The syntheses of metallomacrocycles containing unsymmetrical bridging ligands and the crystal structures of DL-[Mo{HB(3,5-Me2C3HN2)(3)}(NO)(OC6H4CH2CH2O-4)](2)center dot 2CH(2)Cl(2) and DL-[W{HB(3,5-Me2C3HN2)(3)}(NO)(OC6H3NO2-4-CH2CH2O-3)](2)center dot CH2Cl2

Metallomacrocycles containing {M(NO)(Tp(Me2))} [Tp(Me2)=HB(3,5-Me2C3HN2)(3) ; M=Mo or W] have been synthesized by direct reaction between [M(NO)(Tp(Me2 ))I-2] and a heterotopic ligand HE-E'H {1,x-HOC6H4XOH (x=3, X=CO; x=3 or 4, X=CH2 or CH2CH2)} in the presence of NEt3. Only DL and meso isomers were i solated from the reactions where M=Mo, x=4 and X=CO or CH2CH2 but both DL a nd meso and syn and anti isomers from the other reaction mixtures. Stereo-c ontrolled synthetic routes to syn and anti isomers containing the OC6H4CH2O -3 bridging ligand were developed through formation of [M(NO)(Tp(Me2))(OC6H 4CHO-3)](2) (M=Mo or W) followed by reduction to [M(NO)(Tp(Me2))(OC6H4CH2OH -3)](2) and subsequent reaction with [M'(NO)(Tp(Me2))I-2] (M'=W or Mo) to g ive [{M(NO)(Tp(Me2))}(mu -OC6H4CH2O-3)(2){M'(NO)(Tp(Me2))}]. The trinuclear complex [{Mo(Tp(Me2))(NO)}(mu -OC6H4CH2O-3)(2){W(Tp(Me2))(NO)}(2)(mu -1,3- OC6H4O)] was obtained from the reaction of [Mo(NO)(Tp(Me2))(OC6H4CH2OH-3)]( 2) with the binuclear complex [{W(NO)(Tp(Me2))I}(2)(mu -1,3-O2C6H4)]. The c rystal structures of DL-[Mo(Tp(Me2))(NO)(OC6H4CH2CH2O-4)](2) and [W(Tp(Me2) )(NO)(OC6H3NO2-4-CH2CH2O-3)](2) were established.