Chapter 10

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CHM 331

Inorganic Chemistry II(Organometallics)

Part 1: Main Group Elements

Spring 1999

Michael K. Denk

Chapter 10

Compounds of Phosphorus and Arsenic

Following the generally recognized diagonal relationship, Phosphorus is in manyrespects the element that is most similar to carbon.

Phosphorus gives rise to an extensive series of heterocycles.Phosphorus heterocycles can be strongly delocalizedphosphorus forms strong double and triple bonds with carbon

Phosphorus (III) compounds such as PCl3, P(OMe)3, PR3 are synthetic reagents andare extensively used as ligands in transition metal chemistry.

A single type of organophosphorus compounds, the Wittig reagents has gained suchan importance that its discovery was honored with the Nobel Prize in Chemistry 1979(jointly awarded to G. Wittig and H. C. Brown)

http://www.nobel.se/laureates/chemistry-1979.html

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H.C. Brown G. Wittig

The Name Reactions of Phosphorus Chemistry

A number of synthetically important reactions of phosphorus chemistry are referredto by the name of their discoverer:

Wittig Olefin SynthesisStaudinger ReactionMcCormack ReactionKuchtinRamirez ReactionMichaelisArbuzov ReactionMitsunobu ReactionNoyori Reaction

Phosphorus: Oxidation States and Coordination Numbers

The element phosphorus gives rise to a large number of stable compounds indifferent coordination numbers and oxidation states.

The oxidation state of phosphorus compounds is indicated as usual with romannumerals.

A new nomenclature tries to include the coordination number of the central elementby the addition of a greek lambda with the appropriate coordination number assubscript:

A useful way to outline the breadth of bonding types is a classification of phosphoruscompounds according to coordination number and oxidation state:

CoordinationNumber

OxidationState Examples

Phosphaalkynes,

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http://www.nobel.se/laureates/chemistry-1979-2-cv.html

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1 3 RCP

2 2PhospheniumCations, [R2P]+

3 3Phosphines R3PPhosphites (RO)3P

4 4PhosphoniumCations [R4P]+

4 5Phosphonates RP(O)(OR')2

4 5Wittig ReagentsR3P=CR'2

5 5 Phosphoranes R5P

Phosphenium Cations

Phosphenium cations are bent species that isoelectronic to singlet carbenes. They arevery strong electrophiles and usually have some form of bonding with either thecounterion or the solvent

Like carbenes, they can be stabilized by donor substituents especially amines. Suchdonor stabilized phosphenium cations are stable enough to be isolated and some ofthem have been characterized by single crystal Xray crystallography. The N2P anglesare typically close to 90 o and the NP bond distances indicate double bond character.

A surprisingly simple approach to phosphenium cations was reported bySchmidpeter et al.: reaction of PCl3, Ph3P and AlCl3 leads to the formation of thephosphenium cation [(Ph3P)2P]+:

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Tris(dimethylamino)phosphanes reacts similarly to givethe corresponding triphosphane:

Aromatic Phosphenium Cations

Phosphenium cations can be stabilized by aromaticity as the following exampleillustrates:

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The McCormack Reaction

One of the most widely used synthetic reactions is the McCormack reaction:

6,6(Ethylenedioxyl)l methylA32,4,5,6,7,7ahexahydro1 Hphosphindole1oxide [3]

(2).3 A hexane solution of 1vinyl4,4ethylendioxycyclohexlene 1 (20.0 g, 0.12 mol) and freshly distilled CH3PCl2 (18.3 g, 0.156 mol) and copper stearate (0.4 g) as a polymerizationinhibitor, was allowed to stand at rt for 5 days. The adduct wasfiltered and the filtrate was kept for 22 days to get more cycloadduct. The first crop was hydrolyzed by NaHCO3, extractedwith CHCl3, and after evaporation gave 19.36 g of 2 (72.7%), mp.156157 oC.

The KuchtinRamirez Reaction

The McCormack reaction can be extended to a vast number of 1,3heterodienes. Thereaction of P(III) compounds with 1,2diketones is particularly widely used and issometimes called the KuchtinRamirez Reaction:

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References

1. McCormack, W.B., U.S. Pat. 2.663.736 and 2.663.737.2. Hajos, A.G., J. Org. Chem. 1956, 30, 1213.3. Quin, L.D., J. Org. Chem., 1981, 46, 461.4. Kuchtin, V.A., Doklad. Akad. Nauk. USSR, 1958, 121, 466.5. Ramirez, F., J. Am. Chem. Soc. 1960, 82, 2651.6. Mitsuo, S., J. Org. Chem. 1981, 46, 4030.

Phosphaalkynes

Methylidynephosphane, HCP, was first proposed as reactive intermediate by Albers[1] but was only characterize 10 years later by Gier [2] through the pyrolysis of PH3in a rotating arc of carbon electrodes.

The compound is extremely reactive, but sterically shielded derivatives are morestable. The first stable phosphaalkyne was reported by G. Becker in 1981 [3]:

The starting material is obtained from P(SiMe3) + tBuCOCl [4]:

References

1. H. Albers. Angew. Chem. 1950, 62, 443.2. T. E. Gier, JACS, 1961, 83, 1769.3. G. Becker, G. Gresser, W. Uhl, Z. Naturforsch. 1981, 36b, 16. See also W. Rösch,U. Hees, M. Regitz, Chem. Ber. 1987, 120, 1645.; W. Rösch, U. Vogelbacher, T.

