The molecule bis(eta(5)-cyclopentadienyl)molybdenum(IV) dichloride (Cp(2)MoCl(2)), I, is the first known organometallic compound that promotes the phosphoester bond cleavage of activated phosphodiesters and phosphomonoesters in aqueous solution. Under psuedo-first-order conditions, Cp(2)MoCl(2) (110-fold excess) promotes the production of 4-nitrophenol from 4-nitrophenyl phosphate (NPP), and from bis(4-nitrophenyl) phosphate (BNPP). For both NPP and BNPP, 1 equiv of 4-nitrophenol is released, and when compared to no metal added, there are 10(5) and 10(7) enhancements in the observed rate of 4-nitrophenol production (pH 7.0, 20 degrees C), respectively. NMR (P-31) studies show that the reaction of NPP with I (10-fold excess) begins with Cp(2)Mo coordination to form a monodentate Cp(2)Mo(4-nitrophenylphosphate) complex (II) that undergoes intramolecular phosphoester bond cleavage to yield a mononuclear Cp(2)Mo-phosphate complex(III).