Mark Niemeyer

Ambident PCN Heterocycles: N- and P-Phosphanylation of Lithium 1,3-Benzazaphospholides

Synthetic and structural aspects of the phosphanylation of 1,3-benzazaphospholides 1(Li), ambident benzofused azaphosphacyclopentadienides, are presented. The unusual properties of phospholyl-1,3,2-diazaphospholes inspired us to study the coupling of 1(Li) with chlorodiazaphospholene 2, which led to the N-substituted product 3. Reaction of 1(Li) with chlorodiphenyl- and chlorodicyclohexylphosphane likewise gave N-phosphanylbenzazaphospholes 4 and 5, whereas with the more bulky di-tert-butyl- and di-1-adamantylchlorophosphanes, the diphosphanes 6 and 7 are obtained; in the case of 7 they are isolated as a dimeric LiCl(THF) adduct. Structural information was provided by single-crystal X-ray diffraction and solution NMR spectroscopy experiments. 2D exchange spectroscopy confirmed the existence of two rotamers of the aminophosphane 5 at room temperature; variable-temperature NMR spectroscopy studies of 6 revealed two dynamic processes, low-temperature inversion at ring phosphorus (DeltaH( not equal)=22 kJ mol(-1), DeltaS( not equal)=2 J K(-1) mol(-1)) and very low-temperature rotation of the tBu(2)P group. Quantum chemical studies give evidence that 2-unsubstituted benzazaphospholides prefer N-phosphanylation, even with bulky chlorophosphanes, and that substituents at the 2-position of the heterocycle are crucial for the occurrence of P-N rotamers and for switching to alternative P-substitution, beyond a threshold steric bulk, by both P- and 2-position substituents.

Ambident Reactivity of P˭CH‒N‒Heterocycles: Lithiation and Substitution Sites

Abstract Benzofused 1H-1,3-azaphospholes are lithiated at the N-atom by tBuLi but phosphinylation takes place at either the N- or the P-atom. Smaller chlorophosphines react at nitrogen, bulkier react at phosphorus. Substituents at C2 promote the latter mode. N-Substituted 2H-1,3-benzazaphospholes undergo CH-metalation or addition at the P˭C bond, depending on the conditions, and allow access to 2-functionally substituted benzazaphospholes or their 2,3-dihydro derivatives, new σ2P,X or σ3P,X hybrid ligands (X=O,P).

An unsolvated erbium organyl: (2,4,6,2′′,4′′,6′′-hexamethyl-1,1′:3′;1′′-terphenyl-2′-yl)bis(methylcyclopentadienyl)erbium(III)

The title compound, [Er(Dmp)(C5H4Me)2] (Dmp = 2,6-Mes2C6H3, with Mes = 2,4,6-Me3C6H2) or [Er(C6H7)2(C24H25)], was obtained by the reaction of LiDmp with Er(C5H4Me)3. The Er atom is η5-coordinated by two methylxadcycloxadpentaxaddienyl ligands (average Er⋯centroid distance = 2.341u2005A) and η1-coordinated by the ipso-C atom of the aryl substituent [Er—C = 2.434u2005(4)u2005A]. An additional π-arene contact with one of the Mes groups [Er⋯C = 3.077u2005(4)u2005A] gives rise to the pyramidalization of the metal-atom environment.