For 4-bromobenzotrifluoride an order of 0.53 in TMEDA was acquired. Varying Gas Ra;os: Further kineQc runs were conducted in which the parQal pressure of H2 (PH 2 ) was reduced by half, keeping the parQal pressure of CO (PCO) constant using a N2 balance (CO/H2/N2 1:0.5:0.5). IniQal rates of aldehyde formaQon reduced significantly across a range of electron-rich and electron-poor substrates, highlighQng a likely role of H2 pressure in the turnover-limiQng sequence (Table ). A similar experiment in which the parQal pressure of CO (PCO) was reduced by half, keeping the parQal pressure of H2 (PH 2 ) constant using a N2 balance (CO/H2/N2 0.5:1:0.5) also revealed an impact on the iniQal rates across a range of substrates, but to a lesser extent.