Cover Picture

Abstract

The cover picture shows the structure, determined crystallographically, of the tetrakis(trimethylstannyl)phosphonium cation that is formed with surprising ease from the reaction of P(SnMe3)3 with Me3SnOTf (OTf=OSO2CF3) and is isolated as the OTf salt. It is the first completely substituted main group organometallic phosphonium derivative, and, in contrast to the more common tetraorganic‐substituted phosphonium cations is only stable in the solid state; in solution it functions as a masked Me3Sn+ reagent. More about this chameleonlike ion and the N(SnMe3)4 cation homologue, which is equally dynamic in solution and has unusual long Sn−N bond lengths, is reported by M. Driess et al. on p. 3684 ff.

As[P(NMe2)3]2+ as Simultaneous AsI and PI Source: Synthesis and Density Function Calculations of Planar Tetracoordinate Arsonium and Phosphonium Ions

“…Sb. 4 gave a highly distorted tetrahedral coordination geometry at the N atom with Zr-N-Zr angles of 158.0 and 92.08, which should be 390 kJ and 75 kJ mol À1 more favorable than the tetrahedral (109.478) and planar forms (1808), respectively. The energy profiles show that the energy hypersurfaces of the P, As, and Sb onium ions in the region of the minimum structure are not only noticeably flat, but also very similar in appearance.…”

“…[1] The cation is unprecedented amongst the previously known organometallic PR 4 derivatives and forms the first phosphorus analogue of planar tetracoordinate methane derivatives. [2] Previously only tetragonal-pyramidal tetraauryl [3] and tetrahedral tetrastannyl- [4] and tetrasilylphosphonium ions [5] could be prepared.…”

“…[1] The cation is unprecedented amongst the previously known organometallic PR 4 derivatives and forms the first phosphorus analogue of planar tetracoordinate methane derivatives. [2] Previously only tetragonal-pyramidal tetraauryl [3] and tetrahedral tetrastannyl- [4] and tetrasilylphosphonium ions [5] could be prepared. Compound 1 a is formed by the reaction of the triphosphenium salt P[P(NMe 2 ) 3 ] 2 BPh 4 À (2 a) with the Schwartz reagent [Cp 2 Zr(H)Cl] in the presence of an auxiliary base; the diphosphane donor stabilized phosphenium ion functions as the P I source and reacts by cleavage of the P(NMe 2 ) 3 ligands and redox reactions to form the PR 4 ion (R Zr(H)Cp 2 ) [Eq (1)].…”

“…According to ab initio calculations for the model cation P[Zr(H)Cl 2 ] 4 the anti-van×t Hoff ± Le Bel configuration A, unusual for a PR 4 moiety with eight valence electrons, is 290 kJ mol À1 more favorable than the tetrahedral configuration B. The preference for the planar configuration is attributed predominantly to the Zr À P p backbonds and delocalization of the lone pair electrons on the P atom in the HOMO as well as stabilization by the m 2 -bridging H atoms at the Zr atoms by chelation.…”

“…In view of the existence of 1 a the question arises whether in analogy the homologous As salt As[Zr(H)Cp 2 ] 4 BPh 4 À (1 b) exhibits a planar configurated AsR 4 ion, since ab initio calculations for the hypothetical ammonium ion N[Zr(H)Cl 2 ] 4 have shown that a highly distorted tetrahedral configuration would be preferred, not the planar or tetrahedral configurations. [1] In analogy to the synthesis of 1 a, the synthesis of 1 b should be possible by reaction of the diphosphane donor stabilized arsenium salt As[P(NMe 2 ) 3 ] 2 -BPh 4 À (2 b) with [Cp 2 Zr(H)Cl]; however, the precursor 2 b was hitherto unknown.…”