Diversity and design of metal-based carbon monoxide-releasing molecules (CO-RMs) in aqueous systems: revealing the essential trends.
The CO-releasing ability of a diverse library of primary metal carbonyl complexes has been assessed using a deoxymyoglobin-carbonmonoxymyglobin assay. A wide spectrum of rates for the CO-release process was observed in aqueous systems. For octahedral d(6) complexes, the rate was found to decrease in the sequence FeI(2)(CO)(4) > [NEt(4)][V(CO)(6)] > MnBr(CO)(5) > Cr(CO)(6) implying that CO-release is not controlled by the metal-carbon bond strengths. Within the series, [NEt(4)][MX(CO)(5)] (M = Cr, Mo, W; X =Cl, Br, I), the rate of CO-release was found to decrease down the group (Cr > Mo > W), whilst within the chromium series a similar trend was observed for the halide (Cl > Br > I). The d(4) complexes [NEt(4)][MI(3)(CO)(4)] (M = Mo, W) exhibit faster release than their d(6) congeners. A mechanistic investigation into the [NEt(4)][MX(CO)(5)] series revealed the intermediacy of [[M(CO)(5)](2)(mu-X)](-) in the CO-release process and that the hydrolysis of the M-X bond, rather than the intrinsic strength of M-CO bonds, controls the rate of CO-release in aqueous systems.
Zhang
Wei-Qiang
WQ
Department of Chemistry, University of York, Heslington, York, UK.
Atkin
Anthony J
AJ
Thatcher
Robert J
RJ
Whitwood
Adrian C
AC
Fairlamb
Ian J S
IJ
Lynam
Jason M
JM
D000818:Animals; D000838:Anions / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006736:Horses; D007501:Iron / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009206:Myocardium / Q000737:chemistry; D009211:Myoglobin / Q000378:metabolism*; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism*; D014867:Water / Q000737:chemistry
D000838:Anions; D009211:Myoglobin; D009942:Organometallic Compounds; D014867:Water; D002248:Carbon Monoxide; D007501:Iron