The two oxygen‐bridged geminal frustrated Lewis pairs (FLP) tBu2P−O−AlBis2 (Bis=CH(SiMe3)2; 1) and tBu2P−O−Si(C2F5)3 (2) were reacted with the heterocumulenes PhNCO, PhOCN, PhNCS, CS2 and PhNSO as ...well as SO2. With isocyanate and cyanate, both 1 and 2, form addition products under formation of five‐membered rings. With CS2, isothiocyanate and sulfinylaniline, only 1 forms stable adducts, whereas 2 shows reactivity towards sulfinylaniline, but the product decomposed after a few minutes. The reaction of 1 with SO2 led to partial cleavage of the P−O−Al and Al−C units, as confirmed by X‐ray diffraction studies of a complex aggregate. The reaction of 2 with SO2 affords the 1,2‐addition product. All adducts were characterized by means of multinuclear NMR spectroscopy, X‐ray crystallography and CHN analyses.
Frustrated pairs’ different preferences: The geminal oxygen‐bridged frustrated Lewis pairs tBu2P−O−AlBis2 (Bis=CH(SiMe3)2) and tBu2P−O−Si(C2F5)3 show different reactivities towards heterocumulenes (PhNCO, PhOCN, PhNCS, CS2, PhNSO) and sulfur dioxide. Whereas the P−O−Al FLP forms stable adducts with all substrates except for SO2, the P−O−Si FLP does not form adducts with sulfur bound to silicon.
The structures of the three para‐substituted halotetrafluoropyridines with chlorine, bromine, and iodine have been determined in the solid state (X‐ray diffraction). The structures of these compounds ...and that of pentafluoropyridine were also determined in the gas phase (electron diffraction). Structures in the solid state of the bromine and iodine derivatives exhibit halogen bonding as a structure‐determining motif. On the way to an investigation of halogen bond formation of halotetrafluoropyridines in the solid state with the stronger Lewis base pyridine, co‐crystals of benzene adducts were investigated to gain an understanding of the influence of aryl–aryl interactions. These co‐crystals showed halogen bonding only for the two heavier halotetrafluoropyridines. In the pyridine co‐crystals halogen bonding was observed for all three para‐halotetrafluoropyridines. The formation of homodimers and heterodimers with pyridine is also supported by quantum‐chemical calculations of electron density topologies and natural bond orbitals.
Halogen‐bond formation in co‐crystals containing halogentetrafluoropyridines is markedly dependent on the type of halogen atom, the electronegativity of its substituent, and the halogen bond acceptor and it is less pronouncedly dependent on additional π–π stacking interactions.
Difluorothiophosphoryl isocyanate, F2P(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar‐matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas ...electron diffraction (GED) and single crystal X‐ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum‐chemical calculations. Theoretically, the Cs symmetric syn‐conformer is predicted to be the most stable conformation. Rotation about the P−N bond requires about 9 kJ mol−1 and the predicted existence of an anti‐conformer is dependent on the quantum‐chemical method used. This syn‐orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of F2P(S)NCO to form CO, F2P(S)N, and F2PNCO is observed in the solid Ar‐matrix.
All about isocyanates: Difluorothiophosphoryl isocyanate, F2P(S)NCO, was investigated using an experimental multimethod approach in the gaseous, liquid and solid state to elucidate its structure, vibrational behaviour and photodecomposition: spectroscopy (UV/Vis, NMR, IR, Raman) and gas electron as well as single‐crystal X‐ray diffraction and in addition quantum‐chemical calculations.
The geminal Lewis pair (F 5 C 2 ) 2 SbCH 2 P( t Bu) 2 (1) was prepared by reacting (F 5 C 2 ) 2 SbCl with LiCH 2 P( t Bu) 2 . Despite its extremely electronegative pentafluoroethyl substituents, the ...neutral 1 exhibits a relatively soft acidic antimony function according to the HSAB concept (hard–soft acid–base). These properties lead to a reversibility in the binding of CS 2 to 1, as observed by VT-NMR spectroscopy, while no reaction with CO 2 is observed. The reaction behaviour towards heterocumulenes and the specific interaction situation in the CS 2 adduct were analysed by quantum chemical calculations. The FLP-type reactivity of 1 has also been demonstrated by reaction with a variety of small molecules (SO 2 , PhNCO, PhNCS, (MePh 2 P)AuCl). The reactions of 1 with PhNCO and PhNCS led to different types of cyclic addition products: PhNCO adds with its NC bond and PhNCS adds preferentially with its CS bond. The reaction of 1 with (MePh 2 P)AuCl gave an adduct {(F 5 C 2 ) 2 SbCH 2 ( t Bu) 2 P 2 Au} + with a clamp-like structure binding a chloride anion by its two antimony atoms in chelate mode. Compound 1 and its adducts have been characterised by X-ray diffraction experiments, multinuclear NMR spectroscopy, elemental analyses and computational calculations (DFT, QTAIM, IQA).
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