Beiträge zur Chemie des Bors, 216. Über die Komplexbildung von 1,3,2,4‐Diphosphadiboretanen mit Pentacarbonylchrom sowie über die Darstellung und Reaktivität von Borylidenphosphan‐Komplexen

Abstract

Contributions to the Chemistry of Boron, 216 [1] . – On the Complex Formation of 1,3,2,4‐Diphosphadiboretanes with Pentacarbonylchromium and the Preparation and Reactivity of Borylidenephosphane Complexes 2,4‐Bis(dialkylamino)1‐1,3,2,4‐diphosphadiboretanes (R 2 NBP‐CMe 3 ) 2 with sterically undemanding amino substituents are prepared together with the corresponding bis(phosphanyl)1‐boranes R 2 NB(PHCMe 3 ) 2 by the reaction of R 2 NBCl 2 with Li‐P(H)CMe 3 . Complexes of 1,3,2,4‐diphosphadiboretanes with one or two pentacarbonylchromium fragments were obtained by the reaction of the ligands with Cr(CO) 5 ·THF or Cr(CO) 5 ·NMe 3 . If substituents are sterically demanding, cycloreversion is observed with formation of [(aminoborylidene)1‐phosphanyl‐ P ]pentacarbonylchromium compounds tmpBPR[Cr(CO) 5 ] ( 10, 29 ) with an allene‐like structure. Complex 29 may also be prepared by HCl elimination from tmp‐B(Cl)–P(H)CMe 3 [Cr(CO) 5 ] ( 34 ) with lithium diisopropylamide. This reaction can by reversed be the addition of HCl. The diphosphadiboretane 11 reacts with HCl, ethanol, and secondary amines with cleavage of all BP bonds. The X‐ray structures of complexes (Et 2 NB – PCMe 3 ) 2 [Cr(CO) 5 ] 2 ( 23 ) and ( i Pr 2 NB – PCEt 3 ) 2 [Cr(CO) 5 ] ( 25 ) as well as of the diphosphadi‐boretanes (Me 2 NB – PCMe 3 ) 2 ( 11 ) and ( i Pr 2 NB – PCEt 3 ) 2 ( 24 ) are presented. The intra ring angles of 23 remain almost unchanged upon complexation. In contrast, the B 2 P 2 ring of 25 is slightly folded and its noncoordinated P atom approaches a planar environment.