Evaluation of the Stereoelectronic Parameters of Fluorinated

Organometallics 2001, 20, 3429-3435

3429

Evaluation of the Stereoelectronic Parameters of Fluorinated Phosphorus(III) Ligands. The Quantitative Analysis of Ligand Effects (QALE) Anthony L. Fernandez, Matthew R. Wilson, Alfred Prock,* and Warren P. Giering* Department of Chemistry, Metcalf Science and Engineering Center, Boston University, Boston, Massachusetts 02215 Received January 24, 2001

Using the QALE model, we determined the QALE stereoelectronic parameters for the following ligands: P(CF3)3 (χd ) 33 ( 2, θ ) 137 ( 13°, Ear ) 0, πp ) 11.1 ( 0.6), P(CH2CH2C6F13)3 (χd ) 9 ( 3, θ ) 137 ( 2°, Ear ) 0, πp ) 2.5 ( 0.4), P[p-(F13C6)C6H4]3 (χd ) 23 ( 1, θ ) 145°, Ear ) 2.7, πp ) 0), and P(C6F5)3 (χd ) 34 ( 2, θ ) 191 ( 13°, Ear ) 4.3 ( 0.5, πp ) 0). In addition, we evaluated the parameters for P[Pyr-3,4-(CO2Et)2]3 (Pyr ) pyrrolyl; χd ) 43 ( 2, θ ) 145°, Ear ) 3.3, πp ) 2 ( 1). Revised parameters for PF3 are also presented: χd ) 33 ( 2, θ ) 110 ( 24°, Ear ) 0, πp ) 13.2 ( 0.5. The absence of an indicated error means that these values were assigned initially to the particular parameters in the analyses or that the parameters are statistically indistinguishable from zero. Where a comparison can be made, we find that our calculated values of θ are indistinguishable from those of Tolman; therefore, we suggest the continued use of Tolman’s values. It is observed that the perfluoroalkyl groups are highly π acidifying and that this effect is transmitted through intervening CH2 groups. Introduction There has been an explosive growth of the application of fluorinated phosphorus(III) ligands in biphasic catalysis.1-9 The coordination of ligands such as P(CH2CH2C6F13)3 imparts solubility in liquid and supercritical CO2 as well as fluorocarbon solvents.10 Furthermore, the electron-withdrawing effects of the C6F13 group should increase the oxidative stability of the phosphine, while the ethylene group tends to insulate the phosphorus atom from the extreme electron-withdrawing effects of the C6F13 group.10 The relative inertness of the C-F groups further enhances the stability of the ligand.10 It has been observed that the electronic effect of the fluoroalkyl group on the ligating atom can be “finetuned” by varying the number of CH2 groups between the phosphorus atom and the fluoroalkyl groups.11,12 (1) Richter, B.; Spek, A. L.; van Koten, G.; Deelman, B. J. J. Am. Chem. Soc. 2000, 122, 3945. (2) Richter, B.; de Wolf, E.; van Koten, G.; Deelman, B. J. J. Org. Chem. 2000, 65, 3885. (3) Barthel-Rosa, L. P.; Gladysz, J. A. Coord. Chem. Rev. 1999, 190192, 587. (4) Lindner, E.; Schneller, T.; Auer, F.; Mayer, H. A. Angew. Chem., Int. Ed. 1999, 38, 2154. (5) Fish, R. H. Chem. Eur. J. 1999, 5, 1677. (6) Juliette, J. J. J.; Rutherford, D.; Horvath, I. T. G. J. Am. Chem. Soc. 1999, 121, 2696. (7) Sinou, D.; Pozzi, G.; Hope, E. G.; Stuart, A. M. Tetrahedron Lett. 1999, 40, 849. (8) Bhattacharyya, P.; Goodmunsen, D.; Hope, E. G.; Kemmitt, R. D. W.; Paige, D. R.; Sturat, A. M. J. Chem. Soc., Perkin Trans. 1 1997, 24, 3609. (9) Palo, D. R.; Erkey, C. Organometallics 2000, 19, 81. (10) Stibrany, R. T.; Gorun, S. M. J. Organomet. Chem. 1999, 579, 217. (11) Rocaboy, C.; Bauer, W.; Gladysz, J. A. Eur. J. Org. Chem. 2000, 14, 2621.

It has long been thought that pendant fluoro- or trifluoromethyl groups impart unusual stereoelectronic properties to the phosphorus(III) ligands.13 For example, fluorine directly attached to phosphorus is thought to make PF3 a π acid comparable to CO.14 Indeed, we recently reported that the π acidity of PF3 is almost 3 times that of PCl3 and 5 times that of P(OR)3 (R ) alkyl).14,15 We now extend our evaluation of the stereoelectronic properties of phosphorus(III) ligands to the series of fluorinated ligands P(CF3)3, P(CH2CH2C6F13)3, P[p-(C6F13)C6H4]3, and P(C6F5)3. We also include an evaluation of the stereoelectronic properties of P[Pyr3,4-(CO2Et)2]3 (Pyr ) pyrrolyl) as well as a reassessment of the stereoelectronic properties of PF3. Methodology Recently, we reported our method for determining the stereoelectronic parameters of phosphorus(III) ligands.14 In the QALE model, each physicochemical property is described by its own QALE equation (e.g., eq 1) in terms of the stereoelec-

prop ) aχd + b(θ - θst)λ + cEar + dπp + e

(1)

tronic parameters of the phosphorus(III) ligands.15,16 In these equations, χd is the σ donor capacity of the ligand, θ is Tolman’s (12) Alvey, L. J.; Meier, R.; Soos, T.; Bernatis, P.; Gladysz, J. A. Eur. J. Inorg. Chem. 2000, 9, 1975. (13) Grobe, J.; Le Van, D.; Meyring, W. Z. Anorg. Allg. Chem. 1990, 586, 149. (14) Woska, D.; Prock, A.; Giering, W. P. Organometallics 2000, 19, 4629. (15) Fernandez, A. L.; Reyes, C.; Prock, A.; Giering, W. P. J. Chem. Soc., Perkin Trans. 2 2000, 1033. (16) Fernandez, A. L.; Reyes, C.; Wilson, M. R.; Woska, D. C.; Prock, A.; Giering, W. P. Organometallics 1997, 16, 342.

10.1021/om010057+ CCC: $20.00 © 2001 American Chemical Society Publication on Web 06/23/2001

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Organometallics, Vol. 20, No. 16, 2001

Fernandez et al.

