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PREPARATION OF HYDRAZIDO(2-)-N COMPLEXES OF MOLYBDENUM AND TUNGSTEN. THEIR CONDENSATION REACTIONS AND REACTIVITY WITH ACIDS TO GIVE AMMONIA
Abstract
Hydrazido(2-) complexes of molybdenum and tungsten were reacted with selected aldehydes to form diazoalkane complexes. Condensation reactions with FcCHO, where Fc = ferrocene, yielded dark purple complexes such as {WF(dppe)(,2)(NN = CHFc)}BF(,4), dppe = Ph(,2)PCH(,2)CH(,2)PPh(,2), which contained two metal centers. Electrochemical studies have provided a route to carbon-carbon bond formation via electrochemical coupling of the diazoalkane ligands in trans-{WF(dppe)(,2)(NN = CH(,2))}('+) to give the bridging ligand, {-N(,2)CH(,2)CH(,2)N(,2)-}. Attempts to condense metal oxides with {WF(NNH(,2))(dppe)(,2)}BF(,4) to give bimetal species were unsuccessful. The reactivity of the hydrazido(2-) complexes, trans- and cis-{MoX(NNH(,2))(TRIPHOS)(PR(,3))}, where PR(,3) = PPh(,3), X = Br, Cl, F; and PR(,3) = PMePh(,2), X = Br; TRIPHOS = (Ph(,2)CH(,2)CH(,2))(,2)PPh, with acid in various solvents was studied by ('31)P{('1)H} NMR spectroscopy. The isomers could be prepared by reaction of HX (X = Br, Cl) directly with trans-{Mo(N(,2))(,2)(TRIPHOS)(PR(,3))}, 1(PR(,3)), to give a green-brown solid mixture of isomers or by reaction of the bis(dinitrogen) complex with acid in solution. The cis-isomer predominated in ca. a 2:1 ratio except in the case of HBF(,4) where the trans-isomer was more prevalent. The phosphine trans to the hydrazido(2-) ligand in the cis-isomer was labile in the presence of acid in solution. The rate of phosphine loss depended upon the coordinated halide in the order of decreasing phosphine lability: Br > Cl > F. As the basicity of the monodentate phosphine increased the lability of the phosphine decreased in the order PPh(,3) >> PMePh(,2) > PMe(,2)Ph such that with PMe(,2)Ph, the cis-isomer did not appear to react appreciably. Evidence suggested that the trans-isomer slowly isomerized to the cis-isomer and then it proceeded to react to give ammonia. The rate of isomerization was probably dependent upon the lability of the trans-halide in the order of decreasing lability: Br > Cl > F. Evidence also suggests that bromide in the cis-isomer containing coordinated PPh(,3) was also labile. A new complex has been isolated from the reaction of 1(PPh(,3)) with HBr in tetrahydrofuran. The gold solid is paramagnetic and remains uncharacterized. The solid may be a molybdenum dimer formed by dimerization of a hydrazido(2-) complex.
Subject Area
Chemistry
Recommended Citation
LESTER, RICHARD KIMBERLY, "PREPARATION OF HYDRAZIDO(2-)-N COMPLEXES OF MOLYBDENUM AND TUNGSTEN. THEIR CONDENSATION REACTIONS AND REACTIVITY WITH ACIDS TO GIVE AMMONIA" (1983). ETD collection for University of Nebraska-Lincoln. AAI8401388.
https://digitalcommons.unl.edu/dissertations/AAI8401388