M S bonding

The above-mentioned method is useful but metals that form strong M-S bonds (e.g., Hg, Ag, Sn) do not dissolve in W-Melm solutions of sulfur. This problem has been solved by the addition of Mg to the reaction mixture. Metal polysulfides having a variety of metals can be synthesized by the 7 T-Melm/ M-i-Mg/Sg method (Scheme 11) [48]. For example, a mixture of Mg, Sb powder (1 eq.), Sg (15 eq. as S) and W-Melm is heated at 80 °C for 48 h to afford the orange powder of [Mg(N-MeIm)5]Sb2Sj ( x 15) in 88% yield. Rauchfuss et al. proposed the mechanism of these reactions as follows. First, the reduction of Sg with Mg occurs to give the [Mg(W-MeIm)6] salt of Sg , which is probably in equilibrium with Sg, Ss ", Ss" and other species. Independently, the sulfuration of the thiophilic metal takes place. Next, the polysulfide an-... 

The authors confirmed the formation of vinyl Ru-complex 21 by the reaction of [Cp Ru(SBu-t)]2 with methyl propiolate (Eq. 7.15). To my knowledge, this is the first observation of the insertion of an alkyne into the M-S bond within a catalytically active metal complex. In 2000, Gabriele et al. reported the Pd-catalyzed cycloisomerization of (Z)-2-en-4-yne-l-thiol affording a thiophene derivative 22 (Eq. 7.16) [26]. 

FIGURE 16.7 The cone swept out by rotation of SCN around the M-S bond. 

By employing coordination complexes as branch points, dendrimers can be synthesized that contain metal ions throughout their structure. The repetitive unit of such dendrimers contains M-C, M-N, M-P, or M-S bonds [53,62]. The metal ions act as supramolecular glue [63], in which the complexation chemistry directs the assembly and structure of the dendrimer [53]. One of the synthetic procedures used to prepare organometallic dendrimers with coordination centers in every layer is based on a protection/deprotection procedure in which two complexes are used as dendritic building blocks wherein one acts as a metal and the other as a ligand [64,76]. 

Optimal Heat of Formation of M-S Bond [Chianelli et al. (3, 87). High activity is the result of a balance between the strength of the H2S-M bond and the strength of the thiophene S-M bond. If the H2S-M bond is... 

Minimum M-S Bond Energy [Topspe et al (7, 85, 86)]. Low M-S bond energy allows for the maximum number of unoccupied coordination sites for reaction. 

Method of Interesting Bonds [Startsev ef al. (2, SS)]. A proper balance of M-S bond strengths is required. M-S bonds that are either too strong (Ti-S) or too weak (Cu-S) will correspond to low activity. 

Density Function Electronic Structure [Smit and Johnson (67)]. High activity is the result of electron transfer from Co(Ni) to Mo and corresponds to the removal of cr antibonding metal d-sulfur 3p electrons from Co(Ni). Optimal activity is the result of the right oxidation state of the Co(Ni) and the M-S bond length. 

The reaction of dithiooxamide and its tetramethyl and tetraethyl derivatives with zinc, cadmium and mercury halides leads to complexes of stoichiometry MLX2 (M = Zn, Cd or Hg X = C1, Br or I).900,9 1 M—S bonding is involved IR spectra show that the zinc and mercury complexes are four-coordinate, while the cadmium complexes are octahedral with halogen bridges. 

The ligands are asymmetrically bound such that both a short and a long M-S bond arise from each ligand. The short bonds are positioned trans to each other in a PbS4 polyhedron that resembles a distorted square pyramid with Pb at the apex. This structure, which appears to result from lone pair-bonding pair repulsions, is quite similar for the Pb(II) and Sn(II) complexes (Table IV). In the Pb(i-PrXant)2 Py complex, the pyridine molecule is located above the lead atom with a Pb-N distance of 2.55(4) A (288). 

The mean values of the two short and the two long M-S bonds are reported assuming that they are chemically equivalent. 

In summary, these studies and interpretations show that, in general, covalency in the M—S bonds increases strongly in going from copper to silver to gold, and that the metal 3d character of the MO of the unpaired electron decreases from 50% in Cu(Et2Dtc)2 to 26% in Ag(Et2Dtc)2 and 15% in the homologous Au(II) complex (627) (607). 

The question of whether sulfur insertion occurs at the C-S or the M- S bond was raised following the first isolation of the perthio-l,l-dithiolate complexes (156). Early studies of the sulfur-addition and sulfur-abstraction reactions using 33S were reported for Ni(CS3)2" (Eq. 54). It was concluded that the added sulfur was inserted into the C -S bond (156). 

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