Table 1. Stereoelectronic Parameters of Phosphorus(III) Compounds (PZ3, Z ) Any Pendant Group)a no.

PZ3

χdb

θc

Eard

πpe

no.

PZ3

χdb

θc

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69

PH3 PMeH2 P(OCH2)3CEt P(Oct)H2 PBuH2 P(CF3)H2 PF3 P(i-Bu)H2 PPhH2 P(OMe)3 PMe2H P(OEt)3 PMeF2 P(OBu)3 P(OPr)3 P(OCH2CH2Cl)3 PMe(OEt)2 PMe2F PMe2(OEt) PCyH2′ P(CH2CH2CN)2H PMe3 P(t-Bu)H2 P(Oct)2H PBu2H P[O(i-Bu)]3 P(OMe)2Ph PMe2Cl PH(CF3)2 P(OEt)2Ph PPhMe2 PMeCl2 PMe2Et PMe2(CH2CH2CN) P(i-Bu)2H PMe2(CF3) PCl3 PPh2H PF(CF3)2 PMeEt2 PPrCl2 PMe(CH2CH2CN)2 P(O-p-MeC6H4)3 P(O-p-MeOC6H4)3 P(OC6H5)3 P(O-p-ClC6H4)3 PBuCl2 P(O-p-NCC6H4)3 P(CF3)Cl2 P(O-i-Pr)3 P(t-Bu)F2 PMe(CF3)2 P(p-MeOC6H4)Cl2 PPhCl2 PEt3 PMe2(i-Pr) PEt2(CH2CH2CN) PEt(CH2CH2CN)2 P(OMe)Ph2 P(CH2CH2CN)3 P(octyl)(CH2CH2CN)2 P(OEt)Ph2 P(OMe)2(C6F5) PCl(CF3)2 PPr3 PBu(CH2CH2CN)2 PPh(OC6H5)2 PMe(i-Bu)2 P(Oct)2(CH2CH2CN)

17 14.2 20.2 13 13.1 22.3 33 13.2 15.8 17.9 11.4 15.8 24.9 15.9 15.9 20.4 13.4 16.7 11 11.8 17 8.55 11.3 9 9.2 15.5 16.4 19.7 27.7 15 10.5 30.9 7.8 11.4 9.5 16.7 42 14.5 33 7.1 29.8 14.2 22.4 22.5 23.6 27.2 29.8 31.7 39 13.4 22 24.9 31.5 32.4 6.3 6.9 9.9 13.4 14.8 17 13 14.1 23.5 36 5.4 13.1 20.2 6.7 9

87 97 101 103 103 104 104 106 106 107 108 109 109 110 110 110 112 113 115 115 117 118 119 120 120 120 120 120 120 121 122 122 123 123 124 124 124 126 126 127 127 128 128 128 128 128 128 128 128 130 130 131 131 131 132 132 132 132 132 132 133 133 133 133 134 134 134 135 135

0 0 0.2 0 0 0 0 0 1 1 0 1.1 0 1.3 1.3 0.4 0.7 0 0.4 0 0 0 0 0 0 1.4 1.7 1.4 0 1.7 1 2.7 0 0 0 0 4.1 2 0 0 2.7 0 1.4 1.4 1.3 1.3 2.7 1 2.7 1.3 0 0 3.7 3.7 0 0 0 0 2.3 0 0 2.4 2.0 1.4 0 0 1.9 0 0

3.7 2.5 5 2.5 2.5 6.2 13.2 2.5 2.5 2.8 1.2 2.9 8.8 2.7 2.7 3.6 1.9 4.4 1 2.5 2 0 2.5 1.2 1.2 3 1.9 1.8 8.6 1.9 0 3.5 0 0.4 1.2 3.7 5.3 0.4 11.8 0 3.5 0.8 4.1 3.8 4.1 4 3.5 3.7 7.2 2.9 8.8 7.4 3.5 3.5 0 0 0.4 0.8 0.9 1.2 0.8 1 1.9 9.2 0 0.8 2.7 0 0.4

70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138

PBu2(CH2CH2CN) PEt(CF3)2 P(Pent)3 P(Octyl)3 PBu3 PPhEt2 PPh2Me PPh2Vi PPh(CH2CH2CN)2 P(CH2CH2C6F13)3 P(CF3)3 PPhPr2 PPh2Cl P(t-Bu)Me2 PPhBu2 PPh2(OC6H4) PPh2Et PPh2(CH2CH2CN) PMe2(C6F5) PPh2Pr PPh2Bu PPh2(CH2CH2C6F13) P(i-Bu)3 P(t-Bu)Cl2 PCy2H PCl2(C6F5) P(p-Me2NC6H4)3 P(p-MeOC6H4)3 PPh2(p-Me2NC6H4) P(p-MeC6H4)3 PCy(CH2CH2CN)2 PPh2(p-MeC6H4) PPh2(p-MeOC6H4) P(C6H5)3 PPh2(p-ClC6H4) P(p-FC6H4)3 PPh2[p-(F13C6)C6H4] P(p-ClC6H4)3 PPh[p-(F13C6)C6H4]2 PPh2(Pyr)f P(p-F3CC6H4)3 P[p-(F13C6)C6H4]3 PPh(Pyr)2f P(Pyr)3g P[Pyr-3,4-(CO2Et)2]3f PPh[Pyr-3,4-(CO2Et)2]2f PPh2[Pyr-3,4-(CO2Et)2]f P(NC4H8)3g P(m-MeC6H4)3 P(m-ClC6H4)3 PEt2(t-Bu)2 P(t-Bu)2H P(i-Pr)Ph2 P(i-Pr)2(CH2CH2C6F13) PPh2Cy PPh(i-Pr)2 P(t-Bu)2F P(CH2CH2CN)Cy2 PPh2(t-Bu) PPh2(C6F5) PCy2(CH2CH2C6F13) P(i-Pr3) PPhCy2 P(t-Bu)2Cl PCy3 PPh(C6F5)2 P(o-MeC6H4) P(t-Bu)3 P(C6F5)3

9.2 24.1 5 5 5.25 8.6 12.6 13.65 15.8 9 33 8 22.8 5.7 8.1 16.7 11.1 14.5 17.3 10.6 11.3 11.8 5.7 28 6.6 39.6 5.25 10.5 10.6 11.5 11.8 12.1 12.3 13.25 14.4 15.7 16.5 16.8 19.8 19.5 20.5 23 25.7 31.9 43 33.1 23.2 -1.2 11.3 19.6 4.2 5.7 9.6 5.3 9.1 10 11 6.6 8.8 20.4 3.9 3.45 5.7 14 1.4 27.6 10.65 0 34.8

