 (7) 79 (4) 72 (4) 216 (24) 101 (15) 91 (20) 1C8 (19) 88 (18)
59 (15) 81 (18) 135 (22) 182 (28) 171 (27) 179 (24) 150 (21) 109 (20) 194 (29) 224 (30) 272 (38) 207 (34) 215 (33) 96 (17) 152 (29) 249 (33) 214 (31) 295 (39) 223 (31) 83 (17) 169 (26) 247 (33) 228 (31) 154 (25) 106 (20)
812
-29 -19 -59 -3 -2 -36 -19
(6) (3)
(4) (2) (2) (9) (6) -5 (8) - 10 (7) -9 (7) -4 (8) 6 (7) - 3 (7) -11 (IO) -9 (10) 22 (9) 2 (9) 10 (7) 4 (9) 29 (11) 36 ( 1 3) -12 (9) -11 (9) 2 (9) -2 (9) 3 (11) -7 (10) -31 (10) 13 (IO) -13 (7) 3 (8) 20 (9 1 (8)
2 (10) 10 (9)
PI3
19 (17) -16 (7) 67 (8) -3 ( 5 ) 3 (5)
5 (36) 48 (22) 4 (25) - 22 (21) 15 (19) 4 (17) -8 (22) - 20 (23) 1 (27) -32 (27) - 24 (25) 0 (23) 33 (20) 60 (28) 40 (32) 202 (42) 38 (34) 34 (32) 33 (26) -58 (26) -65 (40) -30 (29) -3 (34) -23 (29) -14 (19) 3 (25) 22 (31) -115 (31) - 29 (30) - 37 (23)
893
45 (9) -5 (3)
-4 (6) -2 (3) 4 (3) -12 (19) 42 (13) -17 (14) 8 (12) 7 (9) -17 (13) -12 (11) 4 (14) 2 (19) -29 (18) -24 (16) -31 (15) 3 (12) 22 (17) 19 (19) 31 (21) -33 (16) -29 (16) -6 ( 1 1 ) 49 (16) 46 (26) -11 (19) - 27 (20) -9 (19) - 10 (10) 16 (16) 13 (17) 24 (16) 30 (12) 34 (13)
a All values are X lo4except for Pd which is x 105. The estimated standard deviations are given in parentheses. The temperature factor is of the form exp[-(31,A2 @2?k2 8 d 2 + P l 2 h k f P 1 3 M P&)l.
+
+
Table V. The Final Parameters of Nonhydrogen Atoms in Pd(dpp)(NCS)p
Atom
Y
X
25,000 ( 0 ) b 42,325 (8) 31,922 (5) 3,057 (2) 3,544 (2) 3,362 (2) 2,500 ( 0 ) b 2,590 (2) 1,906 (2) 1,436 (2) 1,649 (3) 2,323 (3) 2,789 (3) 4,337 (2) 4,658 (2) 5,541 (3) 6,079 (2) 5,763 ( 2 ) 4,891 (2)
Z
15,164 (4) --18,429 (10) 32,522 (8) -47 (3) -791 (3) 4,961 (4) 5,837 (6) 3,670 (3) 2,727 (4) 3,043 (5) 4,266 (5) 5,197 ( 5 ) 4,897 (4) 2,678 (4) 2,739 (5) 2,271 (6) 1,734 (5) 1,677 (5) 2,129 (4)
411
a22
861 ( 5 ) 1209 (13) 889 (11) 102 (4) 80 (4) 99 (4) 93 (6) 109 (4) 149 ( 5 ) 226 (7) 209 (7) 137 (6) 113 (5) 106 (4) 194 (6) 272 (8) 210 (7) 187 ( 6 ) 173 ( 5 )
0 (O)b 13,507 ( 5 ) 6,134 (3) 614 (1) 923 (1) 204 (2) 0 (O)*
1,295 (1) 1,454 (2) 1,977 (2) 2,333 (2) 2,180 (2) 1,657 (2) 888 (1) 1 ,520 ( 2 ) 1,714 (2) 1,275 ( 2 ) 648 (2) 451 (2)
833
Bl?
0 (O)b 232 (13) -148 (10) 1 (4) -25 (4) -27 ( 5 ) 0 (O)b 8 (4) -22 (5) -25 (6) 43 (7) 15 (6) -14 (5) -25 (4) -3 ( 5 ) 4 (7) 2 (6) -2 (6) -9 (5)
813
a23
-
All values are X l o 4except for Pd, S , and P which are x 105. The estimated standard deviations are given in parentheses. The temperature factor is of the form exp[-(Pil/z2 P22k2 p Z z P P12hk /313/~1 /3&r)]. Parameters defined by space group symmetry.
