Sulfoxide complexes

C9HnBrN206 C2H6OS 5-Bromouridine - dimethyl sulfoxide complex BURDMS 31 369... 

The unit cell is tetragonal, with a symmetry approximating P2i2 2i. The cell dimensions are a = b= 18.87 A (1.887 nm) and c = 7.99 A (799 pm). The helix diameter is 13.3 A (1.33 nm). One ethylenediamine molecule for every two D-glucose residues is indicated. The location of the ethylenediamine molecule in the lattice was discussed. The structure is almost identical to that of the amy-lose-dimethyl sulfoxide complex. 

This review is intended as an account of the coordination chemistry of both dimethyl sulfoxide and the higher sulfoxides, with particular reference to the mode of bonding and the extent to which this affects the chemistry of transition-metal sulfoxide complexes. No attempt has been made to provide an exhaustive listing of all known sulfoxide complexes, many of which contain coordinated sulfoxide moieties only coincidentally to their other important functions. 

An oxygen-bonded sulfoxide complex will be termed anO-RjSO complex, and similarly, a sulfur-bonded complex will be termed an S-RjSO complex. Where the mode of coordination is not known or is uncertain, formulas of the type [M(R2SO)xC1 ] will be used. 

In order to understand the bonding in transition-metal sulfoxide complexes, it is necessary to summarize the physical data available in the literature and so determine what constraints are necessary in any bonding model. An understanding of the factors affecting the bonding in these complexes is essential if further developments are to be made in the chemistry of transition-metal sulfoxide complexes. 

Crystallographic studies on S-dimethyl sulfoxide complexes (Table III) show that the geometry of the Me2SO moiety is virtually unaffected by coordination. Values of O—C of —107° compare favorably with the values of 106.7° and 106.8° reported for free dimethyl sulfoxide. Similarly, reported values of C—C between 99.4(6)° and 104.5(7)° compare with the value of 97.4° reported for the free molecule. A slight increase in C— —C would be expected on repulsion... 

Early work on sulfoxide complexes (460) led to the empirical observation that coordination to a metal center via oxygen generally leads... 

In the chemistry of main-group element sulfoxide complexes, a relationship between Aj/(S=0) and the enthalpy of formation of the sulfoxide complex has been derived (159). The applicability of the equation has only been examined for O-l SO complexes, and the constraints on using Ai (S=0) as a measure of metal-ligand bond strength should be borne in mind during its application. 

The use of both 8(CH3) values and iftM- H) magnitudes does, however, allow determination of the coordination mode in many instances (e.g., 462). Problems due to ligand dissociation are frequently evident in H-NMR studies of sulfoxide complexes. Thus the dimethyl sulfoxide adduct of niobium oxychloride (409) undergoes solvolysis in acetoni-... 

Other workers have reported reflectance spectra of sulfoxide complexes (for example, 181, 242), but data are too incomplete to allow meaningful comparisons to be made. 

Electronic spectroscopy has been employed to study substitution reactions of sulfoxide complexes. An interesting example (104) is the reaction of [Fe(0-Me2S0) P+ with chloride ion. Addition of one equivalent of chloride ion to a Me2SO solution of [Fe(0-Me2S0)6P+ causes a change in spectrum, but further additions have no effect. Comparisons with known compounds indicate that [Fe(0-Me2S0)5Cip+ is the major species in solution. 

Upon coordination via oxygen, as in uranyl sulfoxide complexes and thorium nitrate sulfoxide complexes, the positive charge on sulfur is virtually unaltered (19), whereas coordination via sulfur, as in palla-dium(II) sulfoxide complexes, causes an increase in the positive charge, as a result of transfer of electron density from the sulfur atom to the metal center (19, 373). 

The technique, although attractive, is experimentally rather complex charging problems can frequently occur, leading to the observation of elevated apparent binding energies, and interpretational difficulties exist. Thus, the X-PES of palladium(II) sulfoxide complexes are difficult to interpret unambiguously as the oxygen Is peak is nearly... 

Great care must be exercised in the thermal analysis of certain sulfoxide complexes. Complexes of the type [Md SOl XX], (X = C104, N03, etc.) are known to be highly explosive on heating to elevated temperatures indeed, sulfoxide complexes with explosive properties equal to TNT and nitroglycerine have been reported in the patent literature (148,149). 

This simple valence-bond rationale, involving a resonance hybrid of forms 1 and 2, appears to explain many of the physical data available for sulfoxide complexes. It appears that S-bonding does not involve such a major internal rearrangement of the molecule as one may initially expect and is almost certainly a result of the increased orbital diffuseness on passing from oxygen to sulfur. Thus with typical hard acids (see ref. 437), orbital overlap will be most favorable with the less diffuse donor orbital of oxygen. In the case of typical soft metals, this overlap is less favorable due to the orbital diffuseness of the soft acid, and so coordination via sulfur occurs, where the orbital diffuseness of the donor and acceptor are more evenly matched. 

Me2SO)(CH2ClCOO)2], 4.96 /lib (107). Accordingly, it seems likely that Co(III) sulfoxide complexes are low spin and as such have the diamagnetic ground state ( g)6. In addition, this model does not seem satisfac-... 

The kinetics and mechanism of ligand substitution reactions of square-planar platinum(II) dimethyl sulfoxide complexes have been exhaustively studied (173), and these workers conclude that the cis and trans influences and the trans effects of Me2SO and ethylene are similar in magnitude whereas the cis effect of Me2SO is about 100 times as large as that of ethylene. The results for reaction (5), where the stability constants, Kt, are reported to be 1.5 x 108 (L = S-Me2SO) and 4.5 x 108 (L = ethylene) corroborate this analogy (213). 

Several methods have been widely used in the preparation of sulfoxide complexes, and these are outlined below. Routes specific to given systems are dealt with in Section V. 

The relatively minor alteration in reaction conditions can be seen to drastically alter the nature of the product (468). In addition many sulfoxide complexes are thermally degraded, and in consequence the extent of drying can alter the nature of the product. Thus, the complex [Co(0-Me2SO)8][I]2 is isolated from a cobaltous iodide-dimethyl sulfoxide system, but extensive drying in vacuo causes degradation to yield [Co(0-Me2SO)6][CoI4] (128). 

---