Cyclopentadienylnickel

A few cyclopentadienylnickel isocyanide complexes 163,164) have been reported, arising in the following reactions ... 

Another member of this series is bis(cyclopentadienylnickel carbonyl), (CsHaNiCO it is dimeric, diamagnetic, and must, therefore, contain a nickel-nickel bond (79). The dipole moment, quoted (79) as 0 0.38 Debye unit, indicates that the molecule must be very nearly centro-sym-metric in benzene. The infrared spectrum, however, shows two carbonyl stretching frequencies in the solid state and in solution, but the vapor at 100°C shows only one band (173, 199). The wave-numbers are shown in Table IV. 

Cyclopentadienylnickel carbonyl dimer is also known to react with acetylenes to form bridged complexes. With bis(trimethylsilyl)acetylene and with l,4-bis(trimethylsilyl)butadiyne it reacts to give organosilyl acetylene complexes 63) [Eqs. (47) and (48)]. The silylated butadiyne... 

The simplest example is bis-cyclopentadienylco-balt(II), where we add one electron. This may go either into one of the 4p orbitals or into the relatively unstable kag orbital. In either of these cases, of course, it lias one unpaired electron (i.e., it is in a doublet state). For bis-cyclopentadienylnickel-(II),1 on the other hand, two electrons must go into these orbitals. Whether they go, one into kag and the other into some 4p level, or both into the 4p levels, is in many ways immaterial. The proximity of the kag orbital energy to that of the 4p orbitals will ensure that we shall be left with two singly occupied orbitals whose electrons are in a triplet state with their spins parallel (Hund s principle of maximum multiplicity). In bis-eyclopentadienylchromium-(II) two electrons arc removed. If the hag orbital is appreciably more stable than the de2g orbitals, both will come from the latter level, leaving one... 

SYNS pi-CYCLOPENTADIENYL COMPOUND with NICKEL DI-pi-CYCLOPENTADIENYLNICKEL NICKEL BISCYCLOPENTADIENE NICKELOCENE... 

An analogous substitution could be obtained from 7r-allyl (200) and TT-cyclopentadienylnickel compounds (151) and from 7r-allyl 7r-cyclopenta-dienylpalladium (80) with phosphines, phosphites, and isocyanides. 

Clemens, J., Neukomm, H., Werner, H. Reactivity of metal rt-complexes. 14. Preparation and formation mechanisms of rc-cyclopentadienylnickel (tert-phosphite) dialkylphosphonate complexes, an organometallic variant of the Michaelis-Arbuzov reaction. Helv. Chim. Acta 1974, 57, 2000-2010. 

Bulk reduction of [NiCp2] in MeCN or thf yields some [Ni(fj3-C5H7)Cp] and uncharacterized products (299, 498). Sodium naphthalide in thf gives a mixture of remarkable polynuclear, cyclopentadienylnickel compounds containing between two and six metal atoms. The octahedral cluster [ NiCp 6] and its monocation are the first to be structurally characterized (519). 

The mechanism of the reaction of nickelocene with methyllithium is complicated and not, as yet, fully explained. The new C-C bond and a number of higher cyclopentadienylnickel clusters are formed in this reaction. The clusters are often unstable and difficult to isolate in a pure state. There is, however, no doubt, that the first step of the reaction is the formation of unstable CpNiCH3. This complex... 

It has been found previously that NiCp2 reacts with phenyllithium or phenyl-magnesium bromide in THF, in the temperature range —40°C - room temperature, to form biphenyl and a mixture of cyclopentadienylnickel clusters. The active dinickel species (NiCp)2) is formed in this reaction as an intermediate (Eqs. (15), (16)). 

This reaction is believed to involve a number of complex processes, by which four alkynes coordinate to a metal center to undergo either a stepwise coupling or a concerted zipper-type cyclization. However, the Ni2(COT)2-catalyzed reaction involves the formation of a bis(cyclopentadienylnickel) complex, a homobimetallic center,as supported by the actual determination of the structure from X-ray crystallography by the fast initiation of the reaction without an induction period when used directly for alkynes compared to other types of catalysts,and by kinetic studies and labeling experiments. An illustrative mechanism catalyzed by Ni2(COT)2 is given here. 

A methyl-substituted compound (XIII) is obtained similarly from nickel carbonyl and methylcyclopentadiene (41a). Analogous to (XIII) is 7r-allyl-cyclopentadienylnickel, which was prepared from 7r-allylnickel (II) bromide and sodium cyclopentadienide (41b). 

Nickel tetracarbonyl also forms an anionic derivative with sodium cyclopentadienide but it has not been characterized in detail. In this reaction polynuclear cyclopentadienylnickel anions may be formed (84). 

Most 7 -allyl- and -cyclopentadienylnickel complexes exhibit 16-electron and 18-electron counts, respectively, differing considerably in structure and properties. For this reason, the two groups of compounds have received separate treatment in GOMG (1985) and GOMG (1995). Few examples of allyl derivatives bearing cr-carbon bonded ligands have appeared in recent years, but a number of 77-indenylnickel complexes, whose structure and properties can be considered somehow intermediate between those of allyl and cyclopentadienyls, have been reported by... 

C17H13O8OS3PS2, M3-Methylenethiolato-M3 Sulfido-(octacarbonyl(di-methylphenylphosphine)triosmium), 45B, 854 Ci7Hii,Fe2Ni06, (7 -Cyclopentadienylnickel)-(Tj-t-butylethynyl)hexa-carbonyldiiron, 46B, 845... 

C12H12CO2O4, Butadiene cobalt dicarbonyl, 31B, 346 Cl2H12Ni2, M Acetylene-bis(cyclopentadienylnickel), 42B, 658 Cl2H120bW, trans-Bis(772-methyl acrylate)tetracarbonyltungsten, 46B, 838... 

C2 H2oNi2f (Diphenylacetylene)bis(cyclopentadienylnickel), 33B, 341 C2i,H2 iBrPRh, Bromo(tris(2-vinylphenyl)phosphine)rhodium(I), 39B, 593 2u 2 iCl8N2Ta, Pyridinium tetrachloro(pyridine)(tolane)tantalate, 46B, 852... 

C3 H2sFeNi03P, Diphenylacetylene-tricarbonyliron-diphenylphos-phido-TT-cyclopentadienylnickel complex, 39B, 600 C34H2sNbO, ir-Cyclopentadienyldi(tolane)carbonylniobium, 34B, 447 C3i,H38N6Pd2 r Di-/i ( 1 r3-di-p-toly 11riazenido)di-(1,3-7j-allyl)dipal-ladium(II), 42B, 672... 

C15H2oCoNiOftP, Di-M"carbony1-dicarbony1(triethylphosphine)cobalt(ir-cyclopentadienylnickel), 40B, 752... 

C2 7H17CoF3NiOftP, Di-M"carbonyl-dicarbonyl(TT-cyclopentadienylnickel-io)(tris-p-fluorophenylphosphine)cobalt, 4IB, 908 C2 7H2 3AsBCOi,F404, Tetrakis (T -cyclopentadienylcarbonylcobalt )ar-sonium tetrafluoroborate hemi(benzene), 43B, 1088 C2 7H2 3M0O3P, trans-Dicarbonyl-TT-cyclopentadienyl(triphenyl-phos-phine)molybdenum acetyl, 33B, 356... 

C2 8H2iFeNi03P, (TT-Cyclopentadienylnickel)(ethynyl)(triphenylphos-phine)iron tricarbonyl, 41B, 909 C28H25ClSiZr, Chlorobis(Tr-cyclopentadienyl)(triphenylsilyl)-zirconium(IV), 37B, 464... 

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