Scandium complexes structures

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

Two other dimeric complexes which are related in structure to [Yb-(C5H4(CH3))2C1]2 are [Ce(C8H8)Cl 2THF]2 and [Sc(C5H5)2Cl]a. The cerium complex was discussed earlier. The structure of the scandium complex 118) is the same as that in Fig. 11. For the planar unit with symmetrical bridges, changing... 

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... 

Addition of Sc-R moieties to metal coordinated carbon monoxide was ascribed to the high Lewis acidity of the organometallic scandium complexes [281b]. R-Substituted scandoxycarbene complexes of type Cp2M=C(R)OScCpf (M = Mo, W R = H, Me) and CpM(CO)[=C(R)OScCpf] (M = Co,Rh, R = H, Me, CH2CH2Ph, NMe2) were obtained. The molecular structure of... 

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... 

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... 

As we shall see, there are now other rare-earth elements that are stable enough in the divalent state in solution, allowing for the successful isolation of molecular complexes that can be fully characterised, including structurally, and their reactivity studied. Recent reviews and highlights have partially addressed this topic (Bochkarev, 2004 Cassani et al., 2002 Evans, 2000, 2002a,b, 2007 Izod, 2002 Meyer, 2008). Eurthermore, there are a few reports on low-valent scandium complexes, and also a number of extremely reactive zero-valent rare-earth molecular compounds that could only be made via metal vapour techniques, which have been reviewed some time ago (Cloke, 1993). 

Metal vapour s)mthesis in rare-earth chemistry has been used as early as 1977 to prepare rare-earth butadiene and alk)me complexes by interaction of butadienes and alk)mes (respectively) with vaporised metals (Evans, 1987 Evans et al., 1977), and we have seen in Section 3 that low-valent scandium complexes can also be made by this technique. Additionally, condensation of rare-earth vapours with a 7i-acceptor such as 1,4-di-(t-Butyl)diazadiene (DAD) has produced compounds of general formula [R(DAD)3], except with scandium where the composition is [Sc(DAD)2]. Extensive metal-ligand electron transfer is effective in these molecules so the real oxidation state of the rare earth (at least at room temperature) is in fact + 3. Note that the first structurally characterised organosamarium(II)... 

The scandium complex Sccp3 has polymeric structure with the Sc( -C5115)2 fragments bonded via bridges. In tetrahydrofuran solution, Sccp3 has... 

The first example of a group 3 NHC complex was reported by Arduengo et al. in 1994 with yttrium (Scheme 14.1) [12]. The seven-coordinate yttrium carbene complex 1 was obtained from the direct reaction of the free carbene 1,3-dimethyl-4,5-dimethylimidazol-2-ylidene with tris(2,2,6,6-tetramethylheptane-3,5-dionato)yttrium, Y(thd)3 and features a NMR doublet resonance for the carbene atom (d 199.4 ppm) with a coupling constant of 33 Hz to the nucleus. The first scandium NHC complexes were only recently described. Cui and coworkers prepared indenyl-functionaUzed NHC carbene scandium complex 2 in 2007 [13,14]. Complex 2 could be structurally characterized by X-ray... 

Figure 14.1 Molecular structure of the scandium complex 14. The hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles O Y(1)-C(1), 2.6420(16) Y(1)-C...

---