Nickel complexes orbital correlations

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

The mechanism proposed to account for the substitution reactions of the Ni(L)r complexes is shown in Fig. 60. A similar mechanism is proposed for substitution reactions with unidentate nucleophiles. Several of the five-coordinate intermediates shown in Fig. 60 were detected and their stabilities were estimated. It was suggested that the trans effect operates through the stability of the five-coordinate intermediate which in turn is correlated to the extent of involvement of the nickel 4pz orbital in n bonding. The implication of the 4pz orbital in n bonding should be considered cum grano salis, however, in view of recent theoretical calculations indicating that the involvement of the 4pz orbital in the n system is very small even in the Ni(MNT)2 complex (123). (See also Sect. 2E.)... 

The higher reactivity of nickel complexes than the palladium congeners was examined theoretically. Fig. 9.1 illustrates a schematic diagram for the orbital correlation on the ethane elimination from cw-M(CH3)2(PH3)2 complexes (M = Ni, Pd) [8,10]. This scheme presumes the least motion process that maintains the C2v symmetry of precursor complex throughout the reaction. The C-M-C angle becomes narrow while the P-M-P angle is gradually extended as the reductive elimination proceeds. Finally, ethane is eliminated with formation of a linear M(PH3)2 complex. 

Bulk crystalline radical ion salts and electron donor-electron acceptor charge transfer complexes have been shown to have room temperature d.c. conductivities up to 500 Scm-1 [457, 720, 721]. Tetrathiafiilvalene (TTF), tetraselenoful-valene (TST), and bis-ethyldithiotetrathiafulvalene (BEDT-TTF) have been the most commonly used electron donors, while tetracyano p-quinodimethane (TCNQ) and nickel 4,5-dimercapto-l,3-dithiol-2-thione Ni(dmit)2 have been the most commonly utilized electron acceptors (see Table 8). Metallic behavior in charge transfer complexes is believed to originate in the facile electron movements in the partially filled bands and in the interaction of the electrons with the vibrations of the atomic lattice (phonons). Lowering the temperature causes fewer lattice vibrations and increases the intermolecular orbital overlap and, hence, the conductivity. The good correlation obtained between the position of the maximum of the charge transfer absorption band (proportional to... 

Allyl Complexes and Complexes Derived from Mono-ol ns Zerovalent Nickle, Platinum, and Palladium.— A series of complexes Ni(ol) (x=l—3, ol=alkyl, chloro, or fluoro olefin) has been detected by matrix condensation of nickel atoms with the olefin the optical spectra show a correlation between the transition energies of the Ni(ol) species and the 7r -orbital energy of... 

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