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Allspach, M. Regitz, JOM, 1986, 306, 39; M. Regitz, W. Rösch, T. Allspach, U.Annen, K. Blatter, J. Fink, H. Hermesdorf, H. Heydt, U. Vogelbacher, O.Wagner, Phosphorus Sulfur, 1987, 30, 47,.

4. G. Becker, Z. Anorg. Allgem. Chem. 1976, 423, 242.

Reactions of Phosphaalkynes

Phosphaalkynes have a fascinating reaction chemistry. At 130 oC, tBuCPtetramerises to a tetraphosphacubane:

Arsaalkynes

Arsaalkynes require even larger substituents to be kinetically stable:

Phosphites

Phosphites (RO)3P are obtained from PCl3 and the corresponding alkoxides /phenoxides.

Phosphines

Phosphines R3P are the phosphorus compounds corresponding to amines.

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Phosphines: Differences Between Nitrogen and Phosphorus

The synthesis of the chelate ligand bis(1,2diphenylphosphinoethane) (dppe)highlights the significant differences between nitrogen and phosphorus:

Chelating Phosphines

The synthesis of chelating phosphine ligands has been the subject of many studies.Especially useful are the general strategies that were developed by R. B. King et al.

King's approach uses the addition of phosphines R2PH to suitably activated olefinsCH2=CHX (Michael systems) [1]:

The phosphines R2PH and RPH2 can be obtained from the phosphonates (viaMichaelis Arbusov reaction) or the chlorides (from PCl3 + Grignard) by LiAlH4reduction.

These reactions are base catalyzed(formation of R2PH as nucleophile) and requirethe presence of electron withdrawing substituents on the double bond.

The addition of PH bonds across non activated CC double bonds can be achievedunder radical conditions [2]:

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The approach has recently been extended to the synthesis of phosphane dendrimers[3]:

The compounds Ph2PH are easily accessible through a somewhat surprisingreduction reaction:

The side product PhLi can be selectively removed ammonia [4].

References

1. R. B. King J. C. Cloyd, JACS, 1975, 97, 46 52 and 53 642. N. Bampos, L. D. Field, B. A. Messerle, R. J. Smernik, Inorg. Chem. 1993, 32,4084 4088.

3. A. Miedaner, C. J. Curtis, R. M. Barkley, D. L. DuBois, Inorg. Chem. 1994, 33,5482 5490.

4. A. J. Ashe, J. W. Kampf, D. B. Puranik, J. Organometal Chem. 1993, 447, 197 201.

Phospholes

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Unlike pyrrole, the higher homologues are nonaromatic diolefins with pyramidalheteroelement.

Aromaticity is insufficient to create a planar geometry at P / As, but lowers theinversion barriers of P and As by ca. 50 kJ / mol.

Inversion barrier of NH3: 24 kJ / molInversion barrier of PH3: 155 kJ / mol

Phosphole Complexes

Phenylgroups can thus be used as protective groups in the synthesis of phosphines.This reaction is also useful for the synthesis of arsanes, stibanes and bismutanes:

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Phosphanes as Ligands

Numerous transition metal complexes have been described for PF3, PCl3 [1], PBr3 [1]and organo phosphines.

1. M. S. Davies, M. J. Aroney, I. E. Buys, T. W. Hambley, J. L. Calvert, Inorg.Chem. 1995, 34, 330 336.

The Tolman Angle

The basicity (pKa of R3PH+) and the steric demand of phosphines influences thestability and reactivity of phosphine complexes and can both vary substantially fromligand to ligand.

The steric demand of phosphines in transition metal complexes can be estimatedwith the Tolman angle. Note that the Tolman angle depends on the MP distance:

Compound ConeAngle

pKaUS $ /g Ref.

P(OMe)3 107 2.60 0.38 2

PMe3 118 8.65 5.55 2

PhP(OMe)2 120 2.64 6.20 2

PhPMe2 122 6.5 6.20 2

Ph2PH 126 0.03 2.59 2

(PhO)3 P 128 2.00 0.02 2

(OiPr)3 P 130 4.04 0.07 2

Ph2POMe 132 2.69 9.64 2

Et3 P 132 8.69 4.30 2

(nBu)3 P 132 8.43 2.88 2

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Ph2PMe 136 4.57 3.77 2

Ph3P 145 2.73 0.12 2

(pMeC6H4)3P 145 3.84 8.34 2

(pMeOC6H4)3P

145 4.59 14.69 2

(iPr)3 P 160 26.20 2

(PhCH2)3 P 165 6.0 13.66 3

(mMeC6H4)3P 165 3.30 45.65 2

(Cy)3P 170 9.70 4.91 2

(tBu)3 P 182 11.40 21.78 2

(2,6MeOC6H3)3P

184 9.33 3.67 4,5

(2,4,6MeOC6H2)3P

184 11.02 2.85 4

(oMeOC6H4)3P

194 3.08 8.31 2

(2,4,6MeC6H2)3P

212 7.3 18.36 6

References:

1. C. A. Tolman, Chem. Rev. 1977, 77, 313.2. M. Rahman et al. Organometallics 1989, 8, 1.3. M. Rahman et al. Organometallics 1987, 6, 650.4. Y. Yamashoui, Chem. Lett. 1988, 43.5. H. Kurosawa et al. Bull. Chem. Soc. Jpn. 1987, 60, 3563.