135 135 136 136 136 136 136 136 136 137 137 138 138 139 139 139 140 140 140 141 142 142 143 143 144 144 145 145 145 145 145 145 145 145 145 145 145 145 145 145 145 145 145 145 145 145 145 146 148 148 149 150 150 152 153 155 156 157 157 158 159 160 162 163 170 171 178 182 184

Eard 0 0 0 0 0 1.1 2.2 1 0 0 1 3.4 0 1.3 2.4 2.3 2 1.4 2 2.1 2 0 2.7 0 4.1 2.7 2.7 2.7 2.7 0 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 3.1 2.7 2.7 3.2 3.3 3.3 3.2 3.1 -0.6 2.7 2.7 0 0 1.7 0 1.6 2 0 0 2 3.4 0 0 1.6 1.4 0 3.7 2.7 0 4.1

πpe 0.4 7.4 0 0 0 0 0 0 0.8 2.5 11.1 0 1.8 0 0 1.4 0 0.4 0 0 0 0.8 0 3.5 0.4 3.5 0 0 0 0 0.8 0 0 0 0 0 0 0 0 0.6 0 0 1.3 1.9 2 1.4 0.7 0.9 0 0 0 1.2 0 0.8 0 0 4.4 0.4 0 0 0.8 0 0 1.8 0 0 0 0 0

a The values in lightface type are taken from the literature, whereas the values in boldface are reported here for the first time. Ligands are listed in order of increasing cone angle. b χd values for the lightface phosphorus(III) compounds are taken from refs 14, 15, and 19-21 or calculated by additivity using the data found in these references. c Values for cone angles (θ, deg) for the lightface phosphorus(III) compounds are taken from ref 22 or calculated by additivity using the data found in these references. θ values for the pyrrolyl- and pyrrolidinylphosphines are taken from ref 21. d Ear values for the lightface phosphorus(III) compounds are taken from refs 14, 15, 20, and 21. e πp values for the lightface phosphorus(III) compounds are taken from refs 14, 15, and 21. f Pyr ) pyrrolyl. g NC4H8 ) pyrrolidinyl.

Stereoelectronic Parameters of Fluorinated P(III) Ligands

Organometallics, Vol. 20, No. 16, 2001 3431

Table 2. Systems, Properties, and Ligands from in the QALE Analyses Used to Determine the Coefficients a-e of Eqs 1 and 2 no.

syst

property

1

PZ3

2

Cr(CO)5(PZ3)

vertical ionization potentials νCO

3 4 5 6

trans-Cr(CO)4(PZ3)2 Cr(1,3,5-MeC6H3)(CO)2(PZ3) Fe(CO)4(PZ3) Fe(CO)3(PZ3)2

νCO νCO νCO -∆Hrx

7

Fe(CO)3(PZ3)2

νCO

8 9 10 11

Ir(CO)(Cl)(PZ3)2 Mn(Cp)(CO)2(PZ3) Mo(CO)5(PZ3) Mo(CO)4(PZ3)2

νCO νCO νCO νCO

12 13

νCO -∆Hrx

14

Mo(CO)3(PZ3)3 [(CO)2RhCl]2 +4 PZ3 ) 2Rh(CO)(Cl)(PZ3)2 +2 CO Rh(CO)(Cl)(PZ3)2

15

Rh(CO)(Cl)(PZ3)2

16

18

Ru(Cp)(cod)Cl + 2PZ3 ) Ru(Cp)(Cl)(PZ3)2 + cod Ru(Cp*)(cod)Cl + 2PZ3 ) Ru(Cp*)(Cl)(PZ3)2 + cod W(CO)5(PZ3)

Rh-P bond length -∆Hrx

19

Os3(CO)11(PZ3)

20

Ni(CO)3(PZ3)

21

Fe2Cp2(CO)3 + PZ3 ) Fe2Cp2(CO)3PZ3 t-BuOOH + PZ3 ) OdPZ3 + t-BuOH

17

22

νCO

-∆Hrx νCO Os-P bond length νCO

ligands used 3, 10, 12, 22, 28, 31, 32, 37, 54, 55, 74, 76, 93, 96, 97, 99, 103, 105, 107, 110, 131, 136, 137 3, 10, 12, 14, 22, 37, 43, 45, 55, 74, 97, 99, 103, 107, 110, 131, 134 7, 10, 12, 22, 45,74, 99, 103, 118 10, 12, 14, 22, 37, 38, 43, 45, 55, 74, 103, 134 10, 12, 22, 37, 45, 55, 74, 103, 105, 110, 134, 136, 137 22, 31, 55, 74, 76, 86, 97, 99, 103, 105, 107, 109, 110, 112, 113, 117, 124, 131, 132, 134 10, 22, 55, 74, 97, 99, 103, 105, 107, 109, 110, 112, 113, 117, 131, 134, 137 10, 45, 55, 74, 96, 97, 99, 103, 105, 107, 110, 131, 134 10, 12, 14, 22, 37, 43, 45, 55, 74, 99, 103, 131, 134 1, 3, 10, 12, 22, 37, 45, 55, 60, 74, 103, 118, 137, 134 1, 3, 10, 12, 22, 37, 45, 50, 55, 60, 74, 99, 103, 118, 131, 134 1, 3, 10, 12, 22, 37, 45, 50, 54, 55, 74, 82, 103 10, 22, 31, 45, 55, 76, 97, 99, 103, 105, 107, 109, 110, 112, 131, 134 10, 22, 45, 55, 97, 99, 103, 105, 107, 109, 110, 112, 113, 131, 134 22, 31, 76, 77, 99, 103, 105, 113, 117, 131, 134 3, 22, 31, 45, 50, 55, 74, 76, 97, 99, 105, 107, 109, 110, 112, 113, 117 3, 22, 31, 45, 50, 55, 74, 76, 97, 105, 107, 109, 110, 112, 113 3, 12, 22, 22, 37, 45, 55, 74, 103, 134, 136

ligands excluded

refs

PZ3-iHia

23-32 15, 33, 34 35-37 33 33, 39-41 42-45 42, 43, 45-47 48-50 33 51 51, 52

60b 113c

51 53-55

117d

53-55 53, 56-66

10e

67-69 67-69 33, 34, 36, 70 71

log k

3, 10, 27, 45.55, 77, 99, 103, 105, 110, 134, 136, 137 3, 10, 12, 26, 22, 37, 45, 46, 48, 50, 55, 60, 74, 92, 96, 97, 99, 103, 105, 107, 131, 134, 137 10, 45, 50, 74, 103, 129, 131, 134, 137, 135

