Heterobimetallics between

LLB, a so-called heterobimetallic catalyst, is believed to activate both nucleophiles and electrophiles.162 For the hydrophosphonylation of comparatively unreactive aldehydes, the activated phosphite can react with only the molecules precoordinated to lanthanum (route A). The less favored route (B) is a competing reaction between Li-activated phosphite and unactivated aldehyde, and this unfavored reaction can be minimized if aldehydes are introduced slowly to the reaction mixture, thus maximizing the ratio of activated to inactivated aldehyde present in solution. Route A regenerates the catalyst and completes the catalysis cycle (Fig. 2-9). 

In the solid state, both 46 and 47 exist as bent monomeric sandwich complexes with ring centroid-lead-ring centroid angles of 152.2° in 46 and 144.2° in 47. Interestingly, if the reaction between PbCl2 and [Li(dme)2][/Bu2G2P3] is carried out in tmen rather than DME, the product formed is not a homoleptic plumbylene but rather the novel heterobimetallic compound 48.73... 

Similarly, the reaction of metallic rubidium with another metal in ammonia led to the appropriate heterobimetallic amides, as in the reaction of Rb with Ca in supercritical ammonia at 573 K yielding RbCa(NH2)3. " " which consists of one-dimensional infinite face-sharing anion-octahedra occupied by calcium and connected into a three-dimensional network by the rubidium ions (Rb N contacts between 3.11 and 3.92 A). 

Ligands with a single carbon atom between phosphorus and a heteroatom have been synthesized and used to prepare heterobimetallic complexes between platinum and a second metal ion. Examples of such complexes are shown in structures (153)-(156).1464-1467... 

Uson and collaborators described an A-frame PdPt complex [C6F5Pd (p-C=N-p-tolyl)(p,-dppa)2PtC6F5] (75),85 and more recently, [XPd(p,-dppm)2 (p-C=N-R)Pt(CN-R)]+ (76-78) and [ClPd(p,-dppm)2(p,-C=N-R)PtCl] (79-81) were reported by Knorr and collaborators86-88 (Fig. 32). In the bis(isonitrile) heterobimetallics 76—78, a site selectivity in the second CNR ligand coordination (Pd vs. Pt) was noticed. The additional isocyanide is systematically coordinated on the Pt site.86,88 This distinct selectivity between Pd and Pt was explained by the greater lability of the Cl- ion on the Pt center as well as a better stabilization of the positive charge on the electron-rich Pt1 center.88 The question arises as to why the addition of ligand isocyanide sometimes produces the A-frame compound whereas under similar conditions, a d9-d9 isocyanide... 

Based on the results obtained for the model ligand o-anisylisocyanide and on X-ray diffraction study (Fig. 37) where the first o-anisylisocyanide spanned the two metal centers and the second is coordinated at the Pt site, the A-frame het-erobimetallic polymer 87 (Fig. 38) based on Pd(p,-dppm)2Pt was prepared from the direct reaction between the heterobimetallic Cl Pd( i,-dppm)2PtX and diNC.87... 

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