Louis D. Quin

Phospholes with reduced pyramidal character from steric crowding III NMR and X-ray diffraction studies on 1-(2,4,6-tri-isopropylphenyl)-3-methylphosphole

Abstract The 2,4,6-tri-isopropylphenyl substituent was placed on the phosphorus of a phosphole to reduce the pyramidal character. That this was accomplished was revealed by single crystal X-ray diffraction analysis; with respect to the plane of C2PC5 in the phosphole ring, the ipso carbon of the benzene ring was deflected by only 58.0°, whereas the deflection is 66.9° in the uncrowded 1-benzylphosphole. This proves that the concept of reducing the pyramidal character (with the goal of increasing the electron delocalization) through steric crowding can be realized. In the crystal the two rings are in orthogonal planes, but this relation is not retained in solution; NMR studies show that the two edges of the benzene ring, as well as the 2,6-isopropyl groups, are identical.

Practical aspects of the chemistry of metaphosphates and other transient dioxophosphoranes

Abstract Practical laboratory procedures now exist for the generation of organic derivatives of metaphosphoric acid (HOPO 2 ), as well as for dioxophosphoranes (RPO 2 ). These methods are evaluated in this review. Although these substances are highly reactive and have but a fleeting existence, they can nevertheless be employed as reactants in synthetic phosphorus chemistry. The various applications that have been demonstrated in the literature are also discussed in this review.

Thermolysis of 2-phosphabicyclo[2.2.2]octa-5,7-dienes: generation and trapping of P-methyl- and P-phenylphosphaethene

Abstract P-Methyl- and P-phenylphosphaethene were generated in solution under very mild conditions in virtually quantitative yield by a thermally-induced extrusion of the phosphorus-containing bridge from appropriately substituted 2-phosphabicyclo[2.2.2]octa-5,7-dienes. The phosphaethenes so formed, the simplest yet produced by conventional methods, are trapped readily in [2+4] cycloadditions with conjugated dienes.

Generation of ester and amide derivatives of metaphosphoric acid by photolysis of 2,3-oxaphosphabicyclo[2.2.2]oct-5-ene derivatives

Abstract Irradiation at 254 nm of P-NMe 2 and P-OEt derivatives of phosphonates where P is incorporated into the 2,3-oxaphosphabicyclo[2.2.2]oct-5-ene framework results in fragmentation of the molecules to release N,N-dimethylamino metaphosphoramidate and ethyl metaphosphate, respectively. Both species polymerize rapidly, but are effectively trapped as phosphate deriva- tives when alcohols are included in the reaction mixtures.

Special Properties Imparted to the 9-Phosphabicyclo[6.1.0]nonatriene system by a P-(2,4,6-tri-t-butylphenyl) substituent; 17O NMR spectrum of a bicyclic phosphirane oxide

Abstract 9-(2,4,6-Tri-t-butylphenyl)-9-phosphabicyclo[6.1.0]nona-2,4,6-triene gave an observable P-oxide with t-butyl hydroperoxide. Decomposition occurred by expulsion of the phosphorus fragment, possibly as ArPO, rather than by the expected ring expansion to a phosphonin oxide. The 17O NMR shift of 18.0 is the most upfield known for a phosphine oxide.

The mechanism of fragmentation of alkyl α-(oxyimino)benzylphosphonates; use of silica gel as a novel hydroxylic trapping reactant for an intermediate alkyl metaphosphate.

Abstract Silica gel was employed to react with the suspected metaphosphate intermediate of the acid-promoted cleavage of monoalkyl α-(oxyimino)benzylphosphonates. The silica gels displayed CP-MAS 31 P NMR signals at about δ −8. A similar value was obtained for silica gel phosphorylated with ethyl metaphosphate from a different source (thermolysis of a P-ethoxy 2,3-oxaphosphabicyclo[2.2.2]octene derivative.

Photolysis of 7‐(2,4,6‐trialkylphenyl‐)7‐phosphanorbornene 7‐oxides in the presence of protic species

Irradiation of 7-(2,4,6-trialkylphenyl-)7-phosphanorbornene 7-oxides at 254 nm in the presence of alcohols or water led to H-phosphinic acid derivatives. The experimental data are consistent with the mechanism established earlier for P-phenyl derivatives, involving a five-coordinate adduct from the interaction of the phosphanorbornene and the protic species which then fragments. There is no evidence that the langer substituent allowed a competing reaction to occur where the first step is unimolecular fragmentation to a two-coordinate phosphoryl species.

Generation of p-dialkylamino methylenephosphine oxides by the photochemical fragmentation of 2-dialkylamino-2-phosphabicyclo[2. 2.2]- octa-5, 7-diene 2-oxides

Abstract A new P-amino phosphabicyclooctadiene is described which together with a similar derivative can be utilized in the generation of dialkylamino methylenephosphine oxides by photolysis. Reaction of these so far unknown intermediates with ethanol gives rise to N,N-dialkyl-O-ethyl methylphosphonamidates. The latter species were also formed by the photolysis of a P-ethoxy phosphabicyclooctadiene carried out in the presence of secondary amines.

THE GENERATION OF METAPHOSPHORAMIDATES BY FRAGMENTATION OF 2,3-OXAPHOSPHABICYCLO[2.2.2]OCTENE DERIVATIVES

Abstract Phosphole oxides with N,N-diethylamino, N-mesitylamino and N-tert-butylamino substituents on phosphorus were generated in the presence of N-phenylmaleimide to give Diels-Alder adducts with the 7-phosphanorbornene framework. Products were characterized by 31P and 13C NMR spectroscopy, and in one case by 17O NMR spectroscopy. Insertion of oxygen into a P[sbnd]C bond of this strained cyclic system occurred smoothly on treatment with m-chloroperbenzoic acid. The resulting derivatives with the 2,3-oxaphosphabicyclo[2.2.2]octene ring system were characterized by 1H, 31P, and 13C NMR spectroscopy. In the case of the N-mesityl derivative, two stable isomers were formed and separated by chromatography. The full structure of one isomer was established by X-ray diffraction analysis. The ring system was fragmented on heating in toluene (110°C, 22–48 hrs) or on irradiation (30–35°C, 254 nm, 24 hrs) with the release of the P[sbnd]O bridging unit as a metaphosphoramidate (RR′N[sbnd]PO.). In the photolytic metho...

FRAGMENTATION OF A PHENYLPHOSPHONAMIDIC ACID AS A NEW TECHNIQUE FOR THE GENERATION OF PHENYL DIOXOPHOSPHORANE

Abstract N-(1-Adamantyl) phenylphosphonamidic acid (3), an easily prepared solid, on heating in toluene or 1,2-dichloroethane gave the crystalline adamantylamine salt of the anhydride PhP(O)(NHAd)[sbnd]O[sbnd]PPh(O)(OH). The mechanism is proposed to involve first the fragmentation of 3 to form phenyl dioxophosphorane, PhPO2, which then acts as a phosphorylating agent to unreacted 3. This mechanism was supported by the observation of first-order kinetics for the consumption of 3. When the phosphonamidic acid was fragmented in the presence of an alcohol, the intermediate PhPO2 was trapped as the monoalkyl phenylphosphonate. The OH groups on the surface of silica gel were also phosphonylated by PhPO2. The acidic OH group of a phosphoric acid monoester (thymyl phosphate) was phosphonylated to give Thy[sbnd]O[sbnd]P(OXOH)[sbnd]O[sbnd]PPh(O)(OH). It is concluded from this study that N-(1-adamantyl) phenylphosphonamidic acid is a useful precursor of phenyl dioxophosphorane, which can perform valuable phosphonyla...