72

log k

10, 12, 27, 45, 50, 55, 59, 74, 97, 99, 103, 105, 107

73

25

a PZ 14 3-iHi are excluded because their inclusion might require an additional parameter i, which refers to the number of hydrogens. Deviates from the line determined by the other ligands by 8σ. c Deviates from the line determined by the other ligands by 7σ. d Deviates from the line determined by the other ligands by 5σ. e Deviates from the line determined by the other ligands by 14σ.

b

cone angle and is a measure of the size of the ligand, Ear is an extra electronic effect originally associated with the number of aromatic pendant groups but is now thought to be more general,15 and πp is a measure of the π acidity. In eq 1, θst is the steric threshold17 and λ is the switching function that turns on the steric term after the size of the ligand surpasses the steric threshold.17 In the absence of a steric threshold, this equation can be reduced to eq 2. In the QALE model, eqs 1

prop ) aχd + bθ + cEar + dπp + e

(2)

and 2 are generally applicable to all phosphorus(III) ligands. Normally, in a QALE analysis we examine the manner in which a physicochemical property changes as the nature of the phosphorus(III) ligand changes. Beginning with the known parameters of the ligands in the particular data set, we then determine the values of the coefficients (a-e) of the QALE equations via regression analysis. On the other hand, if we want to determine the parameters of a given ligand, we can turn this procedure around. Beginning with a number of QALE equations with known coefficients for a number of different properties of a given ligand, we can determine the unknown parameters for this ligand. With a view toward obtaining the parameters of the fluorinated phosphorus(III) ligands, we obtained the QALE equations listed in Table 3 by regression analysis for 22 physicochemical properties (Table 2). We chose (17) Liu, H.-Y.; Eriks, E.; Prock, A.; Giering, W. P. Organometallics 1990, 9, 1758.

these properties because they have been measured not only for the fluorinated ligands of interest but also for a number of other π acidic phosphorus(III) ligands as well as alkyl- and arylphosphines. In deriving the QALE equations, we omit the fluorinated ligands but include alkyl- and arylphosphines (PR3 and P(p-XC6H4)3, respectively), alkyl and aryl phosphites (P(OR)3 and P(O-p-XC6H4)3, respectively), and the π acidic ligands PH3, PCl3, P(CH2CH2CN)3, and P(Pyr)3, for which the stereoelectronic parameters are known (see Table 1). Before using the QALE equations in Table 3 to determine the parameters for PZ3 (Z and Y are used to indicate any pendant group), we weighted them and made them dimensionless by dividing each one by its estimated standard deviation (s). We then put them into the standard form of eq 3. a′-d′

a′χd + b′θ + c′Ear + d′πp + e′ ) 0

(3)

are the QALE coefficients divided by the estimated standard deviation (s). e′ is the sum of all constant terms divided by s. Regression analysis of the collection of equations for a single phosphorus(III) ligand gives estimated values of the QALE parameters and e′calcd. We used the “Minitab” program for all statistical calculations. For illustrative purposes, we have displayed the output, which shows the standard deviation (standard error), “t ratios” and “p values” of the parameters as well as the estimated standard deviation (s) and r2 value of the analysis. Occasionally, within a set of data or within a set of equations, we find an outlier. A data point is identified

3432


Fernandez et al.

Table 3. Results of Regression Analyses (via Eq 1 or 2) of the Physiochemical Properties Listed in Table 2a no.

a

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

0.115 ( 0.003 0.50 ( 0.02 1.6 ( 0.2 2.1 ( 0.1 0.66 ( 0.09 -0.78 ( 0.07 1.40 ( 0.08 1.42 ( 0.09 1.8 ( 0.1 0.51 ( 0.06 1.3 ( 0.1 2.6 ( 0.2 -1.4 ( 0.1 1.7 ( 0.1 -0.0011 ( 0.0002

a

b

0.54 ( 0.05 -0.0026 ( 0.0009 0.92 ( 0.04 -0.04 ( 0.01 -0.9 ( 0.2

c

d

e

0 -0.047 ( 0.007 0.24 ( 0.05 0.16 ( 0.04 -0.06 ( 0.01 -0.45 ( 0.02 -0.13 ( 0.02 -0.13 ( 0.03 0.15 ( 0.02

-0.47 ( 0.03 0 0 -2.2 ( 0.9 -1.6 ( 0.5 -1.4 ( 0.3 4.5 ( 0.4 4.9 ( 0.4 -2.0 ( 0.6

-0.40 ( 0.03 -0.24 ( 0.03 0.000 69 ( 0.00009 -0.90 ( 0.07 -0.72 ( 0.7

-2.5 ( 0.7 4.1 ( 0.5

0 1.67 ( 0.09 7.2 ( 0.4 0 2.0 ( 0.3 -1.3 ( 0.6 12.3 ( 0.5 6.5 ( 0.4 1.5 ( 0.5 1.6 ( 0.3 2.4 ( 0.5 4.8 ( 0.9 -1.5 ( 0.6 5.8 ( 0.5 -0.011 ( -003

7.63 ( 0.05 2063 ( 1 133 ( 6 1842 ( 6 2054 ( 2 46.7 ( 0.5 1875 ( 3 1951 ( 4 1899 ( 3 2066.1 ( 0.6 2006 ( 1 1911 ( 2 136 ( 5 1980 ( 4 2.24 ( 0.01 36.3 ( 0.5 31.8 ( 0.05 2064.6 ( 0.5 2.17 ( 0.05 2057 9.7 ( 0.6 1.7 ( 0.2

0.9 ( 0.3 1.0 ( 0.4

0.0015 ( 0.0003 -0.032 ( 0.004 -0.08 ( 0.1

0.35 ( 0.07 0.20 ( 0.08

1.5 ( 0.2 -0.006 ( 0.003 2.0 ( 0.2 -0.52 ( 0.07

θst (deg)

134

135 127

128

n

σ

r2

23 17 9 12 13 20 16 13 13 14 16 13 16 15 11 18 15 11 14 23 8 13

0.1185 0.3842 1.777 1.907 0.7684 0.8994 1.053 1.091 1.140 1.350 2.238 3.701 1.501 1.276 0.004 04 1.15 1.069 0.8137 0.016 27 1.1111 0.1234 0.1344

0.985 0.998 0.999 0.993 0.996 0.991 0.999 0.998 0.998 0.979 0.984 0.990 0.990 0.998 0.969 0.962 0.959 0.994 0.940 0.993 0.983 0.982

The letters a-e are the regression coefficients of these equations. Entry numbers correspond to the entry numbers in Table 2.

