Scandium complexes, cationic

The base-free dimethyl Sc complex 121 was a highly active catalyst precursor for ethylene polymerization under B(C6F5)3, trityl borate, or methylaluminoxane (MAO)-type activation. The catalytic activity of 121 was similar to those observed of Group 4 metallocene complexes [81]. Generally, cationic scandium complexes are believed to be the active species. Activation of the catalyst was studied by reacting 120 and 121 with various equivalences of B(C6F5)3. The monomeric bulky rBu-substituted dimethyl complex 121 reacted with 1 equiv of B(C6F5)3... 

A cationic scandium complex, [(C5Me4SiMe3)Sc(CH2SiMe3)] [B(QF5)4] , showed remarkable catalytic activity for syndiospecific styrene polymerization, and copolymerization with ethylene afforded multiblock copolymers... 

Scandium A computational study on the C-H addition of a-picoline (2-MeC5H3N) and other pyridine derivatives to terminal olefins RCH=CH2, catalysed by cationic scandium complexes, has demonstrated that the reaction rate is controlled by generation of the active metal-pyridyl species and an insertion step. In agreement with the experimental observation, formation of the branched product 6-[RCH(Me)-(2-MeC5H3N)] is both kinetically and energetically favourable over that of the linear product. ... 

Scandium complexes with chloride ion in aqueous solution, and there is ion-exchange evidence for anionic species, presumably ScClJ aq, in concentrated hydrochloric acid,119 while values of K = 90 and K2 - 37 for the first two association constants have been reported.1211 Solid salts of the anions ScClt-, St Cll- and ScCl2- have been isolated with alkali metal cations.121,122 It seems likely that both the first two species are octahedral and bridged-octahedral respectively, in line with Cs2NaScCl6 which has an X-ray powder pattern in accord with a face-centred cubic structure.123... 

The second approach is a popular route to cationic lanthanide alkyl complexes, which have proven to be the important intermediates for ethylene polymerization and the stereospecific polymerization of diene [5]. Various monocationic lanthanide monoalkyl complexes have been synthesized by the alkyl abstraction/elimination reaction of lanthanide dialkyl complexes. The reaction of a bisbenzyl scandium complex supported by P-diketiminate with B(C6Fs)3 affords the cationic complex with a contact ion pair structure, in which a weak bonding between the cation and the anion exists (Figure 8.21) [77]. The reaction of an amidinate... 

Zeimentz, P.M., Arndt, S., Elvidge, B.R. etal. (2006) Cationic organometallic complexes of scandium, yttrium, and the lanthanoids. Chemical Reviews, 106, 2404. 

The tetraphenylporphyrin scandium complexes were previously reported and now crystal structures have been determined for the p-toly derivatives (ttp). Both scandium and yttrium form (ttp)MCl complexes150,151 but whereas the scandium compound is five-coordinate the yttrium compound coordinates solvent molecules forming seven or eight-coordinate complexes. Reaction of (ttp)ScCl with water forms an oxide dimer [Sc(ttp)]20,151 whereas for yttrium the cation [Y(ttp)(H20)3]+ has been observed.152 The structure of [Sc(ttp)]20 is shown in Figure 7, the bridging oxygen is disordered over two sites with 50% occupancy of each site. The reaction of... 

Unusual cationic scandium methyl complexes supported by a /3-diketiminato ligand (= LBu ) have also recently been reported. As depicted in Scheme 15, the monomeric dimethylscandium precursor reacts with varying... 

Scheme 48 A direct, enantioselective alkylation of pyridines by a cationic half-sandwich scandium complex.

A number of pyridines can be alkylated by alkenes with a cationic halfsandwich scandium complex in an enantioselective manner (Scheme 48). The alkylation occurs at C-2 with high yields and high enantiometric excess (ee).The pyridines can be substituted with alkyl, aryls, and halides with no effect of the yields or selectivity. The reaction also occurs on isoquinolines. A number of alkenes will react with 2-picoline with high selectivity and yields (14JA12209). 

In this and subsequent tables M signifies an alkali metal or organic ammonium, phosphonium, etc., cation. If the scandium complex has been prepared, this will be specifically noted. 

In a systematic study, it was demonstrated that, using a specially designed bulky benzamidinate ligand, it is possible to isolate mono(amidinato) dialkyl complexes over the full size range of the Group 3 and lanthanide metals, i.e., from scandium to lanthanum. The synthetic methods leading to the neutral and cationic bis(alkyls) are summarized in Scheme 56. Figure 18 displays the molecular structures of the cations obtained with Sc, Gd, and La. ... 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

Organolithium compounds of structure 275 can been applied as transfer agents for transition metal ions, for example, as shown in equation 54 for scandium(III) with tetrahedral coordination (276). The structure of these complexes, elucidated by XRD crystallography, shows the transition metals forming part of an anionic entity, paired to solvated lithium cations. Further structural information can be obtained from H, and "B NMR spectroscopies. ... 

This chapter consists of a description of the ions formed in aqueous solutions by the transition elements - the d-block elements - and a discussion of the variations of their redox properties across the Periodic Table from Group 3 to Group 12. There is particular emphasis on the first transition series from scandium to zinc in the fourth period, with summaries of the solution chemistry of the second (Y to Cd) and third (Lu to Hg) series. The d-block ions in solution are those restricted solely to aqua complexes of cations, e.g. [Fe(H20)f,]" +, and the various oxocalions and oxoanions formed, e.g. V02+ and MnCXj". Oxidation states that are not well characterized are omitted or referred to as such. 

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