Phosphoranide Anions (10-P-4) with Electronegative Apical and

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Chapter 10 Phosphoranide Anions (10-P-4) with Electronegative Apical and Electropositive Equatorial Ligands Coordinated to Metals To Form Symmetrical 10-P-5 Species 1

Chester D. Moon, Suman Κ Chopra, and J. C. Martin Department of Chemistry, Vanderbilt University, Nashville, TN 37235 Hypervalent species, such as the 10-Ρ-4 phosphoranide potassium anion 1, are most stable when the apical ligands are very electronegative with two CF3 groups adjacent to the apical oxygens. They also require electropositive ligands in the equatorial positions, such as the two carbons. These stabilize the anions on the apical positions and of 1, the cation on the hypervalent main-group element at the center. Compound 1, with these proper ligands, makes the phosphoranide anion coordinate just to the phosphorus, while many other 10-P-4 species coordinate by metal to both phosphorus and the apical ligand. The gold metal species 5 has an X-ray structure here that makes it understandable. The five-memberedringscontaining the apical and the equatorial groups are also helpful to make the phosphoranide 1 stable. Phosphoranide anion 1 is a stable 10-Ρ-4 (7) hypervalent anionic species that could be considered as a transition state for a nucleophilic substitution reaction at a three coordinate phosphine center (2). The stability of 1 (3) can be attributed to several factors. F3CCF3

1 WF, To begin with, the three-center four-electron (3c-4e) O-P-O bond is stabilized by placing the electronegative hexafluorocumyl groups adjacent to the oxygens at the apical positions of the pseudo-trigonalbipyramidal geometry (Ψ-ΤΒΡ) of 1. Current address: Colgate Palmolive Company, 909 River Road, Piscataway, NJ 08855 0097-6156/92/0486-0128S06.00/0 © 1992 American Chemical Society Walsh et al.; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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These electronegative groups serve to stabilize the negative charge build up at the apical positions. This negative charge build up is due to two electrons of the hypervalent bond being placed into the non bonding orbital of the (3c-4e) bond as shown in the orbital diagram below. Placing two electrons in this orbital clearly would put considerable electron density in the terminal positions of the hypervalent bond. anti-bonding non-bonding bonding Orbital Diagram for (3c-4e) Hypervalent Bonding Although there could be some phosphorus d-orbitals contributing to 10-P-4 or 10-P-5 species, these are in a high enough position to have a very little amount of an electron in the d-orbitals. This hypervalent bonding was suggested by Musher (4) and it was found by others to have a very small amount of an electron in the d-orbitals, as suggested by Musher and by others (5) with calculations. :

[«i—Y —£«]" -0.515 +0.030 -0.515 Calculated Charges for the 10-F-2 Trifluoride Anion The reactions of F" with F2 formed (F3)" with reasonable evidence for the formation of the 10-F-2 species for the first-row element (3.00σ (I)) no. variables 370 reflection/parameter ratio 9.00 residuals: R; R 0.068; 0.095 goodness to fit indicator 3.89 max shift/error in final cycle 0.27 maximum peak in final diff. map 1.92 cA-3 minimum peak in final diff. map -2.86 eÂ-3 *The total amount of the Crystal Data is being deposited with the Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW England. 3

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Walsh et al.; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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PHOSPHORUS CHEMISTRY

Table II. Selected Bond Lengths and Bond Angles of 5 Bond Length (A) Atoms Defining Angle Π Angle Pl-Ol 1.818 (9) Ol-Pl-02 173.7 (5) Pl-02 1.80(1) 01-P1-C5 86.6 (5) Pl-Aul 2.336 (4) 01-P1-C9 89.7 (5) P1-C9 1.79 (1) 02-P1-C5 90.5 (6) P1-C5 1.85 (2) 02-P1-C9 87.0 (6) Aul-P2 2.287 (5) Ol-Pl-Aul 91.2 (3) P2-C19 1.82 (3) 02-Pl-Aul 95.1 (4) P2-C20 1.86 (3) Pl-Aul-P2 175.4 (2) P2-C21 1.89 (6) Aul-Pl-C5 118.8 (4) Aul-Pl-C9 120.5 (5) C5-P1-C9 120.6 (6) equatorial C-P-C angle is 120.6°. The O-P-C apical-equatorial angles of 5 within the five-membered rings are 86.6° and 87.0°, while the other O-P-C angles are 89.7° and 90.5°. There is a smaller angle within either of thefive-memberedrings.The O-P-Au angles on the other side are 91.2° and 95.1°, with the total of 6.3° more than 180°. The O-P-O angle is 186.3° which is 6.3° more than 180° as the P-O bonds are moved direcdy away from the Au. The equatorial hydrogen of 4 is smaller, and the P-O bonds are moved toward the hydrogen with the O-P-O angle being 178.47°, toward the hydrogen. The equatorial O" of 7 is larger than H and negative. It does move the O-P-O angle away from the O" to 188.7°, more than the O-P-O 186.3° of 5. The O-P-O angle of 6 is moved away from the equatorial Fe to 189.7°. The Fe