Table 4. List of Ligands and Equations Used To Determine the Stereoelectronic Parameters of the Phosphorus(III) Compounds Listed in Column 2 no. 1

PZ3 PF3

χd 33 ( 2

θ (deg)

Ear

110 ( 24 0

πp

na

σ

13.2 ( 0.5 19 4.876

r2

eqsb

0.992 1 2,

5,d

7,d

9, 10, 12, 18

ligands usedc

ligands excludedc

7, 13, 18, 51, 126 7

28, 31 24, 33, 36, 37, 41, 52, 70, 71, 74 52

11

2

P(CF3)3

P(CH2CH2C6F13)3

3

33 ( 2

9(3

137 ( 13 0

137 ( 2

0

11.1 ( 0.6 20 2.352

2.5 ( 0.4

14 1.667

7, 13, 18, 51, 126 19 7, 126 0.992 1 36, 49, 52, 64, 80 2 52, 80 3, 10, 11, 18 36, 52, 80 5 80 0.999 6 91, 123, 130 8 13 14

4h P(p-(F13C6)C6H4)3 5d P(C6F5)3

22.7 ( 1.1 145 34 ( 2

P[Pyr-3,443 ( 2 (CO2Et)2]3

6

2.7

0

184 ( 13 4.1 ( 0.5 0

145

3.3

2(1

15 16, 17 8, 14

4 13 3.002

6

0.987 1

13,27,28 21 29 30 0.8308 1.000 20 21

79, 123, 130 79, 91, 123, 130 79, 91 79 111

refs

71 75, 76 36e

79f 91g

77 77 78 47 79 79 79, 80 80, 81 82

63, 88, 95, 129 138 129, 135, 138 129 , 135 129 114-116

83, 84 22, 71, 85 86 72 73 87

114-116

87

a

Numbers of equations from Table 3 that were used in the analyses. b Numbers refer to the properties and equations listed in Tables 2 and 3. c Numbers refer to the entry numbers in Table 1. d We found in the literature three values of νCO for Fe(CO)4(PF3) and two values of νCO for Fe(CO)3(PF3)2. Each of these values was included as a separate data point. e Deviates by 3.6 standard deviations (3.6σ) (see text). f Deviates by 9.4σ. g Deviates by 5.6σ. h See text for the method of analysis.

statistically as an outlier in the following manner.18 We obtain the predicted values and the residuals of the property based on regression analysis, where we omit the suspect data point. Using the regression equation, we calculate the predicted value of the suspect data point. If the difference between the predicted value and the experimental value is greater than 3.5 standard deviations from the set of residuals, then it is an outlier. Within the 22 data sets listed in Table 2 we found only (18) Moore, D. S.; McCabe, G. P. Introduction to the Practice of Statistics; 3rd ed.; Freeman and Company: New York, 1999; p 163.

4 outliers out of 324 data. (The range of r2 is 0.940-0.999 with a median of 0.990.) In the analyses listed in Table 4, we found 3 outliers out of the 76 equations.

Results Reevaluation of the Stereoelectronic Parameters of PF3. Our original analysis of PF3 was based on a limited set of data.14 Accordingly, we revisited this ligand and added 6 new properties to the analysis.



This gave us 19 equations. (The total number of equations is obtained by summing the product of the number of equations by the number of ligands involved.). In addition, we found 3 values for νCO for Fe(CO)4(PZ3) and 2 values for Fe(CO)3(PZ3)2. Each of these values was included in the analysis as a separate equation, bringing the total number of equations to 22 (see entry 1, Table 4). The output of the Minitab program for the analysis of this set of equations gives the results

with s ) 2.352 and r2 ) 0.992. Therefore, the values of χd, θ and πp are 33 ( 2, 137 ( 13°, and 11.1 ( 0.6, respectively. Determination of the Stereoelectronic Parameters of P(CH2CH2C6F13)3. Initial inspection of the 14 equations listed in entry 3 of Table 4 revealed a correlation between the coefficients of the electronic terms. As a result, we were unable to evaluate the separate contributions of the electronic parameters without assigning a value to one of the parameters. Accordingly, we assigned a value of zero to Ear since P(CF3)3 has this value, as do the other PR3 species (R ) alkyl). The final regression analysis gives the results

predictor

coeff

st dev

t ratio

p

χd θ Ear πp

30.671 119.87 0.817 13.894

5.531 31.37 1.561 1.459

5.55 3.82 0.52 9.52

0.000 0.001 0.607 0.000

with s (estimated standard deviation) ) 4.977 and r2 ) 0.992. This regression analysis shows that Ear is statistically indistinguishable from zero by virtue of its small t ratio and large p value. Hence, Ear was set to zero and dropped from the final analysis. Repeating the analysis in terms of χd, θ, and πp only, we obtained predictor χd θ πp

coeff

st dev

t ratio

p

33.029 109.55 13.1882

3.146 23.91 0.5480

10.50 4.58 24.07

0.000 0.000 0.000

with s ) 4.876 and r2 ) 0.992. We see that χd (33 ( 3) is smaller than our earlier reported value of 44 ( 4; πp decreased slightly from 14 ( 1 to 13.2 ( 0.5. The analysis provides θ ) 110 ( 24°, which overlaps Tolman’s value22 of 104°. We suggest the continued use of Tolman’s value. This new value of χd indicates that its σ donor capacity is between that of PCl3 and P(Op-CNC6H4)3 (see Table 1). Its πp value of 13.2 indicates that PF3 is the most π acidic phosphorus(III) ligand in our present listing of ligands. The new stereoelectronic parameters for PF3 and those for the other ligands considered in this study are presented in Table 4. Determination of the Stereoelectronic Parameters of P(CF3)3. We used the equations listed in entry 2 of Table 4 for the determination of the parameters of P(CF3)3. To include the small set of data for νCO for trans-Cr(CO)4L2, we added the data point for PF3 to obtain the QALE equation (entry 3, Table 3). Combining the appropriate data for P(CF3)3 with data for the mixed ligands containing the CF3 groups gave us 20 equations. When we performed the analysis of these equations in terms of the four QALE parameters, we found Ear to be indistinguishable from zero. The results of the regression analysis using χd, θ, and πp gave the results predictor

