NOVELTY - Nucleophilic acyl substitution of acid or ester (acid/ester) involves using specific oxometallic complex to catalyze nucleophilic acyl substitution between acid/ester and protic nucleophilic reagent.    USE - For nucleophilic acyl substitution of acid or ester (acid/ester) useful in the production of biodiesel.    ADVANTAGE - The method can be readily operated under mild reaction conditions with high chemical selectivity and excellent chemical yields. The oxometallic complex displays long-term activity and high water and air compatibilities, reducing production cost. The oxometallic complex can be recycled after the nucleophilic acyl substitution reaction and the recycled catalyst still maintains excellent catalytic function. The method has not only the economic advantages for industrial applications but also environmental friendliness.    DETAILED DESCRIPTION - Nucleophilic acyl substitution of acid or ester (acid/ester) involves using oxometallic complex of formula MOmL1yL2z to catalyze nucleophilic acyl substitution between acid of formula R1-C(O)H or ester of formula R1-C(O)-R2 and protic nucleophilic reagent of formula R3-AH.    A=O, S, or NH;    m, y=greater than or equal to1;    z=greater than or equal to0;    M=Groups IVB, VB, and VIB, or actinide group metal;    R1, R3=alkyl moiety; alkyl moiety including at least one substituted moiety selected from alkene, alkyne, halo, alkoxy, siloxy, ketone, alcohol, thioether, carbamate, or amino; aromatic moiety; heterocyclic moiety; multiple fused ring group; or multiple fused ring group with heteroatoms;    R2= is H or 1-5C alkyl;    L1=OTf, X, RC(O)CHC(O)R, OAc, OEt, O-iPr, or butyl;    X=halo; and    L2=H2O, CH3OH, EtOH, THF, CH3CN, or C4H8O2.    An INDEPENDENT CLAIM is included for production of biodiesel by providing and mixing triglyceride-containing crude oil and first alcohol to form a solution mixture, adding oxometallic complex of formula MomL1yL2z into the solution, and performing trans-esterification reaction between the triglyceride-containing crude oil and first alcohol in the presence of oxometallic complex.