-+
+
+
+
+
the three ligands will have similar electronic properties, t h e steric requirements are different, and a clear separation of steric and electronic effects is possible. A truly remarkable trend was found in t h e structures of these three compounds, namely, t h a t t h e mode of thiocya n a t e coordination changes from S,S for n = 1, t o S,N for n = 2, and to N,N for n = 3-a d r a m a t i c demonstration t h a t t h e mode of bonding of the thiocyanate ion to palladium is controlled by steric considerations. Since Pd(I1) is considered a “soft” metal ion3-6 a n d sulfur is a “soft” base. t h e
Journal of the American Chemical Society
/
97:5
primary mode of bonding of thiocyanate t o Pd(I1) will be via t h e sulfur end. However, since t h e M-S-C angle is usually about 110’ compared t o 180’ for M-N-C (the Nbonded variety), there are larger steric requirements for t h e S-bonded ion. Therefore, when n = 1 and either N- or Sbonded groups c a n be accommodated, t h e fact t h a t both ions a r e S-bonded is not surprising. In fact, one thiocyanate is tipped 23.7’ out of t h e coordination sphere (vide infra) yet t h e g r o u p still remains S bonded. Now a s t h e alkyl chain length increases t h e steric factors become dominant
/ March 5 , I975
1063 Table VIII. Final Parameters of Hydrogen Atoms in Pd(dDD)(NCS)na
Table VI. Final Parameters of Hydrogen Atoms in Pd (dpm)(SCN)f
429 379 412 500 439 336 243 548 656 502 229 123 54 22 27 177 191 - 24 - 25 200 374 374
125 177 130 186 265 285 229 95 18 -40 - 27 40 146 206 287 297 233 67 -5 - 22 44 100
318 316 770 976 886 621 426 597 765 718 590 407 - 190 - 353 -295 -2 170 -22 - 221 - 201 -116 47
5.7 5.1 6.2 7.4 7.5 7.5 6.7 6.7 7.0 7.5 7.6 6.3 5.9 6.7 6.8 6.3 6.5 6.6 8.8 8.0 7.1 5.7
1.ll 1.02 0.91 1.08 1.04 1.06 1.07 0.99 1.06 1.12 1.14 1.14 1.01 0.90 1.13 1.01 1.01 1.01 1.18 1.25 0.98 0.89
The positional parameters are X lo3.The number in parentheses is the number of the carbon atom to which the hydrogen atom is bonded at a distance given in the last column. a
Atom
X
Y
Hl(3) H2(3) Hl(4) H(2a) H(3a) H(4a) H(5a) H(6a) H(2b) H(3b) H(4b) H(5b) H(6b)
378 370 235 176 87 129 250 325 426 577 669 616 466
552 469 651 179 237 464 621 559 316 240 141
Z
49 - 16
131
38 122 205 264 243 153 183 218 140 33
202
-1
B(A2)
Distance (A)
4.7 4.7 5.5 4.6 5.4 5.9 5.9 5.1 5.2 6.3 5.9 5.6 5.0
0.96 0.99 1.05 1.01 1.06 0.94 1.09 0.99 0.99 1.03 0.96 1 .oo 1 .oo
a The positional parameters are X lo3.The number in parentheses is the number of the carbon atom to which the hydrogen atom is bonded at a distance given in the last column. A
C
A
Table VII. Final Parameters of Hydrogen Atoms in Pd(dpe)(NCS) (SCN)a
- 101
- 209
-154 15 38 - 305 - 501 - 579 -477 - 305 15 41 - 36 - 188 - 255 121 304 380 290 104 - 186 - 259 - 232 - 86 9
-151 - 141 - 197 -284 - 260 - 185 - 107 -116 -271 - 352 - 430 -402 - 314 - 160 -152 - 52 -2
- 20
- 30
44 76 44 - 33
-553
- 524 - 540 -407
-171 - 177 - 279
-411 - 357 - 170 - 74 - 217 -456 -422 - 59 - 30 -125 - 294 - 337 -112 - 282 -485 -641 - 574
6.2 6.2 5.4 5.4 5.6 4.0 5.4 6.0 5.5 6.8 5.7 6.5 5.0 7.2 6.0 8.2 6.8 7.2 5.6 5.6 5.8 7 .O 6.5 6.1
1.06 0.88 1 .00 1.21 1.25 0.94 1.16 1.17 0.95 1.23 1.29 1.08 1.07 1.15 1.06 1.15 1.18 0.96 1.01 1.28 1 .oo 1.06 1.01 1.21
Figure 1. A view of dpmPd(SCN)>approximately normal to the coordination plane showing the atomic numbering and pertinent bond distances and angles. The phenyl rings are labeled A, B, c, and D, and individual numbering has been omitted for clarity.
