Complexes ethylene

Fig. 2. Time-evolution of the methyl/ethyl C-C distances for both the zirconocene and the corresponding titanocene catalyst. The two curves starting at around 3.2 A represent the distance between the methyl carbon atom and the nearest-by ethylene carbon atom in the zirconocene-ethylene and the titanocene-ethylene complex, respectively. The two curves starting at around 1.35 A reflect the ethylene internal C-C bond lengths in the two complexes.

Fig. 3. Time evolution of the distance between the Zr atom and each of the three hydrogen atoms belonging to the methyl group (the original methyl group bonded to the Zr) in the zirconocene-ethylene complex. The time-evolution of one of the hydrogen atoms depicted by the dotted curve shows the development of an a-agostic interaction. Later on in the simulation (after about 450 fs) one of the other protons (broken curve) takes over the agostic interaction (which is then a 7-agostic interaction).

A wide range of ethylene complexes, both mononuclear and higher cluster in nature, have been synthesized, and studied, by the metal atom-matrix technique. In this Section, we shall focus on the reactions... 

Nickel atoms have also been allowed to react with C2H4 under cryogenic conditions (101,123). Depending on the metal-concentration conditions and the deposition temperature, either mononuclear species, Ni(C2H4) , n = 1-3(123), or multinuclear species, Ni2(C2H4) ,m = 1-2, and Ni3(CjH4)i, may be isolated. Unlike the copper complexes, these species are all colorless the mononuclear ethylene complexes each dis-... 

Cobalt atom reactions with ethylene were also studied (121). By using techniques similar to those described for Cu (122) and Ni (101), it has proved possible to synthesize a novel series of mononuclear and binuclear cobalt-ethylene complexes, Co(C2H4) , = 1, or 2, and... 

The reaction in the presence of h/s-ethylene complex 38 proceeds in 6 h, while complexes 39 and 40 need a somewhat longer reaction time (Scheme 9). This may be explained by the more facile and irreversible substitution of the volatile ethylene... 

Another interesting example of aurophilic interactions influencing electronic excited state properties is the unusual photochemical cis to trans conversion observed in dinudear goldhalide bis(diphenylphosphino)ethylene complexes, Au2X2(dppee)... 

Schwerdtfeger, P., Bruce, A.E. and Bruce, M.R.M. (1998) Theoretical Studies on the Photochemistry of the cis to trans Conversion in Dinuclear Goldhalide Bis (diphenylphosphino) ethylene Complexes. Journal of the American Chemical Society, 120, 6587-6597. 

Dias, H.V.R., Fianchini, M., Cundari, T.R. and Campana, C.F. (2008) Synthesis and Characterization of the Gold(I) Tris (ethylene) Complex [Au(C2H4)3][SbF6]. Angewandte Chemie International Edition, 47, 556-559. 

As will be discussed in detail in the next section, when the reduction of the parent compound 6 was conducted at low temperature (—20 °C) with 2 equiv. of Na in tetrahydrofuran (THF) saturated with ethylene, complete salt removal was achieved, and the r 2-ethylene complex 20 was isolated.22 Upon irradiation, the latter released ethylene, behaving as a source of the d2 [W / -Bu -calix[4]-(0)4 ] carbenoid, which coupled to give a new W=W dimer [W=W, 2.582(1) A], isolated as the bis-Bu NC adduct 21. In H NMR, 21 exhibits a C5-symmetric pattern of signals for the calix[4]arene moiety. 

Recently, Bercaw and co-workers have described the preparation of the first ethylene complex of titanium (64). The sodium amalgam reduction of a toluene solution of (Tj-C5Me5)2TiCl2 under an ethylene atmosphere afforded (T C5Me5)2Ti(T -C2H4) in 80% yield. Treatment of this complex with CO at low temperature resulted in the displacement of C2H4 and quantitative formation of (rj-C5Me5)2Ti(CO)2 (27). 

Nishiyama et al. introduced a new catalyst, the chiral tr<2 i -RuCl2(Pybox-i-Pr)(ethylene) complex (91), which showed for the first time both enantio- and diastereoselectivity (trans-selectivity) at excellent levels in the reactions of terminal olefins (Scheme 66).251-253 With 4-substituted Ru(Pybox-i-Pr) complexes (92), they studied the substituent effect on enantioselectivity... 

It seems reasonable to assume that biligand silver - ethylene complex formed above 230 K represents the reactive catalytic complex which promotes further transformations of ethylene molecules. 

Copper olefin complexes are usually generated by the direct reaction of a Cu(l) source, the ligand, and the corresponding olefin. Copper ethylene complexes are of interest in view of their biochemical importance,98,98a-98e their applications in organic chemistry,99,99a,99b and industrial applications.100 100 Because of this, many copper alkene complexes have been reported, with different nuclearity, in compounds with one, two, or even three C=C units coordinated to a given copper center. 

Negishi et al. reported the regioselective synthesis of diisoalkyl derivatives from monosubstituted alkenes in yields ranging from 58-95%, Scheme 8, from the in situ prepared ethylene complex Cp2Zr(C2H4).35 The zirconocene-ethylene complex presumably undergoes alkene insertion to furnish a zirconacyclopentane which further reacts with diethylzinc to yield the diisoalkylzinc compound. 

The course of stereospecific olefin polymerization was studied by using the molecular mechanics programs, MM-2 and Biograph, based on the optimized geometries of the ethylene complex and the transition state [13,203]. Interestingly, the steric interaction at the transition state mainly controls the stereochemistry in polymerization, which proceeds specifically isotactic or syndiotactic depending on the kind of catalyst. 

---