Diene complexes crystal structures

The crystal structures of a number of s-trans (diene)metal complexes (3) have been determined10-14. The diene ligand in all s-trans complexes is distinctly non-planar the torsional angle between the two olefin groups is between 114° and 127°. In general, the terminal carbon to metal distance is greater than for the internal carbon to metal distance, and the Cl—C2/C3—C4 bonds are shorter than the C2—C3 bond. 

From their crystal structures, (l,3-diene)CrL4 complexes46 are found to be approximately octahedral coordinate. The low temperature (—90 °C) 13C NMR spectrum of (butadiene)Cr(CO)4, which consists of 3 M-CO signals (1 2 1 ratio), is consistent with this static structure. At higher temperature, these coalesce into a single signal20. The chiral complex (2-ethyl-l,3-butadiene)Cr(CO)4 (8) shows similar behavior, however... 

In contrast, spectroscopic and crystal structure analysis indicates that nucleophilic attack of hydride on 72 occurs on the face of the ligand which is coordinated to the metal (Scheme 17). No intermediate species could be detected for this latter reaction. Monitoring of the reduction of the rhenium analog 74 with sodium borohydride indicated the intermediacy of a rhenium formyl complex 75, presumably formed by attack on a coordinated carbon monoxide. Signals for 75 eventually disappear and are replaced by those of the (diene)rhenium product 76 (Scheme 18)95. 

The preparation and characterization of several octahedral Ru(II) complexes containing s-trans coordinated dienes have been reported. The Zn mediated reduction of Ru(acac)3 in the presence of a 1,3-diene affords (diene)Ru(acac)2 complexes as a mixture of diastereo-mers (eg. 129)13a b. Reaction of [(trispyrazolylborate)RuCl]jt or [(NH3)4Ru(acetone)2]2+ [CIO4 ]2 with acyclic dienes yields complex 130 or cation 131 respectively130,14. Coordination of the ligand as an s-trans diene was indicated either by crystal structure or by determining C2v symmetry on the basis of NMR spectroscopy. 

Crystal structures of [Rh(S,S-chiraphos)COD]Cl04 (38), [Rh(R-prophos)NBD]C104 (39), [Rh(S,S-skewphos)NBD]C104 (39), and [Rh(S,S-skewphos)COD]C104 (39), (where COD is cycloocta-1,5-diene and NBD is norbornadiene) have been determined. The molecular structures of the chiraphos and prophos complexes are essentially those that are depicted in Figure 7 but, whereas the skewphos-COD... 

In the crystal structures of the La3+ and Eu3+ complexes of Ln( 18-DTPA-dien) oligomerization was observed [20]. The coordination of the Ln3+ ion by each DTPA unit, however, was similar to that in the linear bisamides. Vapor pressure osmometry indicated that oligomerization in solution does not occur under the conditions applied (0.2-0.5 M). Because of the constraints imposed by linking the two amide functions in the macrocycle, the isomers 1,1 and 3,3 depicted in Fig. 1 are sterically very unfavorable. In line with this, resonances for only two pairs of enantiomers were observed in the 11 spectra of the Ln( 18-DTPA-dien) complexes. The dynamic behavior showed that one pair was rather static, whereas the other was rapidly interconverting. The AG for the interconversion (65 kj mol-1) was about the same as those observed for the SS AA isomerization in other DTPA-derivatives. In the Ln( 18-DTPA-dien) complex such an isomerization is only possible between mirror images 2 and 2. All other isomerizations require decoordination and, therefore, are much slower. 

Two-electron reduction of the 18-electron [M(T)5-L)(Tj5-C5Me5)]2+ (M = Ir, L = 2,5-dimethylthiophene (55) M = Rh, L = 2,3,4,5-tetra-methylthiophene) complexes gives the corresponding r)4-bound thiophene species in which the ligand has lost its aromaticity and now acts as a 4-electron donor via the diene as shown in Scheme 13 for the Ir complex. This was first demonstrated in the crystal structure of [Ir(774-2,5-dimethylthiophene)(T75-C5Me5)] (56), where the thiophene ring was found to be nonplanar with the sulfur atom lying 0.905 A out of the plane of the... 

Cycloocta-2,4-dien-l-one (95) exists as an equilibrium mixture of the conformers 95a and 95b in solution, and conversion between these two enantiomeric forms is too fast to allow their isolation at room temperature. Photoreaction of 95 in pentane for 1 hr gives racemic 96 in 10% yield along with polymers. When a solution of (—)-ll and 95 was kept at room temperature for 12 h, a 3 2 inclusion complex of (—)-ll with 95a was obtained as colorless needles. Irradiation of the 3 2 complex of (—)-ll with 95a for 48 hr gave (—)-96 of 78% ee in 55% yield. X-ray crystal structure analysis is given in Ref. 51. 

Fig. 5 Crystal structures of a type B complex [Pd(l,2,3,8-r 4-octadiene-l,8-diyl)(PMe3)] (left) and type C complex [Pd(l,2,3,7,8-r 5-octa-2,7-dien-l-yl)(tris(2-methoxyphenyl)phosphine)]BF4 (right). The BF4 anion and hydrogen atoms are omitted for clarity [51, 53]...

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