The positional parameters are X lo3.The number in parentheses is the number of the carbon atom to which the hydrogen atom is bonded at a distance given in the last column.
and t h e m o d e of bonding changes from S,S t o S,N a n d finally t o N , N . This trend parallels t h e steric changes in t h e phenyl groups (vide supra) and is strictly a steric effect. Before any further discussion of t h e factors influencing t h e coordination mode of thiocyanate ion, we should conside r t h e Pd-P, Pd-S, a n d Pd-N distances a n d t h e evidence for x-bonding between the palladium and phosphorus atoms. A compilation of Pd-P bond distances a s a function of t h e trans atom is given in T a b l e XI. We see t h a t t h e longest Pd-P distances occur when P is t r a n s t o P. However, t h e usual problem of separating steric f r o m electronic effects is present. For example, in t h e complex with t h e con-
d
5(2)
Figure 2. A view of the dpePd(SCN)(NCS) approximately normal the coordination plane showing the atomic numbering and pertinent bond distances and angles. Note the movement of the four phenyl rings A, B, C, and D relative to Figure 1 which illustrates the changing steric requirements of the ligand.
strained ligand Ph2PN(C2H5)PPh* t h e Pd-P distances of 2.219 (4) a n d 2.228 (4) A23 a r e significantly shorter t h a n t h e distance of 2.260 (2) A24 found in t h e complex with t h e transbulkier PhP(CH3)z ligand. Similarly, in 12Pd[PhP(CH3)2]2 complexes t h e P I contacts range
Palenik. Mathew, Steffen, Beran
---
/ Palladium- Thiocyanate Complexes
1064 Table IX. Bond Lengths and Angles not Given in Figures 1-3
Pd(dpm)(SCN)*
Pd(dpe)(NCS)(SCN)
Pd(dpp)(NCS), ~~
(a) Bond Lengths (A) 1.804 ( 6 ) 1.772 (13) 1.803 (6) 1.804(11) 1.803 (6) 1.750 (14) 1.837 (11)
1.812 (6)
Y Figure 3. A view of dppPd(NCS)* approximately normal to the coordination plane. The molecule has a twofold axis of symmetry through Pd and C4 and hence the atoms P, P‘, Pd, N , and N’ are required to be coplanar. The phenyl rings A and B are in approximately the same orientation as the C, D rings in the dpePd(SCN)(NCS) complex but the A’, B’ rings have moved relative to the A, B rings in the dpe case. The movement of the phenyl rings is related to the steric factors in the three ligands.
