My PhD dissertation - Institut Fresnel

More documents

Recommendations

Info

3.3 Assessment of the Relative Ease of Alkyl Expulsion from Phosphonium Salts 22 The new method developed during this thesis work for quantitatively determining the relative stabilities of various carbanions, and particularly the alkyl ones, was based on the use of the alkaline decomposition of phosphonium halides. On the basis of their precursor work on this field, G.W. Fenton and C.K. Ingold [30] postulated that the ease of expulsion of one of the phosphonium substituents was governed by the stability of its related anion. These authors, and more recently H.R. Hays and R.G. Laughlin [52] treated a series of mixed phosphonium salts bearing phenyl, allyl, benzyl or various alkyl groups such as methyl, ethyl, propyl, dodecyl or tridodecyl under alkaline conditions and evaluated the ratios of the different products formed. The decomposition of dodecyltrimethyl or tridodecylmethyl phosphonium hydroxide [52] gave in both cases, only one phosphine oxide and its associated alkane, corresponding to the expulsion of the most stable methyl carbanion. On the other hand, when decomposing phosphonium salts bearing different but more similar groups such as ethyltripropyl or triethylpropyl phosphonium salts, G.W. Fenton and C.K. Ingold [30] obtained a mixture of tripropyl and ethyldipropyl phosphine oxide or of diethylpropyl and triethyl phosphine oxide, respectively, and the corresponding alkanes. Unfortunately, since the quantification of the reaction products was relying on gas evolution measurements and isolation of the oxides by distillation, the data collected were only qualitative or, to some extent, gave a vague idea of the relative ease of expulsion for the different alkyl substituents. From these results, the different author involved in these studies proposed an approximate scale of stability for various carbanions: benzyl, allyl > phenyl > methyl > ethyl, higher primary alkyls The aim of this new method was to provide accurate and quantitative data for a series of primary but also previously unstudied secondary and tertiary alkyl substituents to probe relative stabilities of alkyl carbanions and discuss the different parameters influencing their leaving ability. As a matter of fact, even if few primary alkyl anions have been already described [29, 30, 52] , be it only qualitatively, no reports concerning secondary or tertiary alkyl anions stabilities in solution have so far been published. The lack of informations for the alkaline decomposition of tetraalkyl phosphonium salts probably partially accounts for the chemical properties of alkylphosphine compounds which are fairly difficult to handle and easily prone to oxidation. Furthermore, the collected results of this study were analyzed by the light of various mechanistic discussions concerning the alkaline decomposition of phosphoniums halides.
3.3.1 Mechanistic Discussion on the Alkaline Decomposition of Phosphonium Salts 23 Although various authors [29 - 35] assumed this decomposition to proceed trough several independent equilibrated or irreversible steps, the kinetics and other results reported thus far could perfectly match with other alternative mechanisms. A concerted mechanism involving a pentavalent hydroxyphosphorane and a hydroxide ion could also be consistent with the products obtained. This mechanistic pathway would then directly produce an alkane without formation of a free carbanion as proposed by C.K Ingold et al. [29, 30] . R 1 P R3 R 4 R2 K HO I HO R 4 R 1 P + KI R 3 R 2 K HO R1 R2 O H H K O P According to the Bell-Evans-Polanyi theory R 4 R 3 R 2 P R3R4 + R1H O [ - ] 126 128 and provided that the different reactants involved are being slightly polarized, the concerted alternative for this reaction would require lower activation energy than its non-concerted analog. As a matter of fact, if the cleavage of the P−R 1 bond (increase of the r P…R 1 distance) occurs simultaneously to the formation of the R 1 −H bond (decrease of the r R 1 …H distance) the system can lower its activation energy by a "concertation energy" factor. The amount of this stabilisation energy essentially depends, as explained by R.P. Bell [128] , and M.G. Evans and M. Polanyi [126, 127] , on the ability of both bonds involved to be polarized. The concerted mechanism proposed, if consistent, would possibly imply that the relative ease of substituent expulsion could be also governed by other factors than the carbanion stability such as steric