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Redox‐Induced Coordination Isomerization of a Phosphoniobenzophospholide
Author(s) -
Gudat Dietrich,
Lewall Burhanshah,
Nieger Martin,
Detmer Ilka,
Szarvas László,
Saarenketo Pauli,
Marconi Guido
Publication year - 2003
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.200390074
Subject(s) - chemistry , phosphole , isomerization , rhenium , moiety , metal , stereochemistry , crystallography , manganese , redox , agostic interaction , alkyne , coordination complex , hexafluorophosphate , medicinal chemistry , inorganic chemistry , catalysis , organic chemistry , biochemistry , ionic liquid
1‐Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO) 5 Br] (M = Mn, Re) and [Mn(CO) 3 (naphthalene)][BF 4 ] to give complexes cis ‐[M(CO) 4 ( 1 )Br] ( 5 a,b ) and [Mn(CO) 3 ( 1 )][BF 4 ] ( 6 a [BF 4 ]), respectively, featuring η 1 (P)‐ and η 5 (π)‐coordination of the phosphole ring. The corresponding reactions with [M 2 (CO) 10 ] proceed with conservation of the metal–metal bond and yield, depending on the reaction temperature, dinuclear complexes [M 2 (CO) 8 ( 1 )] (M=Mn, 7 a ) or [M 2 (CO) 6 ( 1 ) 2 ] (M=Mn, Re, 8 a,b ) with μ 2 ‐bridging η 1 (P): η 2 (PC) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a [BF 4 ], and 8 a,b were characterized by X‐ray diffraction studies as well. The structural and 31 P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the η 2 ‐bound PC double bond moieties is dominated by the L→M charge‐transfer contribution; this hints at a very low back‐donation ability of the central M 2 (CO) 6 fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF 6 ]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF 6 ] gave spectroscopic evidence for the formation of a Re analogue of 6 a . Electrochemical studies suggested that the oxidation 8 a →2 6 a involves two consecutive single‐electron‐transfer steps, the first of which is electrochemically reversible and produces a metastable radical cation that is detectable by ESR spectroscopy. The mutual interconversion between 6 a and 8 a represents the first case of a reversible coordination isomerization of a phosphaarene that is triggered by a redox process and might stimulate further studies directed at the use of dinuclear phosphaarene complexes in redox‐catalysis.