from 3.414 to 3.523 A30 which is significantly shorter t h a n a van der Waals contact of 4.05A, and a n y c ecrease in t h e I disP d - P distance would produce intolerably short P tances. Unfortunately, t h e trends in steric factors parallel those of a-acceptor properties, and a separation of these effects is virtually impossible. However, before further discussion of a-effects, we might consider t h e P d - S distances in various molecules. Arguments have been g i ~ e n t~h a- t~t h e a-acceptor properties of phosphines changed t h e character of t h e palladium a t o m so t h a t “soft-soft’’ interactions were no longer preferred. Presumably in the case of t h e thiocyanate ion the sulfur atom will not compete effectively with the phosphorus a t o m for t h e d orbitals of t h e palladium a t o m a n d , therefore, t h e nitrogen end bonds t o t h e metal a t o m . Although t h e present study has demonstrated that steric effects will control t h e mode of thiocyanate coordination, a survey of Pd-S distances is informative. A number of Pd-S distances have been summarized in Table X I I . While t h e Pd-S trans to a P a t o m is longer t h a n Pd-S trans to a N a t o m , t h e Pd-S trans to a S a t o m is very similar to Pd-S trans to a P atom. There appears to be a strong steric influence in t h e Pd-S bond lengths. Nevertheless, a reasonable conclusion from t h e d a t a in T a b l e XI1 is that either there is no d-d a-bonding in t h e Pd-S case or t h a t the s a m e amount of a-bonding exists regardless of the nature of the trans atom. A third possibility, t h a t d-d a-bonding does not appeciably alter t h e bond length, would require rationalizing t h e P d - P bond distances on t h e basis of steric arguments. T h e tip of the S C N group has been included in Table XI1 and we find very little correlation between the Pd-S distance and the tip of t h e thiocyanate ion. Unfortunately, t h e absence of a correlation between t h e tip of t h e thiocyanate ion and the Pd-S distance cannot be used to exclude a-bonding in the Pd-S bond. T h e possibility exists t h a t a tip of t h e thiocyanate decreases K-bonding in one direction and increases a-bonding in another direction. T h e net result is t h a t t h e total overlap is independent of t h e tip. T h e experimental evidence gives no definitive proof for or against Kbonding in t h e P d - S bond. However, t h e variations in t h e Pd-S bond lengths c a n be explained on t h e basis of a a-effect related to the trans a t o m a s well as steric constraints. A compilation of P d - N distances in T a b l e XI11 shows a variation in the P d - N bond which is dependent on both ste-
-
Journal of the American Chemical Society
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Pd-P( 1)-C( la) Pd-P( 1)-C( 1b) C(ring)-P( 1 ) C (1a) C(ring)-P( 1)-C( 1b) C( 1a)-P( 1)-C( 1b) Pd-P(2)-C(lc) Pd-P(2)-C( 1d) C(ring)-P(Z)-C(IC) C(ring)-P(2)-C( Id) C( lc)-P(2)-C( Id)
1.808 (3) 1.813 (3)
(b) Bond Angles (deg) 119.1 111.4
114.9 108.3 109.3 108.2
112.9 108.0 106.1
121.5
116.9
107.3
116.9 107.4 108.0 106.5
112.5
109.8 107.3 103.7 108.7
112.0
106.0 105.1
109.1
ric factors and the n a t u r e of t h e trans a t o m . In this case t h e difference between a nitrogen trans to a phosphorus vs. nitrogen trans to a nitrogen is only a b o u t 0.03 8, compared to the P d - P case, where t h e difference was a b o u t 0.08 A. T h e difference between t h e variation of P d - P and P d - N bonds vs. t h e trans atom probably lies in t h e more polarizable nat u r e of t h e P a t o m . T h e importance of t h e ligand geometry is nicely illustrated by t h e differences in P d - N distances in t h e Pd[Me2dpma]CI+Cl- complex34 where t h e P d - N trans to N is one of the longest observed to date, while t h e P d - N trans to CI is one of t h e shortest. These P d - N distances a r e particularly noteworthy since C1 and pyridine a r e almost identical in their trans e f f e ~ t . Furthermore, ~~.~~ t h e N(sp3) radius is expected to be larger t h a n t h a t of N(sp2) which predicts a shorter Pd-N(py) distance compared to PdN ( a m i n e ) . T h e effect of ligand geometry is also important in the Pd [ (CH3)2N (CH2)lPPh2] ( S C N ) ( N C S ) complex. T h e P d - N (of t h e N ( C H 3 ) 2 group) is extremely long compared to t h e other P d - N distances and t o t h a t in Pd(H2NCH2CH2”2)2’+ cation. T h e question is whether t h e lengthening is a trans effect or a steric effect.4’ In the case of t h e C u [ ( C H 3 ) 2 N C H 2 C H 2 N H 2 I 2 + cation t h e C u - N (to CH3 end) is 2.083 (3) A while C u - N (of the N H 2 end) predominantly a steric effect. Therefore, is 1.995 (3) & I C the long P d - N distance in Pd[(CH,)N(CH2)3PPh2]( S C N ) ( N C S ) must result in part from a steric effect of the - N ( C H 3 ) 2 group. This conclusion is important in explaining the N - and S-bonded thiocyanate ions reported in this complex.
Conclusions T h e structural studies reported in this paper together with other studies suggest t h a t steric factors a r e t h e prime reason for the change from S-bonded t o N-bonded thiocyTable X. Summary of Average Estimated Standard Deviations for Bond Lengths and Angles not Given in Figures 1-3
s-c
Pd(dpm)-
Pd(dpe)-
(SCN)?