Phosphines as Reducing Agents: The Mitsunobu Reaction

Inter and intramolecular nucleophilic displacement of alcohols with inversion bymeans of diethylazodicarboxylate (DEAD)triphenylphosphine and a nucleophile.Also dehydration,esterification of alcohols or alkylation of phenols:

()Methyl cis3hydroxy4,5oxycyclohexlenecarboxylate (2).[4]

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To ()methylshikimate 1 (220 mg, 1.06 mmol) and triphenylphosphine (557 mg,2.12 mmol) in THF at 0 oC,under N2 was added with stirring (DEAD) (370 mg, 2.12mmol). After 30 min at 0 oC and 1 h at 20 oC, it was vacuum distilled (Kugelrohr) at165 oC (0.1 mm) and taken up in Et2O Cooling gave bis(carbethoxy)hydrazine (10mg, mp 133 oC). The filtrate was concentrated and chromatographed (preparativeTLCsilica gel Et2O) to afford 140 mg of 2 (77%) on standing; recrystallized fromEt2Opetroleum ether, mp 8182 oC, a25 = 55.4'.

References

1. Mitsunobu, O. Bull. Chem. Soc. Jpn. 1967, 40, 2380.2. Miller, M. J. J. Am. Chem. Soc. 1980, 102, 7026.3. Evans, S.A. J. Org. Chem. 1988, 53, 2300.4. McGovan, D.A. J Org. Chem. 1981, 46, 2381.5. Mitsunobu, O. Synthesis 1981, 1.6. Crich, D. J. Org. Chem. 1988, 54, 257.7. Hassner, A. J. Org. Chem. 1990, 55, 2243.

Chiral Phosphines: The Noyori Reaction

The homogeneous chiral hydrogenation of unsaturated alcohols, or carboxylic acids,enamides, ketones in the presence of BINAP Ru or Rh complex 8 as catalyst.

(R)(+)2,2'Bis(diphenylphosphino)1,1'binaphthyl (BINAP) (7).[2]

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(R)(+)2,2'Bis(diphenylphosphino)1,1'binaphthyl (BINAP) (7).[2]

To Mg (2.62 g, 0. 108 gat) under N2 was added iodine (50 mg), THF (40 mL), 1,2dibromoethane (0.51 mL). 2.2'Dibromo1,l'binaphthyl 1 (20 g, 46.4 mmol) inPhMe (360 mL) was added dropwise over a period of 4 h at 5075 oC. After 2 hstirring at 75 oC the mixture was cooled to 0 oC and diphenyl phosphinyl chloride 2(23.2 g, 98 mmol) in PhMe (23 mL) was added over 30 min. The mixture washeated to 60 oC for 3 h, cooled, quenched with water (60 mL, stirred at 60 oC for 10min and the organic layer concentrated to 60 mL. After 24 h at 20 oC, the productwas filtered, stirred with heptane (45 mL and PhMe (5 mL), filtered and dried toafford 27.5 g of (±) 3 (91 %), mp 295 298 oC (pure 304305 oC). (t)

3 (65.4 g, 0.1 mol), (1 S)(+)camphorsulfonic acid monohydrate 4 (25 g, 0.1 mol)and EtOAc (270 mL) were heated to reflux and HOAc (90 ml) was added to get aclear solution. Gradually cooling to 23 oC, filtration and washing (EtOAc) gave 35.3g of a 1:1:1 complex of 3 : 4 : AcOH. The complex was suspended in PhMe (390mL), treated with water (30 mL) at 60 oC and cooled. The organic layer wasconcentrated to 50 mL and treated with hexane (50 mL). Filtration and drying gave22.2 g of (R)(+) 5 (68%), mp 262263 oC, J4 = +399 o (c 0.5 PhH). (R) 5 (50 g,76.4 mmol), xylene (500 mL), Et3N (324 g, 320 mmol) and trichlorosilane (41.4 g,304 mmol) under Ar were heated 1 h at 100 oC, 1 h at 120 oC and 5 h at reflux 30%NaOH (135 mL) was added under stirring at 60 oC, the organic layer wasconcentrated and the residue treated with MeOH (200 mL) to give 47.5 g of (R)BINAP 7 (95%), mp 241 242 oC, J4 = 228 o (c 0.679 PhH).

Methyl (R)3hydroxybutanoate (10).[4] To Ru(OAc)2 and (R)7 (806 mg,0.975 mmol) in CH2Cl2 (210 mL) was added 1.42 N HOl in 90% MeOH (1.41 mL, 2mmol). After 2.5 h stirring at 20 oC the solvent was evaporated to give (R)BlNAP 6

http://131.104.156.23/Lectures/331/331_supplement.htm#camphorsulfonic acid

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(722 mg) stored under Ar. Catalyst 8 can also be prepared from Ru(COD)Cl2,BlNAP and TEA.[3] A solution of methyl3oxobutanoate 9 (100 g, 0.862 mol) inMeOH (100 mL) was treated with catalyst 8 (341 mg, 0.429 mmol) andhydrogenated at 100 atm and 30 oC. Vacuum distillation afforded 97.5 g of 10(96%), bp 40 oC / 2 mm, a24 = 24.20 (neat), 99% ee.

