Transition metal complex route

A variety of routes is available for the preparation of metal-thionitrosyl complexes. The most common of these are (a) reaction of nitride complexes with a sulfur source, e.g., elemental sulfur, propylene sulfide or sulfur halides, (b) reaction of (NSC1)3 with transition-metal complexes, and (c) reaction of [SN]" salts with transition-metal complexes. An example of each of these approaches is given in Eq. 7.1,... 

Thiazyl trifluoride NSF3 is more thermally stable and easier to handle than NSF (Section 8.3). It can be introduced into transition-metal complexes by SO2 displacement reactions (Eq. 7.8). An alternative route to metal-NSF3 complexes is shown in Eq. 7.9. 

The di- and triborolyl ligands tend to i -coordination in sandwichforming reactions. There is a clear-cut tendency for stacking processes followed by the formation of multidecker species and often stabilization of the unusual oxidation states of the transition metals. The route to the linked sandwich and multidecker complexes is attractive for materials chemistry. Thia- and azaborolyl organome-tallic chemistry follows the same trends, although in the azaborolyl complexes the i -rather than i -coordination is sometimes realized. Moreover, coordination via the boron atom is known. In the B, N, Si-heterocycles, the heteroring is j " -coordinated. 

Although the number of applications of olefin metathesis to transition metal complexes is small compared to the number of applications in organic synthesis, this field is becoming increasingly important. Spectacular examples are the double RCM reactions of copper phenanthroline complexes as a synthetic route to catenanes [113] or a recently reported approach to steric shielding of rhenium complex terminated sp-carbon chains [114]. 

The six-membered 1,4-diborines (1,4-diaboracyclohexadienes) are prepared by cocondensing alkynes with monomeric BF or by the tin route . They form a series of transition-metal complexes VIII-XIV by reaction with various complex... 

The use of chiral diaminocarbenes as transition metal hgands for catalyzed asymmetric synthesis is certainly an emerging field of research. They are relatively easy to prepare and they allow munerous structural modifications. Their transition metal complexes shows very usefull properties such as the thermal and air stability. Even if there is only a few reports of effective asymmetric transformations promoted by these class of catalyst, all these pioneering works open the route to the discovery of efficient new catalysts. 

Other methylphenyl(2-phenylpropyl)stannyl-transition metal complexes are oily compounds 18). Fractional recrystallization could therefore not be applied to separate those diastereomers. For the irondicarbonylcyelopentadienyl compound (77), the diastereomeric ratio (77)A/(77)B = 45/55 could be reached by the standard route (see Fig. 9) but could not be modified by column chromatography. 

As to the first route, we started in 1969 (1) in investigating unconventional transition metal complexes of the 5 and 4f block elements of periodic table, e.g., actinides and lanthanides as catalysts for the polymerization of dienes (butadiene and isoprene) with an extremely high cis content. Even a small increase of cistacticity in the vicinity of 100% has an important effect on crystallization and consequently on elastomer processability and properties (2). The f-block elements have unique electronic and stereochemical characteristics and give the possibility of a participation of the f-electrons in the metal ligand bond. 

An alternative strategy to obtain silica immobilised catalysts, pioneered by Panster [23], is via the polycondensation or co-condensation of ligand functionalised alkoxysilanes. This co-condensation, later also referred to as the sol-gel process [24], appeared to be a very mild technique to immobilise catalysts and is also used for enzyme immobilisation. Several novel functional polymeric materials have been reported that enable transition metal complexation. 3-Chloropropyltrialkoxysilanes were converted into functionalised propyltrialkoxysilanes such as diphenylphosphine propyltrialkoxysilane. These compounds can be used to prepare surface modified inorganic materials. Two different routes towards these functional polymers can be envisioned (Figure 3.4). One can first prepare the metal complex and then proceed with the co-condensation reaction (route I), or one can prepare the metal complex after the... 

Figure S.4. Two different routes to prepare sol-gel immobilised transition metal complexes...

There is another substitution reaction, not involving transition-metal complexes, namely, reaction of trifluoromethyl bromide with sulphur dioxide anion radicals (165) (Andrieux et al., 1990a) (this is an interesting route... 

