Variable Reactivity of a N‐Heterocyclic Phosphenium Complex: P−C Bond Activation or “Abnormal” Deprotonation

Abstract

The reaction of an N-heterocyclic phosphenium complex of manganese with MeLi/Et NHCl under formal addition of CH to the Mn=P double bond can be reversed upon UV photolysis, providing a rare example for selective P-C(alkyl) bond activation. Action of LDA on the phosphenium complex does not proceed via attack at phosphorus but rather via C4-deprotonation to yield a unique P-analogue of an "abnormal" carbene. A transmetalation product of the original complex was fully characterized. The C-metalation is also applicable to bis-phosphenium complexes of other metals.

Reversible Silylium Transfer between P‐H and Si‐H Donors

“…[22] Scalar relativistic DFT calculations with the BP86 functional [23] combined with D4 dispersion corrections [24] (ZORA-BP86 D4) and all-electron SARC-ZORA-TZVP basis sets [25] reproduce the bond shortening for Mo-P2 relative to Mo-P1 in trans-2b,a nd calculated bond order metrics clearly indicate double bond character in the Mo-phosphenium bonds in the cis and trans isomers of 2a,b, as is generally observed for metal-coordinated phosphenium ligands. [15,18,20,26] As expected based on p-backbonding considerations,t his is slightly reduced in the cis relative to the trans isomers.N BO analysis of the Mo-phosphenium interaction in trans-2b indicates one s-bond (polarized 64 % toward P) and one p-bond (polarized 66 %t oward Mo) (Figure 2a,b). The p*L UMO ( Figure 2c)i sd elocalized but shows significant contribution from a p-type lobe at P, the likely site of potential donor-acceptor interactions.T his sets these diarylphosphenium complexes apart from the more commonly studied bis(amido)-substituted phosphenium complexes (and most other P-based LAs) for which calculations show LUMOs of s*-character.…”

Steric Control in Reactions of N‐Heterocyclic Phosphorus Electrophiles with Pentacarbonyl Manganate(–I)

“…Following an earlier report on the synthesis of the cobalt complexes 1 (Scheme ) with N‐heterocyclic phosphenium (NHP) ligands, we recently described a manganese complex 2c that was found to exhibit unique chemical reactivity . In extension of the known ability of neutral phosphenium complexes to undergo reversible addition reactions with protic substrates (H X ), complex 2c allows for the hydrogenation and alkylation of the Mn–P double bond by stepwise attachment of H – /H + or CH 3 – /H + pairs and subsequent photochemical fission of H 2 or CH 4 , respectively , . Moreover, 2c can act as active catalyst enabling the dehydrogenation of ammonia borane under mild conditions, and treatment with BuLi or i Pr 2 NLi resulted in CH deprotonation in 4‐position of the N‐heterocycle.…”

“…Moreover, 2c can act as active catalyst enabling the dehydrogenation of ammonia borane under mild conditions, and treatment with BuLi or i Pr 2 NLi resulted in CH deprotonation in 4‐position of the N‐heterocycle. This reaction was unprecedented for NHPs and resulted in the synthesis of an isolable phosphorus‐analogue of an “abnormal” (or meso ‐ionic) carbene …”

“…Hypothesizing that the diverse regioselectivity revealed in the reactions of 2c with nucleophiles and bases (hydride attack at the phosphorus atom vs. CH deprotonation with lithium alkyls and amides) might be controlled by steric constraints, we became interested in accessing analogues of 2c featuring N‐substituents of different steric bulk. In view of the successful synthesis of the cobalt complexes 1 , complexes with N‐Mes ( 2b ), and N‐ t Bu‐substituents ( 2a ) were considered as viable targets that should like 2c be readily accessible from reactions of appropriate electrophilic NHP precursors with pentacarbonyl manganate(–I).…”

Variable Reaktivität eines N‐heterocyclischen Phosphenium‐Komplexes: P‐C‐Bindungsaktivierung oder “abnormale” Deprotonierung

“…[18] Ihre Molekülstrukturen (Abbildungen 1, 2) zeigen fürP hospheniumkomplexe typische Eigenschaften [9] wie eine planare Umgebung am Phosphoratom und kurze P-Mn-Bindungen (8:2 .0706(7) , 9:2 .083 (7) ), die gegenüber 1 (P-Mn 2.0625(11) [11] )n ur marginal verlängert sind. Der Zn-C-Abstand von 1.969(13) in 9 ist vergleichbar mit den Abständen in 10 a (2.058(3) [6b] )u nd 10 b (2.008(1) [6c] [18] und eine strukturelle ¾hnlichkeit zum Komplex 6 aufweist. [19] Die Reaktion von 11 mit LDAverläuft ebenfalls unter Deprotonierung an der C4-Position des Phospheniumliganden und liefert als Hauptprodukt den monolithiierten Komplex 14,d er spektroskopisch identifiziert, aber bisher nicht isoliert werden konnte.…”