References

1. Noyori, P, J. Am. Chem. Soc. 1980, 102, 7932.2. Noyori, R. J. Org. Chem. 1986, 51, 629.3. Noyori, R. J. Am. Chem. Soc. 1986, 108, 7117.4. Noyori, R. J. Am. Chem. Soc. 1987, 109, 5858.5. Noyori, R. J. Am. Chem. Soc. 1989, 111, 9134.6. Noyori,, R. Chem. Soc. Rev. 1989, 18, 187.7. Noyori, R. Science 1990, 248, 1194.8. Otsuka, S. Synthesis 1991, 668.9. Noyori, R. Acc. Chem. Res. 1990, 23, 345.

Silylated Phosphines

Silylated phosphines, especially tris(trimethylsilyl)phosphine, are covalent synthonsfor the anions R2P, RP2 and P3:

P(SiMe3)3 can be obtained from:

P4 + Na/Kalloy + Me3SiCl (80%)PH3 + Me3SiOTf + Et3N (90%)NaPH2 + Me3SiF (35%)PiperidylPCl2 + Li + Me3SiCl (71%)PCl3 + Mg + Me3SiCl in THF (62%)

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The last method is not only the most cost effective one but also the safest. (H.Schuman, L. Rösch, Chem. Ber. 1974, 107, 854)

Phosphines RP(SiMe3)2 are best obtained from RPCl2 via the salts RPLi2 [13]:

Polyphosphanes (RP)n can be isolated from the distillation residues.

For the use of R2P(SiMe3)2 see [4 6]:

1. O. I. Kolodiazhnyi in "Synthetic Methods of Organometallic and InorganicChemistry" (W. A. Herrmann, ed.) Thieme Verlag, 1996, Vol. 3, p 70.

2. G. Becker, O. Mundt, M. Rössler, E. Schneider, Z. Anorg. Allg. Chem. 1978,443, 42.

3. H. Schuman, L. Rösch, Chem. Ber. 1974, 107, 854.4. Wentrup, H. Briehl, G. Becker, G. Uhl, H. J. Wessely, A. Maquetiau, R.Flamming, JACS, 1983, 105, 7194.

5. R. Appel, W. Paulen, Tetrahedron Lett. 1983, 24, 2639.6. O. I. Kolodiazhnyi, Tetrahedron Lett. 1982, 23, 4933.

Phosphorus Ylides (Wittig Reagents)

Wittig reagents are accessible from phosphines (R = alkyl, aryl) or phosphites (R =alkoxy) in two steps:

Wittig Reagents are highly reactive usually generated in situ. Mesomericallystabilized Wittig reagents can be quite stable and are sometimes even availablecommercially:

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Phosphorus ylides are not only important synthons of the Wittig reaction but havealso been used extensively as alkylligands, notably by the group of Schmidbaur

1. H. Schmidbaur, Angew. Chem. Int. Ed. Engl. 1983, 22, 907 927.2. W. C. Kaska, Coord. Chem. Rev. 1983, 48, 1 58.

Arsenic Ylides

although the first arsenic ylide was reported as early as 1902 by Michaelis [1], arsenicylides remained virtually until the famous Schmidbaur publication in 1975 [2].

Arsenic is much more reluctant to from "good" double bonds to carbon as thecomparison between phosphorus ylides and arsenic ylides illustrates:

Alkylidene arsoranes cleanly decompose to arsines R3As and carbenes (compare thesynthetic use of sulfur ylides as carbene transfer reagents)

1. A. Michaelis, Annalen 1902, 321, 141; ibid. 1901, 320, 271.2. Y. Yamamoto, H. Schmidbaur, J. Chem. Soc. Chem. Commun. 1975, 668 669and references therein.

http://hiris.anorg.chemie.tu-muenchen.de/AC3/



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The Wittig Olefin Synthesis

The term "olefin synthesis" should be used to avoid to confusion with the Wittigrearrangement (the [2,3]sigmatropic rearrangement of allyl ether to homoallylalcohols).

In 1953, G. Wittig and G. Geissler reported, that phosphoraneylides react withaldehydes or ketones to give olefines. cis olefins predominate in aliphatic systems,trans in conjugated olefins.

G. Wittig and G. Geissler "Reactions of pentaphenylphosphorus and several ofits derivatives, Annalen, 1953, 580, 44 57

trans4Nitro4methoxystilbene [3]

Triphenylphosphine (26.3 g, 0.1 mol) and pnitrobenzyl chloride (17.2g, 0.1 mol) inPhH (50 ml) were refluxed for 2 h. After cooling the solid was collected and washedwith PhH to give 25 g of phosphonium salt (58%), mp 270276 oC. Recrystallizedfrom CCl4petroleum ether, mp 278280 oC.