coeff

st dev

t ratio

p

χd θ πp

33.188 137.31 11.0629

2.413 12.51 0.5636

13.75 10.97 19.63

0.000 0.000 0.000

(19) Bartik, T.; Himmler, T.; Schulte, H.; Seevogel, K. J. J. Organomet. Chem. 1984, 272, 29. (20) Fernandez, A. L.; Lee, T. Y.; Reyes, C.; Prock, A.; Giering, W. P.; Haar, C. M.; Nolan, S. P. J. Chem. Soc., Perkin Trans. 2 1999, 2631. (21) Fernandez, A. L.; Reyes, C.; Lee, T. Y.; Prock, A.; Giering, W. P.; Haar, C. M.; Nolan, S. P. J. Chem. Soc., Perkin Trans. 2 2000, 1349. (22) Tolman, C. A. Chem. Rev. 1977, 77, 313.

predictor

coeff

st dev

t ratio

p

χd θ πp

8.880 137.054 2.4553

1.678 1.801 0.4307

5.29 76.08 5.70

0.000 0.000 0.000

with s ) 1.667 and r2 ) 0.999. Thus, we obtain values of 9 ( 2, 137 ( 3°, and 2.5 ( 0.4 for χd, θ, and πp, respectively. Determination of the Stereoelectronic Parameters of P[p-(C6F13)C6H4]3. Only two properties of this ligand have been reported.82 Accordingly, the results we report must be considered tentative. We performed the analysis in the following manner. We assumed that this para-substituted triarylphosphine behaves in no exceptional way as compared to other P(p-XC6H4)3 species. (23) Weiner, M. A.; Lattman, M.; Grim, S. O. J. Org. Chem. 1975, 40, 1292. (24) Stelzer, O.; Unger, E. Chem. Ber. 1975, 108, 1246. (25) Puddephatt, R. J.; Dignard-Bailey, L.; Bancroft, G. M. Inorg. Chim. Acta 1985, 96, L91. (26) Worley, S. D.; Hargis, J. H.; Chang, L.; Mattson, G. A. J. Electron Spectrosc. Related Phenom. 1982, 25, 135. (27) Cowley, A. H.; Lattman, M.; Montag, R. A.; Verkade, J. G. Inorg. Chim. Acta 1977, 25, L151. (28) Boch, H. Pure Appl. Chem. 1975, 44, 343. (29) Cowley, A. H.; Lattman, M.; Montag, R. A.; Verkade, J. G. Inorg. Chem. 1984, 23, 3378. (30) Schafer, W.; Schweig, A. Angew. Chem., Int. Ed. Engl. 1972, 11, 836. (31) Lappert, M. F.; Pedley, J. B.; Wilkins, B. T.; Stelzer, O.; Unger, E. J. Chem. Soc., Dalton Trans. 1975, 1207. (32) Bancroft, G. M.; Dignard-Bailey, L.; Puddephatt, R. J. Inorg. Chem. 1986, 25, 3675. (33) Strohmeier, W.; Mu¨ller, F. J. Chem. Ber. 1967, 100, 2812. (34) Aroney, M. J.; Davies, M. S.; Hambley, T. W.; Pierens, R. K. J. Chem. Soc., Dalton Trans. 1994, 91. (35) Bond, A. M.; Colton, R.; Kevekordes, J. E. Inorg. Chem. 1986, 25, 749. (36) von Apel, J.; Bacher, R.; Grobe, J.; Le Van, D. Z. Anorg. Allg. Chem. 1979, 453, 39. (37) Denham, E. L.; Clark, R. J. J. Chromatography 1984, 301, 253. (38) Brunner, H.; Knott, A.; Benn, R.; Rufinska, A. J. Organomet. Chem. 1985, 295, 211. (39) van Rentergen, M.; van der Kelen, G. P.; Claeys, E. C. J. Mol. Struct. 1982, 80, 317. (40) Howell, J. A. S.; Fey, N.; Lovatt, J. D.; Yates, P. C.; McArdle, P.; Cunningham, D.; Sadch, E.; Gottlieb, H. E.; Goldschmidt, Z.; Hursthouse, M. B.; Light, M. E. J. Chem. Soc., Dalton Trans. 1999, 3015. (41) Tripathi, J. B. P.; Bigorgne, M. J. Organomet. Chem. 1967, 9, 307. (42) Serron, S. A.; Nolan, S. P. Inorg. Chim. Acta 1996, 252, 107. (43) Li, C.; Nolan, S. P. Organometallics 1995, 14, 1327. (44) Li, C.; Stevens, E. D.; Nolan, S. P. Organometallics 1995, 14, 3791. (45) Luo, L.; Nolan, S. P. Inorg. Chem. 1993, 32, 2410. (46) Haar, C. M.; Nolan, S. P. Inorg. Chim. Acta 1999, 291, 32. (47) Smith, D. C.; Klaman, A. L.; Kadoret, J.; Nolan, S. P. Inorg. Chim. Acta 2000, 300-302, 987. (48) Field, L. D.; Lawrenz, E. T.; Ward, A. J. Polyhedron 1999, 18, 3031. (49) Kubota, M. K.; G. W.; Ishikawa, R. M.; Bencala, K. E. Inorg. Chim. Acta 1973, 7, 195.

