7i-component

A wide variety of five-membered zirconacydes 8 may be formed by the formal co-cycliza-tion of two 7i-components (3 and 6 alkene, alkyne, allene, imine, carbonyl, nitrile) on zir-conocene ( Cp2Zr ) (Scheme 3.2) [2,3,8]. The co-cydization takes place via the r 2-complex 5 of one of the components, which is usually formed by complexation of 3 with a zircono-cene equivalent (path a) ( Cp2Zr itself is probably too unstable to be a true intermediate) or by oxidation on the metal (cyclometallation/p-hydrogen elimination) (path b). Two additional routes to zirconocene r 2-complexes are by the reverse of the co-cyclization reaction (i. e. 8 reverting to 5 or 9 via 7), and by rearrangement of iminoacyl complexes (see Section... 

Numerous semiempirical methods have been used to calculate dipole moments (e g, PPP, CNDO/2, CNDO/S, other CNDO variations, INDO, INDO/S, MNDO, MINDO/3, AMI, HAM3, etc ). They can be divided into 7t-electron and all-valence-electron methods. In u-electron methods such as, e g., the PPP (LCI-SCF-MO) method, only the 7i-component of the dipole moment is obtained and the o-component has to be computed separately. As in the case of empirical methods, one possibility is to calculate the o-component as a vector sum of the individual o-bond and group moments. These values are readily available from several sources [4-6,11,18,19,85] The resulting total (overall) dipole moment is then computed as a vector sum of the TT-moment and the o-moment. 

Theoretical investigations have not yet, so far as we are aware, provided a basis to account for the relative importance of o and 7i components of the bonding in diazenido complexes. This problem was studied for carbonyl complexes by... 

An extensive array of nickel-catalyzed reductive coupling processes has been developed, wherein two different Jl-components are coupled concomitant with a net two-electron reduction of the tt-components employed. Union of the two reactive 7i-components is accompanied by hydrogen atom transfer in processes termed... 

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