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Water Reduction and Dihydrogen Addition in Aqueous Conditions With ansa‐ Phosphinoborane
Author(s) -
Sorochkina Kristina,
Chernichenko Konstantin,
Zhivonitko Vladimir V.,
Nieger Martin,
Repo Timo
Publication year - 2022
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/chem.202201927
Subject(s) - phosphonium , chemistry , spin isomers of hydrogen , aqueous solution , dissociation (chemistry) , phosphine , phosphine oxide , hydrogen , medicinal chemistry , oxide , frustrated lewis pair , umpolung , photochemistry , inorganic chemistry , organic chemistry , lewis acids and bases , catalysis , nucleophile
Ortho ‐phenylene‐bridged phosphinoborane (2,6‐Cl 2 Ph) 2 B‐C 6 H 4 ‐PCy 2 1 was synthesized in three steps from commercially available starting materials. 1 reacts with H 2 or H 2 O under mild conditions to form corresponding zwitterionic phosphonium borates 1‐H 2 or 1‐H 2 O . NMR studies revealed both reactions to be remarkably reversible. Thus, when exposed to H 2 , 1‐H 2 O partially converts to 1‐H 2 even in the presence of multiple equivalents of water in the solution. The addition of parahydrogen to 1 leads to nuclear spin hyperpolarization both in dry and hydrous solvents, confirming the dissociation of 1‐H 2 O to free 1 . These observations were supported by computational studies indicating that the formation of 1‐H 2 and 1‐H 2 O from 1 are thermodynamically favored. Unexpectedly, 1‐H 2 O can release molecular hydrogen to form phosphine oxide 1‐O . Kinetic, mechanistic, and computational (DFT) studies were used to elucidate the unique “umpolung” water reduction mechanism.