Trinuclear rhodium complexes

On the basis of H NMR spectra and taking into account the trans geometry of the starting [PdCl2(Hpz)2] complex, the trans arrangement (G) has been considered the most probable structure for this family of trinuclear compounds (123). A trans disposition of the bridging ligands has been observed in the rhodium complex 147. The same trans conformation was also proposed for Compound 152 (121). 

Reaction of CO with the tautomeric mixture of the two aforementioned rhodium complexes (several / flra-substituted imidoaryl groups were tested) afforded a unique bridging isocyanate complex Rh2(CO)2(ii -N,T] -C, x-ArNCO)(p-DPPM)2. The CO insertion is irreversible. Since the two initial tautomers are in equilibrium in solution, insertion of CO may in principle proceed by either of the two (Scheme 20)(next page). However, evidence was given in favour of the amido-path (path b in the Scheme), based on the fact that the cationic complex [Rh2(p-NHPh)(CO)2(DPPM)2] rapidly reacted with CO. No complex could be isolated from this last reaction, but the formation of PhNCO was detected. Two features of this mechanism are worth of note. The first is the contrast between the conclusion reached for this system (amido complex more reactive than imido one in the insertion reaction of CO) and the one reached by Bhaduri et al. [161] for the trinuclear complex Ru3(p-H)(p-NHPh)(CO)io, which, upon deprotonation of the amido group by OH, affords the inserted product [Ru3(p-H)(T] -N,ii -C,p3-PhNCO)(CO)9]. The difference is likely due to the fact that, in this latter case, the complex is trinuclear, so that the inserted CO is already coordinated to the third ruthenium atom and, especially, the formation of the new C-N bond does not require the breaking of any of the pre-existing Ru-N bonds. 

L = C3H3, C H ) and then [Rh(acac)(CO),] to yield the tetranuclear species 180 (85ICA(i00)L5), where the heterocyclic ligands are tridentate. The product reacts with the rhodium(I) dimer [Rh(CO)2Cl]3 to give the trinuclear complex 181. In the solid state, the molecules of this complex form the intermolecular stacks along the z-axis. 

The interaction of small, well defined, rhodium clusters, Rh and Rhs, with O2 has been investigated (220) by matrix infrared, and UV-visible, spectroscopy, coupled with metal/02 concentration studies, warm-up experiments, and isotopic oxygen studies. A number of binuclear O2 complexes were identified, with stoichiometries Rh2(02)n, n = 1-4. In addition, a trinuclear species Rhs(02)m, m = 2 or 6, was identified. The infrared data for these complexes, as well as for the mononuclear complexes Rh(02)x, = 1-2 (229), are summarized in Table XI. Metal-concentration plots that led to the determination of... 

Although there is a severe paucity of vibrational data for the molecular form of O2 chemisorbed on rhodium surfaces, it is possible to visualize the dinuclear and trinuclear complexes as models for the associative chemisorption of O2 on rhodium. The pq-o values of the complexes Rh2(02)i,2 show little... 

In the Rh-BINAP-catalyzed allyl amine isomerization step used in Takasago s Menthol process, the catalyst is inhibited by water through the formation of a hydroxyl-bridged rhodium trinuclear complex [ Rh(BINAP) i(/<2-0H)2]C104 [61]. 

The twofold deprotonation of a hydrosulfide zirconocene with the appropriate rhodium compound results in the clean formation of d°-d trinuclear complex (equation 38). ... 

The reaction of 1 with Rh(PPh3)3CI proceeds directly to the homoleptic complex 18, which has been fully characterized, and we have not been able to detect any intermediate in this reaction. The analogous reaction of 2 with Rh(PPh3)3Cl can be separated into two steps first a trinuclear metal entity 19 is formed, and at higher molar ratios of 2 the homoleptic tin substituted rhodium( 1) complex 20 is formed, which contains six metal atoms clustered at the center of the molecule. The compounds 18, 19 and 20 have been characterized by X-ray structure determination techniques. In 18, the central unit is an almost square planar germanium arrangement in the middle of which the rhodium atom is situated. One of the edges... 

Our approach to the preparation of new imido clusters of rhodium consists of the reactions of equimolar quantities of [ Rh( -Cl)(diolefin) 2] with a solution, prepared in situ, by the addition of butyl lithium to ara-toluidine in a 2 1 molar ratio in diethyl ether. At first glance, a hypothetical trinuclear cluster of formulation [Rh3(/i-N-p-tolyl)2(diolefin)3] could be expected from these reactions on the basis of the formation the isoelectronic thiolate complexes [Rh3(//-SPh)2(diolefin)3]+. However, unexpectedly, the results of these one-pot reactions were the formation of the novel tetranuclear clusters [Rli4( u-N-/7-tolyl)2(diolefin)4] diolefin = 1,5-cyclooctadiene (cod) (1), tetrafluorobenzobarrelene (tfb) (2), isolated as dark-red crystalline solids in good yields. 

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