To stirred phosphonium salt (4.3 g, 10 mmol) in PhH (50 mL) under N2 was addedbutyllithium (0.85 g, 13 mmol) to produce the ylide. After 2 h anisaldehyde (1.63 g,12 mmol) was added, the mixture was diluted with petroleum ether and the darksolid collected. Recrystallization afforded 2.23 g (89%) trans4Nitro4methoxystilbene, mp 131132.5 oC.

References

1. Wittig, G., Liebigs Ann., 1949, 562, 187.2. Wittig, G., Chem. Ber. 1961, 94, 1373.3. Ketcham, R., J. Org. Chem. 1962, 27, 4666.4. Angeletti, E., J. Chem. Soc. Perkin Tr. 1, 1987, 713.5. Doudon, A., Tetrahedron 1988, 44, 2021.6. Emmons, W., Angew. Chem. Int. Ed. 1966, 5, 126.7. Murphy, P. B., Chem. Soc. Rev. 1988, 17, 1.8. Maercker, A., Org. React. 1965, 14, 333.9. Maryanoff, B. E., Chem. Rev. 1989, 89, 863.

Pentacoordinate Phosphorus Compounds (Phosphoranes)

The first organic derivative of pentacoordinate phosphorus was obtained by G. Wittigin 1948:

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The elements of group 15 are reluctant to form compounds R5E. NMe5 and PMe5 arestill unknown at present but AsMe5, SbMe5 and BiMe5 have been prepared. BiMe5decomposes above 100 oC.

Substitution with phenyl groups increases the stability of ER5. Ph3SbMe2 is stable upto +70 oC.

S. Wallenhauer, K. Seppelt, Inorg. Chem. 1995, 34, 116 119.

Phosphoranes: Decomposition Pathways

The existence of PCl5 as [PCl4]+[PCl6] in the solid state demonstrates a way forphosphorus to avoid the coordination number 5. The tendency do dissociate isgreatly diminished in cyclic phosphoranes:

The relative tendency of substituents to occupy the axial position can be determinedby dynamic NMR (1H, 19F, 13C, 31P). The most electronegative substituentsoccupy the axial positions.

Strongly electronegative substituents destabilize the phosphonium cation and hencefavor the phosphorane structure:

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Square pyramidal geometries have been reported for certain cyclic phosphoranes:

Another way for phosphorus to evade coordination number 5 is the elimination ofarylH or alkylH:

This process is much less favorable if the phosphorus atom is part of a ring.

While cyclic phosphites are thermally quite stable, cyclic dioxa phospholanes giveextrusion of trivalent phosphorus under ring contraction:

References on Phosphoranes

1. Emsley, J.; Hall, C. D., The Chemistry of Phosphorus, Harper and Row, NewYork, 1976.

2. Hellwinkel, D., in: Organic Phosphorus Compounds, Kosolapoff, G. M.; Maier,

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L., eds., WileyInterscience, 1973, vol, 3, pp 18S339,3. Cadogen, J. 1. G., ed., Organophosphorus Reagents in Organic Synthesis,Academic Press, New York, 1979.

4. Sheldrick, W. S., in: Topics in Current Chemistry, SpringerVerlag, New York,1978, vol 73, pp. 248, and references cited therein,

5. Trippett, S.: Organophosphorus Chemistry, 19691979, vols, ITI, SpecialistReports, Chemical Society, London,

6. Smith, D. J. H., in Comprehensive Organic Chemistry , Sutherland, 1. 0., Ed.Pergamon Press, New York, 1979, vol. 2. Ch.

7. Westheimer, F., Accounts Chem. Res. 1968, 1, 70 and references cited therein.8. Ramirez, F., lbid, p. 168. and references cited therein.9. Holmes, R. R. , J. Am. Chem. Soc. 1974, 96, 4143.10. Trippett, S., Phos. Sulfur 1976, 1, 89.,11. Hoffmann, R.; Howell, J. M., Muetterties, E. L, J. Am. Chem. Soc. 1972, 94,

3047.12. Ramirez, F. et al, Angew. Chem. Int. Ed. Engl. 1971, 10, 687.13. Berry, R. S., J. Chem. Phys. 1960, 32, 933.14. Muster, J. E., Tet. Letter. 1973, 1093.15. Wittig, G., Bull. Soc. Chim. Fr. 1966, 1162; b. Ramirez, F., et al; J. Am. Chem.

Soc. 1965, 87, 543; C. Ramirez, F., et al, ibid., 1967, 90, 751 and 3531.16. Trippett, S.; Waddling, R. E. L., Tet. Lett. 1979, 193; Trippett, S.; FontFreide,

J., J. Chem. Soc. Chem, Comm. 1980, 157.17. R. J. P., et al. Tetrahedron 1979, 35, 2889, and references cited therein.18. Ramirez, F., Synthesis, 1974, 90, and references cited therein.19. Denney, D. B., et al, J. Org. Chem. 1978, 43, 4672; Denney, D. B., et al. J. Am.

Chem. Soc. 1966, 88, 1839; Denney, D. B., et al, Ibid, 1969, 91, S243.20. Voncken, W. G.; Buck, H. M., Recl. Trav. Chim. PaysBas 1974, 93, 14, 210.21. Ramirez, F., et al, J. Am. Chem. Soc. 1960, 82, 2652; Ramirez, F., et al, J. Org,

Chem. 1968, 33, 20; Ramirez, F., J. Am. Chem. Soc. 1969, 91, 496; Ramirez, F.,et al, ibid., 1970, 92, 6935.

