Ferrocenylmethylation reactions with a phosphinoferrocene betaine

Abstract

A phosphinoferrocene betaine, N-{[1′-(diphenylphosphino)ferrocenyl]methyl}-N,N-dimethyl-3-sulfo-1-propanaminium, inner salt, Ph 2 PfcCH 2 NMe 2 (CH 2) 3 SO 3 (2; fc = ferrocene-1,1′-diyl), was prepared by alkylation of Ph 2 PfcCH 2 NMe 2 (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 Ph 2 PfcCH 2 OH (3) in a 64% yield, whereas a similar reaction with MeONa in dimethylsulfoxide-methanol furnished the corresponding ether, Ph 2 PfcCH 2 OMe (4), in a 47% yield. In subsequent experiments, betaine 2 was employed in the synthesis of phosphinoferrocene sulfones, Ph 2 PfcCH 2 SO 2 R, 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 ZnX 2 /NaX (X = Br and I) afforded unique coordination polymers [ZnNaX 3 (6a)(CH 3 OH)] 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 ZnBr 2 /KBr produced an analogous product, [ZnKBr 3 (6a)(CH 3 OH)] n, while that with ZnBr 2 /LiBr furnished a different, pseudodimeric complex [Zn 2 Li 2 Br 6 (6a) 2 (CH 3 OH) 4 (H 2 O)]·CH 3 OH, featuring tetrahedrally coordinated Zn(ii) and Li(i) centres bridged by 6a. Reactions of 6a with ZnBr 2 /MBr (M = Rb, Cs) and NaCl/ZnCl 2 did not yield similar products because of an easy precipitation (low solubility) of the respective alkali metal halides.