Unique solubility of polyoxoniobate salts in methanol: coordination to cations and POM methylation

摘要

Sodium salts of hybrid organometallic POM complexes consisting of [M _(6) O _(19) ] ~(8?) (M = Nb, Ta) and half-sandwich fragments {Cp*M} ~(2+) (Cp* = η ~(5) -C _(5) (CH _(3) ) _(5) ; M = Rh, Ir) and {(C _(6) H _(6) )Ru} ~(2+) dissolve only in one organic solvent, that is, in methanol. From methanolic solutions, crystals of Na _(4) [ trans -{(C _(6) H _(6) )Ru} _(2) Nb _(6) O _(19) ]·14.125MeOH·2H _(2) O ( 1 ), K _(4) [ trans -{Cp*Rh} _(2) Nb _(6) O _(19) ]·4MeOH·10H _(2) O ( 2 ) and K _(4) [ trans -{Cp*Ir} _(2) Nb _(6) O _(19) ]·10MeOH·4H _(2) O ( 3 ) were isolated and characterized by X-ray analysis. Methoxo species [{LM′} _(2) M _(6) O _(19? n ) (OCH _(3) ) _( n ) ] ( n = 1–3) were detected in solution by ESI-MS and NMR, and they account only for about half of the total speciation in the solution. DFT calculations were used to calculate ~(13) C NMR chemical shifts in the methoxo complexes and to assess their relative stability. Reasons for the preferred solubility in methanol are discussed.