Unusual Bonding and Properties in Main Group Element Chemistry: Rational Synthesis, Characterization, and Experimental Electron Density Determination of Mixed‐Valent Tetraphosphetes

Abstract

Five dispirocyclic λ(3),λ(5)-tetraphosphetes [{R2Si(NR(1))(NR(2))P2}2] (R(1) = R(2) and R(1) ≠ R(2)) are easily prepared in almost quantitative yields via photolysis of the respective bis(trimethylsilyl)phosphanyldiazaphosphasiletidines with intense visible light. These deep-yellow low-coordinate phosphorus compounds can be considered as the first higher congeners of the well-known cyclodiphosphazenes. The tetraphosphetes are remarkably stable in air and show unexpected molecular properties related to the unique bonding situation of the central four-π-electron four-membered phosphorus ring. The extent of rhombic distortion of the central P4 ring is remarkable due to an unusually acute angle at the σ(2)-phosphorus atoms. All of the P-P bonds are approximately equal in length. The distances are in the middle of the range given by phosphorus single and double bonds. The anisotropic absorption of visible light that can easily be observed in the case of the yellow/colorless dichroic crystals of [{Me2Si(NtBu)(NtBu)P2}2] and the exceptional (31)P NMR chemical shift of the σ(2)-phosphorus atoms are the most remarkable features of the λ(3),λ(5)-tetraphosphetes. In the case of [{Me2Si(NtBu)(NtBu)P2}2], the Hansen-Coppens multipole model is applied to extract the electron density from high-resolution X-ray diffraction data obtained at 100 K. Static deformation density and topological analysis reveal a unique bonding situation in the central unsaturated P4 fragment characterized by polar σ-bonding, pronounced out-of-ring non-bonding lone pair density on the σ(2)-phosphorus atoms, and an additional non-classical three-center back-bonding contribution.

Bonding in Phosphanylphosphinidene Complexes of Transition Metals and their Correlation with Structures, 31P NMR Spectra, and Reactivities

“…Additionally, structural, spectral, and chemical properties of Bertrand's free phosphanylphosphinidene, are compared with the structural and spectral properties of t Bu 2 P–P (DFT calculations) and the chemical properties of its PR 3 complex, t Bu 2 P–P=P t Bu 2 (Me) , , . Furthermore, we compare the calculated properties of Frank's putative phosphanylphosphinidene Me 2 Si(µ 2 ‐NR) 2 P–P, which reveals an unusual dimerization mode …”

Stabilization of activated fragments by shell‐wise construction of an embedding environment

“…Reactive molecules usually represent activated species that are decisive for accomplishing a chemical transformation. Prominent examples are transition states, exotic molecules (such as multiply bonded transition metal dimers, small carbon cages, strained ring structures, and radicals), and species that activate inert molecules on binding. A suitable molecular environment may stabilize such peculiar local bonding situations.…”

The crystal structure of 2-chloro-1,3-bis(2,4,6-trimethylphenyl)-4,4-dimethyl-1,3,2λ3,4-diazaphosphasiletidine

“…Their synthesis was rst described more than 50 years ago [1] while their reaction and coordination behavior has been extensively studied during the following years [2][3][4][5][8][9][10][11][12]. Particularly diazaphosphasiletidines resulting from this versatile silylamine precursors have attracted considerable attention in phosphorus chemistry [2][3][4][5].…”