3434


Thus, we assigned values of 145°, 2.7, and 0 to θ, Ear, and πp, respectively. The lack of π acidity for P(C6F5)3 supports the assumption that πp is zero for P[p-(C6F13)C6H4]3 (vide infra). We then used the χd dependence of νCO for M(CO)Cl[P(p-XC6H4)3]2 (M ) Rh, Ir) (eqs 3 and 4, respectively) to calculate χd for this ligand. Using

νCO(Rh) ) (1.70 ( 0.02)χd + (1955.5 ( 0.3) n ) 6, r2 ) 0.999 (3) νCO(Ir) ) (1.46 ( 0.02)χd + (1945.7 ( 0.3) n ) 7, r2 ) 0.999 (4) these two experimental νCO values for P[p-(C6F13)C6H4]3, (1993 and 1979 cm-1, respectively), we calculated the corresponding values for χd. We repeated this operation for all variations of the standard errors and averaged the extreme results to obtain 23 ( 1 for χd. This is noteworthy (vide infra), since the χd value of 23 is close to the value of 20.5 for P(p-F3CC6H4)3. Determination of the Stereoelectronic Parameters of P(C6F5)3. We found 7 sets of data that included P(C6F5)3 or related phosphines. This gave us 13 equations (entry 5, Table 4). Regression analysis in terms of (50) Wilson, M. R.; Liu, H.-Y.; Prock, A.; Giering, W. P. Organometallics 1993, 12, 2044. (51) Alyea, E. C.; Song, S. Comments Inorg. Chem. 1996, 18, 189. (52) Barbeau, C.; Turcotte, J. Can. J. Chem. 1975, 54, 1603. (53) Wilson, M. R.; Fernandez, A. L.; Prock, A.; Giering, W. P.; Haar, C. M.; Nolan, S. P.; Foxman, B. M. Submitted for publication. (54) Serron, S.; Nolan, S. P. Organometallics 1996, 15, 4301. (55) Serron, S.; Nolan, S. P.; Moloy, K. G. Organometallics 1996, 15, 4301. (56) Schumann, H.; Jurgis, S.; Eisen, M.; Blum, J. Inorg. Chim. Acta 1990, 172, 191. (57) Otto, S.; Mzamane, S. N.; Roodt, A. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1999, C55, 67. (58) Chen, Y. J.; Wang, J. C.; Wang, Y. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1991, C47, 2441. (59) Moloy, K. G.; Petersen, J. L. J. Am. Chem. Soc. 1995, 117, 7696. (60) Kessler, J. M.; Nelson, J. H.; Frye, J. S.; DeCian, A.; Fischer, J. Inorg. Chem. 1993, 32, 1048. (61) Dahan, F.; Choukroun, R. Acta Crystallogr. 1985, C41, 704. (62) Monge, A.; Gutierrez-Puebla, E.; Heras, J. V.; Pinilla, E. Acta Crystallogr. 1983, C39, 446. (63) Dunbar, K. R.; Haefner, S. C. Inorg. Chem. 1992, 31, 3676. (64) Chaloner, P. A.; Claver, C.; Hitchcock, P. B.; Masdeu, A. M.; Ruiz, A. Acta Crystallogr. 1991, C47, 1307. (65) Ceriotti, A.; Ciani, G.; Sironi, A. J. Organomet. Chem. 1983, 247, 345. (66) Boyd, S. E.; Field, L. D.; Hambley, T. W.; Partridge, M. G. Organometallics 1993, 12, 1720. (67) Serron, S. A.; Luo, L.; Stevens, E. D.; Nolan, S. P.; Jones, N. L.; Fagan, P. J. Organometallics 1996, 15, 5209. (68) Luo, L.; Nolan, S. P.; Fagan, P. J. Organometallics 1993, 12, 4305. (69) Serron, S. A.; Luo, L.; Li, C.; Cucullu, M. E.; Stevens, E. D.; Nolan, S. P. Organometallics 1995, 14, 5290. (70) Keiter, R. L.; Verkade, J. G. Inorg. Chem. 1969, 8, 2115. (71) Biradha, K.; Hansen, V. M.; Leong, W. K.; Pomeroy, R. K.; Zaworotko, M. J. J. Cluster Sci. 2000, 11, 285. (72) Zhang, S.; Brown, T. L. Organometallics 1992, 11, 4166. (73) Shulman, J. I. J. Org. Chem. 1977, 42, 3970. (74) Haas, H.; Sheline, R. K. J. Chem. Phys. 1967, 47, 2996. (75) Gleiter, R.; Goodmann, W. D.; Schafer, W.; Grobe, J.; Apel, J. Chem. Ber. 1983, 116, 3745. (76) Cowley, A. H.; Dewar, M. J. S.; Goodman, D. W. J. Am. Chem. Soc. 1975, 97, 3653. (77) Apel, J.; Gorbe, J. Z. Anorg. Allg. Chem. 1979, 453, 53. (78) Burg, A. B. Inorg. Chem. 1986, 25, 4751. (79) Smith, D. C.; Stevens, E. D.; Nolan, S. P. Inorg. Chem. 1999, 38, 5277. (80) Guillevic, M. A.; Rocaboy, C.; Arif, A. M.; Horvath, I.; Gladysz, J. A. Organometallics 1998, 17, 707. (81) Li, C.; Nolan, S. P.; Horvath, I. T. Organometallics 1998, 17, 452. (82) Fawcett, J.; Hope, E. G.; Kemmitt, R. D.; Paige, D. R.; Russell, D. R.; Stuart, A. M. J. Chem. Soc., Dalton Trans 1998, 3751.

Fernandez et al.

the four QALE parameters showed that πp was indistinguishable from zero. Accordingly, it was dropped from the final analysis, which gave the following results predictor

coeff

st dev

t ratio

p

χd θ Ear

33.915 190.63 4.2595

1.622 13.14 0.5418

20.91 14.51 7.86

0.000 0.000 0.000

with s ) 3.020 and r2 ) 0.987. Thus, we obtain values of 34 ( 2, 191 ( 13°, and 4.3 ( 0.5 for χd, θ, and Ear, respectively. Determination of the Stereoelectronic Parameters of P[Pyr-3,4-(CO2Et)2]3 (Pyr ) Pyrrolyl). Our results for this analysis must be considered tentative, since there are only two reported properties on which to base our analysis (entry 6 in Table 4). This gave us six equations. Since Ear does not change for P(p-XC6H4)3 as X is varied, we assumed that this is also true for substituted pyrrolylphosphines. Accordingly, for P[Pyr3,4-(CO2Et)2]3 we set Ear ) 3.3 (the value21 for P(Pyr)3). Nolan87 suggested that this ligand is isosteric with P(Pyr)3. Thus, we assigned θ a value of 145°. The results of the regresssion analysis are predictor

