Secondary diphosphine and diphosphido ligands: synthesis, characterisation and group 1 coordination compounds

Two types of secondary diphosphines, 1,8-(ArPH) 2 C 14 H 8 ( 1a : Ar = Tripp, 2,4,6-triisopropylphenyl; 1b : Ar = Mes, 2,4,6-trimethylphenyl) and 1,3-( t BuPHCH 2 ) 2 C 6 H 4 ( 2 ), based on rigid 1,8-anthracene and flexible m -xylyl frameworks, respectively, have been synthesized using different strategies. Compounds 1a and 1b were formed by nucleophilic aromatic substitution of a potassium organophosphido salt onto 1,8-difluoroanthracene, while compound 2 was obtained by addition of the Grignard reagent [1,3-(ClMgCH 2 ) 2 C 6 H 4 ] x to a dichloroorganophosphine, followed by reduction to the diphosphine. These compounds were isolated as ca . 1 : 1 mixtures of rac and meso diastereomers as determined by multinuclear NMR spectroscopy. Borane and selenide derivatives of 2 , 1,3-( t BuPH(BH 3 )CH 2 ) 2 C 6 H 4 ( 3 ) and 1,3-( t BuPH(Se)CH 2 ) 2 C 6 H 4 ( 4 ), were obtained. Preferential crystallization of one diastereomer of 3 and 4 was observed; X-ray crystallographic studies identified this as the rac isomer for diselenide 4 . Metallation studies of compounds 1a and 2 yielded several alkali metal salts. The reaction of KH or K metal with 1a yielded the compounds 1,8-(TrippPK) 2 C 14 H 8 · x THF ( 5 ) and 1,8-(TrippPK) 2 C 14 H 10 · x THF ( 6 ), respectively; in complex 6 the central aromatic ring has been reduced to yield a bent dihydroanthracene backbone. A crown ether derivative of 6 , [K(18-crown-6)(THF) 2 ] 2 [1,8-(TrippP) 2 C 14 H 10 ] ( 7 ), was characterised crystallographically. Double deprotonation of compound 2 with n BuLi/TMEDA (TMEDA = N , N , N ′, N ′-tetramethylethylenediamine) afforded the yellow dilithium complex 1,3-( t BuPLiCH 2 ) 2 C 6 H 4 ·TMEDA ( 8 ), which crystallized as a dimer featuring lithium-arene π interactions. Two new secondary phosphines have been prepared as 1 : 1 mixtures of rac / meso diastereomers. They undergo reactions with group 1 reagents to cleanly afford unusual diphosphido complexes.