Transition metal complexes with functionalized indenyl phosphine ligands: structures and catalytic properties

Transition-metal indenyl complexes usually exhibit different reactivity compared with their cyclopentadienyl analogues. Up to now, at least 10 metal-indenyl bonding modes have been reported. Because of the “indenyl effect”, transition-metal...

Competitive Ligand Exchange and Dissociation in Ru Indenyl Complexes

Kinetic profiles obtained from monitoring the solution phase substitution chemistry of [Ru(η⁵-indenyl)(NCPh)(PPh₃)₂]⁺ (<b>1</b>) by both ESI-MS and ³¹P{¹H} NMR are essentially identical, despite an enormous difference in sample concentrations for these complementary techniques. These studies demonstrate dissociative substitution of the NCPh ligand in <b>1</b>. Competition experiments using different secondary phosphine reagents provide a ranking of phosphine donor abilities at this relatively crowded half-sandwich complex: PEt₂H > PPh₂H >> PCy₂H. The impact of steric congestion at Ru is evident also in reactions of <b>1</b> with tertiary phosphines; initial substitution products [Ru(η⁵-indenyl)(PR₃)(PPh₃)₂]⁺ rapidly lose PPh₃, enabling competitive recoordination of NCPh. Further solution experiments, relevant to the use of <b>1</b> in catalytic hydrophosphination, show that PPh₂H out-competes PPh₂CH₂CH₂CO₂Bu<i>^t</i> (the product of hydrophosphination of <i>tert</i>-butyl acrylate by PPh₂H) for coordination to Ru, even in the presence of a ten-fold excess of the tertiary phosphine. Additional information on relative phosphine binding strengths was obtained from gas-phase MS/MS experiments, including collision-induced dissociation (CID) experiments on the mixed phosphine complexes [Ru(η⁵-indenyl)PP’P’’]⁺, which ultimately appear in solution during the secondary phosphine competition experiments. Unexpectedly, unsaturated complexes [Ru(η⁵-indenyl)(PR₂H)(PPh₃)]⁺, generated in the gas-phase, undergo preferential loss of PR₂H. We propose competing orthometallation of PPh₃ is responsible for the surprising stability of the [Ru(η⁵-indenyl)(PPh₃)]⁺ fragment under these conditions.

Competitive Ligand Exchange and Dissociation in Ru Indenyl Complexes

Kinetic profiles obtained from monitoring the solution phase substitution chemistry of [Ru(η⁵-indenyl)(NCPh)(PPh₃)₂]⁺ (<b>1</b>) by both ESI-MS and ³¹P{¹H} NMR are essentially identical, despite an enormous difference in sample concentrations for these complementary techniques. These studies demonstrate dissociative substitution of the NCPh ligand in <b>1</b>. Competition experiments using different secondary phosphine reagents provide a ranking of phosphine donor abilities at this relatively crowded half-sandwich complex: PEt₂H > PPh₂H >> PCy₂H. The impact of steric congestion at Ru is evident also in reactions of <b>1</b> with tertiary phosphines; initial substitution products [Ru(η⁵-indenyl)(PR₃)(PPh₃)₂]⁺ rapidly lose PPh₃, enabling competitive recoordination of NCPh. Further solution experiments, relevant to the use of <b>1</b> in catalytic hydrophosphination, show that PPh₂H out-competes PPh₂CH₂CH₂CO₂Bu<i>^t</i> (the product of hydrophosphination of <i>tert</i>-butyl acrylate by PPh₂H) for coordination to Ru, even in the presence of a ten-fold excess of the tertiary phosphine. Additional information on relative phosphine binding strengths was obtained from gas-phase MS/MS experiments, including collision-induced dissociation (CID) experiments on the mixed phosphine complexes [Ru(η⁵-indenyl)PP’P’’]⁺, which ultimately appear in solution during the secondary phosphine competition experiments. Unexpectedly, unsaturated complexes [Ru(η⁵-indenyl)(PR₂H)(PPh₃)]⁺, generated in the gas-phase, undergo preferential loss of PR₂H. We propose competing orthometallation of PPh₃ is responsible for the surprising stability of the [Ru(η⁵-indenyl)(PPh₃)]⁺ fragment under these conditions.