Cyclopentadienyl-3-Cyclopentenylnickel(ii)

Reaction of Chromium(III) Chloride with the Cycloheptadienyl Anion: Susceptibility of Edge Bridges To C−H Activation Reactions

“…17 C-H (and even C-C 18 ) bonds in these edge bridges are quite susceptible to bond activation reactions, as can also be seen by the isolation of Ti(C 5 H 5 )(C 8 H 8 ) from reactions of mono(cyclopentadienyl)titanium halides with the cyclooctadienyl anion 19 and by the observed, facile insertion of an alkyne into a C-H bond in the bridge of a (cyclooctadienyl)titanium complex. 20 The selective formation of Ni(C 5 H 5 )(η 3 -C 5 H 7 ) (13; C 5 H 7 ) cyclopentenyl) on hydrogenation of nickelocene 21 and the observation of structures such as Nb(η 7 -C 7 H 7 )(η 4 -C 7 H 8 )-(PMe 3 ), 22 Fe(η 5 -C 5 H 5 )(η 1 -C 5 H 5 )(CO) 2 , 23 Ti(η 5 -C 5 H 5 ) 2 (η 1 -C 5 H 5 ) 2 , 24 and Sc(η 5 -C 5 H 5 ) 2 (η 1 -C 5 H 5 ) 25 provide additional cases demonstrating the favorability of having at least one aromatic ligand. While one could question the relative magnitude of stabilization experienced by a complexed aromatic π system as compared to an uncomplexed one, it is notable that some evidence suggests that the aromaticities of complexed π systems may exceed those of the uncomplexed ones.…”

Olefin and Acetylene Complexes of Transition Metals.

“…The structure of the LXV LXVI complex has been reformulated recently by various groups independently (84,109,117,146,218) as xcyclopentadienyl x-cyclopentenyl nickel x-C6H6NiC6H7 (LXVI), in which the cyclopen tenyl radical is behaving as a three x-electron donor like the allyl radical. The evidence for the revised structure comes principally from the proton resonance spectrum, which shows a sharp peak clearly assignable to the five equivalent protons of the x-cyclopentadienyl ring, together with peaks assignable to the three olefinic and four aliphatic protons of the cyclopen tenyl ring (84,109,146). In addition, an independent synthesis of the complex has been achieved by treating anhydrous nickel bromide with a mixture of NaC6H6 and cyclopentenyl magnesium bromide (84).…”

Solvent-free oligomerization of phenylacetylene catalyzed by (cyclopentadienyl)nickel complexes

“…2, 3 In solution, nickelocene, and also [(η-Cp)Ni] 2 (RC᎐ ᎐ ᎐ CRЈ), catalyze the polymerization of acetylenes but only in the presence of an aromatic heterocyclic amine (e.g. pyridine) 26 or AlBr 3 27 (nickelocene with F 3 CC᎐ ᎐ ᎐ CCF 3 in solution has been reported to give traces of the cyclotrimer 28 ).…”