(NCS)(SCN)
(a) Esd for Bond Lengths,
c-c
0 0 0 0
Pd-P-C S-C-N P-c-c c-P-c
(b) Esd for Angles (deg) 0 4 0 8 1 3 0 5 0 9 0 3 0 5
P-c
N-C
c-c-c
March 5, 1975
008 006
012 011
0 0 0 0
013 012 017 020
0 2
0 7
1 3
(A)
0.003 0.003 0,004 0.005
0.1 0.3 0.2 0.15
0.35
1065 Table XI. A Compilation of Pd-P Bond Distances as a Function of the Trans Atom ~~
Pd-P distance (A)
Atom/group trans to P
2.241 (1) 2.243 (3) 2.243 (2) 2.247 (2) 2.259 (3) 2.265 (3) 2.219 (4) 2.228 (4) 2.260 (2) 2.258 (3) 2.264 (2) 2.282 (2) 2.270 (6) 2.278 (6) 2,270 (2) 2.312 (1) 2.317 (3) 2.318 (1) 2.326 (3) 2.333 (7)
N/NCS N/NCS NiNCS N/NCS (bridge) N/tetrazole N/tetrazole
Coordination sphere
Ref This work This work 12 21 22 22 23 23 24 This work This work This work 25 25 21 26 27 28 29 30
CI
CI c1 SjSCN SjSCN SjSCN SjSCN SjSCN S/SCN (bridge) Piligand Cir-bond P/ligand Piligand Piligand
Table XII. A Compilation of Some Pd-S Bond Distances as a Function of the Trans Atoma
Pd-S distance (A) 2 2 2 2 2 2
392 (9) 371 (6) 369 (6) 366(2) 362 (2) 364 (4) 2 359 (1) 2 340(1) 2 351 (1) 2 352 (2) 2 347 (1) 2 342(1) 2 336 (3) 2 312(9) 2 299 (2) 2 295 (2) 2 28 (1)
Atomigroup trans to S
Tip of SCN (deg)
SjSCN P/ligand P/ligand P/ligand P/ligand Piligand
74.8 24.5 52.6 5.8 23.7 19.6
Coordination sphere
Compound
25 25 This work This work This work 28 28 28 26 28 28 29 31 32 9 33
S[SCN
SjSCN SjSCN SjSCN S/ligand S/ligand SjSCN SjSCN Siligand Niligand
Ref 31
74.3 48.9 45.3 74.0 17.5 9.8
Cl
If the distance involves a thiocyanate group, the tip of the thiocyanate group from the coordination sphere is also listed. Table XIII.
A Compilation of Some Pd-N Distances as a Function of the Trans Atom
Pd-N Distance (A)
2 148 (7) 2 068 (6) 2 063 (7) 2 062 (10) 2 055 ( 3 ) 2 036 (7) 2 032 (3) 2 031 ( 2 ) 2 022 (7) 2 018 (8) ‘I
Atom/group trans to N
Compound
Ref
Pd[PhzP(CHz)zN(CH3)z](SCN)(NCS) CIPd[Mezdpma]+C1Pd[PhzP(CHz),N(CH,Xl(SCN)(NCS) Pd[Ph,PCHzCHzPhzl(SCN)(NCS) Pd[Ph:P(CHr)zPPhz](NCS)z Pd[HzNCHsCHzNHz]z2T2C1Pd[N-isopropyl-3-methylsaljcylaldiminato]~ Pd[N-isopropyl-3-ethylsalicylaldiminato]~ Pd[2,2’-dipyridyliminato]~ CIPd[Merdpma]+C1- a
NjSCN N ligand
P/ligand Pi ligand PI1igand N/ligand N/ ligand
N/llgand N’ligand CI
12 34 12 This work This work 35 36 37 38
34
Me?dpma 17 rnetliyldi[(6-methyl-2-pyridyl)metliyl]amine
a n a t e in palladium complexes. T h e importance of steric factors had been recognized earlier,8 but these results were not generalized to the phosphine case and, unfortunately, have also tended to be ignored. T h e changing mode of coordination of the thiocyanate ion in the series of complexes Pd[Ph2P(CHz),,PPhz](CNS)2, n = 1-3, is most easily explained in terms of a n increasing steric effect. A similar series of complexes P d [ c i s - P h z P C H = C H P P h z ] (SCN)z,42 Pd [cis-Ph2PCH=CHAsPhz] (N C S ) ( S C N ) , 4 3 and Pd [cisP h z A s C H = C H A s P h z ] (SCN)243 can also be easily rationalized on the basis of steric arguments.44 Finally, the preparation and characterization of trans-Pd[P(OPh)3]2-
