A Remarkable cis‐ and trans‐Spanning Dibenzylidene Acetone Diphosphine Chelating Ligand (dbaphos)

Abstract

A multidentate and flexible diolefin-diphosphine ligand, based on the dibenzylidene acetone core, namely dbaphos (1), is reported herein. The ligand adopts an array of different geometries at Pt, Pd and Rh. At Pt(II) the dbaphos ligand forms cis- and trans-diphosphine complexes and can be defined as a wide-angle spanning ligand. (1)H NMR spectroscopic analysis shows that the β-hydrogen of one olefin moiety interacts with the Pt(II) centre (an anagostic interaction), which is supported by DFT calculations. At Pd(0) and Rh(I), the dbaphos ligand exhibits both olefin and phosphine interactions with the metal centres. The Pd(0) complex of dbaphos is dinuclear, with bridging diphosphines. The complex exhibits the coordination of one olefin moiety, which is in dynamic exchange (intramolecular) with the other "free" olefin. The Pd(0) complex of dbaphos reacts with iodobenzene to afford trans-[Pd(II)(dbaphos)I(Ph)]. In the case of Rh(I), dbaphos coordinates to form a structure in which the phosphine and olefin moieties occupy both axial and equatorial sites, which stands in contrast to a related bidentate olefin, phosphine ligand ("Lei" ligand), in which the olefins occupy the equatorial sites and phosphines the axial sites, exclusively.

Metal-ligand cooperation between palladium and a diphosphine ligand with an olefinic backbone

“…This is a result of isomerization and was previously observed in complexes with ligands that have a preference for trans coordination. 38,45,46 A previous report from our group also shows a preference of the diphosphine…”

Ortho-aryl substituted DPEphos ligands: rhodium complexes featuring C–H anagostic interactions and B–H agostic bonds

“…27,83 Common to all the Rh(I) DPEPhos-R complexes structurally described herein (with their associated NBD, CO or vinylborane co-ligands) is the observation of downfield-shifted signals in their 1 H NMR spectra that signal an anagostic M•••H-C interaction, 28 for which the steric bulk of the ligand determines the temperature at which they are observed. As discussed previously, 30,38,40,45 while such anagostic interactions are associated with weak Rh*CH and minimal  CH  Rh orbital donations, the driver for the downfield chemical shift of the C-H protons observed in the 1 H NMR spectrum does not come from these. Instead, the positioning of the anagostic hydrogen with reference to different regions of valence shell for the d 8 metal centre is important, as Scherer 30 has previously elegantly described for Rh(CAAC)(CO)Cl systems (CAAC = cyclic alkyl-aminocarbene).…”

Multielectron Redox Chemistry of Transition Metal Complexes Supported by a Non‐Innocent N3P2 Ligand: Synthesis, Characterization, and Catalytic Properties

“…The red pro‐ligand H L N3P2 was prepared by the condensation of bis(2‐amino‐4‐methylphenyl)amine with two equivalents of 2‐(diphenylphosphanyl)benzaldehyde in toluene . Treatment of H L N3P2 with the appropriate M II X 2 salt (X = ClO 4 – or TfO – ) in a 1:1 mixture of CH 2 Cl 2 and MeCN, followed by addition of base, generated the dark brown complexes 1 – 3 .…”

“…The compound 2‐(diphenylphosphanyl)benzaldehyde was prepared according to published procedures. [14b], …”