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Evidenz für eine Struktur‐Reaktivität‐Beziehung bei sperrig substituierten Lithium(fluorsilyl)phosphaniden
Author(s) -
Drieß Matthias,
Winkler Uwe,
Imhof Wolfgang,
Zsolnai Laszlo,
Huttner Gottfried
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941270610
Subject(s) - chemistry , reactivity (psychology) , lithium (medication) , steric effects , intramolecular force , phosphine , molecule , lithium atom , crystallography , fluorine , oxidative addition , stereochemistry , organic chemistry , ion , catalysis , medicine , alternative medicine , pathology , ionization , endocrinology
Evidence for a Structure‐Reactivity Relationship of Crowded Substituted Lithium (Fluorosilyl)phosphanides The molecular structures and the reactivity of the new solvated lithium (fluorosilyl)phosphanides 1a , 2a , and 2b has been investigated. The unusual solid state structures of 1a and 2b are established by X‐ray crystallography. Whereas the lithium centre in 1a is bound to phosphorus and solvated by three molecules of THF, the electronical saturation of the lithium centre in 2b is achieved by a LiP bond, tridentate chelatization (fluorine, phosphorus, nitrogen), and the additional coordination of one molecule of THF. The trigonal‐planar geometry at phosphorus in 1a is unprecedented for derivatives of this type and reflects the steric demand around the phosphorus and the possibility of π p /σ* sic hyperconjugation. The SiP bond lengths [PSiC(Phenyl) 2.186(2) and PSiF 2.164(2) Å] are significantly shorter than in related pyramidally configurated derivatives ( 1b , c : PSiC 2.21, PSiF 2.18 Å). Both phosphorus atoms in 2b are pyramidally coordinated, but the intramolecular chelate coordination of the lithium centre causes much smaller bonding angles at the SiP phosphorus atom [sum of bonding angles 238.4(2) (PSi), 312.5(1)° (PN)]. 1a as well as 2a , b show quite different reactivity as compared to 1b–d due to their unusual structures. Heating of solutions of 1a and 2a , b in toluene or hexane does not give the expected stable silylidenephosphanes (SiP) by elimination of LiF. Instead, rearrangement reactions of the SiP intermediates 6 , 8 lead to the new heterocycles 5 , 9 . A single‐crystal X‐ray diffraction analysis of 5 has been performed. The Si 2 P 2 cyclobutane ring is planar, and the NMe 2 groups at the ring silicon atoms are cis ‐orientated. — Interestingly, 2b eliminates LiN i Pr 2 at 20°C in a kinetically controlled process to form the tetraphosphacyclobutane 7 as the major product. Presumably, the diphosphene 8 is an intermediate in this reaction.