Derivate des Borols, XIX. (Borol)dicarbonylcobaltat‐Ionen: Synthese, Struktur und Reaktivität

Derivatives of Borole, XIX [1] . – (Borole)dicarbonylcobaltate Ions: Synthesis, Structure, and Reactivity [3] Reduction of the dinuclear (borole)carbonylcobalt complexes [(3,4‐R 2 C 4 H 2 BPh)Co(CO) 2 ] 2 ( 3a : R = H, b : R = Me) with Na/Hg in THF at –30°C affords the anions [(3,4‐R 2 C 4 H 2 BPh)‐Co(CO) 2 ] − ( 2a,b − ) which can be isolated as [Na([15]crown‐5)] + salts. The structural data of PPh 4 · 2a indicate a strong Co – C(CO) interaction and relatively weak cobalt‐to‐boron bonding. Methylation of the anions 2a,b − gives labile metal alkyl complexes (3,4‐R 2 C 4 H 2 BPh)Co(CO) 2 Me while protonation and subsequent addition of phosphanes afford boracyclopentenyl complexes as e.g. (C 4 H 5 BPh)Co(CO) 2 (PMe 3 ) ( 5a ). The latter reacts with Ph 3 CBF 4 to give the salt [(C 4 H 4 BPh)Co(CO) 2 ‐(PMe 3 )]BF 4 ( 6 · BF 4 ). At –80CC cation 6 + undergoes hydride addition at the carbonyl carbon to give the formyl species (C 4 H 4 BPh)Co(CO)(CHO)(PMe 3 ) ( 7 ) which transforms to the hydride (C 4 H 4 BPh)CoH(CO)(PMe 3 ) ( 8 ). At room temperature the same reaction produces 5a . Deuteration studies show that the oxidative formation of 6 + from 5a and the formation of 5a by addition of hydride to 6 + are nonstereospecific processes.