Electron-rich complex

The more electron-rich complex Ru(=CF2)(CO)2(PPh3)2 4 reacts only slowly with some nucleophiles but rapidly with electrophiles (21) (e.g., see reaction with HC1 above. 

The reactivity of these metal hydride-metal carbonyl reactions can be correlated with the nature of the reactants in a manner consistent with the proposed mechanism nucleophilic attack by hydride on coordinated CO. Thus reactions involving the highly nucleophilic group IV hydride, Cp gZrHg, are much faster than those of group V metal hydrides. On the other hand, the relatively electrophilic neutral binary metal carbonyls all react with Cp2NbH under mild conditions (20-50° C), whereas more electron-rich complexes such as cyclopentadienylmetal carbonyls (Cp2NbH(C0), CpV(CO) ) or anionic carbonyls (V(CO)g ) show no reaction under these conditions. 

The above examples demonstrate the enormous synthetic potential of the electron-rich complex fragment Re(dppe)2 " which allows well-defined ligand substitutions in the axial positions and a variety of reactions at the coordinated ligands. This has also been observed for other ligands... 

In addition to interacting with the Lewis acid center of the C02 molecule, these same low-valent metal complexes may also interact with the carbon-oxygen 7t-bonds in C02, in much the same way as olefins interact with electron-rich complexes. Finally, the oxygen atoms in C02 may be expected to show weak electron donating ability, possibly coordinating to a very electron-poor metal, although this mode of coordination of C02 is not presently known. 

In contrast, the kinetics of the alkylation of trans-[Mo(N2)(L)(dppe)2r (L = CN or SCN) with nBuI show a first-order dependence upon both the complex and the alkyl halide (88). These kinetics and the retention of the ligand, L, in the diazenido product are consistent with the mechanism shown in Scheme 4. The electron-rich complexes (A) undergo rate-limiting, outer-sphere electron transfer to yield the alkyl radical and fra/is-[M(N2)L(dppe)2] (B). Subsequent, rapid attack of the radical on the coordinated dinitrogen of (B) yields the diazenido product (C). 

The mechanism for dehydrocoupling utilizing electron-rich complexes has not yet been established. The most commonly proposed route involves oxidative addition of the hydrosilane to the metal center followed by reductive elimination of two silyl groups to form the Si Si bond related to that proposed by Curtis and Epstein.140... 

From a comparison of the coupling of alkyl bromides 1 with aryl Grignard reagents 2 with different catalysts it can be concluded that all provided essentially the same result, although the required reaction temperatures and times varied (Table 1, entries 1-3, 5, 6, 8, and 9). The catalytic system using 4 is the fastest of all. That the most electron-rich complex is the best electron donor to generate radicals is a likely explanation. An Fe(-II)/Fe(-I) manifold (17A-D) accounts for the observed results (Fig. 3, Table 1, entry 2). Whether other catalyst systems can reach this redox state under the reaction conditions remains open. However, other low-valent redox manifolds, such as the Fe(0)/Fe(I) or Fe(I)/Fe(II) manifolds (18A-D, 19A-D), are also viable and may account for the reactivity differences. 

The course of the reactions was rationalized by initial reduction of the Pd(II) precatalyst to a Pd(0) species 190A by diethylzinc. This electron-rich complex reduces the alkyl iodide 187 to a radical 187 A, which undergoes cyclization to the alkene unit. The diastereoselectivity of the cyclizations can be explained by a Beckwith-Houk... 

The electron-rich complex Fe(CO)2[(P(OMe)3]2(r 2-CS2) adds electrophilic alkynes via an apparent 1,3-dipolar addition process to give carbene derivatives that in turn undergo efficient air oxidation to afford the 16 e dithiolene complexes Fe(CO)[(P(OMe)3]2(S2C2RR ) (R, R = C02Me, Ph, CHO, etc.) (298). 

It is not exactly understood how the mixed ligand Rh/dppb/PPh3 catalyst system functions. Matsumoto proposed that the arm-on, arm-off equilibrium shown in Scheme 12 is operational. A species such as (5) would function much like a normal HRh(CO)(PPh3)2 catalyst, but the ability to reform the chelate to form a slightly more electron-rich complex (6) would tend to inhibit alkene isomerization and/or degradation reactions which require 16e unsaturated species. P NMR studies of Rh/chelating phosphine complexes indicate that a variety of species can form, the most dominant of which are... 

Strained carbon-carbon bonds can undergo reaction with electron-rich complexes such as Pd(PEt3 (3. Biphenylene reacts to form two new C-C bonds with Pd(PEt3)3 in a reaction that is undoubtedly aided by the formation of two strong Pd-C bonds as well as by the strain of the bond being broken (equation 17). ... 

A selective method of forming a bond between two different metals is by reaction of an electron-rich complex with either a stable, unsaturated metal complex or a metal complex containing an easily displaeeable ligand. The unsaturated metal eomplex may have a formal metal-metal multiple bond, a multiple bond between a metal and a nonmetal, or a eoordinatively unsaturated metal center. 

Cy3P, i-Pr3P [201], and t-Bu3P [202]. These findings are of exceptional importance since electron-rich complexes of palladium have never been successfully used before for catalysis of SN reactions of nonactivated chloroarenes. It is also remarkable that the Pd/t-Bu3P system exhibited catalytic activity in the animation reaction [202], while failing to catalyze the carbonylation of chlorobenzene [59]. 

Scheme 10 The conversion of complex 32 to the ferraaziridine complex 39 and then to electron-rich complex 40...

Studies of transition-metal silyl chemistry have focused mainly on the later members of the transition series. To some degree this reflects the availability of convenient preparative routes based on oxidative additions to low-valent, electron-rich complexes (e.g. equations 1 and 2). 

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