Binuclear dinitrogen-bridged

There are also a few dimeric complexes containing a bridging bidentate ligand. Particularly noteworthy are the binuclear dinitrogen complexes [ RhH(PR3)2 2N2] (R = Pr1,55 Cy55,56). 

Treatment of (108) (R IV) with the dinitrogen compound Na[(N2)Mo(NButAr)3] provided the binuclear N2-bridged complex (110) (Scheme 20).193 Reduction of the latter produced the anion [L3NbN] (111) whose reaction with I2 in tol yielded a mixture of products frotn which cyclic [(L2Nb(/r2-N)]3 (112) was isolated. The latter contained both short (1.791(7)A) and long (2.004(6)A) Nb—N bonds.193... 

Af-methylsalicylaldiminato, 4,908 pentane-2,4-dionato, 4,908 trifluoroacetato, 4,908 bridged, 4,908-911 cupferron, 2, 512 dinitrogen, 4, 919 binuclear, 4,920 four-coordinate... 

A new representative of a multicopper cluster in a protein is Cuz in nitrous oxide reductase. As was discussed above this enzyme contains a binuclear CuA centre as in COX. While the latter in addition has CuB in the form of a copper-heme group, N20 reductase has Cuz which is the site of dinitrogen formation from the substrate N20. Recently a central inorganic sulfide has been found as a ligand to copper and multiple forms of Cuz were detected in the enzyme from Paracoccus pantotrophus.134 More recently a tetranuclear copper cluster with X-S bridges was proposed as structure for Cuz..135... 

The formation of ammonia and/or hydrazine by protonation of binuclear bridging dinitrogen complexes of Groups IV and V is well established and has been reviewed elsewhere (82, 148). In general, stoichiometries are fairly well defined [Eq. (51)], although as with mononuclear complexes, mechanisms are not clearly understood (282). 

In contrast Shilov and his group propose a very different mechanism (Scheme 20), which involves a bridging dinitrogen and four vanadium atoms, each acting as a one-electron reductant (contrasting to Schrau-zer s proposal that vanadium acts as a two-electron reductant). The hydrazine may then be reduced to ammonia. On theoretical grounds Shilov considers that dA metal ions would make the best dinitrogen reducers in these binuclear systems (44), and there is ample evidence to support the formulation of vanadium(II) dinuclear species in aqueous solution. However, Shilov postulates and finds vanadium(III) products, which Schrauzer ascribed to a conproportionation (289) as shown in Eq. (78). 

Accordingly, we decided to examine a binuclear complex with a bridging N2 ligand that largely preserves its integrity as dinitrogen molecule. For this purpose, we selected the cation [(NH3)50s ( i-N2)0s (NH3)5]° (57,58) (I) for a recent study (59). 

Rhodium)-1) complexes, 904, 905 Rhodium(O) complexes, 905, 906 triphenylphosphine, 905 Rhodium(l) complexes, 906-929 anionic, 906 bidentate anions At-methylsalicylaldiminato, 908 pentane-2,4-dionato, 908 trifluoroacetato. 908 bridged, 908-911 dinitrogen, 919 binuclear, 920 four-coordinate anions, 925 hydrido, 921 hydrido dinitrogen, 920 pen tacoordin ate anions, 929... 

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