Role of through space 2p-3d overlap in the alkylation of (.omega.-N,N-dimethylaminoalkyl)diphenylphosphines and in the alkaline decomposition of related quaternary phosphonium salts

Abstract

A series of (ai-A,A-dimethylamlnoalkyl)diphenylphosphines has been prepared and subjected to reaction with benzyl chloride in benzene-methanol (60:40 v/v) at 31.0 ± 0.1 °C. Each of the quaternization reactions was found to follow the second-order rate law, and the data indicated the operation of a modest degree of through space 2p-3d overlap between the amino nitrogen and the phosphorus atom in the transition state. A series of quaternary phosphonium bromides containing an -A, A-dimethy lamí noalkyl group bonded to phosphorus was prepared and subjected to hydroxide-induced decomposition reactions in MeaSO at 22.0 ± 0.1 °C. Each reaction was found to follow the third-order rate law, and the data indicated the operation of a pronounced through space 2p-3d overlap effect. Finally, a series of quaternary phosphonium iodides containing an -methoxyalkyl group bonded to phosphorus was prepared and subjected to hydroxide-induced decomposition reactions in dioxane-water (1:1) at 45.0 ± 0.1 °C. Each reaction was found to follow the third-order rate law, and the relative velocities of reaction were found to be influenced by the inductive, electron-withdrawing effect of the methoxy group bonded to a saturated carbon atom of sufficient magnitude to mask any possible 2p-3d overlap effect. 146 ± 3 diphenyl(o-anisyl)-1 53.6 ± 0.7 diphenylmethyl-4 35.5 ± 0.3 diphenyl(2-methoxyethyl)-4 33.8 ± 0.3 diphenyl (3-methoxypropyl)-4 31.2 ± 0.2 diphenylethyl-4 27.1 ± 0.1 (TV.TV-dimethylaminomethyl)diphenyl-26.6 ± 0.2 (5-TV,iV-dimethylaminobutyl)diphenyl-26.5 ± 0.2 diphenyl-«-butyl-426.0 ± 0.1 diphenyl-«-propyl-4 25.9 ± 0.1 (/3-A',A'-dimethylaminoethyl)diphenyl-18.9 ± 0.2 (7-A',A'-dimethylaminopropyl)diphenyl-13.7 ±.2triphenyl-1 7.22 ± 0.13 diphenyl (methoxy methyl)-4 0.00* a Average deviation based on four to ten experimental results. b Too slow to measure under conditions cited.

Unequivocal Experimental Evidence for a Unified Lithium Salt-Free Wittig Reaction Mechanism for All Phosphonium Ylide Types: Reactions with β-Heteroatom-Substituted Aldehydes Are Consistently Selective for cis-Oxaphosphetane-Derived Products

“…This results in a 3-centre-4-electron bond, with the acceptor orbital being one of the P-C bond * orbitals, analogous to the (orthogonal) interaction forming the P-O bond. The proposal of such a throughspace interaction has long-time precedent in organophosphorus chemistry, having been used most notably by McEwen and coworkers in simple rationalizations of the rates of quaternization of ortho-substituted arylphosphines, 75 and ω-N,Ndimethylaminoalkylphosphines, 99 and hydrolysis of orthosubstituted arylphosphonium salts. 76 …”

“…This results in a three-center, four-electron (3c4e) bond, with the acceptor orbital being one of the P–C bond σ* orbitals, analogous to the (orthogonal) interaction forming the P–O bond. The proposal of such a through-space interaction has long-time precedent in organophosphorus chemistry, having been used most notably by McEwen and co-workers in simple rationalizations of the rates of quaternization of ortho -substituted arylphosphines and ω- N,N -dimethylaminoalkylphosphines and hydrolysis of ortho -substituted arylphosphonium salts. , More recently, similar through-space interactions have been proposed to explain O–Se peri -interactions in 1,8-substituted naphthalenes , and anthroquinones and large long-range PP coupling constants in 1,8-diphosphanaphthalenes, − a phosphorus-containing carborane, tetraphosphine ferrocenyl complexes, biaryl bisphosphines, and calix[4]­arene bisphosphites …”

Contrasting chemical and physical properties of [o‐ and [p‐(N,N‐dimethylamino) phenyl]phosphines and phosphonium salts

“…Although a much more extensive coverage of spectroscopic investigations of triarylphosphines and their corresponding quaternary phosphonium salts will be provided in a subsequent paper, a relatively brief coverage of this topic is required here. As we have pointed out in previous papers [ 1,6,8,20], the through-space 02,-P(IV) and N2,-P(IV) interactions, which involve transfer of electron density from the 0 and N atoms, respectively, to P(IV), should be of greater importance in quaternary phosphonium salts, where the P(1V) center is fully formed, than in the early transition states of SN2 reactions, where the formation of the P(1V) center is at an incipient stage. This is reflected in the spread of rates for the quaternization reactions as against the spread of rates in the decomposition of the corresponding quaternary phosphonium hydroxides.…”

“…This will reduce the magnitude of K I , at least, and lead to an overall rate reduction. The same would hold true for an essentially electrostatic attraction of the This same type of through-space interaction has been suggested to influence the alkaline cleavage reactions of (w-N,N-dimethylaminoalky1)benzyldiphenylphosphonium bromides [20]. The simple alkylbenzyldiphenylphosphonium hydroxides undergo alkaline cleavage in DMSO at 22.0"C at too rapid a rate to be measured conveniently, whereas the corresponding phosphonium hydroxides containing the w-N,N-dimethylaminoalkyl groups react at rates several orders of magnitude slower.…”

Phospha-Mannich reactions of RPH2, R2PH, and R3P

“…Entry R' R X Method Yield, % 1 H Cl Path A 85 [156] 2 H Cl Path A 78 [156] 3 H I Path A 95 [156] 4 Cl Path A 79 [156] 5 H Cl Path B 66 [159,160] 6 Me H Cl Path B (-)* [161] Table S21. P,N-acetals, derived from secondary phosphines and morpholine or N-substituted piperazines.…”