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PX 4 + , P 2 X 5 + , and P 5 X 2 + (X=Br, I) Salts of the Superweak Al(OR) 4 − Anion [R=C(CF 3 ) 3 ]
Author(s) -
Gonsior Marcin,
Krossing Ingo,
Müller Lutz,
Raabe Ines,
Jansen Martin,
van Wüllen Leo
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20021004)8:19<4475::aid-chem4475>3.0.co;2-m
Subject(s) - chemistry , metathesis , electrophile , medicinal chemistry , salt (chemistry) , carbene , ion , yield (engineering) , crystallography , silver salts , stereochemistry , inorganic chemistry , polymerization , organic chemistry , catalysis , materials science , polymer , metallurgy
PX 4 + [Al(OR) 4 ] − (X=I: 1 a , X=Br: 1 b ) was prepared from X 2 , PX 3 , and Ag[Al(OR) 4 ] [R=C(CF 3 ) 3 ] in CH 2 Cl 2 at −30 °C in 69–86 % yield. P 2 X 5 + salts were prepared from 2 PX 3 and Ag[Al(OR) 4 ] in CH 2 Cl 2 at −30 °C yielding almost quantitatively P 2 X 5 + [Al(OR) 4 ] − (X=I: 3 a , X=Br: 3 b ). The phosphorus‐rich P 5 X 2 + salts arose from the reaction of cold (−78 °C) mixtures of PX 3 , P 4 , and Ag[Al(OR) 4 ] giving P 5 X 2 + [Al(OR) 4 ] − (X=I: 4 a , X=Br: 4 b ) with a C 2v ‐symmetric P 5 cage. Silver salt metathesis presumably generated unstable PX 2 + cations from PX 3 and Ag[Al(OR) 4 ] (X=Br, I) that acted as electrophilic carbene analogues and inserted into the XX (PX/PP) bond of X 2 (PX 3 /P 4 ) leading to the highly electrophilic and CH 2 Cl 2 ‐soluble PX 4 + (P 2 X 5 + /P 5 X 2 + ) salts. Reactions that aimed to synthesize P 2 I 3 + from P 2 I 4 and Ag[Al(OR) 4 ] instead led to anion decomposition and the formation of P 2 I 5 (CS 2 ) + [(RO) 3 Al‐F‐Al(OR) 3 ] − ( 5 ). All salts were characterized by variable‐temperature solution NMR studies ( 3 b also by 31 P MAS NMR), Raman and/or IR spectroscopy as well as X‐ray crystallography (with the exception of 4 a ). The thermochemical volumes of the PX cations are 121 (PBr 4 + ), 161 (PI 4 + ), 194 (P 2 Br 5 + ), 271 (P 2 I 5 + ), and 180 Å 3 (P 5 Br 2 + ). The observed reactions were fully accounted for by thermochemical calculations based on (RI‐)MP2/TZVPP ab initio results and COSMO solvation enthalpy calculations (CH 2 Cl 2 solution). The enthalpies of formation of the gaseous PX cations were derived as +764 (PI 4 + ), +617 (PBr 4 + ), +749 (P 2 I 5 + ), +579 (P 2 Br 5 + ), +762 (P 5 I 2 + ), and +705 kJ mol −1 (P 5 Br 2 + ). The insertion of the intermediately prepared carbene analogue PX 2 + cations into the respective bonds were calculated, at the (RI‐)MP2/TZVPP level, to be exergonic at 298 K in CH 2 Cl 2 by Δ r G (CH 2 Cl 2 )=−133.5 (PI 4 + ), −183.9 (PBr 4 + ), −106.5 (P 2 I 5 + ), −81.5 (P 2 Br 5 + ), −113.2 (P 5 I 2 + ), and −114.5 kJ mol −1 (P 5 Br 2 + ).