Bonding in Palladium(II) and Platinum(II) Allyl MeO- and H-MOP Complexes. Subtle Differences via ¹³C NMR

Abstract

C NMR studies have shown that in both Pd(II)-and Pt(II)-allyl (modified-MOP) (MOP ) (S)-2-diarylphosphino-1,1′-binaphthyl) complexes the substituent on the MOP auxiliary can affect how the naphthyl backbone interacts with a metal center. With the MeO-MOP analogue, the metal binds the carbon in a weak η 1 -fashion, whereas with H-MOP it prefers an η 2 -binding mode. For the Pt complexes, the 1 J( 195 Pt, 13 C) values proved to be diagnostic tools. Both modes of bonding afford relatively weak bonds to the metal. Modifying the MOP ligand structure from a PPh 2 to a P(3,5-di-tert-butylphenyl) 2 analogue can markedly affect the bond distances within the coordination sphere, as indicated by the X-ray structural data for PdCl(η 3 -C 3 H 5 )(modified-MOP). 2-D NMR exchange spectroscopy can be used to recognize and distinguish between the two most common types of η 3 -η 1 -η 3 isomerization process, i.e., rotation around the allyl C-C bond versus rotation around the allyl M-C bond. For the complex PdCl(η 3 -C 3 H 5 )(H-MOP), the fastest isomerization process involves rotation around the allyl C-C bond.Supporting Information Available: Text giving experimental details and a full listing of crystallographic data for 13, including tables of positional and isotropic equivalent displacement parameters, anisotropic displacement parameters, calculated positions of the hydrogen atoms, bond distances, and bond angles. ORTEP figure showing the full numbering schemes. X-ray data are also available as a CIF file. This material is available free of charge via the Internet at http://pubs.acs.org. OM049039T

Chloro(η6‐p‐cymene)(phosphoramidite)ruthenium(II), a 16‐Electron Fragment Stabilized by an η2‐Aryl–Metal Interaction, and Its Use in Asymmetric Cyclopropanation

“…Our results may help explain the remarkable influence of the formal secondary-amine appendage (N-substituent) observed in the same reaction [36]. An analogous interaction involving a binaphthalene group has been claimed for cationic (monophosphine)palladium(II) complexes [37] [38], but it is still controversial whether the coordination mode is h 2 or h 1 [39]. On similar lines, the cyclometalation of the phosphoramidite at the phen-A C H T U N G T R E N N U N G ethyl Me group has been observed in iridium(I) complexes [40] [41], which offers an alternative possibility of turning a 'monodentate' phosphoramidite into a chelating ligand.…”

P-Stereogenic monophosphines in Pd-catalysed enantioselective hydrovinylation of styrene

“…In 13 C NMR the C1 carbon (trans to the phosphine) is shifted downfield in complexes C6 and C8 compared to complexes C13 and C14, in all cases highly deshielded (w25 ppm) compared to the corresponding C3 carbon, cis to the phosphine. As observed in similar complexes [28,40,57], both the carbon and H atoms trans to the phosphorus were coupled to the phosphorus atom.…”

“…To circumvent this difficulty, several approaches such as pure steric shielding [1,23,24] or the dendritic effect [25e27] have been applied but the most successful has been the use of ligands possessing pendant groups capable of interacting with and stabilising the metal centre [28,29]. This strategy has been intensively pursued by RajanBabu [1,22,30e33], Leitner [34e37] and Zhou [8,38] employing Ni systems.…”

The Primary Phosphine Renaissance

“…The result is a significant finding because the ligand is similar to 22a but lacking the lower naphthyl ring. It has been shown in the literature [81] that Pd can bind in an g 2 fashion between C1 0 and C2 00 in the parent H-MOP, and by comparing entries 3, 4 and 5 we can see how critical the presence of the second naphthyl group is to conversion. Perhaps the active complex in palladium-catalyzed asymmetric hydrosilylations with H-MOP ligands is one with this bonding mode between the palladium atom and ligand; since more simple monophosphines such as 2-naphthylphospholane (R,R)-23 cannot offer this type of coordination, the consequence may be low activity in this reaction; mass spectrometry indicates two phosphines bind per palladium in the case of (R,R)-23.…”