Cationic (pentamethylcyclopentadienyl)molybdenum complexes: improved synthesis and characterization

Abstract

The synthesis of the known pentamethylcyclopentadienylmolybdenum compounds [Mp *] 2 ( 1, Mp *Cl ( 3), and Mp *H ( 7) (Mp * = Mo(η 5-C 5Me 5)(CO) 3) has been improved. The cyclic voltammetry of 1 shows a behaviour close to that of [Mp] 2 (Mp = Mo(η 5-C 5H 5)(CO) 3) with a shift of potentials towards more negative values by 0.30 to 0.50 V. The [Mp *CO] + PF 6 − ( 4) has been synthesized by reaction of (a) Mp *Cl ( 3) with CO (100 atm, 95°C) and AlCl 3 followed by treatment with HPF 6 or (b) Mp *H ( 7) with Ph 3C + PF 6 − under CO (1 atm, 20°C) via the coordinatively unsaturated species [Mp *] + PF 6 −. This reaction provides a convenient general route to [Mp *L] + PF 6 − (L = PR 3 ( 8a–8d); P(OPh) 3 ( 9), CH 3CN ( 10)). The new complexes have been obtained in overall yields ranging from 53 to 82% based on the C 5Me 5H initially taken. The cis- and trans-dicarbonyls species [Mo(C 5Me 5)(CO) 2L 1L 2] + PF 6 − (L 1L 2 = dppe ( 13) and L 1 = PMe 3, L 2 = PMePh 2 ( 12)) have been stereospecifically prepared. Cyclic voltammetric and 1H, 13C, 31P NMR, and IR data are discussed.