Electron-rich olefins are nucleophilic and therefore subject to thermal cleavage by various electrophilic transition metal complexes. As the formation of tetraaminoethylenes, i.e., enetetramines, is possible by different methods, various precursors to imidazolidin-2-ylidene complexes are readily available. " Dimerization of nonstable NHCs such as imidazolidin-2-ylidenes is one of the routes used to obtain these electron-rich olefins [Eq. (29)]. The existence of an equilibrium between free NHC monomers and the olefinic dimer was proven only recently for benzimidazolin-2-ylidenes. In addition to the previously mentioned methods it is possible to deprotonate imidazolidinium salts with Grignard reagents in order to prepare tetraaminoethylenes. " The isolation of stable imidazolidin-2-ylidenes was achieved by deprotonation of the imidazolidinium salt with potassium hydride in THF. ... 

As yet, with regard to both ligands C(NHC)2 and C[C(NMe2)2 2. each is only represented by one transition metal complex. The two complexes are confirmed by X-ray analyses. The carbodicarbene C(NHC)2 was allowed to react with [Rh(p-Cl) (CO)2l2 to afford complex 70 in benzene solution. The carbon is able to split the chlorine bridge in the starting Rh complex and the vacant coordination site is occupied by the ligand, a very common synthetic route [10, 11]. 

Anwander R (1996) Routes to Monomeric Lanthanide Alkoxides. 179 149 - 246 Anwander R, Herrmann WA (1996) Features of Organolanthanide Complexes. 179 1-32 Artymiuk PJ, Poirette AR, Rice DW, Willett P (1995) The Use of Graph Theoretical Methods for the Comparison of the Structures of Biological Macromolecules. 174 73-104 Astruc D (1991) The Use of p-Organoiron Sandwiches in Aromatic Chemistry. 160 47-96 Azumi T, Miki H (1997) Spectroscopy of the Spin Sublevels of Transition Metal Complexes. 191 1-40... 

An increase in the ion annihilation exergonicity AG to values comparable to the excited triplet-state energies (AG I LT < 0) opens an additional electron transfer channel (T-route). In the simplest case, only one excited triplet 3 A or 3 D becomes accessible. Triplet emission can be directly observed from the ECL systems involving rare earth and transition metal complexes with allowed (due to extensive spin-orbit coupling) triplet-singlet electronic transition. 

There has been some exploration of the mechanism of reduction of d transition metal complexes by M2+(aq) (M = Eu, Yb, Sm). Both inner- and outer-sphere mechanisms are believed to operate. Thus the ready reduction of [Co(en)3]3+ by Eu2+(aq) is necessarily outer-sphere. 2 However, the strong rate dependence on the nature of X when [Co(NH3)5X]2+ or [Cr(H20)5X]2+ (X = F, Cl, Br or I) are reduced by Eu2+(aq) possibly suggests an inner-sphere mechanism.653 The more vigorous reducing agent Yb2+ reacts with [Co(NH3)6]3+ and [Co(en)3]3+ by an outer-sphere route but with [Cr(H20)5X]2+ (X = halide) by the inner-sphere mechanism.654 Outer-sphere redox reactions are catalyzed by electron-transfer catalysts such as derivatives of isonicotinic acid, one of the most efficient of which is iV-phenyl-methylisonicotinate, as the free radical intermediate does not suffer attenuation through disproportionation. Using this catalyst, the outer-sphere reaction between Eu2+(aq) and [Co(py)(NH3)5]3+ proceeds as in reactions (18) and (19). Values found were ki = 5.8 x KFM-1 s 1 and k kx = 16.655... 

An important focus of organometallic research has been the development and study of transition metal complexes as catalysts for transformations of organic compounds. These systems enable chemical reactions to occur under conditions that are often milder and more environmentally benign than more traditional routes, such as Lewis acid-catalyzed reactions, Grignard... 

Ojima and co-workers first reported the RhCl(PPh2)3-catalyzed hydrosilylation of carbonyl-containing compounds to silyl ethers in 1972.164 Since that time, a number of transition metal complexes have been investigated for activity in the system, and transition metal catalysis is now a well-established route for the reduction of ketones and aldehydes.9 Some of the advances in this area include the development of manganese,165 molybdenum,166 and ruthenium167 complex catalysts, and work by the Buchwald and Cutler groups toward extension of the system to hydrosilylations of ester substrates.168... 

The major route to -cyclopropenylium complexes L M(C3R3) (metallatetrahedranes) is by oxidative addition reactions of cyclopropenylium salts to transition metal complexes of groups 5 (V), 6 (Mo, W), 8 (Fe, Ru), 9 (Co, Rh, Ir) and 10 (Ni, Pd, Pt). The addition is frequently accompanied by loss of one or more carbonyl, olefin or halogen auxiliary ligand. Concurrent formation of oxocyclobutenyl complexes by carbonyl insertion into the cyclopropenyl ring is often observed in reactions with group 9 cobalt triad and early transition metal complexes. 

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