coeff

st dev

t ratio

p

χd πp

42.829 2.0029

2.443 0.9722

17.53 2.06

0.000 0.131

with s ) 0.8308 and r2 ) 100.0. Thus, the parameters for this ligand are 43 ( 2, 145°, 3.3, and 2 ( 1 for χd, θ, Ear and πp, respectively. We discuss the π acidity of this ligand below. Discussion It is noteworthy the values of θ that we obtained for PF3 (110°), P(CF3)3 (137°), and P(C6F5)3 (191°) are remarkably similar to the values reported by Tolman. Tolman does not report θ for P(CH2CH2C6F13)3. Even so, the value θ (137°) which we report for P(CH2CH2C6F13)3 is close to the value of θ (136°) that we find works well for PBu3 in QALE analyses (e.g., see the appropriate analyses in Tables 2 and 3). PF3 is the most π acidic of the phosphorus(III) ligands. Our analysis also reveals that P(CF3)3 has a large value of πp, consonant with Grobe’s assertion13 that this ligand is a strong π acid. Interestingly, P(CH2CH2C6F13)3 also exhibits a significant π acidity, although it is as good a σ donor as PMe3. We also note that there appears to be no π acidity associated with P(C6F5)3. Furthermore, in the absence of π acidity, we expect that the χd value should be the same as Tolman’s value of χ (34.8), as indeed it is. Therefore, we suggest that Tolman’s value be used for χd. P(C6F5)3 does appear to have one of the largest Ear values of any of the phosphorus(III) ligands. (83) Petrachenko, N. E.; Vovna, V. I.; Furin, G. G. Zh. Fiz. Khim. 1992, 66, 515. (84) Krupoder, S. A.; Furin, G. G.; Yakobson, G. G.; Dolenko, G. N.; Mazalov, L. N.; Sultanov, A. S.; Furley, I. I. J. Fluorine Chem. 1983, 22, 305. (85) Holloway, J. H.; Hope, E. G.; Russell, D. R.; Saunders, G. C.; Atheron, M. J. Polyhedron 1996, 15, 173. (86) Kemmitt, R. D. W.; Nichols, D. I.; Peacock, R. D. J. Chem. Soc. A 1968, 1898. (87) Huang, A.; Marcone, J. E.; Mason, K. L.; Marshall, W. J.; Moloy, K. G.; Serron, S.; Nolan, S. P. Organometallics 1997, 16, 3377.


The lack of π acidity for P(C6F5)3 reinforces our contention that P[p-(C6F13)C6H4]3 is not a π acid. The χd value for P[Pyr-3,4-(CO2Et)2]3 is the largest that we have determined, making it the poorest σ donor ligand, so far. Interestingly, even though πp has a large error, its value is very close to the πp value (1.9) of P(Pyr)3, and thus we believe that it is real. The similarity of πp for P[Pyr-3,4-(CO2Et)2]3 and P(Pyr)3 is reminiscent of the P(O-p-XC6H4)3 ligands, whose πp parameters are independent of the para substituent.15 The availability of the stereoelectronic parameters of the fluorinated phosphorus(III) compounds gives us the opportunity to explore how the electronic influence of the fluoroalkyl group is attenuated by intervening atoms (spacers). To accomplish this, we treat the C6F13 like a CF3 group. Certainly, the similarity of χd and πp for P[p(C6F13)C6H4]3 (χd ) 23 and πp ) 0) and P(p-F3CC6H4)3 (χd ) 20.5 and πp ) 0) suggests that this is possible. In support of our view, we note that Hope also concluded that CF3 and C6F13 have similar electronic properties.82 By treating perfluoroalkyl groups as trifluoromethyl groups, we can generate a homologous series of fluorinated phosphorus(III) ligands. For example, P(CH2CH2C6F13)3 is treated like P(CH2CH2CF3)3. To incorporate PF3 into the analysis, we multiplied its πp value by 3, since all the other ligands possess the equivalent of nine fluorine atoms. Examination of the data presented in Table 4 reveals that the π acidifying effect of the CF3 group does not end abruptly as “spacers” are inserted between the phosphorus and the perfluoroalkyl group. Rather, the π effect is smoothly attenuated as the number of atoms separating phosphorus and fluorine increases. This is shown in Figure 1, where we plot πp vs “n”, the number of atoms between phosphorus and the fluorines. We note that the πp contribution of CF3 appears to have vanished by the time there are five intervening atoms separating the fluorine and phosphorus atoms. Qualitatively, our observation agrees with that of Gladysz, who noted that the (total) electronic effect of the fluoroalkyl group is still observable with five intervening CH2 groups and nearly disappears with six CH2 groups.12 This essentially smooth monotonic attenuation of the π effect is not mirrored in the changes in χd. For example, the para CF3 group in P(p-F3CC6H4)3 causes a nine unit increase in χd as compared with P(pMeC6H4)3. In contrast, the C6F3 group (which is closer to the phosphorus) in P(CH2CH2C6F13)3 causes only a 3.6 unit increase in χd as compared to PPr3. Hope compared the νCO values for Ir(CO)(Cl)[P(CH2CH2C6F13)3]2 with Ir(CO)(Cl)[PEt3]2 and, simi-


Figure 1. Plot of the πp values of fluorinated phosphorus(III) ligands vs the number of atoms (n) separating the phosphorus and fluorine atoms.

larly, νCO for Ir(CO)(Cl)[P[p-(F13C6)C6H4]3]2 with Ir(CO)(Cl)(PPh3)2. He noted that the phenyl ring better insulates the phosphorus from the F13C6 than does the array of two CH2 groups.82 We note that Hope’s conclusion is based on the total electronic effect of the phosphine on νCO. However, νCO is strongly influenced by both σ and π effects. When the electronic effect is separated into its components, we see that two CH2 groups, indeed, strongly attenuate the effect on χd more so than does the phenyl group. However, because there is a significant π contribution to νCO and since P(CH2CH2C6F13)3 is a π acid, its relative effect on νCO is greater than that for P[p-(F13C6)C6H4]3. Conclusions The QALE parameters for a series of fluorinated phosphorus(III) compounds are reported. PF3 and P(CF3)3 are by far the most π acidic ligands we have encountered. The π acidifying effect of the fluorine atoms is transmitted to the phosphorus through at least three bonds and appears to have vanished by five bonds. P(CH2CH2C6F13)3 is unique in that it is a good σ donor as well as a modest π acid. P(C6F5)3, which is not a π acid, is a very large and very poor σ donor ligand. The calculated values of θ for PF3, P(CF3)3, and P(C6F5)3 are in excellent agreement with Tolman’s values. The calculated value of θ for P(CH2CH2C6F13)3 is virtually the same as θ for PBu3. OM010057+

Evaluation of the Stereoelectronic Parameters of Fluorinated

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