Titanium complexes coordination mode

Polysulfides of several metals can be prepared by reaction of the metals with excess sulfur in liquid NH3 (group IA metals) or by heating sulfur with the molten metal sulfide. The polysulfide ion binds to metals to form coordination compounds in which it is attached to the metal by both sulfur atoms (as a so-called bidentate ligand). One example is an unusual titanium complex containing the S52-ion that is produced by the following reaction (the use of h to denote the bonding mode of the cyclo-pentadienyl ion is explained in Chapter 16) ... 

The coordination chemistry of Cp titanium carboxylates and related complexes has been reviewed. The synthetic methods, structural characteristics, coordination modes, and reactivities are covered.1570... 

Thioalkyne titanium derivatives with functionalized Cp rings (C5H4R1)(G5H4R2)Ti(SG=CR)2 (R = Ph, Buc, R1 = R2 = SiMe3 R = Buc, R1 = SiMe3, R2 = PPh2 R = Buc, R = R2 = PPh2) have been prepared and used as precursors for the synthesis of heterobinuclear Ti-M (M = Mo, Pd, Pt) complexes with different coordination modes (Scheme 732). The crystal structures of some of these complexes have been reported.1840... 

Several complexes combining q2 and q3 - BH4 ligands in the coordination sphere have been reported with TP, TET, TBP and OCT geometries (Scheme 9). It is worth comparing the tetrahydrobrate coordination modes found in a series of M(BH4)3L2 (M = Sc, Ti, V) complexes. Despite the three compounds exhibiting TBP structures, vanadium shows the three BH4 coordinated q2, scandium prefers two q3 and one q2, and titanium prefers two q2 and one q3-BH4 ligands. These series have been theoretically studied in order to discuss the importance of electronic effects as a main factor... 

Between the first-row transition metals, only titanium and nickel complexes with BH4- ligands coordinated in the a r 3 coordination mode have been characterised (Fig. 3). For titanium, both complexes with one and more than one r]3 - BH4 can be found, whilst for nickel, only one compound with one r 3 - BH4 is known. The longest Ti - B distances are found in complexes with more than two BH4", in contrast with observations done in the case of... 

The basic relationship between the coordination mode and the number of electrons around the metal still applies in rather complicated systems such as those with three BEU- ligands. Complexes of general formula have been characterised with scandium, titanium and vanadium. All the complexes adopt distorted trigonal-bipyramidal geometry with the BH4- ligands at the equatorial positions (Scheme 16). 

Ligands having C2-symnietry have also been used with metals that are undoubtedly octahedral, however the analysis of facial selectivity in octahedral complexes is complicated by several possible competing coordination modes of the dienophile. One class of ligand that has been well studied are the TADDOLs (TADDOL is an acronym for a,a,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol). Both the Narasaka [236] and the Seebach [228] groups have evaluated a number of TADDOLs as ligands for titanium in the asymmetric Diels-Alder reaction. Table... 

As discussed in Sec. 111-15, the mode of coordination of the pseudohalide ion can be determined by vibrational spectroscopy. Burmeister et al. " found that all NCS and NCSe groups are N-bonded in M(Cp) X2-type compounds, where M is Ti, Zr, Hf, or V, and X is NCS or NCSe. In the case of analogous NCO complexes, Ti, Zr, and Hf form O-bonded complexes, whereas V forms an N-bonded complex. Later, Jensen et al suggested the N-bonded structure for the titanium complex. 

The first example of group 4 complexes comprising an annulated derivative with a pendant NHC group was reported in 2006 by Downing and Danopoulos (Scheme 14.20) [14,68]. The titanium (III) complex 37 was obtained by reaction of the Ti(IV) bis-amido precursor TiQ2(NMc2)2 with the corresponding potassium fluorenyl NHC salt and proceeded with Ti(IV) to Ti(III) reduction. Dimethyl-functionalized N-heterocyclic carbene complexes of Ti(IV), Ti(III), and Zr(IV) were also prepared by salt metathesis reactions, and the bidentate coordination mode was confirmed by various X-ray diffraction studies (complexes 38) [69]. 

Complexes of the titanium and vanadium groups are scarce but mainly follow the routine coordination modes. Sometimes for the dihydrobis(pyrazol-l-yl) borates, the role of M H—B agostic interactions is significant. 

With the monodentate fluoride ion, it is difficult to have two H2O ligands in trails allowing condensation of opposed coplanar edges. This mode of condensation is possible only with a bidentate ligand ([HSO4]) which leaves only one water molecule in the coordination sphere. As a result, only anatase can form. In both cases, this mechanism may only take place if the complexes are sufficiently stable. Equilibria between various species are probably involved. Under these conditions, it is difficult to know what is the precursor of the solid. Since the oxide always contains some amount of sulfate difficult to remove, it is reasonable to speculate that the complexes are rather stable and that the formation of the solid takes place by incorporation of the sulfated titanium complexes by olation. This is also probably the case with the fluoride. Therefore, the complexing ions of titanium... 

Dioxygen binds to metal porphyrins in the three expected modes, i.e. u-superoxo, peroxo and bridging peroxo. In contrast to die simple complexes discussed previously, dioxygen coordination occurs with a wide range of transition metals from titanium and niobium through to the Group VIII metals. 

In the calculations of methane interaction with nickel or titanium surfaces, five different modes of coordination have been considered (Figure III.2) [6c], It has been concluded that acts of methane activation by a separate molecule of a metal complex on the one hand and the metal surface on the another hand are very similar. In both processes the C-H bonds of methane are ruptured and new M-H bonds are formed. Intermediate species formed during alkane chemisorption on oxide catalysts have been investigated both by MO calculations and spectroscopic methods [7]. 

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