A reinvestigation of compound CpMo(PMe3)2(CH3)2: alkylation by single electron transfer and radical addition?

Abstract

The thermally unstable compound CpMo(PMe3)2(CH3)2 has been isolated and characterized by X-ray crystallography, low temperature EPR, and cyclic voltammetry. Its formation from CpMo(PMe3)2Cl2 appears to proceed via an initial electron transfer followed by radical addition.

Radical Polymerization of Styrene Controlled by Half-Sandwich Mo(III)/Mo(IV) Couples: All Basic Mechanisms Are Possible

“…We have then carried out BDE investigations of the Mo−X bond for the half-sandwich Mo(III) systems CpMoX 2 L 2 , with X = Cl and CH 3 and with L = PH 3 and PMe 3 , or L 2 = η 4 -C 4 H 6 , for which examples are experimentally available from this and other laboratories. − The BDEs have been calculated by subtracting the energy of the geometry-optimized 17-electron system CpMoX 2 L 2 from the sum of the energies of the two separated and geometry-optimized CpMoXL 2 and X fragments (eq 1). The calculations were carried out at the B3LYP/LANL2DZ level, which has proven satisfactory for the type of systems investigated here, affording results within < 5 kcal/mol of the experiment. −

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Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

“…Another example was discovered in our own laboratory for the reaction of [CpMoCl 2 (PMe 3 ) 2 ] with MeLi, leading to the stable 17‐electron dimethyl complex [CpMo(CH 3 ) 2 (PMe 3 ) 2 ]. Evidence based on redox potentials, kinetics and the chemical behaviour of related complexes led to the mechanistic proposal of initial PMe 3 dissociation and reduction leading to a {[CpMoCl 2 (PMe 3 )] – Li + · CH 3 · } cage pair, which favours the radical addition process because of the diradical ( S = 1) nature of the metal complex 39. It is quite possible that other alkylation reactions occur by the same unsuspected SET/recombination pathway.…”

Half-sandwich molybdenum(III) compounds containing diazadiene ligands and their use in the controlled radical polymerization of styrene

“…Their susceptibility to be oxidized to 16-electron (generally spin triplet) Mo(IV) derivatives or else to be reduced to saturated Mo(II) derivatives depends very strongly on the electronic properties of the ligands. Nevertheless, this family of compounds has been found to be compatible with a broad spectrum of ancillary ligands, from the very -acidic CO, as in [Cp*MoCl(PMe3)2(CO)] + [2], to the very -basic OH, as in [CpMo(OH)(PMe3)3] + [3], through the -neutral alkyls, as in CpMo(CH3)2(PMe3)2 [4]. The dichloride family, CpMoCl2L2, includes members where L or L2 = tertiary phosphine [5], phosphine donors linked as side chains to the cyclopentadienyl ligand [6], or dienes [7].…”