Silyl Cations Stabilized by Pincer Type Ligands with Adjustable Donor Atoms

Abstract

Scheme 1. Spatial arrangement of silyl cations I-IV with different coordination numbers (CN).

Structural and Electronic Effects on Phosphine Chalcogenide Stabilized Silicon Centers in Four-Membered Heterocyclic Cations

“…Hence, disproportionately large steric repulsions between bulky groups on the phosphorus and silicon atoms of the CPOSi heterocycle, caused by the short P–O and O–Si bond lengths, can significantly counteract the greater inherent stability of the O–Si interaction compared to the S–Si and Se–Si interactions. This stability trend follows the one reported for phosphine chalcogenide-stabilized silylium centers in pincer-type bonding modes …”

“…Surprisingly, neither the reaction of phosphine oxide 5 with B­(C 6 F 5 ) 3 nor with [Ph 3 C]­[B­(C 6 F 5 ) 4 ] resulted in hydride abstraction and cation formation, even when heated to 50 °C. As another strategy to provide the oxygen-containing heterocycle, we considered a method recently reported by Beckmann et al for the generation of pincer-type phosphine oxide-stabilized silylium centers, which is based on a reaction of a hydrosilane with 2 equiv of bromine . However, also this approach was unsuccessful for our system.…”

“…The 77 Se NMR spectrum of the selenium-based starting compound 6 shows a doublet at −381.6 ppm and a 1 J P–Se coupling constant of 717.6 Hz (Table ). The 77 Se NMR signal, although more upfield-shifted due to the aliphatic phosphorus-bound substituents, and the 1 J P–Se coupling constant are in the expected region, typical for phosphine selenides . Upon ring formation, the 1 J P–Se coupling constant drops down by more than half to a value of 323.6 Hz in 8 [HB­(C 6 F 5 ) 3 ], accompanied by a significantly large downfield shift [Δδ­( 77 Se)] of 308.7 ppm to δ­( 77 Se) = −72.9 ppm.…”

An Organotin Route for the Preparation of 2,6‐Bis(diphenylphosphino)bromo‐benzene and the Related Bis(Phosphine Oxide). Precursors for Novel Ligands

“…However, for both ligands II and III , the bromo derivatives are available, which might be amenable to oxidative addition and insertion reactions. We are currently study the utility of these ligands II and III for the preparation of main group and transition metal complexes other than Cu, [2] Au [3] and Si [4] …”

“…In search for method that is broadly applicable for the majority of other elements, we now developed an organotin route for the introduction of the bis(2,6‐diphenyl)phosphinophenyl carbanion, [2,6‐(Ph 2 P) 2 C 6 H 3 ] − ( II ). In principle, this route also provides synthetic access to the related bis(phosphine oxide) ligand [2,6‐(Ph 2 P{O}) 2 C 6 H 3 ] − ( III ), [4] which resembles the family of bis(phosphonic ester) ligands [2,6‐{(RO) 2 P(O)} 2 C 6 H 3 ] − ( IV , R=Et, i ‐Pr), prepared by the metal‐catalyzed Arbuzov reaction (Scheme 1). [5,6] This ligand family is sometimes affected by the cleavage of the ester groups, which somewhat hampers it applicability for highly reactive species.…”