Redox-Induced Coordination Isomerization of a Phosphoniobenzophospholide

• Published in: Chemistry : a European journal 2003-02, Vol.9 (3), p.661-670
• Main Authors: Gudat, Dietrich, Lewall, Burhanshah, Nieger, Martin, Detmer, Ilka, Szarvas, László, Saarenketo, Pauli, Marconi, Guido
• Format: Article
• Language: English
• Subjects: bridging ligands; coordination modes; oxidation; phosphorus heterocycles; reduction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200390074

1‐Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)5Br] (M = Mn, Re) and [Mn(CO)3(naphthalene)][BF4] to give complexes cis‐[M(CO)4(1)Br] (5 a,b) and [Mn(CO)3(1)][BF4] (6 a[BF4]), respectively, featuring η1(P)‐ and η5(π)‐coordination of the phosphole ring. The corresponding reactions with [M2(CO)10] proceed with conservation of the metal–metal bond and yield, depending on the reaction temperature, dinuclear complexes [M2(CO)8(1)] (M=Mn, 7 a) or [M2(CO)6(1)2] (M=Mn, Re, 8 a,b) with μ2‐bridging η1(P):η2(PC) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF4], and 8 a,b were characterized by X‐ray diffraction studies as well. The structural and 31P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the η2‐bound PC double bond moieties is dominated by the L→M charge‐transfer contribution; this hints at a very low back‐donation ability of the central M2(CO)6 fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF6]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF6] 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. 1‐Triphenylphosphonio‐benzo[c]phospholid 1 reagiert mit [M(CO)5Br] (M=Mn, Re) und [Mn(CO)3(naphthalen)][BF4] zu den Komplexen cis‐[M(CO)4(1)Br] (5 a,b) bzw. [Mn(CO)3(1)][BF4] (6 a[BF4]) mit η1(P)‐ und η5(π)‐Koordination des Phosphol‐Rings. Die entsprechenden Reaktionen mit [M2(CO)10] verlaufen unter Erhalt der Metall–Metall‐Bindung und liefern je nach Reaktionstemperatur entweder die dinuklearen Komplexe [M2(CO)8(1)] (M=Mn, 7 a) oder [M2(CO)6(1)2] (M=Mn, Re, 8 a,b) mit μ2‐verbrückender η1(P):η2(PC)‐Koordination der Phosphol‐Einheit. Alle gebildeten Komplexe wurden durch spektroskopische Da