Ir-Donors

A model similar to that of the iron complex 31 was proposed for the cobalt species synthesized as a result of co-condensation of cobalt vapors with pyrrole in vacuum. A frozen matrix formed is subsequently warmed to room temperature (89JA3881). An oligomer or a polymer results, in which a- and ir-donor functions are realized simultaneously. The model proposed differs from that for the iron pyrrolyl complex by inclusion of the Co—Co bonds to attain the 18-electron configuration. 

The deprotonation of 132 is favored at Ni and the coordination of 135 occurs preferentially at 82- A second entity of 135 coordinates at N3. A computational study of thiouracil derivatives of the tungsten(O) hexacarbonyl shows that the sulfur-bound thiouracil is serving as a ir-donor during the CO dissociation (Scheme 91) [99IC4715]. DFT calculations show that 137 is significantly stabilized with respect to the alternative reaction product 138. 

Another computational study examined the effect that the boron ligands might have on the reactivity of allyl derivatives.50 The order found is shown below and is related to the level of the boron LUMO. The dominant factor seems to be the ir-donor capacity of the ligands. The calculated order is consistent with experimental data.51... 

Scheme 9. Description of 35 as 77-complex (Dewar-Chatt-Duncanson model) (a) Si=P bond as ir-donor (b) Si=P bond as 77-acceptor.

In the mixed case—one ir-donor and a it-acceptor ligand, as in OsHCl(CO) (P1 Pr3)2—the structure III of Scheme 1 (in which the -ir-donor X ligand and the tt-acceptor A ligand are trans to each other) is more stable.22 In a T structure, which... 

When the chlorine atoms in silene 2 are substituted by other ir-donors the ability to partake in [2+2] cycloaddition reactions is conserved. This has been proved by studies in our group on the reactivity of amino substituted silenes of the type [11] ... 

HOs3(C=CPh)(CO)10, in which the acetylene behaves as a ir-donor to one osmium center and a two-electron 7r-donor to another (134). 

Especially noteworthy is the following feature the oxygen donors, dimethyl-formamide, tetrahydrofuran, methanol, and ethanol seem to allow a stabilization of the CO ligand which is well comparable with that achieved by the much stronger a-donors, triethylamine or N-methylimidazole (Table 10, [50a-/]). It is suggested that these ligands also act as simultaneous a- and ir-donors, as do the imidazoles. With its low basicity, DMF seems to have a very favorable a/ff-donor balance for the trans fixation of rr-acceptor ligands, which are themselves weak o-donors, like CO, N2, NO , or 02, and indeed, the 7r-donor function of DMF is well documented (S). 

Electropositive substituents stabilize the three-membered ring of borirene, whereas ir-donors (NH2, OH) coplanar with the ring lead to destabilization (85MI4). 

Saito, T. In Early Transition Metal Clusters with ir-Donor Ligands Chisholm, M. H Ed. VCH New York, 1995. 

Monocyclic azines are very weak rr-donors and behave mostly as n-donors on interaction with electrophiles. However, ir-donor character is significantly increased in their benzo-derivatives. For instance, acridine forms with chloranil a highly colored 1 1 molecular complex. Perimidine is one of the strongest heterocyclic ir-donors which gives deeply colored molecular complexes with a variety of organic electron acceptors. On the other hand, the rr-acceptor ability of perimidine is moderate. 

III. Electronic Structure of the Bonded ir-Donor-7r-Acceptor Pairs... 

These oversimplified considerations illustrate clearly that, although we do not have ir-donor linked to 7r-acceptor, if the low-lying excited states... 

Xem = 371—430 nm). Clearly, changing from a ir-acceptor anionic ligand in (CyNC)AuICN to a ir-donor anionic ligand in (CyNC)AuIX alters the electronic properties of these complexes and, consequently, their luminescence behavior. Note that the luminescence and absorption characteristics of (CyNC) Au X are rather similar to those communicated for the related compound (CO) Auta.67... 

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