Pyrrole‐based pincer ligands containing iminophosphorane moieties and their coordination chemistry with group 1 metals and magnesium

Abstract

The Staudinger reaction of 2,5‐bis((di‐tert‐butylphosphaneyl)methyl)‐1H‐pyrrole (tBuPNP)H; tBuPNP=C4H2N‐2,5‐CH2PtBu2) with 2 equiv. of Me3SiN3 cleanly furnishes 1,1′‐((1H‐pyrrole‐2,5‐diyl)bis(methylene))bis(1,1‐di‐tert‐butyl‐N‐(trimethylsilyl)‐λ5‐phosphanimine) (1; (NPNPN)H, NPNPN=C4H2N‐2,5‐CH2PtBu2NSiMe3) in excellent yield. Pyrrole 1 is easily deprotonated by alkali metal amides, [MN(SiMe3)2] (M=Li, Na, K, Cs) to yield the corresponding alkali metal pyrrolides, 1‐M. Compound 1‐Li is features a κ‐N,N,N coordination whereby both iminophosphorane side‐arms are coordinated to the lithium cation (with additional short Li⋅⋅⋅H contacts, whereas the heavier congeners form dimeric structures. This results in κ‐N,N coordination within one [(NPNPN)M] (M=Na, Cs) unit, and the dimeric structure is then completed by additional η5‐coordination of the pyrrolyl ligand to the neighbouring alkali metal. Furthermore, heteroleptic magnesium alkyl complexes, 1‐MgR, are isolated from the reaction of [MgR2] (R= CH2SiMe3, CH2CMe3, CH2CMe2Ph) with (PNP*)H (1 equiv).