Side-on bridging

Two type-(v) complexes (Fig. 23) have been reported, both of which contain nickel and lithium. An ethereal solution of phenyllithium and Ni(CDT) (CDT = all-tm j-l,5,9-cyclododecatriene) in the mole ratio of 3 1 absorbed N2 (1 bar) at 0 °C to afford a dimeric complex 20 in ca. 50% yield. The ether content in 20 varied in the range of 2-3Et20 per 

When a mixture of PhLi and PhNa (1 3-4) was employed in place of PhLi under similar reaction conditions. 

Important structural subunits of complexes 20 and 21 are shown in Figs. 30 and 31. In either case, an N2 molecule side-on bridges two diphenylnickel units, allowing a weak Ni— Ni bonding. Furthermore, N2 interacts in the end-on fashion with lithium atoms. In complex 20, the lone pair of one N atom interacts with just one Li ion, while that of the other N atom is involved in a two-electron four-center bond with a Li3 ring. In the case of 21, similar two-electron three-center bonds to Li at both ends of N2 are observed. 

The N—N distances (1.35-1.36 A) are greatly enlarged, lying within the range of those observed for single and double bonds. On hydrolysis of 20 in THF, some N2 (30-38%) is converted into NH3, and the rest liberated as N2 gas.  

The red brown crystalline product has a v(N2) band at 1282cm , and its composition was determined by single-crystal X-ray analysis as 

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A dramatic discovery in this area was made in 1996 when a dicopper-dioxygen adduct was found to have two isomeric forms which featured either a side-on bridging unit Cu(/r ), ) -02)-Cu) " or a cyclic (Cu(/r-0)2Cu) " core depending on whether it was crystallized from CH2CI2 or thf, respectively. The two forms could be readily interconverted by reversible 0-0 bond cleavage and reformation, the 0-0 distance being 141 pm and 229 pm in the two isomers.The... 

Potassium graphite reduction of the dichloro precursors under an atmosphere of N2 in THF according to Scheme 101 allowed access to new families of Group 4 bimetallic "side-on-bridged" dinitrogen complexes... 

The first step of the reaction of Al with the H2 molecule is the coordination of dihydrogen to Al. The product of this step was interpreted as the complex [P2N2]Zr( i.-t 2-N2H)(p-H)Zr[P2N2] on the basis of H and ISN NMR data [9]. However, low-temperature X-ray diffraction data [9] were interpreted in terms of a complex having a side-on bridging H2 unit. Our calculations show that this coordination does not produce the dihydrogen... 

It was of critical importance to evaluate experimentally this unusual electronic structure description for the side-on bridged peroxide and its relation to the spectral features of the p-rt2 rj2 model complex and oxyhemocyanin. This evaluation was accomplished through a series of... 

An interesting reaction takes place when ZrCl3[N(SiMe2CH2PPr92] and Na/Hg are in contact with N2 blue crystals of [Pr 2PCH2Si Me2)2N] ZrCl 2(N2) (18-A-IV) are isolated in which the dinitrogen unit is found in a planar side-on bridging mode.31... 

The first example of a four-electron donor, side-on bridging thiocarbonyl, [HB(pz)jJ-(CO)2W(Tj -CS)Mo(CO) (indenyl), has been reported. Draw the structure of this complex. Why is the bridging CS group in this complex called side-on instead of semibridging (See Doyle, R. A. Daniels, L. M. . Angelici, R. J. Stone, F. G. A. J. Am. Chem. Soc. 1989. Ill, 4995-4997.)... 

Tyrosinase is classified into the type-3 copper protein family, as are catechol oxidase and the respiratory pigment hemocyanin. During the catalytic reaction, the type-3 copper center of tyrosinase exists in three redox forms. The deoxy form (Cu(I)-Cu(I)) is a reduced species, which binds oxygen to give the oxy form (Cu(II)-02 -Cu(II)). In the oxy form, molecular oxygen is bound as peroxide in a side-on bridging mode, which destabilizes the... 

Quite recently, Fryzuk and co-workers observed the N-H bond formation when a dinuclear zirconium complex with a side-on bridging dinitrogen ligand was treated with molecular dihydrogen. However, no ammonia was formed (a) M. D. Fryzuk, J. B. Love, S. J. Rettig, V. G. Young, Science 275 (1997) 1445. (b) H. Basch, D. G. Musaev, K. Morokuma, M. D. Fryzuk, J. B. Love, W. W. Seidel, A. Albinati, T. F. Koetzle, W. T. Klooster, S. A. Mason, J. Eckert, J. Am. Chem. Soc. 121 (1999) 523. 

In another neutron diffraction study of dinitrogen complexes, Fryzuk et have shown that dinitrogen can serve as both an end-on and side-on bridging ligand in [NPN]Ta(/x-H) 20t- 7 7 -N2) (where NPN = PhP(CH2SiMe2NPh)2). 

The X-ray crystal structure of reduced deoxy-Hc shows that each Cu(I) ion is coordinated by three histidines and the Cu-Cu distance is 4.6 A (23). Upon O2 binding, the two Cu(I) ions come closer to each other ( 3.6 A), resulting in the formation of side-on bridging -peroxo (02 ) dicopper(II) oxy-Hc (Scheme 2). 

Terminal angular Side-on terminal Bridging Side-on bridging 2. 2... 

Studt F, MoreUo L, Lehnert N, Fryzuk MD, Tuczek F. Side-on bridging coordination of N2 spectroscopic characterization of the planar Zr2N2 core and theoretical investigation of its butterfly distortion. Chem Eur J. 2003 9 520-530. 

Fryzuk MD, Haddad TS, Rettig SJ. Reduction of dinitrogen by a zirconium phosphine complex to form a side-on-bridging N2 ligand. Crystal structure of [iPr2PCH2SiMe2)2N]ZrCl 2(p-tl q -N2).JHm Chem Soc. 1990 112 8185-8186. 

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