This paper reports on the first example of pH-dependent cross-coupling reactions of water-soluble organic halides (3-X(C6H4)CC2H, 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)PdII(H2O)]2(SO4) (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 pKa values of 2(SO4) and PhB(OH)2.
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