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 water-soluble organic halides (3-X(C 6 H 4 )CO 2 H, where X = Cl, Br, I) with organoboron compounds (PhB(OH) 2 and Ph 4 BNa) to form 3-Ph(C 6 H 4 )CO 2 H, catalyzed by the mononuclear organometallic aqua complex [(SCS)Pd II (H 2 O)] 2 (SO 4 ) ([ 1 ] 2 (SO 4 ), SCS = C 6 H 3 -2,6-(CH 2 SBu t ) 2 ) in basic media (8 < pH < 13, NaHCO 3 /NaOH buffers). The structure of 1 (PF 6 ) 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 Ph 4 BNa shows a flat maximum in a pH range of about 8−11. The pH dependence is discussed on the basis of the p K a values of [ 1 ] 2 (SO 4 ) and PhB(OH) 2 .