Gas and Liquid Phase Diffusivities of Isomeric Metal Complexes Derived from Multifold Ring-Closing Metatheses: Ion Mobility Mass Spectrometry Trumps DOSY NMR
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2016 American Chemical Society. Isomeric octahedral osmium and rhenium complexes of formulas M(CO)y(X)z(P((CH2)n)3P) and M(CO)y(X)z(P(CH2)n1CH2)((CH2)n)(P(CH2)n-1CH2) (n/M/y/z/X = 14/Os/2/2/Cl, 14/Os/2/2/Br, 14/Re/3/1/Cl, 18/Os/2/2/Br), in which the phosphorus donor atoms occupy trans positions, are examined by the title techniques. The former gyroscope-like complexes are spherical or ovoid in shape, whereas the latter have phosphacycle "flaps" that increase the volume. Both types diffuse at identical rates in C6D6 as assayed by DOSY NMR, but ions derived from the latter exhibit up to 10% slower drift times in the gas phase by ion mobility mass spectrometry (IMMS). Thus, IMMS, which is seldom applied to isomeric organometallic or coordination compounds, provides superior differentiation.