22. Corre, E.; Foucand, A., J. Chem. Soc. Chem. Comm. 1971, 570.23. Stephenson, L. M.; Falk, L. C., J. Org. Chem. 1976, 41, 2928.24. Ramirez, F., et al, J. Am. Chem. Soc. 1965, 87, 543; Ramirez, F., et al, J. Org.

Chem. 1965, 30, 2575; Ramirez, F., Tet. Lett. 1965, 261; Ramirez, F., et al, Tet.1968, 24, 1931.

25. Ramirez, F. et al., J. Org. Chem. 1966, 31, 3159; ibid. 1966, 31, 474; ibid., 1967,32, 2194; 3547; ibid., 1968, 33, 1185.

26. Ramirez, F., et al., Tetrahedron 1968, 24, 3153.27. Inouye, Y., et al, Bull. Chem. Soc. Japan 1969, 42, 2948.28. David, S., et al, J. Chem. Soc. Chem. Comm. 1976, 747.29. David, S., et al, J. Chem. Soc. Perkin 1 1980, 1262.30. Burgada, R.; Fauduet, H.; Nouv. J. Chim. 1980, 4, 112,31. Ramirez, et al, J. Am. Chem. Soc. 1967, 89, 3026.

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32. Ramirez, F. et al , J. Org. Chim. 1969, 34, 376.33. Ramirez, F. et al., J. Am. Chem. Soc. 1967, 89, 3030; Ramirez, F. et al., ibid.,

1970, 92, 6935.34. Ramirez, F. et al., Phos., 1973, 2, 185.35. Ramirez,F. et al., Tetrahedron 1975, 31, 2007.36. Ramirez, F. et al., Heterocycles, 1978, 11, 631.37. Mukaiyama, T.; Kumamoto, T.; Bull. Chem. Soc. Jpn. 1966, 39, 879.38. Denney, D. B., et al., J. Am. Chem. Soc. 1969, 91, 5821.39. Denney, D. B. , et al., ibid., 1971, 93, 4004.40. Bartlett, P. D., et al., ibid., 1973, 95, 6486.41. Ramirez, et al., J. Org. Chem. 1968, 33, 13.42. Denney, D. B. , et a. , Phos. , 1971, 1, 151 .43. Ishikawa, M, et al , Chem. Lett. 1979, 845. Ishikawa, N., et al., J. Org. Chem.

1980, 45, 5052.44. Kobayshi, Y., Askahi, C., Chem. Pharm. Bull. 1968, 16, 1009. Witey, G. A., et al,

J. Am. Chem. Soc. 1964, 86, 964.45. Motoyoshiya, J. , et al , J. Org. Chim. 1980, 45, 5385.46. Ohah, G. A., et al, Synthesis, 1974, 506.47. Piers, E., Nagakura, I., Syn. Comm. 1975, 5, 193.48. Appel, R., Chem. Ber. 1970, 109, 814.49. Ramirez, et al, J. Org. Chem. 1968, 33, 1192,50. Harpp, D. N., Mathiaparanam, P., Tet. Lett. 1970, 2089; J. Org. Chem. 1971,

36, 2540; ibid., 1972, 37, 1367.

Rings and Cages of Phosphorus Atoms

Cyclopolyphosphanes have been studied in great detail , notably by the group ofMarianne Baudler

1. Chem. Rev. 1993, 93, 1623 1667

Reactions of Red and White Phosphorus

Reaction of red phosphorus with M = K, Rb, Cs leads to the formation of salts M4P6with isolated, planar P6anions. The PP bond distances in these rings are shorter(215) than typical single bonds (221 p

Attempts to stabilize these interesting ring systems by the derivatization withelectrophiles lead to complex rearrangements. The predominant products are usuallythe cage compounds P7(E)3:

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The pentaphosphacyclopentadienylanion is formed as side product in many ofthese reactions. A high yield synthesis is the reaction of red phosphorus with KPH2 inboiling DMF:

Solutions of [P5] decompose upon attempted concentration or if diluted with lesspolar solvents. Computational studies have confirmed that the anion is aromatic.

T. P. Hamilton, H. F. Schaefer, Angew. Chem. 1989, 101, 500.R. Janoschek, Chem. Ber. 1989, 28, 485.

Reactions with of the aromatic [P5] alkyl halides produce rearranged products oftype P7R3 and P9R3, but in reactions with transition metal compounds, the P5framework is preserved:

Phosphabenzene

sp2 hybridization is prerequisite for the incorporation of phosphorus into anaromatic ring. Phosphanes R3P have a much stronger preference for sp3hybridization than nitrogen. Accordingly, phosphaaromatic heterocycles are rare

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and not particularly stable. This instability does not reflect a lack of delocalization,but rather the high energy of energy of sp2hybridized phosphorus.

