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

<p>Three new carboxylic acid functionalised diphosphines, R₂PCH₂N(Ar)CH₂PR₂ [^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>} R = Cy, Ar = (1-CO₂H)(3-OMe)C₆H₃, ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>2</strong>}R = Cy, Ar = (1-CO₂H)(3-OH)C₆H₃ and ^{<strong>Ph</strong>}<strong>L3</strong> 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 ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>}<strong>,</strong> ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>2</strong>}) in good yield. Reaction of ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>}<strong>,</strong> ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>2</strong>}, or <strong>PhL3</strong>, along with the previously reported diphosphines ^{<strong>Ph</strong>}<strong>L</strong>_{<strong>1</strong>}<strong>,</strong> ^{<strong>Ph</strong>}<strong>L</strong>_{<strong>2</strong>}, and ^{<strong>Ph</strong>}<strong>L</strong>_{<strong>4</strong>}, and [RuCl(μ-Cl)(η⁶-Me₂CHC₆H₄Me)]₂ in CH₂Cl₂ affords the P/P-bridging dinuclear ruthenium(II) complexes {RuCl2(η⁶-Me₂CHC₆H₄Me)}₂(μ-^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>}−^{<strong>Ph</strong>}<strong>L</strong>_{<strong>4</strong>}) <strong>1a</strong>−<strong>f</strong> as red/orange solids. Careful monitoring by³¹P{¹H} NMR spectroscopy of CDCl₃ solutions of <strong>1a</strong>−<strong>e</strong> revealed remarkably clean P−C_sp3 bond cleavage to give Ru^II mononuclear species <strong>2a</strong>−<strong>e</strong> and the known secondary phosphine complexes RuCl₂(η⁶-Me₂CHC₆H₄Me)(PCy₂H) <strong>3</strong> and RuCl₂(η⁶-Me₂CHC₆H₄Me)(PPh₂H) <strong>4</strong>. Furthermore, facile P−C_sp³ bond cleavage of ^{<strong>Ph</strong>}<strong>L</strong>_{<strong>1</strong>} 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 ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>}, ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>}, ^{<strong>Ph</strong>}<strong>L</strong>_{<strong>1</strong>}, and ^{<strong>Ph</strong>}<strong>L</strong>_{<strong>2</strong>} 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 ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>}<strong>, 1d</strong>·3OEt₂, <strong>1f</strong>·2CDCl₃·OEt₂, <strong>2b, 2c, 2d</strong>·CDCl₃, <strong>2e</strong>·0.5OEt₂ and <strong>6b</strong>·1.5CDCl₃. The free phenolic group in ^{<strong>Cy</strong>}<strong>L</strong>_{<strong>1</strong>}<strong>, 1d</strong>·3OEt₂, <strong>1f</strong>·2CDCl₃·OEt₂, <strong>2b</strong> and <strong>2d</strong>·CDCl₃ participates in intra- or intermolecular O−H···O hydrogen bonding. </p>