strains. Indeed, if no free carbanions but only alkanes are produced, a question had to be adressed: does a negative partial charge show up on the alkyl substituent in the course of the decomposition and to what extent does it influence the departure of the alkyl group? An evidence for the presence of a partial negative charge on the leaving alkyl group was provided by surveying the effects of substituents on the alkaline decomposition of several substituted triarylbenzylphosphoniums salts. H. Hoffmann [32] first reported the dependence of the alkaline cleavage rate of variously p-substituted-benzyltriphenylphosphonium salts. Electron withdrawing substituents caused acceleration of the rate of decomposition whereas electron donating ones had the opposite effect. Application of the Hammett equation [ ] 129 gave a good correlation and afforded a rate factor ρ of +4.62 [36] . This result clearly showed the importance of electron withdrawing substituents in stabilizing an anionic character developed
Page 1: Various Facets of Organophosphorus
Page 5: III Remerciements Je tiens à remer
Page 9: 3.3.6 Relevance of the Data Assesse
Page 13: VII Literature References 115 Compo
Page 17: IX Version Abrégée Les composés
Page 21 and 22: 1 Introduction 1 The present thesis
Page 23 and 24: 3 research groups in the field are
Page 25 and 26: 5 However, this mechanism suffers f
Page 27: 7 At first, a double bromine/lithiu
Page 30 and 31: 10 Although the most frequently emp
Page 32 and 33: 12 The preparation of the latter ph
Page 34 and 35: protected to its dioxolane derivati
Page 36 and 37: N (S)-14 1) NBS, THF, - 75 °C 2) -
Page 39 and 40: 3 Alkaline Decomposition of Phospho
Page 41: 3.2 Alkyl Carbanions Stabilities in
Page 45 and 46: 25 The assumption reported by these
Page 47 and 48: 27 However, in the eventuality of a
Page 49 and 50: 29 To prepare tertiary phosphines b
Page 51 and 52: 31 Table 4. Mixed tertiary alkylpho
Page 53 and 54: 33 were comparable to those obtaine
Page 55 and 56: 35 led to the formation of di-tert-
Page 57 and 58: 37 depending on the alkyl substitue
Page 59 and 60: 39 4 A Novel Access to Atropisomeri
Page 61 and 62: 41 Since the homocoupling of the ha
Page 63 and 64: 43 Few other attempts to selectivel
Page 65 and 66: 45 The second phenol ether 36 was f
Page 67 and 68: 47 The enantiomeric purity was chec
Page 69 and 70: 49 A second purpose of this derivat
Page 71 and 72: 51 substrates considered. In conseq
Page 73 and 74: 53 Single-crystal X-ray analysis of
Page 75 and 76: 55 To convert atropisomer Ia into I
Page 77 and 78: 57 This finally allows one to use t
Page 79 and 80: the steric bulk and charge delocali
Page 81 and 82: 61 To check the reproducibility of
Page 83: 63 Figure 9. Full lineshape analysi
Page 86 and 87: 66 suitably substituted dilithiobip
Page 89: Experimental Part
Page 92 and 93:
70 deuterochloroform (CDCl3) unless
Page 94 and 95:
72 1 H NMR: δ = 7.32 (dddd, J = 9,
Page 96 and 97:
1 H NMR: δ = 6.96 (s, 3 H), 6.94 (
Page 98 and 99:
76 C21H21O9P (448.36) calcd. C 56.2
Page 100 and 101:
78 C12H12BrN (250.13) calcd. C 57.6
Page 102 and 103:
80 C13H13NO2 (215.25) calcd. C 72.5
Page 104 and 105:
82 3.1.1 Dialkyl-N,N-diethylaminoph
Page 106 and 107:
84 apparatus. The solution was adde
Page 108 and 109:
86 Di-tert-butylisopropylphosphine
Page 110 and 111:
88 13 C NMR: δ = 32.9 (d, J = 12 H
Page 112 and 113:
90 13 C NMR: δ = 41.5 (d, J = 61 H
Page 114 and 115:
31 P NMR: δ = 53.4 ppm. 92 C16H31O
Page 116 and 117:
94 13 C NMR: δ = 40.8 (d, J = 3 Hz
Page 118 and 119:
96 31 P NMR settings: It is known t
Page 120 and 121:
98 Theoretical ratio: (96.1:3.9) Ex
Page 123 and 124:
101 4 The Preparation and Racemate
Page 125 and 126:
103 extraction protocol with ethyl
Page 127 and 128:
105 extracted with ethyl acetate (2
Page 129 and 130:
107 (+)-(M)-Dimethyl-6,6’-dibromo
Page 131 and 132:
109 (+)-(M)-2,2’-Dibromo-6,6’-b
Page 133 and 134:
111 1 H NMR: δ = 7.2 (m, 20 H), 7.
Page 135 and 136:
113 2,2’-Dilithio-6,6’-bis(meth
Page 137:
References
Page 140 and 141:
116 Conference Proceedings, Naples,
Page 142 and 143:
118 [ 70] J. Drowart, C.E. Myers, R
Page 144 and 145:
120 [117] S.T. Graul, R.R. Squires,
Page 146 and 147:
122 [170] B.H. Lipshutz, F. Kayser,
Page 148:
124 [212] M. Schlosser, in Organome
Page 152:
O P 27i: p. 30, 80 C 9H 21OP P 26b:
Page 156:
P P P O 2: p. 11, 59 3 P O O O 11:
Page 160:
Nom Maurin Prénom Michaël 129 Cur
show all

My PhD dissertation - Institut Fresnel

Create successful ePaper yourself

Delete template?

Save as template?