The first aromatic phosphorus compound was reported by Märkl in 1966:

Märkl et al. Angew. Chem. Int. Ed. Engl. 1966, 5, 846

Unsubstituted derivatives were first described by Ashe:

An interesting alternative approach is the introduction of elementcarbon doublebonds through retroene synthesis has been introduced by Ocando Mavarez [1]:

The strategy has been adopted by Mathey for the synthesis of phosphabenzene byflash vacuum thermolysis:

Under the same conditions, trisallylphosphine gives HCP:

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The mechanism of this reaction involves the formation of the antiaromatic phosphacyclobutadiene:

1. G. Martin, E. OcandoMavarez, Heteroatom Chem. 1991, 2, 651; G. Martin, E.OcandoMavarez, A. Osorio, M. Canestrari, Heteroatom Chem. 1992, 3, 395.

2. P. LeFloch, F. Mathey, J. Chem. Soc. Chem. Commun. 1993, 1295 1296

The structures of phosphabenzene, arsabenzene, stibabenzene and bismabenzeneshow a high degree of delocalization (similarity of formal single and doublebonds):

In view of the great distortions imposed by the heteroelement, this uniform similarityof single and double bonds seems even more surprising .

Phosphabenzene and arsabenzene can be distilled without decomposition, stibaand bisma benzene undergo reversible dimerization:

The of phosphabenzene (indefinitely stable at rt under exclusion of oxygen) is inmarked contrast to the very low stability of silabenzene. This reflects the fact thatSi=C bonds are much weaker than P=C bonds.

To have a quantitative estimate of the relative stability of the Si=C vs. P=C doublebond, transfer hydrogenations reactions can be calculated:

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Relative stability of SiC and PC doublebonds

Phosphabenzene forms eta1 and eta6 complexes with transition metals.

The Staudinger Reaction

The best method for the synthesis of iminophosphoranes is the reaction ofphosphines with azides:

Trimethyl Ncyanophosphoroimidate [2]

Cyanogen azide (7.0 g, 0.1 mol) in MeCN (40 mL) was added slowly to trimethylphosphite (12.4 g, 0.1 mmol) in Et20 (200 mL) with cooling at 15 oC. When nitrogenevolution was complete, the volatiles were removed in vacuum and the residue waswashed with Et2O to give 13.1 g of 3 (80%), mp 56.4 56.8 oC.

Ethyl 3aminopropanoate [5]

To a 1 M solution of 4 in THF (from the bromo ester with NaN3 in DMSO) wasadded a molar equivalent of Ph3P, 1.5 equiv of water and a boiling chip (N2evolution). After 8 h at 200 oC and evaporation, the residue was treated with Et20hexane and Ph3PO was filtered. This process was repeated and 5 was distilled at 40450 and 10.5 torr (83%).References

1. Staudinger, H., Helv. Chim. Acta. 1919, 2, 635.2. Marsh, F.D., J. Org. Chem. 1972, 37, 29663. Cooper, R.D.G., Pure and Appl. Chem. 1987, 59, 485.

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4. Gololobov, Yu G., Tetrahedron, 1981, 37, 437.5. Carrie, R., Bull. Chem. Soc. Fr. 1985, 815.

The MichaelisArbuzovPhosphonate Synthesis

The ArbuzovMichaelis reaction is the synthesis of phosphonates from alkylhalidesand phosphites:

is a Ni catalyzed phosphonate synthesis from phosphites and aryl halides. Reactionof alkyl halides with phosphites proceeds without nickel salts.

Diethyl phenylphosphonate [3]

Tetrakis(triethylphosphite)nickel(0): stirred NiCl2 (5 g) and triethylphosphite 1 (60 mL) was heated and maintained for 1 h at 150 o. The solidwas filtered, triturated with MeCN and washed with MeOH to give 4.6 g of[(EtO)3P]4Ni, mp 106109 oC.

Diethyl phenylphosphonate: to [(EtO)3P]4Ni (10 mg) in iodobenzene(10.0 g. 49 mmol) at 160 o was added slowly 1 (9.37 g, 56.4 mmol). Thesolution (red upon each addition of 1), faded to yellow and EtI was distilled.Vacuum distillation afforded 9.88 g of PhP(O)(OEt)2 (94%), bp 94 101 oC(0. 1 mm).

References

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1. Michaelis, A., Chem. Ber., 1898, 31, 1048.2. Arbuzov, A J. Russ. Phys. Chem. Soc. 1906, 38, 687.3. Balthazar, T.M. J. Org. Chem. 1980, 45, 5425.4. Montero, J.L. Tetrahedron Lett. 1987, 28, 1163.5. Brill, Th.B. Chem. Rev. 1984, 84, 577.6. Kosolapov, G.M. Org. React. 1951, 6, 276.7. Kern, M.K. J. Org. Chem. 1970, 36, 5118.8. Redmore, D. J. Org. Chem. 1981, 46, 4114.

The KuhnWinterstein Reaction

Olefination Olefin formation from glycols by means of P2I4.

3,4Bis(4,4ethylenedioxocyclohexyi)3hexene1,5diine (2) [3]

P2I4 (60 g, 0.135 mol) was extracted with CS2 in a Soxhlett. To this extract wasadded 3,4bis(4,4ethylidenedioxcycyclohexyl)3,4hexanedioldiine 1 (30 g,0.077 mol) in pyridine (600 mL). The mixture was stirred at 20 oC for 2 h andthe solvent was distilled. The residue was treated with Et2O and after work upthe product was chromatographed on Woelm Alumina, active. l 1.Recrystallization from MeOH afforded 12.9 g of 2 (43%).

