Heterobimetallic alkylation

A number of stable heterobimetallic copper alkyne complexes have been reported, based on the strategy of using another metal bis(alkynyl) complex as a chelating ligand for copper. The 1,4-diyne [(r -CsFGSiMe Ti-(C=GSiMe3)2]180 (or related complex) was found to stabilize the copper units GuX, with X = alkyl,180,181 vinyl,180... 

Of great synthetic potential are demetallations with simultaneous formation of C-Sn bonds (Figure 2.20) [137,146,230,281,282]. These reactions presumably proceed via a heterobimetallic intermediate containing an Sn-M-C group. Reductive elimination of the metal M from this intermediate leads to formation of the carbon-tin bond. The resulting alkyl- or vinylstannanes are valuable synthetic intermediates. 

Heterobimetallic homogeneous catalysts [e.g. (12)] have been developed26 for the alkylation of a range of aromatic compounds by n-activated alcohols. The superior electrophilicity is attributed to the high-valent T-Sn core in the structures. A review has appeared of reactions involving the hydroxyalkylation and cycloalkylation of arenes by hydrofurans, lactones, and unsaturated acids 27... 

The relevance of Ln/Al heterobimetallic complexes for the emulation of zirconocene-based polymerization catalysis [13-15] was later on also stressed by the Lanthanide Ziegler-Natta Model [16]. Accordingly, lanthanidocene alkyl complexes were not only successfully employed for clarifying major initiation, propagation, and termination steps (Scheme 3) [17,18]. 

In the course of these studies key features such as olefin coordination [19,20], olefin insertion (propagation) [16,21,22], /(-hydrogen elimination [16,21,22], and /3-alkyl elimination [23] could be spectroscopically and structurally proven. In particular, yttrium aluminates have been proposed to model isoelectronic cationic homo- and heterobridged Zr/Al heterobimetallic complexes as dormant species and potential polymer chain transfer candidates [24]. Such zirconium aluminate complexes seem to be elusive [25], while the first structurally characterized titanium alumi-... 

Although heterobimetallic complexes with alkylated rare-earth metal centers were proposed to promote 1,3-diene polymerization via an allyl insertion mechanism, details of the polymerization mechanism and of the structure of the catalytically active center(s) are rare [58,83,118-125]. Moreover, until now, the interaction of the cationizing chloride-donating reagent with alkylated rare-earth metal centers is not well-understood. Lanthanide carboxylate complexes, which are used in the industrial-scale polymerization of butadiene and isoprene, are generally derived from octanoic, versatic, and... 

First structural evidence for the formation of heterobimetallic Ln/Al complexes in carboxylate-based catalytic systems was obtained from the reaction of homoleptic rare-earth metal trifluoroacetates with equimolar amounts of z -Bu2A1H and EtsAl, respectively [132], Alkylated yttrium, neodymium, and... 

Structural evidence for the formation of alkylated lanthanide metal centers in the ternary catalyst mixtures stems predominantly from ferf.bulanolalc complexes [178-181]. Fully characterized heterobimetallic zzeopentanolate analogues were synthesized in recently [ 142],... 

Aryloxide (phenolate) ligands provide rigid and versatile ancillary ligand sets in order to study the multifunctional reactivity of alkylaluminum and alkylmagnesium reagents toward Ln-OR moieties. Several types of symmetrically substituted phenolate ligands — summarized in Chart 4 — were employed for the synthesis of a variety of heterobimetallic lanthanide(III) and lanthanide(II) metal complexes. Alkylation reactions revealed the preferred... 

Alkylated rare-earth metal complexes with rare-earth metal centers surrounded exclusively by oxygen donor ligands were reported from facile ligand redistribution processes in 2,6-dimethylphenolate/trialkylaluminum mixtures. As shown in Scheme 29 for the yttrium derivatives Y(0ArMe,II)2[(//-OArMe>H)2AlR2](THF)2 (R= Me, Et), heterobimetallic 1 1-species were ac-... 

A mixed-alkylated heterobimetallic Ln/Al complex was reported by the Evans group [191]. In a two-step reaction the donor-functionalized europium(II) alkoxide [Eu(OCH2CH2OMe)2] was combined with [Me2Al(OCH2CH2 OMe)]2 and trimethylaluminum to yield a polymetallic Eu(II)/Al(III) compound (Scheme 37, Fig. 31). 

The isolation and structural characterization of alkylated species was achieved when trinuclear Nd3(/z3-Of-Bu)2(/z2-Of-Bu)3(/z-Of-Bu)4(THF)2 and monomeric Nd(OArt Bu,Me)3(THF) were reacted with Mg(CH2SiMe3)2 (Et20) [192]. As shown in Scheme 38, a heterobimetallic Nd/Mg complex was crystallized from toluene/MMA mixtures (0.03 equiv MMA vs. Nd) in 30-40% yield after a few weeks. X-ray crystallography confirmed the... 

Structural evidence of the formation of alkylated siloxide complexes was obtained from the reaction of homoleptic tetramethylaluminates Ln(AlMe4)3 with one equivalent of tris(ferf.butoxy)silanol HOSi(Of-Bu)3. This fast protonolysis reaction results in heterobimetallic Ln/Al complexes Ln[OSi(Of-Bu)3](AlMe4)2(AlMe3) (Ln = Y, Ce, Pr, Nd, La) via quantitative... 

Structurally characterized heterobimetallic Ln/Al complexes bearing donor-functionalized dianionic diamido ligands of the types [NNN]2" and [NON]2- were obtained from [amide]- [alkyl] (Scheme 52) or [aluminate] [amide] interchange reactions (Scheme 53). 

Fig. 4 Alkyl region of VT-NMR spectra (400 MHz, ds-toluene) of the heterobimetallic Y/Al alkoxide complex (C5Me5)Y(OCH2CMe3)2(AlMe3)2 [142]...

Table 28 Structural parameters of heterobimetallic Ln/Al complexes featuring different alkylated aluminum centers ( mixed-alkylated complexes )... 

---