Tris methyl ligand

A number of methyl substituted PyO have been tried as ligands for coordination with the lanthanides. Depending on the position of the substituent, these ligands impart different degrees of steric strain for the formation of complexes. Since substituents in the 4 or 3 position do not introduce substantial steric hindrance to coordination, Harrison and Watson (160) could synthesize octakis-4-MePyO complexes. Subsequently, Koppikar and Soundararajan (161) could also synthesize octakis-3-MePyO complexes with lanthanide perchlorates. Complexes of 4-MePyO (162, 163) and 3-MePyO (164, 165) with lanthanide iodides and bromides also have a L M of 8 1. 

Similar terpy-like tri-imine ligands are N -(2-pyridylmethyl)picolinamidine (ppa) and its two methyl-substituted derivatives meppa and me2ppa 163. These ligands also form six-coordinate bis-chelate complexes of nickel(II) and iron(II). Magnetic... 

Whereas complexes of unsubstituted and substituted cyclopentadienyl ligands represent the vast majority of all published compounds in organolanthanide chemistry, examples of isolated and fully characterized (including X-ray structural analyses) compounds containing only cr-bonded alkyl and aryl ligands are still fairly rare. The first structurally characterized homoleptic lanthanide alkyls became available through the use of bulky mono-, bis-, and tris(trimethyl-silyl)-substituted methyl ligands. Simple unsolvated alkyls of the rare earth elements have not yet been synthesized. 

The starting point for Eaborn s work is the tris(trimethylsilyl)methyl ligand, 76, now abbreviated to trisyl or Tsi The trisyl ligand, or some variation thereof, is attached to a... 

The unusual bis-silyl methyl ligand, (CH(SiMe3) (SiMe20Me) ), forms a cyclo octamer with lithium (5). The bis(trimethylsilyl)dimethylphenylsilylmethyl ligand forms monomeric compounds with lithium and sodium in the presence of additional electron donors (TMEDA, diethyl ether, and THF). In each structure, there are additional interactions between the metal ions and carbons from the phenyl rings. The tris(dimethylphenylsilyl)methyl compounds of sodium, potassium, rubidium, and cesium crystallize in polymeric chains. Each of these compounds also has intra- and inter-molecular phenyl-metal cation interactions. The monomeric [LiC(SiMe2CH2PPh2)3] forms as a base-free compound even in the presence of a large excess of electron donors (such as TMEN) (6). " ... 

As a consequence of the success of rationally designed tris-bidentate ligands for the straightforward synthesis of [M4L4] tetrahedra (see Sect. 2.4.1), the three-fold symmetric, tris-bidentate pyrazolone-based ligand H3L 30 was prepared. Tris-diketone ligand 30 is generated from 3-methyl-1-phenyl-2-... 

The basic kinetic features of ATRP are similar to NMP, and this can be demonstrated for the copper-mediated polymerization of styrene. The ATRP of styrene in t-butyl benzene, catalyzed by Cu(I)Br/L, where L is the ligand diheptyl bipyridine, and a (PS-Br) adduct in the presence or absence of a radical initiator 2,2 -azobis (2,4,4-tri methyl pentane) VRllO at 110°C, has been studied. The data are shown in Figure 3.9(a) and Figure 3.9(b). Again, it is seen that for the system containing VRl 10, steady-state kinetics apply, and the conversion index is first order in t [Figure 3.9(a)], but in the absence of the initiator power law kinetics are obeyed [Figure 3.9(b)]. 

Data for the gas phase reaction will also be presented. The results suggest that, in the condensed phase, the order of acceptor strength is AlPh > GaPh > BPh > InPh, The same order may be inferred for the tri-methyl compounds of the elements towards the same ligand in the gas phase though complete data for proper comparison are lacking. It is noteworthy that the actual heats of formation are rather similar. 

The dimethyl(hydrido)platinum(iv) complex with tris(3,5-dimethylpyrazolyl)borate (Tp ) as a ligand 992 can be obtained as a stable complex by protonolysis of the anionic dimethylplatinum(ii) complex (Equation (185))7 Similar reactions of HCl and Mel with the dimethyl and diphenyl complexes produce trimethyl-, diphenyl(hydrido)-, and diphenyl(methyl)platinum(iv) complexes. Addition of B(G6F5)3 to the platinate in hydrocarbon solvents leads to a dialkyl(hydrido)platinum(iv) complex 993, probably via abstraction of a methyl ligand followed by oxidative addition of the solvent to the Pt(ii) center (Equation (186)). ... 

These results indicated that highly active titanium compounds exhibit one cylopentadienyl ligand with electron-donative substituents, and bulky substituents reduce the catalytic activities. From this point of view, 1,2,3-tri-methyl-tetrahydroindenyltitanium compounds were examined, resulting in high catalytic activities (Table 2.6). 

Using more basic (electron-donating) ligands generally speeds up the reactions while bulky ligands slow it down. The use of tris(o-tolyl)phosphine is an extreme example of the latter as IrCl(CO)[P(o-tolyl)3]2 fails to add 02, H2 or S02 and only adds HCI slowly the reason is that methyls in an ortho-position tend to block the axial positions (Figure 2.77) [126b]. 

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