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

The Staudinger reaction of 2,5-bis((di-tert-butylphosphaneyl)methyl)-1H-pyrrole ((PNP)-P-tBu)H; (PNP)-P-tBu=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)-lambda(5)-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 kappa-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 kappa-N,N coordination within one [(NPNPN)M] (M=Na, Cs) unit, and the dimeric structure is then completed by additional eta(5)-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).