COMPARATIVE MULTINUCLEAR MAGNETIC-RESONANCE SPECTROSCOPIC STUDY OF TRANSITION-METAL (CR, W AND MN) MESITYLENE TRICARBONYLS AND TRANSITION-METAL (RU AND CO) CARBONYL CLUSTERS

Three mononuclear 1,3,5-trimethylbenzene (mesitylene) carbonyl transit ion metal complexes, mesitylene tricarbonyl chromium, (CH3)3C6H3Cr(CO) 3 (1), Mesitylene tricarbonyl tungsten, (CH3)3C6H3W(CO)3 (2), mesityle ne tricarbonyl manganese tetra-fluoroborate, [(CH3)3C6H3Mn(CO)3]BF4 (3 ); and three clusters, mesitylene nonacarbonyl tetracobalt, (CH3)3C6H3 Co4(CO)9 (4), mesitylene carbido tetradecacarbonyl hexaruthenium, (CH3 )3C6H3Ru6C(CO)14 (5) and carbido heptadecacarbonyl hexarutbenium, RU6C (CO)17 (6), have been studied by means of H-1, C-13 and natural abunda nce 170 NMR spectroscopy. Generally, the H-1 and C-13 NMR chemical shi fts of the aromatic protons and carbons in the compounds studied show clearly shielded values when compared with those of uncomplexed mesity lene. The 13C NMR chemical shifts of the carbonyl groups show an inver se relation with the corresponding O-17 chemical shifts in agreement w ith the effect of pi-backbonding. 1J(C, H) spin-spin coupling constant s of aromatic carbons in mesitylene moiety of chromium and tungsten co mplexes show clearly increased values when compared with uncomplexed m esitylene. This can be explained by an increased s-character in the C- H bond induced by the sigma-effect of the bound metal. Of the NMR meth ods studied, O-17 NMR was shown to have very promising properties owin g to the exceptionally high sensitivity and small line width of NMR si gnals.