The syntheses and characterisation of the [a-(phosphany1)alkyl]cyclopentadienyl anions 2,3,6-8,10, and 11 are described. These anions form metallocenes 12-15 and 11-19 with FeC1, 2 THF and with ZrC1, . 2 THF, respectively. With ICO(CO)~ chelated carbonyl complexes 23-25, 28, and 29 are formed. The unchelated intermediate 20 has been detected by IR spectroscopy. The carbonyl chelate complexes are thermally stable. Under photochemical conditions, ligand exchange reactions are possible which in the case of 1,5-cyclooctadiene proceed with decomplexation of the phosphane arm. This does not prevent a reaction at the cobalt(1) atom, treatment of 35 with diphenylethyne gives the corresponding tetraphenylcyclobutadiene complex 36 in good yield, the phosphane arm remaining uncoordinated.Transition metal complexes with cyclopentadienyl ligands have been intensively studied since their initial synthesis in 1951 ['I. Special aspects of their chemistry are ring-slippage reactions1'] in which the usual -q5 bonding mode changes to an q3 bonding with temporary decomplexation of one double bond. This raised the question in how far chemical reactions with participation of the temporarily decoordinated double bond might be possible. One result of our work was the ring opening reaction of a (bicyclo[3.2.0]hepta-1,3-dienyl)cobalt(I) complex followed by a cycloaddition of the intermediate ortho-quinodimethane speciesL3]. In these ringslippage reactions the cyclopentadienyl ligand can formally be regarded as a bidentate "allyl-ene" ligand, whose "ene" fragment decoordinates in the course of the change in hapticity from q5 to q3 and is recoordinated later. The process reversibly generates a vacant coordination site, which is capable of participating in chemical reactionsr3].Vacant coordination sites are usually generated by decomplexation of a ligand. If the ligand is not present in large excess in the reaction mixture, it will normally not be recoordinated after use of the vacant coordination site for further reaction. However, if the decomplexed ligand is still attached to the complex by other means than by coordination to the metal atom, it will not leave the molecule as a whole and can be later recoordinated. The ring slippage of a cyclopentadienyl ("allyl-ene") ligand mentioned is a very special case, and more generally this line of thought leads to the use of bi-or multidentate ligands. Most bidentate ligands are combinations of two ligands of the same nature, e.g. diphosphanes, bipyridyl derivatives and similar systems. In contrast, heterobidentate ligands should allow use to be made of the different coordination properties of the two ligands involved. In this context we became interested in combinations of cyclopentadienyl and phosphane ligands, which are among the most thoroughly studied ligands in organometallic chemistry. To avoid any interference from resonance interactions we envisaged a connection of the ligands by an alkyl chain. The two partial ligands have rather different properties: whereas the cyclopentadienyl system ...

An improved synthesis of [(2-phosphanylethyl)cyclopentadienyllcobalt(1) chelate complexes is presented, in which the paramagnetic chloride 3 is a precursor of the ethene complex 4. The latter readily undergoes ligand exchange reactions which in the case of bidendate reagents (1 ,!~-cyclooctadiene, 1,2bis( diisopropylphosphanyl) ethane, 2,2' -bipyridine, norbornadiene) cause a decomplexation of the phosphane arm at room temperature with formation of 7, 5, 6, 8 . The ethene ligand in 4 can be replaced by alkynes under equally mild reaction conditions (formation of 9, 11-16). The reaction with ethyne results in the formation of vinylidene complex 10. The yields of the reactions with nonaromatic alkynes could be improved by treating 3 with the alkyne in the presence of sodium amalgam. The unsubstituted vinylidene complex 10 and its tert-butyl derivative 17 were obtained by this route in 88 and 40% yield, respectively.

The trimerization of alkynes to arenes usually observed in the reaction of cyclopentadienyl‐cobalt(I) complexes with alkynes could be prevented by chelation of the metal center with a “phosphane arm” on the cyclopentadienyl ligand. Instead alkyne complexes were obtained in very good yields. The reaction with ethyne leads to the vinylidene complex 1 (88 % yield), a possible precursor to the carbene–cobalt complex.

Die Alkintrimerisierung zu Arenen, die üblicherweise bei der Umsetzung von Cyclopentadienylcobalt (I)‐Komplexen mit Alkinen beobachtet wird, läßt sich durch Chelatbildung mit einem an den Cyclopentadienylliganden gebundenen „Phosphanarm”︁ unterbinden. Statt dessen können Alkinkomplexe in sehr guten Ausbeuten erhalten werden. der Einsatz von Ethin selbst führt in 88 % Ausbeute zum Vinylidenkomplex 1, einem möglichen Vorläufer für carbencobaltkomplexe.