(SCN)2,26 trans-Pd[P(CH3)2CsF~]2(SCN)2,~~ and Pd[SP(Ph2)CH2CH2(Ph2)PS](SCN)22xhave shown t h a t S-bonded thiocyanates in the coordination sphere a r e possible even if other “soft” ligands a r e bonded to the Pd atom. These results suggest t h a t antisymbiosis in palladium complexes m a y actually represent steric effects and should be reconsidered, a t least in the palladium case. A second important conclusion from this study involves the role of 7r-bonding in t h e trans effect. O u r results suggest t h a t t h e variation in bond lengths a s a function of t h e trans atom is not a x-effect transmitted across t h e metal atom. This conclusion is similar to t h a t reached by 0 t h e r s ~ O 3in ~~
Palenik, Mathew, Steffen, Beran
/
P a l l a d i u m - Thiocyanate Complexes
1066 the Case O f P t ( I I ) complexes. In fact our results can be most interpreted in terms Of no x-interactions between phosphine and sulfur ligands and metal, in agreement with the nmr results.']
Acknowledgments.
we are grateful
for a D~~~~~~~~~of
Chemistry Postdoctoral Fellowship (M.M.), a G r a d u a t e Fellowship (w'L's')' and a grant Of computer time from the Northeast Regional D a t a Center a t the University of Florida (G.J.P.). T h e preliminary stages of this research were supported in part by a grant from the National Research Council of C a n a d a (G.J.P.). Supplementary Material Available. A table of the distances and angles in the phenyl rings of the diphosphine ligands together with a comparison of the observed and calculated structure factor amplitudes will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the supplementary material from this paper only or microfiche (105 X 148 mm, 24X reduction, negatives) containing all of the supplementary material for the papers in this issue may be obtained from the Journals Department, American Chemical Society, 1155 16th St., N.W., Washington, D.C. 20036. Remit check or money order for $6.00 for photocopy or $2.00 for microfiche, referring to code number JACS-75- 1059.
References and Notes (a) Center for Molecular Structures, Department of Chemistry, Universi-
ty of Florida, (b) Taken in part from the M.S. Thesis of W.L.S., University of Florida, 1972. (c) Taken in part from the M.S. Thesis of G.B., University of Waterloo, 1971. A. H. Norbury and A. I. P. Sinha, Quart, Rev., Chem. SOC.. 24, 69 (1970). R. G. Pearson, "Hard and Soft Acids and Bases," Dowden, Hutchinson and Ross, Inc., Stroudsberg, Pa., 1973, contains a reprint collection of pertinent references. A. Turco and C. Pecile, Nature(London), 191, 66 (1961), first introduced the idea of ligand control of the mode of thiocyanate coordination. A. H. Norbury, J. Chem. SOC.A, 1089 (1971). R. G. Pearson. lnorg. Chem., 12, 712 (1973). J. L. Burmeister and F. Basolo, lnorg. Chem., 3, 1587 (1964). F. Basolo. W. H. Baddley, and J. L. Burmeister, horg. Chem.. 3, 1202 (1964). D. W. Meek, P. E. Nicpon, and V. I. Meek, J. Amer. Chem. Soc., 92, 5351 (1970). have reviewed much of the older literature and the data available up to that time. Numerous authors in the period from 1964 to about 1970 have quoted the *-bonding arguments as important in controlling thiocyanate coordination. Rather than give a large number of references, the reader is referred to references cited in 4, 5, 9, and 14. (11) L. M. Venanzi. Chem. Brit., 3, 162(1968). (12) G. R. Clark and G. J. Palenik, lnorg. Chem., 9, 2754 (1970). (13) G. Beran and G. J. Palenik, Chem. Common., 1354 (1970).
