Structures, Electronics, and Reactivity of Strained Phosphazane Cages: A Combined Experimental and Computational Study

Abstract

A series of formamidine-bridged P2N2 cages have been prepared. Upon deprotonation, these compounds serve as valuable precursors to hybrid N-heterocyclic carbene ligands, whereas direct metalation gives rearranged dimetallic complexes as a result of cleavage of the formamidine bridge. The latter metal complexes contain an intact cyclophosphazane moiety that coordinates two distinct metal centers in a monodentate and a chelating fashion. A computational study has been carried out to elucidate the bonding within the P2N2 framework as well as the reactivity patterns. Natural bond orbital analysis indicates that the cage motif is poorly described by localized Lewis structures and that negative hyperconjugation effects govern the stability of the bicyclic framework. The donor capacity of the cyclophosphazane unit was assessed by inspection of the frontier molecular orbitals, highlighting the fact that π-back-donation from the metal fragments is crucial for effective metal-ligand binding.

Air‐Stable Oxyallyl Patterns and a Switchable N‐Heterocyclic Carbene

“…As previous synthetic approaches towards stabilized oxyallyls were irrelevant to such a target, our novel strategy relied on the early introduction of a "masked" O-protected oxyallyl pattern. We reacted 1,3-dichlorovinamidinium salt 1, [22] featuring a benzoyl O-protecting group, with one equivalent of N-(trimethylsilyl)amidine 2 [23] (Scheme 2). After work-up, the moisture-sensitive yellow salt 3 was isolated in 55% yield.…”

Air‐Stable Oxyallyl Patterns and a Switchable N‐Heterocyclic Carbene

“…As previous synthetic approaches towards stabilized oxyallyl species were irrelevant to such a target, our novel strategy relied on the early introduction of a “masked” O‐protected oxyallyl pattern. We reacted 1,3‐dichlorovinamidinium salt 1 , featuring a benzoyl O‐protecting group, with one equivalent of N ‐(trimethylsilyl)amidine 2 (Scheme ). After work‐up, the moisture‐sensitive yellow salt 3 was isolated in 55 % yield.…”

“…Theh igh reactivity of electron-rich 1,3-diaminooxyallyl moieties had to be tamed through the addition of electronwithdrawing groups.I nspired by our recent work on pyrimidine-1,3-diium salts, [21] we chose to introduce an N,N'amidinium bridge.Asprevious synthetic approaches towards stabilized oxyallyl species were irrelevant to such atarget, our novel strategy relied on the early introduction of a"masked" O-protected oxyallyl pattern. We reacted 1,3-dichlorovina- midinium salt 1, [22] featuring ab enzoyl O-protecting group, with one equivalent of N-(trimethylsilyl)amidine 2 [23] (Scheme 2). After work-up,the moisture-sensitive yellow salt 3 was isolated in 55 %y ield.…”

A modular approach to neutral P,N-ligands: synthesis and coordination chemistry

“…The nitrogen-attached aryl substituent typically displays an orientation which is perpendicular to the plane of the metallacycle [17]. The P–M bond lengths in all complexes are within the expected range of 2.23–2.27 Å, as are the metal−imine bonds (2.08–2.15 Å) [18–19]. The close structural resemblance between the rhodium and iridium complexes is notable and can be attributed to the similar atomic radii of these metals [20].…”