Synthesis and reactivity of N,N′-bis [o-(diphenylphosphino)benzylidene-2,2′-diimino-1,1′-binaphthylene (Binap-P₂N₂). Crystal structure of [Ag(Binap-P₂N₂)][[BF₄]

The condensation of a racemic mixture of 2,2′-diamino-1,1′-binaphthylene with two equivalents of o-(diphenylphosphino)benzaldehyde gives a racemic mixture of N,N′-bis[o-(diphenylphosphino)benzylidene-2,2′-diimino-1,1′-binaphthylene (Binap-P₂N₂) (I) in good yield. The coordination behaviour of I towards Cu^I and Ag^I has been explored. The interaction of I with one equivalent of Cu(Ph₃P)₂Br and [Cu(CH₃CN)₄][PF₆] in CH₂Cl₂ gives Cu(Binap-P₂N₂)Br(II) and [Cu(Binap-P₂N₂)][PF₆] (III) in 60% and 74% yield, respectively. In II the Binap-P₂N₂ ligand acts as a tridentate chelating agent, with the two phosphino groups and one of the two imino groups coordinated to the Cu, whereas in III it acts in tetradentate chelating mode. A variable temperature ³¹P{¹H} NMR study of II reveals that the coordinated and the uncoordinated imino groups of the tridentate Binap-P₂N₂ ligand undergo a facile intramolecular exchange even at -55°C. The interaction of I with one equivalent of AgBF₄ in CH₂Cl₂ gives [Ag(Binap-P₂N₂)][BF₄] (IV) in 79% yield. In IV, the Binap-P₂N₂ ligand acts as a tridentate chelating agent, with the two phosphino groups and one of the two imino groups coordinated to the Ag. The structure of IV has been established by an X-ray diffraction study. The distance between Ag and N(2) is 2.56(1) Å, and the non-bonding distance between Ag and N(1) is > 3.0 Å.