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coordinated phosphoranide, 6, has 2 CO ligands and C H on the Fe making it much 5

5

-

larger than the Au of 5 and the O of 7 (2). The structural comparisons of the compounds with equatorial hydrogen (4), gold (5), iron (6), and O" (7) (10) have different apical P-O bond lengths. These are 1.746 Â for 4 (H), 1.809 Λ for 5 (Au), 1.824 Â for 6 (Fe), and 1.80 Â for 7 (O").

The equatorial O" of 7 provides anionic electrons, as shown in 7b, into the antibonding orbital of the O-P-O bond, making the apical P-O bonds longer than that for the equatorial H of 4. The Au compound, 5, and the Fe compound, 6, do have even longer apical P-O bonds than those for 7. The electrons on the iron section of 6 are more removed into the antibonding orbital, making its P-O bonds longer than those of 5. The P-O bonds of 5 are longer than those of 4 or 7, made from the electrons of the P(Et)3 P-C bonds moving across the Au to the O-P-O antibonding orbital. The Fe of 6 has electrons in its d-orbitals and p-orbitals because of coordination to its three ligands. The C NMR for the C5H5 ligand of 6 is at δ 87.52 for the five carbons. The compound with the hypervalent phosphorus of 6 replaced by a single iodine, which was used to prepare 6, has the C NMR for the C5H5 on the Fe as δ 85.58. The C5H5 of 6 is thought to donate electrons to the antibonding O-P-O bond (3c-4e), making the C NMR of the C H of 6 to have a position lower by δ 1.94, relative to the single iodine species. The apical P-O bond lengths are longer for 6, with 6>5>7>4. The O-P-O angles mentioned earlier made 6 have the largest angle, relative to the equatorial Fe, with 6(189.7°)>7(188.7 )>5(186.3 )>4(178.47°). It is probable that the longer PO bonds of 6 make the oxygens, in each of thefive-memberedrings,further away from the equatorial Fe. Compound 4 has the shortest P-O bonds and the oxygens are closer to the equatorial H. Tlie other two compounds provide 5>7 for the P-O bond 1 3

1 3

1 3

5

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5

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lengths, while the O-P-O bond angles away from the Au or O" are 7>5. The P-O bond lengths of 5 and 7 are not the only method to change the O-P-O angle. It is probable that both the P-O bond lengths and the size of the equatorial ligand make the O-P-O angle change its positionrelativeto the equatorial ligand. Discussion The phosphoranide anion 1 is stabilized by the bidentate ligands. These ligands contain the stabilizing factors mentioned earlier for stabilizing hypervalent bonding. This ligand system renders the phosphoranide symmetrical. When compared to compound 8a, it is clear that the ligand system of 1 is more suitable for stabilizing phosphoranides. Compound 8a is in equilibrium with 8b. The bidentate ligand system of 8a places two electronegative oxygens in the equatorial positions of the



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(Ψ-ΤΒΡ) geometry (77). Therefore, the bidentate ligand system of 8a provides less stabilization than the ligand system of 1.

The X-ray crystal structure of 5 shows the elongation of the P-0 bonds when compared to 4. This suggests that the gold atom does donate electron density into the antibonding orbital of the (3c-4e) bond. These results are consistent to those seen earlier for 6. The bidentate ligand system does allow the phosphoranide to react with metals to give monodentate complexes. Other phosphoranides such as 9 (72) act as a bidentate ligand to the metal as seen in 10 (75) and 11 (74). However protonation of the apical nitrogens of 11 make them more electronegative and the phosphoranide

becomes monodentate complex 12. This protonation makes the bidentate ligand of 11 similar to that of 1. This indicates that the bidentate ligand of 1 can be used to prepare phosphoranide-metal complexes in which the phosphoranide acts as a monodentate ligand to the metal.

