Rupert E. v. H. Spence

Nuclear magnetic resonance spectroscopic characterisation and the crystal and molecular structures of Ph3PSe·AlCl3and Ph3PSe·AlCl3: a classification of the co-ordinative bonding modes of the phosphine chalcogenides

A series of compounds with the general formula R3PE·AlCl3(R = Ph or NMe2, E = S or Se) has been examined by n.m.r. spectroscopy as a contribution toward the characterisation of the P–E bond and of the co-ordinate bond. Two derivatives, Ph3PS·AlCl3 and Ph3PSe·AlCl3, have been studied by X-ray crystallography. [Crystal data: C18H15AlCl3PS, monoclinic, space group, P21/n, a= 9.710(2), b= 9.464(1), c= 21.893(5)A, β= 95.15(2)°Z= 4, R= 0.042; C18H15AlCl3PSe, triclinic, space group, Pa= 8.967(2), b= 12.626(4), c= 18.242(4)A, α= 84.83(2), β= 89.02(2), γ= 85.67(2)°, Z= 4, R= 0.044.] In contrast to the oxygen analogues, the sulphur and selenium derivatives exhibit bent geometries [P–S–Al 109.62(8), P–Se–Al (mean)= 107.0(1)°]. The structures are maintained in solution, as demonstrated by the 27Al n.m.r. spectra. The 31P and 13C n.m.r. spectra are informative of the changes associated with adduct formation, and show the oxygen derivatives (E = O) to be unique. Disruption of the P–E π interaction due to adduct formation is more dramatic for the sulphur and selenium than for the oxygen derivatives. The extensive information available in the literature is re-evaluated in the light of the present results, and a classification for the co-ordinative bonding modes of the phosphine chalcogenides is proposed.

Chemistry of the diaminochalcogenophosphinic chloride-aluminium trichloride system : preparation and crystal structures of new chalcogenophosphonium cations

A comprehensive investigation of the reactions between diaminothiophosphinic chlorides, (R2N)2P(S)Cl (R = Me, Et, or Pri), and aluminium trichloride confirms the potential for at least two modes of reactivity. Typical Lewis acid–base complexes have been observed at room temperature in solution by 31P and 27Al n.m.r. spectroscopy. However, in the solid state, novel dimeric heterocyclic diphosphonium systems have been isolated for the Me2N and Et2N derivatives (crystal data for [{(Et2N)2PS}2][AlCl4]2: monoclinic, space group P21/n, a= 10.598(2), b= 8.976(2), c= 19.370(4)A, β= 98.65(2)°, Z= 2, R= 0.052). In contrast, the Pri2N derivative maintains the covalent Lewis acid–base adduct structure in the solid state [crystal data for (Pri2N)2P(Cl)S·AlCl3: monoclinic, space group P21/c, a= 12.705(5), b= 9.504(3), c= 18.016(6)A, β= 92.85(3)°, Z= 4, R= 0.066]. The diaminoselenophosphinic chlorides show no evidence of adduct formation in solution; however, identical heterocyclic diphosphonium salts have been isolated in the solid state for the Me2N and Et2N derivatives (crystal data for [{(Et2N)2PSe}2][AlCl4]2: triclinic, space group P, a= 10.635(7), b= 12.335(8), c= 15.159(9)A, α= 95.94(8), β= 93.46(7), γ= 110.99(9)°, Z= 2, R= 0.066). The new heterocycles represent examples of heterocyclic thiophosphonium (and selenophosphonium) cations, and are structurally related to known neutral isovalent phosphetanes. In solution, the thiophosphonium salts dissociate and reform the Lewis acid–base adducts, while the selenium analogues adopt an equilibrium involving only ionic species. The delicate energetic balance between ionic and covalent structures is further demonstrated for the sulphur systems by the promotion of the ionic structures in solutions containing an excess of AlCl3. However, the solution species react with CH2Cl2 by means of an electrophilic attack at the sulphur centre.

