Dinickel compounds

Compounds with Aryl and Aryne Ligands C-H and C-C bond activation/formation has become the most exciting field of research in recent decades. The dinickel(I) aryl and aryne compounds were usually studied as key intermediates in Ni(0) mediated C-H and C-C bond activation/formation on phenyl or other aromatic rings. 

Ni(0) catalyzed ethyne cyclization to afford cyclooctatetraene (COT) and related biphenylene compounds, which involved a series of C-C bond couplings, were studied in the last decade, and dinickel(I) species were postulated as possible catalytic intermediates [31]. However, the mechanistic 

Multidentate N,P-donor ligands were also used to support Ni(I)-Ni(I) bonds. A dinickel(I) compound 59 bearing a Dewar-benzene-type Ni2P2N2 core was reported [26]. In this example, a 

---

Structural Data for Quadruply Bridged Diplatinum, Dipalladium, and Dinickel Compounds"... 

A new set of products have been obtained from analogous reactions involving Ph-substituted internal alkenes. Thus, the reaction of nickelocene with Li in the presence of ( )-PhC(H)=G(Me)Ph has led to the following four species the nickelanickelocene-type compound ( 7 -Gp)(77 -(l-(77 -Cp)-2-phenyl-3-methyl-l-nickela-indenyl)nickel, 139-Me, the /i3-alkylidyne species 140, the dinickel compound (NiGp)2(/x-GpH), 138, and the tetrameric cluster (NiCp)4(M-H)2, 141 (Scheme... 

In this section, advancements on mixed-valent dinickel compounds which were made in... 

Tabie 10.5 Ni-Ni bond lengths in mixed-vaient dinickel compounds. 

Scheme 10.37 Synthesis of a mixed-valent dinickel compound 82 with bridging COj and CO.

These dicobalt and dinickel complexes are of interest, since there is an unusual bridge binding of one water molecule at the expense of the two electronic pairs in the oxygen atom. Moreover, a simultaneous terminal and bridge coordination of the carboxyl groups is characteristic in this kind of compound. 

The preparation of pentadienylsodium was being studied at about the same time as ferrocene was discovered. It was not until 1968, however, that the first binary pentadienyl complex of a transition element, bis(pentadienyl)-chromium, was obtained from PINa and CrCl2 (121). This compound forms green, air-sensitive crystals, and like chromocene it has two unpaired electrons (Ht = 2.74 BM). This discovery was shortly followed by that of the curious complex, bis(pentadienyl)dinickel (12) which was prepared from NiCl2 and triethylaluminium in 1,4-pentadiene (122). The pentadienyl ligands in 12... 

There has been considerable interest in the synthesis of polymers such as structure (6) in which aromatic rings and metal atoms alternate, due to the possibility of building extended electron-delocalized organometallic polymer chains. However, such a multiple decker polymer has not yet been synthesized, and only a few triple decker-sandwich compounds such as tris( 5-cyclopentadienyl)dinickel cation and tris-(cyclooctatetraene)dititanium dianion have been reported10. ... 

Specific active site stmctural features of urease are the bimetalhc arrangement with a Ni Ni distance of 3.5-3.7 A and nonsymmetric N/O-rich coordination environment, the bridging carbamate (often modeled by a bridging carboxylate), and the presence of a hydrolytically active Ni-bound hydroxide or water. Relevant dinickel complexes that emulate at least part of these features are introduced in this chapter. Of course, the ability to bind urea is a prerequisite for urease-like activity, and different urea-binding modes were observed in synthetic model compounds. Those model complexes and artificial systems that mediate the decomposition of urea are discussed in Section III. 

When complex lb, containing a ( j,-aquo)bis( j,-carboxylato) core, was reacted with 1 equiv of trimethylsilyl triflate, followed by the addition of urea, complex 50 could be isolated in 55% yield (Scheme 10) (110). A mononuclear species [Ni(OAc)(urea)2(tmeda)](OTf) was produced as a minor side product in this reaction. Complex 50 represented the first example of a synthetic compound with urea coordinated to a dinickel(II) site. The urea molecule binds in its most common mode, namely, through its carbonyl O, to one of the Ni(II) ions (Fig. 8). 

Dithiolate compounds are similar to the carboxylates, with sulfur atoms taking the place of the oxygen atoms in the polar head. Each of the tetrakis(alkyldithiolato)dinickel(II) complexes ((101) R = C H2 +i, n = 4- ) shows a monotropic lamellar mesophase between 80and 90°C, which has been described as discotic lamellar (Dl) phase (see Figure 22). In the case where R is a branched chain, an enantiotropic Colh and a monotropic Dl mesophases have been found for tetrakis( 1 -ethylpentyldithiolato)dinickel(II) complex. ... 

Reaction of 2,6-dimethyl pyridine with the tris(alkene) dinickel species [(77, 77 -(l,6-heptadiene)Ni)]2(/, 77 r/ -(l,6-heptadiene)) gives the intense yellow compound Ni(77, 77 -(l,6-heptadiene)(2,6-dimethylpyridine). The solid-state structure of this complex showed that the pyridine is oriented perpendicular to the plane of Ni(olefin)2, implying significant vr-backbonding from Ni into the pyridine tt orbitals. The reaction of this bis(alkene) species with alkynes gives the corresponding bis(alkyne) complexes vide infra). 

---