+

The trilithio derivative (13) reacts with D 0 to give a large amount of deuterium (14) replacing the C-Li. We have made a number of hypervalent maingroup element species from 13, by reaction with SOCI2, SeCl4, TeCl4, etc. A few attempted other reactions at 13 did not work, however, for us in this way. 2


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?.. (1) 2 BuLi £ (2)Li° cyclohexane

Recent attempts by Milne (Milne, S. Graduate Chemical Research Assistant now, Vanderbilt University.) to have 13 react with PC1, PCI3, or a mixture of PC1 and PCI3, failed to have the trilithio species 13 replace three chlorines. The trilithio species is not as reactive as most lithium species, since it has the central lithium coordinated to the carbon and to the two apical oxygens probably forming a 3c-4e O-Li-0 bond (15). 5

5

...Li "•Li F

15 ^ Needed hypervalent phosphorus species have not yet been formed with trilithio species 13. Recently considered methods for making needed phosphoranide species are now being tried, and will be reported later. Acknowledgments. Parts of this work were supported by the National Science Foundation (CHE-8910896) and by the Department of Health and Human Services (GM 36844-06). Literature Cited (1) The N-X-L classification scheme characterizes species in terms of the number (N) of formal valence shell electrons about an atom X and the number of ligands (L) bonded to X. Perkins, C. W.; Martin, J. C.; Arduengo, A. J.,III;Lau, W.; Alegria, Α.; Kochi, J. K. J. Am. Chem. Soc. 1980, 102, 7753. (2) Wittig, G.; Maercker, A.J.Organomet. Chem. 1967, 491. (3) Granoth, I.; Martin, J. C.J.Am. Chem. Soc. 1979, 101, 4623. (4) Musher, J. I. Angew. Chem.,Int.Ed. Engl. 1969, 8, 54.


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(5) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654. Pietro, W. J.; Francl, M. M.; Hehre, W. J.; DeFrees, D. J.; Pople, J. Α.; Binkley, J. S.J.Am. Chem. Soc. 1982, 104, 5039. Baybutt, P. Mol. Phys. 1975, 29, 389. Kutzelniggin, W. Angew. Chem., Int. Ed. Engl. 1984, 23, 272. (6) Ault, B. S.; Andrews, L. J. Am. Chem. Soc. 1976, 98, 1591. Ault, B. S.; Andrews, L.J.Org. Chem. 1977, 16, 2024. (7) Cahill, P. Α.; Dykstra, C. E.; Martin, J. C. J. Am. Chem. Soc. 1985, 107, 6359. (8) Hays, R. Α.; Martin, J. C. Organic Sulphur Chemistry: Theoretical and Experimental Advances, I. G . Csizmadia, A . Mangini, and F. Bernardi, Eds.; Elsevier Scientific Publishing Company: Amsterdam, 1985; chap. 8, pp 408-485. (9) Chopra, S. K.; Martin, J. C. Heteroatom Chem. 1991, 2, 71. (10) Perozzi, E. F.; Michalak, R. S.; Figuly, G. D.; Stevenson, W. Η.,III;Dess, D. B.; Ross, M. R.; Martin, J.C.J.Org. Chem. 1981, 46, 1049. (11) Schomburg, D.; Storzer, W.; Bohlen, R.; Kuhn, W.; Roschenthaler, G. V. Chem. Ber. 1983, 116, 3301. (12) Lattman, M.; Olmstead, M. M.; Power, P. P.; Rankin, D. W. H.; Robertson, Η. E. Inorg. Chem. 1988, 22, 3012. (13) Lattman, M.; Chopra, S. K.; Cowley, A. H.; Arif, Α. Μ. Οrganometallics 1986, 5, 677. (14) Khasnis, D. V.; Lattman, M.; Siriwardane, U. Inorg. Chem. 1989, 28, 681. RECEIVED November 12, 1991


Phosphoranide Anions (10-P-4) with Electronegative Apical and

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