Covalent alternatives for the elusive iminophosphonium cation. Crystal structures of PCl(NPri2)2NPh·AlCl3 and P(NPri2)2[NPh(SO2CF3)]O

Reactions between diaminoiminophosphinic chlorides and the chloride-abstracting agents AlCl3 and Ag(SO3CF3) have been comprehensively examined as potential routes to the three-co-ordinate iminophosphonium cation. However, bis(dialkylamino)(phenylimino)phosphinic chlorides react to give the covalent phosphoryl systems PCl(NR2)2NPh·AlCl3 and P(NR2)2[NPh(SO2CF3)]O respectively, in quantitative yield. The AlCl3 complexes are also prepared quantitatively from the reaction of P(NPri2)2+AlCl4– with PhN3(Staudinger reaction). All compounds have been comprehensively characterised and the structures of the isopropyl derivatives confirmed by X-ray crystallography. Crystal data: PCl(NPri2)2NPH·AlCl3, space group P21, a= 8.719(2), b= 15.553(2), c= 9.509(2)A, β= 102.73(2)°, Z= 2, R= 0.029; P(NPri2)2[NPh(SO2CF3)]O, space group P21/n, a= 10.594(3), b= 13.222(2), c= 17.084(3)A, β= 97.71(2)°, Z= 4, R= 0.048. The results indicate that the three-co-ordinate diaminoiminophosphonium cation is thermodynamically unstable with respect to the observed alternative covalent structures, and that steric shielding is responsible for the stability of the analogous diaminomethylenephosphonium cation.

Linear co-ordinative bonding at oxygen: a spectroscopic and structural study of phosphine oxide-Group 13 Lewis acid adducts

A number of adducts composed of phosphine oxides and Group 13 Lewis acids R3PO·EX3(R = Ph, NMe2, or PhO; E = B, Al, or Ga; X = F, Cl, or Br) have been spectroscopically characterised by multinuclear n.m.r. spectroscopy. Three isostructural derivatives have been structurally characterised by X-ray crystallography. Crystal data (all hexagonal, space group 3, Z= 6): Ph3PO·AlCl3, a= 13.663(2), c= 18.258(2)A, R= 0.062; Ph3PO·AlBr3, a= 14.021 (6), c= 18.387(3)A, R= 0.041; Ph3PO·GaCl3, a= 13.753(6), c= 18.345(6)A, R= 0.079. The structures show a uniquely linear or almost linear P–O–E backbone, which lies on the three-fold axis, in contrast to the bent structures observed for the corresponding BF3 adducts and other related systems. Short Al–O bonds [X = Cl, 1.733(4); Br, 1.736(7)A] are observed in both aluminium derivatives (E = Al). These compounds have narrow lines in the solution 27Al n.m.r. spectra, indicative of a highly symmetric environment for the aluminium centre, and consistent with a linear geometry in solution. The results provide experimental evidence for axially symmetric dative bonding by oxygen, support the triple-bond model for the phosphine oxide unit, and imply the possibility of a delocalised π interaction over the P–O–E framework.

Tetrathiadiazafulvalenes; preparation and characterisation of cis- and trans-[RCNS2CCS2NCR](R = Me, Ph)

Tetrathiadiazafulvalenes can be prepared by the reductive coupling of 5-methylthio-1,4,2-dithiazolium salts, and thermolysis of the resulting hexathiooxalates; oxidation of tetrathiadiazafulvalenes affords the corresponding radical cations.

The stability of Carbenic and Alkenic Phosphorus Environments

Abstract The factors responsible for the isolation or identification of (carbenic) phosphenium and (alkenic) tricoordinate phosphonium salts are discussed. Structural features, reactivity and observations of intramolecular rearrangement are presented, which illustrate some of the requirements for stability in each case.

Novel Cyclisations of the Chalcogeno-Phosphoryl Unit and the Formation of Genuine Heterocycles

Abstract A study of the interaction of imino-, oxo-, thio- and seleno- phosphorylic systems with Lewis acids has produced a number of interesting results, which represent a significant experimental contribution towards our understanding of the phosphorylic system. The most novel observations involve the heavier chalcogenophosphoryl systems, which produce new heterocyclic structures.