Journal of the American Chemical Society
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(14) G. J. Palenik, W. L. Steffen, M. Mathew, M. Li, and D. W. Meek, lnorg. Nucl. Chem. Lett., 10, 125 (1974). 9 (15) D, T, Cromerand D, Liberman, J, Chem, phys,, 53, 1891 (1970). (16) W. c. Hamilton, Acta Crysta//ogr.. 18,502 (1965). (17) D. T. Cromer, A. C. Larson, and J. T. Waber. Acta Crystallogr., 17, 1044 (1964). (18) H. P. Hanson. F. Herman. J. D. Lea, and S. Skillman, Acta Crystabgr., 17, 1040 (1964). (19) R. F. Stewart, E. R. Davidson, and w. T. Simpson. J. Chem. fhys., 42, 3175 (1965). (20) See paragraph at end of paper regarding supplementary material. (211 . . D. v. Naik. G. J. Palenik, S. Jacobson, and A. J. Carty, J. Amer. Chem. Soc., 96, 2286 (1974). (22) G. B. Ansell, J. Chem. SOC..Dakon Trans., 371 (1973). (23) J. A. A. Mokuolu, D. S. Payne. and J. C. Speakman, J. Chem. SOC.,DaC ton Trans., 1443 (1973). (24) L. L. Martin and R. A. Jacobson, lnorg. Chem., 10, 1795 (1971). (25) R . T. Simpson, S. Jacobson, A. J. Carty, M. Mathew. and G. J. Palenik, J. Chem. SOC.,Chem. Commun., 388 (1973). (26) S. Jacobson, Y. S. Wong, P. C. Chieh, and A. J. Carty, J. Chem. SOC., Chem. Commun., 520 (1974). (27) R . Mason and P. 0. Whimp, J. Chem. SOC.A, 2709 (1969). (28) W. L. Steffen. M.S. Thesis, University of Florida, 1972. (29) G. Beran, A. J. Carty, P. C. Chieh, and H. A. Patel, J. Chem. Soc.,Dalton Trans., 488 (1973). (30) N. A. Bailey and R. Mason, J. Chem. SOC.A, 2594 (1968). (31) A. Mawby and G. E. Pringle, J. lnorg. Nucl. Chem., 34, 2213 (1972). (32) M. J. Bennet, F. A. Cotton, D. L. Weaver, R. J. Williams, and W. H Watson, Acta Crystallogr., 23, 788 (1967). (33) N. C. Stephenson, J. F. McConnel, and R. Warren, lnorg. Nucl. Chem. Lett., 3, 554 (1967). 134) . . M. G. B. Drew, M. J. Riede. and J. Rodgers, J. Chem. SOC., Dalton Trans., 234 (1972). (35) J. R. Weiner and E. C. Lingafeiter, lnorg. (:hem.,5, 1770 (1966). (36) P. C. Jain and E. C. Lingafelter, Acta Crystallogr., 23, 127 (1967). (37) R. C. Braun and E. C. Lingafelter, Acta Crystallogr.. 22, 787 (1967). 138) H. C. Freeman and M. R. Snow. Acta Crv.;tal/oor.. 18. 843 11965). t39j F. Basoio and R . G. Pearson,' "Mechahms \f' Inorganic Reactions," 2nd ed. Wiley, New York, N.Y. 1967, p 355, give CI- > py in the trans effect. (40) T. G. Appleton, H. C. Clark, and L. E. Manzer, Coord. Chem. Rev., 10, 335 (1973), have reviewed the measurement and significance of the trans influence. The results presented by these authors suggest that CII py in the trans influence. (41) The concept of the "ligand cone angle" has been developed by C. A. Tolman, J. Amer. Chem. SOC.,92, 2956 (1970), and these values for several phosphines have been determined. However, the bulkiness of the dimethylamino group is apparently not appreciated. A comparison of the C-P-C bond angles of 99.1' in P(CH& vs. the C-N-C bond angles of 108.7' in N(CH& gives some estimate of the relative size of the two compounds. in addition to the dependence of the ligand cone angle on the internal bond angles, the effect of the metal-ligand distance must be included. Since M-N bonds are invariably shorter than M-P bonds, the so-called ligand cone angle must again increase. (42) K. K. Chow and C. A. McAuliffe, lnorg. Nucl. Chem. Lett., 8 , 1031 (1972). (43) K. K. Chow and C. A. McAuliffe, private communication. (44) One must remember that the ligands are rigid and that As is larger than P. In the mixed complex the ligand must be tipped (relative to the P,P case) toward the coordination site trans to As. Therefore, the three ligands have different steric requirements. (45) W. A. Gregory, J. A. J. Jarvis, B. T. Kilbourn, and P. G. Owston. J. Chem. SOC.A, 2770 (1970).
March 5, I975
