The d4/d3 redox pairs [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']z (z=0 and 1): structural consequences of electron transfer and implications for the inverse halide order.
The d4 halide complexes [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp'] {X=F, Cl, Br or I; R=Me or Ph; M=Mo or W; Tp'=hydrotris(3,5-dimethylpyrazolyl)borate} undergo one-electron oxidation to the d3 monocations [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+, isolable for M=W, R=Me. X-Ray structural studies on the redox pairs [WX(CO)(eta-MeC[triple bond, length as m-dash]CMe)Tp']z (X=Cl and Br, z=0 and 1), the ESR spectra of the cations [WX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+ (X=F, Cl, Br or I; R=Me or Ph), and DFT calculations on [WX(CO)(eta-MeC[triple bond, length as m-dash]CMe)Tp']z (X=F, Cl, Br and I; z=0 and 1) are consistent with electron removal from a HOMO (of the d4 complexes) which is pi-antibonding with respect to the W-X bond, pi-bonding with respect to the W-C(O) bond, and delta-bonding with respect to the W-Calkyne bonds. The dependence of both oxidation potential and nu(CO) for [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp'] shows an inverse halide order which is consistent with an ionic component to the M-X bond; the small size of fluorine and its closeness to the metal centre leads to the highest energy HOMO and the lowest oxidation potential. In the cations [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+ electronegativity effects become more important, leading to a conventional order for Cl, Br and I. However, high M-F pi-donation is still facilitated by the short M-F distance.
Adams
Christopher J
CJ
School of Chemistry, University of Bristol, Bristol, UK BS8 1TS.
Bartlett
Ian M
IM
Carlton
Susannah
S
Connelly
Neil G
NG
Harding
David J
DJ
Hayward
Owen D
OD
Orpen
A Guy
AG
Patron
Elena
E
Ray
Christopher D
CD
Rieger
Philip H
PH
D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004583:Electrons; D006219:Halogens / Q000737:chemistry*; D006846:Hydrocarbons, Halogenated / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012680:Sensitivity and Specificity; D014414:Tungsten / Q000737:chemistry*
D006219:Halogens; D006846:Hydrocarbons, Halogenated; D009942:Organometallic Compounds; D008982:Molybdenum; D014414:Tungsten