Nickel complexes cyclopropenyl

Nickel complexes with rj3-bonded cyclotriphosphorus and cyclopropenyl fragments are discussed together in a separate Section (50.3). As a matter of fact the bonding mode of these ligands is the same in all of the complexes, irrespective of the different oxidation states which can be assigned to the nickel atom. 

When three molar equivalents of 1,2,3-triphenylcyclopropenylium bromide (7) in methanol was added to a solution of two molar equivalents of bis(ij -cycloocta-l,5-diene)nickel(0) in tetrahydrofuran at 0 C, a triple-decker-type binuclear nickel complex 8 with two // -coordinated cyclopropenyl ligands was obtained in 60% yield. The structure was determined by X-ray crystallography. ... 

In the nickel complex containing pyridine, the cyclopropenyl ring is symmetrically coordinated to the nickel atom " [structure (7.78)]. Symmetrically bonded cyclo-... 

Some metal cyclopropenyl compounds are very stable. Nickel complexes with C3BU3 in the solid state are stable in the air for short periods in the solid state, and the vanadium compound [V(C3Ph3)(CO)5] decomposes only at 503K (Table 7.8). 

In the valence shell electron count for the complex (Ti -C3Ph3)NiCl(py)2 (py = pyridine) (Fig. 4.1), the cyclopropenyl hgand C3Ph3 supplies three electrons, the chlorine atom one electron, and each pyridine ligand supplies two electrons. Added to the 10 electrons in the valence shell of the nickel atom, this generates a total of 18 electrons. In the case of the sandwich compound dibenzenechromium, (q -C/H jiCr (Fig. 4.2),six electrons from each benzene ligand may be added to the six electrons in the metal valence shell to generate the total of 18 electrons. 

The cyclopropenyl cation CsHs , shoxild, on the basis of Huckel s rule, also be an aromatic system with 2 w-electrons the complex [(ir-PhaCa)-NiCl(py)2].py, 8.1, has been shown, by X-ray diffraction, to contain the triphenyl-cyclopropenyl ligand. The geometry around the central nickel atom is a distorted tetrahedron. 

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