Rhodium complexes imino

Rhodium complexes catalyze 1,2-addition of main group metal compounds to aldimines as well. Table 5 summarizes the reported methods. Electron-withdrawing substituents such as sulfonyl and acyl groups on the imino nitrogen atom are important to obtain sufficiently high reactivity. Asymmetric synthesis (diastereoselective and enantioselective) has also been accomplished. 

Hydroformylation reactions that are mediated by rhodium catalysts can also be incorporated into cascade sequences. The zwitterionic rhodium complex 694 promotes a tandem cyclohydrocarbonylation/CO insertion reaction producing pyrroli-none derivatives that contain an aldehyde functional group in good yields (01JA10214). In one example, exposure of a-imino alkyne 693 to catalytic quantities of 694 and (PhO)3P under an atmosphere of CO and H2 at 100 °C produced pyrrolinone 695 in 82% yield (Scheme 113). A variety of alkyl substitutents can be tolerated in this reaction. 

The aziridination of olefins has also been studied, but fewer complexes catalyze this reaction as efficiently as iron and manganese complexes catalyze the epoxida-tion of olefins. Nevertheless, the aziridinations of olefins catalyzed by copper, ruthenium, and rhodium complexes have been reported. The source of nitrogen is usually [N-(p-toluenesulfonyl)imino]phenyliodinane (PhI=NTs) or a precursor to a related iodoarylimine. The aziridine is likely generated from these copper- and rhodium-catalyzed reactions by an outer-sphere process in which the olefin interacts with the LUMO of the complex, which is located at the nitrogen. This mechanism is more likely to be followed by these catalysts than a [2-t-2] process, followed by reductive elimination. 

Seeing the dicationic complex in Figure 3.42 that is stabilised by two solvent molecules (weakly coordinating acetonitrile) immediately raises the expectation that two imino functionalised NHC ligands should in principle be able to coordinate in a chelate fashion to the same metal atom. This is realised in a trigonal bipyramidal rhodium(I) complex, where the two carbene moieties are in the axial position [130] (see Figure 3.43). 

Figure 3,43 Synthesis and structure of rhodium(l) carbene complexes with imino functionalised NffC ligands.

In a somewhat similar study, the kinetics of CH3I addition to [LRh (CO)] in CH2CI2 solution, where L = bis(imino)carbazolide, to form the rhodium(lll) complex [LRh" I(CO)CH3], have been investigated by FTIR spectroscopy.The second-order rate constant was found to be 5 x 10 faster than for reaction of [Rhl2(CO)2]. ... 

Thus, organosilicon hydrides can serve as reducing agents like metal hydrides so far as the catalytic hydrosilylation is effectively achieved. To date, rhodium(I)-phosphine complexes have been found to be by far the most useful catalysts for these purposes, especially for the asymmetric reduction of carbonyl and imino compounds. 

A dimetallic rhodium(l)-rhodium(iii) complex 340 bearing a bis(imino)carbazolide ligand L and an olefin LRh(C2H4) was prepared via a salt metathesis reaction between NaL and the dimeric rhodium precursors [Rh(/t-... 

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