Ferrocenylmethylation reactions with a phosphinoferrocene betaine

Abstract

A phosphinoferrocene betaine, N-{[1′-(diphenylphosphino)ferrocenyl]methyl}-N,N-dimethyl-3-sulfo-1-propanaminium, inner salt, Ph₂PfcCH₂NMe₂(CH₂)₃SO₃ (2; fc = ferrocene-1,1′-diyl), was prepared by alkylation of Ph₂PfcCH₂NMe₂ (1) with 1,3-propanesultone, and was studied as a ferrocenylmethylation agent. The treatment of 2 with NaOH in hot water–dimethyl sulfoxide produced phosphinoalcohol Ph₂PfcCH₂OH (3) in a 64% yield, whereas a similar reaction with MeONa in dimethylsulfoxide–methanol furnished the corresponding ether, Ph₂PfcCH₂OMe (4), in a 47% yield. In subsequent experiments, betaine 2 was employed in the synthesis of phosphinoferrocene sulfones, Ph₂PfcCH₂SO₂R, where R = Me (6a), Ph (6b), and 4-tolyl (6c). Compounds 6a–c and some by-products of the ferrocenylmethylation reactions, namely alcohol 3, 1′-(diphenylphosphino)-1-methylferrocene (5), and 1-{[diphenyl(2,4-cyclopentadien-1-ylidene)phosphoranyl]methyl}-1′-(diphenylphosphino)ferrocene (7) structurally characterised. Reactions of 6a as the representative with ZnX₂/NaX (X = Br and I) afforded unique coordination polymers [ZnNaX₃(6a)(CH₃OH)]_n featuring tetrahedral Zn(II) and octahedral Na(I) centres bridged by halide ions, solvating methanol and the sulfone ligands. The reaction of 6a with ZnBr₂/KBr produced an analogous product, [ZnKBr₃(6a)(CH₃OH)]_n, while that with ZnBr₂/LiBr furnished a different, pseudodimeric complex [Zn₂Li₂Br₆(6a)₂(CH₃OH)₄(H₂O)]·CH₃OH, featuring tetrahedrally coordinated Zn(II) and Li(I) centres bridged by 6a. Reactions of 6a with ZnBr₂/MBr (M = Rb, Cs) and NaCl/ZnCl₂ did not yield similar products because of an easy precipitation (low solubility) of the respective alkali metal halides.