Mild intramolecular P–C(sp3) bond cleavage in bridging diphosphine complexes of RuII RhIII and IrIII

Abstract

Three new carboxylic acid functionalised diphosphines, R2PCH2N(Ar)CH2PR2 [CyL1 R = Cy, Ar = (1-CO2H)(3-OMe)C6H3, CyL2 R = Cy, Ar = (1-CO2H)(3-OH)C6H3 and PhL3 R = Ph, Ar = (1-CO2H)(5-OMe)C6H3] have been prepared from condensation of R2PCH2OH and the appropriate aromatic amine in MeOH, and isolated as colourless solids (for CyL1, CyL2) in good yield. Reaction of CyL1, CyL2, or PhL3, along with the previously reported diphosphines PhL1, PhL2, and PhL4, and [RuCl(μ-Cl)(η6-Me2CHC6H4Me)]2 in CH2Cl2 affords the P/P-bridging dinuclear ruthenium(II) complexes {RuCl2(η6-Me2CHC6H4Me)}2(μ-CyL1−PhL4) 1a−f as red/orange solids. Careful monitoring by 31P{1H} NMR spectroscopy of CDCl3 solutions of 1a−e revealed remarkably clean P−Csp3 bond cleavage to give RuII mononuclear species 2a−e and the known secondary phosphine complexes RuCl2(η6-Me2CHC6H4Me)(PCy2H) 3 and RuCl2(η6-Me2CHC6H4Me)(PPh2H) 4. Furthermore, facile P−Csp3 bond cleavage of PhL1 can be observed using the chloro-bridged dimers [IrCl(μ-Cl)(η5-C5Me5)]2 or [RhCl(μ-Cl)(η5-C5Me5)]2 instead. Deuterium labelling of CyL1, CyL1, PhL1, and PhL2 enabled the assignment of the methylene protons to be confirmed from 1H NMR spectroscopy. All new compounds have been characterised using a range of spectroscopic and analytical techniques. Single crystal X-ray structures have been determined for CyL1, 1d·3OEt2,1f·2CDCl3·OEt2, 2b, 2c, 2d·CDCl3, 2e·0.5OEt2 and 6b·1.5CDCl3. The free phenolic group in CyL1, 1d·3OEt2,1f·2CDCl3·OEt2, 2b and 2d·CDCl3 participates in intra- or intermolecular O−H···O hydrogen bonding.