pH-dependent cross-coupling reactions of water-soluble organic halides with organoboron compounds catalyzed by the organometallic aqua complex [(SCS)PdII(H2O)]+ (SCS=C6H3-2,6-(CH2SBut)2)

This paper reports on the first example of pH-dependent cross-coupling reactions of watersoluble organic halides (3-X(C6H4)CO2H, where X = Cl, Br, I) with organoboron compounds (PhB(OH)(2) and Ph4BNa) to form 3-Ph(C6H4)CO2H, catalyzed by the mononuclear organometallic aqua complex [(SCS)Pd-II(H2O)](2)(SO4) (1)(2)(SO4), SCS = C6H3-2,6-(CH2SBut)(2)) in basic media (8 < PH < 13, NaHCO3/NaOH buffers). The structure of 1(PF6) was unequivocally determined by X-ray analysis. The reactions show unique PH selectivity depending upon the organoboron compounds; i.e., the rate of the reactions with PhB(OH)2 shows a sharp maximum around PH 10, though the rate of the reactions with Ph4BNa shows a flat maximum in a PH range of about 8-11. The PH dependence is discussed on the basis of the pK(a), values of [1](2)(SO4) and PhB(OH)(2).