Synthesis and coordination of hybrid phosphinoferrocenes with extended donor pendants†
Abstract
Combining a phosphinoferrocene fragment with extended multidonor moieties affords novel, flexible multidonor pro-ligands. This contribution describes the synthesis of two structurally similar functional phosphines, Ph2PfcNHC(O)CH2PPh2 (1) and Ph2PfcNHCH2CH2PPh2 (2, fc = ferrocene-1,1′-diyl), and their coordination behaviour towards Pd(II). The former amidophosphine reacts with [PdCl2(MeCN)2] to produce the chelate complex [PdCl2(1-κ2P,P′)] as a mixture of cis and trans isomers, which convert into bis-chelate [PdCl2(Ph2PfcNC(O)CH2PPh2-κ3P,P′,N)] upon reacting with a strong base (KOt-Bu). In contrast, the more flexible and more basic phosphinoamine 2 directly forms the cationic bis-chelate complex [PdCl(2-κ3P,P′,N)]Cl via spontaneous self-ionisation. Subsequent halogen abstraction with Ag[SbF6] results either in counter ion exchange to give [PdCl(2-κ3P,P′,N)][SbF6] or in the formation of a structurally unique complex [PdCl(2-κ4Fe,P,P′,N)][SbF6]2 with an Fe → Pd dative interaction, depending on the amount of silver(I) salt used (1 or 2 equiv.).