Cationic (pentamethylcyclopentadienyl)molybdenum complexes: improved synthesis and characterization

The synthesis of the known pentamethylcyclopentadienylmolybdenum compounds [Mp*]2 (1, Mp*Cl (3), and Mp*H (7) (Mp* = Mo(η5-C5Me5)(CO)3) has been improved. The cyclic voltammetry of 1 shows a behaviour close to that of [Mp]2 (Mp = Mo(η5-C5H5)(CO)3) with a shift of potentials towards more negative values by 0.30 to 0.50 V. The [Mp*CO]+ PF6− (4) has been synthesized by reaction of (a) Mp*Cl (3) with CO (100 atm, 95°C) and AlCl3 followed by treatment with HPF6 or (b) Mp*H (7) with Ph3C+ PF6− under CO (1 atm, 20°C) via the coordinatively unsaturated species [Mp*]+ PF6−. This reaction provides a convenient general route to [Mp*L]+ PF6− (L = PR3 (8a–8d); P(OPh)3 (9), CH3CN (10)). The new complexes have been obtained in overall yields ranging from 53 to 82% based on the C5Me5H initially taken. The cis- and trans-dicarbonyls species [Mo(C5Me5)(CO)2L1L2]+ PF6− (L1L2 = dppe (13) and L1 = PMe3, L2 = PMePh2 (12)) have been stereospecifically prepared. Cyclic voltammetric and 1H, 13C, 31P NMR, and IR data are discussed.