References

1. Kuhn, R., Winterstein, A., Helv. Chim. Acta. 1928, 11, 87.2. Kuhn, R., Winterstein, A., Helv. Chim. Acta. 1955, 27, 309.3. lnhoffen, C. Liebigs Ann. 1965, 684, 24.

The Oleksyszyn Aminophosphonic Acid Synthesis

Synthesis of 1aminoalkane phosphonic and 1aminoalkane phosphinic acids fromketones or aldehydes, chlorophosphines and carbamates.

1Aminocyclohexylphosphonic acid (4).[1]

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Cyclohexanone 1 (7.35 g, 75 mmol) was added at 20 oC to a stirred mixture ofbenzyl carbamate 3 (7.55 g, 50 mmol) and PCl3 2 (6.87 g, 50 mmol) in AcOH (10mL). The mixture was refluxed for 40 min, treated with 4 M HCl (50 mL) and againrefluxed for 0.5 h. After cooling, the organic layer was removed and the aqueoussolution was refluxed with charcoal. After filtration and evaporation in vacuum, theresidue was dissolved in MeOH (25 40 mL). The methanolic solution was treatedwith propene oxide until pH 67 is reached. The precipitate was filtered, washedwith Me2CO and recrystallized from MeOH water to give 7.74 g of 4 (58%), mp264 265 oC.

The Perkow Vinyl Phosphate Synthesis

Reaction of 2haloketones with trialkylphosphite to give ketophosphonate or vinylphosphate.

1,3Butadiene2,3diol bis (diethyl phosphate) (3).4

To a stirred solution of 1,4dibromo2,3butanedione 1 (12.2 g, 50 mmol) in Et2O(50 mL) was added dropwise triethylphosphite 2 (16.6 g, 100 mmol). The reactionmixture was stirred below 10 oC for 2 h. The solvent was removed and the residue17.2 g 3 (98%) was identified by IR, NMR and MS.

References

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1. Perkow, W., Naturwissenschaften 1952, 39, 353.2. Perkow, W., Chem. Ber. 1954, 87, 755.3. Borowitz, I.J., J. Org. Chem. 1971, 36, 3282.4. Hennig, M.L., J. Org. Chem. 1973, 38, 3434.5. Mitsunobu, S., J. Org. Chem. 1981, 46, 4030.6. Lichtenthaler, F. W., Chem. Rev. 1961, 61, 60.

Nerve Gases

In the 1930's, Gerhard Schrader began research on the development and use ofchemical pesticides for the company IG Farben. By chance, Gerhard synthesized thenerve agent Tabun.

Sarin and Soman were produced by Gerhard soon after. Gerhard, who had originallybeen looking for a panacea to the problems of insects and crops had stumbled upon asolution to an even larger possible nuisance, humans.

The reason why Adolf Hitler did not order the use of nerve gases in WWII is still asubject of controversy. The most popular explanation for Hitler's apathy stems backto the previous World War where toxic gases were used in combat. Hitler had beenvictimized by these chemical agents and was unwilling to introduce new and moretoxic agents. There is also evidence that suggests that Hitler was advised againstusing the agents and even stopped their production. Hitler's Minister of Production,

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Albert Speer, said after the war, "All sensible army people turned gas warfare downas being utterly insane, since, in view of America's superiority in the air, it would notbe long before it would bring the most terrible catastrophe upon German cities."

Another, more persistent agent, named VX was discovered by British chemist R.Ghosh after the war.

A famous contemporary incident of use was in the IranIraq war (19841988). In thisconflict the UN confirmed that Iraq used the nerve agent Tabun and otherorganophosphorous nerve agents against Iran. This incident is a prime example ofhow chemical warfare technology was shared during the Cold War. The Sovietswould arm their allies while the US did the same for its allies. Iraq was obviously abenefactor and implemented its chemical stockpiles during the war.

Another contemporary incident of nerve agent use occurred in Japan. The AumShinrikyo Cult was reported to have used the nerve agent Sarin in a Tokyo subway.This incident of use gives some clue as to the new roles that nerve agents play, astools of terrorists instead of powerful nations.

Symptoms

Nerve agents are generally colorless, odorless, and are readily absorbable through thelungs, eyes, skin, and intestinal tract without producing any irritation. They are alsoextremely potent, so even a brief exposure can be fatal. Death may occur in 1 to 10minutes, or be delayed for 1 to 2 hours, depending on the concentration to which avictim has been exposed.

If you were to be exposed to realizable field concentrations, inhalation would beessentially immediately incapacitating. Your general order of symptoms would be asfollows:

First, your nose would begin to run, then your chest would feel constricted. Yourvision would dim as your pupils contracted into pinpoints. You'd begin to drool andsweat excessively. Then would come nausea and vomiting, intestinal cramps andinvoluntary urination or defecation. You'd twitch, jerk, and stagger as you'reovercome with convulsions and possibly coma. Finally, you're breathing would stopas your diaphragm and the muscles of your chest froze, causing you to die ofsuffocation.

continued in chapter 6: Organometallic Chemistry of the Copper and Zinc Triads

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Chapter 10

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