Synthesis and evaluation of the bonding properties of a potentially tridentate ligand: 1-(diphenylphosphino)-2-ethoxy-1-(2-pyridyl)ethane

Abstract

The trifunctional ligand 1-(diphenylphosphino)-2-ethoxy-1-(2-pyridyl)ethane (pepye) has been prepared and its bonding properties toward Mo⁰, Rh^I and Ru^II metallic centres evaluated. The complex fac-[Mo(CO)₃(pepye)] in which the ligand is P,N,O bonded in solution evolves to cis-[Mo(CO)₄(pepye)] where it is P,N bonded. In the complex [Rh(cod)(pepye)] ClO₄(cod = cycloocta-1,5-diene) the ligand is P,N bonded. The cycloocta-1,5-diene can be displaced by carbon monoxide, and [Rh(CO)₂(pepye)] ClO₄ and [{Rh(CO)(pepye)}₂][ClO₄]₂ have been isolated. In the former the ligand is P,N bonded and in the latter the two rhodium atoms are bridged by the phosphine and ether functions of each ligand. The complex all-cis-[RuCl₂(pepye)₂] has been isolated in two diastereoisomeric forms in a 6:4 ratio. In polar solvents it evolves to [RuCl (pepye)₂]⁺ in which one of the ligands is P,N,O bonded and the two diastereoisomers have been isolated as their tetraphenylborate salts. The bonded ether arm of the ligand can be displaced by carbon monoxide leading to [RuCl (CO)(pepye)₂] BPh₄. This reaction can be reversed in boiling acetone, more or less easily, depending upon the diastereoisomers.