Mono-alkylated bisphosphines as dopants for ESI-MS analysis of catalytic reactions

Abstract

Bisphosphines Ph(2)P(CH(2))(n)PPh(2) (n = 1, 2, 4, 6) may be easily monobenzylated to generate cationic phosphine/phosphonium ligands [Ph(2)P(CH(2))(n)PPh(2)CH(2)Ph](+). These ligands may be doped into a catalytic reaction involving neutral complexes with labile phosphine ligands, and replacement of a neutral phosphine with a charged analogue renders the resulting complex amenable to electrospray ionisation mass spectrometry (ESI-MS). Examination of olefin hydrogenation with Wilkinson's catalyst, RhCl(PPh(3))(3), revealed that this approach yielded rapid identification of all off-cycle solution species as well as catalyst poisons. Reactive intermediates could be generated using collision-induced dissociation (CID) of a triphenylphosphine ligand to make three-coordinate RhClP(2) species, and these react with alkenes in the gas phase to form RhClP(2)(alkene). The solution speciation and gas phase behaviour revealed by ESI-MS match closely to what is already known about the system from kinetic and NMR studies.

The application of electrospray ionization mass spectrometry to homogeneous catalysis

“…Their findings explain some general mechanistic findings in palladium cross coupling reactions. Our group's contributions to the area of developing and employing charged and chargeable ESI-MS tags include: the development of various chargeable or charged phosphine ligands analogous to commonly used mono-or bi-dentate neutral phosphine ligands [90][91][92]; using a tethered charged pyridinium group to study distannoxane speciation during esterification catalysis [93]; and examining olefin hydrogenation and silane dehydrocoupling with a charged analogue of Wilkinson's catalyst [91,92].…”

Mechanistic insights from mass spectrometry: examination of the elementary steps of catalytic reactions in the gas phase

“…In terms of how to conduct these experiments successfully, we have covered the practical aspects -especially as practiced in our own laboratory -in a recent review [1]. The review covers issues such as cross-contamination, avoiding aggregation [2], protection from oxygen and water [3], ensuring the softest possible ionization [4], analysis in non-polar solvents such as toluene and hexane [5], selection of counter-ions and the design of charged tags [6,7], and the pressurized sample introduction method for continuous reaction monitoring [8]. Readers interested in these issues should sample the appropriate papers or go straight to the review for an overview of the problems and solutions.…”

Rhodium-Catalyzed Selective Partial Hydrogenation of Alkynes

“…13 This is exacerbated for a cationic metal complex binding a cationic alky(e)ne, as the charges repel each other. (b) Addition of octyne to 1[BAr F 4 ] displaces the fluorobenzene and produces the ions [Rh(P c Pr 3 ) 2 (octyne) n ] + (n = 1 or 2; see Supporting Information).…”