Carboxylation of 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene with CO2 in the presence of AlCl3

3,3′,4,4′-Tetramethyl-1,1′-diphosphaferrocene (1) is carboxylated by CO2 in the presence of AlCl3 at ambient pressure to afford 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxylic acid (2) in moderate (up to 30%) yield.